Phenotypic characterization of genetically selected Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats

Mesolimbic Neural Response Dynamics Predict Future Individual Alcohol Drinking in Mice

BACKGROUND

Individual variability in response to rewarding stimuli is a striking but understudied phenomenon. The mesolimbic dopamine system is critical in encoding the reinforcing properties of both natural reward and alcohol; however, how innate or baseline differences in the response dynamics of this circuit define individual behavior and shape future vulnerability to alcohol remain unknown.

METHODS

Using naturalistic behavioral assays, a voluntary alcohol drinking paradigm, in vivo fiber photometry, in vivo electrophysiology, and chemogenetics, we investigated how differences in mesolimbic neural circuit activity contribute to the individual variability seen in reward processing and, by proxy, alcohol drinking.

RESULTS

We first characterized heterogeneous behavioral and neural responses to natural reward and defined how these baseline responses predicted future individual alcohol-drinking phenotypes in male mice. We then determined spontaneous ventral tegmental area dopamine neuron firing profiles associated with responses to natural reward that predicted alcohol drinking. Using a dual chemogenetic approach, we mimicked specific mesolimbic dopamine neuron firing activity before or during voluntary alcohol drinking to link unique neurophysiological profiles to individual phenotype. We show that hyperdopaminergic individuals exhibit a lower neuronal response to both natural reward and alcohol that predicts lower levels of alcohol consumption in the future.

CONCLUSIONS

These findings reveal unique, circuit-specific neural signatures that predict future individual vulnerability or resistance to alcohol and expand the current knowledge base on how some individuals are able to titrate their alcohol consumption whereas others go on to engage in unhealthy alcohol-drinking behaviors.

Modeling Brain Gene Expression in Alcohol Use Disorder with Genetic Animal Models

Animal genetic models have and will continue to provide important new information about the behavioral and physiological adaptations associated with alcohol use disorder (AUD). This chapter focuses on two models, ethanol preference and drinking in the dark (DID), their usefulness in interrogating brain gene expression data and the relevance of the data obtained to interpret AUD-related GWAS and TWAS studies. Both the animal and human data point to the importance for AUD of changes in synaptic transmission (particularly glutamate and GABA transmission), of changes in the extracellular matrix (specifically including collagens, cadherins and protocadherins) and of changes in neuroimmune processes. The implementation of new technologies (e.g., cell type-specific gene expression) is expected to further enhance the value of genetic animal models in understanding AUD.

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.

Exposure to an enriched environment exerts anxiolytic effects in Sardinian alcohol-preferring rats

Exposure to an enriched environment (EE) has been reported to generate multiple beneficial effects in rodents, including - among the many - amelioration of anxiety-related behaviors. The present study investigated whether living in an EE produced anxiolytic effects also in selectively bred Sardinian alcohol-preferring (sP) rats. The relevance of this research question relied on two factors: sP rats displayed an inherent, high anxiety-like state under different experimental conditions; exposure to EE reduced operant, oral alcohol self-administration in sP rats. Starting from weaning, male sP rats were kept under 3 different housing conditions: impoverished environment (IE; single housing with no environmental enrichment); standard environment (SE; 3 rats/cage with no environmental enrichment); EE (6 rats/cage with various elements of environmental enrichment). At the age of approximately 80 days, rats were exposed to an elevated plus maze test for assessment of anxiety-related behaviors. Compared to IE and SE rats, EE rats displayed higher basal levels of exploratory activity (i.e., increased number of entries into closed arms). Compared to IE and SE rats, EE rats also displayed a less "anxious" profile, as suggested by the increase in percent number of entries into open arms (OAs), percent time spent in OAs, number of head dips, and number of end-arm explorations in OAs. These data extend the protective (anxiolytic) effects of EE to a proposed animal model of comorbid alcohol use disorder and anxiety disorders.

Role of Metabolism on Alcohol Preference, Addiction, and Treatment

Studies presented in this chapter show that: (1) in the brain, ethanol is metabolized by catalase to acetaldehyde, which condenses with dopamine forming salsolinol; (2) acetaldehyde-derived salsolinol increases the release of dopamine mediating, via opioid receptors, the reinforcing effects of ethanol during the acquisition of ethanol consumption, while (3) brain acetaldehyde does not influence the maintenance of chronic ethanol intake, it is suggested that a learned cue-induced hyperglutamatergic system takes precedence over the dopaminergic system. However, (4) following a prolonged ethanol deprivation, the generation of acetaldehyde in the brain again plays a role, contributing to the increase in ethanol intake observed during ethanol re-access, called the alcohol deprivation effect (ADE), a model of relapse behavior; (5) naltrexone inhibits the high ethanol intake seen in the ADE condition, suggesting that acetaldehyde-derived salsolinol via opioid receptors also contributes to the relapse-like drinking behavior. The reader is referred to glutamate-mediated mechanisms that trigger the cue-associated alcohol-seeking and that also contribute to triggering relapse.

Epigenetic Dysregulation in Alcohol-Associated Behaviors: Preclinical and Clinical Evidence

Alcohol use disorder (AUD) is characterized by loss of control over intake and drinking despite harmful consequences. At a molecular level, AUD is associated with long-term neuroadaptations in key brain regions that are involved in reward processing and decision-making. Over the last decades, a great effort has been made to understand the neurobiological basis underlying AUD. Epigenetic mechanisms have emerged as an important mechanism in the regulation of long-term alcohol-induced gene expression changes. Here, we review the literature supporting a role for epigenetic processes in AUD. We particularly focused on the three most studied epigenetic mechanisms: DNA methylation, Histone modification and non-coding RNAs. Clinical studies indicate an association between AUD and DNA methylation both at the gene and global levels. Using behavioral paradigms that mimic some of the characteristics of AUD, preclinical studies demonstrate that changes in epigenetic mechanisms can functionally impact alcohol-associated behaviors. While many studies support a therapeutic potential for targeting epigenetic enzymes, more research is needed to fully understand their role in AUD. Identification of brain circuits underlying alcohol-associated behaviors has made major advances in recent years. However, there are very few studies that investigate how epigenetic mechanisms can affect these circuits or impact the neuronal ensembles that promote alcohol-associated behaviors. Studies that focus on the role of circuit-specific and cell-specific epigenetic changes for clinically relevant alcohol behaviors may provide new insights on the functional role of epigenetic processes in AUD.

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.

Cellular Bioenergetics: Experimental Evidence for Alcohol-induced Adaptations

At-risk alcohol use is associated with multisystemic effects and end-organ injury, and significantly contributes to global health burden. Several alcohol-mediated mechanisms have been identified, with bioenergetic maladaptation gaining credence as an underlying pathophysiological mechanism contributing to cellular injury. This evidence-based review focuses on the current knowledge of alcohol-induced bioenergetic adaptations in metabolically active tissues: liver, cardiac and skeletal muscle, pancreas, and brain. Alcohol metabolism itself significantly interferes with bioenergetic pathways in tissues, particularly the liver. Alcohol decreases states of respiration in the electron transport chain, and activity and expression of respiratory complexes, with a net effect to decrease ATP content. In addition, alcohol dysregulates major metabolic pathways, including glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation. These bioenergetic alterations are influenced by alcohol-mediated changes in mitochondrial morphology, biogenesis, and dynamics. The review highlights similarities and differences in bioenergetic adaptations according to tissue type, pattern of (acute vs. chronic) alcohol use, and energy substrate availability. The compromised bioenergetics synergizes with other critical pathophysiological mechanisms, including increased oxidative stress and accelerates cellular dysfunction, promoting senescence, programmed cell death, and end-organ injury.

Exposure to an enriched environment reduces alcohol self-administration in Sardinian alcohol-preferring rats

Living in an enriched environment (EE) produces a notable impact on several rodent behaviors, including those motivated by drugs of abuse. This picture is somewhat less clear when referring to alcohol-motivated behaviors. With the intent of contributing to this research field with data from one of the few rat lines selectively bred for excessive alcohol consumption, the present study investigated the effect of EE on operant oral alcohol self-administration in Sardinian alcohol-preferring (sP) rats. Starting from Postnatal Day (PND) 21, male sP rats were kept under 3 different housing conditions: impoverished environment (IE; single housing in shoebox-like cages with no environmental enrichment); standard environment (SE; small colony cages with 3 rats and no environmental enrichment); EE (large colony cages with 6 rats and multiple elements of environmental enrichment, including 2 floors, ladders, maze, running wheels, and shelter). From PND 60, rats were exposed to different phases of shaping and training of alcohol self-administration. IE, SE, and EE rats were then compared under (i) fixed ratio (FR) 4 (FR4) schedule of alcohol reinforcement for 20 daily sessions and (ii) progressive ratio (PR) schedule of alcohol reinforcement in a final single session. Acquisition of the lever-responding task (shaping) was slower in EE than IE and SE rats, as the likely consequence of a "devaluation" of the novel stimuli provided by the operant chamber in comparison to those to which EE rats were continuously exposed in their homecage or an alteration, induced by EE, of the rat "emotionality" state when facing the novel environment represented by the operant chamber. Training of alcohol self-administration was slower in EE than IE rats, with SE rats displaying intermediate values. A similar ranking order (IE>SE>EE) was also observed in number of lever-responses for alcohol, amount of self-administered alcohol, and breakpoint for alcohol under FR4 and PR schedules of reinforcement. These data suggest that living in a complex environment reduced the reinforcing and motivational properties of alcohol in sP rats. These results are interpreted in terms of the reinforcing and motivational properties of the main components of EE (i.e., social interactions, physical activities, exploration, novelty) substituting, at least partially, for those of alcohol.

Pituitary adenylate cyclase-activating polypeptide type 1 receptor within the nucleus accumbens core mediates excessive alcohol drinking in alcohol-preferring rats

Alcohol use disorders (AUD) have a strong component of heritability; however, the neurobiological mechanisms mediating the propensity to consume excessive amounts of alcohol are still not well understood. Pituitary adenylate cyclase-activating polypeptide (PACAP), a highly conserved neuropeptide which exerts its effects mainly through the PAC1 receptor (PAC1R), has been suggested to be one of the mediators of the effects of drugs of abuse and alcohol. Here, we investigated the role of the PACAP/PAC1R system in excessive alcohol drinking in alcohol-preferring rats, an established animal model of AUD. Intracerebroventricular (i.c.v.) administration of the PAC1R antagonist PACAP(6-38) blocked excessive alcohol drinking and motivation to drink in Sardinian alcohol-preferring (Scr:sP) rats, without affecting water, saccharin, or sucrose intake. Notably, PACAP(6-38) did not affect ethanol responding in outbred Wistar rats. PACAP(6-38) also significantly reduced alcohol-seeking behavior under a second-order schedule of reinforcement. Using immunohistochemistry, a significant increase in the number of PAC1R positive cells was observed selectively in the nucleus accumbens (NAcc) Core of Scr:sP rats, compared to Wistar rats following alcohol drinking. Finally, excessive drinking in Scr:sP rats was suppressed by intra-NAcc Core, but not intra-NAcc Shell, PACAP(6-38), as well as by virally-mediated PAC1R knockdown in the NAcc Core. The present study shows that hyperactivity of the PACAP/PAC1R system specifically in the NAcc Core mediates excessive drinking of alcohol-preferring rats, and indicates that this system may represent a novel target for the treatment of AUD.

Blockade of the GABAB receptor suppressed alcohol self-administration in rats: an effect similar to that produced by GABAB receptor activation

Literature data suggest that activation and blockade of the GABAB receptor may produce similar effects on several reward-related behaviours. Accordingly, the present study was designed to investigate whether treatment with the GABAB receptor antagonist, SCH 50911, reproduced the suppressing effect of the GABAB receptor agonist, baclofen, and several positive allosteric modulators of the GABAB receptor on operant oral alcohol self-administration in rats. To this end, Sardinian alcohol-preferring (sP) rats were trained to lever-respond for alcohol (15% v/v) under the fixed ratio (FR) 4 (FR4) schedule of reinforcement. Once lever-responding had stabilized, rats were exposed to test sessions preceded by treatment with SCH 50911 (0, 25, 50, and 100 mg/kg; i.p.). Two independent experiments were conducted, differing solely in the set of rats used. Selectivity of SCH 50911 effect on alcohol self-administration was assessed by evaluating the effect of SCH 50911 (0, 25, 50, and 100 mg/kg; i.p.) on self-administration of a sucrose solution (0.7% w/v) in sP rats exposed to the FR4 schedule. In both 'alcohol' experiments, treatment with SCH 50911 reduced lever-responding for alcohol and amount of self-administered alcohol. SCH 50911 effect was characterized by large interindividual variability, with several instances of dose-unrelated reductions, and frequent occurrence of complete suppression of lever-responding for alcohol. Similar data were collected in the 'sucrose' experiment. These results extend to alcohol self-administration with the notion that activation and blockade of GABAB receptor may produce unidirectional effects on reward-related behaviours; these similarities are discussed in terms of differential contribution of pre- and postsynaptic GABAB receptors.

Behavioral Profiles of Adolescent Alcohol-Preferring/Non-preferring (P/NP) and High/Low Alcohol-Drinking (HAD/LAD) Rats Are Dependent on Line but Not Sex

Initial contact with alcohol generally occurs during adolescence, and high consumption during this period is associated with increased risk for later alcohol (AUDs) and/or substance use disorders (SUDs). Rodents selectively bred for high or low alcohol consumption are used to identify behavioral characteristics associated with a propensity for high or low voluntary alcohol intake. The multivariate concentric square field™ (MCSF) is a behavioral test developed to study rodents in a semi-naturalistic setting. Testing in the MCSF creates a comprehensive behavioral profile in a single trial. The current aim was to examine the behavioral profiles of adolescent, bidirectionally selectively bred male and female high alcohol-consuming (P and HAD1/2) and low alcohol-consuming (NP and LAD1/2) rat lines, and outbred Wistar rats. Alcohol-naïve rats were tested once in the MCSF at an age between postnatal days 30 and 35. No common behavioral profile was found for either high or low alcohol-consuming rat lines, and the effect of sex was small. The P/NP and HAD2/LAD2 lines showed within pair-dependent differences, while the HAD1/LAD1 lines were highly similar. The P rats displayed high activity and risk-associated behaviors, whereas HAD2 rats displayed low activity, high shelter-seeking behavior, and open area avoidance. The results from P rats parallel clinical findings that denser family history and risk-taking behavior are strong predictors of future AUDs, often with early onset. Contrarily, the HAD2 behavioral profile was similar to individuals experiencing negative emotionality, which also is associated with a vulnerability to develop, often with a later onset, AUDs and/or SUDs.

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.

Viral-Mediated Knockdown of Nucleus Accumbens Shell PAC1 Receptor Promotes Excessive Alcohol Drinking in Alcohol-Preferring Rats

Alcohol use disorder (AUD) is a chronic, relapsing disorder whose genetic and environmental susceptibility components are not fully understood. Neuropeptidergic signaling has been repeatedly implicated in modulating excessive alcohol drinking, especially within sub-regions of the striatum. Here, we investigated the potential involvement of the selective receptor for pituitary adenylate cyclase-activating polypeptide (PACAP), PAC1R, in the nucleus accumbens shell (NAcc Shell) in excessive alcohol drinking in alcohol-preferring rats, an established animal model of the genetic propensity for alcoholism. Scr:sP alcohol-preferring rats were trained to operantly self-administer alcohol and then either an AAV virus short-hairpin RNA (shRNA) targeted to knockdown PAC1R, or an AAV control virus were microinfused into the NAcc Shell. NAcc Shell PAC1R shRNA knockdown virus was confirmed to significantly decrease PAC1R levels in the NAcc Shell. The effects of NAcc Shell PAC1R shRNA knockdown on ethanol self-administration were investigated using a Fixed Ratio (FR) 1 and a Progressive Ratio (PR) schedule of reinforcement. The effect of PAC1R knockdown on self-administration of an alternative reinforcer, saccharin, was also assessed. The results showed that the reduction in PAC1R in the NAcc Shell led to excessive ethanol drinking, increased preference for ethanol, and higher motivation to drink. NAcc Shell PAC1R shRNA knockdown did not comparably increase saccharin self-administration, suggesting selectivity of action. These data suggest that NAcc Shell PAC1R may serves as a "brake" on alcohol drinking, and thereby the loss of function of PAC1R leads to excessive alcohol consumption. Therefore, the PACAP/PAC1R system may represent a novel target for the treatment of AUD.

Combined and sequential effects of alcohol and methamphetamine in animal models

Comorbid drug use, often alcohol with other drugs, poses significant health and societal concerns. Methamphetamine is among the illicit drugs most often co-used with alcohol. The current review examines the animal literature for impacts of comorbid alcohol and methamphetamine exposure. We found evidence for additive or synergistic effects of combined or sequential exposure on behavior and physiology. Dopaminergic, serotonergic, and glutamatergic systems are all impacted by combined exposure to alcohol and methamphetamine and cyclooxygenase-2 activity plays an important role in their combined neurotoxic effects. Adverse consequences of comorbid exposure include altered brain development with prenatal exposure, impaired learning and memory, motor deficits, gastrotoxicity, hepatotoxicity, and augmented intake under some conditions. Given high susceptibility to drug experimentation in adolescence, studies of co-exposure during the adolescent period and of how adolescent exposure to one drug impacts later use or sensitivity to the other drug should be a priority. Further, to gain traction on prevention and treatment, additional research to identify motivational and neurobiological drivers and consequences of comorbid use is needed.

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.

The effect of telmisartan, an angiotensin receptor blocker, on alcohol consumption and alcohol-induced dopamine release in the nucleus accumbens

Alcohol use disorder remains a major health problem. The mesocorticolimbic dopaminergic system, including the nucleus accumbens region and multiple neural circuits, is involved in its complex underlying mechanism. For instance, alcohol intake stimulates the central and peripheral renin-angiotensin system and increases angiotensin II levels, which predominantly affect angiotensin 1 receptors both in the periphery and in the brain. In this study, we aimed to investigate the effects of the intracerebroventricularly-administered angiotensin 1 receptor blocker telmisartan on the alcohol consumption of male Sardinian alcohol-preferring (sP) rats and on the alcohol-induced dopamine levels in the nucleus accumbens region in Wistar rats. Acute intracerebroventricular administration of telmisartan (100 nM) reduced the alcohol intake for 24 hours without affecting food and water consumption in sP rats. Acute intracerebroventricular injection of the opioid receptor antagonist naloxone (75 nM), tested as a reference compound, also reduced the alcohol consumption in sP rats; however, naloxone's effect lasted only for 30 minutes. In microdialysis experiments, telmisartan administered intracerebroventricularly did not change dopamine levels in the nucleus accumbens that had been induced by acute intraperitoneal alcohol administration in Wistar rats. According to these results, further studies are needed to elucidate the role of the renin-angiotensin system on alcohol use disorder pathophysiology.

The GABAB receptor positive allosteric modulator ASP8062 reduces operant alcohol self-administration in male and female Sprague Dawley rats

RATIONALE

Pre-clinical evidence implicates the GABAergic system in mediating the reinforcing effects of alcohol and offers a therapeutic target for alcohol use disorder (AUD). The orthosteric GABA_B receptor agonist baclofen decreases alcohol self-administration in animals and alcohol use in humans; however side effects limit its utility. Pre-clinical evidence shows positive allosteric GABA_B receptor modulators also decrease alcohol self-administration without untoward side effects.

OBJECTIVES

We assessed the impact of the novel GABA_B-positive allosteric modulator ASP8062 and baclofen on operant alcohol self-administration and their potential non-specific effects.

METHODS

The effects of ASP8062 (1 - 10 mg/kg, PO) and baclofen (0.3 - 3 mg/kg, IP) were evaluated in male and female rats lever pressing for alcohol (10%, w/v) under a fixed ratio 2 schedule of reinforcement. On the fourth consecutive day of vehicle, ASP8062 or baclofen administration, active and inactive lever presses, reinforcers earned, head entries, and estimated alcohol consumed were analyzed. Locomotor activity was assessed in separate groups of rats following dosing.

RESULTS

Both ASP8062 and baclofen decreased alcohol self-administration and amount consumed (g/kg) in male and female rats. ASP8062 decreased operant alcohol self-administration to a greater extent in male rats, whereas baclofen was more efficacious in female rats. ASP8062 did not alter locomotor activity in either sex, whereas baclofen (3.0 mg/kg) decreased activity in male rats yet (1.0 mg/kg) increased activity in female rats.

CONCLUSIONS

ASP8062 decreases alcohol reinforcement like baclofen but without non-specific effects which are influenced by sex. Results support further development of ASP8062 as a potential treatment for AUD in humans.

Role of inflammation in alcohol-related brain abnormalities: a translational study

Brain abnormalities observed in alcohol use disorder are highly heterogeneous in nature and severity, possibly because chronic alcohol consumption also affects peripheral organs leading to comorbidities that can result in exacerbated brain alterations. Despite numerous studies focussing on the effects of alcohol on the brain or liver, few studies have simultaneously examined liver function and brain damage in alcohol use disorder, and even fewer investigated the relationship between them except in hepatic encephalopathy. And yet, liver dysfunction may be a risk factor for the development of alcohol-related neuropsychological deficits and brain damage well before the development of liver cirrhosis, and potentially through inflammatory responses. The use of animal models enables a better understanding of the pathophysiological mechanisms underlying liver–brain relationships in alcohol use disorder, and more particularly of the inflammatory response at the tissue, cerebral and hepatic levels. The objective of this translational study was to investigate, both in alcohol use disorder patients and in a validated animal model of alcohol use disorder, the links between peripheral inflammation, liver damage and brain alterations. To do this, we conducted an in vivo neuroimaging examination and biological measures to evaluate brain volumes, liver fibrosis and peripheral cytokines in alcohol use disorder patients. In selectively bred Sardinian alcohol-preferring rats, we carried out ex vivo neuroimaging examination and immunohistochemistry to evaluate brain and liver inflammatory responses after chronic (50 consecutive weeks) alcohol drinking. In recently abstinent and non-cirrhotic alcohol use disorder patients, the score of liver fibrosis positively correlated with subcortical regions volumes (especially in right and left putamen) and level of circulating proinflammatory cytokines. In Sardinian alcohol-preferring rats, we found macrostructural brain damage and microstructural white matter abnormalities similar to those found in alcohol use disorder patients. In addition, in agreement with the results of peripheral inflammation observed in the patients, we revealed, in Sardinian alcohol-preferring rats, inflammatory responses in the brain and liver were caused by chronic alcohol consumption. Since the liver is the main source of cytokines in the human body, these results suggest a relationship between liver dysfunction and brain damage in alcohol use disorder patients, even in the absence of major liver disease. These findings encourage considering new therapeutic strategies aiming at treating peripheral organs to limit alcohol-related brain damage.

Reducing Effect of Cannabidiol on Alcohol Self-Administration in Sardinian Alcohol-Preferring Rats

Introduction: Cannabidiol (CBD) is a major cannabinoid extracted from Cannabis sativa with no abuse potential. Data from recent rodent studies suggest that amelioration of alcohol-motivated behaviors may be one of the numerous pharmacological effects of CBD. This study was designed to contribute to this research, assessing the effect of CBD on operant oral alcohol self-administration in selectively bred Sardinian alcohol-preferring (sP) rats, a validated animal model of excessive alcohol consumption. In addition, this study investigated the effect of CBD on operant self-administration of a highly palatable chocolate solution in Wistar rats. Materials and Methods: Male sP rats were trained to lever respond for alcohol (15% v/v) under the fixed ratio 4 (FR4) schedule of reinforcement. Once lever responding had stabilized, rats were exposed to test sessions under the FR4 and progressive ratio (PR) schedules of reinforcement. Test sessions were preceded by acute treatment with CBD (0, 6.25, 12.5, and 25 mg/kg or 0, 25, 50, and 100 mg/kg, i.p.; each dose range was tested in an independent experiment). Male Wistar rats were trained to lever respond for a chocolate solution (5% w/v chocolate powder) under the FR10 schedule of reinforcement. Once lever responding had stabilized, rats were exposed to test sessions under the same schedule. Test sessions were preceded by acute treatment with CBD (0, 6.25, 12.5, and 25 mg/kg or 0, 25, 50, and 100 mg/kg, i.p., in two independent experiments). Results: Under the FR schedule, treatment with doses of CBD ≥12.5 mg/kg markedly reduced lever responding for alcohol and amount of self-administered alcohol. Under the PR schedule, treatment with CBD produced a slight tendency toward a decrease in lever responding and breakpoint for alcohol. Finally, no dose of CBD affected lever responding for the chocolate solution and amount of self-administered chocolate solution. Discussion: These results extend previous data on CBD ability to affect alcohol-motivated behaviors to an animal model of genetically-determined proclivity to high alcohol consumption. Because of the predictive validity of sP rats, these results may be of relevance in view of possible future studies testing CBD in patients affected by alcohol use disorder.

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.'

Recent advances with 5-HT3 modulators for neuropsychiatric and gastrointestinal disorders

Serotonin (5-hydroxytryptophan [5-HT]) is a biologically active amine expressed in platelets, in gastrointestinal (GI) cells and, to a lesser extent, in the central nervous system (CNS). This biogenic compound acts through the activation of seven 5-HT receptors (5-HT_1-7 Rs). The 5-HT₃ R is a ligand-gated ion channel belonging to the Cys-loop receptor family. There is a wide variety of 5-HT₃ R modulators, but only receptor antagonists (known as setrons) have been used clinically for chemotherapy-induced nausea and vomiting and irritable bowel syndrome treatment. However, since the discovery of the setrons in the mid-1980s, a large number of studies have been published exploring new potential applications due their potency in the CNS and mild side effects. The results of these studies have revealed new potential applications, including the treatment of neuropsychiatric disorders such as schizophrenia, depression, anxiety, and drug abuse. In this review, we provide information related to therapeutic potential of 5-HT₃ R antagonists on GI and neuropsychiatric disorders. The major attention is paid to the structure, function, and pharmacology of novel 5-HT₃ R modulators developed over the past 10 years.

Differential Effects of Saikosaponins A, B2, B4, C and D on Alcohol and Chocolate Self-Administration in Rats

AIMS

Treatment with saikosaponin A (SSA)-an ingredient of the medicinal herb, Bupleurum falcatum-has been reported to suppress several addictive-like behaviors, including morphine, cocaine, alcohol and chocolate self-administration in male rats. The aim of this investigation was to investigate whether saikosaponins of B. falcatum other than SSA affect alcohol and chocolate self-administration in rats.

METHODS

Ovariectomized female Sardinian alcohol-preferring (sP) and Wistar rats were trained to self-administer alcohol (15%, v/v) and a chocolate solution [5% (w/v) Nesquik® in water], respectively, under fixed ratio schedules of reinforcement. The following saikosaponins were compared to SSA: saikosaponin D (SSD; epimer of SSA), saikosaponin C (SSC), saikosaponin B2 (SSB2) and saikosaponin B4 (SSB4). All saikosaponins were tested acutely at the doses of 0, 0.25, 0.5 and 1 mg/kg (i.p.).

RESULTS

Treatment with SSA and SSD resulted in highly similar, marked reductions in alcohol self-administration; SSC failed to alter lever-responding for alcohol, while SSB2 and SSB4 produced intermediate reductions. Only SSA and SSD reduced chocolate self-administration, with SSC, SSB2 and SSB4 being ineffective.

CONCLUSIONS

The wide spectrum of efficacy of saikosaponins in reducing alcohol and chocolate self-administration suggests that even relatively small structural differences are sufficient to produce remarkable changes in their in vivo pharmacological profile. Together, these results confirm that roots of B. falcatum may be an interesting source of compounds with anti-addictive potential.

Sigma receptor-induced heavy drinking in rats: Modulation by the opioid receptor system

Alcohol use disorder (AUD) is a major cause of morbidity and mortality worldwide, for which new efficacious treatments are necessary. The opioid receptor system is a mediator of the rewarding effects of alcohol; in particular, while activation of μ opioid receptors enhances ethanol intake in rodents, opioid-receptor antagonists, such as naloxone and naltrexone, reduce its pleasurable and reinforcing effects, thereby decreasing alcohol. Sigma receptors (Sig-Rs) have been proposed as modulators of the effects of alcohol and, therefore, as a potential new pharmacological target for AUD. Somewhat analogously to μ opioid ligands, SigR agonists increase, while SigR antagonists decrease alcohol intake in animal models of excessive alcohol drinking. However, a potential cross-talk between these two receptor systems in relation to alcohol consumption has so far not been investigated. Here, we addressed this question pharmacologically, by testing the effects of either activating or inhibiting opioid receptors on the heavy alcohol drinking induced by chronic stimulation of SigR in alcohol-preferring rats. We found that the opioid receptor agonist morphine, which per se increases ethanol intake, at a sub-threshold dose reduces the binge-like drinking induced by the repeated treatment with the SigR agonist 1,3-di-o-tolylguanidine (DTG); conversely, the opioid receptor antagonist naltrexone, which per se reduces ethanol intake, at a sub-threshold dose potentiates the DTG-induced binge-like drinking. Our data show a cross-talk between the opioid and SigR systems relevant to the modulation of alcohol drinking, which provides important insights into the neurobiology of AUD and may lead to the development of novel therapies, either standalone or in combination.

Operant, oral alcohol self-administration: Sex differences in Sardinian alcohol-preferring rats

Sardinian alcohol-preferring (sP) rats have been selectively bred, over almost 40 years, for high alcohol preference and consumption. sP rats have served as an animal model for more than 120 published studies. With very few exceptions, however, these studies have always employed male sP rats, and little is known about alcohol-related behaviors in female sP rats. The present study was designed to fill, at least in part, this gap. Accordingly, alcohol self-administration under the fixed ratio 4 schedule of reinforcement was compared among male, intact female, and ovariectomized female sP rats. Additionally, it was investigated whether i) estrous cycle influenced alcohol self-administration, and ii) alcohol self-administration in the three sP rat groups differed in sensitivity to pharmacological manipulation. Lever-responding for alcohol was steadily higher in male than intact and ovariectomized female sP rats; conversely, because of large sex differences in rat body weight, estimated amount of self-administered alcohol (in g/kg) did not differ among the three sP rat groups or occasionally was higher in intact female than male and ovariectomized female sP rats. Blood alcohol levels derived from self-administered alcohol i) did not differ among the three sP rat groups and ii) were positively correlated with the number of lever-responses for alcohol and the estimated amount of self-administered alcohol. Treatment with the opioid receptor antagonist, naloxone (0, 0.3, 1, and 3 mg/kg, i.p. [intraperitoneally]), and the positive allosteric modulator of the GABA_B receptor, GS39783 (0, 25, 50, and 100 mg/kg, i.g. [intragastrically]), reduced alcohol self-administration with comparable potency and efficacy in the three sP rat groups. The impact of the estrous cycle on alcohol self-administration was relatively modest, limited to a tendency toward a reduction in the number of lever-responses for alcohol and the estimated amount of self-administered alcohol in estrus and metestrus. Together, these results provide the first characterization of alcohol-seeking and -taking behavior in female sP rats.

5-HT3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface

5-HT3 receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT3 receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT3 receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.

Role of Sigma Receptors in Alcohol Addiction

Pharmacological treatments for alcohol use disorder (AUD) are few in number and often ineffective, despite the significant research carried out so far to better comprehend the neurochemical underpinnings of the disease. Hence, research has been directed towards the discovery of novel therapeutic targets for the treatment of AUD. In the last decade, the sigma receptor system has been proposed as a potential mediator of alcohol reward and reinforcement. Preclinical studies have shown that the motivational effects of alcohol and excessive ethanol consumption involve the recruitment of the sigma receptor system. Furthermore, sigma receptor antagonism has been shown to be sufficient to inhibit many behaviors related to AUDs. This paper will review the most current evidence in support of this receptor system as a potential target for the development of pharmacological agents for the treatment of alcohol addiction.

An amylin analogue attenuates alcohol-related behaviours in various animal models of alcohol use disorder

Recent findings have identified salmon calcitonin (sCT), an amylin receptor agonist and analogue of endogenous amylin, as a potential regulator of alcohol-induced activation of the mesolimbic dopamine system and alcohol consumption. Providing that the role of amylin signalling in alcohol-related behaviours remains unknown, the present experiments investigate the effect of sCT on these behaviours and the mechanisms involved. We showed that repeated sCT administration decreased alcohol and food intake in outbred rats. Moreover, single administration of the potent amylin receptor antagonist, AC187, increased short-term alcohol intake in outbred alcohol-consuming rats, but did not affect food intake. Acute administration of sCT prevented relapse-like drinking in the "alcohol deprivation effect" model in outbred alcohol-experienced rats. Additionally, acute sCT administration reduced operant oral alcohol self-administration (under the fixed ratio 4 schedule of reinforcement) in selectively bred Sardinian alcohol-preferring rats, while it did not alter operant self-administration (under the progressive ratio schedule of reinforcement) of a highly palatable chocolate-flavoured beverage in outbred rats. Lastly, we identified differential amylin receptor expression in high compared to low alcohol-consuming rats, as reflected by decreased calcitonin receptor and increased receptor activity modifying protein 1 expression in the nucleus accumbens (NAc) of high consumers. Collectively, our data suggest that amylin signalling, especially in the NAc, may contribute to reduction of various alcohol-related behaviours.

Predisposition to Alcohol Drinking and Alcohol Consumption Alter Expression of Calcitonin Gene-Related Peptide, Neuropeptide Y, and Microglia in Bed Nucleus of Stria Terminalis in a Subnucleus-Specific Manner

Excessive alcohol consumption is often linked to anxiety states and has a major relay center in the anterior part of bed nucleus of stria terminalis (BNST). We analyzed the impact of (i) genetic predisposition to high alcohol preference and consumption, and (ii) alcohol intake on anterior BNST, namely anterolateral (AL), anteromedial (AM), and anteroventral (lateral + medial subdivisions: AVl, AVm) subnuclei. We used two rat lines selectively bred for low- and high-alcohol preference and consumption, named Sardinian alcohol-non preferring (sNP) and -preferring (sP), respectively, the latter showing also inherent anxiety-related behaviors. We analyzed the modulation of calcitonin gene-related peptide (CGRP; exerting anxiogenic effects in BNST), neuropeptide Y (NPY; exerting mainly anxiolytic effects), and microglia activation (neuroinflammation marker, thought to increase anxiety). Calcitonin gene-related peptide-immunofluorescent fibers/terminals did not differ between alcohol-naive sP and sNP rats. Fiber/terminal NPY-immunofluorescent intensity was lower in BNST-AM and BNST-AVm of alcohol-naive sP rats. Activation of microglia (revealed by morphological analysis) was decreased in BNST-AM and increased in BNST-AVm of alcohol-naive sP rats. Prolonged (30 consecutive days), voluntary alcohol intake under the homecage 2-bottle “alcohol vs. water” regimen strongly increased CGRP intensity in BNST of sP rats in a subnucleus-specific manner: in BNST-AL, BNST-AVm, and BNST-AM. CGRP area sum, however, decreased in BNST-AM, without changes in other subnuclei. Alcohol consumption increased NPY expression, in a subnucleus-specific manner, in BNST-AL, BNST-AVl, and BNST-AVm. Alcohol consumption increased many size/shapes parameters in microglial cells, indicative of microglia de-activation. Finally, microglia density was increased in ventral anterior BNST (BNST-AVl, BNST-AVm) by alcohol consumption. In conclusion, genetic predisposition of sP rats to high alcohol intake could be in part mediated by anterior BNST subnuclei showing lower NPY expression and differential microglia activation. Alcohol intake in sP rats produced complex subnucleus-specific changes in BNST, affecting CGRP/NPY expression and microglia and leading to hypothesize that these changes might contribute to the anxiolytic effects of voluntarily consumed alcohol repeatedly observed in sP rats.

Anti-addictive properties of COR659 - Additional pharmacological evidence and comparison with a series of novel analogues

A recent study found that COR659 (methyl 2-[(4-chlorophenyl)carboxamido]-4-ethyl-5-methylthiophene-3-carboxylate) reduced operant alcohol and chocolate self-administration in rats; COR659 also suppressed cue-induced reinstatement of chocolate seeking in rats. COR659 apparently exerts its effects via a composite mechanism, including positive allosteric modulation of the GABA_B receptor and an action at the cannabinoid CB₁ receptor. The present study investigated whether the reducing effect of COR659 on alcohol and chocolate self-administration was maintained after repeated treatment and if COR659 affected cue-induced reinstatement of alcohol seeking; additionally, it evaluated the ability of 9 structural analogues of COR659 - designed modifying the substituents on the phenylcarboxamido moiety and replacing the thiophene with the pyridine ring - to affect alcohol and chocolate self-administration. Alcohol self-administration experiments employed Sardinian alcohol-preferring (sP) rats trained to lever-respond for alcohol (15% v/v). Chocolate self-administration experiments employed Wistar rats trained to lever-respond for a chocolate solution (5% w/v Nesquik^®). In the reinstatement experiment, previously extinguished lever-responding for alcohol in sP rats was reinstated by the non-contingent presentation of an alcohol-associated complex of cues. All drugs were tested at the doses of 0, 2.5, 5, and 10 mg/kg (i.p.). 10-Day treatment with COR659 produced a dose-related reduction of both alcohol and chocolate self-administration, with limited loss of efficacy on continuing treatment. Acute COR659 suppressed reinstatement of alcohol seeking. Among the 9 tested analogues, only COR657 (methyl 2-(benzoylamino)-4-ethyl-5-methylthiophene-3-carboxylate) decreased alcohol self-administration similarly to COR659; all other compounds produced modest, or even no, effect on alcohol self-administration. COR659 excluded, no compound altered chocolate self-administration. These results confirm and extend the ability of COR659 to reduce several behaviors motivated by alcohol and palatable food in rats. Comparison of COR659 to its analogues provided disparate results that do not currently allow any conclusive structure-activity relationship to be hypothesized, as their diverse pharmacological profile apparently does not depend on physicochemical properties.

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.

The role of the orbitofrontal cortex in alcohol use, abuse, and dependence

One of the major functions of the orbitofrontal cortex (OFC) is to promote flexible motivated behavior. It is no surprise, therefore, that recent work has demonstrated a prominent impact of chronic drug use on the OFC and a potential role for OFC disruption in drug abuse and addiction. Among drugs of abuse, the use of alcohol is particularly salient with respect to OFC function. Although a number of studies in humans have implicated OFC dysregulation in alcohol use disorders, animal models investigating the association between OFC and alcohol use are only beginning to be developed, and there is still a great deal to be revealed. The goal of this review is to consider what is currently known regarding the role of the OFC in alcohol use and dependence. I will first provide a brief, general overview of current views of OFC function and its contributions to drug seeking and addiction. I will then discuss research to date related to the OFC and alcohol use, both in human clinical populations and in non-human models. Finally I will consider issues and strategies to guide future study that may identify this brain region as a key player in the transition from moderated to problematic alcohol use and dependence.

Liver Injury, Endotoxemia, and Their Relationship to Intestinal Microbiota Composition in Alcohol-Preferring Rats

BACKGROUND

There is strong evidence that alcoholism leads to dysbiosis in both humans and animals. However, it is unclear how changes in the intestinal microbiota (IM) relate to ethanol (EtOH)-induced disruption of gut-liver homeostasis. We investigated this issue using selectively bred Sardinian alcohol-preferring (sP) rats, a validated animal model of excessive EtOH consumption.

METHODS

Independent groups of male adult sP rats were exposed to the standard, home-cage 2-bottle "EtOH (10% v/v) versus water" choice regimen with unlimited access for 24 h/d (Group Et) for 3 (T1), 6 (T2), and 12 (T3) consecutive months. Control groups (Group Ct) were composed of matched-age EtOH-naïve sP rats. We obtained samples from each rat at the end of each experimental time, and we used blood and colon tissues for intestinal barrier integrity and/or liver pathology assessments and used stool samples for IM analysis with 16S ribosomal RNA gene sequencing.

RESULTS

Rats in Group Et developed hepatic steatosis and elevated serum transaminases and endotoxin/lipopolysaccharide (LPS) levels but no other liver pathological changes (i.e., necrosis/inflammation) or systemic inflammation. While we did not find any apparent alteration of the intestinal colonic mucosa, we found that rats in Group Et exhibited significant changes in IM composition compared to the rats in Group Ct. These changes were sustained throughout T1, T2, and T3. In particular, Ruminococcus, Coprococcus, and Streptococcus were the differentially abundant microbial genera at T3. The KEGG Ortholog profile revealed that IM functional modules, such as biosynthesis, transport, and export of LPS, were also enriched in Group Et rats at T3.

CONCLUSIONS

We showed that chronic, voluntary EtOH consumption induced liver injury and endotoxemia together with dysbiotic changes in sP rats. This work sets the stage for improving our knowledge of the prevention and treatment of EtOH-related diseases.

Involvement of Activated Brain Stress Responsive Systems in Excessive and "Relapse" Alcohol Drinking in Rodent Models: Implications for Therapeutics

Addictive diseases, including addiction to alcohol, pose massive public health costs. Addiction is a chronic relapsing disease caused by both the direct effects induced by drugs and persistent neuroadaptations at the molecular, cellular, and behavioral levels. These drug-type specific neuroadaptations are brought on largely by the reinforcing effects of drugs on the central nervous system and environmental stressors. Results from animal experiments have demonstrated important interactions between alcohol and stress-responsive systems. Addiction to specific drugs such as alcohol, psychostimulants, and opioids shares some common direct or downstream effects on the brain's stress-responsive systems, including arginine vasopressin and its V1b receptors, dynorphin and the κ-opioid receptors, pro-opiomelanocortin/β-endorphin and the μ-opioid receptors, and the endocannabinoids. Further study of these systems through laboratory-based and translational research could lead to the discovery of novel treatment targets and the early optimization of interventions (for example, combination) for the pharmacologic therapy of alcoholism.

Administration of the metabotropic glutamate receptor subtype 5 allosteric modulator GET 73 with alcohol: A translational study in rats and humans

Preclinical work suggests that GET 73 (N-[4-(trifluoromethyl)benzyl]-4-methoxybutyramide), a novel metabotropic glutamate receptor subtype 5 negative allosteric modulator, may represent a novel pharmacological treatment for alcohol use disorder. Two independent experiments evaluated the effect of acutely administered GET 73 (0, 30, and 100 mg/kg, intragastrically) on alcohol-induced hypolocomotion ( n=72) and sedation/hypnosis ( n=36) in rats. In healthy male volunteers ( n=14), an open-label, randomised, crossover study was conducted to compare adverse events and pharmacokinetic parameters, in two experiments in which 300 mg GET 73 was administered, with and without alcohol, once and thrice. In rats, when administered with alcohol-vehicle, 100 mg/kg, but not 30 mg/kg, GET 73 reduced spontaneous locomotor activity. When administered with alcohol, no dose of GET 73 altered either alcohol-induced hypolocomotion or sedation/hypnosis. In humans, both single and thrice 300 mg GET 73 administration were well tolerated, in the presence and absence of alcohol, with no differences in adverse events. There were no significant differences in relative bioavailability between administering 300 mg GET 73 in the presence or absence of alcohol.

Marked Differences in the Submandibular Salivary Proteome between Sardinian Alcohol-Preferring and Sardinian Alcohol-Non Preferring Rats Revealed by an Integrated Top-Down-Bottom-Up Proteomic Platform

Sardinian alcohol-preferring (sP) and Sardinian alcohol-non preferring (sNP) rats have been selectively bred for opposite alcohol preference and consumption. Aiming to verify possible differences at the proteomics level between sP and sNP rats, we investigated the salivary proteome by a a liquid chromatography-mass spectrometry top-down-bottom-up integrated approach. For this purpose, submandibular saliva was collected from alcohol-naive sP and sNP rats under isoprenaline stimulation. A total of 200 peptides and proteins were detected and quantified in the two rat lines, 149 of which were characterized in their naturally occurring structure. The data are available via ProteomeXchange with identifier PXD006997. Surprisingly, sP rats exhibited marked quantitative and qualitative differences with respect to sNP rats, namely higher levels of proteoforms originating from submandibular gland protein C, and from submandibular rat protein 2, as well as those of several unidentified peptides and proteins. sP rats expressed some proteins not detectable in sNP rats such as the glutamine and glutamic acid-rich protein (GRP)-CB. The isoform GRP-B, detectable in both rat lines, was more abundant in sNP rats. The submandibular saliva of sNP rats was also characterized by very high levels of GRP-B proteolytic peptides and rat salivary protein 1. Whether these differences could contribute to the opposite alcohol preference and consumption of sP and sNP rats is currently unknown and requires further investigation.

Evaluation of Alcohol Preference and Drinking in msP Rats Bearing a Crhr1 Promoter Polymorphism

Alcoholism is a pervasive societal problem, yet available pharmacotherapies fail to treat most sufferers. The type 1 corticotropin-releasing factor (CRF₁) receptor has received much attention for its putative role in the progression to alcohol dependence, although at present its success in clinical trials has been limited. Two single-nucleotide polymorphisms in the rat Crhr1 promoter have been identified in the Marchigian substrain of Sardinian alcohol-preferring (msP) rats. Unlike other Wistar-derived alcohol-preferring lines, nondependent msP rats reduce their alcohol self-administration in response to CRF₁ antagonists and show increased brain CRF₁ expression. The current study tested the hypotheses that the A alleles in the Crhr1 promoter polymorphisms are: (1) unique to msP (vs. CRF₁ antagonist-insensitive) alcohol-preferring lines and (2) associate with greater alcohol preference or intake. Two related polymorphisms were observed in which both loci on a given chromosome were either mutant variant (A) or wild-type (G) alleles within the distal Crhr1 promoter of 17/25 msP rats (68%), as compared to 0/23 Indiana P rats, 0/20 Sardinian alcohol-preferring rats bred at Scripps (Scr:sP) and 0/21 outbred Wistar rats. Alcohol consumption in msP rats did not differ according to the presence of Crhr1 A alleles, but greater alcohol preference (98%) was observed in A allele homozygous msP rats (AA) compared to msP rats with wild-type (GG, 91%) or heterozygous (GA, 91%) genotypes. The greater alcohol preference reflected decreased water intake, accompanied by reduced total calories consumed by AA rats. The data show that msP rats differentially possess mutant A variant alleles in the polymorphic promoter region of the Crhr1 gene that may differentially regulate consumption.

V1b Receptor Antagonist SSR149415 and Naltrexone Synergistically Decrease Excessive Alcohol Drinking in Male and Female Mice

BACKGROUND

A recent clinical trial found that pharmacological blockade of V1b receptors reduces alcohol relapse in alcohol-dependent patients. SSR149415 is a selective V1b receptor antagonist that has potential for development as an alcohol dependency treatment. In this study, we investigated whether SSR149415 alone or in combination with the mu-opioid receptor (MOP-r) antagonist naltrexone (NTN) would alter excessive alcohol drinking in mice.

METHODS

Both sexes of C57BL/6J (B6) mice were subjected to a chronic intermittent access (IA) drinking paradigm (2-bottle choice, 24-hour access every other day) for 3 weeks. Sucrose and saccharin drinking were used as controls for alcohol-specific drug effects. Neuronal proopiomelanocortin (POMC) enhancer (nPE) knockout mice with hypothalamic-specific loss of POMC (including beta-endorphin, the main endogenous ligand of MOP-r) were used as a genetic control for the effects of NTN.

RESULTS

Acute administration of SSR149415 (1 to 30 mg/kg) reduced alcohol intake and preference in a dose-dependent manner in both male and female B6 mice after IA. To investigate potential synergistic effects between NTN and SSR149415, we tested 6 different combination doses of SSR149415 and NTN, and found that a combination of SSR149415 (3 mg/kg) and NTN (1 mg/kg) reduced alcohol intake profoundly at doses lower than the individual effective doses in both sexes of B6 mice. We confirmed the effect of SSR149415 on reducing alcohol intake in nPE-/- male mice, consistent with independent mechanisms by which SSR149415 and NTN decrease alcohol drinking.

CONCLUSIONS

The combination of V1b antagonist SSR149415 with NTN at individual subthreshold doses shows potential in alcoholism treatment, possibly with less adverse effects.

Effects of morphine on place conditioning and ERK1/2 phosphorylation in the nucleus accumbens of psychogenetically selected Roman low- and high-avoidance rats

RATIONALE

Extracellular signal-regulated kinase (ERK_1/2) phosphorylation is critical for neuronal and behavioural functions; in particular, phosphorylated ERK_1/2 (pERK_1/2) expression in the nucleus accumbens (Acb) of the rat is stimulated by addictive drugs with the exception of morphine, which decreases accumbal ERK_1/2 phosphorylation in the Sprague-Dawley and Wistar rats. The psychogenetically selected Roman low- (RLA) and high-avoidance (RHA) rats differ behaviourally and neurochemically in many responses to addictive drugs. In particular, morphine elicits a greater increment in locomotor activity and in dopamine transmission in the Acb of RHA vs RLA rats. However, the effects of morphine on place conditioning (conditioned place preference (CPP)) and ERK_1/2 phosphorylation in the Roman lines remain unknown.

OBJECTIVES AND METHODS

To characterize in the Roman lines the reinforcing properties of morphine (i.e. morphine-elicited CPP acquisition) and the relationship between these properties and its effects on ERK_1/2 phosphorylation in the Acb, the behavioural effects of morphine were evaluated in a place-conditioning apparatus and ERK_1/2 phosphorylation was assessed by immunohistochemistry in the shell and core subregions of the Acb of rats both acutely administered with morphine or undergoing conditioning.

RESULTS

Morphine elicited CPP in both Roman lines and decreased pERK_1/2 expression in the Acb of RLA but not RHA rats. Such decrease was prevented by conditioning.

CONCLUSIONS

These findings indicate that the selective breeding of the Roman lines has generated a divergence, in terms of morphine-elicited pERK_1/2 expression but not of morphine-elicited CPP, between RLA and RHA rats and sustain the observation that changes in pERK_1/2 expression in the Acb are not a requisite for the reinforcing effects of morphine.

Reduced Levels of mGlu2 Receptors within the Prelimbic Cortex Are Not Associated with Elevated Glutamate Transmission or High Alcohol Drinking

BACKGROUND

A Grm2 cys407* stop codon mutation, which results in a loss of the metabotropic glutamate 2 (mGlu2) receptor protein, was identified as being associated with high alcohol drinking by alcohol-preferring (P) rats. The objectives of the current study were to characterize the effects of reduced levels of mGlu2 receptors on glutamate transmission and alcohol drinking.

METHODS

Quantitative no-net-flux microdialysis was used to test the hypothesis that basal extracellular glutamate levels in the prelimbic (PL) cortex and nucleus accumbens shell (NACsh) will be higher in P than Wistar rats. A lentiviral-delivered short-hairpin RNA (shRNA)-mediated knockdown was used to test the hypothesis that reduced levels of mGlu2 receptors within the PL cortex will increase voluntary alcohol drinking by Wistar rats. A linear regression analysis was used to test the hypothesis that there will be a significant correlation between the Grm2 cys407* mutation and level of alcohol intake.

RESULTS

Extracellular glutamate concentrations within the PL cortex (3.6 ± 0.6 vs. 6.4 ± 0.6 μM) and NACsh (3.2 ± 0.4 vs. 6.6 ± 0.6 μM) were significantly lower in female P than female Wistar rats. Western blot detected the presence of mGlu2 receptors in these regions of female Wistar rats, but not female P rats. Micro-infusion of shRNAs into the PL cortex significantly reduced local mGlu2 receptor levels (by 40%), but did not alter voluntary alcohol drinking in male Wistar rats. In addition, there was no significant correlation between the Grm2 mutation and alcohol intake in 36 rodent lines (r = 0.29, p > 0.05).

CONCLUSIONS

Collectively, these results suggest a lack of association between the loss of mGlu2 receptors and glutamate transmission in the NACsh and PL cortex of female P rats, and between the level of mGlu2 receptors in the PL cortex and alcohol drinking of male Wistar rats.

Short-term selection for high and low ethanol intake yields differential sensitivity to ethanol's motivational effects and anxiety-like responses in adolescent Wistar rats

Alcohol use disorders are modulated by genetic factors, but the identification of specific genes and their concomitant biological changes that are associated with a higher risk for these disorders has proven difficult. Alterations in the sensitivity to the motivational effects of ethanol may be one way by which genes modulate the initiation and escalation of ethanol intake. Rats and mice have been selectively bred for high and low ethanol consumption during adulthood. However, selective breeding programs for ethanol intake have not focused on adolescence. This phase of development is associated with the initiation and escalation of ethanol intake and characterized by an increase in the sensitivity to ethanol's appetitive effects and a decrease in the sensitivity to ethanol's aversive effects compared with adulthood. The present study performed short-term behavioral selection to select rat lines that diverge in the expression of ethanol drinking during adolescence. A progenitor nucleus of Wistar rats (F₀) and filial generation 1 (F₁), F₂, and F₃ adolescent rats were derived from parents that were selected for high (STDRHI) and low (STDRLO) ethanol consumption during adolescence and were tested for ethanol intake and responsivity to ethanol's motivational effects. STDRHI rats exhibited significantly greater ethanol intake and preference than STDRLO rats. Compared with STDRLO rats, STDRHI F₂ and F₃ rats exhibited a blunted response to ethanol in the conditioned taste aversion test. F₂ and F₃ STDRHI rats but not STDRLO rats exhibited ethanol-induced motor stimulation. STDRHI rats exhibited avoidance of the white compartment of the light-dark box, a reduction of locomotion, and a reduction of saccharin consumption, suggesting an anxiety-prone phenotype. The results suggest that the genetic risk for enhanced ethanol intake during adolescence is associated with lower sensitivity to the aversive effects of ethanol, heightened reactivity to ethanol's stimulating effects, and enhanced innate anxiety.

Binge drinking and anxiety at the end of the nocturnal period in alcohol-preferring sP rats

Previous studies suggested that exposure of Sardinian alcohol-preferring (sP) rats to daily drinking sessions of 1 h, during the dark phase of the light/dark cycle, with multiple alcohol concentrations, and unpredictable access to alcohol, resulted in exceptionally high intakes of alcohol when the drinking session occurred over the last hours of the dark phase. Additionally, higher levels of anxiety-related behaviors were observed at the 12th, rather than 1st, hour of the dark phase, suggesting that uncertainty of time of alcohol access and expectation of alcohol availability produced an emotional "distress". The present study was designed to provide pharmacological support to the hypothesis that high alcohol intake under this drinking procedure is secondary to exacerbation of the anxiety-like state of sP rats. To this end, sP rats were initially exposed to daily 1-h drinking sessions during the dark phase and with multiple alcohol concentrations (0%, 10%, 20%, and 30%; v/v); time of alcohol exposure was changed each day and was unpredictable to rats. Rats were then treated acutely with non-sedative doses of diazepam (0, 1, 2, and 3 mg/kg; intraperitoneally [i.p.]) before two drinking sessions occurring at the 1st and 12th hour of the dark phase, respectively. Treatment with diazepam was ineffective at the 1st hour; conversely, it selectively reduced alcohol intake (up to 50% at the dose of 3 mg/kg) at the 12th hour. The preferential effectiveness of diazepam in reducing alcohol intake when the drinking session occurred at the 12th hour of the dark phase is consistent with the hypothesis that uncertainty of time of alcohol access and expectation of alcohol availability generated an emotional "distress" that rats counterbalanced with high alcohol drinking; the results of the present study are interpreted as the anxiolytic effects of diazepam substituting for those of alcohol, resulting in the observed reduction in alcohol intake.

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.

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".

A Phase I randomized clinical trial testing the safety, tolerability and preliminary pharmacokinetics of the mGluR5 negative allosteric modulator GET 73 following single and repeated doses in healthy volunteers

Preclinical work suggests that the metabotropic glutamate receptor subtype 5 (mGlu5) may represent a novel target to treat neuropsychiatric disorders, including alcohol use disorder and obesity. The goal of this first-in-man study was to evaluate the safety, tolerability and pharmacokinetics (PK) of GET 73 (PubChem SID: 329974174), a novel mGluR5 negative allosteric modulator. This was a double-blind, placebo-controlled, ascending dose, Phase I study conducted in healthy male volunteers in two experiments. GET 73 was administered as single ascending doses (N=48; Experiment 1; 10, 30, 100, 300, 450, 600-mg) or multiple ascending doses (N=32; Experiment 2; 100, 300, 450, 450-mg twice a day). Primary endpoints were the incidence of adverse events (AEs) among drug conditions and drug tolerability. The secondary endpoints were the PK parameters of GET 73 and its metabolite MET 2. Single GET 73 doses of up to 600-mg and repeated ascending doses of up to 450-mg twice/day were safe and well-tolerated. There were no serious or severe AEs. All AEs were mild or moderate in severity. Total GET 73 exposure increased with each increased GET 73 dose. A dose-related increase in mean maximum plasma drug concentration was observed after repeated dosing. Maximum plasma drug concentrations occurred between 0.5 and 2.05h after administration in all groups for both single and repeated doses. This first-in-human study indicates that GET 73, as single or multiple ascending doses, is safe and well-tolerated when administered to healthy male volunteers.

Voluntary induction and maintenance of alcohol dependence in rats using alcohol vapor self-administration

RATIONALE

A major issue in the addiction field is the limited number of animal models of the voluntary induction and maintenance of alcohol dependence in outbred rats.

OBJECTIVES

To address this issue, we developed a novel apparatus that vaporizes alcohol for 2-10 min after an active nosepoke response.

METHODS

Male Wistar rats were allowed to self-administer alcohol vapor for 8 h/day every other day for 24 sessions (escalated) or eight sessions (non-escalated). Escalated and non-escalated rats were then tested for progressive ratio responding. Anxiety-like behavior, somatic signs of withdrawal, and hyperalgesia were assessed during acute withdrawal.

RESULTS

The results showed that rats exhibited excellent discrimination between the active and inactive operanda (>85%), and the escalated rats quickly increased their blood alcohol levels from ~50 to >200 mg% in ~6 weeks. Compared with non-escalated rats, escalated rats exhibited severe addiction-like behavior, including somatic signs of withdrawal, anxiety-like behavior, hyperalgesia, and higher responding on a progressive ratio schedule of reinforcement.

CONCLUSIONS

These results demonstrate that outbred rats will voluntarily self-administer alcohol vapor to the point of dependence without the use of forced alcohol administration, sweeteners, food/water restriction, operant pretraining, or behavioral/genetic selection. This novel animal model may be particularly useful for medication development to help unveil the neuronal circuitry that underlies the voluntary induction of alcohol addiction and identify novel molecular targets that are specifically recruited after the voluntary induction and maintenance of alcohol dependence.

Sigma Receptors and Substance Use Disorders

Thanks to advances in neuroscience, addiction is now recognized as a chronic brain disease with genetic, developmental, and cultural components. Drugs of abuse, including alcohol, are able to produce significant neuroplastic changes responsible for the profound disturbances shown by drug addicted individuals. The current lack of efficacious pharmacological treatments for substance use disorders has encouraged the search for novel and more effective pharmacotherapies. Growing evidence strongly suggests that Sigma Receptors are involved in the addictive and neurotoxic properties of abused drugs, including cocaine , methamphetamine , and alcohol. The present chapter will review the current scientific knowledge on the role of the Sigma Receptor system in the effects of drugs and alcohol, and proposes that this receptor system may represent a novel therapeutic target for the treatment of substance use disorders and associated neurotoxicity.