Improvement of memory in mice and increase of hippocampal excitability in rats by ginsenoside Rg1's metabolites ginsenoside Rh1 and protopanaxatriol.

Ginsenoside Rg1 has been reported to improve cognitive function in many memory-impaired animal models. However, little is known about the bioactivity of its metabolites in the central nervous system in vivo. In the present study, we employed the step through test and electrophysiological approach to investigate the effects of ginsenoside Rg1's primary metabolite ginsenoside Rh1 and end metabolite protopanaxatriol (Ppt) on learning and memory as well as hippocampal excitability. The behavioral study showed that both ginsenoside Rh1 and Ppt significantly ameliorated memory-impaired models induced by scopolamine in mice. Consistently, the electrophysiological work revealed that ginsenoside Rh1 and Ppt as well as their precursor ginsenoside Rg1 all increased hippocampal excitability in the dentate gyrus of anesthetized rats. These results demonstrated that both ginsenoside Rh1 and Ppt had similar but more potent actions than ginsenoside Rg1 in improving memory and hippocampal excitability, suggesting the role of ginsenoside's sugar moieties in biological activities is not as necessary as traditionally considered.