Differential modulation of dopamine D2 receptors by chronic haloperidol, nitrendipine, and pimozide.

Chronic administration of the neuroleptic haloperidol, the calcium channel antagonist nitrendipine, and the calcium channel antagonist neuroleptic pimozide produce differential effects on rat striatal 3H-spiperone binding. Following 7 days of 10 mg/kg i.p. administration, haloperidol significantly increases (p less than 0.01) dopamine D2 receptor binding to 123% +/- 6% of control values, whereas pimozide treatment significantly reduces (p less than 0.001) striatal 3H-spiperone binding to 46% +/- 6% of control values. Chronic administration of the calcium channel antagonist nitrendipine does not alter 3H-spiperone binding relative to control values. Saturation analysis reveals an increase in Bmax following chronic haloperidol and a decrease in Bmax following chronic pimozide treatment. No alterations in muscarinic cholinergic sites, dopamine uptake sites, or calcium channel antagonist sites result following chronic drug administration. These results are the first demonstration of a decrease in dopamine D2 binding sites after chronic neuroleptic treatment.