[Alteration of inositol 1,4,5-trisphosphate receptor binding after 6-hour hemispheric ischemia in the gerbil brain]

Inositol 1,4,5-trisphosphate (IP3) has recently been known to play vital roles as one of the second messengers to control intracellular metabolism of calcium ion. Therefore, alterations of IP3 receptor binding and local cerebral blood flow (1CBF) were evaluated at 6 hours after occlusion of the right common carotid artery in the gerbil brain. The autoradiographic method developed in our laboratory enabled us to measure both parameters in the same brain. Animals attaining more than 5 in their ischemic scores, which were assessed at 1 hour after the occlusion, were utilized. LCBF was measured by the 14C-iodoantipyrine method at the end of the experiment. After frozen brains were cut into serial slices on a cryostat, the IP3 receptor binding was evaluated in vitro by using 3H-inositol 1,4,5-trisphosphate as the ligand. LCBF fell below 10 ml/100 g/min in most of the cerebral regions on the occluded side. In contrast a significant reduction in IP3 binding was noted only in the hippocampus CA1 on the occluded side. The IP3 binding tended to decrease when the values of 1CBF were reduced below 20 ml/100 g/min in this region. These findings suggest that the selective alteration of IP3 receptor binding in the hippocampus CA1 may be closely associated with the selective vulnerability of this region to ischemia.