Identification of direct competition for, and indirect influences on, striatal muscarinic cholinergic receptors: in vivo [3H]quinuclidinyl benzilate binding in rats.

[3H]Quinuclidinyl benzilate (QNB) binds to specific muscarinic receptors of rat striatum, in vivo. The binding is saturable and displaceable by muscarinic drugs. Clozapine and thioridazine are unique antipsychotic agents with low liability for extrapyramidal side-effects, and both displaced ONB, while several other neuroleptics did not. In addition to this apparent direct competition for cholinergic receptors, morphine and amphetamine increased ONB binding by indirect influences on muscarinic receptors. In vivo QNB binding not only confirms in vitro findings, but it also detects indirect, probably transsynaptic, alterations of muscarinic cholinergic receptor dynamics.