Abstract
The effect of pirenzepine, a selective muscarinic antagonist, was tested on the oxotremorine facilitation of the K+-evoked release of [14C]-dopamine from tissue slices of rat nucleus accumbens. The effect of pirenzepine was compared with that of scopolamine and other antagonists which show no heterogeneity in their action on muscarinic receptors in order to determine whether a selective action at a single receptor subtype, M1 or M2, could be distinguished. Pirenzepine and scopolamine both antagonized the oxotremorine-induced (EC50 = 3 X 10(-7) M) facilitation of [14C]-dopamine release with pA2 values of 7.5 and 8.9 respectively. This result indicated that the high affinity pirenzepine receptor (M1) was involved in this response. Low concentrations of 3-quinuclidinyl benzilate (3 X 10(-10) M), N-methylscopolamine (3 X 10(-9) M) and methyl atropine (10(-8) M) also abolished this facilitatory effect of oxotremorine.