CHOLINERGIC MODULATION OF [H-3] DOPAMINE RELEASE FROM DENDROSOMES OF RAT SUBSTANTIA-NIGRA

Dendrosomes prepared from substantia nigra are able to take up and release [H-3]dopamine in a Ca2+- dependent manner. The V(max) values of [H-3]dopamine uptake in substantia nigra dendrosomes was about 5 times lower than that in caudate putamen synaptosomes. The pattern of the K+-dependency of the [H-3]dopamine release in substantia nigra dendrosomes was significantly different from that found in caudate putamen synaptosomes. The release of [H-3]dopamine evoked by 15 mmol/l KCl from superfused dendrosomes was increased in a concentration-dependent manner by acetylcholine. The maximal potentiation produced by acetylcholine was about 40%. The potentiation of [H-3]dopamine release by 10-mu-mol/l acetylcholine was insensitive to mecamylamine but antagonized by atropine and by pirenzepine. The effects of acetylcholine on the release of [H-3]acetylcholine from substantia nigra nerve endings was also studied. Exogenous acetylcholine added to the superfusion medium decreased in a concentration-dependent manner the release of acetylcholine. This effect was not antagonized by mecamylamine or pirenzepine but fully antagonized by atropine. The data suggest the existence, in the substantia nigra of the rat, of two distinct muscarinic receptor subtypes regulating respectively dopamine release from dopamine dendrites and acetylcholine release from cholinergic nerve terminals.