42 A recent finding in FM patients demonstrated strong negative correlations between the serum concentrations of substance P and 5-HIAA and between substance P and serum tryptophan.43 These findings support the hypothesis of a systemic involvement of 5-HT and substance P in FM. Genes of the serotonergic system As regards the 5-HTT gene HTTLPR polymorphism, we have observed a higher frequency of the SS genotype in FM patients compared with healthy controls and,

interestingly, patients with the SS genoytpe exhibited higher Inhibitors,research,lifescience,medical levels of click here depression and psychological distress.44 This preliminary finding was recently confirmed in patients of two different ethnicities (Jewish and Arabian populations), and extended by the observation that the FM patients were characterized by extremes of temperament extensions, Inhibitors,research,lifescience,medical especially harm avoidance.45 These results are in concordance with our previous findings, as the personality trait of harm avoidance and neuroticism are correlates of clinical depression and anxiety-related

disorders. Taken together, these findings suggest that the correlation between FM and the short allele (S) of the HTTLPR polymorphism could either (i) be indicative of common pathophysiological mechanisms with depression; or (ii) be mediated by depressionand Inhibitors,research,lifescience,medical anxietyrelated traits, and thus indicative of a subgroup of patients more likely to suffer depression. The 5-HT2A receptor also seems to be of great interest, since a recent finding with animal experiments suggested that the 5-HT2a Inhibitors,research,lifescience,medical receptor is involved in the thermal hyperalgesic mechanism of 5-HT in periphery46 The facts that the cerebral expressions of the 5-HT2A, 5-HT2C, and 5-HT6 receptors in rats are colocalized extensively with synthesis and expression of the neuropeptides enkephalin, substance P, and dynorphin47

Inhibitors,research,lifescience,medical and that substance P immunoreactivity was found to be higher in lumbar CSF of FM patients48 further highlight the importance of the 5-HT2 receptor family in the underlying pathophysiological process of this disorder. In a large cohort of FM from patients, we showed a significantly different genotype distribution in FM patients with a decrease in T/T and an increase in T/C and C/C genotypes of the 5-HT2A C102T polymorphism. Although there were no correlations between genotype and age of onset, duration of the disorder, or psychopathological symptoms rated on the Beck Depression Inventory, we found a reduced pain threshold in patients with the T/T genotype.49 Recently, the significant correlation between the 5-HT2A TT genotype and increased pain perception was replicated in a different sample, but no overall differences between patients and controls were observed.