Mesolimbic a6* nicotinic acetylcholine receptors (nAChRs) are thought to have an important role in nicotine behavioral effects. However, little is known about the role of the various a6*-nAChRs subtypes in the rewarding effects of nicotine. In this report, we investigated and compared the role of a6*-nAChRs subtypes and their neuro-anatomical locus in nicotine and cocaine reward-like effects in the conditioned place preference (CPP) paradigm, using pharmacological antagonism of a6b2* nAChRs and genetic deletion of the a6 or a4 subunits in mice. We found that a6 KO mice exhibited a rightward shift in the nicotine dose-response curve compared with WT littermates but that a4 KO failed to show nicotine preference, suggesting that a6a4b2*-nAChRs are involved. Furthermore, a6b2* nAChRs in nucleus accumbens were found to have an important role in nicotine-conditioned reward as the intra-accumbal injection of the selective a6b2* a-conotoxin MII [H9A; L15A], blocked nicotine CPP. In contrast to nicotine, a6 KO failed to condition to cocaine, but cocaine CPP in the a4 KO was preserved. Intriguingly, a-conotoxin MII [H9A; L15A], blocked cocaine conditioning in a4 KO mice, implicating a6b2* nAChRs in cocaine reward. Importantly, these effects did not generalize as a6 KO showed both a conditioned place aversion to lithium chloride as well as CPP to palatable food. Finally, dopamine uptake was not different between the a6 KO or WT mice. These data illustrate that the subjective rewarding effects of both nicotine and cocaine may be mediated by mesolimbic a6b2* nAChRs and that antagonists of these receptor subtypes may exhibit therapeutic potential.

Rationale N-acetylcysteine can increase extrasynaptic glutamate and reduce nicotine self-administration in rats and smoking rates in humans. Objectives The aim of this study was to determine if N-acetylcysteine modulates the development of nicotine place conditioning and withdrawal in mice. Methods N-acetylcysteine was given to nicotine-treated male ICR mice. Experiment 1: reward-like behavior. N-acetylcysteine (0, 5, 15, 30, or 60 mg/kg, i.p.) was given 15 min before nicotine (0.5 mg/kg, s.c.) or saline (10 ml/kg, s.c.) in an unbiased conditioned place preference (CPP) paradigm. Conditioning for highly palatable food served as control. Experiment 2: spontaneous withdrawal. The effect of N-acetylcysteine (0, 15, 30, 120 mg/kg, i.p.) on anxiety-like behavior, somatic signs, and hyperalgesia were measured 18 - 24 hrs after continuous nicotine (24 mg/kg/day, 14 days). Experiment 3: Mecamylamine-precipitated, withdrawal-induced aversion. The effect of N-acetylcysteine (0, 15, 30, 120 mg/kg, i.p.) on mecamylamine (3.5 mg/kg, i.p.) precipitated withdrawal was determined after continuous nicotine (24 mg/kg, i.p., 28 days) using the conditioned place aversion (CPA) paradigm. Results Dose-related reductions in the development of nicotine CPP, somatic withdrawal signs, hyperalgesia, and CPA were observed after N-acetylcysteine pretreatment. No effect of N-acetylcysteine were found on palatable food CPP, anxiety-like behavior, or motoric capacity (crosses between plus maze arms). Finally, N-acetylcysteine did not affect any measure in saline-treated mice at doses effective in nicotine-treated mice. Conclusions These are the first data suggesting that N-acetylcysteine blocks specific mouse behaviors associated with nicotine reward and withdrawal, which adds to the growing appreciation that N-acetylcysteine may have high clinical utility in combating nicotine dependence.