Autoradiographic quantification of neurochemical markers of serotonin, dopamine and opioid systems in rat brain mesolimbic regions following chronic St John's wort treatment.

Effects of chronic treatment with St John's wort (SJW, Hypericum perforatum) on neurochemical markers of serotonin, dopamine and opioid systems in mesolimbic regions of the fawn-hooded rat were investigated by quantitative autoradiography. After 10 days' treatment, SJW significantly increased [(3)H]citalopram binding to 5-HT transporters in multiple mesolimbic regions. In contrast, SJW resulted in a region-specific alteration of [(3)H]mazindol binding to dopamine transporters, such as increased binding of [(3)H]mazindol in the olfactory tubercle and decreased binding in the ventral tegmental area. In addition, SJW also resulted in differential modulation of the binding properties of 5-HT(1A)-, 5-HT(2A)- and mu-opioid receptors in a region-specific manner. The ability of SJW to affect 5-HT, dopamine and opioid systems in mesolimbic regions in the CNS, either by a direct or by indirect (adaptation) mechanism, may help to explain the efficacy of SJW in the treatment of depression clinically and in some of the behavioural effects observed in experimental rodents.