Characteristics of dopamine and beta-adrenergic sensitive adenylate cyclases in the frontal cerebral cortex of the rat. Comparative effects of neuroleptics on frontal cortex and striatal dopamine sensitive adenylate cyclases.

Homogenates of frontal cerebral cortex of the rat were prepared from microdiscs punched out in areas rich in dopaminergic terminals. Under optimal assay conditions, dopamine (10-4 M) stimulated an adenylate cyclase present in these homogenates by 80-100%. This stimulation reached 200% when microdiscs were punched out from the medial part of the frontal cerebral cortex, adjacent to the forceps minor. Dopamine interacted with an homogeneous population of receptor sites which had an apparent affinity (KD) of 3.8 +/- 0.9 x 10-6 M (N = 4). The dopamine receptor was blocked by fluphenazine and phentolamine but had no affinity for pindolol, propranolol or L-isoproterenol. The affinities of several neuroleptics having different chemical structures were simultaneously determined on striatal and on frontal cerebral cortex dopamine sensitive adenylate cyclases. Fluphenazine was more potent in blocking the striatal than the frontal cerebral cortex dopaminergic receptors. In contrast, in all experiments, haloperidol had an higher affinity for the cerebral frontal cortex than for the striatal dopaminergic receptors. Thus, haloperidol was less effective than fluphenazine in blocking the striatal dopaminergic receptors, and equally potent than fluphenazine in inhibiting the frontal cerebral cortex dopamine sensitive adenylate cyclase. Chlorpromazine, thioridazine and clozapine had the same affinity for the two dopaminergic adenylate cyclase systems. L-isoproterenol interacted with an homogeneous population of beta-adrenergic receptor sites (KD = 3 +/- 2 X 10-7 M; N = 4) coupled with an adenylate cyclase distince from the dopamine sensitive adenylate cyclase. This beta-receptor had no affinity for dopamine or fluphenazine but was blocked by propranolol or pindolol. L-Norepinephrine was shown to stimulate both the dopamine (KD = 1.8 +/- 1 X 10-5 M; N = 4) and the beta-adrenergic (KD = 8 +/- 3 X 10-7 M; N = 4) sensitive adenylate cyclases. Thus, the L-norepinephrine effect was totally blocked in the combined presence of fluphenazine and pindolol.