APOPTOSIS AND DELAYED NEURONAL DAMAGE AFTER CARBON-MONOXIDE POISONINGIN THE RAT

Delayed neurological damage after CO hypoxia was studied in rats to de termine whether programmed cell death (PCD), in addition to necrosis, is involved in neuronal death. In rats exposed to either air or CO (25 00 ppm), microdialysis in brain cortex and hippocampus was performed t o determine the extent of glutamate release and hydroxyl radical gener ation during the exposures. Groups of control and CO-exposed rats also were tested in a radial maze to assess the effects of the CO exposure on learning and memory. At 3, 7, and 21 days after CO exposure brains were perfusion-fixed and hematoxylin-eosin (H&E) was used to assess i njury and to select regions for further examination. DNA fragmentation was sought by examining cryosections with the terminal deoxynucleotid yl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) reaction . We found significant increases in glutamate release and .OH generati on during and immediately after CO hypoxia, CO-exposed rats showed lea rning and memory deficits after exposure associated with heterogeneous cell loss in cortex, globus pallidus, and cerebellum. The frontal cor tex was affected most seriously; the damage was slight at Day 3, incre ased at Day 7, and persistent at Day 21 after CO exposure. TUNEL stain ing was positive at all three time points, and TUNEL-labeled cells wer e distributed similarly to eosinophilic cells. The number of cells sta ined by TUNEL was less than by H&E and amounted to 2 to 5% of all cell nuclei in regions of injury. Ultrastructural features of both neurona l necrosis and apoptosis also were observed readily by electron micros copy These findings indicate that both necrosis and apoptosis (PCD) co ntribute to CO poisoning-induced brain cell death. (C) 1997 Academic P ress.