Studies on the role of dopaminergic systems in morphine-induced motor activity. Comparison with noradrenergic and cholinergic systems.

The role of dopaminergic, noradrenergic and cholinergic systems in morphine-induced motor activity was investigated in mice using both blockers and stimulators of the receptors of the respective systems. The dopaminergic blocking drugs, spiroperidol and clothiapine, significantly reduced while stimulating dopaminergic receptors with amantadine significantly increased morphine-induced motor activity. Blockade of noradrenergic receptors with phenoxybenzamine and cholinergic receptors with atropine significantly reduced morphine activity whereas stimulation of either of these systems with DOPS and physostigmine respectively, had no effect. These data suggest that a dopaminergic system mediates morphine-induced motor activity and that this can be modified by interrupting either noradrenergic or cholinergic systems.