The pharmacology of gross behavioural effects of cholinomimetic substances injected into the cerebral ventricles of unanaesthetized cats: Evidence for central muscarinic mediation

Abstract

Choline esters (acetylcholine, methacholine and carbachol) as well as substances with a peripheral muscarinic type of action, such as pilocarpine and arecoline, injected intraventricularly to unanaesthetized cats. evoked emotional behaviour, autonomic changes, motor phenomena and clonic-tonic convulsions. The gross behavioural effects of various single doses of these agents were dose-dependent. Of choline esters and substances with peripheral muscarinic type of actions that were administered, carbachol was the most potent. The emotional behaviour effects after pilocarpine were slight and a few in number in comparison with those produced by choline esters. Arecoline caused only miaowing. Atropine and scopolamine, injected intraventricularly, abolished the emotional behaviour, autonomie changes, motor phenomena and clonic-tonic convulsions of intraventricularly injected choline esters, while only scopolamine antagonized the gross behavioural effects of pilocarpine and arecoline. On the other hand, the excitant behavioural changes of choline esters, pilocarpine and arecoline were resistant to intraventricular administration of ganglionic (tetraethylammonium, hexamethonium. nicotine and dimethylphenylpiperazinium) or neuromuscular ( + )-tubocurarine and gallamine) blocking agents. In fact, ganglionic and neuromuscular blocking agents potentiated the behavioural effects of choline esters, pilocarpine and arecoline. It is concluded that choline esters, applied intraventricularly to unanaesthetized cats, elicit excitant behavioural phenomena by an action on central muscarinic cholinoceptive sites.