Basic investigations link a Val158Met polymorphism (rs4680) in the catechol-O-methyltransferase (COMT) gene to not only its enzymatic activity, but also to its dopaminergic tone in the prefrontal cortex. Previous PET studies have documented the relationship between COMT Val158Met polymorphism and D1 and D2/3 receptor binding potential (BP), and interpreted them in terms of dopaminergic tone. The use of baseline dopamine D1 and D2/3 receptor binding potential (BPND) as a proxy for dopaminergic tone is problematic because they reflect both endogenous dopamine levels (a change in radiotracer's apparent affinity) and receptor density. In this analysis of 31 healthy controls genotyped for the Val158Met polymorphism (Val/Val, Val/Met, and Met/Met), we used amphetamine-induced displacement of [11C]FLB 457 as a direct measure of dopamine release. Our analysis failed to show a relationship between COMT genotype status and prefrontal cortical dopamine release. COMT genotype was also not predictive of baseline dopamine D2/3 receptor BPND.
Post-traumatic stress disorder (PTSD) is a stress disorder that develops in only some individuals following a traumatic event. Data suggest that a substantial fraction of women recover after sexual violence. Thus, the investigation of stress and anti-stress neuropeptides in this sample has the potential to inform the neurochemistry of resilience following trauma. Nociceptin is an anti-stress neuropeptide in the brain that promotes resilience in animal models of PTSD. METHODS: [ 11 C]NOP-1A PET was used to measure the in vivo binding to nociceptin receptors in 18 college women who had experienced sexual violence irrespective of whether they met DSM-5 diagnostic criteria for PTSD. [ 11 C]NOP-1A data from 18 healthy controls was also included to provide a contrast with the sexual violence group. [ 11 C]NOP-1A total distribution volume (V T) in the regions of interest were measured with kinetic analysis using the arterial input function. The relationships between regional V T and Clinician-Administered PTSD Scale total symptom and subscale severity were examined using correlational analyses. RESULTS: No differences in [ 11 C]NOP-1A V T were noted between the sexual violence and control groups. V T in the midbrain and cerebellum were positively correlated with PTSD total symptom severity in the past month prior to PET. Intrusion/re-experiencing and avoidance subscale symptoms drove this relationship. Stratification of subjects by a DSM-5 PTSD diagnosis and contrasting their V T with that in controls showed no group differences. CONCLUSION: Decreased midbrain and cerebellum nociceptin receptors are associated with less severe PTSD symptoms. Medications that target nociceptin should be explored to prevent and treat PTSD.
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