Dopamine ?Autoreceptors?: Pharmacological characterization by microiontophoretic single cell recording studies

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Abstract
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 α-agonist clonidine had no depressant effect and the β-agonist isoproteronol had only a weak depressant action on DA neurons. Furthermore, the α-antagonist piperoxane and the β-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 α or β 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”.