Demonstration of autoreceptors on dopamine neurons in different brain regions of rats treated with gammabutyrolactone.

Following interruption of the nerve impulse flow in the dopamine neurons by treatment with gammabutyrolactone, the selective dopamine autoreceptor agonist B-HT 920 reduced the DOPA accumulation after DOPA decarboxylase inhibition and the 3,4-dihydroxyphenylacetic acid concentration in the corpus striatum, the nucleus accumbens, the olfactory tubercle, the limbic cortex and the rostral part of the cerebral cortex of rats. The effects were completely inhibited by the dopamine receptor antagonist haloperidol, indicating that they were caused by stimulation of dopamine autoreceptors. In the caudal part of the cerebral cortex and the cerebellum, B-HT 920 somewhat reduced the concentration of dihydroxyphenylacetic acid via a haloperidol-sensitive mechanism, suggesting that there are a few dopamine neurons with autoreceptors in these regions. No evidence was obtained for the presence of autoreceptors on the dopamine neurons in the hypothalamus. The gammabutyrolactone-induced elevation of the dopamine concentration was not reduced by B-HT 920 in any region, suggesting that this effect of gammabutyrolactone was caused by decreased release rather than increased synthesis of dopamine under our experimental circumstances.