Effects of combined systemic alcohol and central nicotine administration into ventral tegmental area on dopamine release in the nucleus accumbens.

BACKGROUND: Alcoholism is associated with a higher incidence of smoking. The mesolimbic dopaminergic pathway is believed to play an important role in the reinforcing effects of both ethanol and nicotine. This study was undertaken to determine whether simultaneous administration of systemic ethanol and microinjection of nicotine into the ventral tegmental area (VTA) would result in exaggerated release of dopamine (DA) in the shell region of nucleus accumbens. METHODS: Microdialysis was applied in awake, freely moving adult male Wistar rats, and DA concentration in the dialysate was measured by HPLC-electrochemical detectors. RESULTS: Systemic administration of ethanol or microinjection of nicotine into VTA resulted in a dose-dependent increase in DA release (extracellular DA concentration). Simultaneous administration of lower doses of nicotine and ethanol resulted in an additive effect on the released DA. This additive effect was not observed with higher doses of nicotine and ethanol. Administration of the nicotinic antagonist mecamylamine into VTA completely blocked ethanol-induced DA release. CONCLUSIONS: These data support the hypothesis that the reinforcing effects of ethanol are at least partially mediated through the nicotinic receptors in the VTA. Furthermore, administration of selective nicotinic antagonists may be of therapeutic potential in reducing the rewarding effects of ethanol. The data also suggest that the combined effects of ethanol and nicotine on the "reward pathway" may be a contributing factor to the high incidence of smoking in alcoholics.

Effect of nicotine on quinpirole-induced checking behavior in rats: implications for obsessive-compulsive disorder.

BACKGROUND: Rats treated chronically in a large, open field with the dopamine D2/D3 receptor agonist quinpirole (QNP) develop compulsive checking behavior as defined by a set of behavioral criteria. This paradigm has been suggested as an animal model of obsessive-compulsive disorder (OCD). Because nicotine blocks various behaviors induced by ontogenetic QNP administration, we asked whether nicotine could attenuate QNP-induced compulsive checking. METHODS: Adult male Long-Evans rats (n = 14/group) were treated twice weekly with saline (control), or with QNP (0.5 mg/kg) for 14-16 injections. On the last two injections, rats were pretreated in random order with an acute dose of nicotine (0.3 mg/kg base) or saline 10 min before administration of QNP or saline; and the effects on checking behavior was examined. The effects of chronic QNP treatment on nicotinic receptors in discrete brain regions were also determined. RESULTS: Chronic QNP resulted in compulsive checking and increases in cerebellar alpha4beta2 and alpha7 nicotinic receptor densities. Nicotine pretreatment significantly reduced one of the three measures of compulsive checking behavior. CONCLUSIONS: Nicotine attenuates some symptoms of compulsive checking in a rat model of OCD; however, the mechanisms of this effect and therapeutic efficacy of nicotinic agonists in OCD require further study.