TIME-COURSE OF MICROGLIA ACTIVATION AND APOPTOSIS IN VARIOUS BRAIN-REGIONS AFTER PERMANENT FOCAL CEREBRAL-ISCHEMIA IN MICE

We investigated the temporal course of microglia activation in differe nt brain regions after permanent middle cerebral artery (MCA) occlusio n in mice and compared this microglia response with the appearance of apoptotic cells, Microglia activation and morphological changes of mic roglial cells were visualized using an immunohistochemical method with a polyclonal antibody recognizing the mouse CR3 complement receptor. Cells showing morphological and biochemical features of apoptosis were identified using the terminal deoxynucleotidyl transferase nick end-l abeling (TUNEL) method and light microscopy. As early as 30 min after onset of MCA occlusion activated microglia with hypertrophic cell bodi es and stout processes were detected in the periphery of the ischemic lesion as identified by diffusion-weighted magnetic resonance imaging. A wider distribution and a progressive increase in the number of acti vated microglia was found with increasing lime. Only few TUNEL-positiv e cells with apoptotic features were observed within the lesion area a t 6 h after onset of cerebral ischemia. From 12 h after MCA occlusion onward a tremendous increase in the number of TUNEL-positive cells was found. Within the thalamus from 24 h onward microglia cells with few processes, irregular morphology and fragmented appearance were detecte d. Microglia activation in the thalamus progressed up to 4 weeks after MCA occlusion, but had declined after 90 days. Neuronal degeneration in the thalamus as determined by anti-neuronal nuclei immunohistochemi stry progressed from 6 days after MCA occlusion onward. Only a few TUN EL-positive cells were found in the thalamus. In summary. microglia ac tivation both in the primary cortical lesion area and in the secondari ly affected thalamus preceded the manifestation of tissue injury. Thes e observations encourage further studies on the role of microglia in f ocal cerebral ischemia.