Effects of a κ-receptor agonist, U-50,488H, on the release of endogenous brain dopamine

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Abstract
The potential interaction between κ-opiate receptors and dopamine activity was examined in this study by monitoring the effect of U-50,488H on the release of endogenous dopamine from rat striatal slices in both the absence and presence of 10 μM nomifensine, a potent dopamine uptake inhibitor. Basal dopamine release was increased 10-fold in the presence of nomifensine, and the normally steady base line was observed to increase gradually under these conditions. U-50,488H, a potent κ-agonist, enhanced the spontaneous release of dopamine, but only at relatively high concentrations (40.0 μM) and only in the absence of nomifensine. Likewise, nomifensine and U-50,488H (40.0 μM) each significantly inhibited the synaptosomal uptake of [3H]dopamine. As with basal release, nomifensine markedly enhanced the potassium-evoked release of dopamine, and this evoked release was significantly attenuated by U-50,488H (0.4 and 40.0 μM) in both the absence and presence of nomifensine. This opiate-mediated inhibition of evoked dopamine release was antagonized in a time-dependent manner by the putative κ-antagonist, WIN 44,441-3, suggesting that striatal κ-receptor activation modulates dopamine release.