Honors & Awards

  • Advanced Postdoctoral-to-Independent Career Transition Award (K99/R00), HEAL Initiative; NIH (NIAMS and NINDS) (2023)
  • Postdoctoral NSRA Fellowship (F32), NIH (NINDS) (2021)
  • Trainee Innovator Grant, Stanford University Department of Psychiatry and Behavioral Sciences (2020)
  • Pain in Childhood SIG Poster Award, International Association for the Study of Pain (2018)
  • Trainee Professional Development Award, Society for Neuroscience (2017)
  • Young Investigator Travel Award, American Pain Society (2017)

Professional Education

  • PhD, University of Cincinnati, Neuroscience (2019)
  • BS, Northern Kentucky University, Psychology, minors in chemistry and biology (2015)

Stanford Advisors

All Publications

  • Low-frequency stimulation of Trpv1-lineage peripheral afferents potentiates the excitability of spino-periaqueductal gray projection neurons. The Journal of neuroscience : the official journal of the Society for Neuroscience Brewer, C. L., Kauer, J. A. 2023


    High-threshold dorsal root ganglion (HT DRG) neurons fire at low frequencies during inflammatory injury, and low-frequency stimulation (LFS) of HT DRG neurons selectively potentiates excitatory synapses onto spinal neurons projecting to periaqueductal gray (spino-PAG). Here, in male and female mice, we have identified an underlying peripheral sensory population driving this plasticity and its effects on the output of spino-PAG neurons. We provide the first evidence that Trpv1-lineage sensory neurons predominantly induce burst firing, a unique mode of neuronal activity, in lamina I spino-PAG projection neurons. We modeled inflammatory injury by optogenetically stimulating Trpv1+ primary afferents at 2 Hz for 2 min (LFS), as peripheral inflammation induces 1-2 Hz firing in high-threshold C fibers. LFS of Trpv1+ afferents enhanced the synaptically evoked and intrinsic excitability of spino-PAG projection neurons, eliciting a stable increase in the number of action potentials (APs) within a Trpv1+ fiber-induced burst, while decreasing the intrinsic AP threshold and increasing the membrane resistance. Further experiments revealed that this plasticity required Trpv1+ afferent input, postsynaptic G protein-coupled signaling, and NMDA receptor activation. Intriguingly, an inflammatory injury and heat exposure in vivo also increased APs per burst, in vitro These results suggest that inflammatory injury-mediated plasticity is driven though Trpv1+ DRG neurons and amplifies the spino-PAG pathway. Spinal inputs to the PAG could play an integral role in its modulation of heat sensation during peripheral inflammation, warranting further exploration of the organization and function of these neural pathways.Significance Statement Peripheral injury can lead to long-term modifications in spinal cord circuits and nociceptive processing. Electrical stimulation that models nerve activity during inflammatory injury selectively potentiates dorsal root ganglion (DRG) excitatory C fiber synapses onto spino-periaqueductal gray (spino-PAG) projection neurons. However, it is unknown if this potentiation 1) is driven by specific DRG subtypes and 2) alters the supraspinal output of this pathway. Here we demonstrate that Trpv1-lineage DRG neurons can persistently enhance both the synaptically driven and intrinsic excitability of spino-PAG projection neurons. We examine the mechanistic underpinnings of this enhanced excitability and provide evidence that this plasticity is evoked specifically during inflammatory injury and heat exposure and could influence inflammation-induced heat sensitization and pain perception.

    View details for DOI 10.1523/JNEUROSCI.1184-23.2023

    View details for PubMedID 38050062

  • Postnatal maturation of spinal dynorphin circuits and their role in somatosensation. Pain Brewer, C. L., Styczynski, L. M., Serafin, E. K., Baccei, M. L. 2020; 161 (8): 1906-1924


    Inhibitory interneurons in the adult spinal dorsal horn (DH) can be neurochemically classified into subpopulations that regulate distinct somatosensory modalities. Although inhibitory networks in the rodent DH undergo dramatic remodeling over the first weeks of life, little is known about the maturation of identified classes of GABAergic interneurons, or whether their role in somatosensation shifts during development. We investigated age-dependent changes in the connectivity and function of prodynorphin (DYN)-lineage neurons in the mouse DH that suppress mechanosensation and itch during adulthood. In vitro patch clamp recordings revealed a developmental increase in primary afferent drive to DYN interneurons and a transition from exclusive C-fiber monosynaptic input to mixed A-fiber and C-fiber innervation. Although most adult DYN interneurons exhibited tonic firing as expected from their inhibitory phenotype, neonatal and adolescent DYN cells were predominantly classified as phasic or single-spiking. Importantly, we also found that most of the inhibitory presynaptic terminals contacting lamina I spinoparabrachial projection neurons (PNs) originate from DYN neurons. Furthermore, inhibitory synaptic input from DYN interneurons onto PNs was weaker during the neonatal period, likely reflecting a lower number of GABAergic terminals and a reduced probability of GABA release compared to adults. Finally, spinal DYN interneurons attenuated mechanical sensitivity throughout development, but this population dampened acute nonhistaminergic itch only during adulthood. Collectively, these findings suggest that the spinal "gates" controlling sensory transmission to the brain may emerge in a modality-selective manner during early life due to the postnatal tuning of inhibitory synaptic circuits within the DH.

    View details for DOI 10.1097/j.pain.0000000000001884

    View details for PubMedID 32701849

  • Neonatal Injury Evokes Persistent Deficits in Dynorphin Inhibitory Circuits within the Adult Mouse Superficial Dorsal Horn. The Journal of neuroscience : the official journal of the Society for Neuroscience Brewer, C. L., Li, J. n., O'Conor, K. n., Serafin, E. K., Baccei, M. L. 2020; 40 (20): 3882–95


    Neonatal tissue damage induces long-term deficits in inhibitory synaptic transmission within the spinal superficial dorsal horn (SDH) that include a reduction in primary afferent-evoked, feedforward inhibition onto adult projection neurons. However, the subpopulations of mature GABAergic interneurons which are compromised by early-life injury have yet to be identified. The present research illuminates the persistent effects of neonatal surgical injury on the function of inhibitory SDH interneurons derived from the prodynorphin (DYN) lineage, a population that synapses directly onto lamina I spinoparabrachial neurons and is known to suppress mechanical pain and itch in adults. The results demonstrate that hindpaw incision at postnatal day 3 (P3) significantly decreased the strength of primary afferent-evoked glutamatergic drive onto DYN neurons within the adult mouse SDH while increasing the appearance of afferent-evoked inhibition onto the same population. Neonatal injury also dampened the intrinsic membrane excitability of mature DYN neurons, and reduced their action potential discharge in response to sensory input, compared with naive littermate controls. Furthermore, P3 incision decreased the efficacy of inhibitory DYN synapses onto adult spinoparabrachial neurons, which reflected a prolonged reduction in the probability of GABA release. Collectively, the data suggest that early-life tissue damage may persistently constrain the ability of spinal DYN interneurons to limit ascending nociceptive transmission to the adult brain. This is predicted to contribute to the loss of feedforward inhibition onto mature projection neurons, and the "priming" of nociceptive circuits in the developing spinal cord, following injuries during the neonatal period.SIGNIFICANCE STATEMENT Neonatal injury has lasting effects on pain processing in the adult CNS, including a reduction in feedforward inhibition onto ascending projection neurons in the spinal dorsal horn. While it is clear that spinal GABAergic interneurons are comprised of multiple subpopulations that play distinct roles in somatosensation, the identity of those interneurons which are compromised by tissue damage during early life remains unknown. Here we document persistent deficits in spinal inhibitory circuits involving dynorphin-lineage interneurons previously implicated in gating mechanical pain and itch. Notably, neonatal injury reduced the strength of dynorphin-lineage inhibitory synapses onto mature lamina I spinoparabrachial neurons, a major output of the spinal nociceptive network, which could contribute to the priming of pain pathways by early tissue damage.

    View details for DOI 10.1523/JNEUROSCI.0029-20.2020

    View details for PubMedID 32291327

    View details for PubMedCentralID PMC7219299

  • Adolescent sleep shapes social novelty preference in mice. Nature neuroscience Bian, W. J., Brewer, C. L., Kauer, J. A., de Lecea, L. 2022


    Sleep disturbances frequently occur in neurodevelopmental disorders such as autism, but the developmental role of sleep is largely unexplored, and a causal relationship between developmental sleep defects and behavioral consequences in adulthood remains elusive. Here, we show that in mice, sleep disruption (SD) in adolescence, but not in adulthood, causes long-lasting impairment in social novelty preference. Furthermore, adolescent SD alters the activation and release patterns of dopaminergic neurons in the ventral tegmental area (VTA) in response to social novelty. This developmental sleep function is mediated by balanced VTA activity during adolescence; chemogenetic excitation mimics, whereas silencing rescues, the social deficits of adolescent SD. Finally, we show that in Shank3-mutant mice, improving sleep or rectifying VTA activity during adolescence ameliorates adult social deficits. Together, our results identify a critical role of sleep and dopaminergic activity in the development of social interaction behavior.

    View details for DOI 10.1038/s41593-022-01076-8

    View details for PubMedID 35618950

  • The development of pain circuits and unique effects of neonatal injury JOURNAL OF NEURAL TRANSMISSION Brewer, C. L., Baccei, M. L. 2020; 127 (4): 467–79


    Pain is a necessary sensation that prevents further tissue damage, but can be debilitating and detrimental in daily life under chronic conditions. Neuronal activity strongly regulates the maturation of the somatosensory system, and aberrant sensory input caused by injury or inflammation during critical periods of early postnatal development can have prolonged, detrimental effects on pain processing. This review will outline the maturation of neuronal circuits responsible for the transmission of nociceptive signals and the generation of pain sensation-involving peripheral sensory neurons, the spinal cord dorsal horn, and brain-in addition to the influences of the neuroimmune system on somatosensation. This summary will also highlight the unique effects of neonatal tissue injury on the maturation of these systems and subsequent consequences for adult somatosensation. Ultimately, this review emphasizes the need to account for age as an independent variable in basic and clinical pain research, and importantly, to consider the distinct qualities of the pediatric population when designing novel strategies for pain management.

    View details for DOI 10.1007/s00702-019-02059-z

    View details for Web of Science ID 000524953600007

    View details for PubMedID 31399790

    View details for PubMedCentralID PMC7007840

  • Single-nucleus characterization of adult mouse spinal dynorphin-lineage cells and identification of persistent transcriptional effects of neonatal hindpaw incision. Pain Serafin, E. K., Paranjpe, A. n., Brewer, C. L., Baccei, M. L. 2020


    Neonatal tissue damage can have long-lasting effects on nociceptive processing in the central nervous system, which may reflect persistent injury-evoked alterations to the normal balance between synaptic inhibition and excitation in the spinal dorsal horn. Spinal dynorphin-lineage (pDyn) neurons are part of an inhibitory circuit which limits the flow of nociceptive input to the brain and is disrupted by neonatal tissue damage. To identify the potential molecular underpinnings of this disruption, an unbiased single-nucleus RNAseq analysis of adult mouse spinal pDyn cells characterized this population in depth and then identified changes in gene expression evoked by neonatal hindpaw incision. The analysis revealed 11 transcriptionally distinct subpopulations (ie, clusters) of dynorphin-lineage cells, including both inhibitory and excitatory neurons. Investigation of injury-evoked differential gene expression identified 15 genes that were significantly upregulated or downregulated in adult pDyn neurons from neonatally incised mice compared with naive littermate controls, with both cluster-specific and pan-neuronal transcriptional changes observed. Several of the identified genes, such as Oxr1 and Fth1 (encoding ferritin), were related to the cellular stress response. However, the relatively low number of injury-evoked differentially expressed genes also suggests that posttranscriptional regulation within pDyn neurons may play a key role in the priming of developing nociceptive circuits by early-life injury. Overall, the findings reveal novel insights into the molecular heterogeneity of a key population of dorsal horn interneurons that has previously been implicated in the suppression of mechanical pain and itch.

    View details for DOI 10.1097/j.pain.0000000000002007

    View details for PubMedID 33045156

  • Transcriptional profile of spinal dynorphin-lineage interneurons in the developing mouse PAIN Serafin, E. K., Chamessian, A., Li, J., Zhang, X., McGann, A., Brewer, C. L., Berta, T., Baccei, M. 2019; 160 (10): 2380–97


    Mounting evidence suggests that the spinal dorsal horn (SDH) contains multiple subpopulations of inhibitory interneurons that play distinct roles in somatosensory processing, as exemplified by the importance of spinal dynorphin-expressing neurons for the suppression of mechanical pain and chemical itch. Although it is clear that GABAergic transmission in the SDH undergoes significant alterations during early postnatal development, little is known about the maturation of discrete inhibitory "microcircuits" within the region. As a result, the goal of this study was to elucidate the gene expression profile of spinal dynorphin (pDyn)-lineage neurons throughout life. We isolated nuclear RNA specifically from pDyn-lineage SDH interneurons at postnatal days 7, 21, and 80 using the Isolation of Nuclei Tagged in Specific Cell Types (INTACT) technique, followed by RNA-seq analysis. Over 650 genes were ≥2-fold enriched in adult pDyn nuclei compared with non-pDyn spinal cord nuclei, including targets with known relevance to pain such as galanin (Gal), prepronociceptin (Pnoc), and nitric oxide synthase 1 (Nos1). In addition, the gene encoding a membrane-bound guanylate cyclase, Gucy2d, was identified as a novel and highly selective marker of the pDyn population within the SDH. Differential gene expression analysis comparing pDyn nuclei across the 3 ages revealed sets of genes that were significantly upregulated (such as Cartpt, encoding cocaine- and amphetamine-regulated transcript peptide) or downregulated (including Npbwr1, encoding the receptor for neuropeptides B/W) during postnatal development. Collectively, these results provide new insight into the potential molecular mechanisms underlying the known age-dependent changes in spinal nociceptive processing and pain sensitivity.

    View details for DOI 10.1097/j.pain.0000000000001636

    View details for Web of Science ID 000512905700023

    View details for PubMedID 31166300

  • Enhanced Postsynaptic GABA(B) Receptor Signaling in Adult Spinal Projection Neurons after Neonatal Injury NEUROSCIENCE Brewer, C. L., Baccei, M. L. 2018; 384: 329–39


    Clinical and basic science research have revealed persistent effects of early-life injury on nociceptive processing and resulting pain sensitivity. While recent work has identified clear deficits in fast GABAA- and glycine receptor-mediated inhibition in the adult spinal dorsal horn after neonatal tissue damage, the effects of early injury on slow, metabotropic inhibition within spinal pain circuits are poorly understood. Here we provide evidence that neonatal surgical incision significantly enhances postsynaptic GABAB receptor signaling within the mature superficial dorsal horn (SDH) in a cell type-dependent manner. In vitro patch-clamp recordings were obtained from identified lamina I projection neurons and GABAergic interneurons in the SDH of adult female mice following hindpaw incision at postnatal day (P)3. Early tissue damage increased the density of the outward current evoked by baclofen, a selective GABAB receptor agonist, in projection neurons but not inhibitory interneurons. This could reflect enhanced postsynaptic expression of downstream G protein-coupled inward-rectifying potassium channels (GIRKs), as the response to the GIRK agonist ML297 was greater in projection neurons from neonatally incised mice compared to naive littermate controls. Meanwhile, presynaptic GABAB receptor-mediated reduction of spontaneous neurotransmitter release onto both neuronal populations was unaffected by early-life injury. Collectively, our findings suggest that ascending nociceptive transmission to the adult brain is under stronger control by spinal metabotropic inhibition in the aftermath of neonatal tissue damage.

    View details for DOI 10.1016/j.neuroscience.2018.05.046

    View details for Web of Science ID 000436608600027

    View details for PubMedID 29885525

    View details for PubMedCentralID PMC6053268