Behavioral and neurochemical effects of Ginkgo biloba extract on the young mouse brain

Ginkgo biloba extract (EGb) is currently used as symptomatic treatment for cerebral insufficiency that occurs during normal aging or which may be due to degenerative dementia, vascular dementia or mixed forms of both, and for neurosensory disturbances. To assess the possibility that EGb may be effective for enhancing the plasticity in young CNS, we examined its effects on the acquisition of conditioned avoidance responses and the synaptic states of the whole brain in young BALB/c mice, by the behavioral technique and immunohistochemical method using the antibodies against synaptophysin, NMDA receptor and choline acetyltransferase (ChAT). EGb-treated mice showed a significant increase of the acquisition of conditioned avoidance responses, as compared to untreated mice. This effect increased the longer the training persisted. EGb-treated mice also induced an increase in the immunoreactivity to synaptophysin in the hippocampus, parietal cortex and amygdala, and that to NMDA receptor in the former two regions. Furthermore, EGb produced an increased number of ChAT-positive neurons in the medial septal region, from which cholinergic fibers arise and end on pyramidal neurons of the hippocampus and granule neurons of the dentate gyrus. These results suggest that EGb enhances plasticity by its multiple active constituents linked with conditioned avoidance training even in the young brain.