Abstract: Objective To investigate the protective effect of methylene blue (MB) on blood-brain barrier (BBB) injury after focal cerebral ischemia-reperfusion in rats. Methods 18 male Sprague-Dawley rats were randomly divided into sham-operated group (n=6), model group (n=6) and MB treatment group (n=6). The left middle cerebral arteries were occluded for 1 hour and reperfused. MB was infused intravenously immediately after reperfusion (3 mg/kg) and again 2 hours post-reperfusion (1.5 mg/kg), while normal saline was administered in the model group. The sham-operated group was treated as same as the model group without occlusion and infusion. HE staining was used to observe the histological injury in the cortex around the infarcted region 47 hours after reperfusion, while albumin immunohistochemistry was used to evaluate the permeability of the BBB, and immunohistochemistry and double immunofluorescence staining were used to examine the expressions of glial fibrillary acidic protein (GFAP) and aquaporin-4 (AQP-4). Results HE staining showed that cells and blood vessels were not intact in the cortex around the infarcted region in the model group and they were better in the MB treatment group. The expressions of the albumin, GFAP and AQP-4 were higher in the model group than in the sham-operated group (P<0.01), and were lower in MB treatment group than in the model group (P<0.05). The double immunofluorescence staining showed the colocalization of GFAP and AQP-4 in the astrocytes. Conclusion MB may ameliorate the BBB disruption induced by focal cerebral ischemia-reperfusion through reducing gliocyte proliferation and down-regulation of AQP-4 expression in rats.

Key words: cerebral ischemia-reperfusion, methylene blue, blood-brain barrier, glial fibrillary acidic protein, aquaporin-4, rats