Bio


My research is in the field of Psychoneuroimmunology, which is the study of how the immune system affects the brain and the behavior. In my doctoral thesis, I used experimental inflammatory models to understand how inflammation affects the perception of pain, and how the brain is affected by inflammation. In my postdoctoral studies, I have chosen a translational approach, where the theories from experimental research are tested in clinical settings. I am studying the effects of low-grade inflammation in different chronic pain populations, focusing on psychological comorbidity and treatment outcomes.

Professional Education


  • Doctor of Philosophy, Karolinska Institutet (2015)
  • Master of Science, Stockholms Universitet (2006)

All Publications


  • Detection of Inflammation via Volatile Cues in Human Urine. Chemical senses Gordon, A. R., Kimball, B. A., Sorjonen, K., Karshikoff, B., Axelsson, J., Lekander, M., Lundstrom, J. N., Olsson, M. J. 2018; 43 (9): 711–19

    Abstract

    Contagious disease is a major threat to survival, and the cost of relying on the immune system to defeat pathogens is high; therefore, behavioral avoidance of contagious individuals is arguably an adaptive strategy. Animal findings demonstrate the ability to detect and avoid sick individuals by the aid of olfactory cues, and a recent study indicated that human axillary odor also becomes more aversive as a function of immune activation. By injecting healthy human participants with lipopolysaccharide (0.6 ng/kg body weight) to experimentally induce inflammation, this study demonstrates that natural daily rhythms of urine odor-its perceived dimensions and volatile profile-are altered within hours of inflammation onset. Whereas healthy human urine decreases in averseness over the course of a single day, inflammation interrupts this process and results in an increased urine odor averseness and an altered volatile composition. These results support the notion that subtle and early cues of sickness may be detected and avoided, thereby complementing the immune system in its role of keeping us alive and healthy.

    View details for DOI 10.1093/chemse/bjy059

    View details for PubMedID 30321293

  • A global measure of sickness behaviour: Development of the Sickness Questionnaire JOURNAL OF HEALTH PSYCHOLOGY Andreasson, A., Wicksell, R. K., Lodin, K., Karshikoff, B., Axelsson, J., Lekander, M. 2018; 23 (11): 1452–63

    Abstract

    Symptoms after inflammatory activation, so-called sickness behaviour, overlap with trans-diagnostic complaints. As no self-report questionnaire to assess sickness behaviour exists, we aimed to develop such an instrument, the Sickness Questionnaire. Items responsive to experimentally induced inflammatory activation (randomized double-blind study endotoxin (0.6 ng/kg) versus placebo, n = 52) were selected and the statistical properties were examined in 172 primary care patients. A principal component analysis indicated a one-factor solution (Cronbach's alpha = .86). This 10-item scale correlated with depression ( β = .41, p < .001), anxiety ( β = .36, p < .001), self-rated health ( β = .28, p < .001) and a single item of feeling sick ( β = .55, p < .001). The results support the adequacy of Sickness Questionnaire as a brief assessment instrument of perceived sickness behaviour.

    View details for DOI 10.1177/1359105316659917

    View details for Web of Science ID 000443365600006

    View details for PubMedID 27458105

  • Sex differences in how inflammation affects behavior: What we can learn from experimental inflammatory models in humans FRONTIERS IN NEUROENDOCRINOLOGY Lasselin, J., Lekander, M., Axelsson, J., Karshikoff, B. 2018; 50: 91–106

    Abstract

    Human models demonstrate that experimental activation of the innate immune system has profound effects on brain activation and behavior, inducing fatigue, worsened mood and pain sensitivity. It has been proposed that inflammation is a mechanism involved in the etiology and maintenance of depression, chronic pain and long-term fatigue. These diseases show a strong female overrepresentation, suggesting that a better understanding of sex differences in how inflammation drives behavior could help the development of individualized treatment interventions. For this purpose, we here review sex differences in studies using experimental inflammatory models to investigate changes in brain activity and behavior. We suggest a model in which inflammation accentuates sex differences in brain networks and pre-existing vulnerability factors. This effect could render women more vulnerable to the detrimental effects of immune-to-brain communication over time. We call for systematic and large scale investigations of vulnerability factors for women in the behavioral response to inflammation.

    View details for DOI 10.1016/j.yfrne.2018.06.005

    View details for Web of Science ID 000445443600007

    View details for PubMedID 29935190

  • Evidence of fatigue, disordered sleep and peripheral inflammation, but not increased brain TSPO expression, in seasonal allergy: A [C-11]PBR28 PET study BRAIN BEHAVIOR AND IMMUNITY Tamm, S., Cervenka, S., Forsberg, A., Estelius, J., Grunewald, J., Gyllfors, P., Karshikoff, B., Kosek, E., Lampa, J., Lensmar, C., Strand, V., Akerstedt, T., Halldin, C., Ingvar, M., Hoglund, C., Lekander, M. 2018; 68: 146–57

    Abstract

    Allergy is associated with non-specific symptoms such as fatigue, sleep problems and impaired cognition. One explanation could be that the allergic inflammatory state includes activation of immune cells in the brain, but this hypothesis has not been tested in humans. The aim of the present study was therefore to investigate seasonal changes in the glial cell marker translocator protein (TSPO), and to relate this to peripheral inflammation, fatigue and sleep, in allergy. We examined 18 patients with severe seasonal allergy, and 13 healthy subjects in and out-of pollen season using positron emission tomography (n = 15/13) and the TSPO radioligand [11C]PBR28. In addition, TNF-α, IL-5, IL-6, IL-8 and IFN-γ were measured in peripheral blood, and subjective ratings of fatigue and sleepiness as well as objective and subjective sleep were investigated. No difference in levels of TSPO was seen between patients and healthy subjects, nor in relation to pollen season. However, allergic subjects displayed both increased fatigue, sleepiness and increased percentage of deep sleep, as well as increased levels of IL-5 and TNF-α during pollen season, compared to healthy subjects. Allergic subjects also had shorter total sleep time, regardless of season. In conclusion, allergic subjects are indicated to respond to allergen exposure during pollen season with a clear pattern of behavioral disruption and peripheral inflammatory activation, but not with changes in brain TSPO levels. This underscores a need for development and use of more specific markers to understand brain consequences of peripheral inflammation that will be applicable in human subjects.

    View details for DOI 10.1016/j.bbi.2017.10.013

    View details for Web of Science ID 000424068600015

    View details for PubMedID 29054675

  • Lifetime Modulation of the Pain System via Neuroimmune and Neuroendocrine interactions FRONTIERS IN IMMUNOLOGY Zouikr, I., Karshikoff, B. 2017; 8: 276

    Abstract

    Chronic pain is a debilitating condition that still is challenging both clinicians and researchers. Despite intense research, it is still not clear why some individuals develop chronic pain while others do not or how to heal this disease. In this review, we argue for a multisystem approach to understand chronic pain. Pain is not only to be viewed simply as a result of aberrant neuronal activity but also as a result of adverse early-life experiences that impact an individual's endocrine, immune, and nervous systems and changes which in turn program the pain system. First, we give an overview of the ontogeny of the central nervous system, endocrine, and immune systems and their windows of vulnerability. Thereafter, we summarize human and animal findings from our laboratories and others that point to an important role of the endocrine and immune systems in modulating pain sensitivity. Taking "early-life history" into account, together with the past and current immunological and endocrine status of chronic pain patients, is a necessary step to understand chronic pain pathophysiology and assist clinicians in tailoring the best therapeutic approach.

    View details for DOI 10.3389/fimmu.2017.00276

    View details for Web of Science ID 000396206400001

    View details for PubMedID 28348566

    View details for PubMedCentralID PMC5347117

  • Lipopolysaccharide Alters Motivated Behavior in a Monetary Reward Task: a Randomized Trial NEUROPSYCHOPHARMACOLOGY Lasselin, J., Treadway, M. T., Lacourt, T. E., Soop, A., Olsson, M. J., Karshikoff, B., Paues-Goranson, S., Axelsson, J., Dantzer, R., Lekander, M. 2017; 42 (4): 801–10

    Abstract

    Inflammation-induced sickness is associated with a large set of behavioral alterations; however, its motivational aspects remain poorly explored in humans. The present study assessed the effect of lipopolysaccharide (LPS) administration at a dose of 2 ng/kg of body weight on motivation in 21 healthy human subjects in a double-blinded, placebo (saline)-controlled, cross-over design. Incentive motivation and reward sensitivity were measured using the Effort Expenditure for Rewards Task (EEfRT), in which motivation for high-effort/high-reward trials vs low-effort/low-reward trials are manipulated by variations in reward magnitude and probability to win. Because of the strong interactions between sleepiness and motivation, the role of sleepiness was also determined. As expected, the probability to win predicted the choice to engage in high-effort/high-reward trials; however, this occurred at a greater extent after LPS than after saline administration. This effect was related to the level of sleepiness. Sleepiness increased motivation to choose the high-effort/high-reward mode of response, but only when the probability to win was the highest. LPS had no effect on reward sensitivity either directly or via sleepiness. These results indicate that systemic inflammation induced by LPS administration causes motivational changes in young healthy subjects, which are associated with sleepiness. Thus, despite its association with energy-saving behaviors, sickness allows increased incentive motivation when the effort is deemed worthwhile.

    View details for DOI 10.1038/npp.2016.191

    View details for Web of Science ID 000393725600003

    View details for PubMedID 27620550

    View details for PubMedCentralID PMC5312062

  • Role of inflammation in Human Fatigue: Relevance of Multidimensional Assessments and Potential Neuronal Mechanisms FRONTIERS IN IMMUNOLOGY Karshikoff, B., Sundelin, T., Lasselin, J. 2017; 8: 21

    Abstract

    Fatigue is a highly disabling symptom in various medical conditions. While inflammation has been suggested as a potential contributor to the development of fatigue, underlying mechanisms remain poorly understood. In this review, we propose that a better assessment of central fatigue, taking into account its multidimensional features, could help elucidate the role and mechanisms of inflammation in fatigue development. A description of the features of central fatigue is provided, and the current evidence describing the association between inflammation and fatigue in various medical conditions is reviewed. Additionally, the effect of inflammation on specific neuronal processes that may be involved in distinct fatigue dimensions is described. We suggest that the multidimensional aspects of fatigue should be assessed in future studies of inflammation-induced fatigue and that this would benefit the development of effective therapeutic interventions.

    View details for DOI 10.3389/fimmu.2017.00021

    View details for Web of Science ID 000392330000001

    View details for PubMedID 28163706

    View details for PubMedCentralID PMC5247454

  • Why sickness hurts: A central mechanism for pain induced by peripheral inflammation BRAIN BEHAVIOR AND IMMUNITY Karshikoff, B., Jensen, K. B., Kosek, E., Kalpouzos, G., Soop, A., Ingvar, M., Hoglund, C., Lekander, M., Axelsson, J. 2016; 57: 38–46

    Abstract

    Low-grade systemic inflammation has been implicated in chronic pain, as well as in comorbid diseases like depression and fatigue. We have previously shown that women's pain perception and regulation is more affected by systemic inflammation than that of men. Here we investigated the neural substrates underlying these effects using an fMRI paradigm previously employed in a clinical population. Fifty-one participants (29 women) were injected with 0.6ng/kg lipopolysaccharide (LPS) or saline to induce a peripheral inflammatory response. The subjects were then tested with a pressure pain fMRI paradigm designed to capture descending pain inhibitory activity 2h after injection, and blood was sampled for cytokine analysis. The subjects injected with LPS became more pain sensitive compared to the placebo group, and the heightened pain sensitivity was paralleled by decreased activity in the ventrolateral prefrontal cortex and the rostral anterior cingulate cortex (rACC) compared to placebo; areas involved in descending pain regulation. The LPS group also had higher activity in the anterior insular cortex, an area underpinning affective and interoceptive pain processing. Women displayed overall less pain-evoked rACC activity compared to men, which may have rendered women less resilient to immune provocation, possibly explaining sex differences in LPS-induced pain sensitivity. Our findings elucidate the pain-related brain circuits affected by experimental peripheral inflammation, strengthening the theoretical link between systemic inflammation and weakened pain regulation in chronic pain disorders. The results further suggest a possible mechanism underlying the female predominance in many chronic pain disorders.

    View details for DOI 10.1016/j.bbi.2016.04.001

    View details for Web of Science ID 000383306200006

    View details for PubMedID 27058164

  • Health Anxiety in a Disease-Avoidance Framework: Investigation of Anxiety, Disgust and Disease Perception in Response to Sickness Cues JOURNAL OF ABNORMAL PSYCHOLOGY Hedman, E., Lekander, M., Karshikoff, B., Ljotsson, B., Axelsson, E., Axelsson, J. 2016; 125 (7): 868–78

    Abstract

    Severe health anxiety is characterized by a debilitating fear of somatic illness, and avoidance of disease-related stimuli plays a key role in the maintenance of the disorder. The aim of this study was to investigate severe health anxiety within an evolutionary disease-avoidance framework. We hypothesized that, compared to healthy controls, participants with severe health anxiety would perceive others as sicker, more contagious, and less attractive. We also expected individuals with severe health anxiety to be more prone to avoid interaction with persons who appeared sick, as well as to respond with more health-related worry, more disgust, and more anxiety when confronting such individuals. In addition, this sensitivity was expected to be larger if people showed manifest sickness symptoms. Participants with and without severe health anxiety (N = 224) were exposed to facial photos with a varying degree of apparent sickness. Patients with severe health anxiety, compared to controls, rated apparently healthy people as being less healthy and less attractive. There were significant interaction effects showing that that the increase in disgust, anxiety, perceived contagiousness, and worry over one's own health as a function of how sick the person in the photo appeared, was significantly larger in the clinical sample compared to the healthy control sample (ps < .047). Results from regression analyses using health anxiety as a dimensional predictor also supported our hypotheses. We suggest that disgust and cognitive biases relating to the disease-avoidance model are significant features of severe health anxiety. (PsycINFO Database Record

    View details for DOI 10.1037/abn0000195

    View details for Web of Science ID 000386059700002

    View details for PubMedID 27732023

  • Mood disturbance during experimental endotoxemia: Predictors of state anxiety as a psychological component of sickness behavior BRAIN BEHAVIOR AND IMMUNITY Lasselin, J., Elsenbruch, S., Lekander, M., Axelsson, J., Karshikoff, B., Grigoleit, J., Engler, H., Schedlowski, M., Benson, S. 2016; 57: 30–37

    Abstract

    Lipopolysaccharide (LPS) administration is a well-established model to assess afferent immune-to-brain communication and behavioral aspects of inflammation. Nevertheless, only few studies in comparatively small samples have assessed state anxiety as a psychological component of sickness behavior despite possible clinical implications for the pathophysiology of neuropsychiatric conditions. Thus, the goal of the present analyses carried out in a large, pooled dataset from two independent study sites was to analyze the state anxiety response to LPS administration and to investigate predictors (i.e., cytokine changes; pre-existing anxiety and depression symptoms assessed with the Hospital Anxiety and Depression Scale) of the LPS-induced state anxiety changes at different time points after LPS administration. Data from 186 healthy volunteers who participated in one of six randomized, placebo-controlled human studies involving intravenous administration of LPS at doses of 0.4-0.8ng/kg body weight were combined. State anxiety as well as circulating interleukin (IL)-6, tumor necrosis factor (TNF)-α and IL-10 concentrations were significantly increased 2h and 3h after LPS administration, with a peak at 2h, and returned to baseline 6h after administration. Greater changes in IL-6 from baseline to 3h after LPS administration significantly and independently predicted a more pronounced LPS-induced state anxiety response. In addition, higher pre-existing subclinical anxiety symptoms significantly predicted a lower increase in state anxiety 3h and 6h after LPS-administration, which was mediated by TNF-α changes. In conclusion, our findings give additional support for a putative role of inflammatory mechanisms in the pathophysiology of stress-related and anxiety disorders and give new insight on the potential role of pre-existing subclinical affective symptoms.

    View details for DOI 10.1016/j.bbi.2016.01.003

    View details for Web of Science ID 000383306200005

    View details for PubMedID 26790758

  • Intrinsic functional connectivity of insular cortex and symptoms of sickness during acute experimental inflammation BRAIN BEHAVIOR AND IMMUNITY Lekander, M., Karshikoff, B., Johansson, E., Soop, A., Fransson, P., Lundstrom, J. N., Andreasson, A., Ingvar, M., Petrovic, P., Axelsson, J., Nilsonne, G. 2016; 56: 34–41

    Abstract

    Task-based fMRI has been used to study the effects of experimental inflammation on the human brain, but it remains unknown whether intrinsic connectivity in the brain at rest changes during a sickness response. Here, we investigated the effect of experimental inflammation on connectivity between areas relevant for monitoring of bodily states, motivation, and subjective symptoms of sickness. In a double-blind randomized controlled experiment, 52 healthy volunteers were injected with 0.6ng/kg LPS (lipopolysaccharide) or placebo, and participated in a resting state fMRI experiment after approximately 2h 45min. Resting state fMRI data were available from 48 participants, of which 28 received LPS and 20 received placebo. Bilateral anterior and bilateral posterior insula sections were used as seed regions and connectivity with bilateral orbitofrontal and cingulate (anterior and middle) cortices was investigated. Back pain, headache and global sickness increased significantly after as compared to before LPS, while a non-significant trend was shown for increased nausea. Compared to placebo, LPS was followed by increased connectivity between left anterior insula and left midcingulate cortex. This connectivity was significantly correlated to increase in back pain after LPS and tended to be related to increased global sickness, but was not related to increased headache or nausea. LPS did not affect the connectivity from other insular seeds. In conclusion, the finding of increased functional connectivity between left anterior insula and middle cingulate cortex suggests a potential neurophysiological mechanism that can be further tested to understand the subjective feeling of malaise and discomfort during a sickness response.

    View details for DOI 10.1016/j.bbi.2015.12.018

    View details for Web of Science ID 000378985600005

    View details for PubMedID 26732827

  • Sick man walking: Perception of health status from body motion BRAIN BEHAVIOR AND IMMUNITY Sundelin, T., Karshikoff, B., Axelsson, E., Hoglund, C., Lekander, M., Axelsson, J. 2015; 48: 53–56

    Abstract

    An ability to detect subtle signs of sickness in others would be highly beneficial, as it would allow for behaviors that help us avoid contagious pathogens. Recent findings suggest that both animals and humans are able to detect distinctive odor signals of individuals with activated innate immune responses. This study tested whether an innate immune response affects a person's walking speed and whether other people perceive that person as less healthy. 43 subjects watched films of persons who were experiencing experimental immune activation, and rated the walking individuals in the films with respect to health, tiredness, and sadness. Furthermore, the walking speed in the films was analyzed. After LPS injections, participants walked more slowly and were perceived as less healthy and more tired as compared to when injected with placebo. There was also a trend for the subjects to look sadder after LPS injection than after placebo. Furthermore, there were strong associations between walking speed and the appearance of health, tiredness, and sadness. These findings support the notion that walking speed is affected by an activated immune response, and that humans may be able to detect very early signs of sickness in others by merely observing their gait. This ability is likely to aid both a "behavioral immune system", by providing more opportunities for adaptive behaviors such as avoidance, and the anticipatory priming of biochemical immune responses.

    View details for DOI 10.1016/j.bbi.2015.03.007

    View details for Web of Science ID 000358460700008

    View details for PubMedID 25801061

  • Modality and sex differences in pain sensitivity during human endotoxemia BRAIN BEHAVIOR AND IMMUNITY Karshikoff, B., Lekander, M., Soop, A., Lindstedt, F., Ingvar, M., Kosek, E., Hoglund, C., Axelsson, J. 2015; 46: 35–43

    Abstract

    Systemic inflammation can induce pain hypersensitivity in animal and human experimental models, and has been proposed to be central in clinical pain conditions. Women are overrepresented in many chronic pain conditions, but experimental studies on sex differences in pain regulation during systemic inflammation are still scarce. In two randomized and double blind placebo controlled experiments, we used low doses of lipopolysaccharide (LPS) as an experimental model of systemic inflammation. The first study employed 0.8ng/kg LPS in a within-subject design of 8 individuals (1 woman), and the second study 0.6ng/kg LPS in a between-subject design of 52 participants (29 women). We investigated the effect on (a) pressure, heat, and cold pain thresholds, (b) suprathreshold noxious heat and cold sensitivity, and (c) conditioned pain modulation (CPM), and differences between men and women. LPS induced significantly lower pressure pain thresholds as compared to placebo (mean change with the 0.8ng/kg dose being -64±30kPa P=.04; with the 0.6ng/kg dose -58±55kPa, P<.01, compared to before injection), whereas heat and cold pain thresholds remained unaffected (P's>.70). Suprathreshold noxious pain was not affected by LPS in men (P's⩾.15). However, LPS made women rated suprathreshold noxious heat stimuli as more painful (P=.01), and showed a tendency to rate noxious cold pain as more painful (P=.06) as compared to placebo. Furthermore, LPS impaired conditioned pain modulation, a measure of endogenous pain inhibition, but this effect was also restricted to women (P<.01, for men P=.27). Pain sensitivity correlated positively with plasma IL-6 and IL-8 levels. The results show that inflammation more strongly affects deep pain, rather than cutaneous pain, and suggest that women's pain perception and modulation is more sensitive to immune activation than men's.

    View details for DOI 10.1016/j.bbi.2014.11.014

    View details for Web of Science ID 000353751100005

    View details for PubMedID 25486090

  • The Scent of Disease Human Body Odor Contains an Early Chemosensory Cue of Sickness PSYCHOLOGICAL SCIENCE Olsson, M. J., Lundstrom, J. N., Kimball, B. A., Gordon, A. R., Karshikoff, B., Hosseini, N., Sorjonen, K., Hoglund, C., Solares, C., Soop, A., Axelsson, J., Lekander, M. 2014; 25 (3): 817–23

    Abstract

    Observational studies have suggested that with time, some diseases result in a characteristic odor emanating from different sources on the body of a sick individual. Evolutionarily, however, it would be more advantageous if the innate immune response were detectable by healthy individuals as a first line of defense against infection by various pathogens, to optimize avoidance of contagion. We activated the innate immune system in healthy individuals by injecting them with endotoxin (lipopolysaccharide). Within just a few hours, endotoxin-exposed individuals had a more aversive body odor relative to when they were exposed to a placebo. Moreover, this effect was statistically mediated by the individuals' level of immune activation. This chemosensory detection of the early innate immune response in humans represents the first experimental evidence that disease smells and supports the notion of a "behavioral immune response" that protects healthy individuals from sick ones by altering patterns of interpersonal contact.

    View details for DOI 10.1177/0956797613515681

    View details for Web of Science ID 000332596800022

    View details for PubMedID 24452606

  • Allergy influences the inflammatory status of the brain and enhances tau-phosphorylation JOURNAL OF CELLULAR AND MOLECULAR MEDICINE Sarlus, H., Hoglund, C., Karshikoff, B., Wang, X., Lekander, M., Schultzberg, M., Oprica, M. 2012; 16 (10): 2401–12

    Abstract

    Despite the existing knowledge regarding the neuropathology of Alzheimer's disease (AD), the cause of sporadic forms of the disease is unknown. It has been suggested that systemic inflammation may have a role, but the exact mechanisms through which inflammatory processes influence the pathogenesis and progress of AD are not obvious. Allergy is a chronic inflammatory disease affecting more than 20% of the Western population, but the effects of allergic conditions on brain functions are largely unknown. The aim of this study was to investigate whether or not chronic peripheral inflammation associated with allergy affects the expression of AD-related proteins and inflammatory markers in the brain. On the basis of previously described models for allergy in mice we developed a model of chronic airway allergy in mouse, with ovalbumin as allergen. The validity of the chronic allergy model was confirmed by a consistent and reproducible eosinophilia in the bronchoalveolar lavage (BAL) fluid of allergic animals. Allergic mice were shown to have increased brain levels of both immunoglobulin (Ig) G and IgE with a widespread distribution. Allergy was also found to increase phosphorylation of tau protein in the brain. The present data support the notion that allergy-dependent chronic peripheral inflammation modifies the brain inflammatory status, and influences phosphorylation of an AD-related protein, indicating that allergy may be yet another factor to be considered for the development and/or progression of neurodegenerative diseases such as AD.

    View details for DOI 10.1111/j.1582-4934.2012.01556.x

    View details for Web of Science ID 000309237500017

    View details for PubMedID 22356650

    View details for PubMedCentralID PMC3823434

  • Serotonin-1A Receptor Polymorphism (rs6295) Associated with Thermal Pain Perception PLOS ONE Lindstedt, F., Karshikoff, B., Schalling, M., Hoglund, C., Ingvar, M., Lekander, M., Kosek, E. 2012; 7 (8): e43221

    Abstract

    Serotonin (5-HT) is highly involved in pain regulation and serotonin-1A (5-HT1A) receptors are important in determining central 5-HT tone. Accordingly, variation in the 5-HT1A receptor gene (HTR1A) may contribute to inter-individual differences in human pain sensitivity. The minor G-allele of the HTR1A single nucleotide polymorphism (SNP) rs6295 attenuates firing of serotonergic neurons and reduces postsynaptic expression of the receptor. Experiments in rodents suggest that 5-HT1A-agonism modulates pain in opposite directions at mild compared to high noxious intensities. Based upon this and several other similar observations, we hypothesized that G-carriers would exhibit a relative hypoalgesia at mild thermal stimuli but tend towards hyperalgesia at higher noxious intensities.Fourty-nine healthy individuals were selectively genotyped for rs6295. Heat- and cold-pain thresholds were assessed along with VAS-ratings of a range of suprathreshold noxious heat intensities (45°C-49°C). Nociceptive-flexion reflex (NFR) thresholds were also assessed.Volunteers did not deviate significantly from Hardy-Weinberg equilibrium. G-carriers were less sensitive to threshold-level thermal pain. This relative hypoalgesia was abolished at suprathreshold noxious intensities where G-carriers instead increased their ratings of heat-pain significantly more than C-homozygotes. No differences with regard to NFR-thresholds emerged.To the best of our knowledge this is the first study of human pain perception on the basis of variation in HTR1A. The results illustrate the importance of including a range of stimulus intensities in assessments of pain sensitivity. In speculation, we propose that an attenuated serotonergic tone may be related to a 'hypo- to hyperalgesic' response-pattern. The involved mechanisms could be of clinical interest as variation in pain regulation is known to influence the risk of developing pain pathologies. Further investigations are therefore warranted.

    View details for DOI 10.1371/journal.pone.0043221

    View details for Web of Science ID 000308221300010

    View details for PubMedID 22952650

    View details for PubMedCentralID PMC3432037