Effects of ischemia on regional ligand binding to adrenoceptors in the rat brain.

Changes in ligand binding to adrenoceptors ([3H]prazosin to alpha 1-receptors, [3H]idazoxan to alpha 2-receptors and [125I]cyanopindolol to beta-receptors) following transient cerebral ischemia were investigated using autoradiographic methods. The binding was quantified in brain sections from control rats, rats subjected to 15 min of 2-vessel occlusion ischemia, and rats with recirculation times of 1 h, 1 week or 4 weeks after ischemia. No significant change in alpha 1-receptor binding was observed during and immediately following ischemia, but a decrease was noted in the vulnerable hippocampal CA1 region following 1 week's survival. In the parietal cortex, the ligand binding to alpha 1-receptors increased at 4 weeks. A reduced [3H]idazoxan binding was observed 1 h after ischemia in the temporal cortex and amygdala. No change in ligand binding to beta-receptors was seen in the early phase postischemia, but a marked increase had occurred in the hippocampal CA1 region at 1 and 4 weeks after ischemia (+163% and +142%, respectively), presumably due to accumulation of macrophages expressing beta-receptors. The early postischemic changes in receptor binding may represent downregulation of the adrenoceptors by processes activated during ischemia, while neuronal degeneration, compensatory mechanisms in surviving neurons and proliferation of non-neuronal cells may account for the subsequent changes.