Reduction of excessive alcohol drinking by a novel GABAB receptor positive allosteric modulator ADX71441 in mice

Positive allosteric modulators of the GABAB receptor: a new class of ligands with therapeutic potential for alcohol use disorder

BACKGROUND

Positive allosteric modulators (PAMs) of the GABAB receptor constitute a new class of GABAB-receptor ligands. GABAB PAMs reproduce several pharmacological effects of the orthosteric GABAB receptor agonist, baclofen, although displaying a better safety profile.

AIMS

This paper reviews the reducing or, frequently, even suppressing effects of all GABAB PAMs tested to date on multiple alcohol-related behaviours in laboratory rodents exposed to validated experimental models of human alcohol use disorder.

RESULTS

Acute or repeated treatment with CGP7930, GS39783, BHF177, rac-BHFF, ADX71441, CMPPE, COR659, ASP8062, KK-92A, and ORM-27669 reduced excessive alcohol drinking, relapse- and binge-like drinking, operant alcohol self-administration, reinstatement of alcohol seeking, and alcohol-induced conditioned place preference in rats and mice.

CONCLUSIONS

These effects closely mirrored those of baclofen; notably, they were associated to remarkably lower levels of tolerance and toxicity. The recent transition of ASP8062 to clinical testing will soon prove whether these highly consistent preclinical data translate to AUD patients.

The neutral CB1 antagonist AM6527 reduces ethanol seeking, binge-like consumption, reinforcing, and withdrawal effects in male and female mice

RATIONALE

Alcohol use disorder (AUD) is a debilitating physiological and psychiatric disorder which affects individuals globally. The current pharmacological interventions to treat AUD are limited, and hence there is an urgent need for a novel pharmacological therapy which can be effective and safe across the population.

OBJECTIVE

We aimed to investigate a novel neutral cannabinoid receptor-1 (CB1R) antagonist, AM6527, in several preclinical models of ethanol consumption using male and female C57BL6/J mice.

METHODS

Independent groups of male and female mice were subjected to repeated cycles of drinking in the dark (DID), or intermittent access to alcohol (IAA) procedures. Twenty minutes prior to ethanol access in each procedure, animals were treated with intraperitoneal injections of either 1, 3, and 10 mg/kg of AM6527 or its respective vehicle. Acamprosate (100, 200, 300, and 400 mg/kg) or its respective vehicle was used as a positive control. Separate groups of male mice were subjected to a chain schedule of ethanol reinforcement to gain access to ethanol wherein completion of a fixed interval (FI; 5 min) schedule (link 1: "Seeking") was reinforced with continuous access to ethanol (fixed ratio; FR1) for up to 1.8 g/kg (link 2: "consumption"). All the animals were treated with 1, 3, and 10 mg/kg of AM6527 or its respective vehicle 20 mins prior to the start of the FI chain of the procedure. Separately, AM6527 was also evaluated in male and female mice undergoing acute ethanol withdrawal following 8 weeks of intermittent or continuous access to 20% ethanol drinking.

RESULTS

In both DID and IAA procedures, AM6527 reduced ethanol consumption in a dose-related manner in both male and female mice. AM6527 produced no tolerance in the DID procedure; mice treated with 3 mg/kg of AM6527 for 3 weeks continuously drank significantly smaller amounts of ethanol as compared to vehicle-treated mice over a period of three DID cycles. Moreover, in the IAA procedure, AM6527 caused an increase in water intake over the 24-h period. Acamprosate transiently reduced ethanol intake in male mice in both the DID and the IAA procedures but failed to produce any significant effect in female mice. AM6527 also produced a decrease in the FI responding ("ethanol seeking") in animals trained to self-administer ethanol. Lastly, AM6527 mitigated neurological withdrawal signs, i.e., handling induced convulsions (HIC) in mice undergoing acute ethanol withdrawal.

CONCLUSIONS

Current findings support previous studies with CB1R neutral antagonist in reducing voluntary ethanol intake and seeking behavior. Based on results shown in this work, AM6527 can be developed as a first in class CB1R neutral antagonist to treat AUD in both males and females.

Delving into the reducing effects of the GABAB positive allosteric modulator, KK-92A, on alcohol-related behaviors in rats

Recent studies have demonstrated the ability of the positive allosteric modulator (PAM) of the GABAB receptor (GABAB PAM), KK-92A, to suppress operant alcohol self-administration and reinstatement of alcohol seeking in selectively bred Sardinian alcohol-preferring (sP) rats. The present study was designed to scrutinize the suppressing effects of KK-92A on alcohol-related behaviors; to this end, four separate experiments were conducted to address just as many new research questions, some of which bear translational value. Experiment 1 found that 7-day treatment with KK-92A (0, 5, 10, and 20 mg/kg, intraperitoneally [i.p.]) effectively reduced alcohol intake in male sP rats exposed to the home-cage 2-bottle "alcohol (10% v/v) vs. water" choice regimen with 1 hour/day limited access, extending to excessive alcohol drinking the ability of KK-92A to suppress operant alcohol self-administration. Experiment 2 demonstrated that the ability of KK-92A to reduce lever-responding for alcohol was maintained also after acute, intragastric treatment (0, 20, and 40 mg/kg) in female sP rats trained to lever-respond for 15% (v/v) alcohol under the fixed ratio 5 schedule of reinforcement. In Experiment 3, acutely administered KK-92A (0, 5, 10, and 20 mg/kg, i.p.) dampened alcohol-seeking behavior in female sP rats exposed to a single session under the extinction responding schedule. Experiment 4 used a taste reactivity test to demonstrate that acute treatment with KK-92A (0 and 20 mg/kg, i.p.) did not alter either hedonic or aversive reactions to a 15% (v/v) alcohol solution in male sP rats, ruling out that KK-92A-induced reduction of alcohol drinking and self-administration could be due to alterations in alcohol palatability. Together, these results enhance the behavioral pharmacological profile of KK-92A and further strengthen the notion that GABAB PAMs may represent a novel class of ligands with therapeutic potential for treating alcohol use disorder.

GABAergic signaling in alcohol use disorder and withdrawal: pathological involvement and therapeutic potential

Alcohol is one of the most widely used substances. Alcohol use accounts for 5.1% of the global disease burden, contributes substantially to societal and economic costs, and leads to approximately 3 million global deaths yearly. Alcohol use disorder (AUD) includes various drinking behavior patterns that lead to short-term or long-lasting effects on health. Ethanol, the main psychoactive molecule acting in alcoholic beverages, directly impacts the GABAergic system, contributing to GABAergic dysregulations that vary depending on the intensity and duration of alcohol consumption. A small number of interventions have been developed that target the GABAergic system, but there are promising future therapeutic avenues to explore. This review provides an overview of the impact of alcohol on the GABAergic system, the current interventions available for AUD that target the GABAergic system, and the novel interventions being explored that in the future could be included among first-line therapies for the treatment of AUD.

Alcoholic neuropathy associated with chronic alcohol intake

Alcoholic neuropathy (AN), a debilitating condition that mainly affects chronic alcohol drinkers, is thought to cause lesions in the peripheral nervous system leading to sensory, autonomic, and motor dysfunctions. Despite many studies, the pathogenesis of these lesions is still not completely understood. We investigated few aspects on the development of alcohol-induced peripheral neuropathy, by assessing sensory, motor and autonomic functions, as well as stereological analysis of axonal fibers and myelin sheath of the sciatic nerve. Twelve male Wistar rats were divided into Control group and Alcohol group that was submitted to Two Bottle-Choice Paradigm of intermittent and voluntary alcohol solution intake (20%; v/v) during eight weeks. At the end of treatment, three different sensorium-motor tests were applied - Tactile Sensitivity, Thermal Sensitivity, and Functional Observational Battery (FOB). Quantitative morphometric analysis of sciatic nerve structures was performed by stereological method. Alcohol concentration in the blood was measured to analyze possible correlation between availability of alcohol in the blood and the magnitude of the peripheral nerve lesion. Our data showed a peripheral effect of chronic alcohol intake associated with hyperalgesia and a process of demyelination with a strong correlation with alcohol consumption. This process was associated with increased tactile sensitivity, with behavioral reflexes such as locomotor hyperactivity, changes in gait and balance, and autonomic reflexes such as piloerection.

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Alcoholic neuropathy and its consequences.

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Neuropathy and sensitive and motor alterations.

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Alcoholic neuropathy and thinner myelin sheath thickness.

Development of tolerance upon repeated administration with the GABAB receptor positive allosteric modulator, COR659, on alcohol drinking in rodents

Background: Recent work has demonstrated that acute administration of the novel positive allosteric modulator of the GABAB receptor, COR659, reduces several alcohol-related behaviors in rodents.Objective: To assess whether COR659 continues to lessen alcohol intake after repeated administration, a fundamental feature of drugs with therapeutic potential.Methods: Male C57BL/6J mice (n = 40) were exposed to daily 2-hour drinking sessions (20% (v/v) alcohol) under the 1-bottle "drinking in the dark" protocol and male Sardinian alcohol-preferring rats (n = 40) were exposed to daily 1-hour drinking sessions under the 2-bottle "alcohol (10%, v/v) vs water" choice regimen. COR659 (0, 10, 20, and 40 mg/kg in the mouse experiment; 0, 5, 10, and 20 mg/kg in the rat experiment) was administered intraperitoneally before 7 consecutive drinking sessions.Results: Alcohol intake in vehicle-treated mice and rats averaged 2.5-3.0 and 1.5-1.6 g/kg/session, respectively, indicative of high basal levels. In both experiments, treatment with COR659 resulted in an initial, dose-related suppression of alcohol intake (up to 70-80% compared to vehicle treatment; P < .0005 and P < .0001 in mouse and rat experiments, respectively). The magnitude of the reducing effect of COR659 on alcohol drinking diminished progressively, until vanishing over the subsequent 2-4 drinking sessions.Conclusion: COR659 effectively reduced alcohol intake in two different rodent models of excessive alcohol drinking. However, tolerance to the anti-alcohol effects of COR659 developed rapidly. If theoretically transposed to humans, these data would represent a possible limitation to the clinical use of COR659.

Subregional Differences in Alcohol Modulation of Central Amygdala Neurocircuitry

Alcohol use disorder is a highly significant medical condition characterized by an impaired ability to stop or control alcohol use, compulsive alcohol seeking behavior, and withdrawal symptoms in the absence of alcohol. Understanding how alcohol modulates neurocircuitry critical for long term and binge-like alcohol use, such as the central amygdala (CeA), may lead to the development of novel therapeutic strategies to treat alcohol use disorder. In clinical studies, reduction in the volume of the amygdala has been linked with susceptibility to relapse to alcohol use. Preclinical studies have shown the involvement of the CeA in the effects of alcohol use, with lesions of the amygdala showing a reduction in alcohol drinking, and manipulations of cells in the CeA altering alcohol drinking. A great deal of work has shown that acute alcohol, as well as chronic alcohol exposure via intake or dependence models, alters glutamatergic and GABAergic transmission in the CeA. The CeA, however, contains heterogeneous cell populations and distinct subregional differences in neurocircuit architecture which may influence the mechanism by which alcohol modulates CeA function overall. The current review aimed to parse out the differences in alcohol effects on the medial and lateral subregions of the CeA, and what role neuroinflammatory cells and markers, the endocannabinoid system, and the most commonly studied neuropeptide systems play in mediating these effects. A better understanding of alcohol effects on CeA subregional cell type and neurocircuit function may lead to development of more selective pharmacological interventions for alcohol use disorder.

Reducing effect of the novel positive allosteric modulator of the GABAB receptor, COR659, on binge-like alcohol drinking in male mice and rats

RATIONALE

Binge drinking (BD) is a widespread drinkingpattern that may contribute to promote the development of alcohol use disorder (AUD). The comprehension of its neurobiological basis and the identification of molecules that may prevent BD are critical. Preclinical studies demonstrated that positive allosteric modulators (PAMs) of the GABA_B receptor effectively reduced, and occasionally suppressed, the reinforcing and motivational properties of alcohol in rodents, suggesting their potential use as pharmacotherapy for AUD, including BD. Recently, we demonstrated that COR659, a novel GABA_B PAM, effectively reduced (i) alcohol drinking under the 2-bottle choice regimen, (ii) alcohol self-administration under both fixed and progressive ratio schedules of reinforcement, and (iii) cue-induced reinstatement of alcohol-seeking behavior in Sardinian alcohol-preferring (sP) rats.

OBJECTIVES

The present study investigated whether the "anti-alcohol" properties of COR659 extend to binge-like drinking in rodents.

METHODS

COR659 was tested on the "drinking in the dark" (DID) paradigm in C57BL/6J mice and the 4-bottle "alcohol [10%, 20%, 30% (v/v)] versus water" choice regimen with limited and unpredictable access to alcohol in sP rats.

RESULTS

Acute administration of non-sedative doses of COR659 (10, 20, and 40 mg/kg; i.p.) effectively and selectively suppressed the intake of intoxicating amounts of alcohol (> 2 g/kg) consumed by C57BL/6J mice and sP rats exposed to these binge-like drinking experimental procedures.

CONCLUSIONS

The present data demonstrate the ability of COR659 to suppress binge-like drinking in rodents and strengthen the hypothesis that GABA_B PAMs may represent a potentially effective pharmacotherapy for alcohol misuse.

GABAB Receptors and Alcohol Use Disorders: Preclinical Studies

Preclinical research over the past several decades has demonstrated a role for the γ-aminobutyric acid_B (GABA_B) receptor in alcohol use disorder (AUD). This chapter offers an examination of preclinical evidence on the role of the GABA_B receptor on alcohol-related behaviors with a particular focus on the GABA_B receptor agonist baclofen, for which effects have been most extensively studied, and positive allosteric modulators (PAMs) of the GABA_B receptor. Studies employing rodent and non-human primate models have shown that activation of the GABA_B receptor can reduce (1) stimulating and rewarding effects of alcohol; (2) signs of alcohol withdrawal in rats made physically dependent on alcohol; (3) acquisition and maintenance of alcohol drinking under a two-bottle alcohol versus water choice procedure; (4) alcohol intake under oral operant self-administration procedures; (5) motivational properties of alcohol measured using extinction and progressive ratio procedures; (6) the increase in alcohol intake after a period of alcohol abstinence (the alcohol deprivation effect or ADE); and (7) the ability of alcohol cues and stress to reinstate alcohol seeking when alcohol is no longer available. Baclofen and GABA_B PAMs reduce the abovementioned behaviors across different preclinical models, which provides strong evidence for a significant role of the GABA_B receptor in alcohol-related behaviors and supports development of medications targeting GABA_B receptors for the treatment of AUD. This chapter highlights the value of examining mechanisms of alcohol-related behaviors across multiple animal models to increase the confidence in identification of new therapeutic targets.

The Novel Positive Allosteric Modulator of the GABAB Receptor, KK-92A, Suppresses Alcohol Self-Administration and Cue-Induced Reinstatement of Alcohol Seeking in Rats

Positive allosteric modulators (PAMs) of the GABA_B receptor (GABA_B PAMs) are of interest in the addiction field due to their ability to suppress several behaviors motivated by drugs of abuse. KK-92A is a novel GABA_B PAM found to attenuate intravenous self-administration of nicotine and reinstatement of nicotine seeking in rats. This present study was aimed at extending to alcohol the anti-addictive properties of KK-92A. To this end, Sardinian alcohol-preferring rats were trained to lever-respond for oral alcohol (15% v/v) or sucrose (0.7% w/v) under the fixed ratio (FR) 5 (FR5) schedule of reinforcement. Once lever-responding behavior had stabilized, rats were exposed to tests with acutely administered KK-92A under FR5 and progressive ratio schedules of reinforcement and cue-induced reinstatement of previously extinguished alcohol seeking. KK-92A effect on spontaneous locomotor activity was also evaluated. Treatment with 10 and 20 mg/kg KK-92A suppressed lever-responding for alcohol, amount of self-administered alcohol, and breakpoint for alcohol. Treatment with 20 mg/kg KK-92A reduced sucrose self-administration. Combination of per se ineffective doses of KK-92A (2.5 mg/kg) and the GABA_B receptor agonist, baclofen (1 mg/kg), reduced alcohol self-administration. Treatment with 5, 10, and 20 mg/kg KK-92A suppressed reinstatement of alcohol seeking. Only treatment with 80 mg/kg KK-92A affected spontaneous locomotor activity. These results demonstrate the ability of KK-92A to inhibit alcohol-motivated behaviors in rodents and confirm that these effects are common to the entire class of GABA_B PAMs. The remarkable efficacy of KK-92A is discussed in terms of its ago-allosteric properties.

Recent Advances in the Potential of Positive Allosteric Modulators of the GABAB Receptor to Treat Alcohol Use Disorder

Aims

The effects of alcohol on gamma-aminobutyric acid (GABA) transmission are key for the development and maintenance of alcohol use disorder (AUD). Previous research consistently indicates that GABA_B receptor agonists such as baclofen can attenuate addiction-related behaviors in preclinical models of AUD. More importantly, baclofen has also shown promise in clinical studies, particularly in severely alcohol-dependent patients. However, despite this promise, other clinical studies have not confirmed its efficacy and chiefly, larger clinical trials have not been conducted. Therefore, with the exception of France, baclofen is not approved for the treatment of AUD in any other country. Furthermore, it is also important to keep in mind that some patients treated with baclofen may experience important side-effects, including sedation, drowsiness and sleepiness.

Methods

This short review will first discuss the history of baclofen for AUD treatment. We will then summarize preclinical behavioral results that have investigated the efficacy of GABA_B PAMs for addiction treatment, with a special focus on our recent work that investigated the effects of ADX71441, a novel GABA_B PAM, on several alcohol-related behaviors in rats that model important aspects of human AUD. Finally, in light of the recent criticism about the translational value of animal models of addiction, the specific translational potential of our work and of other preclinical studies that have unanimously reported the efficacy of GABA_B PAMs to attenuate multiple alcohol-related behaviors will be discussed.

Results

Positive allosteric modulators (PAMs) of the GABA_B receptor offer an attractive alternative approach to baclofen and have the potential to achieve mechanistic and therapeutic effects similar to GABA_B agonists, while avoiding the tolerance and toxicity issues associated with baclofen. To date, all preclinical behavioral results have invariably shown the efficacy of GABA_B PAMs for addiction treatment.

Conclusions

Preclinical studies indicate that GABA_B PAMs have a higher therapeutic index than orthosteric agonists, at least in terms of mitigating the sedative effects of GABA_B agonism. This predicts that GABA_B PAMs have a high translational potential in humans and merit being tested clinically, in particular in patients with severe AUD.

Pharmacological targeting of the GABAB receptor alters Drosophila's behavioural responses to alcohol

When exposed to ethanol, Drosophila melanogaster display a variety of addiction-like behaviours similar to those observed in mammals. Sensitivity to ethanol can be quantified by measuring the time at which 50% of the flies are sedated by ethanol exposure (ST50); an increase of ST50 following multiple ethanol exposures is widely interpreted as development of tolerance to ethanol. Sensitivity and tolerance to ethanol were measured after administration of the gamma-aminobutyric acid receptor B (GABA_B ) agonist (SKF 97541) and antagonist (CGP 54626), when compared with flies treated with ethanol alone. Dose-dependent increases and decreases in sensitivity to ethanol were observed for both the agonist and antagonist respectively. Tolerance was recorded in the presence of GABA_B drugs, but the rate of tolerance development was increased by SKF 97451 and unaltered in presence of CGP 54626. This indicates that the GABA_B receptor contributes to both the sensitivity to ethanol and mechanisms by which tolerance develops. The data also reinforce the usefulness of Drosophila as a model for identifying the molecular components of addictive behaviours and for testing drugs that could potentially be used for the treatment of alcohol use disorder (AUD).

Clinical Trials for Stimulant Use Disorders: Addressing Heterogeneities That May Undermine Treatment Outcomes

In recent years, use of cocaine and amphetamines and deaths associated with stimulants have been on the rise, and there are still no FDA-approved medications for stimulant use disorders. One contributing factor may involve heterogeneity. At the neurobiological level, dual dopamine dysfunction may be undermining medication efficacy, suggesting a need for combination pharmacotherapies. At the population level, individual variability is expressed in a number of ways and, if left unaddressed, may interfere with medication efficacy. This chapter reviews studies investigating medications to address dopamine dysfunction, and it also identifies several prominent heterogeneities associated with stimulant (and other substance) use disorders. The chapter has implications for improving interventions to treat stimulant use disorders, and the theme of individual heterogeneity may have broader application across substance use disorders.

GABAB receptor positive allosteric modulators with different efficacies affect neuroadaptation to and self-administration of alcohol and cocaine

Drugs of abuse induce widespread synaptic adaptations in the mesolimbic dopamine (DA) neurons. Such drug-induced neuroadaptations may constitute an initial cellular mechanism eventually leading to compulsive drug-seeking behavior. To evaluate the impact of GABA_B receptors on addiction-related persistent neuroplasticity, we tested the ability of orthosteric agonist baclofen and two positive allosteric modulators (PAMs) of GABA_B receptors to suppress neuroadaptations in the ventral tegmental area (VTA) and reward-related behaviors induced by ethanol and cocaine. A novel compound (S)-1-(5-fluoro-2,3-dihydro-1H-inden-2-yl)-4-methyl-6,7,8,9-tetrahydro-[1,2,4]triazolo[4,3-a]quinazolin-5(4H)-one (ORM-27669) was found to be a GABA_B PAM of low efficacy as agonist, whereas the reference compound (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one (rac-BHFF) had a different allosteric profile being a more potent PAM in the calcium-based assay and an agonist, coupled with potent PAM activity, in the [³⁵ S] GTPγS binding assay in rat and human recombinant receptors. Using autoradiography, the high-efficacy rac-BHFF and the low-efficacy ORM-27669 potentiated the effects of baclofen on [³⁵ S] GTPγS binding with identical brain regional distribution. Treatment of mice with baclofen, rac-BHFF, or ORM-27669 failed to induce glutamate receptor neuroplasticity in the VTA DA neurons. Pretreatment with rac-BHFF at non-sedative doses effectively reversed both ethanol- and cocaine-induced plasticity and attenuated cocaine i.v. self-administration and ethanol drinking. Pretreatment with ORM-27669 only reversed ethanol-induced neuroplasticity and attenuated ethanol drinking but had no effects on cocaine-induced neuroplasticity or self-administration. These findings encourage further investigation of GABA_B receptor PAMs with different efficacies in addiction models to develop novel treatment strategies for drug addiction.

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.

Suppressing effect of CMPPE, a new positive allosteric modulator of the GABAB receptor, on alcohol self-administration and reinstatement of alcohol seeking in rats

Positive allosteric modulators (PAMs) of the GABA_B receptor constitute a class of pharmacological agents gaining increasing attention in the alcohol research field because of their ability to suppress several alcohol-related behaviors in rodents. CMPPE is a novel GABA_B PAM, still limitedly characterized in vivo. It was therefore of interest to test its ability to affect operant, oral self-administration of alcohol and cue-induced reinstatement of alcohol seeking in alcohol-preferring rats. To this end, female Sardinian alcohol-preferring (sP) rats were trained to lever-respond for alcohol (15% v/v) under the fixed ratio (FR) 5 (FR5) schedule of reinforcement. Once lever-responding had stabilized, rats were exposed to test sessions (under the FR5 [Experiment 1] and progressive ratio [PR; Experiment 2] schedules of reinforcement) preceded by treatment with CMPPE (0, 2.5, 5, and 10 mg/kg; intraperitoneally [i.p.]). In Experiment 3, once lever-responding had stabilized, rats underwent an extinction responding phase and then a single reinstatement session during which lever-responding was resumed by the non-contingent presentation of a complex of alcohol-associated cues; CMPPE (0, 2.5, 5, and 10 mg/kg; i.p.) was administered before the reinstatement session. Selectivity of CMPPE action was assessed by evaluating the effect of CMPPE (0, 2.5, 5, and 10 mg/kg; i.p.) on self-administration of a chocolate solution in male Wistar rats (Experiment 4). In Experiments 1 and 2, treatment with 5 and 10 mg/kg CMPPE reduced lever-responding and breakpoint for alcohol. In Experiment 3, treatment with 5 and 10 mg/kg CMPPE suppressed reinstatement of alcohol seeking. In Experiment 4, no dose of CMPPE affected lever-responding for the chocolate solution. These results extend to CMPPE the ability of all previously tested GABA_B PAMs to affect alcohol-motivated behaviors in rodents and confirm that these effects are a shared feature of the entire class of GABA_B PAMs. This conclusion is of relevance in view of the forthcoming transition of GABA_B PAMs to clinical testing.

Potential of GABAB Receptor Positive Allosteric Modulators in the Treatment of Alcohol Use Disorder

The orthosteric γ-aminobutyric acid_B (GABA_B) receptor agonist baclofen is currently considered a therapeutic option for alcohol use disorder (AUD); however, the safety profile of baclofen is a concern, thus arousing interest in the positive allosteric modulators (PAMs) of the GABA_B receptor (GABA_B PAMs), a new class of ligands expected to possess a better safety profile. The present paper summarizes the several lines of experimental evidence indicating the ability of GABA_B PAMs to inhibit multiple alcohol-motivated behaviors in rodents. All GABA_B PAMs tested to date have invariably been reported to reduce, or even suppress, excessive alcohol drinking, relapse- and binge-like drinking, operant oral alcohol self-administration, reinstatement of alcohol seeking, and alcohol-induced locomotor stimulation and conditioned place preference in rats and mice. The use of validated animal models of several aspects of AUD confers translational value to these findings. The reducing effects of GABA_B PAMs on alcohol-motivated behaviors (1) occurred at doses largely lower than those inducing sedation, suggesting that GABA_B PAMs may possess, if compared with baclofen, a higher therapeutic index and a more favorable safety profile, and (2) were often not associated with reductions on other non-drug consummatory behaviors. Additional findings with therapeutic potential were (1) the lack of tolerance, after repeated treatment, to the reducing effect of GABA_B PAMs on alcohol drinking and self-administration; (2) the efficacy of GABA_B PAMs after intragastric administration; and (3) the ability of GABA_B PAMs to selectively potentiate the suppressing effect of baclofen on alcohol self-administration. The recent transition of the first GABA_B PAMs to the initial steps of clinical testing makes investigation of the efficacy of GABA_B PAMs in AUD patients a feasible option.

Increasing kynurenine brain levels reduces ethanol consumption in mice by inhibiting dopamine release in nucleus accumbens

Recent research suggests that ethanol (EtOH) consumption behaviour can be regulated by modifying the kynurenine (KYN) pathway, although the mechanisms involved have not yet been well elucidated. To further explore the implication of the kynurenine pathway in EtOH consumption we inhibited kynurenine 3-monooxygenase (KMO) activity with Ro 61-8048 (100 mg/kg, i.p.), which shifts the KYN metabolic pathway towards kynurenic acid (KYNA) production. KMO inhibition decreases voluntary binge EtOH consumption and EtOH preference in mice subjected to "drinking in the dark" (DID) and "two-bottle choice" paradigms, respectively. This effect seems to be a consequence of increased KYN concentration, since systemic KYN administration (100 mg/kg, i.p.) similarly deters binge EtOH consumption in the DID model. Despite KYN and KYNA being well-established ligands of the aryl hydrocarbon receptor (AhR), administration of AhR antagonists (TMF 5 mg/kg and CH-223191 20 mg/kg, i.p.) and of an agonist (TCDD 50 μg/kg, intragastric) demonstrates that signalling through this receptor is not involved in EtOH consumption behaviour. Ro 61-8048 did not alter plasma acetaldehyde concentration, but prevented EtOH-induced dopamine release in the nucleus accumbens shell. These results point to a critical involvement of the reward circuitry in the reduction of EtOH consumption induced by KYN and KYNA increments. PNU-120596 (3 mg/kg, i.p.), a positive allosteric modulator of α7-nicotinic acetylcholine receptors, partially prevented the Ro 61-8048-induced decrease in EtOH consumption. Overall, our results highlight the usefulness of manipulating the KYN pathway as a pharmacological tool for modifying EtOH consumption and point to a possible modulator of alcohol drinking behaviour.

Alcohol intake in two different mouse drinking models after recovery from the lipopolysaccharide-induced sickness reaction

Neuroinflammation may play an important role in the development of alcohol addiction. Recent preclinical reports suggest that enhanced innate immune system signaling increases consumption of alcohol. Our aim was to study whether consequences of lipopolysaccharide (LPS)-induced sickness reaction increase long-term alcohol intake. Adult male C57BL/6J mice, housed in individually ventilated cages, were injected with LPS intraperitoneally (i.p.) and allowed to recover from an acute sickness reaction for 1 week before analysis of their alcohol intake in two different drinking models. Effects of LPS challenge were tested in a continuous two-bottle free choice test with increasing concentrations of alcohol and in a drinking in the dark (DID) binge model. In addition, the effect of repeatedly administered LPS during abstinence periods between binge drinking was analyzed in the DID model. In addition, the DID model was used to study the effects of the microglia inhibitor minocycline (50 mg/kg/day, 4 days) and purinergic P2X7 receptor antagonist Brilliant Blue G (75 mg/kg/day, 7 days) on alcohol intake. In contrast to previous findings, pretreatment with a 1-mg/kg dose of LPS did not significantly increase ethanol consumption in the continuous two-bottle choice test. As a novel finding, we report that increasing the LPS dose to 1.5 mg/kg reduced consumption of 18 and 21% (v/v) ethanol. In the DID model, pretreatment with LPS (0.2-1.5 mg/kg) did not significantly alter 15% or 20% ethanol consumption. Neither did repeated LPS injections affect binge alcohol drinking. Minocycline reduced alcohol, but also water, intake regardless of LPS pretreatment. No data on effects of P2X7 antagonists on alcohol consumption have been previously published; therefore, we report here that subchronic Brilliant Blue G had no effect on alcohol intake in the DID model. As a conclusion, further studies are needed to validate this LPS model of the interaction between immune system activation and alcohol consumption.

Microinjection of baclofen and CGP7930 into the ventral tegmental area suppresses alcohol self-administration in alcohol-preferring rats

Systemic administration of the orthosteric agonist, baclofen, and several positive allosteric modulators (PAMs) of the GABA_B receptor has repeatedly been reported to decrease operant oral alcohol self-administration in rats. The aim of the present study was to evaluate the contribution of the mesolimbic dopamine system to the reducing effect of baclofen and GABA_B PAMs on the reinforcing properties of alcohol. To this end, baclofen or the GABA_B PAM CGP7930 were microinjected into the ventral tegmental area (VTA) of selectively bred, Sardinian alcohol-preferring (sP) rats trained to self-administer alcohol. Baclofen (0, 0.03, 0.1, and 0.3 μg) or CGP7930 (0, 5, 10, and 20 μg) were microinjected via indwelling unilateral guide cannula aiming at the left hemisphere of the VTA. Treatment with baclofen resulted in a dose-related suppression of the number of lever-responses for alcohol and the amount of self-administered alcohol. No dose of baclofen altered rat motor-performance, evaluated by the inverted screen test immediately before the self-administration session. Treatment with CGP7930 halved the number of lever-responses for alcohol and amount of self-administered alcohol, with no effect on rat motor-performance. Site-specificity was investigated testing the effect of microinjection of baclofen and CGP7930 into the left hemisphere of deep mesencephalic nucleus: compared to vehicle, neither 0.3 μg baclofen nor 20 μg CGP7930 altered lever-responding for alcohol and amount of self-administered alcohol. Collectively, the results of the present study suggest the involvement of GABA_B receptors located in the VTA in the mediation of alcohol reinforcing properties in sP rats. This article is part of the "Special Issue Dedicated to Norman G. Bowery".

Suppressing effect of COR659 on alcohol, sucrose, and chocolate self-administration in rats: involvement of the GABAB and cannabinoid CB1 receptors

RATIONALE AND OBJECTIVES

COR659 [methyl2-(4-chlorophenylcarboxamido)-4-ethyl-5-methylthiophene-3-carboxylate] is a new, positive allosteric modulator (PAM) of the GABA_B receptor. This study evaluated whether COR659 shared with previously tested GABA_B PAMs the capacity to reduce alcohol self-administration in rats.

RESULTS

Treatment with non-sedative doses of COR659 (2.5, 5, and 10 mg/kg; i.p.) suppressed lever-responding for alcohol (15% v/v) in Sardinian alcohol-preferring (sP) rats under the fixed ratio (FR) 4 (FR4) and progressive ratio (PR) schedules of reinforcement; COR659 was more potent and effective than the reference GABA_B PAM, GS39783. Treatment with COR659, but not GS39783, suppressed (a) lever-responding for a sucrose solution (1-3% w/v) in sP rats under the FR4 and PR schedules, (b) lever-responding for a chocolate solution [5% (w/v) Nesquik®] in Wistar rats under the FR10 and PR schedules, and (c) cue-induced reinstatement of chocolate seeking in Wistar rats. Treatment with COR659 was completely ineffective on lever-responding (FR10) for regular food pellets in food-deprived Wistar rats. Pretreatment with the GABA_B receptor antagonist, SCH50911, partially blocked COR659-induced reduction of alcohol self-administration, being ineffective on reduction of chocolate self-administration. Pretreatment with the cannabinoid CB₁ receptor antagonist, AM4113, fully blocked COR659-induced reduction of chocolate self-administration, being ineffective on reduction of alcohol self-administration.

CONCLUSIONS

COR659 might exert its behavioral effects via a composite mechanism: (i) positive allosteric modulation of the GABA_B receptor, responsible for a large proportion of reduction of alcohol self-administration; (ii) an action at other receptor system(s), including the cannabinoid CB₁ receptor, through which COR659 affects seeking and consumption of highly palatable foods.

Analgesic effect of ADX71441, a positive allosteric modulator (PAM) of GABAB receptor in a rat model of bladder pain

Therapeutic use of GABA_B receptor agonists for conditions like chronic abdominal pain, overactive bladder (OAB) and gastroesophageal reflux disease (GERD) is severely affected by poor blood-brain barrier permeability and potential side effects. ADX71441 is a novel positive allosteric modulator (PAM) of the GABA_B receptor that has shown encouraging results in pre-clinical models of anxiety, pain, OAB and alcohol addiction. The present study investigates the analgesic effect of ADX71441 to noxious stimulation of the urinary bladder and colon in rats. In female Sprague-Dawley rats, systemic (i.p), but not intrathecal (i.t), administration of ADX71441 produced a dose-dependent decrease in viscero-motor response (VMR) to graded urinary bladder distension (UBD) and colorectal distension (CRD). Additionally, intra-cerebroventricular (i.c.v.) administration of ADX71441 significantly decreased the VMRs to noxious UBD. In electrophysiology experiments, the drug did not attenuate the responses of UBD-sensitive pelvic nerve afferent (PNA) fibers to UBD. In contrast, ADX71441 significantly decreased the responses of UBD-responsive lumbosacral (LS) spinal neurons in spinal intact rats. However, ADX71441 did not attenuate these LS neurons in cervical (C1-C2) spinal transected rats. During cystometrogram (CMG) recordings, ADX71441 (i.p.) significantly decreased the VMR to slow infusion without affecting the number of voiding contraction. These results indicate that ADX71441 modulate bladder nociception via its effect at the supra-spinal sites without affecting the normal bladder motility and micturition reflex in naïve adult rats.

The GABAB Positive Allosteric Modulator ADX71441 Attenuates Alcohol Self-Administration and Relapse to Alcohol Seeking in Rats

GABAergic signaling is involved in modulating the reinforcing properties of alcohol, and GABA_B receptors have been proposed as a potential target for clinical treatment of alcoholism. The orthosteric GABA_B receptor agonist baclofen has been shown to suppress operant self-administration of alcohol in animals and alcohol use in alcohol-dependent patients, but its utility is limited by a narrow therapeutic index. We tested the effects of ADX71441, a novel GABA_B receptor positive allosteric modulator, on alcohol-related behaviors in rats. We first assessed the effects of ADX71441 (1, 3, 10 and 30 mg/kg, I.P.) on both non-dependent and dependent male Wistar rats trained to self-administer 20% alcohol. We then determined the effects of ADX71441 on stress-induced as well as cue-induced relapse-like behavior. Finally, we sought to identify the brain regions through which ADX71441 may act to prevent relapse-like behavior by mapping the neuronal activation induced by stress-induced reinstatement of alcohol-seeking using c-Fos immunohistochemistry. ADX71441 dose-dependently decreased alcohol self-administration of both dependent and non-dependent animals, but its potency was higher in alcohol-dependent rats. Furthermore, both cue- and stress-induced alcohol seeking were blocked by the GABA_B receptor positive allosteric modulator. Finally, pretreatment with 3 mg/kg of ADX71441 before stress-induced reinstatement significantly decreased c-Fos expression in a network of brain regions implicated in stress-induced relapse, comprising the nucleus accumbens shell, the dorsal raphe nucleus and the medial prefrontal cortex. Our findings support a causal role of GABA_B receptors in alcohol reinforcement and relapse to alcohol seeking. These effects are observed in the absence of significant sedative side effects. Jointly, these observations indicate that GABA_B receptor positive allosteric modulators merit being tested clinically for the treatment of alcoholism. Our data also point to a potential biomarker of target engagement for early clinical studies.

The drug candidate, ADX71441, is a novel, potent and selective positive allosteric modulator of the GABAB receptor with a potential for treatment of anxiety, pain and spasticity

Positive allosteric modulation of the GABA_B receptor is a promising alternative to direct activation of the receptor as a therapeutic approach for treatment of addiction, chronic pain, anxiety, epilepsy, autism, Fragile X syndrome, and psychosis. Here we describe in vitro and in vivo characterization of a novel, potent and selective GABA_B positive allosteric modulator (PAM) N-(5-(4-(4-chloro-3-fluorobenzyl)-6-methoxy-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)-2-fluorophenyl)acetamide (ADX71441). In vitro, Schild plot and reversibility tests at the target confirmed PAM properties of the compound. In mice and rats ADX71441 is bioavailable after oral administration and is brain penetrant. A single dose of ADX71441 had an anxiolytic-like profile in the mouse marble burying test (minimum effective dose; MED 3 mg/kg) as well as in the elevated plus maze test in mice and rats (both MED 3 mg/kg). Also, in mice, acute administration of ADX71441 reduced visceral pain-associated behaviors in the acetic acid-induced writhing test. ADX71441 dose-dependently reduced time on rotarod in rats (MED 10 mg/kg) indicative of muscle-relaxant qualities. ADX71441 reduced locomotor activity in mice (10 mg/kg) and rats (3 mg/kg) after single dose; however, following sub-chronic administration in mice, 30 mg/kg ADX71441 was associated with normal locomotor activity. While acute administration of ADX71441 reduced body temperature in rats and mice (both MED 10 mg/kg), the effect in the former was transient, rapidly returning to normal levels despite high concentrations of the compound remaining in plasma. Thus, the GABA_B PAM ADX71441 represents a valid therapeutic approach for development of novel treatment of anxiety, pain and spasticity.

Dissociation of μ-opioid receptor and CRF-R1 antagonist effects on escalated ethanol consumption and mPFC serotonin in C57BL/6J mice

Both the opioid antagonist naltrexone and corticotropin-releasing factor type-1 receptor (CRF-R1) antagonists have been investigated for the treatment of alcoholism. The current study examines the combination of naltrexone and CP154526 to reduce intermittent access ethanol drinking [intermittent access to alcohol (IAA)] in C57BL/6J male mice, and if these compounds reduce drinking via serotonergic mechanisms in the dorsal raphe nucleus (DRN). Systemic injections and chronic intracerebroventricular infusions of naltrexone, CP154526 or CP376395 transiently decreased IAA drinking. Immunohistochemistry revealed CRF-R1 or μ-opioid receptor immunoreactivity was co-localized in tryptophan hydroxylase (TPH)-immunoreactive neurons as well as non-TPH neurons in the DRN. Mice with a history of IAA or continuous access to alcohol were microinjected with artificial cerebral spinal fluid, naltrexone, CP154526 or the combination into the DRN or the median raphe nucleus (MRN). Either intra-DRN naltrexone or CP154526 reduced IAA in the initial 2 hours of fluid access, but the combination did not additively suppress IAA, suggesting a common mechanism via which these two compounds affect intermittent drinking. These alcohol-reducing effects were localized to the DRN of IAA drinkers, as intra-MRN injections only significantly suppressed water drinking, and continuous access drinkers were not affected by CRF-R1 antagonism. Extracellular serotonin was measured in the medial prefrontal cortex (mPFC) using in vivo microdialysis after intra-DRN microinjections in another group of mice. Intra-DRN CP154526 increased serotonin impulse flow to the mPFC while naltrexone did not. This suggests the mPFC may not be an essential location to intermittent drinking, as evidenced by different effects on serotonin signaling to the forebrain yet similar behavioral findings.

Effects of Withania somnifera on oral ethanol self-administration in rats

Recent evidence has shown that Withania somnifera Dunal (Ashwagandha or Indian ginseng), a herbal remedy used in traditional medicine, impairs morphine-elicited place conditioning. Here, we investigated the effect of W. somnifera roots extract (WSE) on motivation for drinking ethanol using operant self-administration paradigms. Wistar rats were trained to self-administer ethanol (10%) by nose-poking. The effects of WSE (25-75 mg/kg) were evaluated on acquisition and maintenance, on ethanol breakpoint under a progressive-ratio schedule of reinforcement and on the deprivation effect and reinstatement of seeking behaviours. Moreover, on the basis of the recent suggestion of an involvement of GABAB receptors in WSE central effects, we studied the interaction between WSE and GABAB ligands. The effect of WSE on saccharin (0.05%) oral self-administration was also tested. The results show that WSE reduced the acquisition, maintenance and breakpoint of ethanol self-administration. WSE also reduced the deprivation effect, reinstatement of ethanol-seeking behaviours and saccharin reinforcement. Furthermore, the GABAB receptor antagonist, phaclofen, counteracted the ability of WSE to impair the maintenance of ethanol self-administration. These findings show that WSE, by an action that may involve GABAB receptors, impairs motivation for drinking ethanol and suggest that further investigations should be performed to determine whether W. somnifera may represent a new approach for the management of alcohol abuse.

Inhibition of alcohol self-administration by positive allosteric modulators of the GABAB receptor in rats: lack of tolerance and potentiation of baclofen

RATIONALE

Treatment with positive allosteric modulators (PAMs) of the GABAB receptor (GABAB PAMs) inhibits several alcohol-motivated behaviors in rodents, including operant, oral alcohol self-administration.

OBJECTIVES

The present study assessed the effects of (a) repeated administration of the GABAB PAMs, GS39783, and rac-BHFF and (b) a combination of an ineffective dose of either GS39783, or rac-BHFF, and an ineffective dose of the prototypic GABAB receptor agonist, baclofen, on operant, oral alcohol self-administration.

METHODS

Studies were conducted using selectively bred Sardinian alcohol-preferring (sP) rats exposed to a standard procedure of fixed ratio (FR) 4 (FR4) schedule of reinforcement for 15 % (v/v) alcohol.

RESULTS

Repeated treatment with GS39783 (50 mg/kg, i.g.) or rac-BHFF (50 mg/kg, i.g.) produced an initial 40 % reduction in number of lever responses for alcohol and amount of self-administered alcohol that was maintained unaltered throughout the 10-day period of the GS39783 treatment and increased throughout the 5-day period of the rac-BHFF treatment. Combination of per se ineffective doses of GS39783 (5 mg/kg, i.g.), or rac-BHFF (5 mg/kg, i.g.), and baclofen (1 mg/kg, i.p.) reduced, by 35-45 %, both number of lever responses for alcohol and amount of self-administered alcohol.

CONCLUSIONS

GS39783 and rac-BHFF (a) reduced alcohol reinforcing properties when given repeatedly, with no development of tolerance, and (b) potentiated baclofen effect. Both sets of data possess translational interest, as they suggest potential effectiveness of GABAB PAMs under chronic treatment and selective potentiation of baclofen effect.

Targeting GABAB receptors for anti-abuse drug discovery

INTRODUCTION

There is increasing evidence encouraging the development of drugs that positively modulate the γ-aminobutyric acid type B (GABA(B)) receptor for combating addiction. Compounds that target GABA(B) receptors are unique as anti-abuse therapies because of their impact against multiple addictive drugs.

AREAS COVERED

The authors present the basic information concerning the drug actions of GABA and GABA(B) receptor orthosteric agonists and positive allosteric modulators (PAM). Furthermore, they discuss several recent excellent reviews and newer results pertaining to GABA(B) receptor drug effects on responses to and self-administration of: alcohol (ethanol), nicotine, cocaine, (meth)amphetamine, and opioids. Preclinical and clinical data are considered.

EXPERT OPINION

Clinical data exist only for baclofen and mostly for alcohol use disorders. Additional trials are needed, but effects are promising. Whether PAMs, given alone or in combination with a direct GABA(B) receptor agonist, will be clinically effective and have fewer side effects requires investigation. The sedative effects of baclofen, a Food and Drug Administration (FDA)-approved drug, become less severe over time. Based on existing data, baclofen is well-tolerated. However, genetic and physiological differences are likely to contribute to individual responses to different therapeutic agents. The more immediate development of baclofen as a therapeutic for alcohol use disorders may be of significant benefit to some individuals.

Investigational therapies for the pharmacological treatment of alcoholism

Introduction: Alcohol dependence is one of the most important psychiatric disorders leading to enormous harm in individuals and indeed within society. Yet, although alcohol dependence is a disease of significant importance, the availability of efficacious pharmacological treatment is still limited. Areas covered: The current review focuses on neurobiological pathways that are the rationale for recent preclinical and clinical studies testing novel compounds that could be used as treatments for alcohol dependence. These neurobiological mechanisms include the: glutamatergic, dopaminergic and GABA mediated pathways as well as neuroendocrine systems. There is also an interest in the approaches for influencing chromatin structure. Expert opinion: There are several compounds in Phase I and Phase II clinical studies that have produced potentially useful results for the treating alcoholism. Further evaluation is still necessary, and the implementation of Phase III studies will help to elucidate the usefulness of these compounds. It is important that personalized approaches (e.g., pharmacogenomics) are investigated in these later studies, as the efficacy of different compounds may vary substantially between subgroups of patients.

GABAB receptor ligands for the treatment of alcohol use disorder: preclinical and clinical evidence

The present paper summarizes the preclinical and clinical studies conducted to define the "anti-alcohol" pharmacological profile of the prototypic GABAB receptor agonist, baclofen, and its therapeutic potential for treatment of alcohol use disorder (AUD). Numerous studies have reported baclofen-induced suppression of alcohol drinking (including relapse- and binge-like drinking) and alcohol reinforcing, motivational, stimulating, and rewarding properties in rodents and monkeys. The majority of clinical surveys conducted to date-including case reports, retrospective chart reviews, and randomized placebo-controlled studies-suggest the ability of baclofen to suppress alcohol consumption, craving for alcohol, and alcohol withdrawal symptomatology in alcohol-dependent patients. The recent identification of a positive allosteric modulatory binding site, together with the synthesis of in vivo effective ligands, represents a novel, and likely more favorable, option for pharmacological manipulations of the GABAB receptor. Accordingly, data collected to date suggest that positive allosteric modulators of the GABAB receptor reproduce several "anti-alcohol" effects of baclofen and display a higher therapeutic index (with larger separation-in terms of doses-between "anti-alcohol" effects and sedation).

Alcohol dependence and free-choice drinking in mice

Alcohol dependence continues to be an important health concern and animal models are critical to furthering our understanding of this complex disease. A hallmark feature of alcoholism is a significant increase in alcohol drinking over time. While several different animal models of excessive alcohol (ethanol) drinking exist for mice and rats, a growing number of laboratories are using a model that combines chronic ethanol exposure procedures with voluntary ethanol drinking with mice as experimental subjects. Primarily, these studies use a chronic intermittent ethanol (CIE) exposure pattern to render mice dependent and a 2-h limited access procedure to evaluate drinking behavior. Compared to non-dependent mice that also drink ethanol, the ethanol-dependent mice demonstrate significant increases in voluntary ethanol drinking. The increased drinking significantly elevates blood and brain ethanol concentrations compared to the non-dependent control mice. Studies report that the increased drinking by dependent mice is driven by neuroadaptations in glutamatergic and corticotropin-releasing factor signaling in different brain regions known to be involved in alcohol-related behaviors. The dysregulation of these systems parallels findings in human alcoholics and treatments that demonstrate efficacy in alcoholics can also reduce drinking in this model. Moreover, preclinical findings have informed the development of human clinical trials, further highlighting the translational potential of the model. As a result of these features, the CIE exposure and free-choice drinking model is becoming more widely used and promises to provide more insight into mechanisms of excessive drinking that may be important for developing treatments for human alcoholics. The salient features and possible future considerations for CIE exposure and free-choice drinking in mice are discussed.

ADX71441, a novel, potent and selective positive allosteric modulator of the GABA(B) receptor, shows efficacy in rodent models of overactive bladder

BACKGROUND AND PURPOSE

The GABAB receptor agonist baclofen reduces urethral resistance and detrusor overactivity in patients with spasticity. However, baclofen's side effects limit its use for the treatment of overactive bladder (OAB). Here, we tested a novel GABAB positive allosteric modulator (PAM) ADX71441 in models of OAB in mice and guinea pigs.

EXPERIMENTAL APPROACH

Mice were left untreated or given (p.o.) vehicle (1% CMC), ADX71441 (1, 3, 10 mg kg(-1) ) or oxybutynin (100 mg kg(-1) ; Experiment 1) or vehicle (1% CMC), baclofen (1, 3, 6 mg kg(-1) ) or oxybutynin (Experiment 2). Treated mice were then overhydrated with water, challenged with furosemide, before being placed into micturition chambers and monitored for urinary parameters. In anaesthetized guinea pigs, intravesical infusion of acetic acid was used to induce OAB and the effects of ADX71441 (1, 3 mg kg(-1) ) or baclofen (1 mg kg(-1) ), administered i.v., on cystometric parameters were monitored.

KEY RESULTS

In mice, 10 mg kg(-1) ADX71441 increased urinary latencies, reduced the number of urinary events and the total and average urinary volumes. In guinea pigs, ADX71441 (1 and 3 mg kg(-1) ) increased the intercontraction interval (ICI) and bladder capacity (BC), and reduced micturition frequency (MF) compared to vehicle. At 3 mg kg(-1) ADX71441 completely inhibited the micturition reflex and induced overflow incontinence in five out of 10 animals. Baclofen slightly increased ICI and BC and reduced MF.

CONCLUSION AND IMPLICATIONS

Our findings demonstrate, for the first time, that a GABAB PAM has potential as a novel approach for the treatment of OAB.