Recently, the smoking cessation therapeutic varenicline, a nicotinic acetylcholine receptor (nAChR) partial agonist, has been shown to reduce alcohol consumption. However, the mechanism and nAChR subtype(s) involved are unknown. Here we demonstrate that varenicline and alcohol exposure, either alone or in combination, selectively activates dopaminergic (DAergic) neurons within the posterior, but not the anterior, ventral tegmental area (VTA). To gain insight into which nAChR subtypes may be involved in the response to alcohol, we analyzed nAChR subunit gene expression in posterior VTA DAergic neurons. Ethanol-activated DAergic neurons expressed higher levels of ␣4, ␣6, and ␤3 subunit genes compared with nonactivated neurons. To examine the role of nicotinic receptors containing the ␣4 subunit (␣4* nAChRs) in varenicline-induced reduction of alcohol consumption, we examined the effect of the drug in two complementary mouse models, a knock-out line that does not express the ␣4 subunit (␣4 KO) and another line that expresses ␣4* nAChRs hypersensitive to agonist (Leu9ЈAla). While varenicline (0.1-0.3 mg/kg, i.p.) reduced 2% and 20% alcohol consumption in wild-type (WT) mice, the drug did not significantly reduce consumption in ␣4 KO animals. Conversely, low doses of varenicline (0.0125-0.05 mg/kg, i.p.) that had little effect in WT mice dramatically reduced ethanol intake in Leu9ЈAla mice. Infusion of varenicline into the posterior, but not the anterior VTA was sufficient to reduce alcohol consumption. Together, our data indicate that activation of ␣4* nAChRs is necessary and sufficient for varenicline reduction of alcohol consumption.

Rationale-Recent reports describe a restricted access ethanol consumption paradigm where C57Bl/6J mice drink until intoxicated. Termed "drinking in the dark" (DID), this paradigm has been used as a model of binge drinking. Although neuronal nicotinic acetylcholine receptors (nAChRs) have been implicated in alcohol drinking in rats pre-trained to self-administer ethanol, their role in binge-like ethanol consumption is unknown.Objectives-To determine if nAChRs are involved in binge drinking as measured by the DID assay in C57Bl/6J mice.Methods-Adult male C57Bl/6J mice were injected i.p. with nicotinic receptor antagonists including mecamylamine, hexamethonium, dihydro-β erythroidine, and methyllycaconitine. Immediately following injection mice were presented with 20 % ethanol for 2 hours in the DID assay to measure ethanol consumption. Nicotinic agonists including cytisine and nicotine were also evaluated. The effects of mecamylamine and nicotine on ethanol-induced dopaminergic neuronal activation in the VTA were evaluated via immunohistochemistry.Results-Mecamylamine dose dependently reduced ethanol consumption; whereas the peripheral antagonist hexamethonium had no significant effect. Nicotinic agonists cytisine and nicotine reduced ethanol consumption. None of the effective nicotinic receptor drugs reduced sucrose drinking. Mecamylamine blocked ethanol activation of dopaminergic neurons while nicotine alone activated them without additional activation by ethanol.Conclusions-Neuronal nAChRs are involved in ethanol consumption in the DID paradigm. The effects of mecamylamine, nicotine, and cytisine on ethanol intake appear to be specific because they do not reduce sucrose drinking. Mecamylamine reduces alcohol consumption by blocking activation of dopaminergic neurons; whereas nicotinic agonists may activate the same reward pathway as alcohol.

Tolerance, described as the loss of drug effectiveness over time, is an important component of addiction. The degree of acute behavioral tolerance to alcohol exhibited by a naïve subject can predict the likelihood of alcohol abuse. Thus, the determinants of acute tolerance are important to understand. Calcium-and voltage-gated (BK) potassium channels, consisting of pore forming ␣ and modulatory ␤ subunits, are targets of ethanol (EtOH) action. Here, we examine the role, at the molecular, cellular, and behavioral levels, of the BK ␤4 subunit in acute tolerance. Single channel recordings in HEK-293 cells show that, in the absence of ␤4, EtOH potentiation of activity exhibits acute tolerance, which is blocked by coexpressing the ␤4 subunit. BK channels in acutely isolated medium spiny neurons from WT mice (in which the ␤4 subunit is well-represented) exhibit little tolerance. In contrast, neuronal BK channels from ␤4 knockout (KO) mice do display acute tolerance. Brain slice recordings showed tolerance to EtOH's effects on spike patterning in KO but not in WT mice. In addition, ␤4 KO mice develop rapid tolerance to EtOH's locomotor effects, whereas WT mice do not. Finally, in a restricted access ethanol self-administration assay, ␤4 KO mice drink more than their WT counterparts. Taken together, these data indicate that the ␤4 subunit controls ethanol tolerance at the molecular, cellular, and behavioral levels, and could determine individual differences in alcohol abuse and alcoholism, as well as represent a therapeutic target for alcoholism.electrophysiology ͉ knockout mice ͉ striatum ͉ addiction ͉ plasticity A lcohol abuse is the third largest cause of preventable mortality in the world. Tolerance, described as the gradual loss of drug effectiveness over time, is a hallmark of abused drugs. This phenomenon is particularly important in the response to acute alcohol because the degree of tolerance exhibited by a naïve subject can predict the likelihood to develop alcohol abuse (1-4). Thus, identifying the mechanistic and molecular underpinnings of tolerance is essential for understanding the pathophysiology of alcoholism, as well as determining potential therapeutic targets for alcohol abuse. The neurobiology of tolerance is thought to involve several types of adaptation, ranging from alteration in membrane lipid composition (5) to neuroadaptative changes in target proteins (6, 7).In recent years, large conductance calcium-and voltage-gated potassium (BK) channels have emerged as one of the key targets of ethanol action, yet their role in the physiological and behavioral response to alcohol are unknown. Invertebrate studies suggest that BK channels may be important for the development of tolerance to ethanol (8, 9). In mammals, BK channels exist as a complex formed by the association of the pore-forming ␣ subunit with the auxiliary ␤ subunit. The ␣ subunit is encoded by only one gene (slo) with several splice variants (STREX, P27, insertless, etc.), whereas the ␤ subunit is the product of four distinct genes (␤1-␤4)...