Deletion Of Alpha 5 Nicotine Receptor Subunits Abolishes Nicotinic Aversive Motivational Effects In A Manner That Phenocopies Dopamine Receptor Antagonism

Nicotine addiction is a worldwide epidemic that claims millions of lives each year. Genetic deletion of 5 nicotinic acetylcholine receptor (nAChR) subunits has been associated with increased nicotine intake, however, it remains unclear whether acute nicotine is less aversive or more rewarding, and whether mice lacking the 5 nAChR subunit can experience withdrawal from chronic nicotine. We used place conditioning and conditioned taste avoidance paradigms to examine the effect of 5 subunit-containing nAChR deletion (5 -/-) on conditioned approach and avoidance behaviour in nondependent and nicotine-dependent and -withdrawn mice, and compared these motivational effects with those elicited after dopamine receptor antagonism. We show that nondependent 5 -/- mice find low, non-motivational doses of nicotine rewarding, and do not show an aversive conditioned response or taste avoidance to higher aversive doses of nicotine. Furthermore, nicotine-dependent 5 -/- mice do not show a conditioned aversive motivational response to withdrawal from chronic nicotine, although they continue to exhibit a somatic withdrawal syndrome. These effects phenocopy those observed after dopamine receptor antagonism, but are not additive, suggesting that 5 nAChR subunits act in the same pathway as dopamine and are critical for the experience of nicotine's aversive, but not rewarding motivational effects in both a nondependent and nicotine-dependent and -withdrawn motivational state. Genetic deletion of 5 nAChR subunits leads to a behavioural phenotype that exactly matches that observed after antagonizing dopamine receptors, thus we suggest that modulation of nicotinic receptors containing 5 subunits may modify dopaminergic signalling, suggesting novel therapeutic treatments for smoking cessation.