Structural and chemical changes in glial cells in the rat neocortex induced by constant occlusion of the middle cerebral artery

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Stroke-induced changes in neuroglia determine the basic conditions for the survival and damage of neurons in the ischemic core. Here, we studied the immunolocalization of glial cell line-derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba-1), and S-100β in the rat parietal cortex after constant occlusion of the middle cerebral artery. These cytoplasmic proteins are specific for different glial cell types. They are used as indicators of activated microglia and astrocytes in immunocytochemical studies.The distribution pattern of all markers changed dramatically with time. GFAP- and S-100β-positive astrocytes were observed in the penumbra zone and marked its boundaries. In days 1–8 after surgery, in the ischemic core, the number of S-100β-immunoreactive astrocytes decreased, and individual pyramidal cells appeared. S-100β-expressing pyramidal cells were localized in cortical layers III and V. They were only found in the ischemic core. Their proportion to the total number of cells was 37.3 ± 3.9 %, 22.2 ± 1.2 %, 16.3 ± 2.3 %, and 5.4 ± 0.3 % on days 1, 3, 8, and 14 after surgery. On day 21, no S-100β-expressing pyramidal cells were observed. The spatial density of GFAP- and S-100β-positive astrocytes increased in the penumbra region adjacent to the ischemic core and decreased in the penumbral periphery. As a result, the width of the perifocal penumbra zone decreased substantially at later stages of the stroke. In the penumbra, on days 1–3 after ischemic injury, GDNF immunoreactivity was mainly localized in neurons, while later on (days 8–21) it was mainly constrained to astrocyte glia. In intact rats, GDNF-positive neurons were situated in cortical layers II/III and V/VI and made up 52 ± 4.5 % of the total neuron population. Their proportion to the total number of neurons was 29 ± 2.1 %, 13.8 ± 0.6 %, and 3.1 ± 0.2 % on days 1, 8, and 21 after surgery. The number of GDNF-positive astrocytes, on the opposite, increased with time after ischemic injury. Iba-1-reactive microglia was mainly localized to the ischemic core. Microglial cells appeared activated as evidenced by their increased size and decreased number of processes and branching density. The spatial density of microglia reached a peak ​​on day 8 after ischemic injury both in the ischemic core and penumbra. An increase in the number of Iba-1-reactive microglia in the ischemic core correlated with a decrease of the number of GFAP-positive astrocytes. The results are discussed in the context of participation of neuroglia in regulation of various neuroprotective and destructive processes.