THE PYRAMIDAL CELL LAYER OF SECTOR CA-1 SHOWS THE LOWEST HIPPOCAMPAL SUCCINATE-DEHYDROGENASE ACTIVITY IN NORMAL AND POSTISCHEMIC GERBILS

We examined regional differences in the activity of a mitochondrial re spiratory enzyme, succinic dehydrogenase (SDH), in the hippocampi of n ormal and postischemic gerbils, using a quantitative imaging method. G erbils (n = 21) without ischemia, and gerbils which had experienced 5 min of bilateral common carotid artery occlusion 12 h or 2 days previo usly, were sacrificed. Coronal sections of the brains were prepared fo r quantitative imaging of SDH activity and histological examination. I n the control gerbils, SDH activity in the pyramidal cell layer of the CA 1 sector (Sommer's sector) was 106.3 +/- 10.3% (mean +/- SD; SDH a ctivity as a percentage of the cerebellar SDH activity), which was low er than in the other subfields of the hippocampus. SDH activity in the oriens layer, stratum radiatum and lacunosum molecular layer of the C A 1 sector was lower than in the corresponding layers of the CA 2 and CA 3 sectors. After transient ischemia, SDH activity remained unchange d in the CA 1 sector. Histologically, selective neuronal necrosis was observed in the pyramidal cell layer of the CA 1 sector 2 days after i schemia. The observed low level of this mitochondrial respiratory enzy me in the pyramidal cell layer of the CA 1 sector should be taken into account as a possible trigger of the selective vulnerability of the r egion to ischemia.