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Background Systemic inflammation and pain sensitivity may contribute to the development and maintenance of chronic pain conditions. Purpose We examined the relationship between systemic inflammation as measured by C-reactive protein (CRP), and cold pain sensitivity in 198 female twins from the University of Washington Twin Registry. We also explored the potential role of familial factors in this relationship. Methods Linear regression modeling with generalized estimating equations examined the overall and within-pair associations. Results Higher levels of CRP were associated with higher pain sensitivity ratings at pain threshold (p = 0.02) and tolerance (p = 0.03) after adjusting for age, body mass index, time to reach pain threshold or tolerance, and clinical pain status. The magnitude of the associations remained the same in within-pair analyses controlling for familial factors. Conclusions The link between CRP and pain sensitivity may be due to non-shared environmental factors. CRP and pain sensitivity can be examined as potential biomarkers for chronic pain and other inflammatory conditions.

Background There is a dearth of knowledge about the link between cortisol and pain sensitivity. Purpose We examined the association of salivary cortisol with indices of cold pain sensitivity in 198 female twins and explored the role of familial confounding. Methods Three-day saliva samples were collected for cortisol levels and a cold pressor test was used to collect pain ratings and time to threshold and tolerance. Linear regression modeling with generalized estimating equations examined the overall and within-pair associations. Results Lower diurnal variation of cortisol was associated with higher pain ratings at threshold (p = 0.02) and tolerance (p < 0.01). The relationship of diurnal variation with pain ratings at threshold and tolerance was minimally influenced by familial factors (i.e., genetics and common environment). Conclusions Understanding the genetic and non-genetic mechanisms underlying the link between HPA axis dysregulation and pain sensitivity may help to prevent chronic pain development and maintenance.

Background The etiology of chronic fatigue syndrome (CFS) remains unknown. Personality traits influence well-being and may play a role in CFS and unexplained chronic fatigue. Purpose To examine the association of emotional instability and extraversion with chronic fatigue and CFS in a genetically informative sample. Methods We evaluated 245 twin pairs for two definitions of chronic fatigue. They completed the Neuroticism and Extraversion subscales of the NEO-FFI. Using a co-twin control design, we examined the association between personality and chronic fatigue. Results Higher emotional instability was associated with both definitions of chronic fatigue and was confounded by shared genetics. Lower extraversion was also associated with both definitions of fatigue, but was not confounded by familial factors. Conclusions Both emotional instability and extraversion are related to chronic fatigue and CFS. Whereas emotional instability and chronic fatigue are linked by shared genetic mechanisms, the relationship with extraversion may be causal and bi-directional.

To investigate the dependence of the satiating action of cholecystokinin on serotonergic function in rats, we examined the effects of systemic pretreatment with serotonin (5-HT) antagonists of varying selectivity for 5-HT receptor subtypes on suppression of food intake induced by systemic administration of cholecystokinin octapeptide (CCK-8). Mianserin, a 5-HT1C/2-selective antagonist, significantly attenuated the satiating action of CCK-8. Ketanserin, a 5-HT2 antagonist, and three 5-HT3 antagonists, MDL-72222, ICS 205-930, and ondansetron, however, had no effect on the satiating action of CCK-8. These results demonstrate that the satiating action of exogenous CCK depends on activation of 5-HT1 (probably 5-HT1C) receptors and that activation of 5-HT2 or 5-HT3 receptors is not required.