Effect of Nicotinic and Muscarinic Drugs on Amphetamine‐ and Apomorphine‐induced Circling Behaviour in Rats

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Abstract
The effect of drugs modulating the activity of nicotinic or muscarinic cholinergic receptors on the circling behavior induced by amphetamine and apomorphine in rats with unilateral 6-hydroxydopamine lesion of nigrostriatal dopaminergic pathway was studied. Nicotine (0.2 mg/kg s.c.) significantly increased amphetamine-induced circling behavior and tended to inhibit apomorphine-induced circling behavior. Mecamylamine and pempidine (both 2 mg/kg i.p.) slightly but significantly depressed the intensity of circling behavior induced by amphetamine, but failed to modify that induced by apomorphine. Pilocarpine (10 mg/kg i.p.) clearly inhibited both amphetamine- and apomorphine-induced circling behavior. Unlike pilocarpine, atropine (10 mg/kg i.p.) significantly increased the intensity of the circling behavior induced by amphetamine and also to some extent that induced by apomorphine. Neither hexamethonium (5 mg/kg i.p.) nor methylatropine (1 mg/kg s.c.) modified the circling behavior induced by either amphetamine or apomorphine. Stimulation of central nicotinic and muscarinic receptors may have some opposite effects on the dopamine-dependent circling behavior. The presynaptic nicotinic cholinergic receptors on the terminals of the nigrostriatal dopaminergic neurons, stimulation of which may increase the release of dopamine, might be involved in the action of nicotinic drugs. The muscarinic cholinergic receptors in the striatum and or in the substantia nigra might be involved in the action of muscarinic drugs.

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