Immunocytochemical and morphometric changes in astroglial cells in the perifocal zone of the cerebral infarction model

Introduction. The perifocal zone of cerebral infarction contains dying and reactively altered neurons whose fate depends on the type of intracellular interactions and, in particular, on the response of astrocytes partaking both in neuronal damage and neuroprotection. The features of the response of astrocytes to ischemic injury and the role of their activation in gliosis have been studied insufficiently.

Objective. To evaluate the changes in astroglia in the perifocal zone of cerebral infarction depending on its reproduction time by immunomorphology and computerassisted morphometry.

Materials and methods. Infarction was induced in the left hemisphere of rat brain cortex (n=10) by middle cerebral artery occlusion. Astrocyte distribution and shape were assessed on day 3 and 21 after surgery; localization of gliofibrillar acidic protein (GFAP), aquaporin 4 (AQP4), and glutamine synthetase (GlnS) in the perifocal zone was measured.

Results. Astrocyte shape and distribution, as well as GFAP expression, significantly altered depending on time that has passed since the infarction and distance to the injury focus. On day 3, the area occupied by astrocyte processes decreased by 15% of the control value, while increasing by 35% on day 21. Expression of GlnS and AQP4 near the infarction focus decreased on day 3, while opposite changes were observed on day 21. Redistribution of the studied proteins in processes of reactive astrocytes was also detected. Two morphological types of astrocytes were differentiated: the scarring polarized astrocytes, which were characterized by redistribution of marker proteins in processes, and the moderately altered transiently activated ones.

Conclusions. Astrocytes were found to be heterogeneous in the perifocal zone of cerebral infarction; a dependence between changes in their structure and function and the distance to the injury focus and time that passed after the infarction was revealed. The scarring and transiently activated astrocytes, which play different roles in remodeling and repair of ischemic neural tissue in the perifocal zone of cerebral infarction, were characterized by immunohistochemical and morphometric analysis.