These agents decreased the duration of immobility in SHR, but proved ineffective in WKY.20,21 Moreover, human data indicate that the efficacy of antidepressants has a strong genetic substrate, partly through the allelic variation in the activity of drug-metabolizing enzymes such as the cytochrome P450.22 Our preliminary observation that SHR and WKY differ in both their anxiety profile (these strains display low and high anxiety scores, respectively) and their activity profile (these strains

display high and low activity scores, respectively) led us to analyze their psychoneuroendocrine responses to several Inhibitors,research,lifescience,medical antidepressants. Thus, in one study, repeated fluoxetine Inhibitors,research,lifescience,medical treatments (5 or 10 mg/kg intraperitoneally [IP] daily, for 3 weeks) were administered to control SHR and WKY, whereas, in another study, repeated fluoxetine treatments were compared with imipramine and desipramine

treatments (all 10 mg/kg orally daily, for 4 weeks). Both these studies were carried out in control and repeatedly stressed SHR and WKY (2 h of restraint daily throughout the 4th week). Repeated fluoxetine treatment in control SHR and WKY Two days after the last fluoxetine injection in the control check details experiments,23 the two strains had undetectable plasma levels of fluoxetine, but detectable and Inhibitors,research,lifescience,medical similar levels of its metabolite, norfluoxetine. The elevated plus-maze Inhibitors,research,lifescience,medical test (29-30 h after the 13th administration of fluoxetine) and an open field test (48 h after the last injection of fluoxetine) were used to show that fluoxetine pretreatment did not produce anxiolysis; hence, some, but not all, behaviors were indicative of anxiety and hypolocomotion (as assessed through principal component analyses and acute diazepam studies). In both strains, the 10 mg/kg dose of fluoxetine decreased hypothalamus 5-HT and 5-HIAA levels, and reduced Inhibitors,research,lifescience,medical midbrain and/or hippocampus [3H]citalopram binding at 5-HTTs, but did not affect [3H]8-OH-DPAT binding at hippocampal 5-HT1A receptors. However, the fluoxetine-elicited reduction in hippocampal

5-HTT binding, which was unlikely to be due to residual norfluoxetine, was much greater in WKY than in Parvulin SHR, and this strain-dependent effect in WKY was associated with a reduction in cortical [3H]ketanserin binding at the 5-HT2A receptors. Finally, in WKY, repeated fluoxetine administration increased adrenal weights and the plasma corticosterone response to open field exposure, but did not affect the binding capacities of hippocampal mineralocorticoid and glucocorticoid receptors. Beside the complex neurochemical results that are beyond the scope of the present survey, our study mainly illustrates how key psychoneuroendocrine responses to repeated fluoxetine administration maybe strain-dependent.