Anti-addictive actions of an iboga alkaloid congener: a novel mechanism for a novel treatment.

18-Methoxycoronaridine (18-MC), a synthetic compound related to iboga, reduces self-administration of multiple addictive drugs in animal models. It decreased intravenous morphine, cocaine, methamphetamine, and nicotine self-administration, as well as oral alcohol and nicotine intake, and eased opioid withdrawal signs, without affecting responding for a nondrug reinforcer (water) or causing apparent toxicity. 18-MC also blocked sensitized dopamine responses to morphine and cocaine in the nucleus accumbens. Receptor studies identified it as a potent antagonist at alpha3beta4 nicotinic receptors. Low-dose combinations of 18-MC with other alpha3beta4 antagonists reduced drug self-administration at otherwise ineffective doses. The findings suggest that alpha3beta4 nicotinic receptor antagonists may offer a novel, broad-spectrum treatment for addiction.

Study at a glance

Abstract

18-Methoxycoronaridine (18-MC), a novel iboga alkaloid congener that decreases drug self-administration in several animal models, may be a potential treatment for multiple forms of drug abuse. In animal models, 18-MC reduced intravenous morphine, cocaine, methamphetamine and nicotine self-administration, oral alcohol and nicotine intake, and attenuated signs of opioid withdrawal, but had no effect on responding for a nondrug reinforcer (water) and produced no apparent toxicity [Brain Res. 719 (1996) 29; NeuroReport 11 (2000) 2013; Pharmacol. Biochem. Behav. 58 (1997) 615; Psychopharmacology (Berl.) 139 (1998) 274; NeuroReport 9 (1998) 1283; Ann. N. Y. Acad. Sci. 914 (2000) 369]. Consistent with a relationship among drug sensitization, mesolimbic dopamine, and drug-seeking behavior, 18-MC also blocked the sensitized dopamine responses to morphine and cocaine in the nucleus accumbens. An extensive series of receptor studies showed that 18-MC was most potent and somewhat selective as an antagonist at alpha3beta4 nicotinic receptors. Low-dose combinations of 18-MC with other drugs known to have this same action (e.g., mecamylamine, dextromethorphan, bupropion) decreased morphine, methamphetamine, and nicotine self-administration in rats at doses that were ineffective if administered alone. Together, the data support the hypothesis that diencephalic pathways having high densities of alpha3beta4 nicotinic receptors modulate mesocorticolimbic pathways more directly involved in drug reinforcement. Antagonists of alpha3beta4 nicotinic receptors may represent a totally novel approach to treating multiple addictive disorders, and 18-MC might be the first of a new class of synthetic agents acting via this novel mechanism and having a broad spectrum of activity.