Regional changes in [3H]inositol 1,4,5-triphosphate binding in the gerbil brain following repeated sublethal ischemia

We investigated the regional changes in [3H]inositol 1,4,5-triphosphate (IP3) binding in the brain following ischemia using in vitro autoradiography. Three 2-min ischemic insults at 1-hr intervals and a 6-min period of ischemia were induced in gerbils and they were killed after 1, 4, and 28 days. Normal animals had high [3H]IP3 binding in the CA1 subfield of the hippocampus and the striatum. The binding in the CA1 decreased strikingly after both 6-min ischemia and three 2-min ischemic insults. The [3H]IP3 binding also decreased in the lateral striatum after three 2-min ischemic insults but not after 6 min of ischemia. Histological observations confirmed neuronal damage to these areas of reduced binding. By contrast, we found a marked increase in [3H]IP3 binding in the ventral thalamus 28 days after three 2-min ischemic insults. Histological observations with Nissl staining revealed an accumulation of fine granular deposits there. Thus, repeated ischemic insults produced more extensive neuronal damage and changes in [3H]IP3 binding than a single equivalent period of ischemia. The increased [3H]IP3 binding in the thalamus coincidentally with an accumulation of Nissl-positive granules at the chronic stage after repeated ischemia is of considerable interest.