Dopamine"autoreceptors": pharmacological characterization by microiontophoretic single cell recording studies.

The effects on the firing of single dopamine (DA) neurons in the substantia nigra (and adjacent ventral tegmental area) of a representative group of catecholamine agonists and antagonists were studied in rats using single cell recording and microiontophoretic techniques. Microiontophoretic application of DA or the DA agonist apomorphine depressed the firing of these cells; the DA antagonist trifluoperazine blocked this effect. However, the alpha-agonist clonidine had no depressant effect and the beta-agonist isoproteronol had only a weak depressant action on DA neurons. Furthermore, the alpha-antagonist piperoxane and the beta-antagonist sotolol were completely ineffective in blocking the depressant effects of DA. These results show that DA-sensitive receptors on the soma of DA neurons are pharmacologically distinct from alpha or beta adrenoreceptors. Because of their location and selective responsiveness to DA agonists, the catecholamine receptors on the soma of DA neurons appear best classified as DA "autoreceptors".