Central noradrenergic--cholinergic interaction and locomotor behavior.

Depletion of forebrain noradrenaline by intracerebral injection of 4 micrograms of 6-hydroxydopamine into the fibres of the dorsal noradrenergic bundle was found to block the cataleptic effects of the muscarinic cholinergic agonist arecoline and to potentiate the locomotor stimulant effects of the muscarinic cholinergic blocker scopolamine. The nicotinic drugs, mecamylamine, a nicotinic blocker, and nicotine itself were unaffected in their actions by the depletion of forebrain noradrenaline. It is concluded that a noradrenergic--cholinergic interaction of the muscarinic type exists in brain and may have a function in the control of arousal, with catalepsy at one extreme and locomotor stimulation at the other.