Opposing effects of D-1 and D-2 receptor antagonists on acetylcholine levels in the rat striatum.

In contrast to D-2 or mixed D-1/D-2 receptor antagonists which decrease rat striatal acetylcholine levels, the D-1 receptor antagonist SCH 23390 increased this biochemical parameter (ED50 = 0.04 mg/kg s.c.) suggesting a reduction of acetylcholine turnover. SCH 23390 blocked the ability of haloperidol or sulpiride to diminish striatal acetylcholine levels and potentiated the increase in this biochemical parameter induced by the selective D-2 receptor agonist LY 141865. These findings indicate that blockade of D-1 and D-2 receptors causes opposite actions on striatal cholinergic neurons.