Are cholinergic mechanisms involved in morphine effects on motility?

Summary Experiments were performed to study the relevance of cholinergic mechanisms in morphine-induced effects on striatal dopamine metabolism and on motility. In rats, atropine slightly decreased the striatal homovanillic acid (HVA) concentration, but affected neither the morphine-induced rise of HVA concentration nor the catalepsy after morphine. In mice, even high doses of atropine induced only a moderate locomotor activity, compared with that observed after morphine application. Furthermore, the combination of morphine and atropine on locomotor activity seemed to be supra-additive. Although physostigmine antagonized the morphine-induced locomotor activity, the results suggest that primary effects of morphine on cholinergic mechanisms in brain are of minor importance in inducing an increase of striatal dopamine turnover and effects on motility of rats and mice.