Native human neocortex release-regulating dopamine D2 type autoreceptors are dopamine D2 subtype

Dopamine (DA) autoreceptors expressed at DA nerve terminals regulate DA release. Considerable evidence has indicated that, in rodents, these autoreceptors belong to the D2 type of the DA receptor family, which, in turn, comprises the D-2, D-3 and D-4 subtypes. We investigated here, for the first time, the subclassification of native human DA autoreceptors by studying the release of [H-3]DA evoked by electrical stimulation in fresh human neocortical slices. The results have been compared with those obtained in three animal systems: rat neocortical and striatal slices and rat mesencephalic neuronal cultures. In human neocortical slices, the D-2/D-3 receptor agonist quinpirole (1 nM-10 mu M) inhibited tritium release with a calculated EC50 of 17 nM and a maximal inhibition of approximate to 75% reached at 1 mu M. In the presence of the D-2/D-3 receptor antagonist (-)-sulpiride (0.1 and 1 mu M), the concentration-response curve of quinpirole was shifted to the right, and the apparent pA(2) mean value was 8.5 (8.14-8.77); on the other hand, the inhibitory effects of quinpirole were not affected by the D-3 receptor-selective antagonist [7-N,N-dipropylamino-5,6,7,8-tetrahydro-naphtho(2,3b) dihydro,2,3-furane] (S 14297) and the D-4 receptor-selective antagonist 3-(4-[4-chlorophenyl]piperazin-1-yl)-methyl-1H-pyrrolo [2,3-b]pyridine (L-745,870) (0.01-1 mu M in each case). Superimposable results have been obtained when the release was elicited from rat striatal slices or dopamine mesencephalic neurons in culture, whereas quantitative differences emerged in the case of rat cortical slices. It is concluded that in human brain, as well as in rat brain, the release of DA in the terminal region of midbrain dopaminergic neurons is regulated through autoreceptors of the D-2 subtype.