The acute anti-craving effect of acamprosate in alcohol-preferring rats is associated with modulation of the mesolimbic dopamine system

Acamprosate reduces ethanol intake in the rat by a combined action of different drug components

Alcohol misuse accounts for a sizeable proportion of the global burden of disease, and Campral® (acamprosate; calcium-bis-(N-acetylhomotaurinate)) is widely used as relapse prevention therapy. The mechanism underlying its effect has in some studies been attributed to the calcium moiety and not to the N-acetylhomotaurine part of the compound. We recently suggested that the dopamine elevating effect of acamprosate is mediated both by N-acetylhomotaurine and calcium in a glycine receptor dependent manner. Here we aimed to explore, by means of in vivo microdialysis, if our previous study using local administration was functionally relevant and if systemic administration of the sodium salt of N-acetylhomotaurine (sodium acamprosate; 200 mg/kg, i.p.) enhanced the effects of calcium chloride (CaCl2; 73.5 mg/kg, i.p.) on nucleus accumbens (nAc) dopamine and/or taurine levels in male Wistar rats. In addition, we investigated the impact of regular acamprosate and the combination of CaCl2 and N-acetylhomotaurine on the alcohol deprivation effect (ADE). Finally, we assessed if N-acetylhomotaurine potentiates the ethanol-intake reducing effect of CaCl2 in a two-bottle choice voluntary ethanol consumption model followed by an ADE paradigm. Systemic administration of regular acamprosate, sodium acamprosate and CaCl2 all trended to increase nAc dopamine whereas the combination of CaCl2 and sodium acamprosate produced a significant increase. Sodium acamprosate elevated extracellular taurine levels without additional effects of CaCl2. Ethanol intake was significantly reduced by systemic administration of CaCl2 without additional effects of the combination of CaCl2 and sodium acamprosate. Both acamprosate and CaCl2 combined with sodium acamprosate blocked the ADE following acute treatment. The data presented suggest that CaCl2 and N-acetylhomotaurine act in concert on a neurochemical level, but calcium appears to have the predominant effect on ethanol intake.

Genetic Addiction Risk and Psychological Profiling Analyses for "Preaddiction" Severity Index

Since 1990, when our laboratory published the association of the DRD2 Taq A1 allele and severe alcoholism in JAMA, there has been an explosion of genetic candidate association studies, including genome-wide association studies (GWAS). To develop an accurate test to help identify those at risk for at least alcohol use disorder (AUD), a subset of reward deficiency syndrome (RDS), Blum's group developed the genetic addiction risk severity (GARS) test, consisting of ten genes and eleven associated risk alleles. In order to statistically validate the selection of these risk alleles measured by GARS, we applied strict analysis to studies that investigated the association of each polymorphism with AUD or AUD-related conditions, including pain and even bariatric surgery, as a predictor of severe vulnerability to unwanted addictive behaviors, published since 1990 until now. This analysis calculated the Hardy-Weinberg Equilibrium of each polymorphism in cases and controls. Pearson's χ2 test or Fisher's exact test was applied to compare the gender, genotype, and allele distribution if available. The statistical analyses found the OR, 95% CI for OR, and the post risk for 8% estimation of the population's alcoholism prevalence revealed a significant detection. Prior to these results, the United States and European patents on a ten gene panel and eleven risk alleles have been issued. In the face of the new construct of the "preaddiction" model, similar to "prediabetes", the genetic addiction risk analysis might provide one solution missing in the treatment and prevention of the neurological disorder known as RDS.

mGlu2 mechanism-based interventions to treat alcohol relapse

Recently we identified a deficiency in metabotropic glutamate receptor 2 (mGlu2) function in the corticoaccumbal pathway, as a common pathological mechanism underlying alcohol-seeking and relapse behavior. Based on this mechanism, we hypothesized that mGlu2/3 agonists and mGlu2 positive allosteric modulators (PAMs) may be effective in reducing relapse-like behavior. Two mGlu2/3 agonists, LY379268 and LY354740 (a structural analog of LY379268 six-fold more potent in activating mGlu2 over mGluR3), were tested in a well-established rat model of relapse, the alcohol deprivation effect (ADE) with repeated deprivation phases. Since these agonists do not readily discriminate between contributions of mGlu2 and mGluR3, we also tested LY487379, a highly specific PAM that potentiates the effect of glutamate on the mGlu2 with less specificity on other mGlu receptor subtypes. Both LY379268 and LY354740 significantly and dose-dependently reduced the expression of the ADE. No significant changes in water intake, body weight and locomotor activity were observed. Importantly, repeated administration of mGlu2/3 agonist did not lead to tolerance development. mGlu2 PAM LY487379 treatment significantly reduced expression of the ADE in both male and female rats. Combination treatment of mGlu2/3 agonist and PAM had similar effect on relapse-like drinking to that seen in mGlu2/3 agonist treatment alone. Together with other preclinical data showing that PAMs can reduce alcohol-seeking behavior we conclude that mGlu2 PAMs should be considered for clinical trials in alcohol-dependent patients.

Sodium acamprosate and calcium exert additive effects on nucleus accumbens dopamine in the rat

Acamprosate (Campral® – calcium‐bis[N‐acetylhomotaurinate]) is one of few available pharmacotherapies for individuals suffering from alcohol use disorder. Previously, we suggested that acamprosate reduces ethanol intake by increasing dopamine in the nucleus accumbens (nAc), thereby partly substituting for alcohol's dopamine releasing effect. An experimental study suggested the calcium moiety of acamprosate to be the active component of the drug and to mediate the relapse preventing effect. The aim of the present study was to, by means of reversed in vivo microdialysis, elucidate if the dopamine elevating properties of acamprosate are mediated by N‐acetylhomotaurine or by the calcium moiety. Male rats were equipped with a microdialysis probe in the nAc and received acute local treatment with regular acamprosate (CaAcamp 0.5 mM), calcium chloride (CaCl₂ 0.5 mM), sodium acamprosate (NaAcamp 0.5–1 mM), the glycine receptor (GlyR) antagonist strychnine (Stry 20 μM), or vehicle. In all experiments, extracellular levels of dopamine and taurine were examined. We found that local perfusion with both CaAcamp and CaCl₂ increased dopamine levels in a GlyR‐dependent manner. NaAcamp did not influence dopamine levels, but concomitant administration with CaCl₂ resulted in an additive dopamine output compared to the drugs administrated alone. We also found CaAcamp and the combination of CaCl₂ and NaAcamp to increase accumbal taurine levels, suggesting that CaAcamp may act indirectly on GlyRs via taurine release. The present results indicate that both N‐acetylhomotaurine and the calcium moiety of acamprosate have dopamine elevating properties within the nAc and that, in this respect, these substances are beneficial in combination.

Statistical Validation of Risk Alleles in Genetic Addiction Risk Severity (GARS) Test: Early Identification of Risk for Alcohol Use Disorder (AUD) in 74,566 Case–Control Subjects

Since 1990, when our laboratory published the association of the DRD2 Taq A1 allele and severe alcoholism in JAMA, there has been an explosion of genetic candidate association studies, including GWAS. To develop an accurate test to help identify those at risk for at least Alcohol Use Disorder (AUD), Blum’s group developed the Genetic Addiction Risk Severity (GARS) test, consisting of ten genes and eleven associated risk alleles. In order to statistically validate the selection of these risk alleles measured by GARS, we applied strict analysis to studies that investigated the association of each polymorphism with AUD or AUD-related conditions published from 1990 until 2021. This analysis calculated the Hardy–Weinberg Equilibrium of each polymorphism in cases and controls. If available, the Pearson’s χ2 test or Fisher’s exact test was applied to comparisons of the gender, genotype, and allele distribution. The statistical analyses found the OR, 95% CI for OR, and a post-risk for 8% estimation of the population’s alcoholism prevalence revealed a significant detection. The OR results showed significance for DRD2, DRD3, DRD4, DAT1, COMT, OPRM1, and 5HTT at 5%. While most of the research related to GARS is derived from our laboratory, we are encouraging more independent research to confirm our findings.

Relapse prevention for alcohol use disorders: combined acamprosate and cue exposure therapy as aftercare

AIMS

Many patients with alcohol use disorders are challenged by cravings leading to repeated relapses. Both cue exposure therapy (CET) and acamprosate target alcohol cravings and are often combined (CET + acamprosate). The main aim of this study was to investigate whether aftercare treatment consisting of CET combined with acamprosate is equivalent to (A) CET as monotherapy, (B) aftercare as usual (AAU) as monotherapy or (C) AAU combined with acamprosate.

METHODS

Patients were randomized to receive either CET with urge-specific coping skills (USCS) as aftercare or AAU. Acamprosate prescription data were extracted from patient case records. Alcohol consumption, cravings, and USCS were assessed at pre-aftercare, post-aftercare, and 6-month follow-up.

RESULTS

Overall, patients increased their alcohol consumption during and following aftercare treatment, thereby relapsing despite any treatment. However, CET + acamprosate achieved greater abstinence compared to AAU + acamprosate at follow-up (p=.047). CET + acamprosate also reduced number of drinking days (p=.020) and number of days with excessive drinking (p=.020) at post-aftercare, when compared to AAU monotherapy. CET monotherapy increased sensible drinking at post-aftercare compared to AAU monotherapy (p=.045) and AAU + acamprosate (p=.047). Only CET monotherapy showed improvement in cravings, when compared to AAU at follow-up (mean urge level: p=.032; peak urge level: p=.014).

CONCLUSION

The study showed that CET both as monotherapy and combined with acamprosate was superior to AAU monotherapy and AAU + acamprosate in reducing alcohol consumption. Only CET + acamprosate was capable of reducing alcohol consumption in the longer term, indicating that anti-craving medication may not impede CET from exerting an effect on alcohol consumption. Trial registration: ClinicalTrials.gov ID: NCT02298751 (24/11-2014).

A Novel Precision Approach to Overcome the "Addiction Pandemic" by Incorporating Genetic Addiction Risk Severity (GARS) and Dopamine Homeostasis Restoration

This article describes a unique therapeutic precision intervention, a formulation of enkephalinase inhibitors, enkephalin, and dopamine-releasing neuronutrients, to induce dopamine homeostasis for detoxification and treatment of individuals genetically predisposed to developing reward deficiency syndrome (RDS). The formulations are based on the results of the addiction risk severity (GARS) test. Based on both neurogenetic and epigenetic evidence, the test evaluates the presence of reward genes and risk alleles. Existing evidence demonstrates that the novel genetic risk testing system can successfully stratify the potential for developing opioid use disorder (OUD) related risks or before initiating opioid analgesic therapy and RDS risk for people in recovery. In the case of opioid use disorders, long-term maintenance agonist treatments like methadone and buprenorphine may create RDS, or RDS may have been in existence, but not recognized. The test will also assess the potential for benefit from medication-assisted treatment with dopamine augmentation. RDS methodology holds a strong promise for reducing the burden of addictive disorders for individuals, their families, and society as a whole by guiding the restoration of dopamine homeostasisthrough anti-reward allostatic neuroadaptations. WC 175.

Genetically selected alcohol-preferring msP rats to study alcohol use disorder: Anything lost in translation?

For several decades, genetically selected alcohol-preferring rats have been successfully used to mimic and study alcohol use disorders (AUD). These rat lines have been instrumental in advancing our understanding of the neurobiology of alcoholism and enabling pharmacological studies to evaluate drug efficacy on alcohol drinking and relapse. Moreover, the results of these studies have identified genetic variables that are linked to AUD vulnerability. This is an up-to-date review that focuses on genetically selected Marchigian Sardinian alcohol-preferring (msP) rats. To support the translational relevance of the findings that are obtained from msP rats and highlight important similarities to AUD patients, we also discuss the results of recent brain imaging studies. Finally, to demonstrate the importance of studying sex differences in animal models of AUD, we present original data that highlight behavioral differences in the response to alcohol in male and female rats. Female msP rats exhibited higher alcohol consumption compared with males. Furthermore, msP rats of both sexes exhibit higher anxiety- and depressive-like behaviors in the elevated plus maze and forced swim test, respectively, compared with unselected Wistar controls. Notably, voluntary alcohol drinking decreases foot-shock stress and depressive-like behavior in both sexes, whereas anxiety-like behavior in the elevated plus maze is attenuated only in males. These findings suggest that male and female msP rats both drink high amounts of alcohol to self-medicate negative affective symptoms. For females, this behavior may be driven by an attempt to treat stress and depressive-like conditions. For males, generalized anxiety appears to be an important additional factor in the motivation to drink alcohol. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'

Building better strategies to develop new medications in Alcohol Use Disorder: Learning from past success and failure to shape a brighter future

Alcohol Use Disorder (AUD) is a chronic disease that develops over the years. The complexity of the neurobiological processes contributing to the emergence of AUD and the neuroadaptive changes occurring during disease progression make it difficult to improve treatments. On the other hand, this complexity offers researchers the possibility to explore new targets. Over years of intense research several molecules were tested in AUD; in most cases, despite promising preclinical data, the clinical efficacy appeared insufficient to justify futher development. A prototypical example is that of corticotropin releasing factor type 1 receptor (CRF1R) antagonists that showed significant effectiveness in animal models of AUD but were largely ineffective in humans. The present article attempts to analyze the most recent venues in the development of new medications in AUD with a focus on the most promising drug targets under current exploration. Moreover, we delineate the importance of using a more integrated translational framework approach to correlate preclinical findings and early clinical data to enhance the probability to validate biological targets of interest.

Acamprosate's ethanol intake-reducing effect is associated with its ability to increase dopamine

Previous studies indicate that the anti-craving substance acamprosate modulates nucleus accumbens (nAc) dopamine levels via a dopamine-controlling nAc-VTA-nAc neurocircuitry. It was demonstrated that glycine receptors in the nAc are involved both in the dopamine-elevating effect and the ethanol intake-reducing effect of the drug. Here we wanted to explore the interaction of ethanol and acamprosate on nAc dopamine and investigate whether dopaminergic transmission may be related to the ethanol intake-reducing effects. In three separate studies we investigated nAc extracellular dopamine levels by means of in vivo microdialysis after administration of acamprosate and ethanol in 1) naïve rats, 2) rats pre-treated with acamprosate for two days or 3) ethanol medium- and high-preferring rats receiving ten days of acamprosate pre-treatment. In the first two studies, acamprosate elevated dopamine and simultaneously prevented ethanol from further increasing dopamine output. In the third study, long-term acamprosate pre-treatment produced a loss of the ethanol intake-reducing as well as the dopamine-elevating effects of acamprosate, and the dopamine elevating property of ethanol was restored. We suggest that acamprosate may partly substitute for the dopamine-elevating effect of ethanol but once tolerance develops to this effect, the ability to decrease ethanol intake is lost.

Rat animal models for screening medications to treat alcohol use disorders

The purpose of this review is to present animal research models that can be used to screen and/or repurpose medications for the treatment of alcohol abuse and dependence. The focus will be on rats and in particular selectively bred rats. Brief introductions discuss various aspects of the clinical picture, which provide characteristics of individuals with alcohol use disorders (AUDs) to model in animals. Following this, multiple selectively bred rat lines will be described and evaluated in the context of animal models used to screen medications to treat AUDs. Next, common behavioral tests for drug efficacy will be discussed particularly as they relate to stages in the addiction cycle. Tables highlighting studies that have tested the effects of compounds using the respective techniques are included. Wherever possible the Tables are organized chronologically in ascending order to describe changes in the focus of research on AUDs over time. In general, high ethanol-consuming selectively bred rats have been used to test a wide range of compounds. Older studies usually followed neurobiological findings in the selected lines that supported an association with a propensity for high ethanol intake. Most of these tests evaluated the compound's effects on the maintenance of ethanol drinking. Very few compounds have been tested during ethanol-seeking and/or relapse and fewer still have assessed their effects during the acquisition of AUDs. Overall, while a substantial number of neurotransmitter and neuromodulatory system targets have been assessed; the roles of sex- and age-of-animal, as well as the acquisition of AUDs, ethanol-seeking and relapse continue to be factors and behaviors needing further study. This article is part of the Special Issue entitled "Alcoholism".

The Nicotinic α6-Subunit Selective Antagonist bPiDI Reduces Alcohol Self-Administration in Alcohol-Preferring Rats

Cigarettes and alcohol are the most abused substances in the world and are commonly co-abused. Nicotine primarily acts in the brain on nicotinic acetylcholine receptors (nAChR), which are also a target for alcohol. The alpha6 subunit of nAChR is expressed almost exclusively in the brain reward system and may modulate the rewarding properties of alcohol and nicotine. Recently, N,N-decane-1,10-diyl-bis-3-picolinium diiodide (bPiDI) was synthesized as a selective, brain penetrant α6 subunit antagonist that reduces nicotine self-administration. The current study aimed to examine the effects of bPiDI on alcohol self-administration in inbred alcohol-preferring (iP) rats. Adult, male iP rats were trained to self-administer alcohol or sucrose. Once stable responding was achieved, rats were injected with bPiDI (1, 3 mg/kg, i.p.) and tested for self-administration under fixed and progressive ratio schedules of reinforcement. They subsequently underwent extinction, in which no rewards or cues were presented in the operant chambers. Then, they were injected with bPiDI prior to testing for cue-induced reinstatement of reward seeking. bPiDI (3 mg/kg) significantly reduced alcohol self-administration in both fixed and progressive ratios without any effects on sucrose self-administration or locomotor activity. In contrast, bPiDI (3 mg/kg) did not inhibit cue-induced reinstatement of either alcohol or sucrose seeking. The results support the involvement of α6 containing nAChR in reinforcing effects of alcohol, but not relapse to alcohol-seeking, without any impact on responding for a natural reward or general activity. bPiDI may be a potential lead molecule for a therapeutic strategy to limit nicotine and alcohol consumption.

Nucleus incertus Orexin2 receptors mediate alcohol seeking in rats

Alcoholism is a chronic relapsing disorder and a major global health problem. Stress is a key precipitant of relapse in human alcoholics and in animal models of alcohol seeking. The brainstem nucleus incertus (NI) contains a population of relaxin-3 neurons that are highly responsive to psychological stressors; and the ascending NI relaxin-3/RXFP3 signalling system is implicated in stress-induced reinstatement of alcohol seeking. The NI receives orexinergic innervation and expresses orexin1 (OX1) and orexin2 (OX2) receptor mRNA. In alcohol-preferring (iP) rats, we examined the impact of yohimbine-induced reinstatement of alcohol seeking on orexin neuronal activation, and the effect of bilateral injections into NI of the OX1 receptor antagonist, SB-334867 (n = 16) or the OX2 receptor antagonist, TCS-OX2-29 (n = 8) on stress-induced reinstatement of alcohol seeking. We also assessed the effects of orexin-A on NI neuronal activity and the involvement of OX1 and OX2 receptors using whole cell patch-clamp recordings in rat brain slices. Yohimbine-induced reinstatement of alcohol seeking activated orexin neurons. Bilateral NI injections of TCS-OX2-29 attenuated yohimbine-induced reinstatement of alcohol seeking. In contrast, intra-NI injection of SB-334867 had no significant effect. In line with these data, orexin-A (600 nM) depolarized a majority of NI neurons recorded in coronal brain slices (18/28 cells), effects prevented by bath application of TCS-OX2-29 (10 μM), but not SB-334867 (10 μM). These data suggest an excitatory orexinergic input to NI contributes to yohimbine-induced reinstatement of alcohol seeking, predominantly via OX2 receptor signalling.

Orexin-1 receptor signalling in the prelimbic cortex and ventral tegmental area regulates cue-induced reinstatement of ethanol-seeking in iP rats

Orexins (hypocretins) are hypothalamic neuropeptides that innervate the entire neuraxis, including the prelimbic cortex and ventral tegmental area and have been implicated in ethanol-seeking behaviour. The present study aimed to use the orexin-1 (OX1 ) receptor antagonist SB-334867 to examine the role of prelimbic cortex and ventral tegmental area OX1 receptors in cue-induced reinstatement of ethanol-seeking. Ethanol-preferring rats (iP) rats were trained to self-administer ethanol (10 percent v/v, FR3) or sucrose (0.2-1 percent w/v, FR3) in the presence of reward-associated cues before being implanted with indwelling guide cannulae. Rats then underwent extinction training for 11 days. On test days, rats were given a microinjection of vehicle or SB-334867 (3 μg/side) and presented with reward-associated cues to precipitate reinstatement. Results show SB-334867 infused into the prelimbic cortex attenuated cue-induced reinstatement of ethanol-seeking, but not sucrose-seeking. OX1 antagonism in the ventral tegmental area also attenuated cue-induced reinstatement of ethanol-seeking. These findings suggest that OX1 receptors located in the prelimbic cortex and ventral tegmental area are part of a circuit driving cue-mediated ethanol-seeking behaviour.

Combination of acamprosate and baclofen as a promising therapeutic approach for Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterised by the loss of dopaminergic nigrostriatal neurons but which involves the loss of additional neurotransmitter pathways. Mono- or polytherapeutic interventions in PD patients have declining efficacy long-term and no influence on disease progression. The systematic analysis of available genetic and functional data as well as the substantial overlap between Alzheimer’s disease (AD) and PD features led us to repurpose and explore the effectiveness of a combination therapy (ABC) with two drugs – acamprosate and baclofen – that was already effective in AD animal models, for the treatment of PD. We showed in vitro that ABC strongly and synergistically protected neuronal cells from oxidative stress in the oxygen and glucose deprivation model, as well as dopaminergic neurons from cell death in the 6-hydroxydopamine (6-OHDA) rat model. Furthermore, we showed that ABC normalised altered motor symptoms in vivo in 6-OHDA-treated rats, acting by protecting dopaminergic cell bodies and their striatal terminals. Interestingly, ABC also restored a normal behaviour pattern in lesioned rats suggesting a symptomatic effect, and did not negatively interact with L-dopa. Our results demonstrate the potential value of combining repurposed drugs as a promising new strategy to treat this debilitating disease.

Assessing ethanol's actions in the suprachiasmatic circadian clock using in vivo and in vitro approaches

Research over the past decade has demonstrated substantial interactions between the circadian system and the processes through which alcohol affects behavior and physiology. Here we summarize the results of our collaborative efforts focused on this intersection. Using a combination of in vivo and in vitro approaches, we have shown that ethanol affects many aspects of the mammalian circadian system, both acutely as well as after chronic administration. Conversely, we have shown circadian influences on ethanol consumption. Importantly, we are beginning to delve into the cellular mechanisms associated with these effects. We are also starting to form a picture of the neuroanatomical bases for many of these actions. Finally, we put our current findings into perspective by suggesting new avenues of inquiry for our future efforts.

The development of acamprosate as a treatment against alcohol relapse

INTRODUCTION

Globally, alcohol abuse and dependence are significant contributors to chronic disease and injury and are responsible for nearly 4% of all deaths annually. Acamprosate (Campral), one of only three pharmacological treatments approved for the treatment of alcohol dependence, has shown mixed efficacy in clinical trials in maintaining abstinence of detoxified alcoholics since studies began in the 1980s. Yielding inconsistent results, these studies have prompted skepticism.

AREAS COVERED

Herein, the authors review the preclinical studies which have assessed the efficacy of acamprosate in various animal models of alcohol dependence and discuss the disparate findings from the major clinical trials. Moreover, the authors discuss the major limitations of these preclinical and clinical studies and offer explanations for the often-contradictory findings. The article also looks at the importance of the calcium moiety that accompanies the salt form of acamprosate and its relevance to its activity.

EXPERT OPINION

The recent discovery that large doses of calcium largely duplicate the effects of acamprosate in animal models has introduced a serious challenge to the widely held functional association between this drug and the glutamate neurotransmission system. Future research on acamprosate or newer pharmacotherapeutics should consider assessing plasma and/or brain levels of calcium as a correlate or mediating factor in anti-relapse efficacy. Further, preclinical research on acamprosate has thus far lacked animal models of chemical dependence on alcohol, and the testing of rodents with histories of alcohol intoxication and withdrawal is suggested.

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

AIM

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.

METHODS

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.

RESULTS

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.

CONCLUSION

BRU selectively decreases ethanol consumption with minimal adverse effects. Therefore, BRU may represent a new pharmacotherapy for alcoholism.

Acamprosate produces its anti-relapse effects via calcium

Alcoholism is one of the most prevalent neuropsychiatric diseases, having an enormous health and socioeconomic impact. Along with a few other medications, acamprosate (Campral-calcium-bis (N-acetylhomotaurinate)) is clinically used in many countries for relapse prevention. Although there is accumulated evidence suggesting that acamprosate interferes with the glutamate system, the molecular mode of action still remains undefined. Here we show that acamprosate does not interact with proposed glutamate receptor mechanisms. In particular, acamprosate does not interact with NMDA receptors or metabotropic glutamate receptor group I. In three different preclinical animal models of either excessive alcohol drinking, alcohol-seeking, or relapse-like drinking behavior, we demonstrate that N-acetylhomotaurinate by itself is not an active psychotropic molecule. Hence, the sodium salt of N-acetylhomotaurinate (i) is ineffective in alcohol-preferring rats to reduce operant responding for ethanol, (ii) is ineffective in alcohol-seeking rats in a cue-induced reinstatement paradigm, (iii) and is ineffective in rats with an alcohol deprivation effect. Surprisingly, calcium salts produce acamprosate-like effects in all three animal models. We conclude that calcium is the active moiety of acamprosate. Indeed, when translating these findings to the human situation, we found that patients with high plasma calcium levels due to acamprosate treatment showed better primary efficacy parameters such as time to relapse and cumulative abstinence. We conclude that N-acetylhomotaurinate is a biologically inactive molecule and that the effects of acamprosate described in more than 450 published original investigations and clinical trials and 1.5 million treated patients can possibly be attributed to calcium.

Central orexin (hypocretin) 2 receptor antagonism reduces ethanol self-administration, but not cue-conditioned ethanol-seeking, in ethanol-preferring rats

Orexins are hypothalamic neuropeptides which bind to two G-protein-coupled receptors, orexin-1 (OX(1)R) and orexin-2 (OX(2)R) receptor. While a role for OX(1)R has been established in both ethanol reinforcement and ethanol-seeking behaviour, the role of OX(2)R in these behaviours is relatively less-studied. The aim of this study was to determine the role of central OX(2)R in ethanol-taking and ethanol-seeking behaviour. Indiana ethanol-preferring rats were trained to self-administer ethanol (10% w/v) or sucrose (0.7–1% w/v) in the presence of reward-associated cues before being implanted with indwelling guide cannulae. The selective OX(2)R antagonist TCS-OX2-29 was administered i.c.v. to assess its effect on operant self-administration and cue-induced reinstatement following extinction. Following i.c.v. injection TCS-OX2-29 reduced self-administration of ethanol, but not sucrose. Despite reducing ethanol self-administration, TCS-OX2-29 had no impact on cue-induced reinstatement of ethanol seeking. To determine where in the brain OX(2)R were acting to modulate ethanol self-administration, TCS-OX2-29 was microinjected into either the shell or core of the nucleus accumbens (NAc). Intra-NAc core, but not shell, infusions of TCS-OX2-29 decreased responding for ethanol. Importantly, the doses of TCS-OX2-029 used were non-sedating. Collectively, these findings implicate OX(2)R in the NAc in mediating the reinforcing effects of ethanol. This effect appears to be drug-specific as antagonism of central OX(2)R had no impact on sucrose self-administration. Thus, OX(2)R in addition to OX(1)R may represent a potential therapeutic target for the treatment of ethanol-use disorders. However, unlike OX(1)R, no impact of OX(2)R antagonism was observed on cue-induced reinstatement, suggesting a more prominent role for OX(2)R in ethanol self-administration compared to cue-conditioned ethanol-seeking.

Genetically selected alcohol preferring rats to model human alcoholism

Animal models have been successfully developed to mimic and study alcoholism. These models have the unique feature of allowing the researcher to control for the genetic characteristics of the animal, alcohol exposure and environment. Moreover, these animal models allow pharmacological, neurochemical and behavioral manipulations otherwise impossible. Unquestionably, one of the major contributions to the understanding of the neurobiological basis of alcoholism comes from data that have been obtained from the study of genetically selected alcohol preferring rat lines and from the consequences that alcohol drinking and environmental manipulations, (i.e., protracted alcohol drinking, intoxication, exposure to stress, etc.) have on them. In fact, if on the one hand genetic factors may account for about 50-60% of the risk of developing alcohol dependence, on the other hand protracted alcohol exposure is a necessary precondition to actually develop the disease, while environmental vulnerability factors may be crucial for disease progression. The present article will offer an overview of the different genetically selected alcohol preferring rat lines developed and used to study alcoholism. The predictive, face and construct validity of these animal models and the translational significance of findings achieved through their use will be critically discussed.

Animal models for medications development targeting alcohol abuse using selectively bred rat lines: neurobiological and pharmacological validity

The purpose of this review paper is to present evidence that rat animal models of alcoholism provide an ideal platform for developing and screening medications that target alcohol abuse and dependence. The focus is on the 5 oldest international rat lines that have been selectively bred for a high alcohol-consumption phenotype. The behavioral and neurochemical phenotypes of these rat lines are reviewed and placed in the context of the clinical literature. The paper presents behavioral models for assessing the efficacy of pharmaceuticals for the treatment of alcohol abuse and dependence in rodents, with particular emphasis on rats. Drugs that have been tested for their effectiveness in reducing alcohol/ethanol consumption and/or self-administration by these rat lines and their putative site of action are summarized. The paper also presents some current and future directions for developing pharmacological treatments targeting alcohol abuse and dependence.

The glycine reuptake inhibitor Org24598 and acamprosate reduce ethanol intake in the rat; tolerance development to acamprosate but not to Org24598

Extracellular glycine modulates accumbal dopamine levels as well as ethanol-induced dopamine overflow. Glycine availability is also crucial for regulating alcohol consumption and the glycine transporter 1 (GlyT-1) inhibitor Org25935 robustly decreases alcohol intake in rats. To explore whether the alcohol-intake reducing effect of Org25935 is substance bound, we examined the effect of a different selective GlyT-1 inhibitor, Org24598, on ethanol consumption in rats and compared the effect with that of acamprosate, a drug currently in clinical use. We studied the effects of daily Org24598 and acamprosate injections on male Wistar rats with ~60% ethanol preference in a limited access two bottle free-choice model for 12 days, followed by alcohol deprivation for 14 days before a second test period of 10 days. Finally, rats underwent in vivo microdialysis where dopamine, glycine, taurine and β-alanine in n. accumbens were measured. Org24598 profoundly reduced ethanol intake and the effect remained throughout both treatment periods. Acamprosate promptly reduced ethanol intake, but on the third day tolerance developed to this effect and acamprosate failed to influence alcohol consumption during the second test period. Neither Org24598 nor acamprosate reduced water intake. Following the drinking study, the Org24598 group displayed higher basal accumbal dopamine levels compared with acamprosate and vehicle groups. Both Org24598 and acamprosate reduced the ethanol-induced dopamine response in n. accumbens. The study demonstrates a robust anti-alcohol intake effect of the GlyT-1 inhibitor Org24598, supporting the new concept that GlyT-1 inhibition reduces ethanol consumption. GlyT-1 inhibition may represent a new treatment principle for alcoholism that is superior to acamprosate.

Critical thoughts on current rodent models for evaluating potential treatments of alcohol addiction and withdrawal

Despite years of neurobiological research that have helped to identify potential therapeutic targets, we do not have a reliable pharmacological treatment for alcoholism. There are a range of possible explanations for this failure, including arguments that alcoholism is a spectrum disorder and that different population subtypes may respond to different treatments. This view is supported by categorisations such as early- and late-onset alcoholism, whilst multifactorial genetic factors may also alter responsivity to pharmacological agents. Furthermore, experience of alcohol withdrawal may play a role in future drinking in a way that may distinguish alcoholism from other forms of addiction. Additionally, our neurobiological models, based largely upon results from rodent studies, may not mimic specific aspects of the human condition and may reflect different underlying phenomena and biological processes from the clinical pattern. As a result, potential treatments may be targeting inappropriate aspects of alcohol-related behaviours. Instead, we suggest a more profitable approach is (a) to identify well-defined intermediate behavioural phenotypes in human experimental models that reflect defined aspects of the human clinical disorder and (b) to develop animal models that are homologous with those phenotypes in terms of psychological processes and underlying neurobiological mechanisms. This review describes an array of animal models currently used in the addiction field and what they tell us about alcoholism. We will then examine how established pharmacological agents have been developed using only a limited number of these models, before describing some alternative novel approaches to achieving homology between animal and human experimental measures.

Beer promotes high levels of alcohol intake in adolescent and adult alcohol-preferring rats

Previous studies suggest that high levels of alcohol consumption can be obtained in laboratory rats by using beer as a test solution. The present study extended these observations to examine the intake of beer and equivalent dilute ethanol solutions with an inbred line of alcohol-preferring P rats. In Experiment 1, male adolescent P rats and age-matched Wistar rats had access to either beer or equivalent ethanol solutions for 1h daily in a custom-built lickometer apparatus. In subsequent experiments, adolescent (Experiment 2) and adult (Experiment 3) male P rats were given continuous 24-h home cage access to beer or dilute ethanol solutions, with concomitant access to lab chow and water. In each experiment, the alcohol content of the beer and dilute ethanol solutions was gradually increased from 0.4, 1.4, 2.4, 3.4, 4.4, 5 to 10% EtOH (vol/vol). All three experiments showed a major augmentation of alcohol intake when rats were given beer compared with equivalent ethanol solutions. In Experiment 1, the overall intake of beer was higher in P rats compared with Wistar rats, but no strain difference was found during the 1-h sessions with plain ethanol consumption. Experiment 1 also showed that an alcohol deprivation effect was more readily obtained in rats with a history of consuming beer rather than plain ethanol solutions. In Experiments 2 and 3, voluntary beer intake in P rats represented ethanol intake of 10-15 g/kg/day, among the highest reported in any study with rats. This excessive consumption was most apparent in adolescent rats. Beer consumption markedly exceeded plain ethanol intake in these experiments except at the highest alcohol concentration (10%) tested. The advantage of using beer rather than dilute ethanol solutions in both selected and nonselected rat strains is therefore confirmed. Our findings encourage the use of beer with alcohol-preferring rats in future research that seeks to obtain high levels of alcohol self-administration.

Acamprosate-responsive brain sites for suppression of ethanol intake and preference

Acamprosate suppresses alcohol intake and craving in recovering alcoholics; however, the central sites of its action are unclear. To approach this question, brain regions responsive to acamprosate were mapped using acamprosate microimplants targeted to brain reward and circadian areas implicated in alcohol dependence. mPer2 mutant mice with nonfunctional mPer2, a circadian clock gene that gates endogenous timekeeping, were included, owing to their high levels of ethanol intake and preference. Male wild-type (WT) and mPer2 mutant mice received free-choice (15%) ethanol/water for 3 wk. The ethanol was withdrawn for 3 wk and then reintroduced to facilitate relapse. Four days before ethanol reintroduction, mice received bilateral blank or acamprosate-containing microimplants releasing ∼50 ng/day into reward [ventral tegmental (VTA), peduculopontine tegmentum (PPT), and nucleus accumbens (NA)] and circadian [intergeniculate leaflet (IGL) and suprachiasmatic nucleus (SCN)] areas. The hippocampus was also targeted. Circadian locomotor activity was measured throughout. Ethanol intake and preference were greater in mPer2 mutants than in wild-type (WT) mice (27 g·kg(-1)·day(-1) vs. 13 g·kg(-1)·day(-1) and 70% vs. 50%, respectively; both, P < 0.05). In WTs, acamprosate in all areas, except hippocampus, suppressed ethanol intake and preference (by 40-60%) during ethanol reintroduction. In mPer2 mutants, acamprosate in the VTA, PPT, and SCN suppressed ethanol intake and preference by 20-30%. These data are evidence that acamprosate's suppression of ethanol intake and preference are manifest through actions within major reward and circadian sites.

Discrete cue-conditioned alcohol-seeking after protracted abstinence: pattern of neural activation and involvement of orexin₁ receptors

BACKGROUND AND PURPOSE

The enduring propensity for alcoholics to relapse even following years of abstinence presents a major hurdle for treatment. Here we report a model of relapse following protracted abstinence and investigate the pattern of neuronal activation following cue-induced reinstatement and administration of the orexin₁ receptor antagonist SB-334867 in inbred alcohol-preferring rats.

EXPERIMENTAL APPROACH

Rats were trained to self-administer alcohol under operant conditions and divided into two groups: immediate (reinstated immediately following extinction) and delayed (extinguished and then housed for 5 months before reinstatement). Prior to reinstatement, animals were treated with vehicle (immediate n= 11, delayed n= 11) or SB-334867 (20 mg·kg⁻¹ i.p.; immediate n= 6, delayed n= 11). Fos expression was compared between each group and to animals that underwent extinction only.

KEY RESULTS

SB-334867 significantly attenuated cue-induced reinstatement in both groups. Immediate reinstatement increased Fos expression in the nucleus accumbens (NAc), infra-limbic (IL), pre-limbic (PrL), orbitofrontal (OFC) and piriform cortices, the lateral and dorsomedial hypothalamus, central amygdala and basolateral amygdala (BLA), and the bed nucleus of the stria terminalis. Following delayed reinstatement, Fos expression was further elevated in cortical structures. Concurrent with preventing reinstatement, SB-334867 decreased Fos in NAc core, PrL and OFC following immediate reinstatement. Following protracted abstinence, SB-334867 treatment decreased reinstatement-induced Fos in the PrL, OFC and piriform cortices.

CONCLUSIONS AND IMPLICATIONS

Cue-induced alcohol seeking can be triggered following protracted abstinence in rats. The effects of SB-334867 on both behaviour and Fos expression suggest that the orexin system is implicated in cue-induced reinstatement, although some loci may shift following protracted abstinence.

Translational research in addiction: toward a framework for the development of novel therapeutics

The development of novel substance use disorder (SUD) therapeutics is insufficient to meet the medical needs of a growing SUD patient population. The identification of translatable SUD models and tests is a crucial step in establishing a framework for SUD therapeutic development programs. The present review begins by identifying the clinical features of SUDs and highlights the narrow regulatory end-point required for approval of a novel SUD therapeutic. A conceptual overview of dependence is provided, followed by identification of potential intervention targets in the addiction cycle. The main components of the addiction cycle provide the framework for a discussion of preclinical models and their clinical analogs, all of which are focused on isolated behavioral end-points thought to be relevant to the persistence of compulsive drug use. Thus, the greatest obstacle to successful development is the gap between the multiplicity of preclinical and early clinical end-points and the regulatory end-point of sustained abstinence. This review proposes two pathways to bridging this gap: further development and validation of the preclinical extended access self-administration model; inclusion of secondary end-points comprising all of the measures highlighted in the present discussion in Phase 3 trials. Further, completion of the postdictive validation of analogous preclinical and clinical assays is of high priority. Ultimately, demonstration of the relevance and validity of a variety of end-points to the ultimate goal of abstinence will allow researchers to identify truly relevant therapeutic mechanisms and intervention targets, and establish a framework for SUD therapeutic development that allows optimal decision-making and resource allocation.

Glycine transporter-1 blockade leads to persistently reduced relapse-like alcohol drinking in rats

BACKGROUND

Residual dysfunction of multiple neurotransmitter systems due to chronic alcohol use is likely responsible for the occurrence of compulsive alcohol seeking during abstinence and relapse behavior. There is increasing evidence that glycine, which activates both glycine and N-methyl-D-aspartate receptors, contributes to excessive alcohol consumption. We therefore hypothesized that the blockade of glycine transporter 1 might interfere with compulsive alcohol consumption and relapse behavior.

METHODS

We used our animal model of alcoholism--long-term alcohol consumption with repeated deprivation phases in rats--to study the effects of a selective blocker of glycine transporter 1 Org25935. The abstinence-promoting drug acamprosate was used as a reference compound. Subsequently, we examined alterations in dorsal striatal gene expression caused by chronic ethanol (EtOH) consumption, focusing on glycinergic and glutamatergic signaling-related genes. Gene expression profiles of Org25935-treated EtOH-drinking rats were compared with vehicle-treated EtOH-drinking versus age-matched EtOH-naive rats.

RESULTS

We found that repeated treatment with Org25935 reduced compulsive relapse-like drinking without the development of tolerance. Importantly, these antirelapse properties were maintained for at least 6 weeks in a treatment-free period. This persistent effect was paralleled by a reversal of altered expression levels of a set of glycinergic and glutamatergic signaling-related genes to the levels found in EtOH-naive control rats.

CONCLUSIONS

This study shows that treatment of rats with Org25935 leads to a reduction of compulsive alcohol consumption and relapse-like drinking behavior--an effect that persists into treatment-free periods. This long-term antirelapse effect might result from a restoration of normal glycinergic and glutamatergic signaling function.

The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats

BACKGROUND/OBJECTIVE

The galanin-3 receptor (GALR3) subtype has been identified as having a role in both feeding behaviour and the regulation of emotional states including anxiety. Despite the evidence for an association between galanin and alcohol, the current study is the first to explore the direct role of GALR3 in this context. The present study investigated the potential of the novel selective GALR3 antagonist, SNAP 37889, to reduce anxiety-like behaviour and voluntary ethanol consumption in the iP (alcohol-preferring) rat. This was achieved through a number of behavioural paradigms testing for anxiety, along with the operant self-administration model.

RESULTS

Overall, male iP rats treated with SNAP 37889 at a dose of 30 mg/kg (i.p.) did not show altered locomotor activity or changes in anxiety-like behaviour in the elevated plus maze or light-dark paradigms. Treatment with SNAP 37889 (30 mg/kg, i.p.) reduced operant responding for solutions containing ethanol, sucrose and saccharin. Collectively, results from the current study showed that SNAP 37889 (30 mg/kg, i.p.) is effective in reducing operant responding for ethanol, independent of a sedative effect.

CONCLUSIONS

These findings provide evidence that GALR3 antagonism reduces alcohol consumption and further suggest that GALR3 may be implicated in the rewarding effects of natural and drug reinforcers.

Cue-conditioned alcohol seeking in rats following abstinence: involvement of metabotropic glutamate 5 receptors

BACKGROUND AND PURPOSE

The current study was designed to: (i) examine whether functional interactions occur between receptors known to regulate alcohol self-administration; and (ii) characterize relapse to alcohol seeking following abstinence.

EXPERIMENTAL APPROACH

The selective cannabinoid CB(1) receptor antagonist SR141716A (0.03-1.0 mg.kg(-1) i.p.) resulted in a dose-dependent reduction in ethanol self-administration in ethanol-preferring Indiana-preferring rats. SR141716A was then co-administered with either the selective glutamate metabotropic glutamate 5 (mGlu(5)) receptor antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) or the selective adenosine A(2A) receptor antagonist SCH58261.

KEY RESULTS

When administered at individually sub-threshold doses, a combination of SR141716A (0.1 mg.kg(-1)) and SCH58261 (0.5 mg.kg(-1) i.p.) produced a reduction (28%) in ethanol self-administration. Combinations of threshold doses of SR141716A (0.3 mg.kg(-1)) and SCH58261 (2.0 mg.kg(-1), i.p.) caused an essentially additive reduction (68%) in alcohol self-administration. A combination of individually sub-threshold doses of CB(1) and mGlu(5) receptor antagonists did not affect alcohol self-administration; however, combined threshold doses of SR141716A (0.3 mg.kg(-1)) and MTEP (1.0 mg.kg(-1) i.p.) did reduce ethanol self-administration markedly (80%). Cue-conditioned alcohol seeking was attenuated by pretreatment with MTEP (1.0 mg.kg(-1)) co-administered with SR141716A (0.3 mg.kg(-1) i.p.). In contrast, SCH58261 (2.0 mg.kg(-1)) co-administered with SR141716A (0.3 mg.kg(-1) i.p.) did not reduce cue-conditioned alcohol seeking.

CONCLUSIONS AND IMPLICATIONS

Adenosine A(2A) and cannabinoid CB(1) receptors regulated alcohol self-administration additively, but combined low-dose antagonism of these receptors did not prevent cue-conditioned alcohol seeking after abstinence. In contrast, combined low-dose antagonism of mGlu(5) and CB(1) receptors did prevent relapse-like alcohol seeking after abstinence, suggesting a prominent role for mGlu(5) receptors in this paradigm.

Glycine receptors involved in acamprosate's modulation of accumbal dopamine levels: an in vivo microdialysis study

BACKGROUND

Glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area (VTA) have been suggested to be involved in the positive reinforcing and dopamine elevating effects of ethanol. Recent studies have also shown that ethanol high-preferring rats substantially decrease their ethanol intake when treated with a glycine transporter 1 inhibitor (ORG 25935). Acamprosate, a drug used for relapse prevention in treatment of alcohol dependence, has also been demonstrated to elevate extracellular dopamine levels in the nAc. However, the underlying mechanism of action of acamprosate is not fully understood. Here we investigated whether acamprosate interferes with a neuronal circuitry that previously has been demonstrated to be involved in the dopamine elevating effects of ethanol and taurine.

METHODS

In vivo microdialysis in freely moving rats was used to assess accumbal dopamine levels before and during local (nAc) or systemic administration of acamprosate.

RESULTS

Perfusion of 0.5 mM acamprosate in the nAc significantly increased dopamine levels. Pretreatment either with 10 microM strychnine in the nAc or 100 microM mecamylamine in the VTA, completely antagonized the acamprosate-induced elevation of accumbal dopamine levels. Also, systemic acamprosate administration elevated accumbal dopamine output, an effect that was abolished by local (nAc) pretreatment with 10 microM strychnine.

CONCLUSIONS

These results suggest that both systemic and local application of acamprosate elevate extracellular dopamine levels in the nAc by activating accumbal GlyRs, and, secondarily, tegmental nAChRs.

Glycine receptors in the nucleus accumbens involved in the ethanol intake-reducing effect of acamprosate

BACKGROUND

We have previously demonstrated that strychnine-sensitive glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area are involved in mediating ethanol (EtOH)-induced elevation of dopamine in the rat mesolimbic dopamine system. This neuronal circuitry was also demonstrated to mediate dopamine elevation in the nAc after both taurine, an endogenous agonist of GlyRs, and acamprosate, a synthetic derivate of homotaurine. The aim of this study was to investigate whether the EtOH intake-reducing effect of acamprosate involves accumbal GlyRs.

METHODS

For this purpose, we used a voluntary EtOH consumption model where EtOH medium- and high-preferring rats were implanted with guide cannulae in the nAc. The animals received daily injections of acamprosate or 0.9% NaCl before accessing a bottle of 6% EtOH and a bottle of water. After 2 days, a microinjection of strychnine or vehicle preceded the daily systemic injection and bottle-access period.

RESULTS

Acamprosate, but not saline, decreased EtOH intake. Pretreatment with Ringer in the nAc did not influence EtOH intake in saline or acamprosate-treated animals. Pretreatment with strychnine had no effect on EtOH intake in saline-treated animals, whereas it completely reversed the EtOH intake-reducing effect of acamprosate.

CONCLUSIONS

Based on current and previous results, we suggest that acamprosate primarily interacts with accumbal GlyRs and secondarily with ventral tegmental nAChRs, in a similar manner to that previously observed with EtOH and taurine. The interaction between acamprosate and GlyRs does not only influence dopamine output in the nAc but also EtOH consumption, giving further support for our hypothesis that GlyRs are of importance in EtOH reinforcement.

Medical treatment of Parkinson disease

The cardinal characteristics of Parkinson disease (PD) include resting tremor, rigidity, and bradykinesia. Patients may also develop autonomic dysfunction, cognitive changes, psychiatric symptoms, sensory complaints, and sleep disturbances. The treatment of motor and non-motor symptoms of Parkinson disease is addressed in this article.

The effects of acamprosate on alcohol-cue reactivity and alcohol priming in dependent patients: a randomized controlled trial

RATIONALE

Acamprosate is a widely utilized, efficacious treatment for relapse prevention in alcohol-dependent patients; yet, little is known regarding its therapeutic mechanism of action.

OBJECTIVES

The aim of the present study was to examine the effect of acamprosate on cue reactivity and alcohol priming in alcohol-dependent patients.

METHODS

In a double-blind design, 56 treatment seeking patients were randomized to 21 days of either acamprosate or placebo treatment and then participated in a series of cue- and alcohol-priming sessions. Alcohol cues consisted of a mixture of alcohol related visual, tactile, olfactory, and auditory stimuli. Non-alcohol-related cues were contextually similar but had no connection to alcohol. In the alcohol-priming procedure, patients were provided with an alcohol drink of their own choice at a dose corresponding to 0.20 gr. EtOH/kg bodyweight. Subjective, physiological, and biological measurements were recorded before and after each test session. Following study completion, all patients were referred to formal treatment.

RESULTS

The results showed that acamprosate attenuated the subjective craving induced by alcohol priming in comparison to placebo-treated patients. Furthermore, acamprosate reduced alcohol-induced elevation in blood-cortisol levels. Lastly, there was a negative correlation between acamprosate plasma levels and alcohol craving following a priming drink. No effects of acamprosate on cue reactivity, or on the acute rewarding and sedating effects of the priming drink, were observed.

CONCLUSION

These results suggest a potential mechanism by which acamprosate mediates its therapeutic effect in the treatment of alcoholism, by attenuating the urge to drink following an alcohol slip.

Acamprosate and naltrexone treatment effects on ethanol and sucrose seeking and intake in ethanol-dependent and nondependent rats

RATIONALE

Two pharmacotherapies are approved for treating alcohol craving (acamprosate and naltrexone), but both have shown mixed findings in animals and humans.

OBJECTIVES

The present experiments utilized a "reinforcer blocking" approach (i.e., rats were able to consume ethanol during treatment) to better understand the efficacy of these treatments for ethanol seeking and drinking using ethanol-dependent and nondependent rats.

MATERIALS AND METHODS

In "nondependent" experiments, drugs (acamprosate 50, 100, and 200 mg/kg; naltrexone 0.1, 0.3, and 1.0 mg/kg) were administered over 3-week periods prior to operant sessions with a low response requirement to gain access to reinforcers for 20 min. For "dependent" experiments, rats were made dependent in vapor/inhalation chambers.

RESULTS

Acamprosate and naltrexone had similar effects on intake in nondependent and dependent rats; neither drug was selective for ethanol over sucrose drinking. In nondependent animals, naltrexone was more efficacious at more doses than acamprosate, and acamprosate's effects were limited to a dose that also had adverse effects on body weight. Both pharmacotherapies showed more selectivity when examining reinforcer seeking. In nondependent rats, acamprosate and naltrexone had response-attenuating effects in ethanol, but not sucrose, groups. In dependent animals, acamprosate had selective effects limited to a decrease in sucrose seeking. Naltrexone, however, selectively decreased ethanol-seeking in nondependent rats.

CONCLUSIONS

The naltrexone-induced decreases in seeking suggested a change in incentive motivation which was selective for ethanol in nondependent rats. The "nondependent" paradigm may model early stages of "problem drinking" in humans, and the findings suggest that naltrexone could be a good intervention for this level of alcohol abuse and relapse prevention.

Therapeutics for alcoholism: what's the future?

As with other addictions, human alcoholism is characterised as a chronically relapsing condition. Consequently, the therapeutic goal is the development of clinically effective, safe drugs that promote high adherence rates and prevent relapse. These products can then be used in conjunction with psychosocial approaches. In this review, preclinical studies are highlighted that indicate the mechanism of action of currently used anti-craving medications or demonstrate the potential of novel pharmacological agents for the treatment of alcohol use disorders. While current pharmacological strategies are far from ideal, there are a number of candidate molecules that may ultimately be developed into therapeutic agents. In addition, prescribing clinicians should also consider strategies such as combinations of various drugs to aid in the regulation of aberrant alcohol consumption.

Acamprosate: recent findings and future research directions

This article explores the mechanisms of action and the potential responder profile of acamprosate, a compound efficacious in relapse prevention of alcoholism. New evidence at the molecular and cellular level suggests that acamprosate attenuates hyper-glutamatergic states that occur during early abstinence and involves iono (NMDA)- and metabotrotropic (mGluR5) glutamate receptors along with augmented intracellular calcium release and electrophysiological changes. Thus mutant mice with enhanced glutamate levels exhibit higher alcohol consumption than wild type mice and respond better to acamprosate, demonstrating that acamprosate acts mainly on a hyper-glutamatergic system. This mode of action further suggests that acamprosate exhibits neuroprotective properties. In rats, cue-induced reinstatement behavior is significantly reduced by acamprosate treatment whereas cue-induced craving responses in alcohol-dependent patients seem not to be affected by this treatment. An ongoing study ("Project Predict") defines specific responder profiles for an individualized use of acamprosate and naltrexone. Neurophysiological as well as psychometric data are used to define 2 groups of patients: "reward cravers" and "relief cravers". While naltrexone should work better in the first group, acamprosate is hypothesized to be efficacious in the latter where withdrawal associated and/or cue induced hyper-glutamatergic states are thought to trigger relapse. Further research should target the definition of subgroups applying endophenotypic approaches, e.g. by detecting a hyperglutamatergic syndrome using MR spectroscopy.

High temporal resolution of amino acid levels in rat nucleus accumbens during operant ethanol self-administration: involvement of elevated glycine in anticipation

Capillary electrophoresis coupled with laser-induced fluorescence detection (CE-LIF) provides 15-s temporal resolution of amino acid levels in microdialysate, which, for the first time, allows almost real time measurement of changes during episodes of behavior. We trained Sprague-Dawley rats to self-administer either 10% ethanol-containing gelatin or non-alcoholic gelatin in a typical operant chamber. After rats reached stable daily levels of responding, microdialysis probes were inserted into nucleus accumbens and samples were collected before, during and after operant sessions with on-line analysis via CE-LIF. During the first 15 min of the operant session, there was a significant increase in taurine that correlated with the amount of ethanol consumed (R(2)=0.81) but no change in rats responding for plain gel. There were large, consistent increases in glycine in both the ethanol and plain gel groups which correlated with the amount of gel consumed. A smaller increase was observed in rats with free non-operant access to plain gel compared to the increase seen with the same amount of gel consumed under operant conditions. When rats were given a time out after each delivery of gel in the operant protocol, the greatest increase of glycine was obtained with the longest time out period. Thus, increases in glycine in nucleus accumbens appear to be related to anticipation of reinforcement.

Varenicline ameliorates ethanol-induced deficits in learning in C57BL/6 mice

Ethanol is a frequently abused drug that impairs cognitive processes such as learning. Varenicline, an alpha4beta2 nicotinic receptor partial agonist and alpha7 nicotinic receptor full agonist prescribed for smoking cessation, has been shown to decrease ethanol consumption. The current study investigated whether varenicline could ameliorate ethanol-induced deficits in learning and whether varenicline alters blood alcohol concentration in C57BL/6 mice. Conditioning consisted of two auditory conditioned stimulus (CS; 30s, 85dB white noise)-foot shock unconditioned stimulus (US; 2s, 0.57mA) pairings. For all studies, saline or ethanol (1.0, 1.5, 2.0g/kg i.p.) was administered 15min before training, and saline or varenicline (0.05, 0.1, 0.2mg/kg i.p.) was administered 60min before either training or testing. For blood alcohol analysis, saline or varenicline (0.1mg/kg) was administered 60min before collection, and saline or ethanol (1.0, 1.5, 2.0g/kg) was administered 15min before collection. Varenicline dose-dependently ameliorated ethanol-induced conditioning deficits for all three doses of ethanol when administered before training but not when administered 24h later, before testing. In addition, varenicline did not alter blood alcohol concentration. The smoking cessation aid varenicline may have therapeutic uses for treating ethanol-associated disruptions in cognitive processes.

Combined antagonism of glutamate mGlu5 and adenosine A2A receptors interact to regulate alcohol-seeking in rats

Adenosine and glutamate have been implicated as mediators involved in the self-administration of alcohol. In the present study we sought to determine whether adenosine receptors could interact with metabotropic glutamate receptors to regulate operant responding for alcohol and also the integration of the salience of alcohol-paired cues. Alcohol-preferring (iP) rats were trained to self-administer alcohol under operant conditions. The availability of alcohol was paired with an olfactory cue plus a stimulus light. Rats were examined under fixed ratio responding and also following extinction under a cue-induced reinstatement paradigm. Administration of the selective adenosine A2A receptor antagonist, SCH 58261, reduced fixed ratio responding for alcohol in iP rats in a dose-related manner. Furthermore, the combination of a subthreshold dose of SCH 58261 with a subthreshold dose of the mGlu5 receptor antagonist MTEP also reduced alcohol self-administration and increased the latency to the first reinforced response, suggesting a pre-ingestive effect. Moreover, this combination of SCH 58261 and MTEP also prevented the conditioned reinstatement of alcohol-seeking elicited by the re-presentation of cues previously paired with alcohol availability. In contrast, combinations of the selective adenosine A1 receptor antagonist, DPCPX, with either SCH 58261 or MTEP had no effect on alcohol responding. Collectively, these data suggest a functional interaction between adenosine A2A and mGlu5 receptors in relation to alcohol-seeking and the integration of the drug-related cues.

Acamprosate in the treatment of alcohol dependence: clinical and economic considerations

Acamprosate has been commercially available in the USA since 2004 to treat alcohol dependence. Its safety and efficacy have been demonstrated in a number of clinical trials worldwide, which overall have shown significant improvements in abstinence compared with placebo. As with all alcoholism pharmacotherapies, acamprosate is used in conjunction with psychosocial interventions. One frequently described mechanism stipulates that acamprosate supports abstinence by normalizing the often protracted dysregulation of NMDA-mediated glutamatergic neurotransmission that follows chronic heavy alcohol use and withdrawal. This article reviews the clinical safety and efficacy of acamprosate, as well as results from recent pharmacoeconomic and human laboratory studies. These data elucidate the economic benefits of acamprosate, as well as its effects on cognition and alcohol-related sleep disturbances.

Evidence for the role of dopamine D3 receptors in oral operant alcohol self-administration and reinstatement of alcohol-seeking behavior in mice

The present study examined the effects of the acute intraperitoneal (i.p.) administration of the selective dopamine (DA) D(3) receptor antagonist SB-277011A (10, 20 or 30 mg/kg i.p.) on the oral operant self-administration of alcohol in male C57BL/6N mice. These effects were compared with those of naltrexone (0.5, 1 and 2 mg/kg i.p.) and acamprosate (100, 200 and 400 mg/kg i.p.). Compared with vehicle, the acute administration of SB-277011A (10 or 20 mg/kg) did not significantly alter the operant self-administration of alcohol, whereas the 30 mg/kg dose significantly reduced alcohol intake (g/kg), the number of reinforcers, and the number of active lever presses. The oral self-administration of alcohol was not significantly altered by the acute administration of either naltrexone or acamprosate, compared with vehicle-treated mice. SB-277011A, naltrexone and acamprosate were also tested in a model of drug/cue-triggered reinstatement of alcohol-seeking behavior. In this model, neither naltrexone (2 mg/kg) nor acamprosate (400 mg/kg) prevented relapse to alcohol-seeking behavior. In contrast, SB-277011A significantly reduced reinstatement of alcohol seeking in a dose-dependent manner. Provided these results can be extrapolated to humans, they suggest that selective DA D(3) receptor antagonists may be useful in the pharmacotherapeutic management of alcohol intake and prevention of relapse to alcohol-seeking behavior.

Assessing appetitive and consummatory phases of ethanol self-administration in C57BL/6J mice under operant conditions: regulation by mGlu5 receptor antagonism

RATIONALE

The development of mouse models of ethanol consumption and ethanol-seeking behavior is of particular importance in understanding the underlying mechanisms of drug abuse because these models can enable an analysis of an effect of specific genotype on drug-seeking behavior and the interaction of potential therapeutics with genotype. However, there are some limitations with present models, notably the inability to examine appetitive and consummatory behavior separately.

MATERIALS AND METHODS

In the present study, C57BL/6 mice were trained to self-administer 10% ethanol in a modified operant protocol that allowed a clear delineation of consummatory and appetitive phases. The utility of this procedure was confirmed with the use of the metabotropic glutamate 5 (mGlu5) receptor antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine (MTEP).

RESULTS

Limited-access consumption during the dark phase of the light-dark cycle with intermittent access (every second or third day) led to a high level of consumption by the mice. MTEP caused a dose-dependent decrease in both the consumption of ethanol and the appetitive response for ethanol. Furthermore, this effect was unrelated to any effect of MTEP on locomotor activity.

CONCLUSIONS

The model provides a useful paradigm for examining both the appetitive and consummatory phases of ethanol consumption in mice; furthermore, the data indicate mGlu5 receptors are involved in both phases.