St. John's Wort modulates brain regional serotonin metabolism in swim stressed rats.

Present study has investigated acute effects of Saint Johns Wort (SJW, 500mg/kg) administration on behavioral, neuroendocrine responses and serotonergic activity following forced swim test (FST) exposure in rats. The results show that SJW increased swimming and climbing behaviour of rats during FST exposure. Swim stress produced significant reduction in serum total tryptophan (P<0.01), increase in corticosterone (P<0.01) and 5-hydroxytryptamine (serotonin, 5-HT) turnover in hypothalamus by 100% (P<0.01), amygdala by 148 % (P<0.01), and hippocampus by 41% (P<0.05) when compared with unstressed saline injected group. SJW in swim stressed rats when compared with saline injected stressed rats altered neither lowered serum tryptophan nor enhanced HPA axis response, however 5HT was found to be increased by 110% (P<0.01), 163% (P<0.01) and 172% (P<0.01), in hypothalamus, amygdala and hippocampus respectively. 5-hydroxyindoleacetic acid (5HIAA) was also found to be increased in hypothalamus by 74% (P<0.01), amygdala by 45% (P<0.01) and hippocampus by 143.5% (P<0.01). Further SJW administration in unstressed rats showed decrease in tryptophan (P<0.01), increase in corticosterone (P<0.01), 5HT was found to be decreased in hypothalamus (47%, P<0.01) and in amygdala (13 %, P<0.05) with no change in hippocampus, while 5HIAA was found increased in hypothalamus by 58 %(P<0.01), amygdale by 203 % (P<0.01) and hippocampus by 171% (P<0.01). The data shows that SJW affects circulating tryptophan and corticosterone in absence of conditioned stress but not in its presence. In conclusion, SJW increases intraneuronal 5HT metabolism but inhibits its release under adverse conditions proving its anxiolytic property. Thus, these effects produced by the SJW add to our understanding of the interactions between SJW and stress induced behavioral, neuroendocrine and serotonergic alterations.