Spatiotemporal relationship of apoptotic cell death to lymphomonocytic infiltration in photochemically induced focal ischemia of the rat cerebral cortex

In this study we examined the time course of apoptotic cell death after photochemically induced focal ischemia of the rat cerebral cortex. For unequivocal differentiation between apoptosis and necrosis two criteria of programmed cell death were used: terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) and morphological evidence of fragmentation and marginalization of nuclei. After photothrombosis, many TUNEL-positive cells were found within the infarct region from 12h to 3 days. By day 6 they were preferentially located in the boundary zone of the infarct, and by day 14 they had disappeared. A high proportion of TUNEL-positive cells displayed fragmentation or marginalization of their nuclei, indicating apoptosis. Neurons, but not T cells and macrophages, were apoptotic. Inflammatory infiltrates were in close contact to apoptotic neurons throughout the infarct areas at day 1 and in the boundary zone between days 2 and 6 after photothrombosis. In summary, our study shows that neuronal apoptosis after cerebral ischemia is a prolonged process to which leukocyte-derived cytokines may contribute. In contrast to autoimmune diseases of the nervous system, termination of the local inflammatory response after cerebral ischemia does not involve apoptosis.