The K(+)-evoked release of [3H]acetylcholine from slices of rat globus pallidus: modulation by delta-opioid receptors.

Previous investigations have shown that the activation of delta-opioid receptors depresses the release of acetylcholine (ACh) in the rat caudate putamen. This finding raised the possibility that the release of ACh is similarly modulated in the globus pallidus, a region containing a distinct population of cholinergic neurons and enriched in enkephalinergic nerve terminals. In the present study the pallidal release of ACh was characterized and the effects of delta-opioid receptor activation on this release were examined. The results show that this release is stimulated by high K+ in a concentration- and Ca(2+)-dependent manner. D-Pen2,L-Pen5-enkephalin (0.1-10 microM), a selective delta-opioid receptor agonist, produced a dose-related inhibition of the 25 mM K(+)-evoked tritium release. The maximal inhibitory effect, representing a 34% decrease in the K(+)-induced tritium release, was observed at a concentration of 1 microM. This opioid effect was attenuated by the selective delta-opioid receptor antagonist, ICI 174864 (1 microM). These findings support the role of a delta-opioid receptor in the modulation of ACh release in the rat globus pallidus.