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

Abstract

Purpose: Ginkgo biloba extract (EGb 761) has been shown to facilitate behavioral 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 brain injury. Methods: Rats were treated with either saline or EGb 761 and killed at 2 hrs, 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 after injury in all animals. The side contralateral to the injury showed minimal microglial activation and there were no significant effects of drug treatment. On the side ipsilateral to the lesion EGb 761 enhanced microglial activation at 3, 7, and 14 days in the molecular layer and the hilus of the dentate gyrus; the areas of most profound deaf-ferentation after EC injury. Regions of the corpus callosum also showed enhanced microglial activation over the same time course. Reactive astrocytes were stained with GFAP and were found to be more numerous than activated microglia, particularly in the ipsilateral corpus callo-sum. EGb 761 treatment enhanced astrocytosis at 3 days in the molecular layer, the hilus, and the corpus callosum on the ipsilateral side. Conclusions: Taken together our results show that EGb 761 enhances, accelerates and prolongs the activation of microglia and astrocytosis at the site of injury.