Abstract
Despite almost forty years of widespread use, the mode of action of antidepressant drugs is still largely unknown. There is agreement that these drugs interact with central neurotransmission. Common findings are acute inhibitory actions on reuptake mechanisms for norepinephrine (NE) and for serotonin (5-HT) at presynaptic axons and chronic adaptive effects on neurotransmitter receptors on postsynaptic membranes. In particular, beta-adrenoceptor downregulation has been observed after chronic treatment with most antidepressants in vivo and in cell culture systems. We studied the effectiveness of Ze 117 (St. John's wort) extract (Hypericum perforatum) on NE- and 5-HT-uptake into rat brain slices. Potency and efficacy of the Ze 117 extract were compared with those of tricyclic (TCA) and selective serotonin reuptake inhibitor (SSRI)-type antidepressants. A dose-dependent inhibition was seen on NE and 5-HT uptake into brain slices. The Ze 117 extract was more selective for the uptake of NE than for that of 5-HT. The maximal extent of uptake inhibition by Ze 117 extract was comparable to that of imipramine (IMI), desipramine (DMI) or fluvoxamine for 5-HT, but lower for NE transport, than that of the synthetic antidepressants. Chronic exposure (8 days) of confluent C6-cell cultures to Ze 117 extract resulted in a dose-dependent beta-adrenoceptor downregulation equal to that induced by DMI, a potent TCA. None of these effects could be achieved with either hypericin or hyperforin alone in a relevant dose range. Our results indicate that the St. John's wort extract Ze 117 contains active, but as yet unknown antidepressant principles with effects comparable to those of TCAs.