Muscarinic receptor activation attenuates D2 dopamine receptor mediated inhibition of acetylcholine release in rat striatum: indications for a common signal transduction pathway

In the present investigations, we used a superfusion system to study the effect of simultaneous activation of D2 dopamine receptors and so-called muscarinic "autoreceptors" on the K(+)-evoked in vitro release of [3H]acetylcholine from rat striatal tissue slices. Activation of D2 receptors with the selective agonist LY 171555 (0.01-1 microM) clearly decreased the evoked release of [3H]acetylcholine. This effect was markedly attenuated in the presence of either the selective muscarinic receptor agonist oxotremorine (3 microM) or the cholinesterase inhibitor physostigmine (1 microM). Conversely, D2 receptor activation with LY 171555 (1 microM) completely abolished the muscarinic receptor mediated inhibition of evoked [3H]acetylcholine release induced by oxotremorine (0.03-10 microM). These results show that the inhibitory effects of D2 dopamine receptor and muscarinic receptor activation on striatal acetylcholine release are non-additive and therefore are interdependent processes. In addition, we investigated some aspects of the signal transduction mechanism by which the muscarinic receptor mediates inhibition of K(+)-evoked in vitro release of [3H]acetylcholine from rat striatal tissue slices. It appeared that the effect of muscarinic receptor activation was not significantly influenced either by a lowering of the extracellular Ca2+ concentration from the usual 1.2-0.12 mM or by an increase of the intracellular cyclic adenosine-3',5'-monophosphate content. However, increasing extracellular K+ strongly decreased the inhibition of evoked [3H]acetylcholine release mediated by activation of muscarinic receptors. This set of results indicates that the muscarinic "autoreceptor" mediates the decrease of depolarization induced [3H]acetylcholine release from rat striatum to a large extent through stimulation of K+ efflux (opening of K+ channels) in a cyclic adenosine-3',5'-monophosphate independent manner.(ABSTRACT TRUNCATED AT 250 WORDS)