Effects of Gingko biloba extract on gap junction changes induced by reperfusion/reoxygenation after ischemia/hypoxia in rat brain

Gap junction communication between astrocytes plays an important role in the brain. The purpose of this study was to investigate the effects of Gingko biloba extract (GBE) on the changes of connexin 43 (Cx43) mRNA and protein expression levels of rat cortex and hippocampus induced by ischemia-reperfusion and astrocyte gap junction intercellular communication (GJIC) induced by hypoxia-reoxygenation. After 2 hours of middle cerebral artery occlusion (MCAO) followed by 24 hours of reperfusion, there was obvious neurological deficit in rats. Cx43 mRNA and protein expression levels of rat cortex and hippocampus in the ischemia hemisphere were decreased significantly. When GBE at doses of 50 and 100 mg/kg body weight was administrated by p.o. daily for 7 days, the neurological deficit was improved, and lower Cx43 mRNA and protein expression levels induced by ischemia-reperfusion were recovered to normal. The i.p. injection of nimodipine (0.7 mg/kg weight body) also showed improvement on neurological deficit and Cx43 expression levels. Astrocyte GJIC was measured by the fluorescence recovery after photobleaching (FRAP). Hypoxia-reoxygenation induced a significant decrease in GJIC. Pretreatment with GBE (100 mg/l) and nimodipine (1.6 mg/l) significantly prevented the hypoxia-reoxygenation inhibition of GJIC. These results suggest that GBE could exert its neuroprotective effects by improvement of Cx43 expression and GJIC induced by hypoxia/ischemia-reoxygenation/ reperfusion injury.