The ameliorating effects of aqueous and ethanolic extracts of LiuWei Dihuang Wang (LDWW and LDWE) after single, 1-week or 2-week consecutive treatment on the cycloheximide-induced amnesia by using the passive avoidance task in rats were studied. After single treatment, LDWW and LDWE (1 and 2 g/kg) significantly prolonged the shortened step-through latency induced by CXM and their potency was equal. LDWW at 1 g/kg after 1-week consecutive treatment or at 0.1 g/kg after 2-week consecutive treatment almost completely reversed CXM-induced amnesia. LDWW at any dose alone after single, 1-week or 2-week consecutive treatment did not influence the step-through latency in the training trial in rats. Furthermore, muscarinic antagonist scopolamine, peripheral cholinergic antagonist scopolamine methylbromide, serotonin precursor 5-hydroxytryptamine and serotonin releaser p-chloroamphetamine could block the ameliorating effects of LDWW. GABAA receptor antagonist bicuculline and GABAB receptor agonist baclofen also blocked the ameliorating effects of LDWW. These results suggest that the ameliorating effects of LDW whose potency were parallel to treatment duration might be related to activating peripheral cholinergic neuronal system and modulating the central nervous system.
