The effect of Ginkgo biloba extract (EGb 761) on gliotic reactions in the hippocampal formation after unilateral entorhinal cortex lesions

Purpose: Ginkgo biloba extract (EGb 761) has been shown to facilitate behav ioral and neuro-morphological recovery from brain injury, but less is known about its effects on glia. Since gliosis may be an important component of the recovery process, we tested the hypothesis that EGb 761 alters the time course and development of microglial activation and astrocytosis after bra in injury. Methods. Rats were treated with either saline or EGb 761 and killed at 2 hr s, 1, 3, 7, and 14 days following unilateral entorhinal cortex (EC) lesions . Microglia and their precursors were visualized with a silver impregnation method. and astrocytes with GFAP. Results: Blood-borne monocytes/macrophages were seen as early as 2 hrs afte r injury in all animals. The side contralateral to the injury showed minima l microglial activation and there were no significant effects of drug treat ment. On the side ipsilateral to the lesion EGb 761 enhanced microglial act ivation at 3, 7, and 14 days in the molecular layer and the hilus of the de ntate gyrus; the areas of most profound deafferentation after EC injury. Re gions of the corpus callosum also showed enhanced microglial activation ove r the same time course. Reactive astrocytes were stained with GFAP and were found to be more numerous than activated microglia, particularly in the ip silateral corpus callosum. EGb 761 treatment enhanced astrocytosis at 3 day s in the molecular layer, the hilus, and the corpus callosum on the ipsilat eral side. Conclusions. Taken together our results show that EGb 761 enhances, acceler ates and prolongs the activation of microglia and astrocytosis at the site of injury.