Effects of a methanolic extract and a hyperforin-enriched CO2 extract of St. John's Wort (Hypericum perforatum) on intracerebral field potentials in the freely moving rat (Tele-Stereo-EEG).

Two extracts of St. John's Wort (Hypericum perforatum) were investigated in the animal model "Tele-Stereo-EEG" which consisted of continuous recording of intracerebral field potentials in the freely moving rat. One was a CO2 extract for research purposes containing 30.14% hyperforin, a phloroglucine derivative known to occur within the reproductive parts of the plant, and lacking other major constituents like naphtodianthrones and flavonoids according to HPLC fingerprint. The other extract was the methanolic extract LI 160S (4.67% hyperforin). The dosage schedule was elaborated for the application of identical amounts of hyperforin in both extracts in each dosing group. Both extracts produced nearly identical patterns of electrical power changes during the first two hours of recording. These changes mainly consisted of reproducible power increases within the alpha1 band of the striatum. Comparison with earlier data obtained by identical protocols revealed that the early action was very similar to that following the application of serotonin reuptake inhibitors, thus matching biochemical in vitro data previously reported. These changes might be due to the presence of hyperforin. Only LI 160S developed a late action not seen with the CO2 extract, consisting in increases in delta activity. This late action of LI 160S matched data obtained by analysis of the action of NMDA-antagonists like MK 801 or memantine. Again, these results support previously reported biochemical findings of the interaction of hypericum extract with the glutamatergic system. In all probability, this action stems from substances only present in LI 160S, not in the CO2 extract. Which of the components contained within hypericum extracts are responsible for the clinical efficacy of St. John's wort in depression remains to be determined.