Effect of Cholingeric Drugs on Methadone-induced Catalepsy and Stereotypies in Rats Treated Chronically with Methadone

The effects of antimuscarinic (atropine, scopolamine, methylscopolamine), muscarinic (RS86, pilocarpine), antinicotinic (mecamylamine, hexamethonium) and nicotinic (nicotine) cholinergic drugs on the catalepsy and stereotypies induced by acute methadone in rats treated chronically with methadone were studied. The antimuscarinic drugs potentiated and the muscarinic drugs antagonized the cataleptic effect of methadone, whereas the antimuscarinic drugs tended to antagonize and the muscarinic drugs potentiated the methadone-induced stereotypies. Nicotine initially slightly potentiated, and mecamylamine antagonized the cataleptic effect of methadone. The actions of the cholinergic drugs on the extrapyramidal motor effects of methadone were most probably central, because methylscopolamine and hexamethonium had only very weak actions. These results show that the effects of antimuscarinic and muscarinic drugs on the catalepsy and stereotypies induced by methadone are opposite to their effects on the catalepsy and stereotypies produced by drugs which are thought to act on the postsynaptic dopaminergic receptors.