Dicyclomine- and pirenzepine-sensitive muscarinic receptors mediate inhibition of [3H]serotonin release in different rat brain areas.

The effects of acetylcholine (ACh) on the release of [3H]5-hydroxytryptamine ([3H]5-HT) were investigated in synaptosomes prepared from rat cerebral cortex, hypothalamus and hippocampus and depolarized with 15 mM KCl under superfusion conditions. ACh inhibited the release of [3H]5-HT in all three brain areas. This effect was not modified by hexamethonium but was antagonized by atropine and by the non-classical antagonists pirenzepine and dicyclomine.