INVOLVEMENT OF CHOLINERGIC PRESYNAPTIC RECEPTORS OF NICOTINIC AND MUSCARINIC TYPES IN CONTROL OF SPONTANEOUS RELEASE OF DOPAMINE FROM STRIATAL DOPAMINERGIC TERMINALS IN RAT

  • 1 January 1977
    • journal article
    • research article
    • Vol. 200  (3) , 535-544
Abstract
Rat striatal slices (2) were superfused continuously with L-3,5-3H tyrosine and 3H-dopamine (3H-DA) release was estimated in serial fractions of superfusates. The spontaneous release of 3H-DA was reduced by about 50% when slices were superfused with a Ca-free medium containing ethylene glycol bis (.beta.-aminoethyl ether)-N,N''-tetraacetic acid (EGTA) (10-4 M) or with a medium containing tetrodotoxin (5 .times. 10-7 M). These effects were not related to a change in 3H-DNA synthesis since the rate of L-3,5-3H tyrosine hydroxylation, as measured by 3H-H2O formation was not significantly reduced. Acetylcholine (ACh) (10-5 M) stimulated the release of 3H-DA (about 100%). This effect was abolished in the absence of Ca; it was partially blocked by pempidine (10-5 M), atropine (10-6 M) or scopolamine (10-5, 10-6 M). Oxotremorine (10-5 M) enhanced 3H-DA release but to a lesser extent (60%) than ACh (10-5 M); its action was completely blocked by atropine (10-6 M) and unaffected by pempidine (10-5 M). The ACh- (10-5 M) and oxotremorine- (10-5 M) stimulating effects on 3H-DA spontaneous release were still detected in slices superfused in the presence of tetrodotoxin (5 .times. 10-7 M). In the presence of the neurotoxin, the effect of ACh (10-5 M) was significantly reduced by pempidine (10-5 M) and the effect of oxotremorine (10-5 M) was blocked by atropine (10-6 M). The presence of cholinergic presynaptic receptors of the nicotinic and muscarinic types on striatal dopaminergic terminals was suggested.