Decreased Ethanol Consumption Research Articles

Nucleus accumbens lentiviral-mediated gain of function of the oxytocin receptor regulates anxiety- and ethanol-related behaviors in adult mice

Anxiety is believed to influence ethanol use human in alcoholics. Studies using laboratory animals suggested an interaction between oxytocin and the behavioral effects of ethanol. Our previous study implicated a potential role for the oxytocin receptor (OxtR) in regulating ethanol-conditioned place preference. Here, we examined anxiety and the behavioral responses to ethanol in C57BL/6 mice stereotaxically injected in the nucleus accumbens (NAcc) with lentiviral vectors expressing an empty vector (Mock) or the OxtR cDNA. For anxiety we used the elevated-plus maze, the open-field and the marble-burying tests and for ethanol we used the two-bottle choice paradigm, the wire-hanging and ethanol-induced loss-of-righting-reflex tests. We found that, compared to Mock, OxtR overexpression led to anxiolytic-like behavior without altering spontaneous locomotor activity. Most importantly, we found that, relative to Mock controls, increased expression of the OxtR in the NAcc led to decreased ethanol consumption and preference in the two-bottle choice protocol and increased resistance to ethanol-induced sedation. We also compared the consequence of OxtR modulation on the consumption and preference of saccharin and quinine and found that the two experimental groups did not differ for any tastant. These results provide further evidence that the oxytocin system contributes to the regulation of ethanol drinking and sensitivity and position OxtR as a central molecular mediator of ethanol's effects within the mesolimbic system. Taken together, the current findings suggest that OxtR manipulation may be a relevant strategy to address ethanol use disorders.

Selective chemical genetic inhibition of protein kinase C epsilon reduces ethanol consumption in mice

Reducing expression or inhibiting translocation of protein kinase C epsilon (PKCε) prolongs ethanol intoxication and decreases ethanol consumption in mice. However, we do not know if this phenotype is due to reduced PKCε kinase activity or to impairment of kinase-independent functions. In this study, we used a chemical-genetic strategy to determine whether a potent and highly selective inhibitor of PKCε catalytic activity reduces ethanol consumption. We generated ATP analog-specific PKCε (AS-PKCε) knock-in mice harboring a point mutation in the ATP binding site of PKCε that renders the mutant kinase highly sensitive to inhibition by 1-tert-butyl-3-naphthalen-1-ylpyrazolo[3,4-d]pyrimidin-4-amine (1-NA-PP1). Systemically administered 1-NA-PP1 readily crossed the blood brain barrier and inhibited PKCε-mediated phosphorylation. 1-NA-PP1 reversibly reduced ethanol consumption by AS-PKCε mice but not by wild type mice lacking the AS-PKCε mutation. These results support the development of inhibitors of PKCε catalytic activity as a strategy to reduce ethanol consumption, and they demonstrate that the AS- PKCε mouse is a useful tool to study the role of PKCε in behavior.

The novel mu-opioid antagonist, GSK1521498, reduces ethanol consumption in C57BL/6J mice.

RationaleUsing the drinking-in-the-dark (DID) model, we compared the effects of a novel mu-opioid receptor antagonist, GSK1521498, with naltrexone, a licensed treatment of alcohol dependence, on ethanol consumption in mice.ObjectiveWe test the ability of GSK1521498 to reduce alcohol consumption and compare its intrinsic efficacy to that of naltrexone by comparing the two drugs at doses matched for equivalent receptor occupancy.MethodsThirty-six C57BL/6J mice were tested in a DID procedure. In 2-day cycles, animals experienced one baseline, injection-free session, and one test session when they received two injections, one of test drug and one placebo. All animals received GSK1521498 (0, 0.1, 1 and 3 mg/kg, i.p., 30 min pre-treatment) and naltrexone (0, 0.1, 1 and 3 mg/kg, s.c. 10 min pre-treatment) in a cross-over design. Receptor occupancies following the same doses were determined ex vivo in separate groups by autoradiography, using [3H]DAMGO. Binding in the region of interest was measured integrally by computer-assisted microdensitometry and corrected for non-specific binding.ResultsBoth GSK1521498 and naltrexone dose-dependently decreased ethanol consumption. When drug doses were matched for 70–75 % receptor occupancy, GSK1521498 3 mg/kg, i.p., caused a 2.5-fold greater reduction in alcohol consumption than naltrexone 0.1 mg/kg, s.c. Both GSK1521498 and naltrexone significantly reduced sucrose consumption at a dose of 1 mg/kg but not 0.1 mg/kg. In a test of conditioned taste aversion, GSK1521498 (3 mg/kg) reduced sucrose consumption 24 h following exposure to a conditioning injection.ConclusionsBoth opioid receptor antagonists reduced alcohol consumption but GK1521498 has higher intrinsic efficacy than naltrexone.Electronic supplementary materialThe online version of this article (doi:10.1007/s00213-015-3995-x) contains supplementary material, which is available to authorized users.

Inhibition of phosphodiesterase‐4 (PDE4) by roflumilast decreases ethanol consumption

Excessive alcohol drinking normally causes alcoholism, which is one of the most damaging psychiatric disorders in the world. However, there are no ideal treatments for alcoholism in clinic. Phosphodiesterase‐4, an enzyme that specifically hydrolyzes intracellular cyclic AMP (cAMP), may play an important role in the regulation of ethanol consumption. This is supported by the findings that inhibition of PDE4 by rolipram, a prototypic PDE4 inhibitor, reduces ethanol intake and self‐administration. Roflumilast, another selective PDE4 inhibitor, has been approved for treatment of chronic obstructive pulmonary diseases in clinic. It was of interest to know whether roflumilast altered ethanol consumption. The two‐bottle choice paradigm was used to assess ethanol intake and preference in C57BL/6J mice treated with roflumilast (1, 3, or 10 mg/kg) or rolipram (0.5 mg/kg; positive control). The effect of roflumilast was verified using ethanol drinking‐in‐dark. Locomotor activity was determined using the open‐field test. Roflumilast decreased ethanol intake and preference in two‐bottle choice in a dose‐dependent manner, with the significant change at the highest dose (10 mg/kg) of roflumilast, similar to rolipram. Neither roflumilast nor rolipram affected sucrose or quinine drinking, although roflumilast at the highest dose decreased locomotor activity. These data provide additional demonstration for the role of PDE4 in ethanol intake and suggest that roflumilast may be beneficial for treatment of alcoholism.

Zonisamide, topiramate, and levetiracetam: efficacy and neuropsychological effects in alcohol use disorders.

The anticonvulsant topiramate not only decreases ethanol consumption in alcohol dependence (AD) but also may produce several adverse events including cognitive impairment. Zonisamide is a structurally related anticonvulsant that is a promising agent for the treatment of AD and may have greater tolerability than topiramate. This study evaluated the effects of zonisamide (400 mg/d) on alcohol consumption and its neurotoxic effects in subjects with AD. A double-blind placebo-controlled clinical trial was conducted using 2 comparator anticonvulsant drugs, topiramate (300 mg/d) and levetiracetam (2000 mg/d), which does not impair cognition. Study medications were administered for 14 weeks, including a 2-week taper period. Medication adherence was facilitated using Brief Behavioral Compliance Enhancement Treatment. The neurotoxicity of the study drugs was assessed using neuropsychological tests and the AB-Neurotoxicity Scale. Compared with placebo, both zonisamide and topiramate produced significant reductions in the drinks consumed per day, percent days drinking, and percent days heavy drinking. Only the percent days heavy drinking was significantly decreased in the levetiracetam group. The topiramate cell was the only group that had a significant increase on the mental slowing subscale of the Neurotoxicity Scale compared with placebo at study weeks 11 and 12. Topiramate and zonisamide both produced modest reductions in verbal fluency and working memory. These findings indicate that zonisamide may have efficacy in the treatment of AD, with effect sizes similar to topiramate. Both of these drugs produced similar patterns of cognitive impairment, although only the topiramate group reported significant increases in mental slowing.

Effect of nucleus accumbens shell infusions of ganaxolone or gaboxadol on ethanol consumption in mice

Allopregnanolone (ALLO) is an endogenous neuroactive steroid thought to alter the reinforcement value of alcohol (ethanol) due to its actions as a positive modulator of the GABAA receptor (GABAAR). Extrasynaptic GABAARs may be a particularly sensitive target of ethanol and neuroactive steroids. Previous work showed that systemic injections of an ALLO analog, ganaxolone (GAN), or an extrasynaptic GABAAR agonist (gaboxadol; THIP) decreased ethanol intake in male mice with limited access to ethanol. The present studies tested whether activation of GABAARs in the nucleus accumbens (NAc) shell by GAN or THIP was sufficient to reduce ethanol intake. C57BL/6J male mice had 2-h access to 10% ethanol (10E) and water, and 10E intake was measured following site-specific infusions of GAN or THIP. Decreases in limited-access 10E consumption were observed following site-specific bilateral infusions of either drug into the NAc shell. Significant changes in intake were absent when the drugs were infused in a region dorsal to the target site (GAN) or into the lateral ventricle (THIP). Locomotor data confirmed that the decreases in intake were not due to a sedative effect of the drugs. These data demonstrate the sufficiency of GABAAR activation by a positive allosteric modulator or an agonist with selectivity for extrasynaptic GABAARs to decrease ethanol consumption in mice. Importantly, more refined GABAAR-active targets that decrease ethanol intake may enhance our understanding and ability to treat alcohol use disorders.

P-11 * SEX DIFFERENCES IN THE EFFECTS OF CHRONIC SOCIAL ISOLATION ON ALCOHOL CONSUMPTION IN MU-OPIOID RECEPTOR KNOCKOUT MICE

Introduction. Early social experience has been consistently shown increase alcohol consumption, perhaps by influencing stress systems. However, the connection between these effects and alcohol consumption is complex and poorly understood. This experiment was based on the hypothesis that the effects of chronic social isolation on alcohol consumption would be influenced by both sex and the functioning of Mu-opioid receptor (MOP) systems. Method. The present study assessed the effects of isolation-rearing on later ethanol intake using a two-bottle home-cage consumption (ethanol 8% vs. water) paradigm in wild-type and MOP gene knockout (KO) mice. A total of 97 male and female mice were used in this study. Results. Isolation rearing had no effects upon ethanol consumption in WT mice under the conditions used in the present experiments; however, isolation rearing did have effects in both male and female MOP KO mice, but these effects were in the opposite direction, increasing ethanol consumption in male mice, but decreasing ethanol consumption in female mice. Conclusion. These results indicate that MOP influences ethanol consumption, but does so in quite different ways depending on sex and previous social experience during adolescent development.

PPAR agonists regulate brain gene expression: Relationship to their effects on ethanol consumption

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that act as ligand-activated transcription factors. Although prescribed for dyslipidemia and type-II diabetes, PPAR agonists also possess anti-addictive characteristics. PPAR agonists decrease ethanol consumption and reduce withdrawal severity and susceptibility to stress-induced relapse in rodents. However, the cellular and molecular mechanisms facilitating these properties have yet to be investigated. We tested three PPAR agonists in a continuous access two-bottle choice (2BC) drinking paradigm and found that tesaglitazar (PPARα/γ; 1.5 mg/kg) and fenofibrate (PPARα; 150 mg/kg) decreased ethanol consumption in male C57BL/6J mice while bezafibrate (PPARα/γ/β; 75 mg/kg) did not. We hypothesized that changes in brain gene expression following fenofibrate and tesaglitazar treatment lead to reduced ethanol drinking. We studied unbiased genomic profiles in areas of the brain known to be important for ethanol dependence, the prefrontal cortex (PFC) and amygdala, and also profiled gene expression in liver. Genomic profiles from the non-effective bezafibrate treatment were used to filter out genes not associated with ethanol consumption. Because PPAR agonists are anti-inflammatory, they would be expected to target microglia and astrocytes. Surprisingly, PPAR agonists produced a strong neuronal signature in mouse brain, and fenofibrate and tesaglitazar (but not bezafibrate) targeted a subset of GABAergic interneurons in the amygdala. Weighted gene co-expression network analysis (WGCNA) revealed co-expression of treatment-significant genes. Functional annotation of these gene networks suggested that PPAR agonists might act via neuropeptide and dopaminergic signaling pathways in the amygdala. Our results reveal gene targets through which PPAR agonists can affect alcohol consumption behavior.

Intra-nucleus accumbens shell injections of R(+)- and S(−)-baclofen bidirectionally alter binge-like ethanol, but not saccharin, intake in C57Bl/6J mice

The GABAB agonist baclofen has been widely researched clinically and preclinically as a treatment of alcohol use disorders (AUDs). However, the efficacy of baclofen remains uncertain. The clinically used racemic compound can be separated into separate enantiomers. These enantiomers have produced different profiles in behavioral assays, with the S- compound often being ineffective compared to the R- compound, or the S- compound antagonizing the effects of the R- compound. We have previously demonstrated that the R(+)-baclofen enantiomer decreases binge-like ethanol intake in the Drinking-in-the-Dark (DID) paradigm, whereas the S(-)-baclofen enantiomer increases ethanol intake. One area implicated in drug abuse is the nucleus accumbens shell (NACsh).The current study sought to define the role of the NACsh in the enantioselective effects of baclofen on binge-like ethanol consumption by directly microinjecting each enantiomer into the structure. Following bilateral cannulation of the NACsh, C57Bl/6J mice were given 5 days of access to ethanol or saccharin for 2h, 3h into the dark cycle. On Day 5 mice were given an injection of aCSF, 0.02 R(+)-, 0.04R(+)-, 0.08 S(-)-, or 0.16 S(-)-baclofen (μg/side dissolved in 200nl of aCSF). It was found that the R(+)-baclofen dose-dependently decreased ethanol consumption, whereas the high S(−)-baclofen dose increased ethanol consumption, compared to the aCSF group. Saccharin consumption was not affected. These results further confirm that GABAB receptors and the NACsh shell are integral in mediating ethanol intake. They also demonstrate that baclofen displays bidirectional, enantioselective effects which are important when considering therapeutic uses of the drug.

Varenicline decreases ethanol intake and increases dopamine release via neuronal nicotinic acetylcholine receptors in the nucleus accumbens

BACKGROUND AND PURPOSEVarenicline, a neuronal nicotinic acetylcholine receptor (nAChR) modulator, decreases ethanol consumption in rodents and humans. The proposed mechanism of action for varenicline to reduce ethanol consumption has been through modulation of dopamine (DA) release in the nucleus accumbens (NAc) via α4*-containing nAChRs in the ventral tegmental area (VTA). However, presynaptic nAChRs on dopaminergic terminals in the NAc have been shown to directly modulate dopaminergic signalling independently of neuronal activity from the VTA. In this study, we determined whether nAChRs in the NAc play a role in varenicline's effects on ethanol consumption.EXPERIMENTAL APPROACHRats were trained to consume ethanol using the intermittent-access two-bottle choice protocol for 10 weeks. Ethanol intake was measured after varenicline or vehicle was microinfused into the NAc (core, shell or core-shell border) or the VTA (anterior or posterior). The effect of varenicline treatment on DA release in the NAc was measured using both in vivo microdialysis and in vitro fast-scan cyclic voltammetry (FSCV).KEY RESULTSMicroinfusion of varenicline into the NAc core and core-shell border, but not into the NAc shell or VTA, reduced ethanol intake following long-term ethanol consumption. During microdialysis, a significant enhancement in accumbal DA release occurred following systemic administration of varenicline and FSCV showed that varenicline also altered the evoked release of DA in the NAc.CONCLUSION AND IMPLICATIONSFollowing long-term ethanol consumption, varenicline in the NAc reduces ethanol intake, suggesting that presynaptic nAChRs in the NAc are important for mediating varenicline's effects on ethanol consumption.

Brucine suppresses ethanol intake and preference in alcohol-preferring Fawn-Hooded rats.

Brucine (BRU) extracted from the seeds of Strychnos nux-vomica L is glycine receptor antagonist. We hypothesize that BRU may modify alcohol consumption by acting at glycine receptors, and evaluated the pharmacodynamic profiles and adverse effects of BRU in rat models of alcohol abuse. Alcohol-preferring Fawn-Hooded (FH/Wjd) rats were administered BRU (10, 20 or 30 mg/kg, sc). The effects of BRU on alcohol consumption were examined in ethanol 2-bottle-choice drinking paradigm, ethanol/sucrose operant self-administration paradigm and 5-d ethanol deprivation test. In addition, open field test was used to assess the general locomotor activity of FH/Wjd rats, and conditioned place preference (CPP) was conducted to assess conditioned reinforcing effect. In ethanol 2-bottle-choice drinking paradigm, treatment with BRU for 10 consecutive days dose-dependently decreased the ethanol intake associated with a compensatory increase of water intake, but unchanged the daily total fluid intake and body weight. In ethanol/sucrose operant self-administration paradigms, BRU (30 mg/kg) administered before each testing session significantly decreased the number of lever presses for ethanol and the ethanol intake, without affecting the number of sucrose (10%) responses, total sucrose intake, and the number of lever presses for water. Acute treatment with BRU (30 mg/kg) completely suppressed the deprivation-induced elevation of ethanol consumption. Treatment with BRU (10, 20, and 30 mg/kg) did not alter locomotion of FH/Wjd rats, nor did it produce place preference or aversion. BRU selectively decreases ethanol consumption with minimal adverse effects. Therefore, BRU may represent a new pharmacotherapy for alcoholism.

The Kv7 potassium channel activator retigabine decreases alcohol consumption in rats

Background: Activation of Kv7 potassium channels may decrease the reactivity of mesolimbic dopaminergic neurons that are implicated in mediating the reinforcing effects of ethanol. Objectives: The objective of this study was to determine whether the administration of the Kv7 potassium channel opener retigabine would decrease ethanol intake in Long Evans rats. Methods: A limited access two-bottle choice model of alcohol (10% solution) consumption was used in this study. A separate group of animals was tested to evaluate the actions of retigabine on sucrose (5% solution) consumption to determine whether this drug might produce non-selective impairment of the ability of rats to drink liquids. Animals were treated with either vehicle or increasing doses (2.5–7.5 mg/kg SC) of retigabine administered over a 3-day period. Results: Compared to vehicle, retigabine at a dose of 7.5 mg/kg produced a reduction in the amount of ethanol consumed. These effects did not occur in association with significant changes in water consumption. A significant time effect was found for the actions of retigabine in sucrose-drinking rats with a trend for an increase in sucrose intake with the highest dose of retigabine administered. Conclusions: These results indicate that the administration of retigabine may produce a decrease in ethanol consumption by rats at doses that do not significantly reduce the drinking of either water or a sucrose solution. These findings are consistent with the hypothesis that activation of Kv7 channels facilitates the reduction of alcohol consumption in the rat.

Evaluation of Ampicillin and Ceftriaxone on Ethanol Consumption as Compared to Naltrexone in Alcohol Dependant Rats

Context: Extracellular glutamate level in reward centre of brain increases during ethanol drinking sessions. Hence, it can be hypothesized that drugs which decrease extracellular glutamate might have deaddictive properties. It has been shown that β-lactam antibiotics are potent stimulators of glutamate transporter 1(GLT1) expression. Previous studies have shown that ceftriaxone decreases ethanol consumption but this has not been compared to standard line of treatment (naltrexone). Also, no study was conducted for testing ampicillin even if in an in-vitro experiment ampicillin has shown to increase GLT1 levels more than ceftriaxone. Hence, our study’s objectives were to compare efficacy of ceftriaxone and ampicillin with naltrexone on ethanol consumption in rats.Methods: Permission of ethics committee was taken. Study was divided into two parts. Part I included standardization of model & Part II included 8 groups of six rats each. Group 1: vehicle control, Group 2: 1mg/kg/d naltrexone, Group 3: 100mg/kg/d ceftriaxone, Group 4: 200mg/kg/d ceftriaxone, Group 5: 100mg/kg/d ampicillin, Group 6: 200mg/kg/d ampicillin were given i.p injections for 15 days and Group 7: 200mg/kg ceftriaxone & Group 8: 200mg/kg ampicillin i.p. single dose. Parameters measured were ethanol & water intake per day for 15 days.Results: Groups 2 to 8 showed statistically significant decrease in ethanol intake as compared to vehicle control. Also, group 3 & 4 showed an increase in water consumption as compared to Group 1.Conclusions: Our study recommends that drugs acting on glutamate pathways like ceftriaxone and ampicillin can be explored for treatment of alcohol dependence.

Increased Extracellular Glutamate In the Nucleus Accumbens Promotes Excessive Ethanol Drinking in Ethanol Dependent Mice

Using a well-established model of ethanol dependence and relapse, this study examined adaptations in glutamatergic transmission in the nucleus accumbens (NAc) and their role in regulating voluntary ethanol drinking. Mice were first trained to drink ethanol in a free-choice, limited access (2 h/day) paradigm. One group (EtOH mice) received repeated weekly cycles of chronic intermittent ethanol (CIE) exposure with intervening weeks of test drinking sessions, whereas the remaining mice (CTL mice) were similarly treated but did not receive CIE treatment. Over repeated cycles of CIE exposure, EtOH mice exhibited significant escalation in drinking (up to ∼3.5 g/kg), whereas drinking remained relatively stable at baseline levels (2-2.5 g/kg) in CTL mice. Using in vivo microdialysis procedures, extracellular glutamate (GLUEX) levels in the NAc were increased approximately twofold in EtOH mice compared with CTL mice, and this difference was observed 7 days after final CIE exposure, indicating that this hyperglutamatergic state persisted beyond acute withdrawal. This finding prompted additional studies examining the effects of pharmacologically manipulating GLUEX in the NAc on ethanol drinking in the CIE model. The non-selective glutamate reuptake antagonist, threo-β-benzyloxyaspartate (TBOA), was bilaterally microinjected into the NAc and found to dose-dependently increase drinking in nondependent (CTL) mice to levels attained by dependent (EtOH) mice. TBOA also further increased drinking in EtOH mice. In contrast, reducing glutamatergic transmission in the NAc via bilateral injections of the metabotropic glutamate receptor-2/3 agonist LY379268 reduced drinking in dependent (EtOH) mice to nondependent (CTL) levels, whereas having a more modest effect in decreasing ethanol consumption in CTL mice. Taken together, these data support an important role of glutamatergic transmission in the NAc in regulating ethanol drinking. Additionally, these results indicate that ethanol dependence produces adaptations that favor elevated glutamate activity in the NAc which, in turn, promote excessive levels of ethanol consumption associated with dependence.

Ethanol self‐administration in serotonin transporter knockout mice: unconstrained demand and elasticity

Low serotonin function is associated with alcoholism, leading to speculation that increasing serotonin function could decrease ethanol consumption. Mice with one or two deletions of the serotonin transporter (SERT) gene have increased extracellular serotonin. To examine the relationship between SERT genotype and motivation for alcohol, we compared ethanol self-administration in mice with zero (knockout, KO), one (HET) or two copies (WT) of the SERT gene. All three genotypes learned to self-administer ethanol. The SSRI, fluvoxamine, decreased responding for ethanol in the HET and WT, but not the KO mice. When tested under a progressive ratio schedule, KO mice had lower breakpoints than HET or WT. As work requirements were increased across sessions, behavioral economic analysis of ethanol self-administration indicated that the decreased breakpoint in KO as compared to HET or WT mice was a result of lower levels of unconstrained demand, rather than differences in elasticity, i.e. the proportional decreases in ethanol earned with increasing work requirements were similar across genotypes. The difference in unconstrained demand was unlikely to result from motor or general motivational factors, as both WT and KO mice responded at high levels for a 50% condensed milk solution. As elasticity is hypothesized to measure essential value, these results indicate that KO value ethanol similarly to WT or HET mice despite having lower break points for ethanol.

Reverse Pharmacogenetic Modulation of the Nucleus Accumbens Reduces Ethanol Consumption in a Limited Access Paradigm

Bilateral stereotactic lesioning of the nucleus accumbens (NAc) core reduces relapse rates in alcohol-dependent patients but may cause irreversible cognitive deficits. Deep brain stimulation has similar effects but requires costly implanted hardware and regular surgical maintenance. Therefore, there is considerable interest in refining these approaches to develop reversible, minimally invasive treatments for alcohol dependence. Toward this end, we evaluated the feasibility of a reverse pharmacogenetic approach in a preclinical mouse model. We first assessed the predictive validity of a limited access ethanol consumption paradigm by confirming that electrolytic lesions of the NAc core decreased ethanol consumption, recapitulating the effects of similar lesions in humans. We then used this paradigm to test the effect of modulating activity in the NAc using the Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) hM3Dq and hM4Di. We found that increasing activity with hM3Dq had no effect, but suppressing activity with hM4Di reduced alcohol consumption to a similar extent as lesioning without affecting consumption of water or sucrose. These results may represent early steps toward a novel neurosurgical treatment modality for alcohol dependence that is reversible and externally titratable, yet highly targetable and less invasive than current approaches such as lesioning or deep brain stimulation.

Role of phosphodiesterase‐4 (PDE4) in alcohol‐ and heroinseeking behavior

Cyclic AMP (cAMP) signaling is important in mediating drug abuse and dependence, including alcoholism. As a critical controller of intracellular cAMP levels in the brain, phosphodiesterase‐4 (PDE4), an enzyme that specifically hydrolyzes cAMP, may play a role in drug dependence. Here we examined the effects of rolipram, a selective PDE4 inhibitor, on alcohol or heroin seeking behavior in mice and/or rats. Treatment with rolipram (0.1–0.5 mg/kg) decreased ethanol (7–12%) intake and preference in high alcohol preferring mice and rats in two‐bottle choice and/or ethanol drink‐in‐dark tests. Deficiency of PDE4B diminished rolipram‐induced decreases in ethanol consumption in mice. In addition, rolipram (0.025–0.05) also decreased ethanol responses in operant self‐administration in rats. Further, in heroin self‐administration, rolipram (0.03–0.3 mg/kg) decreased cues‐ or heroin priming‐induced responses, but did not alter responses to heroin injections. These results suggest that PDE4 plays an important role in the regulation of ethanol‐ and heroin‐seeking behaviors, which are attenuated by PDE4 inhibitors such as rolipram. Targeting PDE4, in particular PDE4B, may be an efficient approach for treatment alcoholism and heroin dependence [This work was supported by research grants from NIH/NIAAA (AA020042; to HTZ), National Nature Science Foundation of China (30870894; to JHL/81071077; to WHZ), and National Basic Research Program of China (2009CB522008; to WHZ)].

Mutation of a Zinc-Binding Residue in the Glycine Receptor α1 Subunit Changes Ethanol Sensitivity In Vitro and Alcohol Consumption In Vivo

Ethanol is a widely used drug, yet an understanding of its sites and mechanisms of action remains incomplete. Among the protein targets of ethanol are glycine receptors (GlyRs), which are potentiated by millimolar concentrations of ethanol. In addition, zinc ions also modulate GlyR function, and recent evidence suggests that physiologic concentrations of zinc enhance ethanol potentiation of GlyRs. Here, we first built a homology model of a zinc-bound GlyR using the D80 position as a coordination site for a zinc ion. Next, we investigated in vitro the effects of zinc on ethanol action at recombinant wild-type (WT) and mutant α1 GlyRs containing the D80A substitution, which eliminates zinc potentiation. At D80A GlyRs, the effects of 50 and 200 mM ethanol were reduced as compared with WT receptors. Also, in contrast to what was seen with WT GlyRs, neither adding nor chelating zinc changed the magnitude of ethanol enhancement of mutant D80A receptors. Next, we evaluated the in vivo effects of the D80A substitution by using heterozygous Glra1(D80A) knock-in (KI) mice. The KI mice showed decreased ethanol consumption and preference, and they displayed increased startle responses compared with their WT littermates. Other behavioral tests, including ethanol-induced motor incoordination and strychnine-induced convulsions, revealed no differences between the KI and WT mice. Together, our findings indicate that zinc is critical in determining the effects of ethanol at GlyRs and suggest that zinc binding at the D80 position may be important for mediating some of the behavioral effects of ethanol action at GlyRs.

MC4-R signaling within the nucleus accumbens shell, but not the lateral hypothalamus, modulates ethanol palatability in rats

The Melanocortin (MC) system is one of the crucial neuropeptidergic systems that modulate energy balance. The roles of endogenous MC and MC-4 receptor (MC4-R) signaling within the hypothalamus in the control of homeostatic aspects of feeding are well established. Additional evidence points to a key role for the central MC system in ethanol consumption. Recently, we have shown that nucleus accumbens (NAc), but not lateral hypothalamic (LH), infusion of a selective MC4-R agonist decreases ethanol consumption. Given that MC signaling might contribute to non-homeostatic aspects of feeding within limbic circuits, we assessed here whether MC4-R signaling within the NAc and the lateral hypothalamus (LH) alters normal ingestive hedonic and/or aversive responses to ethanol in rats as measured by a taste reactivity test. Adult male Sprague-Dawley rats were given NAc- or LH- bilateral infusion of the selective MC4-R agonist cyclo (NH-CH2-CH2-CO-His-D-Phe-Arg-Trp-Glu)-NH2 (0, 0.75 or 1.5μg/0.5μl/site) and following 30min, the animals received 1ml of ethanol solution (6% w/v) intraoral for 1minute and aversive and hedonic behaviors were recorded. We found that NAc-, but not LH-administration, of a selective MC4-R agonist decreased total duration of hedonic reactions and significantly increased aversive reactions relative to saline-infused animals which support the hypothesis that MC signaling within the NAc may contribute to ethanol consumption by modulating non-homeostatic aspects (palatability) of intake.

Disruption of Phosphodiesterase-4 (PDE4) Subtypes to Reduce Ethanol Consumption

Cyclic AMP (cAMP)-protein kinase A (PKA) signaling has been implicated in regulating alcohol consumption. Our previous studies showed that inhibitors of phosphodiesterase-4 (PDE4) increased cAMP in the brain and decreased ethanol intake in the two-bottle choice test in mice. However, since there are no selective inhibitors of individual PDE4 subtypes (PDE4A-D), it is not known which PDE4 subtype(s) is (are) involved. Using mice deficient in PDE4A, PDE4B, or PDE4D, the major PDE4 subtypes in the brain, we determined the contributions of individual PDE4 subtypes to ethanol intake and preference. Mice deficient in either PDE4A or PDE4B displayed decreases in ethanol (7–12%) intake and ethanol preference by more than 50% relative to wild-type controls in the two-bottle choice test. They also exhibited decreases in ethanol intake in the ethanol (9%) drinking-in-the-dark paradigm. In contrast, mice deficient in PDE4D showed only slight decreases in ethanol consumption. Sucrose (2% and 4%) intake was also decreased in mice deficient in PDE4A or PDE4B relative to WT controls, but quinine intake was not changed between the genotypes. Therefore, both PDE4A and PDE4B appear to be important PDE4 subtypes in the regulation of ethanol consumption. Selective inhibitors of PDE4A or PDE4B may be used for treatment of alcohol dependence.