Effects of ginseng saponins on β-amyloid-induced amnesia in rats

We have previously demonstrated that ginseng saponins (GS) can reverse the inhibitory effect of β-amyloid on acetylcholine (ACh) release in the hippocampal slices. The present study was carried out to examine whether GS has any beneficial effects against amnesia induced by β-amyloid peptides in vivo. Intracerebroventricular injection of 50 μg, but not 10 μg, β-amyloid fragment25–35 markedly impaired the performance of rats in avoiding a shock prod, confirming the amnesiac effect of β-amyloid. Chronically treating the rats with GS (orally, 5 days before icv β-amyloid injection and 7 days afterward) resulted in a dose-related improvement against β-amyloid-induced amnesia; a significant reversion was observed at the highest GS dose (80 mg/kg/day). Post-treatment analysis on K+-evoked [3H]-ACh release from the hippocampal slices showed that β-amyloid-treatment significantly reduced ACh release from that of the control group. However, pre-treatment with GS completely protected the animal against β-amyloid-induced reduction of hippocampal ACh release. In contrast, treating the animals with the same optimal dose of GS and duration but only after icv β-amyloid injection was found to be ineffective in obliterating β-amyloid's amnesiac effect. Taken together, these observations indicated that GS pre-treatment can functionally prevent the β-amyloid-induced memory loss possibly by minimizing the inhibitory effect of β-amyloid on hippocampal cholinergic transmission.