The role of the dorsal hippocampus on the Ginkgo biloba facilitation effect of fear extinction as assessed with fear-potentiated startle

Ginkgo biloba extract, EGb761, is widely used as herbal supplements throughout Western society. It has been used in the treatment of various common geriatric complaints including short-term memory loss. Our previous study has shown that acute systemic administration of EGb761 enhanced extinction of fear-potentiated startle (FPS) in rats. Little is known about the behavioral effects of hippocampally administered EGb761 on the extinction of FPS. The current study was performed to evaluate the involvement of the dorsal hippocampus (DH) in the EGb761 facilitation effect on the extinction of FPS. Male adult SD rats were used. EGb761 (28 ng/side, bilaterally) was infused into DH bilaterally 10 min prior to extinction training. Animals were then tested for FPS 24 h later. Results showed that intra-hippocampal infusion of EGb761 prior to extinction training facilitated extinction, which was not due to impairments of expression of conditioned fear. Intra-hippocampal injection of ERK1/2 inhibitor PD98059 partially attenuates the above EGb761 effect. Therefore, acute EGb761 administration modulated extinction of conditioned fear, which might be mediated by more than one signal cascade. These results suggest that DH may participate in the facilitation effect of EGb761 on the extinction of conditioned fear. In addition to ERK1/2, another signal cascade may also be involved in the EGb761 facilitation effect on extinction.