Josephine R. Tarren

The antihypertensive drug pindolol attenuates long-term but not short-term binge-like ethanol consumption in mice

Alcohol dependence is a debilitating disorder with current therapies displaying limited efficacy and/or compliance. Consequently, there is a critical need for improved pharmacotherapeutic strategies to manage alcohol use disorders (AUDs). Previous studies have shown that the development of alcohol dependence involves repeated cycles of binge‐like ethanol intake and abstinence. Therefore, we used a model of binge–ethanol consumption (drinking‐in‐the‐dark) in mice to test the effects of compounds known to modify the activity of neurotransmitters implicated in alcohol addiction. From this, we have identified the FDA‐approved antihypertensive drug pindolol, as a potential candidate for the management of AUDs. We show that the efficacy of pindolol to reduce ethanol consumption is enhanced following long‐term (12 weeks) binge–ethanol intake, compared with short‐term (4 weeks) intake. Furthermore, pindolol had no effect on locomotor activity or consumption of the natural reward sucrose. Because pindolol acts as a dual beta‐adrenergic antagonist and 5‐HT1A/1B partial agonist, we examined its effect on spontaneous synaptic activity in the basolateral amygdala (BLA), a brain region densely innervated by serotonin and norepinephrine‐containing fibres. Pindolol increased spontaneous excitatory post‐synaptic current frequency of BLA principal neurons from long‐term ethanol‐consuming mice but not naïve mice. Additionally, this effect was blocked by the 5‐HT1A/1B receptor antagonist methiothepin, suggesting that altered serotonergic activity in the BLA may contribute to the efficacy of pindolol to reduce ethanol intake following long‐term exposure. Although further mechanistic investigations are required, this study demonstrates the potential of pindolol as a new treatment option for AUDs that can be fast‐tracked into human clinical studies.

The effect of varenicline on binge-like ethanol consumption in mice is β4 nicotinic acetylcholine receptor-independent.

BACKGROUND Our laboratory has previously shown that the smoking-cessation agent varenicline, an agonist/partial agonist of α4β2*, α3β4*, α3β2*, α6β2* (* indicates the possibility of additional subunits) and α7 subunits of nicotinic acetylcholine receptors (nAChRs), reduces ethanol consumption in rats only after long-term exposure (12 weeks). As compounds having partial agonistic activity on α3β4* nAChRs were shown to decrease ethanol consumption in rodents, we assessed here the involvement of the β4 subunit in the effect of varenicline in the reduction of short- and long-term binge-like ethanol drinking in mice. METHODS We used the well-validated drinking-in-the-dark (DID) paradigm to model chronic binge-like ethanol drinking in β4-/- and β4+/+ littermate mice and compare the effect of intraperitoneal injection of varenicline (2mg/kg) on ethanol intake following short- (4 weeks) or long-term (12 weeks) exposure. RESULTS Drinking pattern and amounts of ethanol intake were similar in β4-/- and β4+/+ mice. Interestingly, our results showed that varenicline reduces ethanol consumption following short- and long-term ethanol exposure in the DID. Although the effect of varenicline on the reduction of ethanol consumption was slightly more pronounced in β4-/- mice than their β4+/+ littermates no significant differences were observed between genotypes. CONCLUSION In mice, varenicline reduces binge-like ethanol consumption both after short- and long-term exposure in the DID and this effect is independent of β4 nAChR subunit.

Alcohol and nicotine interactions: pre-clinical models of dependence

ABSTRACT While the co-morbidity of alcohol (ethanol) and tobacco (nicotine) dependence is well described, the processes that underpin this strong connection are still under debate. With the increasing popularity of electronic cigarettes (e-cigarettes), it is now becoming more important to look to the neurobiological mechanisms involving alcohol and nicotine interactions to effectively treat a new generation of co-dependent individuals. Researchers have already recognized that the neuropathology produced by the combination of nicotine and ethanol is likely to produce an addictive nature very different to that of either one alone, and are employing a mixture of pre-clinical techniques to establish and investigate every stage in the development of both nicotine and ethanol-seeking behaviors. While it is agreed that multiple pathways orchestrate the complex reward profile of alcohol and nicotine co-addiction, several lines of evidence suggest the convergent site of action is within the mesolimbic dopaminergic system, at neuronal nicotinic acetylcholine receptors (nAChRs). A whole host of strategies are currently being employed to discover and unravel previously unknown or ill understood neurobiological processes in the brain, contributing greatly toward the development of novel pharmacotherapies with the aim of improving patient outcomes. This review intends to shed some light on the most influential and most recent pre-clinical work that is leading the charge in modeling this complicated relationship.

Acute Ethanol Administration Upregulates Synaptic α4-Subunit of Neuronal Nicotinic Acetylcholine Receptors within the Nucleus Accumbens and Amygdala

Alcohol and nicotine are two of the most frequently abused drugs, with their comorbidity well described. Previous data show that chronic exposure to nicotine upregulates high-affinity nicotinic acetylcholine receptors (nAChRs) in several brain areas. Effects of ethanol on specific brain nAChR subtypes within the mesolimbic dopaminergic (DA) pathway may be a key element in the comorbidity of ethanol and nicotine. However, it is unknown how alcohol affects the abundance of these receptor proteins. In the present study, we measured the effect of acute binge ethanol on nAChR α4 subunit levels in the prefrontal cortex (PFC), nucleus accumbens (NAc), ventral tegmental area (VTA), and amygdala (Amg) by western blot analysis using a knock-in mouse line, generated with a normally functioning α4 nAChR subunit tagged with yellow fluorescent protein (YFP). We observed a robust increase in α4-YFP subunit levels in the NAc and the Amg following acute ethanol, with no changes in the PFC and VTA. To further investigate whether this upregulation was mediated by increased local mRNA transcription, we quantified mRNA levels of the Chrna4 gene using qRT-PCR. We found no effect of ethanol on α4 mRNA expression, suggesting that the upregulation of α4 protein rather occurs post-translationally. The quantitative counting of YFP immunoreactive puncta further revealed that α4-YFP protein is upregulated in presynaptic boutons of the dopaminergic axons projecting to the shell and the core regions of the NAc as well as to the basolateral amygdala (BLA), but not to the central or lateral Amg. Together, our results demonstrate that a single exposure to binge ethanol upregulates level of synaptic α4∗ nAChRs in dopaminergic inputs to the NAc and BLA. This upregulation could be linked to the functional dysregulation of dopaminergic signalling observed during the development of alcohol dependence.

Effects of alcohol on nicotinic acetylcholine receptors and impact on addiction

While it is widely known that alcohol and nicotine addictions commonly co-occur, no pharmacotherapies are yet marketed for codependent individuals. This is a striking observation given the broad implications and detrimental impacts that arise from this drug combination. Over the past decade, clinical and research efforts have exposed a common effector-neuronal nicotinic acetylcholine receptors (nAChRs). In this chapter, we describe alcohols actions as a powerful reinforcer. Through neuronal nAChRs, alcohol hijacks the natural reward circuitry and creates conditioned drug associations. This endows it with the power to sustain, prolong, and reinstate further alcohol and nicotine-seeking behaviors. The narrative is based on experience and considerations made in the course of our research, and it highlights key cholinergic receptors indicated in alcohols modulation of addiction, tolerance, withdrawal, and relapse. We believe that the delineation of these cholinergic receptors is the key to creating targeted therapeutics for alcohol use disorders and reducing the comorbidity of nicotine addiction.

Sex Specific Alterations in α4*Nicotinic Receptor Expression in the Nucleus Accumbens

Background: The mechanisms leading from traumatic stress to social, emotional and cognitive impairment and the development of mental illnesses are still undetermined and consequently there remains a critical need to develop therapies for preventing the adverse consequences of traumatic stress. Research indicates nicotinic acetylcholine receptors containing α4 subunits (α4*nAChRs) are both impacted by stress and capable of modulating the stress response. In this study, we investigated whether varenicline, a partial α4β2*nAChR agonist which reduces nicotine, alcohol and sucrose consumption, can reduce stress, a driving factor in substance use disorders. We also examined the effect of stress on nucleus accumbens (NAc) α4*nAChR expression. Methods: Transgenic mice with fluorescent tags attached to α4*nAChRs were administered varenicline and/or yohimbine (a pharmacological stressor) and plasma corticosterone and NAc α4*nAChR expression were measured. A separated group of mice were exposed to maternal separation (MS) during post-natal day (P) 2–14, then restraint stressed (30 min) at six weeks of age. Body weight, anxiety-like behaviours (elevated plus maze), plasma corticosterone and NAc α4*nAChR levels were measured. Results: Varenicline attenuated yohimbine-induced plasma corticosterone increases with no effect on NAc α4*nAChR expression. MS reduced unrestrained plasma corticosterone levels in both sexes. In females, MS increased body weight and NAc α4*nAChR expression, whereas, in males, MS and restraint caused a greater change in anxiety-like behaviours and plasma corticosterone levels. Restraint altered NAc α4*nAChR expression in both male and female MS mice. Conclusions: The effects of stress on NAc α4*nAChR are sex-dependent. While varenicline attenuated acute stress-induced rises in corticosterone levels, future studies are required to determine whether varenicline is effective for relieving the effects of stress.