Academic Appointments


Administrative Appointments


  • Chairman, Department of Neurology and Neurological Sciences, Stanford Univ. School of Medicine (1970 - 1989)

Honors & Awards


  • Special Lecturer, Society for Neuroscience (2008)
  • Lothman Lecturer, University of Virginia (2007)
  • The Larry Benardo Research and Education Fund Lecturer ., SUNY Downstate Medical Center, New York (2006)
  • Servier Lecturer, University of Montreal (2002)
  • Bronte Lecturer, University of California, Davis (2001)
  • Peter Kellaway Lecturer, Baylor College of Medicine, Houston, Texas (1998)
  • George Bishop Lecturer, Washington University, St. Louis (1997)
  • Sachs Lecturer, Child Neurology Society (1994)
  • Lennox Lecturer, American Epilepsy Society (1987)
  • Herbert Jasper Lecture, Montreal Neurological Institute, Montreal, Quebec, Canada. (1984)
  • First Morris B. Bender Memorial Lectureship., Mount Sinai Medical School, New York, New York. (1984)
  • Arthur Bloomfield Award for excellence in clinical teaching., Stanford Univ. School of Medicine (1986)
  • Javits Neuroscience Investigator Award, NINDS, National Institute of Neurological Disorders and Stroke (1987-1995; 1995-2001)
  • Research Recognition Award in Basic Neuroscience, Americal Epilepsy Society (1991)
  • Lennox Award for contributions in the field of epilepsy., American Epilepsy Society (1978)
  • Principal Investigator, USPHS Research Grant NS 06477 "Cellular mechanisms in focal epileptogenesis", National Institute of Neurological Diseases and Stroke (1966-current)
  • Program Director,Principal Investigator Epilepsy Program Project Grant NS 12151, National Institute of Neurological Diseases and Stroke (1975-present)
  • Program Director, NIH Training Grant NS07280 "Epilepsy Training Program", National Institute of Neurological Diseases and Stroke (1985-2003)
  • Program Director, Dana Fellowship Program in Neuroscience, Dana Foundation (1988-1995)
  • Principal Investigator, NS39579 Modulation of Neocortical Interneuronal Functionƒ°, NINDS (7/00-current)

Professional Education


  • B.S., Univ. of Vermont, Psychology (1953)
  • M.D., Univ. of Pennsylvania, Medicine (1956)

Current Research and Scholarly Interests


My work deals with regulation of excitability in neurons of mammalian cerebral cortex and thalamus and mechanisms underlying development of epilepsy. Long-term goals are to understand how injury produces changes in structure and function of neurons and neuronal networks that lead to hyperexcitability and epileptogenesis, and approaches to prevention of epilepsy after cortical injury. Areas of interest include regulation of voltage dependent membrane properties, neuropharmacology of transmitters and modulators including neuropeptides, synaptic mechanisms, and intrinsic properties of single, anatomically identified neurons. Techniques include use of in vivo mammalian preparations as well as in vitro slices and acutely dissociated neurons for recordings of synaptic activities and membrane properties, using patch-clamp techniques to study whole cell currents and membrane channels. Electrophysiological approaches are combined with intracellular labeling and immunocytochemistry to identify types of neurons and responses to injury.

Current studies include:
i) Reorganization of neocortical neuronal synaptic activities,and intrinsic neuronal properties after cortical trauma.
ii) Electrophysiologic and neuroanatomic studies of axonal sprouting following chronic neocortical injury.
iii) Anatomy and pathophysiology of neocortical developmental malformations.
iv) Effects of neuropeptides and GABAergic inhibition on intrinsic, synaptic and network properties of thalamic neurons; and generation of normal and pathophysiologic rhythms.
v) Modulation of neocortical inhibitory interneuronal activities by neurotransmitters and injury.

2013-14 Courses


Postdoctoral Advisees


Graduate and Fellowship Programs


Journal Articles


  • Enhanced synaptic connectivity and epilepsy in C1q knockout mice PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chu, Y., Jin, X., Parada, I., Pesic, A., Stevens, B., Barres, B., Prince, D. A. 2010; 107 (17): 7975-7980

    Abstract

    Excessive CNS synapses are eliminated during development to establish mature patterns of neuronal connectivity. A complement cascade protein, C1q, is involved in this process. Mice deficient in C1q fail to refine retinogeniculate connections resulting in excessive retinal innervation of lateral geniculate neurons. We hypothesized that C1q knockout (KO) mice would exhibit defects in neocortical synapse elimination resulting in enhanced excitatory synaptic connectivity and epileptiform activity. We recorded spontaneous and evoked field potential activity in neocortical slices and obtained video-EEG recordings from implanted C1q KO and wild-type (WT) mice. We also used laser scanning photostimulation of caged glutamate and whole cell recordings to map excitatory and inhibitory synaptic connectivity. Spontaneous and evoked epileptiform field potentials occurred at multiple sites in neocortical slices from C1q KO, but not WT mice. Laser mapping experiments in C1q KO slices showed that the proportion of glutamate uncaging sites from which excitatory postsynaptic currents (EPSCs) could be evoked ("hotspot ratio") increased significantly in layer IV and layer V, although EPSC amplitudes were unaltered. Density of axonal boutons was significantly increased in layer V pyramidal neurons of C1q KO mice. Implanted KO mice had frequent behavioral seizures consisting of behavioral arrest associated with bihemispheric spikes and slow wave activity lasting from 5 to 30 s. Results indicate that epileptogenesis in C1q KO mice is related to a genetically determined failure to prune excessive excitatory synapses during development.

    View details for DOI 10.1073/pnas.0913449107

    View details for Web of Science ID 000277088700067

    View details for PubMedID 20375278

  • Targets for preventing epilepsy following cortical injury NEUROSCIENCE LETTERS Li, H., McDonald, W., Parada, I., Faria, L., Graber, K., Takahashi, D. K., Ma, Y., Prince, D. 2011; 497 (3): 172-176

    Abstract

    Prophylaxis of posttraumatic epilepsy will require a detailed knowledge of the epileptogenic pathophysiological processes that follow brain injury. Results from studies of experimental models and human epilepsy highlight alterations in GABAergic interneurons and formation of excessive new excitatory synaptic connectivity as prominent targets for prophylactic therapies. Promising laboratory results suggest that it will be possible to experimentally modify these aberrant processes and interfere with epileptogenesis. However, a number of key issues must be addressed before these results can be used to frame clinical antiepileptogenic therapy.

    View details for DOI 10.1016/j.neulet.2011.02.042

    View details for Web of Science ID 000292411600004

    View details for PubMedID 21354270

  • Reorganization of Inhibitory Synaptic Circuits in Rodent Chronically Injured Epileptogenic Neocortex CEREBRAL CORTEX Jin, X., Huguenard, J. R., Prince, D. A. 2011; 21 (5): 1094-1104

    Abstract

    Reduced synaptic inhibition is an important factor contributing to posttraumatic epileptogenesis. Axonal sprouting and enhanced excitatory synaptic connectivity onto rodent layer V pyramidal (Pyr) neurons occur in epileptogenic partially isolated (undercut) neocortex. To determine if enhanced excitation also affects inhibitory circuits, we used laser scanning photostimulation of caged glutamate and whole-cell recordings from GAD67-GFP-expressing mouse fast spiking (FS) interneurons and Pyr cells in control and undercut in vitro slices to map excitatory and inhibitory synaptic inputs. Results are 1) the region-normalized excitatory postsynaptic current (EPSC) amplitudes and proportion of uncaging sites from which EPSCs could be evoked (hotspot ratio) "increased" significantly in FS cells of undercut slices; 2) in contrast, these parameters were significantly "decreased" for inhibitory postsynaptic currents (IPSCs) in undercut FS cells; and 3) in rat layer V Pyr neurons, we found significant decreases in IPSCs in undercut versus control Pyr neurons. The decreases were mainly located in layers II and IV, suggesting a reduction in the efficacy of interlaminar synaptic inhibition. Results suggest that there is significant synaptic reorganization in this model of posttraumatic epilepsy, resulting in increased excitatory drive and reduced inhibitory input to FS interneurons that should enhance their inhibitory output and, in part, offset similar alterations in innervation of Pyr cells.

    View details for DOI 10.1093/cercor/bhq181

    View details for Web of Science ID 000289578900012

    View details for PubMedID 20855494

  • Differential effects of Na plus -K plus ATPase blockade on cortical layer V neurons JOURNAL OF PHYSIOLOGY-LONDON Anderson, T. R., Huguenard, J. R., Prince, D. A. 2010; 588 (22): 4401-4414

    Abstract

    Sodium-potassium ATPase ('Na(+)-K(+) ATPase') contributes to the maintenance of the resting membrane potential and the transmembrane gradients for Na(+) and K(+) in neurons. Activation of Na(+)-K(+) ATPase may be important in controlling increases in intracellular sodium during periods of increased neuronal activity. Down-regulation of Na(+)-K(+) ATPase activity is implicated in numerous CNS disorders, including epilepsy. Although Na(+)-K(+) ATPase is present in all neurons, little is known about its activity in different subclasses of neocortical cells. We assessed the physiological properties of Na(+)-K(+) ATPase in fast-spiking (FS) interneurons and pyramidal (PYR) cells to test the hypothesis that Na(+)-K(+) ATPase activity would be relatively greater in neurons that generated high frequency action potentials (the FS cells). Whole-cell patch clamp recordings were made from FS and PYR neurons in layer V of rat sensorimotor cortical slices maintained in vitro using standard techniques. Bath perfusion of Na(+)-K(+) ATPase antagonists (ouabain or dihydro-ouabain) induced either a membrane depolarization in current clamp, or inward current under voltage clamp in both cell types. PYR neurons were divided into two subpopulations based on the amplitude of the voltage or current shift in response to Na(+)-K(+) ATPase blockade. The two PYR cell groups did not differ significantly in electrophysiological properties including resting membrane potential, firing pattern, input resistance and capacitance. Membrane voltage responses of FS cells to Na(+)-K(+) ATPase blockade were intermediate between the two PYR cell groups (P < 0.05). The resting Na(+)-K(+) ATPase current density in FS interneurons, assessed by application of blockers, was 3- to 7-fold larger than in either group of PYR neurons. Na(+)-K(+) ATPase activity was increased either through direct Na(+) loading via the patch pipette or by focal application of glutamate (20 mM puffs). Under these conditions FS interneurons exhibited the largest increase in Na(+)-K(+) ATPase activity. We conclude that resting Na(+)-K(+) ATPase activity and sensitivity to changes in internal Na(+) concentration vary between and within classes of cortical neurons. These differences may have important consequences in pathophysiological disorders associated with down-regulation of Na(+)-K(+) ATPase and hyperexcitability within cortical networks.

    View details for DOI 10.1113/jphysiol.2010.191858

    View details for Web of Science ID 000284276000011

    View details for PubMedID 20819946

  • Excitatory Input Onto Hilar Somatostatin Interneurons Is Increased in a Chronic Model of Epilepsy JOURNAL OF NEUROPHYSIOLOGY Halabisky, B., Parada, I., Buckmaster, P. S., Prince, D. A. 2010; 104 (4): 2214-2223

    Abstract

    The density of somatostatin (SOM)-containing GABAergic interneurons in the hilus of the dentate gyrus is significantly decreased in both human and experimental temporal lobe epilepsy. We used the pilocarpine model of status epilepticus and temporal lobe epilepsy in mice to study anatomical and electrophysiological properties of surviving somatostatin interneurons and determine whether compensatory functional changes occur that might offset loss of other inhibitory neurons. Using standard patch-clamp techniques and pipettes containing biocytin, whole cell recordings were obtained in hippocampal slices maintained in vitro. Hilar SOM cells containing enhanced green fluorescent protein (EGFP) were identified with fluorescent and infrared differential interference contrast video microscopy in epileptic and control GIN (EGFP-expressing Inhibitory Neurons) mice. Results showed that SOM cells from epileptic mice had 1) significant increases in somatic area and dendritic length; 2) changes in membrane properties, including a small but significant decrease in resting membrane potential, and increases in time constant and whole cell capacitance; 3) increased frequency of slowly rising spontaneous excitatory postsynaptic currents (sEPSCs) due primarily to increased mEPSC frequency, without changes in the probability of release; 4) increased evoked EPSC amplitude; and 5) increased spontaneous action potential generation in cell-attached recordings. Results suggest an increase in excitatory innervation, perhaps on distal dendrites, considering the slower rising EPSCs and increased output of hilar SOM cells in this model of epilepsy. In sum, these changes would be expected to increase the inhibitory output of surviving SOM interneurons and in part compensate for interneuronal loss in the epileptogenic hippocampus.

    View details for DOI 10.1152/jn.00147.2010

    View details for Web of Science ID 000282649900037

    View details for PubMedID 20631216

  • Presynaptic Inhibitory Terminals Are Functionally Abnormal in a Rat Model of Posttraumatic Epilepsy JOURNAL OF NEUROPHYSIOLOGY Faria, L. C., Prince, D. A. 2010; 104 (1): 280-290

    Abstract

    Partially isolated "undercut" neocortex with intact pial circulation is a well-established model of posttraumatic epileptogenesis. Results of previous experiments showed a decreased frequency of miniature inhibitory postsynaptic currents (mIPSCs) in layer V pyramidal (Pyr) neurons of undercuts. We further examined possible functional abnormalities in GABAergic inhibition in rat epileptogenic neocortical slices in vitro by recording whole cell monosynaptic IPSCs in layer V Pyr cells and fast-spiking (FS) GABAergic interneurons using a paired pulse paradigm. Compared with controls, IPSCs in Pyr neurons of injured slices showed increased threshold and decreased peak amplitude at threshold, decreased input/output slopes, increased failure rates, and a shift from paired pulse depression toward paired pulse facilitation (increased paired pulse ratio or PPR). Increasing [Ca(2+)](o) from 2 to 4 mM partially reversed these abnormalities in Pyr cells of the epileptogenic tissue. IPSCs onto FS cells also had an increased PPR and failures. Blockade of GABA(B) receptors did not affect the paired results. These findings suggest that there are functional alterations in GABAergic presynaptic terminals onto both Pyr and FS cells in this model of posttraumatic epileptogenesis.

    View details for DOI 10.1152/jn.00351.2010

    View details for Web of Science ID 000279586400026

    View details for PubMedID 20484536

  • Focal Cortical Infarcts Alter Intrinsic Excitability and Synaptic Excitation in the Reticular Thalamic Nucleus JOURNAL OF NEUROSCIENCE Paz, J. T., Christian, C. A., Parada, I., Prince, D. A., Huguenard, J. R. 2010; 30 (15): 5465-5479

    Abstract

    Focal cortical injuries result in death of cortical neurons and their efferents and ultimately in death or damage of thalamocortical relay (TCR) neurons that project to the affected cortical area. Neurons of the inhibitory reticular thalamic nucleus (nRT) receive excitatory inputs from corticothalamic and thalamocortical axons and are thus denervated by such injuries, yet nRT cells generally survive these insults to a greater degree than TCR cells. nRT cells inhibit TCR cells, regulate thalamocortical transmission, and generate cerebral rhythms including those involved in thalamocortical epilepsies. The survival and reorganization of nRT after cortical injury would determine recovery of thalamocortical circuits after injury. However, the physiological properties and connectivity of the survivors remain unknown. To study possible alterations in nRT neurons, we used the rat photothrombosis model of cortical stroke. Using in vitro patch-clamp recordings at various times after the photothrombotic injury, we show that localized strokes in the somatosensory cortex induce long-term reductions in intrinsic excitability and evoked synaptic excitation of nRT cells by the end of the first week after the injury. We find that nRT neurons in injured rats show (1) decreased membrane input resistance, (2) reduced low-threshold calcium burst responses, and (3) weaker evoked excitatory synaptic responses. Such alterations in nRT cellular excitability could lead to loss of nRT-mediated inhibition in relay nuclei, increased output of surviving TCR cells, and enhanced thalamocortical excitation, which may facilitate recovery of thalamic and cortical sensory circuits. In addition, such changes could be maladaptive, leading to injury-induced epilepsy.

    View details for DOI 10.1523/JNEUROSCI.5083-09.2010

    View details for Web of Science ID 000276685100033

    View details for PubMedID 20392967

  • Neocortical Posttraumatic Epileptogenesis. Epilepsia Prince, D. A., Parada, I., Li, H., McDonald, W., Graber, K. 2010; 51 Suppl 5: 30

    Abstract

    Development of new excitatory connectivity and decreases in GABAergic inhibition are mechanisms underlying posttraumatic epileptogenesis in animal models. Experimental strategies that interfere with these processes, applied between the trauma andseizure onset, are antiepileptogenic in the laboratory, and have promise for prophylaxis of epileptogenesis after cortical injury in man. For an expanded treatment of this topic see Jasper's Basic Mechanisms of the Epilepsies, Fourth Edition (Noebels JL, Avoli M, Rogawski MA, Olsen RW, Delgado-Escueta AV, eds) published by Oxford University Press. Available on NCBI Bookshelf.

    View details for PubMedID 22056919

  • Neocortical posttraumatic epileptogenesis. Epilepsia Prince, D. A., Parada, I., Li, H., McDonald, W., Graber, K. 2010; 51 Suppl s5: 30

    Abstract

    Development of new excitatory connectivity and decreases in ?-aminobutyric acid (GABA)ergic inhibition are mechanisms underlying posttraumatic epileptogenesis in animal models. Experimental strategies that interfere with these processes, applied between the trauma and seizure onset, are antiepileptogenic in the laboratory, and have promise for prophylaxis of epileptogenesis after cortical injury in humans. For an expanded treatment of this topic see Jasper's Basic Mechanisms of the Epilepsies, Fourth Edition (Noebels JL, Avoli M, Rogawski MA, Olsen RW, Delgado-Escueta AV, eds) National Library of Medicine Bookshelf [NCBI] at http://www.ncbi.nlm.nih.gov/books).

    View details for PubMedID 21158780

  • Surviving Hilar Somatostatin Interneurons Enlarge, Sprout Axons, and Form New Synapses with Granule Cells in a Mouse Model of Temporal Lobe Epilepsy JOURNAL OF NEUROSCIENCE Zhang, W., Yamawaki, R., Wen, X., Uhl, J., Diaz, J., Prince, D. A., Buckmaster, P. S. 2009; 29 (45): 14247-14256

    Abstract

    In temporal lobe epilepsy, seizures initiate in or near the hippocampus, which frequently displays loss of neurons, including inhibitory interneurons. It is unclear whether surviving interneurons function normally, are impaired, or develop compensatory mechanisms. We evaluated GABAergic interneurons in the hilus of the dentate gyrus of epileptic pilocarpine-treated GIN mice, specifically a subpopulation of somatostatin interneurons that expresses enhanced green fluorescence protein (GFP). GFP-immunocytochemistry and stereological analyses revealed substantial loss of GFP-positive hilar neurons (GPHNs) but increased GFP-positive axon length per dentate gyrus in epileptic mice. Individual biocytin-labeled GPHNs in hippocampal slices from epileptic mice also had larger somata, more axon in the molecular layer, and longer dendrites than controls. Dual whole-cell patch recording was used to test for monosynaptic connections from hilar GPHNs to granule cells. Unitary IPSCs (uIPSCs) recorded in control and epileptic mice had similar average rise times, amplitudes, charge transfers, and decay times. However, the probability of finding monosynaptically connected pairs and evoking uIPSCs was 2.6 times higher in epileptic mice compared to controls. Together, these findings suggest that surviving hilar somatostatin interneurons enlarge, extend dendrites, sprout axon collaterals in the molecular layer, and form new synapses with granule cells. These epilepsy-related changes in cellular morphology and connectivity may be mechanisms for surviving hilar interneurons to inhibit more granule cells and compensate for the loss of vulnerable interneurons.

    View details for DOI 10.1523/JNEUROSCI.3842-09.2009

    View details for Web of Science ID 000271664000019

    View details for PubMedID 19906972

  • TEMPORAL AND TOPOGRAPHIC ALTERATIONS IN EXPRESSION OF THE alpha 3 ISOFORM OF Na+,K+-ATPase IN THE RAT FREEZE LESION MODEL OF MICROGYRIA AND EPILEPTOGENESIS NEUROSCIENCE Chu, Y., Parada, I., Prince, D. A. 2009; 162 (2): 339-348

    Abstract

    Na(+),K(+)-ATPase contributes to the asymmetrical distribution of sodium and potassium ions across the plasma membrane and to maintenance of the membrane potential in many types of cells. Alterations in this protein may play a significant role in many human neurological disorders, including epilepsy. We studied expression of the alpha3 isoform of Na(+),K(+)-ATPase in the freeze lesion (FL) microgyrus model of developmental epileptogenesis to test the hypothesis that it is downregulated following neonatal cortical injury. FL and sham-operated rat brains were examined at postnatal day (P)7, P10, P14, P21-28 and P50-60 after placement of a transcranial freeze lesion at P0 or P1. Immunohistochemistry and in situ hybridization were used to assess the expression of the alpha3 isoform of Na(+),K(+)-ATPase (termed alpha3, or alpha3 subunit below) in neuropil and the perisomatic areas of pyramidal cells and parvalbumin-containing interneurons. There was a significant decrease (P<0.05) in alpha3 subunit immunoreactivity (IR) in the neuropil of FL cortical layer V of the P14 and P21-28 groups that extended up to 360 mum from the border of the microgyrus, an area that typically exhibits evoked epileptiform activity. Alpha-3 was decreased in the perisomatic area of pyramidal but not parvalbumin-containing cells in P21-28 FL animals. A reduction in alpha3 mRNA was observed in the neuropil of FL cortical layer V up to 1610 mum from the microgyral edge. The developmental time course for expression of the alpha3 subunit between P7 and P60 was examined in naive rat cortices and results showed that there was a significant increase in alpha3 IR between P7 and P10. The significant decreases in Na(+),K(+)-ATPase in the paramicrogyral cortex may contribute to epileptogenesis.

    View details for DOI 10.1016/j.neuroscience.2009.04.003

    View details for Web of Science ID 000267787500012

    View details for PubMedID 19362129

  • Epilepsy following cortical injury: Cellular and molecular mechanisms as targets for potential prophylaxis EPILEPSIA Prince, D. A., Parada, I., Scalise, K., Graber, K., Jin, X., Shen, F. 2009; 50: 30-40

    Abstract

    The sequelae of traumatic brain injury, including posttraumatic epilepsy, represent a major societal problem. Significant resources are required to develop a better understanding of the underlying pathophysiologic mechanisms as targets for potential prophylactic therapies. Posttraumatic epilepsy undoubtedly involves numerous pathogenic factors that develop more or less in parallel. We have highlighted two potential "prime movers": disinhibition and development of new functional excitatory connectivity, which occur in a number of animal models and some forms of epilepsy in humans. Previous experiments have shown that tetrodotoxin (TTX) applied to injured cortex during a critical period early after lesion placement can prevent epileptogenesis in the partial cortical ("undercut") model of posttraumatic epilepsy. Here we show that such treatment markedly attenuates histologic indices of axonal and terminal sprouting and presumably associated aberrant excitatory connectivity. A second finding in the undercut model is a decrease in spontaneous inhibitory events. Current experiments show that this is accompanied by regressive alterations in fast-spiking gamma-aminobutyric acid (GABA)ergic interneurons, including shrinkage of dendrites, marked decreases in axonal length, structural changes in inhibitory boutons, and loss of inhibitory synapses on pyramidal cells. Other data support the hypothesis that these anatomic abnormalities may result from loss of trophic support normally provided to interneurons by brain-derived neurotrophic factor (BDNF). Approaches that prevent these two pathophysiologic mechanisms may offer avenues for prophylaxis for posttraumatic epilepsy. However, major issues such as the role of these processes in functional recovery from injury and the timing of the critical period(s) for application of potential therapies in humans need to be resolved.

    View details for DOI 10.1111/j.1528-1167.2008.02008.x

    View details for Web of Science ID 000262827500006

    View details for PubMedID 19187292

  • The Endocannabinoid 2-Arachidonoylglycerol Is Responsible for the Slow Self-Inhibition in Neocortical Interneurons JOURNAL OF NEUROSCIENCE Marinelli, S., Pacioni, S., Bisogno, T., Di Marzo, V., Prince, D. A., Huguenard, J. R., Bacci, A. 2008; 28 (50): 13532-13541

    Abstract

    In the CNS, endocannabinoids are identified mainly as two endogenous lipids: anandamide, the ethanolamide of arachidonic acid, and 2-arachidonoylglycerol (2-AG). Endocannabinoids are known to inhibit transmitter release from presynaptic terminals; however we have recently demonstrated that they are also involved in slow self-inhibition (SSI) of layer V low-threshold spiking (LTS) interneurons in rat somatosensory cortex. SSI is induced by repetitive firing in LTS cells, which can express either cholecystokinin or somatostatin. SSI is triggered by an endocannabinoid-dependent activation of a prolonged somatodendritic K(+) conductance and associated hyperpolarization in the same cell. The synthesis of both endocannabinoids is dependent on elevated [Ca(2+)](i) such as occurs during sustained neuronal activity. To establish whether 2-AG mediates autocrine LTS-SSI, we blocked its biosynthesis from phospholipase C (PLC) and diacylglycerol lipases (DAGLs). Current-clamp recordings from LTS interneurons in acute neocortical slices showed that inclusion of DAGL inhibitors in the whole-cell pipette prevented the long-lasting hyperpolarization triggered by LTS cell repetitive firing. Similarly, extracellular applications of a PLC inhibitor prevented SSI in LTS interneurons. Moreover, metabotropic glutamate receptor-dependent activation of PLC produced a long-lasting hyperpolarization which was prevented by the CB1 antagonist AM251, as well as by PLC and DAGL inhibitors. The loss of SSI in the presence of intracellular DAGL blockers confirms that endocannabinoid production occurs in the same interneuron undergoing the persistent hyperpolarization. Since DAGLs produce no endocannabinoid other than 2-AG, these results identify this compound as the autocrine mediator responsible for the postsynaptic slow self-inhibition of neocortical LTS interneurons.

    View details for DOI 10.1523/JNEUROSCI.0847-08.2008

    View details for Web of Science ID 000261601800018

    View details for PubMedID 19074027

  • Modulation of epileptiform activity by glutamine and system A transport in a model of post-traumatic epilepsy NEUROBIOLOGY OF DISEASE Tani, H., Bandrowski, A. E., Parada, I., Wynn, M., Huguenard, J. R., Prince, D. A., Reimer, R. J. 2007; 25 (2): 230-238

    Abstract

    Epileptic activity arises from an imbalance in excitatory and inhibitory synaptic transmission. To determine if alterations in the metabolism of glutamate, the primary excitatory neurotransmitter, might contribute to epilepsy we directly and indirectly modified levels of glutamine, an immediate precursor of synaptically released glutamate, in the rat neocortical undercut model of hyperexcitability and epilepsy. We show that slices from injured cortex take up glutamine more readily than control slices, and an increased expression of the system A transporters SNAT1 and SNAT2 likely underlies this difference. We also examined the effect of exogenous glutamine on evoked and spontaneous activity and found that addition of physiological concentrations of glutamine to perfusate of slices isolated from injured cortex increased the incidence and decreased the refractory period of epileptiform potentials. By contrast, exogenous glutamine increased the amplitude of evoked potentials in normal cortex, but did not induce epileptiform potentials. Addition of physiological concentrations of glutamine to perfusate of slices isolated from injured cortex greatly increased abnormal spontaneous activity in the form of events resembling spreading depression, again while having no effect on slices from normal cortex. Interestingly, similar spreading depression like events were noted in control slices at supraphysiological levels of glutamine. In the undercut cortex addition of methylaminoisobutyric acid (MeAIB), an inhibitor of the system A glutamine transporters attenuated all physiological effects of added glutamine suggesting that uptake through these transporters is required for the effect of glutamine. Our findings support a role for glutamine transport through SNAT1 and/or SNAT2 in the maintenance of abnormal activity in this in vitro model of epileptogenesis and suggest that system A transport and glutamine metabolism are potential targets for pharmacological intervention in seizures and epilepsy.

    View details for DOI 10.1016/j.nbd.2006.08.025

    View details for Web of Science ID 000243981400002

    View details for PubMedID 17070687

  • Electrophysiological classification of somatostatin-positive interneurons in mouse sensorimotor cortex JOURNAL OF NEUROPHYSIOLOGY Halabisky, B., Shen, F., Huguenard, J. R., Prince, D. A. 2006; 96 (2): 834-845

    Abstract

    Classification of inhibitory interneurons is critical in determining their role in normal information processing and pathophysiological conditions such as epilepsy. Classification schemes have relied on morphological, physiological, biochemical, and molecular criteria; and clear correlations have been demonstrated between firing patterns and cellular markers such as neuropeptides and calcium-binding proteins. This molecular diversity has allowed generation of transgenic mouse strains in which GFP expression is linked to the expression of one of these markers and presumably a single subtype of neuron. In the GIN mouse (EGFP-expressing Inhibitory Neurons), a subpopulation of somatostatin-containing interneurons in the hippocampus and neocortex is labeled with enhanced green fluorescent protein (EGFP). To optimize the use of the GIN mouse, it is critical to know whether the population of somatostatin-EGFP-expressing interneurons is homogeneous. We performed unsupervised cluster analysis on 46 EGFP-expressing interneurons, based on data obtained from whole cell patch-clamp recordings. Cells were classified according to a number of electrophysiological variables related to spontaneous excitatory postsynaptic currents (sEPSCs), firing behavior, and intrinsic membrane properties. EGFP-expressing interneurons were heterogeneous and at least four subgroups could be distinguished. In addition, multiple discriminant analysis was applied to data collected during whole cell recordings to develop an algorithm for predicting the group membership of newly encountered EGFP-expressing interneurons. Our data are consistent with a heterogeneous population of neurons based on electrophysiological properties and indicate that EGFP expression in the GIN mouse is not restricted to a single class of somatostatin-positive interneuron.

    View details for DOI 10.1152/jn.01079.2005

    View details for Web of Science ID 000238974700033

    View details for PubMedID 16707715

  • Enhanced excitatory synaptic connectivity in layer V pyramidal neurons of chronically injured epileptogenic neocortex in rats JOURNAL OF NEUROSCIENCE Jin, X. M., Prince, D. A., Huguenard, J. R. 2006; 26 (18): 4891-4900

    Abstract

    Formation of new recurrent excitatory circuits after brain injuries has been hypothesized as a major factor contributing to epileptogenesis. Increases in total axonal length and the density of synaptic boutons are present in layer V pyramidal neurons of chronic partial isolations of rat neocortex, a model of posttraumatic epileptogenesis. To explore the functional consequences of these changes, we used laser-scanning photostimulation combined with whole-cell patch-clamp recording from neurons in layer V of somatosensory cortex to map changes in excitatory synaptic connectivity after injury. Coronal slices were submerged in artificial CSF (23 degrees C) containing 100 microM caged glutamate, APV (2-amino-5-phosphonovaleric acid), and high divalent cation concentration to block polysynaptic responses. Focal uncaging of glutamate, accomplished by switching a pulsed UV laser to give a 200-400 micros light stimulus, evoked single- or multiple-component composite EPSCs. In neurons of the partially isolated cortex, there were significant increases in the fraction of uncaging sites from which EPSCs could be evoked ("hot spots") and a decrease in the mean amplitude of individual elements in the composite EPSC. When plotted along the cortical depth, the changes in EPSCs took place mainly between 150 and 200 microm above and below the somata, suggesting a specific enhancement of recurrent excitatory connectivity among layer V pyramidal neurons of the undercut neocortex. These changes may shift the balance within cortical circuits toward increased synaptic excitation and contribute to epileptogenesis.

    View details for DOI 10.1523/JNEUROSCI.4361-05.2006

    View details for Web of Science ID 000237271700020

    View details for PubMedID 16672663

  • Barrel cortex microcircuits: Thalamocortical feedforward inhibition in spiny stellate cells is mediated by a small number of fast-spiking interneurons JOURNAL OF NEUROSCIENCE Sun, Q. Q., Huguenard, J. R., Prince, D. A. 2006; 26 (4): 1219-1230

    Abstract

    Inhibitory and excitatory neurons located in rodent barrel cortex are known to form functional circuits mediating vibrissal sensation. Excitatory neurons located in a single barrel greatly outnumber interneurons, and form extensive reciprocal excitatory synaptic contacts. Inhibitory and excitatory networks must interact to shape information ascending to cortex. The details of these interactions, however, have not been completely explored. Using paired intracellular recordings, we studied the properties of synaptic connections between spiny neurons (i.e., spiny stellate and pyramidal cells) and interneurons, as well as integration of thalamocortical (TC) input, in layer IV barrels of rat thalamocortical slices. Results show the following: (1) the strength of unitary excitatory connections of spiny neurons is similar among different targets; (2) although inhibition from regular-spiking nonpyramidal interneurons to spiny neurons is comparable in strength to excitatory connections, inhibition mediated by fast-spiking (FS) interneurons is 10 times more powerful; (3) TC EPSPs elicit reliable and precisely timed action potentials in FS neurons; and (4) a small number of FS neurons mediate thalamocortical feedforward inhibition in each spiny neuron and can powerfully shunt TC-mediated excitation. The ready activation of FS cells by TC inputs, coupled with powerful feedforward inhibition from these neurons, would profoundly influence sensory processing and constrain runaway excitation in vivo.

    View details for DOI 10.1523/JNEUROSCI.4727-04.2006

    View details for Web of Science ID 000234896200020

    View details for PubMedID 16436609

  • Modulation of neocortical interneurons: extrinsic influences and exercises in self-control TRENDS IN NEUROSCIENCES Bacci, A., Huguenard, J. R., Prince, D. A. 2005; 28 (11): 602-610

    Abstract

    Neocortical GABAergic interneurons are a highly heterogeneous cell population that forms complex functional networks and has key roles in information processing within the cerebral cortex. Mechanisms that control the output of these cells are therefore crucial in regulating excitability within the neocortex during normal and pathophysiological activities. In addition to subtype-specific modulation of GABAergic cells by neurotransmitters released by afferents from subcortical nuclei, interneurons belonging to different classes are controlled by distinct self-modulatory mechanisms, each unique and powerful. In this article, we review the diverse responses of neocortical interneurons to extrinsic and intrinsic neuromodulators. We discuss how specificity of responses might differentially influence inhibition in somatodendritic compartments of pyramidal neurons and affect the balance of activities in neocortical circuits.

    View details for DOI 10.1016/j.tins.2005.08.007

    View details for Web of Science ID 000233213700006

    View details for PubMedID 16139371

  • Impaired Cl- extrusion in layer V pyramidal neurons of chronically injured epileptogenic neocortex JOURNAL OF NEUROPHYSIOLOGY Jin, X. M., Huguenard, J. R., Prince, D. A. 2005; 93 (4): 2117-2126

    Abstract

    In the mature brain, the K(+)/Cl- cotransporter KCC2 is important in maintaining low [Cl-]i, resulting in hyperpolarizing GABA responses. Decreases in KCC2 after neuronal injuries result in increases in [Cl-]i and enhanced neuronal excitability due to depolarizing GABA responses. We used the gramicidin perforated-patch technique to measure E(Cl) ( approximately E(GABA)) in layer V pyramidal neurons in slices of partially isolated sensorimotor cortex of adult rats to explore the potential functional consequence of KCC2 downregulation in chronically injured cortex. E(GABA) was measured by recording currents evoked with brief GABA puffs at various membrane potentials. There was no significant difference in E(Cl) between neurons in control and undercut animals (-71.2 +/- 2.6 and -71.8 +/- 2.8 mV, respectively). However, when loaded with Cl- by applying muscimol puffs at 0.2 Hz for 60 s, neurons in the undercut cortex had a significantly shorter time constant for the positive shift in E(Cl) during the Cl- loading phase (4.3 +/- 0.5 s for control and 2.2 +/- 0.4 s for undercut, P < 0.01). The positive shift in E(Cl) 3 s after the beginning of Cl- loading was also significantly larger in the undercut group than in the control, indicating that neurons in undercut cortex were less effective in maintaining low [Cl-]i during repetitive activation of GABA(A) receptors. Application of furosemide eliminated the difference between the control and undercut groups for both of these measures of [Cl-]i regulation. The results suggest an impairment in Cl- extrusion resulting from decreased KCC2 expression that may reduce the strength of GABAergic inhibition and contribute to epileptogenesis.

    View details for DOI 10.1152/jn.00728.2004

    View details for Web of Science ID 000227701600029

    View details for PubMedID 15774713

  • REORGANIZATION OF BARREL CIRCUITS LEADS TO THALAMICALLY-EVOKED CORTICAL EPILEPTIFORM ACTIVITY. Thalamus & related systems Sun, Q. Q., Huguenard, J. R., Prince, D. A. 2005; 3 (4): 261-273

    Abstract

    We studied circuit activities in layer IV of rat somatosensory barrel cortex containing microgyri induced by neonatal freeze lesions. Structural abnormalities in GABAergic interneurons are present in the epileptogenic paramicrogyral area (PMG) and we therefore tested the hypothesis that decreased postsynaptic inhibition within barrel microcircuits occurs in the PMG and contributes to epileptogenesis when thalamocortical afferents are activated. In thalamocortical (TC) slices from naïve animals, single electrical stimuli within the thalamic ventrobasal (VB) nucleus evoked transient cortical multi-unit activity lasting 65±42 ms. Similar stimuli in TC slices from lesioned barrel cortex elicited prolonged 850 ±100 ms paroxysmal discharges that originated in the PMG and propagated laterally over several mm. Paroxysmal discharges were shortened in duration by ~70 % when APV was applied, and were totally abolished by CNQX. The cortical paroxysmal discharges did not evoke thalamic oscillations. Whole cell patch clamp recordings showed that there was a shift in the balance of TC evoked responses in the PMG that favored excitation over inhibition. Dual whole-cell recordings in layer IV of the PMG indicated that there was selective loss of inhibition from fast-spiking interneurons to spiny neurons in the barrel circuits that likely contributed to unconstrained cortical recurrent excitation with generation and spread of paroxysmal discharges.

    View details for PubMedID 18185849

  • Cortical injury affects short-term plasticity of evoked excitatory synaptic currents JOURNAL OF NEUROPHYSIOLOGY Li, H. F., Bandrowski, A. E., Prince, D. A. 2005; 93 (1): 146-156

    Abstract

    The hypothesis that plastic changes in the efficacy of excitatory neurotransmission occur in areas of chronic cortical injury was tested by assessing short-term plasticity of evoked excitatory synaptic currents (EPSCs) in neurons of partially isolated neocortical islands (undercut cortex). Whole cell recordings were obtained from layer V pyramidal neurons of sensorimotor cortical slices prepared from P36-P43 control and undercut rats. AMPA/kainate receptor-mediated EPSCs elicited by stimuli delivered at 40 to 66.7 Hz exhibited more paired-pulse depression (PPD) in undercut cortex than control, the time constant of depression evoked by trains of 20- to 66.7-Hz stimuli was faster, and the steady-state amplitude of EPSCs reached after five to seven EPSCs was lower. An antagonist of the glutamate autoreceptor, group II mGluR, increased the steady-state amplitude of EPSCs from undercut but not control cortex, suggesting that activation of presynaptic receptors by released glutamate is more prominent in undercut cortex. In contrast, the GABA(B) receptor antagonist (2S)-3-[[(1S)-1-(3,4-dichlorophenyl)ethyl]amino-2-hydroxypropyl](phenylmethyl)phosphinic acid had no effect. Increasing [Ca(2+)](o) from 2 to 4 mM increased PPD, with a smaller effect in neurons of the undercut. The I-V relationship of AMPA/kainate receptor-mediated EPSCs was close to linear in both control and undercut neurons, and spermine had no significant effect on the EPSCs, suggesting that decreases in postsynaptic glutamate receptors containing the GluR2 subunit were not involved in the alterations in short-term plasticity. Results are compatible with an increase in the probability of transmitter release at excitatory synapses in undercut cortex due to functional changes in presynaptic terminals.

    View details for DOI 10.1152/jn.00665.2004

    View details for Web of Science ID 000225777900015

    View details for PubMedID 15342719

  • Long-lasting self-inhibition of neocortical interneurons mediated by endocannabinoids NATURE Bacci, A., Huguenard, J. R., Prince, D. A. 2004; 431 (7006): 312-316

    Abstract

    Neocortical GABA-containing interneurons form complex functional networks responsible for feedforward and feedback inhibition and for the generation of cortical oscillations associated with several behavioural functions. We previously reported that fast-spiking (FS), but not low-threshold-spiking (LTS), neocortical interneurons from rats generate a fast and precise self-inhibition mediated by inhibitory autaptic transmission. Here we show that LTS cells possess a different form of self-inhibition. LTS, but not FS, interneurons undergo a prominent hyperpolarization mediated by an increased K+-channel conductance. This self-induced inhibition lasts for many minutes, is dependent on an increase in intracellular [Ca2+] and is blocked by the cannabinoid receptor antagonist AM251, indicating that it is mediated by the autocrine release of endogenous cannabinoids. Endocannabinoid-mediated slow self-inhibition represents a powerful and long-lasting mechanism that alters the intrinsic excitability of LTS neurons, which selectively target the major site of excitatory connections onto pyramidal neurons; that is, their dendrites. Thus, modulation of LTS networks after their sustained firing will lead to long-lasting changes of glutamate-mediated synaptic strength in pyramidal neurons, with consequences during normal and pathophysiological cortical network activities.

    View details for DOI 10.1038/nature02913

    View details for Web of Science ID 000223864000042

    View details for PubMedID 15372034

  • A critical period for prevention of posttraumatic neocortical hyperexcitability in rats ANNALS OF NEUROLOGY Graber, K. D., Prince, D. A. 2004; 55 (6): 860-870

    Abstract

    Penetrating cortical trauma frequently results in delayed development of epilepsy. In the rat undercut model of neocortical posttraumatic hyperexcitability, suppression of neuronal activity by exposing the injured cortex to tetrodotoxin (TTX) in vivo for approximately 2 weeks prevents the expression of abnormal hypersynchronous discharges in neocortical slices. We examined the relationship between neuronal activity during the latent period after trauma and subsequent expression of hyperexcitability by varying the timing of TTX treatment. Partially isolated islands of rat sensorimotor cortex were treated with Elvax polymer containing TTX to suppress cortical activity and slices obtained for in vitro experiments 10 to 15 days later. TTX treatment was either started immediately after injury and discontinued after a variable number of days or delayed for a variable time after the lesion was placed. Immediate treatment lasting only 2 to 3 days and treatment delayed up to 3 days prevented hyperexcitability. Thus, there is a critical period for development of hyperexcitability in this model that depends on cortical activity. We propose that the hyperexcitability caused by partial cortical isolation may represent an early stage of posttraumatic epileptogenesis. A hypothetical cascade of events leading to subsequent pathophysiological activity is likely initiated at the time of injury but remains plastic during this critical period.

    View details for DOI 10.1002/ana.20124

    View details for Web of Science ID 000221716300013

    View details for PubMedID 15174021

  • Target-specific neuropeptide Y-ergic synaptic inhibition and its network consequences within the mammalian thalamus JOURNAL OF NEUROSCIENCE Sun, Q. Q., Baraban, S. C., Prince, D. A., Huguenard, J. R. 2003; 23 (29): 9639-9649

    Abstract

    Neuropeptides are commonly colocalized with classical neurotransmitters, yet there is little evidence for peptidergic neurotransmission in the mammalian CNS. We performed whole-cell patch-clamp recording from rodent thalamic brain slices and repetitively stimulated corticothalamic fibers to strongly activate NPY-containing GABAergic reticular thalamic (RT) neurons. This resulted in long-lasting (approximately 10 sec) feedforward slow IPSPs (sIPSPs) in RT cells, which were mimicked and blocked by NPY1 (Y1) receptor agonists and antagonists, respectively, and were present in wild-type mice but absent in NPY-/- mice. NPYergic sIPSPs were mediated via G-proteins and G-protein-activated, inwardly rectifying potassium channels, as evidenced by sensitivity to GDP-beta-S and 0.1 mm Ba2+. In rat RT neurons, NPYergic sIPSPs were also present but were surprisingly absent in the major synaptic targets of RT, thalamic relay neurons, where instead robust GABA(B) IPSPs occurred. In vitro oscillatory network responses in rat thalamus were suppressed and augmented by Y1 agonists and antagonists, respectively. These findings provide evidence for segregation of postsynaptic actions between two targets of RT cells and support a role for endogenously released NPY within RT in the regulation of oscillatory thalamic responses relevant to sleep and epilepsy.

    View details for Web of Science ID 000186107100018

    View details for PubMedID 14573544

  • Major differences in inhibitory synaptic transmission onto two neocortical interneuron subclasses JOURNAL OF NEUROSCIENCE Bacci, A., Rudolph, U., Huguenard, J. R., Prince, D. A. 2003; 23 (29): 9664-9674

    Abstract

    Locally projecting GABAergic interneurons are the major providers of inhibition in the neocortex and play a crucial role in several brain functions. Neocortical interneurons are connected via electrical and chemical synapses that may be crucial in modulating complex network oscillations. We investigated the properties of spontaneous and evoked IPSCs in two morphologically and physiologically identified interneuron subtypes, the fast-spiking (FS) and low threshold-spiking (LTS) cells in layer V of rodent sensorimotor cortex. We found that IPSCs recorded in FS cells were several orders of magnitude more frequent, larger in amplitude, and had faster kinetics than IPSCs recorded in LTS cells. GABA(A) receptor alpha- and beta-subunit selective modulators, zolpidem and loreclezole, had different effects on IPSCs in FS and LTS interneurons, suggesting differential expression of GABA(A) receptor subunit subtypes. These pharmacological data indicated that the alpha1 subunit subtype is poorly expressed by LTS cells but makes a large contribution to GABA(A) receptors on FS cells. This was confirmed by experiments performed in genetically modified mice in which the alpha1 subunit had been made insensitive to benzodiazepine-like agonists. These results suggest that differences in IPSC waveform are likely attributable to distinctive expression of GABA(A) receptor subunits in FS and LTS cells. The particular properties of GABAergic input on different interneuronal subtypes might have important consequences for generation and pacing of cortical rhythms underlying several brain functions. Moreover, selective pharmacological manipulation of distinct inhibitory circuits might allow regulation of pyramidal cell activities under specific physiological and pathophysiological conditions.

    View details for Web of Science ID 000186107100020

    View details for PubMedID 14573546

  • Vasoactive intestinal polypeptide and pituitary adenylate cyclase-activating polypeptide activate hyperpolarization activated cationic current and depolarize thalamocortical neurons in vitro JOURNAL OF NEUROSCIENCE Sun, Q. Q., Prince, D. A., Huguenard, J. R. 2003; 23 (7): 2751-2758

    Abstract

    Ascending pathways mediated by monoamine neurotransmitters regulate the firing mode of thalamocortical neurons and modulate the state of brain activity. We hypothesized that specific neuropeptides might have similar actions. The effects of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) were tested on thalamocortical neurons using whole-cell patch-clamp techniques applied to visualized neurons in rat brain slices. VIP (2 microm) and PACAP (100 nm) reversibly depolarized thalamocortical neurons (7.8 +/- 0.6 mV; n = 16), reduced the membrane resistance by 33 +/- 3%, and could convert the firing mode from bursting to tonic. These effects on resting membrane potential and membrane resistance persisted in the presence of TTX. Morphologically diverse thalamocortical neurons located in widespread regions of thalamus were all depolarized by VIP and PACAP38. In voltage-clamp mode, we found that VIP and PACAP38 reversibly activated a hyperpolarization-activated cationic current (I(H)) in thalamocortical neurons and altered voltage- and time-dependent activation properties of the current. The effects of VIP on membrane conductance were abolished by the hyperpolarization-activated cyclic-nucleotide-gated channel (HCN)-specific antagonist ZD7288, showing that HCN channels are the major target of VIP modulation. The effects of VIP and PACAP38 on HCN channels were mediated by PAC(1) receptors and cAMP. The actions of PACAP-related peptides on thalamocortical neurons suggest an additional and novel endogenous neurophysiological pathway that may influence both normal and pathophysiological thalamocortical rhythm generation and have important behavioral effects on sensory processing and sleep-wake cycles.

    View details for Web of Science ID 000182107200028

    View details for PubMedID 12684461

  • Baseline glutamate levels affect group I and II mGluRs in layer V pyramidal neurons of rat sensorimotor cortex JOURNAL OF NEUROPHYSIOLOGY Bandrowski, A. E., Huguenard, J. R., Prince, D. A. 2003; 89 (3): 1308-1316

    Abstract

    Possible functional roles for glutamate that is detectable at low concentrations in the extracellular space of intact brain and brain slices have not been explored. To determine whether this endogenous glutamate acts on metabotropic glutamate receptors (mGluRs), we obtained whole cell recordings from layer V pyramidal neurons of rat sensorimotor cortical slices. Blockade of mGluRs with (+)-alpha-amino-4-carboxy-alpha-methyl-benzeacetic acid (MCPG, a general mGluR antagonist) increased the mean amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), an effect attributable to a selective increase in the occurrence of large amplitude sEPSCs. 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495, a group II antagonist) increased, but R(-)-1-amino-2,3-dihydro-1H-indene-1,5-dicarboxylic acid (AIDA) and (RS)-hexyl-HIBO (group I antagonists) decreased sEPSC amplitude, and (R,S)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, a group III antagonist) did not change it. The change in sEPSCs elicited by MCPG, AIDA, and LY341495 was absent in tetrodotoxin, suggesting that it was action potential-dependent. The increase in sEPSCs persisted in GABA receptor antagonists, indicating that it was not due to effects on inhibitory interneurons. AIDA and (S)-3,5-dihydroxyphenylglycine (DHPG, a group I agonist) elicited positive and negative shifts in holding current, respectively. LY341495 and (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV, a group II agonist) elicited negative and positive shifts in holding current, respectively. The AIDA and LY341495 elicited currents persisted in TTX. Finally, in current clamp, LY341495 depolarized cells by approximately 2 mV and increased the number of action potentials to a given depolarizing current pulse. Thus ambient levels of glutamate tonically activate mGluRs and regulate cortical excitability.

    View details for DOI 10.1152/jn.00644.2002

    View details for Web of Science ID 000181426400014

    View details for PubMedID 12626613

  • Heterogeneous actions of serotonin on interneurons in rat visual cortex JOURNAL OF NEUROPHYSIOLOGY Xiang, Z. X., Prince, D. A. 2003; 89 (3): 1278-1287

    Abstract

    The effects of serotonin (5-HT) on excitability of two cortical interneuronal subtypes, fast-spiking (FS) and low threshold spike (LTS) cells, and on spontaneous inhibitory postsynaptic currents (sIPSCs) in layer V pyramidal cells were studied in rat visual cortical slices using whole-cell recording techniques. Twenty-two of 28 FS and 26 of 35 LTS interneurons responded to local application of 5-HT. In the group of responsive neurons, 5-HT elicited an inward current in 50% of FS cells and 15% of LTS cells, an outward current was evoked in 41% of FS cells and 81% of LTS cells, and an inward current followed by an outward current in 9% of FS cells and 4% LTS cells. The inward and outward currents were blocked by a 5-HT(3) receptor antagonist, tropisetron, and a 5-HT(1A) receptor antagonist, NAN-190, respectively. The 5-HT-induced inward and outward currents were both associated with an increase in membrane conductance. The estimated reversal potential was more positive than -40 mV for the inward current and close to the calculated K(+) equilibrium potential for the outward current. The 5-HT application caused an increase, a decrease, or an increase followed by a decrease in the frequency of sIPSCs in pyramidal cells. The 5-HT(3) receptor agonist 1-(m-chlorophenyl) biguanide increased the frequency of larger and fast-rising sIPSCs, whereas the 5-HT(1A) receptor agonist (+/-)8-hydroxydipropylaminotetralin hydrobromide elicited opposite effects and decreased the frequency of large events. These data indicate that serotonergic activation imposes complex actions on cortical inhibitory networks, which may lead to changes in cortical information processing.

    View details for DOI 10.1152/jn.00533.2002

    View details for Web of Science ID 000181426400011

    View details for PubMedID 12626611

  • Functional autaptic neurotransmission in fast-spiking interneurons: A novel form of feedback inhibition in the neocortex JOURNAL OF NEUROSCIENCE Bacci, A., Huguenard, J. R., Prince, D. A. 2003; 23 (3): 859-866

    Abstract

    Autapses are synapses made by a neuron onto itself. Although morphological evidence for existence of autapses has been reported in several brain areas, it is not known whether such self-innervation in the neocortex is functional and robust. Here we report that GABAergic autaptic activity is present in fast-spiking, but not in low-threshold spiking, interneurons of layer V in neocortical slices. Recordings made with the perforated-patch technique, in which physiological intracellular chloride homeostasis was unperturbed, demonstrated that autaptic activity has significant inhibitory effects on repetitive firing and increased the current threshold for evoking action potentials. These results show that autapses are not rudimentary nonfunctional structures, but rather they provide a novel and powerful form of feedback inhibitory synaptic transmission in one class of cortical interneurons.

    View details for Web of Science ID 000180865400016

    View details for PubMedID 12574414

  • Light microscopic study of glur1 and calbindin expression in interneurons of neocortical microgyral malformations NEUROSCIENCE Kharazia, V. N., Jacobs, K. M., Prince, D. A. 2003; 120 (1): 207-218

    Abstract

    Rat neocortex that has been injured on the first or second postnatal day (P0-1) develops an epileptogenic, aberrantly layered malformation called a microgyrus. To investigate the effects of this developmental plasticity on inhibitory interneurons, we studied a sub-population of GABAergic cells that co-express the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor GluR1 subunit and the calcium-binding protein, calbindin (CB). Both malformed and control cortex of adult (P40-60) animals contained numerous interneurons double-stained for CB and GluR1. Immunoreactivity (IR) for CB was up-regulated in perikarya of interneurons within supragranular layers of control cortex between P12 and P40. However, in malformed adult (P40) cortex, CB-IR levels were significantly lower than in adult controls, and fell midway between levels in immature and adult control animals. Between P12 and P40, GluR1-IR was down-regulated in perikarya of interneurons in control cortex. Somatic GluR1-IR levels in malformed adult (P40) cortex were not different from adult controls. These neurons formed a dense plexus of highly GluR1-positive spiny dendrites within layer II. The dendritic plexus in the malformation was more intensely GluR1-immunoreactive than that in layer II of control cortex. This was due to apparent changes in thickness and length of dendrites, rather than to significant changes in the number of interneuronal perikarya in the microgyral cortex. Results indicate that the population of GluR1/CB-containing interneurons is spared in malformed microgyral cortex, but that these cells sustain lasting decreases in their somatic expression of calbindin and alterations of dendritic structure. Potential functional implications of these findings are discussed.

    View details for DOI 10.1016/S0306-4522(03)00282-3

    View details for Web of Science ID 000184257500019

    View details for PubMedID 12849753

  • Differential modulation of synaptic transmission by neuropeptide Y in rat neocortical neurons PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Bacci, A., Huguenard, J. R., Prince, D. A. 2002; 99 (26): 17125-17130

    Abstract

    Neuropeptide Y (NPY) is widely expressed throughout the nervous system and is known to reduce excitatory (but also inhibitory) synaptic transmission in many CNS areas, leading to the proposal that it is an endogenous antiepileptic agent. In the neocortex, where NPY is present in gamma-aminobutyric acid (GABA)ergic interneurons, its effects on inhibitory and excitatory synaptic activities have not been completely explored. Here we report that NPY application elicits a long-lasting decrease in evoked excitatory postsynaptic current amplitude and a delayed, long-lasting increase in the amplitude of evoked monosynaptic inhibitory postsynaptic current (IPSC) in layer V pyramidal neurons of rat neocortex. The novel, late, NPY-mediated increase of inhibitory synaptic transmission is caused by modulation of Ca2+-dependent GABA release onto pyramidal neurons, as it was accompanied by an increase in Ca2+-dependent miniature IPSC frequency. NPY decreased evoked monosynaptic IPSCs in GABAergic interneurons, indicating that this neuropeptide has differential effects on different neuronal subtypes in the neocortex. Each of these NPY actions would decrease excitability in cortical circuits, a result that has important implications for both physiological neocortical operations as well as pathophysiological epileptiform activities.

    View details for Web of Science ID 000180101600110

    View details for PubMedID 12482942

  • Synaptic inhibition of pyramidal cells evoked by different interneuronal subtypes in layer V of rat visual cortex JOURNAL OF NEUROPHYSIOLOGY Xiang, Z. X., Huguenard, J. R., Prince, D. A. 2002; 88 (2): 740-750

    Abstract

    Properties of GABA(A) receptor-mediated unitary inhibitory postsynaptic currents (uIPSCs) in pyramidal (P) cells, evoked by fast spiking (FS) and low-threshold spike (LTS) subtypes of interneurons in layer V of rat visual cortex slices were examined using dual whole cell recordings. uIPSCs evoked by FS cells were larger and faster rising than those evoked by LTS cells, consistent with the known primary projections of FS and LTS cell axons to perisomatic and distal dendritic areas of layer V pyramidal cells, respectively, and the resulting electrotonic attenuation for LTS-P synaptic events. Unexpectedly, the decay time constants for LTS-P and FS-P uIPSCs were not significantly different. Modeling results were consistent with differences in the underlying GABA(A) receptor-mediated conductance at LTS-P and FS-P synapses. Paired-pulse depression (PPD), present at both synapses, was associated with an increase in failure rate and a decrease in coefficient of variation, indicating that presynaptic mechanisms were involved. Furthermore, the second and first uIPSC amplitudes during PPD were not inversely correlated, suggesting that PPD at both synapses is independent of previous release and might not result from depletion of the releasable pool of synaptic vesicles. Short, 20-Hz trains of action potentials in presynaptic interneurons evoked trains of uIPSCs with exponentially decreasing amplitudes at both FS-P and LTS-P synapses. FS-P uIPSC amplitudes declined more slowly than those of LTS-P uIPSCs. Thus FS and LTS cells, with their differences in firing properties, synaptic connectivity with layer V P cells, and short-term synaptic dynamics, might play distinct roles in regulating the input-output relationship of the P cells.

    View details for DOI 10.1152/jn.00635.2001

    View details for Web of Science ID 000177276100018

    View details for PubMedID 12163526

  • Somatostatin inhibits thalamic network oscillations in vitro: Actions on the GABAergic neurons of the reticular nucleus JOURNAL OF NEUROSCIENCE Sun, Q. Q., Huguenard, J. R., Prince, D. A. 2002; 22 (13): 5374-5386

    Abstract

    We examined the effects of somatostatin (SST) on neurons in the thalamic reticular nucleus (RT) using whole-cell patch-clamp techniques applied to visualized neurons in rat thalamic slices. SST, acting via sst(5) receptors and pertussis toxin-sensitive G-proteins, activated an inwardly rectifying K(+) (GIRK) current in 20 of 28 recorded cells to increase input conductance 15 +/- 3% above control and inhibited N-type Ca(2+) currents in 17 of 24 neurons via voltage-dependent mechanisms. SST reversibly depressed evoked EPSCs (eEPSCs) to 37 +/- 8% of control without altering their kinetics. SST-mediated inhibition of eEPSCs showed short-term relief from block during 25 Hz stimulus trains. SST also reduced the frequency (33 +/- 8%) but not the amplitude of miniature EPSCs (mEPSCs). These data indicate that SST mediates presynaptic inhibition of glutamate release onto RT neurons. In current-clamp recordings, SST preferentially inhibited burst discharges mediated by near-threshold corticothalamic EPSPs and intracellularly applied depolarizing currents. SST had powerful effects on in vitro intrathalamic rhythms, which included a shortening of the duration and a reduction in spike count within each oscillatory event. Furthermore, there was a paradoxical increase in the synchrony of epileptiform oscillations, likely mediated by a suppression of the responses to weak synaptic inputs in RT. We conclude that SST suppresses discharges in RT neurons, via presynaptic inhibition of glutamate release and postsynaptic activation of GIRK channels, leading to the dampening of both spindle-like and epileptiform thalamic network oscillations. SST may act as an important endogenous regulator of physiological and pathological thalamocortical network activities.

    View details for Web of Science ID 000176599100017

    View details for PubMedID 12097489

  • Synaptic activity in chronically injured, epileptogenic sensory-motor neocortex JOURNAL OF NEUROPHYSIOLOGY Li, H. F., Prince, D. A. 2002; 88 (1): 2-12

    Abstract

    We recorded spontaneous and evoked synaptic currents in pyramidal neurons of layer V in chronically injured, epileptogenic neocortex to assess changes in the efficacy of excitatory and inhibitory neurotransmission that might promote cortical hyperexcitability. Partial sensory-motor neocortical isolations with intact blood supply ("undercuts") were made in 20 rats on postnatal day 21-25 and examined 2-6 wk later in standard brain slice preparations using whole cell patch-clamp techniques. Age-matched, uninjured naive rats (n = 20) were used as controls. Spontaneous and miniature excitatory and inhibitory postsynaptic currents (s- and mEPSCs; s- and mIPSCs) were recorded using patch-clamp techniques. The average frequency of s- and mEPSCs was significantly higher, while that of s- and mIPSCs was significantly lower in neurons of undercuts versus controls. The increased frequency of excitatory events was due to an increase in both s- and mEPSC frequency, suggesting an increased number of excitatory contacts and/or increased release probability at excitatory terminals. No significant difference was observed in 10-90% rise time of these events. The input-output slopes of fast, short-latency, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate (AMPA/KA) receptor-mediated components of evoked EPSCs were steeper in undercuts than in controls. The peak amplitude of the AMPA/KA component of EPSCs evoked by supra-threshold stimuli was significantly greater in the partially isolated neocortex. In contrast, the N-methyl-D-aspartate receptor-mediated component of evoked EPSCs was not significantly different in neurons of injured versus control cortex, suggesting that the increased AMPA/KA component was due to postsynaptic alterations. Results support the conclusion that layer V pyramidal neurons receive increased AMPA/KA receptor-mediated excitatory synaptic drive and decreased GABA(A) receptor-mediated inhibition in this chronically injured, epileptogenic cortex. This shift in the balance of excitatory and inhibitory synaptic activation of layer V pyramidal cells toward excitation might be maladaptive and play a critical role in epileptogenesis.

    View details for DOI 10.1152/jn.00507.2001

    View details for Web of Science ID 000176493800002

    View details for PubMedID 12091528

  • Kinetic and pharmacological properties of GABA(A) receptors in single thalamic neurons and GABA(A) subunit expression JOURNAL OF NEUROPHYSIOLOGY Browne, S. H., Kang, J., Akk, G., Chiang, L. W., Schulman, H., Huguenard, J. R., Prince, D. A. 2001; 86 (5): 2312-2322

    Abstract

    Synaptic inhibition in the thalamus plays critical roles in sensory processing and thalamocortical rhythm generation. To determine kinetic, pharmacological, and structural properties of thalamic gamma-aminobutyric acid type A (GABA(A)) receptors, we used patch-clamp techniques and single-cell reverse transcriptase polymerase chain reaction (RT-PCR) in neurons from two principal rat thalamic nuclei-the reticular nucleus (nRt) and the ventrobasal (VB) complex. Single-channel recordings identified GABA(A) channels with densities threefold higher in VB than nRt neurons, and with mean open time fourfold longer for nRt than VB [14.6 +/- 2.5 vs. 3.8 +/- 0.7 (SE) ms, respectively]. GABA(A) receptors in nRt and VB cells were pharmacologically distinct. Zn(2+) (100 microM) reduced GABA(A) channel activity in VB and nRt by 84 and 24%, respectively. Clonazepam (100 nM) increased inhibitory postsynaptic current (IPSC) decay time constants in nRt (from 44.3 to 77.9 ms, P < 0.01) but not in VB. Single-cell RT-PCR revealed subunit heterogeneity between nRt and VB cells. VB neurons expressed alpha1-alpha3, alpha5, beta1-3, gamma2-3, and delta, while nRt cells expressed alpha3, alpha5, gamma2-3, and delta. Both cell types expressed more subunits than needed for a single receptor type, suggesting the possibility of GABA(A) receptor heterogeneity within individual thalamic neurons. beta subunits were not detected in nRt cells, which is consistent with very low levels reported in previous in situ hybridization studies but inconsistent with the expected dependence of functional GABA(A) receptors on beta subunits. Different single-channel open times likely underlie distinct IPSC decay time constants in VB and nRt cells. While we can make no conclusion regarding beta subunits, our findings do support alpha subunits, possibly alpha1 versus alpha3, as structural determinants of channel deactivation kinetics and clonazepam sensitivity. As the gamma2 and delta subunits previously implicated in Zn(2+) sensitivity are both expressed in each cell type, the observed differential Zn(2+) actions at VB versus nRt GABA(A) receptors may involve other subunit differences.

    View details for Web of Science ID 000172012800017

    View details for PubMedID 11698521

  • Differential regulation of GABA release and neuronal excitability mediated by neuropeptide Y-1 and Y-2 receptors in rat thalamic neurons JOURNAL OF PHYSIOLOGY-LONDON Sun, Q. Q., Akk, G., Huguenard, J. R., Prince, D. A. 2001; 531 (1): 81-94

    Abstract

    1. Neuropeptide Y (NPY) produced inhibitory effects on neurons of the thalamic reticular nucleus (RT; n = 18) and adjacent ventral basal complex (VB; n = 22), which included hyperpolarization (approximately 4 mV), a reduction in rebound and regular spikes and an increased membrane conductance. These effects were mediated predominantly via NPY1 receptor activation of G-protein-activated, inwardly rectifying K+ (GIRK) channels. 2. NPY reduced the frequency of spontaneous GABAA receptor-mediated inhibitory postsynaptic currents (sIPSCs) in RT (by 60 +/- 7 %, n = 14) and VB neurons (by 25 +/- 11 %, n = 16), but had no effect on the kinetic properties of sIPSCs. After removal of the RT nucleus, the inhibitory effects of NPY on sIPSCs in VB neurons remained (29 +/- 7 %, n = 5). The synaptic effects were mediated via NPY2 receptors. 3. NPY inhibited the frequency of miniature IPSCs (mIPSCs) in RT and VB neurons (by 63 +/- 7 %, n = 5, and 37 +/- 8 %, n = 10, respectively) in the presence of tetrodotoxin (TTX) (1 microM) but not TTX (1 microM) and Cd2+ (200 microM). 4. NPY inhibited evoked IPSCs in both RT (by 18 +/- 3 %, n = 6) and VB (by 5 +/- 4 %, n = 6) neurons without change in short-term synaptic plasticity. 5. We conclude that NPY1 and NPY2 receptors are functionally segregated in the thalamus: NPY1 receptors are predominantly expressed at the somata and dendrites and directly reduce the excitability of neurons in both the RT and VB nuclei by activating GIRK channels. NPY2 receptors are located at recurrent (RT) and feed-forward GABAergic terminals (VB) and downregulate GABA release via inhibition of Ca2+ influx from voltage-gated Ca2+ channels.

    View details for Web of Science ID 000167409800007

    View details for PubMedID 11179393

  • Neuropeptide Y receptors differentially modulate G-protein-activated inwardly rectifying K+ channels and high-voltage-activated Ca2+ channels in rat thalamic neurons JOURNAL OF PHYSIOLOGY-LONDON Sun, Q. Q., Huguenard, J. R., Prince, D. A. 2001; 531 (1): 67-79

    Abstract

    1. Using whole-cell patch-clamp recordings, infrared videomicroscopy and fast focal solution exchange methods, the actions of neuropeptide Y (NPY) were examined in thalamic slices of postnatal (10-16 days) rats. 2. NPY activated a K+-selective current in neurons of the thalamic reticular nucleus (RT; 20/29 neurons) and ventral basal complex (VB; 19/25 neurons). The currents in both nuclei had activation and deactivation kinetics that were very similar to those of GABAB receptor-induced currents, were totally blocked by 0.1 mM Ba2+ and showed voltage-dependent relaxation. These properties indicate that the NPY-sensitive K+ current is mediated by G-protein-activated, inwardly rectifying K+ (GIRK) channels. 3. In RT neurons, NPY application reversibly reduced high-voltage-activated (HVA) currents to 33 +/- 5 % (n = 40) of the control level but did not affect the T-type currents. Inhibition of Ca2+ currents was voltage independent and was largely mediated by effects on N- and P/Q-type channels. 4. NPY activation of GIRK channels was mediated via NPY1 receptors, whereas inhibition of N- and P/Q-type Ca2+ channels was mediated by NPY2 receptors. 5. These results show that neuropeptide Y activates K+ channels and simultaneously inhibits HVA Ca2+ channels via different receptor subtypes.

    View details for Web of Science ID 000167409800006

    View details for PubMedID 11179392

  • Changes of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors in layer V of epileptogenic, chronically isolated rat neocortex NEUROSCIENCE Kharazia, V. N., Prince, D. A. 2001; 102 (1): 23-34

    Abstract

    In vivo chronic partial isolation of neocortical islands results in epileptogenesis that involves pyramidal neurons of layer V. To test whether an alteration in glutamate receptors might contribute to the epileptiform activity, we analysed the time-course of light microscopic changes in expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors using subunit-specific antibodies. The isolation caused a rapid down-regulation of immunoreactivity for GluR1 and GluR2/3 subunits in deep layer V pyramidal neurons within the neocortical island which was evident 24h post-lesion, and within three days was reduced to about 40-60% of the control level. Many pyramidal cells in deep layer V completely lacked GluR2. Between one and four weeks of survival, down-regulation of GluR2/3 and GluR2 involved the majority of pyramidal layer V neurons, except for cells in the upper part of layer V, and those within narrow areas of all sub-laminae of layer V ("micro-islands"). Initial down-regulation was also observed one to three days post-lesion for subunits 1 and 2 of the N-methyl-D-aspartate receptor, but in contrast to GluR2/3 immunoreactivity, NMDAR2A/B immunoreactivity was enhanced three weeks post-lesion. The present data provide evidence for plastic changes in glutamate receptors in neurons of partially isolated neocortical island. A sub-population of layer V neurons remains relatively unaffected, and would presumably be capable of generating fast glutamatergic synaptic potentials necessary for the development of synchronous epileptiform activity.

    View details for Web of Science ID 000166562300003

    View details for PubMedID 11226667

  • Experimental microgyri disrupt the barrel field pattern in rat somatosensory cortex CEREBRAL CORTEX Jacobs, K. M., Mogensen, M., Warren, E., Prince, D. A. 1999; 9 (7): 733-744

    Abstract

    Transcranial freeze lesions in neonatal rat pups produce microgyri and adjacent epileptogenic regions of neocortex that can be used to model human polymicrogyria. The hypothesis that the presence of microgyri is associated with abnormal cortical organization occurring within as well as adjacent to the microgyri was tested by creating microgyri within the face representation of somatosensory cortex. Microgyri were associated with a widespread disruption of the stereotypic whisker barrel field pattern delineated with cytochrome oxidase (CO) staining. CO-stained patches resembling barrel hollows were absent within the microgyrus, and were abnormally shaped and distributed outside of the microgyrus. Adjacent Nissl- or acetylcholinesterase-stained sections demonstrated that both cell clusters and thalamocortical afferents contributed to the abnormally organized paramicrogyral zone identified in CO-stained sections. Field potential recordings showed that this region of heavy CO staining corresponded to the epileptogenic zone adjacent to the microgyrus. Results support our hypothesis that the epileptogenic paramicrogyral zone develops an abnormal organization of cell clusters and thalamocortical projections that could contribute to epileptogenesis in the paramicrogyral zone.

    View details for Web of Science ID 000083300500009

    View details for PubMedID 10554996

  • Tetrodotoxin prevents posttraumatic epileptogenesis in rats ANNALS OF NEUROLOGY Graber, K. D., Prince, D. A. 1999; 46 (2): 234-242

    Abstract

    Severe cortical trauma frequently causes epilepsy that develops after a long latency. We hypothesized that plastic changes in excitability during this latent period might be initiated or sustained by the level of neuronal activity in the injured cortex. We therefore studied effects of action potential blockade by application of tetrodotoxin (TTX) to areas of cortical injury in a model of chronic epileptogenesis. Partially isolated islands of sensorimotor cortex were made in 28- to 30-day-old male Sprague-Dawley rats and thin sheets of Elvax polymer containing TTX or control vehicle were implanted over lesions. Ten to 15 days later neocortical slices were obtained through isolates for electrophysiological studies. Slices from all animals (n = 12) with lesions contacted by control-Elvax (58% of 36 slices) exhibited evoked epileptiform field potentials, and those from 4 rats had spontaneous epileptiform events. Only 2 of 11 lesioned animals and 6% of slices from cortex exposed to TTX in vivo exhibited evoked epileptiform potentials, and no spontaneous epileptiform events were observed. There was no evidence of residual TTX during recordings. TTX-Elvax was ineffective in reversing epileptogenesis when implanted 11 days after cortical injury. These data suggest that development of antiepileptogenic drugs for humans may be possible.

    View details for Web of Science ID 000081876900013

    View details for PubMedID 10443889

  • Focal epileptogenesis in a rat model of polymicrogyria JOURNAL OF NEUROPHYSIOLOGY Jacobs, K. M., Hwang, B. J., Prince, D. A. 1999; 81 (1): 159-173

    Abstract

    Polymicrogyria, a developmental cortical malformation associated with epilepsy, can be modeled in rats with a transcortical freeze lesion on the day of birth (P0) or P1. We have used field potential recordings to characterize the incidence, propagation patterns, and distribution of epileptiform activity in slices from rats with experimental microgyri. Interictal-like epileptiform activity was evoked in slices from 85% of freeze-lesioned rats aged P12-P118. These data show age-specific properties of epileptogenesis, including: a delay in onset, a decrease in the incidence of epileptiform activity in rats >P40 that was specific to those lesioned on P0 as opposed to P1, and a shift in the likely site of initiation to areas further from the microgyrus in mature animals. Several observations suggest that the area adjacent to the microgyrus, which appears histologically normal in Nissl stains, contains the necessary epileptogenic neuronal circuits: 1) in 78% of slices, epileptiform activity could be evoked only from a focal zone adjacent to the microgyrus (paramicrogyral zone) and not within the microgyrus proper; 2) epileptiform activity consistently originated from a particular site within this paramicrogyral zone, independent of the location of the stimulating electrode, suggesting that the generator is outside of the microgyrus; 3) evoked epileptiform activities in the paramicrogyral cortex were unaltered after separation of this zone from the microgyrus with a transcortical cut; and 4) the short-latency graded field potential evoked in the paramicrogyral zone contained an additional negativity not seen in control slices. The epileptiform activity was blocked reversibly by N-methyl--aspartate receptor antagonists in slices from mature as well as immature freeze-lesioned rats. These results suggest that aberrant synaptic connectivity develops in rat cortex surrounding the microgyrus and produces a focal epileptogenic zone whose capacity to generate epileptiform activities does not depend on connections with the malformation itself. We hypothesize that afferents, originating from cortical and extracortical sites, lose their targets in the region of the malformation and make appropriate laminar contacts in the cortex adjacent to the malformation, creating an overabundance of excitatory input to this cortical zone. Increased excitatory feedback onto specific cortical elements may be one factor involved in epileptogenesis in this model of a cortical malformation.

    View details for Web of Science ID 000078353800016

    View details for PubMedID 9914277

  • Epileptogenic neurons and circuits. Advances in neurology Prince, D. A. 1999; 79: 665-684

    View details for PubMedID 10514854

  • Inhibitory function in two models of chronic epileptogenesis EPILEPSY RESEARCH Prince, D. A., Jacobs, K. 1998; 32 (1-2): 83-92

    Abstract

    Although drug-induced disinhibition is a potent method for producing acute epileptogenesis, data with respect to possible disorders of GABAergic inhibitory function in models of chronic epilepsy are incomplete and inconsistent. We examined rat models of cortical post-traumatic epilepsy, and epileptogenic cortical microgyri. Results suggest enhanced rather than decreased inhibitory function in cortical networks in these preparations. In brain slices from epileptogenic chronically isolated cortex, the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature (m)IPSCs in layer V pyramidal neurons is increased compared to control. In the epileptogenic zone adjacent to the microgyrus, both spontaneous and stimulus-induced IPSCs are larger in amplitude than control, and the frequency of sIPSCs is more dependent upon glutamatergic excitation of interneurons than in control layer V neurons of homotopic cortex. Immunocytochemical studies show that there is enhanced immunoreactivity for several proteins in GABAergic interneurons of chronic cortical isolations, and suggest that there may be sprouting of GABAergic axons in the area of injury. This conclusion is supported by anatomic data showing an approximate doubling of the number of presumed inhibitory synapses on somata of layer V pyramidal neurons. These anatomic findings are consistent with the increased frequency of mIPSCs on these neurons. Inhibition is robust in both of these chronic models of epileptogenesis. Increased inhibitory electrogenesis might be pictured as part of the epileptogenic process, e.g. a mechanism for synchronizing the discharge of pyramidal neurons, or as a compensatory mechanism that might prevent the development of abnormal activities in some cases, or limit the intensity of epileptogenesis in others.

    View details for Web of Science ID 000076034000009

    View details for PubMedID 9761311

  • Cholinergic switching within neocortical inhibitory networks SCIENCE Xiang, Z. X., Huguenard, J. R., Prince, D. A. 1998; 281 (5379): 985-988

    Abstract

    Differential actions of acetylcholine on the excitability of two subtypes of interneurons in layer V of the rat visual cortex were examined. Acetylcholine excited low-threshold spike (LTS) cells through nicotinic receptors, whereas it elicited hyperpolarization in fast spiking (FS) cells through muscarinic receptors. Axons of LTS cells were mainly distributed vertically to upper layers, and those of FS cells were primarily confined to layer V. Thus, cortical cholinergic activation may reduce some forms of intralaminar inhibition, promote intracolumnar inhibition, and change the direction of information flow within cortical circuits.

    View details for Web of Science ID 000075412700046

    View details for PubMedID 9703513

  • Adrenergic modulation of GABA(A) receptor-mediated inhibition in rat sensorimotor cortex JOURNAL OF NEUROPHYSIOLOGY Bennett, B. D., Huguenard, J. R., Prince, D. A. 1998; 79 (2): 937-946

    Abstract

    The effect of adrenoceptor activation on pharmacologically isolated monosynaptic inhibitory postsynaptic currents (IPSCs) detected in layer V pyramidal neurons was examined by using whole cell voltage-clamp in a slice preparation of rat sensorimotor cortex. Epinephrine (EPI; 10 muM) reversibly altered the amplitude of evoked IPSCs (eIPSCs) in slices from postnatal day 9-12 (P9-12) and P15-18 rats. The effects of EPI were heterogeneous in both age groups, and in individual cases an enhancement, a depression or no effect of eIPSCs was observed, although depression was observed more commonly in the younger age group. The effects of EPI on eIPSC amplitude were likely mediated through presynaptic mechanisms because they occurred in the absence of any alteration in the current produced by direct application of gamma-aminobutyric acid (GABA), or in input resistance. EPI always elicited an increase in the frequency of spontaneous IPSCs (sIPSCs) irrespective of whether or not it induced any change in the amplitude of eIPSCs in the same neuron. The increase in sIPSC frequency was blocked by phentolamine (10 muM) but not by propranolol (10 muM), supporting the conclusion that EPI-mediated effects on sIPSC frequency result from activation of alpha-adrenoceptors located on presynaptic inhibitory interneurons. In a subpopulation of neurons (3/9) from P15-18 rats, EPI increased both the amplitude and frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin (TTX) and under conditions where postsynaptic EPI effects were blocked, suggesting activation of adrenoceptors on presynaptic terminals in these cells. Results of these experiments are consistent with an action of EPI at adrenoceptors located on presynaptic GABAergic interneurons. Adrenergic activation thus has multiple and complex influences on excitability in cortical circuits, some of which are a consequence of interactions that regulate the strength of GABAergic inhibition.

    View details for Web of Science ID 000072115600038

    View details for PubMedID 9463454

  • GABA(A) receptor-mediated currents in interneurons and pyramidal cells of rat visual cortex JOURNAL OF PHYSIOLOGY-LONDON Xiang, Z. X., Huguenard, J. R., Prince, D. A. 1998; 506 (3): 715-730

    Abstract

    1. We compared gamma-aminobutyric acid (GABA)-mediated responses of identified pyramidal cells and fast spiking interneurons in layer V of visual cortical slices from young rats (P11-14). 2. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was similar in pyramidal cells and interneurons (1.7 vs. 1.9 Hz). For events with 10-90% rise times less than 0.9 ms, no significant differences were found in mean amplitude (61 vs. 65 pA), mean rise time (0.58 vs. 0.61 ms), or the first time constant of decay (tau 1, 6.4 vs. 6.5 ms) between pyramidal cells and interneurons. The second decay time constant (tau 2) was significantly longer in interneurons than in pyramidal cells (49 vs. 22 ms). The difference in sIPSC decay kinetics between two cell types also existed in adult rats (P36-42), suggesting the kinetic difference in not due to differential development of GABAA receptors in these cell types. 3. The decay kinetics of monosynaptic evoked IPSCs were also longer in interneurons. As in the case of sIPSCs, the difference was accounted for by the second decay time constant. tau 1 and tau 2 were, respectively, 13 and 64 ms for interneurons and 12 and 47 ms for pyramidal cells. 4. Cell-attached patch recordings revealed that the mean open time for single Cl- channels in response to 2 microM GABA was significantly longer in interneurons than pyramidal cells (5.0 vs. 2.8 ms). The chord conductance of these channels in interneurons (12 pS) was significantly smaller than in pyramidal cells (15 pS). Single channel currents reversed polarity when the pipette potential was approximately -10 mV for both cell types. 5. These results show that there is a functional diversity of GABAA receptors in electrophysiologically and morphologically identified cortical pyramidal cells and interneurons. This diversity might derive from the different molecular composition of the receptors in these two cell types.

    View details for Web of Science ID 000072026800011

    View details for PubMedID 9503333

  • GABA(A) receptor-mediated Cl- currents in rat thalamic reticular and relay neurons JOURNAL OF NEUROPHYSIOLOGY ZHANG, S. L., Huguenard, J. R., Prince, D. A. 1997; 78 (5): 2280-2286

    Abstract

    GABAA receptor-mediated Cl- currents in rat thalamic reticular and relay neurons. J. Neurophysiol. 78: 2280-2286, 1997. Spontaneous and evoked inhibitory postsynaptic currents (sIPSCs and eIPSCs) and responses to exogenously applied gamma-aminobutyric acid (GABA), mediated by GABA type A (GABAA) receptors, were recorded in inhibitory neurons of nucleus reticularis thalami (nRt) and their target relay cells in ventrobasal (VB) nuclei by using patch clamp techniques in rat thalamic slices. The decay of sIPSCs in both nRt and VB neurons was best fitted with two exponential components. The decay time constants of sIPSCs in nRt neurons were much slower (tau1 = 38 ms; tau2 = 186 ms) than those previously reported in a variety of preparations and two to three times slower than those in VB neurons (tau1 = 17 ms; tau2 = 39 ms). GABAA receptor-mediated Cl- currents directly evoked by local GABA application also had a much slower decay time constant in nRt (225 ms) than in VB neurons (115 ms). Slow decay of GABA responses enhances the efficacy of recurrent intranuclear inhibition in nRt. The results suggest a functional diversity of GABAA receptors that may relate to the known heterogeneity of GABAA receptor subunits in these two thalamic nuclei.

    View details for Web of Science ID A1997YG93900005

    View details for PubMedID 9356381

  • Nucleus reticularis neurons mediate diverse inhibitory effects in thalamus PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Cox, C. L., Huguenard, J. R., Prince, D. A. 1997; 94 (16): 8854-8859

    Abstract

    Detailed information regarding the contribution of individual gamma-aminobutyric acid (GABA)-containing inhibitory neurons to the overall synaptic activity of single postsynaptic cells is essential to our understanding of fundamental elements of synaptic integration and operation of neuronal circuits. For example, GABA-containing cells in the thalamic reticular nucleus (nRt) provide major inhibitory innervation of thalamic relay nuclei that is critical to thalamocortical rhythm generation. To investigate the contribution of individual nRt neurons to the strength of this internuclear inhibition, we obtained whole-cell recordings of unitary inhibitory postsynaptic currents (IPSCs) evoked in ventrobasal thalamocortical (VB) neurons by stimulation of single nRt cells in rat thalamic slices, in conjunction with intracellular biocytin labeling. Two types of monosynaptic IPSCs could be distinguished. "Weak" inhibitory connections were characterized by a significant number of postsynaptic failures in response to presynaptic nRt action potentials and relatively small IPSCs. In contrast, "strong" inhibition was characterized by the absence of postsynaptic failures and significantly larger unitary IPSCs. By using miniature IPSC amplitudes to infer quantal size, we estimated that unitary IPSCs associated with weak inhibition resulted from activation of 1-3 release sites, whereas stronger inhibition would require simultaneous activation of 5-70 release sites. The inhibitory strengths were positively correlated with the density of axonal swellings of the presynaptic nRt neurons, an indicator that characterizes different nRt axonal arborization patterns. These results demonstrate that there is a heterogeneity of inhibitory interactions between nRt and VB neurons, and that variations in gross morphological features of axonal arbors in the central nervous system can be associated with significant differences in postsynaptic response characteristics.

    View details for Web of Science ID A1997XQ12400100

    View details for PubMedID 9238067

  • Adrenoceptor-mediated elevation of ambient GABA levels activates presynaptic GABA(B) receptors in rat sensorimotor cortex JOURNAL OF NEUROPHYSIOLOGY Bennett, B. D., Huguenard, J. R., Prince, D. A. 1997; 78 (1): 561-566

    Abstract

    At inhibitory synapses in the mature neocortex and hippocampus in vitro, spontaneous action-potential-dependent and -independent release of gamma-aminobutyric acid (GABA) activates postsynaptic GABA(A) receptors but not pre- or postsynaptic GABA(B) receptors. Elevation of synaptic GABA levels with pharmacological agents or electrical stimulation can cause activation of GABA(B) receptors, but the physiological conditions under which such activation occurs need further elucidation. In rodent sensorimotor cortex, epinephrine produced a depression in the amplitude of evoked monosynaptic inhibitory postsynaptic currents (IPSCs) and a concomitant, adrenoceptor-mediated increase in the frequency of spontaneous IPSCs. Blockade of GABA(B) receptors prevented the depression of evoked IPSC amplitude by epinephrine but did not affect the increase in spontaneous IPSC frequency. These data show that adrenoceptor-mediated increases in spontaneous IPSCs can cause activation of presynaptic GABA(B) receptors and indirectly modulate impulse-related GABA release, presumably through elevation of synaptic GABA levels.

    View details for Web of Science ID A1997XM21100054

    View details for PubMedID 9242307

  • Axonal sprouting and epileptogenesis. Advances in neurology Prince, D. A., Salin, P., Tseng, G. F., Hoffman, S., Parada, I. 1997; 72: 1-8

    View details for PubMedID 8993679

  • Peptidergic modulation of intrathalamic circuit activity in vitro: Actions of cholecystokinin JOURNAL OF NEUROSCIENCE Cox, C. L., Huguenard, J. R., Prince, D. A. 1997; 17 (1): 70-82

    Abstract

    Cholecystokinin (CCK)-mediated actions on intrathalamic rhythmic activities were examined in an in vitro rat thalamic slice preparation. Single electrical stimuli in the thalamic reticular nucleus (nRt) evoked rhythmic activity (1-15 sec duration) in nRt and the adjacent ventrobasal nucleus (VB). Low CCK concentrations (20-50 nM) suppressed rhythmic oscillations in 43% of experiments but prolonged such activities in the remaining slices. Higher CCK concentrations (100-400 nM) had a predominantly antioscillatory effect. Suppression of oscillations was associated with a relatively large membrane depolarization of nRt neurons that changed their firing mode from phasic (burst) to tonic (single-spike) output. This decreased burst discharge of nRt neurons during CCK application reduced inhibitory drive onto VB neurons from multiple peaked inhibitory postsynaptic currents (IPSCs) to single peaked inhibitory events. We hypothesize that suppression of inhibitory drive onto VB neurons decreases their probability of burst output, which, together with a reduction of nRt burst output, dampens the oscillatory activity. Low CCK concentrations, which produced little or no depolarization of nRt neurons, did not alter the firing mode of the nRt neurons. However, the probability of burst output from nRt neurons in response to subthreshold stimuli was increased in low CCK concentrations, presumably leading to an increase in the number of nRt neurons participating in the rhythmic activity. Our findings suggest that the neuropeptide CCK, by altering the firing characteristics of nRt neurons, has powerful modulatory effects on intrathalamic rhythms; the ultimate action was dependent on CCK concentration and resting state of these cells.

    View details for Web of Science ID A1997WJ67700007

    View details for PubMedID 8987737

  • Two types of BK channels in immature rat neocortical pyramidal neurons JOURNAL OF NEUROPHYSIOLOGY Kang, J., Huguenard, J. R., Prince, D. A. 1996; 76 (6): 4194-4197

    Abstract

    1. The properties of large conductance Ca(2+)-activated K+ channels (BK channels) were investigaed in neocortical infragranular pyramidal neurons by the use of inside-out patch recordings. Neurons were acutely isolated from slices of newborn to 28-day-old rats (P0-P28) by using minimal protease exposure followed by trituration with a vibrating glass probe. Two types of BK channels, slow-gating and fast-gating, were observed in immature neurons (P0-P5), whereas only slow-gating BK were found in more mature neurons. Fast-gating BK channels differed in conductance, voltage dependence, and kinetics from the slow-gating ones. 2. The properties of fast-gating channels included a conductance of 145 +/- 12.9 (SE) pS; frequent openings with short mean open times that were relatively voltage-independent, mean closed times that showed a voltage-dependent increase, a voltage-dependent decrease in open probability (Po). The properties of slow-gating channels contrasted with those of the fast-gating ones, in that the former had a conductance of 181 +/- 3.9 pS, longer mean open times that showed a voltage-dependent increase, mean closed times that showed a marked voltage-dependent decrease, a voltage-dependent increase in Po, and slight inward rectification. The significance of these developmental variations in channel properties is discussed.

    View details for Web of Science ID A1996WA80300056

    View details for PubMedID 8985914

  • Development of BK channels in neocortical pyramidal neurons JOURNAL OF NEUROPHYSIOLOGY Kang, J., Huguenard, J. R., Prince, D. A. 1996; 76 (1): 188-198

    Abstract

    1. Postnatal development of a large conductance Ca(2+)-activated K+ channel (BK channel) was investigated in neocortical infragranular pyramidal neurons with inside-out and outside-out patchclamp configurations. Neurons were acutely isolated from slices of 1- to 28-day-old rats (P1-P28) by using a vibrating glass probe after preincubation with low concentrations of enzymes. Patch membrane area was estimated by measuring membrane capacitance. The density, distribution, voltage dependence, Ca2+ sensitivity, kinetics, and pharmacological properties of BK channels were examined in neurons from animals of different ages. 2. In somata, the density of BK channels was 0.056 +/- 0.011/ micron 2 in P1 neurons and 0.312 +/- 0.008/micron 2 in P28 neurons. There was an abrupt increase between P5 and P7 at a rate of approximately 0.042/ micron 2/day. Before P5 and after P7, the density of BK channels also increased but at slower rates. 3. The density of BK channels in proximal apical dendrites underwent a similar developmental sequence. There was a relatively large increase between P5 and P7 with a rate of approximately 0.021/ micron 2/day, and after P7, channel density increased more slowly (approximately 0.002/microns 2/day). In P1 neurons, channel density in apical dendrites was 0.039 +/- 0.008/micron 2, which was close to that in somata, whereas in P28 neurons, channel density (0.134 +/- 0.008/micron 2) was less than one-half of that in somata. 4. The distribution of BK channels was different in immature and mature neurons. In somata of P1 neurons, BK channels were distributed singly without evidence of clustering, whereas in P28 neurons BK channels were clustered in groups of approximately 4. 5. BK channels in both P1 and P14 neurons showed a steep increase in the probability of opening (Po) as intracellular Ca2+ concentration was raised from 50 to 100 nM, especially at positive membrane potentials. The Ca2+ dependence, as measured by the [Ca2+]i that provided half-maximal Po at a variety of membrane potentials, was not different in patches from P1 and P14 neurons. On the other hand, the voltage dependence of BK channels shifted during ontogeny such that Po was larger at negative potentials in P14 than in P1 neurons. 6. The voltage dependence of P1 BK channels was bimodally distributed with 57% of channels exhibiting an "immature" pattern consisting of a more positive V1/2 and a smaller change in voltage required to produce an e-fold increase in Po. Immature type P1 BK channels showed a longer mean closed time at negative membrane potentials than either P14 or "mature" P1 BK channels. 7. No postnatal developmental changes in pharmacological properties of BK channels were observed. In both mature and immature neurons, BK channels were partially inhibited by 30 or 100 nM charybdotoxin (ChTX) and fully blocked by 1 microM ChTX. The IC50 for ChTX was 100 nM, indicating that BK channels in neocortical pyramidal neurons are much less sensitive to ChTX than those in muscle cells and sympathetic ganglion neurons. BK channels were also inhibited by 0.5 mM tetraethylammonium chloride (TEA) and 50 microM trifluoperazine. 8. These data indicate that functional somatic and dendritic BK channels are inserted into neuronal membranes during neocortical development, with an especially rapid increment in density occurring around P5-P7. These changes, which occur at a time when other voltage-gated ion channels are known to be increasing in density, contribute to the development of neocortical excitability.

    View details for Web of Science ID A1996UY79300015

    View details for PubMedID 8836218

  • Hyperexcitability in a model of cortical maldevelopment CEREBRAL CORTEX Jacobs, K. M., Gutnick, M. J., Prince, D. A. 1996; 6 (3): 514-523

    Abstract

    The presence of developmental cortical malformations has been associated with the occurrence of epilepsy, and correlative anatomic-clinical electrophysiological studies suggest that microdysgenic lesions may actually initiate epileptiform activity. We have investigated the electrophysiological properties of an animal model of polymicrogyria created by making cortical freeze lesions in rat pups at P0 or P1. Such lesions create microgyri with histological features similar to those of human polymicrogyria. We have determined that there is a focal region of hyperexcitability around the lesion in this rat microgyrus. Field potentials evoked by stimulation within a few millimeters of the microgyrus have characteristics typical of epileptiform activity. This aberrant activity is seen as early as 12 d after the lesion, as well as in animals as old as 118 d. Immunochemical staining for the calcium binding protein, parvalbumin, shows a decrease in neuronal and neuropil staining within the microgyrus. These findings suggest that inhibition might be decreased within the lesion, which may contribute to generation of the adjacent hyperexcitable region. These results demonstrate that this animal model is appropriate for examining the mechanisms contributing to epileptogenesis associated with a cortical malformation.

    View details for Web of Science ID A1996UL40900018

    View details for PubMedID 8670677

  • Spontaneous GABA(A) receptor-mediated inhibitory currents in adult rat somatosensory cortex JOURNAL OF NEUROPHYSIOLOGY Salin, P. A., Prince, D. A. 1996; 75 (4): 1573-1588

    Abstract

    1. Spontaneous inhibitory synaptic currents (sIPSCs) were studied with whole cell voltage-clamp recordings from 131 pyramidal cells in adult rat somatosensory cortical slices. Neurons were intracellulary labeled with biocytin and classified as supragranular (SG, layers 2-3), layer IV (IV), or infragranular (IG, layer V) on the basis of the laminar localization of their somata. Somatic areas were similar for SG, IV, and IG neurons. All identified pyramidal cells generated high-frequency gamma-aminobutyric acid (GABAA) receptor-mediated synaptic events. 2. Bath application of bicuculline blocked the sIPSCs and resulted in a decrease of approximately 0.5 nS in resting conductance and an inward shift in baseline current. 3. sIPSC frequency was significantly lower in SG versus IG or IV neurons, and this difference was accounted for by the occurrence of a higher percentage of bursts of sIPSCs in the IG and IV neurons. 4. Bath application of the alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) decreased the frequency of sIPSCs by 13-21%. By contrast, application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovaleric acid (D-AP5) generally had no effect on spontaneous IPSC frequency, suggesting that AMPA rather than NMDA receptor activation contributed to resting discharge of inhibitory interneurons. 5. Addition of tetrodotoxin (TTX) to the perfusion medium reduced the spontaneous IPSC frequency by approximately 30-55%. The miniature IPSCs (mIPSCs) seen in TTX-containing solutions had a frequency of approximately 10 Hz and an average conductance of 0.42-0.48 nS. 6. The kinetic properties of mIPSCs generated in pyramidal cells of different layers were the same, with the rise times of approximately 0.9 ms and decay time constants of approximately 8 ms at a holding potential of 0 mV. The decay phase of mIPSCs was generally fitted by one exponential and displayed a voltage dependence with an e-fold increase in decay time constant for a every 198-mV depolarization. 7. These results show that there is ongoing spontaneous release of GABA in neocortical slices that gives rise to high-frequency impulse-related and non-impulse-related postsynaptic inhibitory currents. Activation of AMPA receptors on inhibitory interneurons accounts for only a small proportion of the GABAA receptor-mediated events. Judging from the distribution of mIPSC frequencies in neurons of different laminae, there is a relatively uniform distribution of inhibitory synapses throughout the cortex. Tonic activation of GABAA receptors on neocortical pyramidal neurons generates an increase in resting membrane conductance that may play an important role in vivo by preventing the development of hyperexcitability, modulating excitatory synaptic events, and controlling the rate and patterns of spike discharge.

    View details for Web of Science ID A1996UE79800018

    View details for PubMedID 8727397

  • Electrophysiological mapping of GABA(A) receptor-mediated inhibition in adult rat somatosensory cortex JOURNAL OF NEUROPHYSIOLOGY Salin, P. A., Prince, D. A. 1996; 75 (4): 1589-1600

    Abstract

    1. gamma-Aminobutyric acid-A (GABAA) receptor-mediated synaptic currents evoked by intracortical stimulation in rat somatosensory cortical slices maintained in vitro were studied using the whole cell patch-clamp technique. All anatomically identified pyramidal neurons of layer II-III (SG neurons), layer IV (IV neurons), and layer V (IG neurons) generated evoked inhibitory postsynaptic currents (eIPSCs) that were blocked by bicuculline. At threshold, eIPSCs had kinetic properties (rise time of 0.9 ms and decay time constant of 9 ms) similar to those of spontaneous IPSCs generated in the same cells. 2. The strength of inhibition was quantified by determining the stimulus threshold for evoking responses and the relationship between stimulus strength and eIPSC peak amplitudes (input/output curve). For eIPSCs recorded in control solution, the input/output curve was about four times steeper than for eIPSCs recorded in the presence of the ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and D-2-amino-5-phosphonovalerate (D-AP5), suggesting the dependence of GABAA inhibition on synpatic excitation of interneurons. 3. In the presence of CNQX and D-AP5, monosynaptic IPSCs, evoked by stimulation close to the recording patch pipette, had similar input/output curves in SG and IG neurons. This suggests that the level of monosynaptic inhibition generated in these two populations of cells is similar. 4. When the stimulus was moved to a distant site > 350 microns from the recorded neuron, either in vertical or in horizontal direction, the stimulus intensity required for evoking IPSCs was higher, and the input/output curve was less steep. This suggests that the density of GABAergic somata and axons projecting to the recorded neuron is lower at these distances than at more proximal sites. 5. The maximum horizontal distance over which IPSCs could be evoked ("horizontal field") was larger in layer V than in other layers. The horizontal field (distance between stimulating and recording pipettes) was 600 microns in layer II-III, 580 microns in layer IV, and 720 microns in layer V. Anatomic identification of the somatosensory cortical barrels indicated that the extent of GABAergic projections was larger than the barrel hollow and might thus form a substrate for interbarrel inhibition in layer IV during cross-wisker stimulation. 6. The maximum vertical inhibitory field was larger than the maximum horizontal field. IPSCs could be evoked in layer V neurons by layer I stimuli, showing that a powerful interlaminar inhibition is present that may play a role in synchronizing the activity of neurons in a column. IPSCs evoked by layer I stimulation frequently had slower kinetics than those elicited by stimulation at sites close to the soma. 7. These findings suggest that functional GABAergic projections are characterized by a large degree of convergence. Quantification of GABAA-mediated IPSCs indicates that this zone of inhibitory synaptic convergence onto a given pyramidal neuron is subdivided into a powerful local inhibitory zone and a surrounding area of long-range, less effective, inhibitory projections. Potential roles for these concentric inhibitory areas in cortical processing of sensory information are discussed.

    View details for Web of Science ID A1996UE79800019

    View details for PubMedID 8727398

  • Heterogeneous axonal arborizations of rat thalamic reticular neurons in the ventrobasal nucleus JOURNAL OF COMPARATIVE NEUROLOGY Cox, C. L., Huguenard, J. R., Prince, D. A. 1996; 366 (3): 416-430

    Abstract

    The gamma-aminobutyric acid (GABA)-containing neurons of the thalamic reticular nucleus (nRt) are a major source of inhibitory innervation in dorsal thalamic nuclei. Individual nRt neurons were intracellularly recorded and labelled in an in vitro rat thalamic slice preparation to investigate their projection into ventrobasal thalamic nuclei (VB). Camera lucida reconstructions of 37 neurons indicated that nRt innervation ranges from a compact, focal projection to a widespread, diffuse projection encompassing large areas of VB. The main axons of 65% of the cells gave rise to intra-nRt collaterals prior to leaving the nucleus and, once within VB, ramified into one of three branching patterns: cluster, intermediate, and diffuse. The cluster arborization encompassed a focal region averaging approximately 25,000 mu m2 and contained a high density of axonal swellings, indicative of a topographic projection. The intermediate structure extended across an area approximately fourfold greater and also contained numerous axonal swellings. The diffuse arborization of nRt neurons covered a large region of VB and contained a relatively low density of axonal swellings. Analysis of somatic size and shape revealed that diffuse arborizations arose from significantly smaller, fusiform-shaped somata. Cytochrome oxidase reactivity or parvalbumin immunoreactivity was used to delineate a discontinuous staining pattern representing thalamic barreloids. The size of a cluster arborization closely approximated that of an individual barreloid. The heterogeneous arborizations from nRt neurons may reflect a dynamic range of inhibitory influences of nRt on dorsal thalamic activity.

    View details for Web of Science ID A1996TY11300004

    View details for PubMedID 8907356

  • Excitability changes in thalamic and neocortical neurons after injury. Epilepsy research. Supplement Huguenard, J. R., Chung, J. M., Prince, D. A. 1996; 12: 129-135

    View details for PubMedID 9302511

  • Axonal sprouting in layer V pyramidal neurons of chronically injured cerebral cortex JOURNAL OF NEUROSCIENCE Salin, P., Tseng, G. F., Hoffman, S., Parada, I., Prince, D. A. 1995; 15 (12): 8234-8245

    Abstract

    We performed experiments to determine whether axonal sprouting occurs in neurons of chronic neocortical epileptogenic lesions. Partially isolated somatosensory cortical islands with intact pial blood supply were prepared in mature rats. Neocortical slices from these lesions, studied 6-39 d later, generated spontaneous and/or evoked epileptiform field potentials (Prince and Tseng, 1993) during which neurons displayed prolonged polyphasic excitatory and inhibitory synaptic potentials/currents. Single electrophysiologically characterized layer V pyramidal neurons in control and epileptogenic slices were filled with biocytin using sharp and patch-electrode techniques, their axonal arbors reconstructed and compared quantitatively. Neurons in injured cortex had a 56% increase in total axonal length, a 64% increase in the number of axonal collaterals and more than a doubling (115% increase) of the number of axonal swellings. The presumed boutons were smaller and more closely spaced than those of control cells. In some neurons the main descending axon had hypertrophic segments from which branches arose. These highly significant changes were most marked in the perisomatic region of layer V. The axonal sprouting was associated with a decrease in somatic area but no significant change in dendritic arbors. Results suggest that a significant degree of axonal reorganization takes place in the chronically injured cortex where it might be an adaptive mechanism for recovery of function after injury, or might be maladaptive and play an important role in the generation of epileptiform events by increasing the numbers and density of synaptic contacts between neurons.

    View details for Web of Science ID A1995TP15400041

    View details for PubMedID 8613757

  • CHOLECYSTOKININ DEPOLARIZES RAT THALAMIC RETICULAR NEURONS BY SUPPRESSING A K+ CONDUCTANCE JOURNAL OF NEUROPHYSIOLOGY Cox, C. L., Huguenard, J. R., Prince, D. A. 1995; 74 (3): 990-1000

    Abstract

    1. The thalamic reticular nucleus (nRt) is innervated by cholecystokinin (CCK)-containing neurons and contains CCK binding sites. We used tight-seal, whole cell recording techniques with in vitro rat thalamic slices to investigate the action of CCK on neurons in nRt and ventrobasal thalamus (VB). 2. Brief applications of the CCK agonist cholecystokinin octapeptide (26-33) sulfated (CCK8S) evoked prolonged spike discharges in nRt neurons but had no direct effects on VB neuron activity. This selective excitatory action of CCK8S in nRt resulted from a long-lasting membrane depolarization (2-10 min) associated with an increased input resistance. Voltage-clamp recordings revealed that CCK8S reduced membrane conductance by 0.6-3.8 nS, which amounted to 5-54% of the resting conductance of these neurons. 3. The conductance blocked by CCK8S was linear over the range of -50 to -100 mV and reversed near the potassium equilibrium potential. Modifications of extracellular K+ concentration altered the reversal potential of the conductance as predicted by the Nernst equation. The K+ channel blocker Cs+, applied either intracellularly or combined intra- and extracellularly, blocked the response to CCK8S. 4. The CCK8S-induced depolarization persisted after suppression of synaptic transmission by either tetrodotoxin or a low-Ca2+, high-Mg2+ extracellular solution, indicating that the depolarization was primarily due to activation of postsynaptic CCK receptors and not mediated through the release of other neurotransmitters. 5. The selective CCKA antagonists L364,718 and Cam-1481 attenuated the CCK8S-induced depolarization, whereas the CCKB antagonist L365,260 had little or no effect on the depolarization. 6. Our findings indicate that CCK8S, acting via CCKA-type receptors, reduces a K+ leak current, resulting in a long-lasting membrane depolarization that can presumably modify the firing mode of nRt neurons. Through this effect, CCK actions in nRt may strongly influence thalamocortical function.

    View details for Web of Science ID A1995RU95200007

    View details for PubMedID 7500167

  • EPILEPTOGENESIS IN IMMATURE NEOCORTICAL SLICES INDUCED BY 4-AMINOPYRIDINE DEVELOPMENTAL BRAIN RESEARCH Hoffman, S. N., Prince, D. A. 1995; 85 (1): 64-70

    Abstract

    The laminar site of onset of 4-aminopyridine (4AP)-induced epileptiform discharges in immature neocortical brain slices was localized to layer V using conventional extracellular field electrodes, current source-density analysis (CSD), and subdivided slices. Intracellular patch-electrode recordings in immature layer V neurons confirmed that intrinsically bursting (IB) neurons were not present at the ages studied or with bath application of 50-200 microM 4AP. IB properties were not being masked in the younger animals by the patch electrodes because typical IB neurons in layer V were seen in older rats when the same intracellular techniques were used. These results demonstrate that epileptiform activity can be initiated in the absence of IB neurons, and suggest that other factors are responsible for the preferential onset in layer V.

    View details for Web of Science ID A1995QM54500008

    View details for PubMedID 7781169

  • TEACHING SPANISH TO EMERGENCY-MEDICINE RESIDENTS ACADEMIC EMERGENCY MEDICINE Prince, D., Nelson, M. 1995; 2 (1): 32-37

    Abstract

    To determine the effects of teaching medical Spanish to eight PGY1 emergency medicine residents on their subsequent interactions with Spanish-speaking patients.Eight PGY1 residents completed a 45-hour medical Spanish course administered during their first residency month. Thirty-four subsequent physician-patient interactions by these residents were audiotaped over a six-month period at a suburban teaching ED. The tapes were transcribed and analyzed for errors by a professional medical Spanish interpreter and a native Spanish speaker.Minor errors (e.g., technically incorrect grammar or vocabulary with generally appropriate patient understanding) were found in more than half of the interactions and major errors (e.g., misunderstanding duration of symptoms, misunderstanding of vocabulary) were found in 14% of the interactions. In addition, although the course was designed to supplement, not replace, professional interpreters, the residents called for an interpreter only 46% of the time.Although medical language courses may be a useful adjunct to interpreters, they are not designed to replace them. Significant errors may occur when participants in such courses assume their knowledge is sufficient to obtain a good history, give patient release instructions, and provide medical care in general without an interpreter present.

    View details for Web of Science ID A1995RA29600008

    View details for PubMedID 7606608

  • INTRATHALAMIC RHYTHMICITY STUDIED IN-VITRO - NOMINAL T-CURRENT MODULATION CAUSES ROBUST ANTIOSCILLATORY EFFECTS JOURNAL OF NEUROSCIENCE Huguenard, J. R., Prince, D. A. 1994; 14 (9): 5485-5502

    Abstract

    Thalamocortical oscillations mediate both physiological and pathophysiological behaviors including sleep and generalized absence epilepsy (GA). Reciprocal intrathalamic circuitry and robust burst firing, dependent on underlying transient Ca current (IT) in thalamic neurons, support generation of such rhythms. In order to study the regulation of intrathalamic rhythm generation and the effects of GA anticonvulsants previously shown to reduce IT in acutely isolated thalamic neurons, we developed an in vitro rat thalamic slice preparation that retains sufficient intrathalamic circuitry to support evoked oscillations (range = 2.0-4.6 Hz, average = 2.7, n = 38), associated with burst firing in the thalamic reticular nucleus (nRt) and thalamic relay neurons. Extracellular stimulation of nRt evoked in relay neurons a biphasic inhibitory response with prominent GABAA and GABAB receptor-mediated components. The GABAA component was picrotoxin sensitive, outwardly rectifying and Cl- dependent, with a very negative reversal potential (-94 mV), indicating that an active extrusion mechanism exists in these cells to keep [Cl-]i < 5 mM. The GABAB component had a linear conductance, a reversal potential of -103 mV, and was quite long lasting (about 300 msec) so that rebound bursts often were generated on its decay phase, presumably leading to reexcitation of nRt through known excitatory connections. GABAB-mediated responses thus provide a timing mechanism for promoting slow intrathalamic oscillations. Reduction of IT (30-40%) by succinimides slightly increased the threshold for burst generation in relay and nRt cells, but there was little effect on either number of spikes/burst or intraburst frequency, and there were no other direct effects on other measures of cellular excitability. Intrathalamic oscillations were significantly reduced by these agents through a slight decrease in burst probability of thalamic neurons. We conclude that interactions between the intrinsic properties of thalamic neurons and intrathalamic circuitry lead to generation of slow oscillations. A similar mechanism may underlie the pathophysiological 3 Hz spike and wave EEG activity that characterizes GA. Furthermore, anti-GA drugs such as ethosuximide probably exert their action by reducing the burst-firing probability of neurons within populations of reciprocally interconnected relay and nRt neurons, thus producing a desynchronization of the thalamic circuit that prevents spike/wave generation.

    View details for Web of Science ID A1994PJ12600028

    View details for PubMedID 8083749

  • CLONAZEPAM SUPPRESSES GABA(B)-MEDIATED INHIBITION IN THALAMIC RELAY NEURONS THROUGH EFFECTS IN NUCLEUS-RETICULARIS JOURNAL OF NEUROPHYSIOLOGY Huguenard, J. R., Prince, D. A. 1994; 71 (6): 2576-2581

    Abstract

    1. Experiments were carried out using patch-clamp techniques in rat thalamic slices, maintained in vitro, to examine the effects of the benzodiazepine compound, clonazepam (CZP), on intrathalamic inhibition. Bath-applied CZP reduced the gamma-aminobutyric acid-B (GABAB) component of inhibitory postsynaptic potentials and currents (IPSPs and IPSCs, respectively) evoked in rat thalamic somatosensory relay neurons by stimulation of nucleus reticularis thalami (nRt), without consistently affecting the GABAA IPSP. Secondary IPSPs, which occur as a result of intrathalamic oscillations, were dramatically reduced. 2. Voltage-clamp experiments combined with local or bath perfusion of the GABAA antagonist bicuculline methiodide (BMI), demonstrated that nRt is a site of GABAA-mediated postsynaptic inhibition that affects inhibitory output onto relay neurons. BMI enhanced both GABAA and GABAB postsynaptic inhibition in relay neurons when applied to nRt. Focal applications in the ventrobasal relay nucleus near the recording electrode blocked the GABAA-mediated IPSP but had no effects on GABAB inhibitory potentials. 3. Results suggest that CZP acts to facilitate recurrent inhibition in nRt and decrease its inhibitory output onto relay neurons. Intra-nRt GABAA-mediated inhibition thus has an important role in controlling thalamic excitability and in the anti-absence actions of CZP.

    View details for Web of Science ID A1994NQ73400048

    View details for PubMedID 7931539

  • CHRONIC NEOCORTICAL EPILEPTOGENESIS IN-VITRO JOURNAL OF NEUROPHYSIOLOGY Hoffman, S. N., Salin, P. A., Prince, D. A. 1994; 71 (5): 1762-1773

    Abstract

    1. We used an in vitro model to explore critical aspects of chronic epileptogenesis. Partial neocortical isolations having intact blood supply were made in rat and guinea pig from postnatal day 7 to 34 and then examined 1 to 150 days later in standard brain slice preparations. 2. The epileptogenic potential of several different types of lesions was assessed. Slices containing transcortical (i.e., gray matter) lesions, with or without a contiguous white matter injury (i.e., "undercut"), developed chronic epileptogenesis after a latency of approximately 1-2 wk, manifested by evoked and spontaneous "interictal" discharges and evoked "ictal" events. The region of hyperexcitability did not extend beyond approximately 2 mm from the chronic transcortical lesion and was rarely observed in slices having only an apparent white matter injury. 3. Multiple recordings and current source density (CSD) analysis identified layer V as the source of the interictal discharge. 4. Significant differences in CSD profiles of the evoked interictal discharge occurred between chronically epileptogenic slices and control (noninjured) slices bathed in the convulsant, bicuculline methiodide, suggesting that mechanisms other than disinhibition must be involved in posttraumatic epileptogenesis. 5. Interictal events were blocked in most but not all chronically injured slices by application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovalerate (D-AP5), suggesting that non-NMDA receptors were predominantly involved in some preparations. 6. This model of chronic epileptogenesis in vitro will be useful in studies relevant to mechanisms of posttraumatic epilepsy in man.

    View details for Web of Science ID A1994NL77300014

    View details for PubMedID 8064347

  • HETEROGENEITY OF RAT CORTICOSPINAL NEURONS JOURNAL OF COMPARATIVE NEUROLOGY Tseng, G. F., Prince, D. A. 1993; 335 (1): 92-108

    Abstract

    In order to examine the degree of diversity within a population of cortical projection neurons, rat corticospinal cells were retrogradely labeled in vivo by injecting rhodamine-tagged microspheres into the cervical spinal cord, and subsequently studied electrophysiologically and anatomically in neocortical slices maintained in vitro, by use of standard current clamp techniques and a double-labeling protocol (Tseng et al., J. Neurosci. Meth. 37:121-131, 1991). Three different subgroups were distinguished on the basis of their spiking behavior: (1) Adapting cells had a marked fast (50 ms) and slow phase (200 ms) of spike frequency adaptation; (2) regular spiking (RS) cells had only a period of fast adaptation; (3) some regular spiking neurons had prominent depolarizing afterpotentials (DAPs) and could generate bursts of spikes, often in repetitive fashion (RSDAP cells). Subgroups of RSDAP cells had different patterns of burst responses to depolarizing current pulses, suggesting differences in the types and/or sites of underlying ionic conductances. Adapting cells had a slightly higher membrane input resistance and more prominent slow hyperpolarizing afterpotentials than RS and RSDAP neurons; however, the activation of presumed anomalous rectifier current by intracellular hyperpolarizations was less prominent in adapting neurons. Orthodromic stimulation in layer I evoked presumed excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs)in all three types of cells, but prominent short-latency IPSPs were found in a higher percentage of adapting neurons. The morphology of electrophysiologically characterized corticospinal neurons was studied following intracellular injection of biocytin. All three spiking types were typical layer V pyramids with apical dendrites reaching layer 1, basal dendrites in infragranular layers, and deep-directed axons that had a moderate density of local collaterals in lower cortical layers. The profuseness of dendrites, examined by Sholl's analysis of two-dimensional, camera lucida-reconstructed neurons was comparable in the three neuronal subgroups, although a smaller somatic area and more slender apical dendritic trunk were found in adapting neurons. Our results suggest that corticospinal cells in rats are a heterogeneous population of projection neurons with respect to their spiking behavior, membrane properties, synaptic connections, and, to a lesser extent, their morphology. This diversity revealed in vitro adds new complexity to the classification of corticospinal neurons.

    View details for Web of Science ID A1993LR89100006

    View details for PubMedID 8408775

  • POSTNATAL-DEVELOPMENT OF CHOLINERGIC PRESYNAPTIC INHIBITION IN RAT HIPPOCAMPUS DEVELOPMENTAL BRAIN RESEARCH Milburn, C. M., Prince, D. A. 1993; 74 (1): 133-137

    Abstract

    Muscarinic depression of field potential excitatory postsynaptic potentials (fEPSPs) in striatum radiatum of area CA1 was compared in hippocampal slices from rats of different ages. Bath application of 4 microM muscarine reversibly depressed the fEPSP slope by 68.4% in slices from adult animals (P43-P60), but caused only a 32.2% depression in slices from P5-P7 animals. The magnitude of the depression increased with age during the first postnatal month. Reduced sensitivity of excitatory synaptic transmission to cholinergic depression during postnatal development could be one factor contributing to the hyperexcitability of immature hippocampus.

    View details for Web of Science ID A1993LN33100017

    View details for PubMedID 8403367

  • TRANSIENT CA2+ CURRENTS IN NEURONS ISOLATED FROM RAT LATERAL HABENULA JOURNAL OF NEUROPHYSIOLOGY Huguenard, J. R., Gutnick, M. J., Prince, D. A. 1993; 70 (1): 158-166

    Abstract

    1. The properties of the low-voltage-activated transient Ca2+ current (LVA, IT) that underlies rhythmic burst firing in neurons of the lateral habenula (LHb) were examined to further our understanding of mechanisms that promote rhythmogenesis in the CNS. We compared these properties with those of IT in thalamic ventrobasal relay neurons (IVB) and of the more slowly inactivating ITs of thalamic reticular neurons (InRt). 2. Patch-clamp techniques were used to record whole cell Ca2+ currents in LHb cells acutely isolated from rats ranging in age from postnatal days 6 to 34 (P6-P34). The LVA current in LHb (ILHb) had a number of properties similar to those of IVB, including activation threshold (near -65 mV) and voltage-dependent steady-state activation [half-activation voltage (V1/2) = -58.5 mV, slope = 3.4 mV-1] and inactivation (V1/2 = -83.5 mV, slope = 5.0 mV-1) functions. 3. ILHb was characterized by biphasic inactivation, with a fast, voltage-dependent time constant (20-50 ms) similar to that of IVB and a slower, voltage-independent decay phase (time constant approximately 120 ms) that was much more prominent than in IVB. Recovery of ILHb from inactivation was monophasic (time constant, 507 ms at -90 mV), and was slower than for IVB and about the same as for InRt. 4. ILHb was relatively insensitive to equimolar substitution of Ba2+ for Ca2+, in contrast to IVB, which was decreased, and InRt, which was enhanced. 5. In computer simulations, these results could not be accounted for by a mixture of the two previously described IT types (IVB and InRt) in individual LHb cells.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1993LM76000013

    View details for PubMedID 8395572

  • DIFFERENTIAL ONTOGENY OF PRESYNAPTIC AND POSTSYNAPTIC GABA(B) INHIBITION IN RAT SOMATOSENSORY CORTEX JOURNAL OF NEUROPHYSIOLOGY Fukuda, A., Mody, I., Prince, D. A. 1993; 70 (1): 448-452

    Abstract

    1. The postnatal maturation of gamma-aminobutyric acid (GABA)B receptor-mediated presynaptic inhibition was studied in brain slices of rat somatosensory cortex maintained in vitro. Patchclamp techniques were used to record whole-cell inhibitory post-synaptic currents from layer II-III neurons in animals from postnatal days (P) 7-24. Monosynaptic inhibitory postsynaptic currents (IPSCs) were evoked after N-methyl-D-aspartate (NMDA) and non-NMDA type glutamate receptors had been blocked by D-amino-phosphonovaleric acid (D-AP5, 20 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), respectively. These IPSCs were solely mediated by postsynaptic GABAA receptors because they were abolished by bicuculline (10 microM), reversed polarity near the chloride equilibrium potential, and were recorded with electrodes that contained Cs+ to block postsynaptic GABAB responses. 2. When pairs of stimuli separated by intervals of 0.1-10 s were used to evoke IPSCs, the second response was depressed, an effect that was maximal at 300 ms. Evoked IPSCs were also depressed by baclofen (10 microM). The paired pulse depression (PPD) of monosynaptic IPSCs was decreased or eliminated by 2-OH-saclofen (200 microM). These findings indicate that PPD of monosynaptic IPSCs was due to presynaptic GABAB receptor-mediated inhibition of GABA release. 3. There were no significant differences in the amounts of PPD in neurons from different age groups (P7-10, P12-17, P22-24) at any interstimulus interval tested (0.1-10 s).(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1993LM76000035

    View details for PubMedID 8395587

  • TRANSIENT ENHANCEMENT OF LOW-THRESHOLD CALCIUM CURRENT IN THALAMIC RELAY NEURONS AFTER CORTICECTOMY JOURNAL OF NEUROPHYSIOLOGY Chung, J. M., Huguenard, J. R., Prince, D. A. 1993; 70 (1): 20-27

    Abstract

    1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1993LM76000003

    View details for PubMedID 8395574

  • EPILEPTOGENESIS IN CHRONICALLY INJURED CORTEX - INVITRO STUDIES JOURNAL OF NEUROPHYSIOLOGY Prince, D. A., Tseng, G. F. 1993; 69 (4): 1276-1291

    Abstract

    1. Field potentials and intracellular activities were examined in neocortical slices obtained through areas of chronic cortical injury produced by cortical undercutting and transcortical lesions made in vivo 7-122 days before the terminal in vitro slice experiment. 2. Abnormal field potentials characterized by long- and variable-latency multiphasic events could be evoked by layer VI-white matter or subpial stimulation in 9 of 15 animals that had adequate partial cortical isolations. These "epileptiform" field potentials were recorded in layers II-V and propagated across the cortex. They appeared at threshold in an all-or-none fashion and, in most slices, could be blocked by increasing stimulus intensity. In one slice, spontaneous epileptiform events occurred that were similar to those evoked by extracellular stimulation. 3. Intracellular activities during the epileptiform field potentials consisted of polyphasic synaptic events that were predominantly depolarizing and that could last < or = 400-500 ms, synchronous with the field potential activities. A variety of observations suggested that the neuronal activities underlying epileptiform field potentials were relatively asynchronous and much less intense than those previously found in chemically induced epileptogenesis within the neocortex. 4. Inhibitory postsynaptic potentials (IPSPs) were not prominent in neurons when threshold stimuli evoked epileptiform events; however, suprathreshold stimuli could elicit biphasic IPSPs and block the long-latency polysynaptic activity and abnormal field potential in most slices. Depolarizing components of the polysynaptic activity had the appearance of excitatory postsynaptic potentials in terms of their responses to alterations in membrane potential. 5. Comparison of spike parameters in layer V neurons of epileptogenic slices with those in control layer V neurons showed no significant differences in spike height, threshold, duration, or rise time. Resting membrane potentials were also not significantly different. 6. There was a highly significant difference in input resistance (RN) between layer V neurons in control and injured slices; the mean value for neurons in lesioned cortex was 68.1 M omega, whereas that in control cells was 30.5 M omega. There was also a significant prolongation of the slow membrane time constant in neurons of injured cortex (19.4 ms) as opposed to that in control cells (12.2 ms), suggesting that a change in specific resistivity or capacitance contributed to the higher RNS. 7. The relationship between adapted spike frequency and applied current (f-I slope) was steeper in layer V neurons from injured cortical slices (44.3 Hz/nA) than in normal layer V cells (28.2 Hz/nA).(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1993KX59700024

    View details for PubMedID 8492163

  • A NOVEL T-TYPE CURRENT UNDERLIES PROLONGED CA2+-DEPENDENT BURST FIRING IN GABAERGIC NEURONS OF RAT THALAMIC RETICULAR NUCLEUS JOURNAL OF NEUROSCIENCE Huguenard, J. R., Prince, D. A. 1992; 12 (10): 3804-3817

    Abstract

    The inhibitory GABAergic projection of thalamic nucleus reticularis (nRt) neurons onto thalamocortical relay cells (TCs) is important in generating the normal thalamocortical rhythmicity of slow wave sleep, and may be a key element in the production of abnormal rhythms associated with absence epilepsy. Both TCs and nRt cells can generate prominent Ca(2+)-dependent low-threshold spikes, which evoke bursts of Na(+)-dependent fast spikes, and are influential in rhythm generation. Substantial differences in the pattern of burst firing in TCs versus nRt neurons led us to hypothesize that there are distinct forms of transient Ca2+ current (I(T)) underlying burst discharges in these two cell types. Using whole-cell voltage-clamp recordings, we analyzed I(T) in acutely isolated TCs and nRt neurons and found three key differences in biophysical properties. (1) The transient Ca2+ current in nRt neurons inactivated much more slowly than I(T) in TCs. This slow current is thus termed I(Ts). (2) The rate of inactivation for I(Ts) was nearly voltage independent. (3) Whole-cell I(Ts) amplitude was increased when Ba2+ was substituted for Ca2+ as the charge carrier. In addition, activation kinetics were slower for I(Ts) and the activation range was depolarized compared to that for I(T). Other properties of I(Ts) and I(T) were similar, including steady-state inactivation and sensitivities to blockade by divalent cations, amiloride, and antiepileptic drugs. Our findings demonstrate that subtypes of transient Ca2+ current are present in two different classes of thalamic neurons. The properties of I(Ts) lead to generation of long-duration calcium-dependent spike bursts in nRt cells. The resultant prolonged periods of GABA release onto TCs would play a critical role in maintaining rhythmicity by inducing TC hyperpolarization and promoting generation of low-threshold calcium spikes within relay nuclei.

    View details for Web of Science ID A1992JT19700010

    View details for PubMedID 1403085

  • EXCESSIVE INTRACELLULAR CA-2+ INHIBITS GLUTAMATE-INDUCED NA+-K+ PUMP ACTIVATION IN RAT HIPPOCAMPAL-NEURONS JOURNAL OF NEUROPHYSIOLOGY Fukuda, A., Prince, D. A. 1992; 68 (1): 28-35

    Abstract

    1. The effects of increased intracellular Ca2+ concentration ([Ca2+]i) on Na(+)-K+ pump activity in CA1 pyramidal neurons of rat hippocampal slices were investigated. The postglutamate hyperpolarization (PGH), which follows glutamate (GLU)-induced depolarization (GD), was used as an index of Na(+)-K+ pump activity, as was a ratio of PGH area to the preceding GD area (PGH ratio). 2. Perfusion of slices with saline containing Ca2+ ionophore (A23187, 10 microM) inhibited the PGH without producing apparent signs of cell deterioration. A 60-100% (85 +/- 15%, mean +/- SD) reduction in the PGH ratio occurred after 20-50 min of A23187 superfusion in 12 of 18 neurons tested. Complete abolition of the PGH occurred in 8 of these 12 cells exposed to A23187 for 30-120 min. 3. Application of A23187 in Ca(2+)-free/high-Mg2+ solution did not abolish the PGH, although small (less than 50%; 37 +/- 10%) reductions in the PGH ratio were observed after perfusion of 50 min or longer in five neurons tested. 4. Intracellular injection of the Ca2+ chelator bis-(o-amino-phenoxy)-N,N,N',N'-tetraacetic acid (BAPTA, 300-400 mM) blocked inhibition of the PGH by A23187. After 50 min of perfusion with Ca2+ ionophore, no reduction of the PGH ratio was observed in five neurons tested. 5. Rundown of the PGH without apparent change in membrane properties was observed in three neurons that were stable for greater than 2-3 h, allowing repetitive GLU applications. 6. Block of the PGH produced by a Na(+)-K(+)-adenosinetriphosphatase (ATPase) inhibitor (strophanthidin) prolonged the duration of GDs because of a delay in repolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1992JE00100005

    View details for PubMedID 1355527

  • POSTNATAL-DEVELOPMENT OF ELECTROGENIC SODIUM-PUMP ACTIVITY IN RAT HIPPOCAMPAL PYRAMIDAL NEURONS DEVELOPMENTAL BRAIN RESEARCH Fukuda, A., Prince, D. A. 1992; 65 (1): 101-114

    Abstract

    We assessed the development of electrogenic sodium pump (Na+ pump) activity in CA1 pyramidal neurons of rat hippocampal slices by studying the prolonged hyperpolarization which follows glutamate-induced depolarization (postglutamate hyperpolarization or PGH) at different postnatal ages. We also examined the development of membrane-bound enzyme in the hippocampal CA1 subfield with light microscopic immunocytochemistry and an antiserum against Na+,K(+)-ATPase. The PGH, which has previously been shown to be due to activation of an electrogenic Na+ pump in adult hippocampal CA1 neurons, was eliminated by strophanthidin, a Na+,K(+)-ATPase inhibitor, at all ages. It was unaffected by several potassium channel blockers, an intracellular calcium chelator, intracellular Cl- injection or tetrodotoxin (TTX) perfusion. The PGH thus appeared to be independent of K+ and Cl- conductances and produced by an electrogenic Na+ pump in adult and immature animals activated in large part by entry of Na+ through the glutamate receptor-channel complex. The size (integrated area) of the PGH was directly proportional to the area of preceding glutamate-induced depolarization (GD) and relatively voltage independent. Similar GDs could be elicited from postnatal day (P) 7 to P greater than or equal to 35, however, only very small PGHs were produced in neurons from P7-11 animals. A ratio of PGH area to GD area (PGH ratio) was calculated for each neuron and used to compare Na+ pump activity at different ages. There was a significant increase in the mean PGH ratio with age when P7-11, P21-25 and P35-39 groups were compared. Na+ pump activity estimated from the PGH ratio is very low in the first postnatal week but develops gradually over the first 5 weeks of life. Immunostaining for Na+,K(+)-ATPase in adult rat hippocampi revealed a punctate reaction product surrounding pyramidal cell bodies, whereas the staining was uniform along plasmalemma of dendrites in stratum radiatum and stratum oriens. By contrast, only minimum staining was present surrounding cell bodies and dendrites of P7 hippocampi and staining in stratum pyramidale was not punctate at this age. Na+,K(+)-ATPase activity estimated grossly from immunocytochemical staining is very low in the first postnatal week, increases during the first 5 weeks and develops a characteristic focal localization.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1992HC44100012

    View details for PubMedID 1372539

  • FUNCTIONAL ALTERATIONS IN GABAERGIC INHIBITION DURING ACTIVITY EPILEPSY RESEARCH Prince, D. A., Deisz, R. A., Thompson, S. M., CHAGNACAMITAI, Y., GUTNICK, Feltz, P., HEINEMANN, U. F. 1992: 31-38

    View details for Web of Science ID A1992KA43400007

    View details for PubMedID 1384541

  • A FAST TRANSIENT POTASSIUM CURRENT IN THALAMIC RELAY NEURONS - KINETICS OF ACTIVATION AND INACTIVATION JOURNAL OF NEUROPHYSIOLOGY Huguenard, J. R., Coulter, D. A., Prince, D. A. 1991; 66 (4): 1304-1315

    Abstract

    1. Whole-cell voltage-clamp techniques were used to record K+ currents in relay neurons (RNs) that had been acutely isolated from rat thalamic ventrobasal complex and maintained at 23 degrees C in vitro. Tetrodoxin (TTX; 0.5 microM) was used to block Na+ currents, and reduced extracellular levels of Ca2+ (1 mM) were used to minimize contributions from Ca2+ current (ICa). 2. In RNs, depolarizing commands activate K+ currents characterized by a substantial rapidly inactivating (time constant approximately 20 ms) component, the features of which correspond to those of the transient K+ current (IA) in other preparations, and by a smaller, more slowly activating K+ current, "IK". IA was reversibly blocked by 4-aminopyridine (4-AP, 5 mM), and the reversal potential varied with [K+]o as predicted by the Nernst equation. 3. IA was relatively insensitive to blockade by tetraethylammonium [TEA; 50%-inhibitory concentration (IC50) much much greater than 20 mM]; however, two components of IK were blocked with IC50S of 30 microM and 3 mM. Because 20 mM TEA blocked 90% of the sustained current while reducing IA by less than 10%, this concentration was routinely used in experiments in which IA was isolated and characterized. To further minimize contamination by other conductances, 4-AP was added to TEA-containing solutions and the 4-AP-sensitive current was obtained by subtraction. 4. Voltage-dependent steady-state inactivation of peak IA was described by a Boltzman function with a slope factor (k) of -6.5 and half-inactivation (V1/2) occurring at -75 mV. Activation of IA was characterized by a Boltzman curve with V1/2 = -35 mV and k = 10.8. 5. IA activation and inactivation kinetics were best fitted by the Hodgkin-Huxley m4h formalism. The rate of activation was voltage dependent, with tau m decreasing from 2.3 ms at -40 mV to 0.5 ms at +50 mV. Inactivation was relatively voltage independent and nonexponential. The rate of inactivation was described by two exponential decay processes with time constants (tau h1 and tau h2) of 20 and 60 ms. Both components were steady-state inactivated with similar voltage dependence. 6. Temperature increases within the range of 23-35 degrees C caused IA activation and inactivation rates to become faster, with temperature coefficient (Q10) values averaging 2.8. IA amplitude also increased as a function of temperature, albeit with a somewhat lower Q10 of 1.6. 7. Several voltage-dependent properties of IA closely resemble those of the transient inward Ca2+ current, IT. (ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1991GK79300015

    View details for PubMedID 1662262

  • SLOW INACTIVATION OF A TEA-SENSITIVE K-CURRENT IN ACUTELY ISOLATED RAT THALAMIC RELAY NEURONS JOURNAL OF NEUROPHYSIOLOGY Huguenard, J. R., Prince, D. A. 1991; 66 (4): 1316-1328

    Abstract

    1. Voltage-gated K currents were studied in relay neurons (RNs) acutely isolated from somatosensory (VB) thalamus of 7- to 14-day-old rats. In addition to a rapidly activated, transient outward current, IA, depolarizations activated slower K+ currents, which were isolated through the use of appropriate ionic and pharmacological conditions and measured via whole-cell voltage-clamp. 2. At least two slow components of outward current were observed, both of which were sensitive to changes in [K+]o, as expected for K conductances. The first, IK1, had an amplitude that was insensitive to holding potential and a relatively small conductance of 150 pS/pF. It was blocked by submillimolar levels of tetraethylammonium [TEA, 50%-inhibitory concentration (IC50 = 30 microM)] and 4-aminopyridine (4-AP, 40 microM). In the absence of intracellular Ca2+ buffering, the amplitude of IK1 was both larger and dependent on holding potential, as expected for a Ca(2+)-dependent current. Replacement of [Ca2+]o by Co2+ reduced IK1, although the addition of Cd2+ to Ca(2+)-containing solutions had no effect. 3. The second component, IK2, had a normalized conductance of 2.0 nS/pF and was blocked by millimolar concentrations of TEA (IC50 = 4 mM) but not by 4AP. The kinetics of IK2 were analogous to (but much slower than) those of IA in that both currents displayed voltage-dependent activation and voltage-independent inactivation. IK2 was not reduced by the addition of Cd2+ to Ca(2+)-containing solutions or by replacement of Ca2+ by Co2+. 4. IK2 had a more depolarized activation threshold than IA and attained peak amplitude with a latency of approximately 100 ms at room temperature. IK2 decay was nonexponential and could be described as the sum of two components with time constants (tau) near 1 and 10 s. 5. IK2 was one-half steady-state inactivated at a membrane potential of -63 mV, near the normal resting potential for these cells. The slope factor of the Boltzman function describing steady-state inactivation was 13 mV-1, which indicates that IK2 varies in availability across a broad voltage range between -100 and -20 mV. 6. Activation kinetics of IK2 were voltage dependent, with peak latency shifting from 300 to 50 ms in the voltage range -50 to +30 mV. Deinactivation and deactivation were also voltage dependent, in contrast to inactivation, which showed little dependence on membrane potential. Increase in temperature sped the kinetics of IK2, with temperature coefficient (Q10) values near 3 for activation and inactivation. Heating increased the amplitude of IK2 with a Q10 value near 2.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1991GK79300016

    View details for PubMedID 1761985

  • DOUBLE-LABELING WITH RHODAMINE BEADS AND BIOCYTIN - A TECHNIQUE FOR STUDYING CORTICOSPINAL AND OTHER PROJECTION NEURONS INVITRO JOURNAL OF NEUROSCIENCE METHODS Tseng, G. F., Parada, I., Prince, D. A. 1991; 37 (2): 121-131

    Abstract

    Corticospinal neurons retrogradely labelled with rhodamine-labelled latex microspheres (RLMs) in vivo were studied intracellularly in a slice preparation up to 13 months later with electrodes containing biocytin. The physiological properties of these double-labelled corticospinal neurons were indistinguishable from those of comparable neurons which were impaled with biocytin-containing electrodes without prior RLM-labelling, and neurons studied with potassium acetate-filled electrodes in similar areas. Thus, neither labelling with RLMs nor injection of biocytin affected neuronal properties. This important advantage of RLMs makes them suitable for prelabelling projection neurons in vivo for subsequent studies that take advantage of the versatility of a brain slice preparation. In addition to its lack of effects on neuronal properties, intracellular labelling with biocytin also provides high-quality morphological details ideal for anatomical analysis. The compatibility of retrograde labelling with RLMs and intracellular staining with biocytin make this a useful combined technique for tracking electrophysiological and anatomical changes in identified projection neurons over time.

    View details for Web of Science ID A1991FL91000004

    View details for PubMedID 1908929

  • POSTNATAL MATURATION OF THE GABAERGIC SYSTEM IN RAT NEOCORTEX JOURNAL OF NEUROPHYSIOLOGY Luhmann, H. J., Prince, D. A. 1991; 65 (2): 247-263

    Abstract

    1. The postnatal maturation of intracortical inhibitory circuitry and the development of responses to applied gamma-aminobutyric acid (GABA) and baclofen were studied in pyramidal and nonpyramidal neurons from layers II and III of the rat primary somatosensory and primary visual cortex, in vitro. 2. Depolarizing spontaneous inhibitory postsynaptic potentials (IPSPs) could be recorded in approximately 70% of the young (postnatal day 4-10; P4-10), juvenile (P11-16), and adult cells (P28-41), respectively, when they were loaded with nitrate. At all ages these spontaneous events could be blocked by application of the GABAA receptor antagonist bicuculline methiodide (BMI), indicating that they were mediated by activation of GABAA receptors. 3. In 122 of the 130 adult cells tested, standardized electrical stimulation of the white matter or layer VI evoked a brief excitatory postsynaptic potential (EPSP), followed by both a fast (f-) and a long-latency (l-)IPSP. Similar stimuli evoked a biphasic IPSP in only 51 of the 98 juvenile and in only 1 of the 56 young neurons studied. The mean peak conductance of the f-IPSP and the l-IPSP increased significantly from 50.2 and 7.5 nS, respectively, in juvenile cells to 84.2 and 18.0 nS, respectively, in adult neurons. 4. Application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-amino-phosphonovaleric acid (D-APV) to juvenile cells induced a significant negative shift in the reversal potential of both the f-IPSP and l-IPSP. This effect was accompanied by a reduction in the peak conductance during these events by 31 and 48%, respectively, indicating that a prominent long-lasting NMDA receptor-mediated EPSP occurs concurrent with the early and late IPSP in immature neurons. In adult neurons, D-APV had no significant effect on the reversal potential of the f- and l-IPSP, although the peak conductance decreased by 20 and 5%, respectively, suggesting that there was a smaller concurrent activation of NMDA receptors in this age group. 5. The functional maturation of GABAA and GABAB receptors was studied using focal applications of GABA to the soma and the apical dendrite. Somatic GABA applications to adult neurons held at depolarized membrane potentials evoked a triphasic response, consisting of 1) a GABAA-mediated hyperpolarizing fast component (GABAhf; reversal potential, -76 mV), 2) a GABAA-mediated depolarizing phase (GABAd; -54 mV), and 3) a hyperpolarizing late response (GABAhl; -80 mV). The GABAd response could be demonstrated at all ages in almost every neuron.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1991EY28600008

    View details for PubMedID 1673153

  • Patch-Clamp Studies of Voltage-Gated Currents in Identified Neurons of the Rat Cerebral Cortex CEREBRAL CORTEX Hamill, O. P., Huguenard, J. R., Prince, D. A. 1991; 1 (1): 48-61

    Abstract

    In the cerebral cortex, neurons can be classified into 2 broad morphological classes, referred to as pyramidal and nonpyramidal (stellate) cells, which correspond to functional classes of projection neurons and local circuit interneurons, respectively. In this study, we demonstrate that specific morphological, immunohistochemical, and physiological features, that allow class distinction of neurons in situ, are retained in acutely isolated neocortical neurons. Furthermore, voltage-clamp analysis with patch-clamp techniques indicate the differences in functional properties in adult neurons, reflect cell-specific, developmental changes in the density and type of specific classes of Na+, K+ and Ca2+ channels expressed. The differences in channel properties contribute to the different input-output relations of neocortical neurons, which enable inhibitory neurons to follow excitatory inputs faithfully and projection neurons to have more integrative roles.

    View details for DOI 10.1093/cercor/1.1.48

    View details for Web of Science ID 000208047200003

    View details for PubMedID 1668364

  • THE LATERAL SPREAD OF ICTAL DISCHARGES IN NEOCORTICAL BRAIN-SLICES EPILEPSY RESEARCH Wong, B. Y., Prince, D. A. 1990; 7 (1): 29-39

    Abstract

    The in vitro brain slice technique was used to examine the lateral propagation of spontaneous electrographic ictal episodes across adjacent areas of guinea pig neocortex. Epileptiform activity was induced by perfusing slices with Mg-free artificial CSF. Simultaneous field potential recordings of ictal episodes were obtained from 4 micropipettes placed 1-3 mm apart across coronal slices in middle-cortical layers. Two types of lateral spread were characterized. Ictal episodes often developed focally and then spread as a slowly moving wavefront traveling at less than 0.3 mm/sec into adjacent, uninvolved cortex. By contrast, other episodes began nearly synchronously at all cortical sites. The individual afterdischarges that composed each ictal episode propagated rapidly across the cortex at greater than 30 mm/sec and were triggered by multiple pacemakers. Ictal episodes always terminated abruptly across the entire slice. The NMDA-receptor antagonist, 2-amino-phosphono-valerate, applied focally between recording sites, blocked rapid propagation across treated areas and resulted in the emergence of spatially separate, independent pacemakers. Pacemaker failure is the proposed mechanism for simultaneous and generalized termination of ictal episodes in this in vitro model of epileptogenesis.

    View details for Web of Science ID A1990EB79800003

    View details for PubMedID 1981355

  • DIFFERENTIAL-EFFECTS OF PETIT-MAL ANTICONVULSANTS AND CONVULSANTS ON THALAMIC NEURONS - GABA CURRENT BLOCKADE BRITISH JOURNAL OF PHARMACOLOGY Coulter, D. A., Huguenard, J. R., Prince, D. A. 1990; 100 (4): 807-813

    Abstract

    1. Currents evoked by applications of gamma-aminobutyric acid (GABA) to acutely dissociated thalamic neurones were analysed by voltage-clamp techniques, and the effects of the anticonvulsant succinimides ethosuximide (ES) and alpha-methyl-alpha-phenylsuccinimide (MPS) and the convulsants tetramethylsuccinimide (TMS), picrotoxin, pentylenetetrazol (PTZ), and bicuculline methiodide were assessed. 2. TMS (1 microM-10 microM) reduced responses to iontophoretically applied GABA, as did picrotoxin (0.1-100 microM), PTZ (1-100 mM) and bicuculline (1-100 microM). 3. ES, in high concentrations (1-10 mM), reduced GABA responses to a lesser extent, and also occluded the reductions in GABA-evoked currents produced by TMS, picrotoxin, and PTZ. ES did not occlude the effects of bicuculline on GABA responses. Therefore, we propose that ES acts as a partial agonist at the picrotoxin GABA-blocking receptor. 4. MPS had no effect on GABA responses (at a concentration of 1 mM), and, like ES, occluded the GABA-blocking actions of TMS, apparently acting as a full antagonist. 5. The anticonvulsant actions of ES and MPS against TMS and PTZ-induced seizures may thus involve two independent mechanisms: (1) the occlusion of TMS and PTZ GABA-blocking effects; and (2) the previously described specific effect of ES and MPS on low-threshold calcium current of thalamic neurones. The latter cellular mechanism may be more closely related to petit mal anticonvulsant activity.

    View details for Web of Science ID A1990DQ01800025

    View details for PubMedID 2119843

  • DIFFERENTIAL-EFFECTS OF PETIT-MAL ANTICONVULSANTS AND CONVULSANTS ON THALAMIC NEURONS - CALCIUM CURRENT REDUCTION BRITISH JOURNAL OF PHARMACOLOGY Coulter, D. A., Huguenard, J. R., Prince, D. A. 1990; 100 (4): 800-806

    Abstract

    1. Succinimide derivatives can be either convulsant (tetramethylsuccinimide (TMS)), or anticonvulsant (ethosuximide (ES); alpha-methyl-alpha-phenylsuccinimide (MPS)). ES, an anticonvulsant succinimide, has previously been shown to block calcium currents of thalamic neurones, while the convulsant succinimide TMS blocks gamma-aminobutyric acid (GABA) responses in a similar fashion to the convulsant pentylenetetrazol (PTZ). 2. Using voltage-clamp techniques, we analysed the effects of the anticonvulsant succinimides ES and MPS and the convulsants TMS and PTZ on calcium currents of acutely isolated thalamic relay neurones of the rat. 3. MPS and ES reduced low-threshold calcium current (LTCC) in a voltage-dependent manner, without affecting steady-state inactivation. MPS was less potent than ES (IC50 of 1100 vs 200 microM) but greater in efficacy (100% maximal reduction vs 40% for ES). 4. PTZ had no effect on calcium currents, and TMS only reduced LTCC at very high concentrations, and did not occlude MPS effects when applied concurrently. 5. These results, which demonstrate that anticonvulsant, but not convulsant, succinimides block LTCC, provide additional support for the hypothesis that LTCC reduction is a mechanism of action of the anticonvulsant succinimides related to their effects in petit mal epilepsy.

    View details for Web of Science ID A1990DQ01800024

    View details for PubMedID 2169941

  • CONTROL OF NMDA RECEPTOR-MEDIATED ACTIVITY BY GABAERGIC MECHANISMS IN MATURE AND DEVELOPING RAT NEOCORTEX DEVELOPMENTAL BRAIN RESEARCH Luhmann, H. J., Prince, D. A. 1990; 54 (2): 287-290

    Abstract

    The effects of diazepam and low concentrations of bicuculline methiodide (BMI) on the expression of long-latency N-methyl-D-aspartate (NMDA) receptor-mediated activity was studied in supragranular layers of juvenile (14-18 days old) and adult rat (greater than or equal to 28 days) primary somatosensory cortex. In juvenile slices, orthodromic stimulation of layer VI/white matter evoked a long-lasting oscillatory field potential response which could be blocked by the NMDA receptor antagonist D(-)-2-amino-5-phosphonovaleric acid (D-APV) and by diazepam. Similar D-APV-sensitive responses could be observed in adult slices when the GABAergic system was slightly suppressed by adding low doses of BMI to the bathing solution. Our findings indicate that a small decrease in the efficacy of the inhibitory system, whether caused by developmental events or by processes that modulate inhibitory electrogenesis, can lead to NMDA receptor-mediated synchronized afterdischarges, which might play an important role in the functional maturation of the neocortex and in susceptibility to epileptogenesis.

    View details for Web of Science ID A1990DQ19800016

    View details for PubMedID 1975777

  • BURST GENERATING AND REGULAR SPIKING LAYER-5 PYRAMIDAL NEURONS OF RAT NEOCORTEX HAVE DIFFERENT MORPHOLOGICAL FEATURES JOURNAL OF COMPARATIVE NEUROLOGY CHAGNACAMITAL, Y., Luhmann, H. J., Prince, D. A. 1990; 296 (4): 598-613

    Abstract

    Intracellular recordings were obtained from pyramidal neurons in layer 5 of rat somatosensory and visual cortical slices maintained in vitro. When directly depolarized, one subclass of pyramidal neurons had the capacity to generate intrinsic burst discharges and another generated regular trains of single spikes. Burst responses were triggered in an all-or-none manner from depolarizing afterpotentials in most bursting neurons. Regular spiking cells responded to electrical stimulation of ascending afferents with a typical EPSP-IPSP sequence, whereas IPSPs were hard to detect in bursting cells. Orthodromic activation of the latter evoked a prominent voltage-dependent depolarization that could trigger a burst response. Intracellularly labelled bursting and regular spiking cells were located in layer 5b, but had distinctly different morphologies. Bursting neurons had a large pyramidal soma, a gradually emerging apical dendrite, and an extensive apical and basal dendritic tree. Their axonal collateral arborization was predominantly limited to layers 5/6. In contrast, regular spiking cells had a more rounded soma with abruptly emerging apical dendrite, a smaller dendritic arborization, and 2 to 8 ascending axonal collaterals that arborized widely in the supragranular layers. Both bursting and regular spiking cells had main axons that entered the subcortical white matter. These data show that some subgroups of pyramidal neurons within the deeper parts of layer 5 of rat cortex are morphologically and physiologically distinct and have different intracortical connections. Bursting cells presumably function to amplify and synchronize cortical outputs, whereas regular spiking output neurons provide excitatory feedback to neurons at all cortical levels and receive a more effective orthodromic inhibitory input. These data support the hypothesis that differences in gross neuronal structure, perhaps even the subtle differences that distinguish subclasses of neurons in a given lamina, are predictive of underlying differences in the type and distribution of ion channels in the nerve cell membrane and connections of cells within the cortical circuit.

    View details for Web of Science ID A1990DG98400006

    View details for PubMedID 2358553

  • TRANSIENT EXPRESSION OF POLYSYNAPTIC NMDA RECEPTOR-MEDIATED ACTIVITY DURING NEOCORTICAL DEVELOPMENT NEUROSCIENCE LETTERS Luhmann, H. J., Prince, D. A. 1990; 111 (1-2): 109-115

    Abstract

    During a restricted period of early postnatal development, rat neocortical neurons receive a powerful N-methyl-D-aspartate (NMDA) receptor-mediated synaptic input of variable onset latency and duration. These large-amplitude excitatory postsynaptic potentials are especially pronounced in supragranular layers and are generated by activities in polysynaptic circuits. Their occurrence in cortical slices from juvenile (postnatal (P) days 11-20), but not neonatal (P5-10) or adult (greater than or equal to P28) animals, appears to be in part a consequence of the relative immaturity of gamma-aminobutyric acid (GABA)-mediated inhibition, at a time when the requisite functional excitatory circuitry has been established. The transient manifestation of strong NMDA receptor-mediated potentials coincides temporally with a 'developmental window' within which there is enhanced sensitivity for epileptogenesis and for induction of long-term synaptic modifications in rat cortex.

    View details for Web of Science ID A1990CX50300020

    View details for PubMedID 1970856

  • CALCIUM CURRENTS IN RAT THALAMOCORTICAL RELAY NEURONS - KINETIC-PROPERTIES OF THE TRANSIENT, LOW-THRESHOLD CURRENT JOURNAL OF PHYSIOLOGY-LONDON Coulter, D. A., Huguenard, J. R., Prince, D. A. 1989; 414: 587-604

    Abstract

    1. Calcium currents were recorded with whole-cell voltage-clamp procedures in relay neurones of the rat thalamus which had been acutely isolated by an enzymatic dissociation procedure. 2. Low-threshold and high-threshold Ca2+ currents were elicited by depolarizing voltage steps from holding potentials more negative than -60 mV. A transient current, analogous to the T-current in sensory neurones, was activated at low threshold near -65 mV and was completely inactivating at command steps up to -35 mV. Voltage steps to more depolarized levels activated a high-threshold current that inactivated slowly and incompletely during a 200 ms step depolarization. 3. The high-threshold current contained both non-inactivating and slowly inactivating components which were insensitive and sensitive to holding potential, respectively. 4. A 'T-type' current was prominent in relay neurones, in both absolute terms (350 pA peak current average) and in relation to high-threshold currents. The average ratio of maximum transient to maximum sustained current was greater than 2. 5. T-current could be modelled in a manner analogous to that employed for the fast Na+ current underlying action potential generation, using the m3h format. The rate of activation of T-current was voltage dependent, with a time constant (tau m) varying between 8 and 2 ms at command potentials of -60 to -10 mV at 23 degrees C. The rate of inactivation was also voltage dependent, and the time constant tau h varied between 50 and 20 ms over the same voltage range. With command potentials more positive than -35 mV, the inactivation of Ca2+ current could no longer be fitted by a single exponential. 6. Steady-state inactivation of T-current could be well fitted by a Boltzman equation with slope factor of 6.3 and half-inactivated voltage of -83.5 mV. 7. Recovery from inactivation of T-current was not exponential. The major component of recovery (70-80% of total) was not very voltage sensitive at potentials more negative than -90 mV, with tau r of 251 ms at -92 mV and 23 degrees C, compared to 225 ms at -112 mV. A smaller, voltage-sensitive component accounted for the remainder of recovery. 8. All kinetic properties, including rates of activation, inactivation, and recovery from inactivation, as well as the amplitude of T-current, were temperature sensitive with Q10 (temperature coefficient) values of greater than 2.5.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1989AH41500033

    View details for PubMedID 2607443

  • CHARACTERIZATION OF ETHOSUXIMIDE REDUCTION OF LOW-THRESHOLD CALCIUM CURRENT IN THALAMIC NEURONS ANNALS OF NEUROLOGY Coulter, D. A., Huguenard, J. R., Prince, D. A. 1989; 25 (6): 582-593

    Abstract

    The mechanism by which ethosuximide reduces thalamic low-threshold calcium current (LTCC) was analyzed using voltage-clamp techniques in acutely isolated ventrobasal complex neurons from rats and guinea pigs. The ethosuximide-induced reduction of LTCC was voltage dependent: it was most pronounced at more-hyperpolarized potentials and did not affect the time course of activation or inactivation of the current. Ethosuximide reduced LTCC without altering the voltage dependence of steady-state inactivation or the time course of recovery from inactivation. Dimethadione reduced LTCC by a similar mechanism, while valproic acid had no effect on LTCC. We conclude that ethosuximide reduction of LTCC in thalamic neurons is consistent with a reduction in the number of available LTCC channels or in the single LTCC channel conductance, perhaps indicating a direct channel-blocking action of this drug. Given the importance of LTCC in thalamic oscillatory behavior, a reduction in this current by ethosuximide would be a mechanism of action compatible with the known anticonvulsant effects of this drug in typical absence seizures.

    View details for Web of Science ID A1989AA44400009

    View details for PubMedID 2545161

  • FREQUENCY-DEPENDENT DEPRESSION OF INHIBITION IN GUINEA-PIG NEOCORTEX INVITRO BY GABAB RECEPTOR FEEDBACK ON GABA RELEASE JOURNAL OF PHYSIOLOGY-LONDON Deisz, R. A., Prince, D. A. 1989; 412: 513-541

    Abstract

    1. The mechanisms involved in the lability of inhibition at higher frequencies of stimulation were investigated in the guinea-pig in vitro neocortical slice preparation by intracellular recording techniques. We attempted to test the possibility of a feedback depression of GABA on subsequent release. 2. At resting membrane potential (Em, -75.8 +/- 5.2 mV) stimulation of either the pial surface or subcortical white matter evoked a sequence of depolarizing and hyperpolarizing synaptic components in most neurones. An early hyperpolarizing component (IPSPA) was usually only obvious as a pronounced termination of the EPSP, followed by a later hyperpolarizing event (IPSPB). Current-voltage relationships revealed two different conductances of about 200 and 20 nS and reversal potentials of -73.0 +/- 4.4 and -88.6 +/- 6.1 mV for the early and late component, respectively. 3. The conductances of IPSPA and IPSPB were fairly stable at a stimulus frequency of 0.1 Hz. At frequencies between 0.5 and 2 Hz both IPSPs were attenuated with the second stimulus and after about five stimuli a steady state was reached. Concomitantly IPSPs were shortened. The average decrease in synaptic conductance between 0.1 and 1 Hz was 80% for the IPSPA and 60% for the IPSPB. At these frequencies the reversal potentials decreased by 5 and 2 mV, respectively; Em and input resistance (Rin) were not consistently affected. 4. The amplitudes of field potentials, action potentials and EPSPs of pyramidal cells were attenuated less than 10% at stimulus frequencies up to 1 Hz, suggesting that alterations in local circuits between the stimulation site and excitatory input onto inhibitory interneurones may play only a minor role in the frequency-dependent decay of IPSPs. 5. Localized application of GABA produced multiphasic responses. With low concentrations and application near the soma an early hyperpolarization prevailed followed by a depolarizing late component. Brief application of GABA at low frequencies induced constant responses; at higher frequencies, the responses sometimes declined. The current-voltage relationships of the two GABA responses were similar to each other and to the early IPSP. An apparently fivefold higher conductance was estimated at lower Ems, suggesting that the GABA response had a voltage sensitivity. The slope conductance of IPSPs was decreased by up to 50% for tens of seconds after postsynaptically detectable effects of GABA had dissipated. 6. Application of the GABA uptake inhibitor nipecotic acid (50-500 microM) reduced the conductance of both components of orthodromically evoked inhibition and shortened the IPSP at low frequencies, but had no additional effects at higher stimulation rates.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1989U587300029

    View details for PubMedID 2557431

  • SODIUM-CHANNELS IN DENDRITES OF RAT CORTICAL PYRAMIDAL NEURONS PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Huguenard, J. R., Hamill, O. P., Prince, D. A. 1989; 86 (7): 2473-2477

    Abstract

    The voltage-dependent properties that have been directly demonstrated in Purkinje cell and hippocampal pyramidal cell dendrites play an important role in the integrative capacities of these neurons. By contrast, the properties of neocortical pyramidal cell dendritic membranes have been more difficult to assess. Active dendritic conductances near sites of synaptic input would have an important effect on the input-output characteristics of these neurons. In the experiments reported here, we obtained direct evidence for the existence of voltage-dependent Na+ channels on the dendrites of neocortical neurons by using cell-attached patch and whole cell recordings from acutely isolated rat neocortical pyramidal cells. The qualitative and quantitative properties of dendritic and somatic currents were indistinguishable. Insofar as Na+ currents are concerned, the soma and primary apical dendrite can be considered as one relatively uniform compartment. Similar dendritic Na+ currents on dendrites in mature neurons would play an important role in determining the integrative properties of these cortical units.

    View details for Web of Science ID A1989U042300073

    View details for PubMedID 2538843

  • SPECIFIC PETIT MAL ANTICONVULSANTS REDUCE CALCIUM CURRENTS IN THALAMIC NEURONS NEUROSCIENCE LETTERS Coulter, D. A., Huguenard, J. R., Prince, D. A. 1989; 98 (1): 74-78

    Abstract

    Low-threshold calcium current (LTCC) in thalamic neurons is important in generation of normal thalamocortical rhythms, and may be involved in the genesis of abnormal activities such as spike-wave discharges that characterize petit mal epilepsy. Ethosuximide and dimethadione, anticonvulsants effective in petit mal, reduced the LTCC when applied to thalamic neurons at clinically relevant concentrations. Therapeutic concentrations of phenytoin and carbamazepine, drugs ineffective in the control of petit mal, had minimal effects on calcium conductances. Reduction in LTCC may be an important mechanism of action by which specific petit mal anticonvulsants depress spike-wave activity.

    View details for Web of Science ID A1989T655000014

    View details for PubMedID 2710401

  • RELATIVE CONTRIBUTIONS OF PASSIVE EQUILIBRIUM AND ACTIVE-TRANSPORT TO THE DISTRIBUTION OF CHLORIDE IN MAMMALIAN CORTICAL-NEURONS JOURNAL OF NEUROPHYSIOLOGY Thompson, S. M., Deisz, R. A., Prince, D. A. 1988; 60 (1): 105-124

    Abstract

    1. Active and passive factors affecting the chloride gradient of cortical neurons were assessed using intracellular recordings from neurons in slices of cingulate cortex maintained in vitro. The chloride equilibrium potential (ECl-) was estimated indirectly from the reversal potentials of responses to perisomatic gamma-aminobutyric acid (GABA) application and the Cl(-)-dependent inhibitory postsynaptic potential (IPSP). Under control conditions the mean resting potential (Vm; -69.7 mV) was not significantly different than the mean IPSP reversal potential (EIPSP; -70.1 mV). 2. Increasing the external potassium concentration ([K+]o) from 1 to 10 mM shifted the mean EIPSP from -80.4 to -61.8 mV. The mean EIPSP was approximately equal to the mean Vm at all [K+]oS. The conditions of Donnan equilibrium are not met in [K+]o less than 10 mM. 3. Polarization of Vm up to 20 mV away from EIPSP for 4 min with maintained current injection had no significant effect on EIPSP. 4. The GABA reversal potential was maintained 37-52 mV less negative than Vm after equilibration in saline in which the external chloride concentration had been reduced from 133 to 5 mM by substitution with isethionate. Vm and input resistance were not significantly different from control values in cells recorded under these conditions. 5. We conclude that Cl- is not passively distributed in cortical neurons, perhaps due to a low resting Cl- permeability. 6. Impalement with electrodes containing 2 M KCl resulted in a rapid 10 mV depolarizing shift in EIPSP that then remained relatively constant. Intracellular iontophoresis of Cl- resulted in a further depolarizing shift of EIPSP of 5-10 mV that returned to control in less than 1 min. The time course of recovery of IPSP amplitude could be fit with a single exponential having a mean time constant of 6.9 +/- 1.5 s and was independent of the amount of Cl- injected or stimulation frequency. 7. Reductions in temperature from 37 to 32 degrees C significantly increased the mean time constant of IPSP recovery from Cl- injection to 11.1 +/- 3.3 s, corresponding to Q10 = 2.6.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1988P258300006

    View details for PubMedID 3404212

  • OUTWARD CHLORIDE CATION CO-TRANSPORT IN MAMMALIAN CORTICAL-NEURONS NEUROSCIENCE LETTERS Thompson, S. M., Deisz, R. A., Prince, D. A. 1988; 89 (1): 49-54

    Abstract

    The mechanism underlying outward chloride transport in guinea pig cingulate cortical neurons of in vitro slices was characterized with respect to its pharmacological antagonists and anion selectivity, and the nature of other ion movements coupled to Cl- transport. Changes in intracellular Cl- concentration, following iontophoresis of Cl- from KCl-filled intracellular recording electrodes, were estimated from changes in the amplitude of GABAergic, Cl(-)-mediated inhibitory postsynaptic potentials (IPSPs). The rate of outward Cl- transport was found to be reduced by bumetanide but not by SITS. SCN-, but not NO3-, was found to be actively transported. Increasing the extracellular K+ concentration ([K+]o) from 2.5 to 10 mM was found to inhibit Cl- extrusion. These data suggest that active Cl- extrusion from mammalian cortical neurons is mediated by an outwardly directed chloride/cation cotransport mechanism. Inhibition of this process by elevated [K+]o may be important in epilepsy.

    View details for Web of Science ID A1988N803400009

    View details for PubMedID 3399141

  • DEXTROMETHORPHAN, A COMMON ANTITUSSIVE, REDUCES KINDLED AMYGDALA SEIZURES IN THE RAT NEUROSCIENCE LETTERS FEESER, H. R., KADIS, J. L., Prince, D. A. 1988; 86 (3): 340-345

    Abstract

    Dextromethorphan (DM), a non-prescription antitussive, has anticonvulsant properties and antagonizes N-methyl-D-aspartate (NMDA) receptor-mediated responses in rat spinal and cortical neurons. The effects of daily intraperitoneal injections of DM on amygdala-kindled seizures were examined. DM was found both to prevent the development of full kindling in rats and to decrease seizure intensity in previously fully kindled animals. The findings of this study, combined with the ready availability of DM and its apparent safety in antitussive doses suggest that clinical testing of this drug as an anticonvulsant is warranted.

    View details for Web of Science ID A1988M789000017

    View details for PubMedID 3380326

  • DEXTROMETHORPHAN PROTECTS AGAINST CEREBRAL INFARCTION IN A RAT MODEL OF HYPOXIA-ISCHEMIA NEUROSCIENCE LETTERS Prince, D. A., FEESER, H. R. 1988; 85 (3): 291-296

    Abstract

    We assessed the cerebral protective effects of the noncompetitive N-methyl-D-aspartate antagonist dextromethorphan (DM; 10-35 mg/kg i.p.) in 8-day-old rats that were subjected to brain hypoxia-ischemia by tying one carotid artery and placing them in 8% O2-92% N2 for 2 h. Light microscopic examination of brains perfused one week after the insult revealed that all control animals developed a frank infarction with cavitation and brain shrinkage in the middle cerebral artery territory. There was a highly significant decrease in the incidence of frank infarction in DM-pre-treated pups vs saline-treated littermates, although there was no clear relationship between drug dose and the degree of brain protection. DM and its active metabolite dextrorphan may prove to be clinically useful in protecting against hypoxia-ischemia.

    View details for Web of Science ID A1988M253900002

    View details for PubMedID 3362419

  • DEVELOPMENTAL-CHANGES IN NA+ CONDUCTANCES IN RAT NEOCORTICAL NEURONS - APPEARANCE OF A SLOWLY INACTIVATING COMPONENT JOURNAL OF NEUROPHYSIOLOGY Huguenard, J. R., Hamill, O. P., Prince, D. A. 1988; 59 (3): 778-795

    Abstract

    1. Na+ conductances have been characterized in rat neocortical neurons from the sensorimotor area. Neurons were obtained by acute dissociation from animals at developmental stages from embryonic day 16 (E16) to postnatal day 50 (P50) to quantify any developmental changes in the kinetic properties of the Na+ conductance. 2. Neurons were divided into two classes, based on morphology, to determine whether there are any cell-type specific differences in Na+ conductances that contribute to the different action potential morphologies seen in current-clamp recordings in vitro. 3. Upon isolation, neurons were voltage clamped using the whole-cell variation of the patch-clamp technology. Both cell types, pyramidal and nonpyramidal, demonstrate large increases in Na+ current density during this developmental period (E16-P50). Normalized conductances were near 10 pS/micron2 in neurons from embryonic animals, and increased 6- to 10-fold during the first 2 wk postnatal. The final conductance reached in pyramidal neurons was higher than in non-pyramidal neurons. 4. We found no differences between the two cell types, pyramidal and nonpyramidal, in the voltage dependence of activation, inactivation kinetics, voltage dependence of steady-state inactivation, and recovery from inactivation. 5. The time course of Na+ current in immature neurons were fit with classical Hodgkin-Huxley kinetics. However, in more mature neurons the kinetics of inactivation became more complicated such that two decay components were required to obtain good fit. The slowly decaying component had a time course 5 to 10 times slower than the fast component. 6. Several procedures were used to reduce the magnitude of Na+ conductance in mature neurons to ensure graded, voltage-dependent inward currents. These included reduced extracellular [Na+], submaximal tetrodotoxin concentrations, and reduced holding potential. Under each of these conditions we were able to verify the observation that Na+ current inactivation occurs with two exponentials. 7. Single-channel Na+ currents were obtained from cell-attached patches. The membrane density of active Na+ channels increases with development, and ensemble averages from mature neurons demonstrated two inactivation processes. The slow inactivation process was accounted for by long-latency single-channel openings of the same amplitude as the short-latency openings. 8. We conclude that there are no kinetic differences in the Na+ channels between cell types. Differences in action potentials are then not explained by differences in Na+ current kinetics, but might be partially explained by the different densities.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1988M531600006

    View details for PubMedID 2452862

  • NORADRENERGIC MODULATION OF FIRING PATTERN IN GUINEA-PIG AND CAT THALAMIC NEURONS, INVITRO JOURNAL OF NEUROPHYSIOLOGY McCormick, D. A., Prince, D. A. 1988; 59 (3): 978-996

    Abstract

    1. The electrophysiological actions of norepinephrine (NE) in the guinea pig and cat thalamus were investigated using intracellular recordings from neurons of in vitro thalamic slices. 2. Application of NE to neurons of the lateral and medial geniculate nuclei, nucleus reticularis, anteroventral nucleus, and the parataenial (PT) nucleus resulted in a slow depolarization associated with a 2- to 15-nS decrease in input conductance and an increase in the slow membrane time constant from an average of 27.7 to 37.7 ms. The slow depolarization was not abolished by blockade of synaptic transmission, indicating that it was a direct (postsynaptic) effect. 3. The reversal potential of the NE-induced slow depolarization varied as a Nernstian function of extracellular potassium concentration ([K]o), indicating that it is due to a decrease in potassium conductance. This conclusion was supported by the finding that the amplitude of the NE-evoked depolarization was affected by changes in [K]o between 0.5 and 5.0 mM as expected for a K-mediated response. 4. Neurons of the PT nucleus displayed unusually large afterhyperpolarizations (AHPs) in comparison to cells in other thalamic nuclei. NE application to PT neurons caused not only a marked slow depolarization and decreased conductance, but also selectively reduced the slow AHP. 5. The NE-induced slow depolarization effectively suppressed burst firing and promoted the occurrence of single spike activity. NE-induced reduction of the slow AHP in PT neurons was accompanied by a decrease in spike frequency accommodation and the emergence of a slow afterdepolarization. 6. We suggest that through these electrophysiological actions, NE can effectively inhibit the generation of thalamocortical rhythms and greatly facilitate the faithful transfer of information through the thalamus to the cerebral cortex.

    View details for Web of Science ID A1988M531600016

    View details for PubMedID 3367206

  • DEXTRORPHAN AND DEXTROMETHORPHAN, COMMON ANTITUSSIVES, ARE ANTIEPILEPTIC AND ANTAGONIZE N-METHYL-D-ASPARTATE IN BRAIN-SLICES NEUROSCIENCE LETTERS Wong, B. Y., Coulter, D. A., Choi, D. W., Prince, D. A. 1988; 85 (2): 261-266

    Abstract

    The antitussive, dextromethorphan (DM), and its metabolite, dextrorphan (DX), were evaluated for antiepileptic properties in vitro. Interictal bursts and prolonged ictal epileptiform afterdischarges, induced by perfusion of guinea pig neocortical brain slices with Mg2+-free solution, were blocked by DX (1-250 microM) or DM (100 microM). Intracellular records showed that these agents blocked N-methyl-D-aspartate (NMDA)-induced depolarizations without altering intrinsic membrane properties. DX blocked NMDA but not quisqualate-evoked multi-unit excitatory responses. DM is a widely available, orally effective drug with low toxicity in antitussive doses, which has antiepileptic and NMDA-antagonist properties in vitro. Its toxicity and effectiveness as an anticonvulsant should be expeditiously examined in clinical trials.

    View details for Web of Science ID A1988M143100017

    View details for PubMedID 2897648

  • POSTNATAL-DEVELOPMENT OF ELECTROPHYSIOLOGICAL PROPERTIES OF RAT CEREBRAL CORTICAL PYRAMIDAL NEURONS JOURNAL OF PHYSIOLOGY-LONDON McCormick, D. A., Prince, D. A. 1987; 393: 743-762

    Abstract

    1. The post-natal development of the electrophysiological properties of cortical layer V pyramidal neurons was investigated with intracellular recordings from rat sensorimotor cortical slices, in vitro. 2. At all ages post-natally (post-natal day 1 to day 36; P1-P36) neurons were capable of generating a train of Na+-dependent action potentials in response to intracellular injection of sufficient depolarizing current. During the second and third week post-natally, these action potentials changed substantially, becoming faster in both their rising and falling phases, shorter in duration, and larger in amplitude. 3. Both mature (greater than P21) and immature (P2-P4) cortical neurones could generate Ca2+-dependent action potentials only if a substantial portion of K+ conductances were blocked. The maximum rate of rise of Ca2+ spikes also increased with age. 4. The apparent input resistance, specific membrane resistance, and membrane time constant all decreased with age from P1 to P30. Immature neurones had I-V relationships that were substantially more linear than those of adult cells, although rectification was often present in both the hyperpolarizing and depolarizing range. Inward rectification in the depolarizing range was Na+ dependent and was substantially larger in mature versus immature neurones. 5. Single, or trains of, action potentials in immature neurones were followed by short duration (10-50 ms) and long duration (1-5 s) after-hyperpolarizations (a.h.p.s) respectively. The duration of the latter appeared to decrease with age. The presence of large a.h.p.s indicates that Ca2+ entry occurs during the action potential of immature, as well as mature, neurones. 6. Responses to intracellular injection of depolarizing current pulses indicated that immature neurones have frequency versus injected current (f-I) relationships which are in general less steep than those for adult neurones and more limited in terms of the range of firing frequencies. 7. Our results are consistent with the hypothesis that there is a considerable increase in the density of voltage-dependent ionic channels underlying the electro-responsiveness of cortical pyramidal neurones during post-natal development.

    View details for Web of Science ID A1987K883900046

    View details for PubMedID 2895811

  • ACTIONS OF ACETYLCHOLINE IN THE GUINEA-PIG AND CAT MEDIAL AND LATERAL GENICULATE NUCLEI, INVITRO JOURNAL OF PHYSIOLOGY-LONDON McCormick, D. A., Prince, D. A. 1987; 392: 147-165

    Abstract

    1. The mechanisms of action of acetylcholine (ACh) in the medial (m.g.n.) and dorsal lateral geniculate (l.g.n.d.) nuclei were investigated using intracellular recordings techniques in guinea-pig and cat in vitro thalamic slices. 2. Application of ACh to neurones in guinea-pig geniculate nuclei resulted in a hyperpolarization in all neurones followed by a slow depolarization in 52% of l.g.n.d. and 46% of m.g.n. neurones. Neither the hyperpolarization nor the slow depolarization were eliminated by blockade of synaptic transmission and both were activated by acetyl-beta-methylcholine and DL-muscarine and blocked by scopolamine, indicating that these responses are mediated by direct activation of muscarinic receptors on the cells studied. 3. The ACh-induced hyperpolarization was associated with an increase in apparent input conductance (Gi) of 4-13 nS. The reversal potential of the ACh-induced hyperpolarization varied in a Nernstian manner with changes in extracellular [K+] and was greatly reduced by bath application of the K+ antagonist Ba2+ or intracellular injection of Cs+. These findings show that the muscarinic hyperpolarization is mediated by an increase in K+ conductance. 4. The ACh-induced slow depolarization was associated with a decrease in Gi of 2-15 nS, had an extrapolated reversal potential near EK, and was sensitive to [K+]o, indicating that this response is due to a decrease in K+ conductance. 5. In contrast to effects on guinea-pig geniculate neurones, applications of ACh to cat l.g.n.d. and m.g.n. cells resulted in a rapid depolarization in nearly all cells, followed in some neurones by a hyperpolarization and/or a slow depolarization. The rapid excitatory response was associated with an increase in membrane conductance, had an estimated reversal potential of -49 to -4 mV and may be mediated by nicotinic receptors. The hyperpolarization and slow depolarization were similar to those of the guinea-pig in that they were associated with an increase and decrease, respectively, of Gi, and were mediated by muscarinic receptors. 6. The muscarinic hyperpolarization interacted with the intrinsic properties of the thalamic neurones to inhibit single-spike activity while promoting the occurrence of burst discharges. The muscarinic slow depolarization had the opposite effect; it brought the membrane potential into the range where burst firing was blocked and single-spike firing predominated. Depending upon the membrane potential, the rapid excitatory response of cat geniculate neurones could activate either a burst or a train of action potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1987K463300010

    View details for PubMedID 2833597

  • 2 DISTINCT EFFECTS OF 5-HYDROXYTRYPTAMINE ON SINGLE CORTICAL-NEURONS BRAIN RESEARCH Davies, M. F., Deisz, R. A., Prince, D. A., Peroutka, S. J. 1987; 423 (1-2): 347-352

    Abstract

    The ability of the indoleamine serotonin (5-hydroxytryptamine; 5-HT) to alter membrane characteristics of neocortical neurons was analyzed using intracellular recording techniques. The present study demonstrates that 5-HT primarily depolarized 68% of cortical neurons probably by decreasing a resting K+ conductance, an effect blocked by the antagonists ritanserin and cinanserin and apparently mediated by 5-HT2 receptors. A hyperpolarization associated with an increased conductance state and insensitive to 5-HT2 antagonists was observed in 26% of the neurons and could be mimicked by the selective 5-HT1A agonist (+/-)-8-hydroxy-2-(di-N-propyl-amino)tetralin (8-OH-DPAT). Therefore cortical pyramidal neurons contain at least two distinct functional 5-HT receptors whose activation produces opposing effects on membrane potential and conductance.

    View details for Web of Science ID A1987K456400044

    View details for PubMedID 3119155

  • EFFECT OF D890 ON MEMBRANE-PROPERTIES OF NEOCORTICAL NEURONS BRAIN RESEARCH Deisz, R. A., Prince, D. A. 1987; 422 (1): 63-73

    Abstract

    D890, a derivative of the Ca2+ channel antagonist D600, was intracellularly applied from conventional microelectrodes into pyramidal neurons of neocortical slices. The effects of D890 were ascertained by evaluating alterations in membrane properties following drug administration and by comparing these neurons to untreated controls. The amplitude of action potentials (APs) evoked by depolarizing current pulses was attenuated by up to 30% within about 15 min after impalement with D890-containing electrodes. AP rate of rise was reduced by up to 80% and duration was increased. These effects were dependent upon the rate of stimulation. When depolarizing pulses were delivered at low rates of stimulation (e.g. 0.1 Hz), the overshoot of evoked APs declined by about 10%. At higher frequencies (greater than 2 Hz) the AP overshoot decreased by up to 90%. These effects were mostly reversible on decreasing the frequency of stimulation. A half maximal effect was attained at about 1 Hz, when APs of control neurons were unaltered. In neurons impaled with D890-containing electrodes, depolarizing current pulses delivered in the presence of tetraethylammonium (TEA) and tetrodotoxin elicited high threshold calcium spikes which had a duration between 20 and 200 ms. In the early phase of D890 application, the duration of Ca2+ spikes decreased in a reversible frequency-dependent manner; after prolonged application, however, the recovery was incomplete. On the average, Ca2+ spike amplitude and duration decreased by 20% and 50%, respectively, suggesting that D890 usually produces an incomplete blockade of the underlying CA current. The duration of the slow envelope of orthodromically evoked epileptiform paroxysmal depolarizing shifts (DSs), induced by bath application of 10(-5) M bicuculline, was frequency dependent and consistently increased from about 20 ms to 150 ms (half amplitude width) at frequencies above 0.5 Hz. In the presence of D890, the action potentials superimposed on the slow envelope of the DS were attenuated, but neither the amplitude nor the frequency-dependent progressive prolongation of the DS was altered. Application of TEA in the presence of bicuculline (10(-5) M) increased the amplitude and duration of the DS in neurons impaled with D890-containing electrodes. Under these conditions, the durations of DSs evoked by low frequency orthodromic stimulation (greater than 0.5 Hz) were still progressively prolonged, while, in the same neuron, directly evoked Ca2+ spikes progressively decreased in amplitude and duration.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1987K194300008

    View details for PubMedID 2890419

Conference Proceedings


  • Benign focal epilepsies of childhood: Genetically determined pathophysiology - Epilepsy that comes and goes Prince, D. A. WILEY-BLACKWELL PUBLISHING, INC. 2000: 1085-1087

    Abstract

    Developmental processes; the types of neuron expressing particular gene products; the sites of these receptors/channels, transporters, etc., on neurons and in circuits; and compensatory processes such as activation of other genes, sprouting, pruning, and receptor plasticity will determine the nature of the epileptic phenotype induced by a particular genetic alteration, and the ultimate functional outcome.

    View details for Web of Science ID 000088661000038

    View details for PubMedID 10961652

  • Postlesional epilepsy: The ultimate brain plasticity Jacobs, K. M., Graber, K. D., Kharazia, V. N., Parada, I., Prince, D. A. WILEY-BLACKWELL. 2000: S153-S161

    Abstract

    Lesions that occur either during fetal development or after postnatal brain trauma often result in seizures that are difficult to treat. We used two animal models to examine epileptogenic mechanisms associated with lesions that occur either during cortical development or in young adults. Results from these experiments suggest that there are three general ways that injury may induce hyperexcitability. Direct injury to cortical pyramidal neurons causes changes in membrane ion channels that make these cells more responsive to excitatory inputs, including increases in input resistance and a reduction in calcium-activated potassium conductances that regulate the rate of action potential discharge. The connectivity of cortical circuits is also altered after injury, as shown by axonal sprouting within pyramidal cell intracortical arbors. Enhanced excitatory connections may increase recurrent excitatory loops within the epileptogenic zone. Hyperinnervation attributable to reorganization of thalamocortical, callosal, and intracortical circuitry, and failure to prune immature connections, may be prominent when lesions affect the developing neocortex. Finally, focal injury can produce widespread changes in gamma-aminobutyric acid and glutamate receptors, particularly in the developing brain. All of these factors may contribute to epileptogenesis.

    View details for Web of Science ID 000089156500028

    View details for PubMedID 10999537

  • Mechanisms underlying epileptogenesis in cortical malformations Jacobs, K. M., Kharazia, V. N., Prince, D. A. ELSEVIER SCIENCE BV. 1999: 165-188

    Abstract

    The presence of developmental cortical malformations is associated with epileptogenesis and other neurological disorders. In recent years, animal models specific to certain malformations have been developed to study the underlying epileptogenic mechanisms. Teratogens (chemical, thermal or radiation) applied during cortical neuroblast division and migration result in lissencephaly and focal cortical dysplasia. Animals with these malformations have a lowered seizure threshold as well as histopathologies typical of those found in human dysgenic brains. Alterations that may promote epileptogenesis have been identified in lissencephalic brains, such as increased numbers of bursting types of neurons, and abnormal connections between hippocampus, subcortical heterotopia, and neocortex. A distinct set of pathological properties is present in animal models of 4-layered microgyria, induced with cortical lesions made during late stages of cortical neuroblast migration. Hyperexcitability has been demonstrated in cortex adjacent to the microgyrus (paramicrogyral zone) in in vitro slice preparations. A number of observations suggest that cellular differentiation is delayed in microgyric brains. Other studies show increases in postsynaptic glutamate receptors and decreases in GABA(A) receptors in microgyric cortex. These alterations could promote epileptogenesis, depending on which cell types have the altered receptors. The microgyrus lacks thalamic afferents from sensory relay nuclei, that instead appear to project to the paramicrogyral region, thereby increasing excitatory connectivity within this epileptogenic zone. These studies have provided a necessary first step in understanding molecular and cellular mechanisms of epileptogenesis associated with cortical malformations.

    View details for Web of Science ID 000082861200009

    View details for PubMedID 10515164

  • Inhibitory function in chronic focal epileptogenesis Prince, D. A. ELSEVIER SCIENCE BV. 1999: 437-442

    View details for Web of Science ID 000085689700051

    View details for PubMedID 10689491

  • Chronic focal neocortical epileptogenesis: Does disinhibition play a role? Prince, D. A., Jacobs, K. M., Salin, P. A., Hoffman, S., Parada, I. NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS. 1997: 500-507

    Abstract

    Several lines of evidence have suggested that decreases in postsynaptic inhibition may have a role in epileptogenesis in cortical structures. However, other studies have suggested that GABAergic inhibition is spared, or even augmented in some forms of post-lesional epilepsy. In the studies described here, inhibitory events were recorded in two models of post-lesional chronic epileptogenesis. (i) As previously reported (D.A. Prince and G.-F. Tseng. J. Neurophysiol. 69: 1276-1291. 1993), epileptiform activity develops in slices from partially isolated rat neocortical islands 2-3 weeks after the initial in vivo lesion. In this model of post-traumatic epilepsy, large amplitude polyphasic inhibitory postsynaptic currents (IPSCs) in layer V pyramidal neurons are associated with each interictal epileptiform field potential. The frequency of spontaneous IPSCs as well as miniature IPSCs was significantly increased in neocortical slices from the epileptogenic chronically injured cortex versus controls. Immunocytochemical reactions for parvalbumin and calbindin, calcium binding proteins present in subgroups of GABAergic neurons, showed an increased staining of both neuropil and somata within the epileptogenic tissue. Immunoreactivity for glutamic acid decarboxylase (GAD) and GABA also appeared to be increased in the neuropil. (ii) Cortical microgyri resembling human malformations were produced by freeze lesions made transcranially in P0 rat cortex (K.M. Jacobs, M.J. Gutnick, and D.A. Prince. Cereb. Cortex, 6: 514-523. 1996). The boundary between the four-layered microgyrus and surrounding cortex become epileptogenic within about 2 weeks, as judged by evoked extracellular field potentials and cellular activities. Epileptogenesis in the surrounding cortex is not altered when the microgyrus itself is isolated by transcortical cuts. Patch-clamp recordings from layer V neurons in the epileptogenic zone showed that spontaneous IPSCs are larger and more dependent on glutamatergic synapses than in control neurons. The amplitudes of polysynaptic IPSCs evoked by threshold stimulation were also larger than in control cells. Although evaluation of inhibitory events in these models is still incomplete, results to date suggest that GABAergic inhibition may be enhanced in epileptogenic areas associated with chronic cortical injury. Sprouting of axonal arborizations of pyramidal cells onto interneurons, upregulation of GABAergic neurons, and perhaps sprouting of inhibitory axons that make increased numbers of contacts onto pyramidal cells may all contribute to the increased inhibitory drive. Results in these models do not support the disinhibitory hypothesis of chronic epileptogenesis.

    View details for Web of Science ID A1997XM24600018

    View details for PubMedID 9250384