Intra-amygdaloid infusion of Ginkgo biloba leaf extract (EGb761) facilitates fear-potentiated startle in rats

Ginkgo biloba extract, EGb761, is one of the most commonly used herbal supplements throughout Western society. It has been used in the treatment of various common geriatric complaints including short-term memory loss. We showed that acute systemic administration of EGb761 enhanced fear-potentiated startle (FPS) in rats. Little is known about the behavioral effects of centrally administered EGb761 on FPS. The current study was performed to evaluate the involvement of basolateral nucleus of amygdala (BLA) in the EGb761 facilitation effect on FPS. Male adult SD rats were used. EGb761 was infused into cerebroventricle or basolateral nucleus of amygdala 10 min prior to fear conditioning. Animals were then tested for FPS 24 h later. Results showed that (1) intra-cerebroventricular infusion of EGb761 (0.1, 1.0, or 3.0 mu g/3.0 mu l per side, bilaterally) and intra-amygdaloid infusion of EGb761 (1.0, 14.0, or 28.0 ng/mu l per side, bilaterally) 30 and 10 min prior to fear conditioning, respectively, facilitated FPS in a dose-dependent manner. (2) Administration of EGb761 did not impair an animal's basal startle response or pain perception. (3) Subsequent control experiment's results indicated that the facilitation effect of EGb761 on the acquisition was not due to anxiogenic effect or non-specific effect. These results suggested that a single dose of EGb761 also has memory-enhancing effects in young animals. In addition, BLA is the central locus for EGb761 facilitation effect on FPS.