In vivo binding of [3H]nimodipine in rat brain after transient forebrain ischemia.

We report the regional variation in relative in vivo binding of the L-type voltage sensitive calcium channel (VSCC) antagonist [3H]nimodipine to brain following transient forebrain ischemia in the rat. At 30-min of reperfusion after 20 min of forebrain ischemia, [3H]nimodipine binding was significantly increased in striatum, CA3 and CA4, and dentate relative to binding in sham-operated rats, suggesting that VSCCs were responding to ischemic depolarization. Two h following ischemia, binding in all brain structures returned to normal levels indicating repolarization of cell membranes. At 24 h of recirculation, increased [3H]nimodipine binding was again observed in striatum and dentate. Binding remained elevated in the striatum and dentate, and increased binding became evident in the CA1 region of the hippocampus after 48 h of reperfusion. With the exception of the dentate gyrus, the second rise in [3H]nimodipine binding anticipated or coincided with the observed regional ischemic cell changes. These observations in global cerebral ischemia support previous work indicating that in vivo binding of [3H]nimodipine to the L-type VSCC may be an early and sensitive indicator of impending ischemic injury. Such measurements may be of use in identifying vulnerable brain regions and defining a therapeutic window of opportunity in models of cerebral ischemia.