Dopamine release in human neocortical slices:: Characterization of inhibitory autoreceptors and of nicotinic acetylcholine receptor-evoked release

The autoinhibitory control of electrically evoked release of [H-3]-dopamine and the properties of that induced by nicotinic receptor (nAChR) stimulation were studied in slices of the human neocortex. In both models [H-3]-dopamine release was action potential-induced and exocytotic. The selective dopamine D-2 receptor agonist (-)-quinpirole reduced electrically evoked release of [H-3]-dopamine, yielding IC50 and I-max values of 23 nM and 76%, respectively. Also, the effects of several other subtype- selective dopamine receptor ligands confirmed that the terminal dopamine autoreceptor belongs to the D-2 subtype. The autoinhibitory feedback control was slightly operative under stimulation conditions of 90 pulses and 3 Hz, with a biophase concentration of endogenous dopamine of 3.6 nM, and was enhanced under blockade of dopamine reuptake. [H-3]-dopamine release evoked in an identical manner in mouse neocortical slices was not inhibited by (-)-quinpirole, suggesting the absence of dopamine autoreceptors in this tissue and underlining an important species difference. Also, nAChR stimulation-induced release of [H-3]-dopamine revealed a species difference: [H-3]-doparnine release was evoked in human, but not in rat neocortical slices. The nAChRs inducing [H-3]-dopamine release most probably belong to the alpha(3)/beta(2)-subtype, according to the potencies and efficacies of subtype-selective nAChR ligands. Part of these receptors may be located on glutamatergic neurons. (C) 2005 Elsevier Inc. All rights reserved.