Astrocytes reorganization in the rat hippocampus following a 20-min occlusion of common carotid arteries

Abstract

Aim. To study hippocampal astrocytes of Wistar rats following a 20-min occlusion of common carotid arteries (OCCA). Method. Histological (Nissl hematoxylin and eosin staining), immunohistochemistry (GFAP, MAP-2, Ki-67), and morphometry were used. Astrocytes and neurons were studied in thin (4 µm) serial frontal sections of the hippocampus from control rats (sham-operated animals) and at 6 h, and at one, three, 7, 14, and 30 days (n = 5 in each group) of OCCA. Fractal analysis was used to obtain additional quantitative information about spatial organization of astrocyte and neuronal networks (ImageJ 1.52; plugin FracLac 2.5). Statistical hypotheses were tested using nonparametric criteria. Results and discussion. The study showed significant heterogeneity and heterochronicity of changes in the spatial organization of astrocytes in different layers of the hippocampus after OCCA. The fractal dimension (FD) of hippocampal astrocyte network was significantly reduced whereas the lacunarity (L) was increased compared to the control on days 1 and 3 following OCCA as a result of focal destruction and fragmentation of thin processes. Signs of reactive astrogliosis evident as a large relative area of GFAP-positive material, FD greater and L lower than the control were observed on day 3, locally and on the background of activated proliferation, and on days 7, 14, and 30, in all layers of the hippocampus. The fractal space was uniformly filled with astrocyte processes in all hippocampal layers. Conclusion. The study produced new data on qualitative and quantitative changes in hippocampal reactive astrocytes after acute ischemia induced by 20-min OCCA. We interpret these changes as a reflection of natural defense of the cerebral nervous tissue during reperfusion.