Absence of a 'cholinergic link' in the apomorphine-induced feedback inhibition of dopamine synthesis in rat striatum.

The blocking effect of apomorphine on the rise in striatal dopamine (DA) content, induced by 1-hydroxy-3-amino-pyrrolidone-2 (HA-966) was taken as a measure for the intrastriatal feedback inhibition of DA synthesis. The effects of cholinergic drugs on this feedback system were assessed in order to verify the hypothesis that this mechanism is mediated via an intrastriatal cholinergic link. We presumed that DA receptors were located on a cholinergic neuron, while the cholinergic terminals in turn made direct or indirect axon-axonal contact with the dopaminergic nigro-striatal pathway (N.S.P.). Although cholinergic agents could modify the effect of HA-966 on striatal DA content, it proved to be impossible to counteract the blocking effect of apomorphine with cholinergic drugs as was to be expected. Therefore we concluded that the effect of apomorphine was not brought about in the way which had been postulated.