Dopamine neurons projecting to the medial prefrontal cortex possess release-modulating autoreceptors

The ability of dopamine (DA) agonists and antagonists to modulate the K⁺-evoked overflow of radioactivity from superfused slices of prefrontal cortex of the rat, preincubated with [³H]DA in the presence of 1 μM desipramine, was examined. Apomorphine and the putative autoreceptor-selective DA agonist EMD 23 448 inhibited the K⁺-evoked overflow of radioactivity, while the DA antagonist sulpiride enhanced the evoked overflow in a dose-dependent and stereoselective manner. The latter effect was partially reversed by EMD 23 448. More than 95% of the radioactivity retained by the slices chromatographed with DA, while deaminated metabolites represented the majority of both the basal efflux (84% metabolites, 4-5% DA) and evoked overflow (84% metabolites, 14% DA) of radioactivity. These findings indicate that mesoprefrontal DA neurons possess release-modulating nerve terminal autoreceptors. Previous studies have shown that these neurons lack synthesis-modulating autoreceptors. Thus, autoreceptors on prefrontal DA terminals appear to be coupled to regulation of the release but not the synthesis of DA.