Scopolamine self-administration: cholinergic involvement in reward mechanisms.

Naive rats readily learned to self-administer scopolamine, a centrally active anticholinergic antimuscarinic agent, by the intravenous route; drug intake remained constant while response rates decreased with increasing unit dose ((0.005-0.02 mg/kg/infusion). Increases and decreases in scopolamine responding were elicited by pretreatment with muscarinic agonists and antagonists, respectively. An anticholinergic action at muscarinic synapses appears to be sufficient for reinforcing efficacy; such an action may mediate, in part, the addictive properties of other drugs (e.g., opiates and phencyclidine-like hallucinogens) that are known to have anticholinergic effects.