Alteration of dopamine D1 receptor in the strionigral system of the postischemic rat brain.

Chronological changes of dopamine D1 receptor binding were determined in the strionigral system of the rat brain by using [3H]SCH 23390, a highly selective dopamine D1 antagonist, in vitro autoradiography after 90 min of right middle cerebral artery (MCA) occlusion and after such occlusion followed by different periods of recirculation. One day after the ischemia, dopamine D1 receptor sites decreased significantly compared with the control value in the lateral segment of the caudate putamen supplied by the occluded MCA. Moreover, 3 days after the ischemia, a significant decrease of dopamine D1 receptor sites was observed in the substantia nigra on the ischemic side which had not been directly affected by the original ischemic insult. The present study indicates that the postischemic delayed reduction of dopamine D1 receptor sites observed in the substantia nigra is due to the degeneration of the dopaminergic nerve terminals in the strionigral system caused by the precedent ischemic damage of the ipsilateral caudate putamen.