FLOW THRESHOLD FOR REDUCTION OF CYCLIC-AMP BINDING IN THE HIPPOCAMPUSCA(1) AND OTHER BRAIN-REGIONS DURING STROKE DEVELOPMENT IN GERBILS

The flow threshold for alterations of the in vitro [H-3]cyclic AMP (cA MP) binding, an indicator of the total amount of particulate cAMP-depe ndent protein kinase, was evaluated in the gerbil brain after 30 min, 2 h, and 6 h of unilateral common carotid artery occlusion, respective ly. The autoradiographic method developed in our laboratory enabled us to measure the [H-3]cAMP binding and local CBF in each region of the same brain. The ischemic flow thresholds for reduction of the cAMP bin ding in the hippocampus CA(1) were 18, 34, and 49 ml 100 g(-1) min(-1) after 30-min, 2-h, and 6-h ischemia, respectively. These values were higher than those in other regions such as the hippocampus CA(3) and t emporal cerebral cortex in each duration of ischemia. These findings i ndicate that (a) the ischemic flow threshold for perturbation of the c AMP system may be higher in the hippocampus CA(1) than in other brain regions, suggesting that the hippocampus CA(1) could be especially vul nerable to acute ischemic stress; and (b) the level of the aforementio ned threshold may increase progressively during the time course of isc hemia in particular regions such as the hippocampus CA(1) and CA(3), s uggesting that the duration of ischemia exerts a definite influence on the viability of the ischemic neuronal cells in these regions.