The presynaptic stimulating effect of acetylcholine on dopamine release is suppressed during activation of nigro-striatal dopaminergic neurons in the cat.

Acetylcholine (ACh) (10(-5) M) in the presence of eserine (2 . 10(-4) M) stimulated the release of [3H]dopamine (DA) continuously formed from [3H]tyrosine, when delivered to a push-pull cannula implanted in the left caudate nucleus of halothane anaesthetized cats. This effect was transient and followed by a second increase in [3H]DA release after removal of ACh and eserine. These changes in [3H]DA release during and after ACh application were no longer seen during activation of the dopaminergic neurons by continuous delivery of substance P to the ipsilateral substantia nigra (SN). These results indicate that the presynaptic regulation of DA release by ACh is dependent on the rate of firing of nigro-striatal dopaminergic neurons.