Striatal D2 dopamine receptor binding characteristics in vivo in patients with alcohol dependence

Altered Structural Connectivity and Functional Brain Dynamics in Individuals With Heavy Alcohol Use Elucidated via Network Control Theory

BACKGROUND

Heavy alcohol use and its associated conditions, such as alcohol use disorder, impact millions of individuals worldwide. While our understanding of the neurobiological correlates of alcohol use has evolved substantially, we still lack models that incorporate whole-brain neuroanatomical, functional, and pharmacological information under one framework.

METHODS

Here, we utilized diffusion and functional magnetic resonance imaging to investigate alterations to brain dynamics in 130 individuals with a high amount of current alcohol use. We compared these alcohol-using individuals to 308 individuals with minimal use of any substances.

RESULTS

We found that individuals with heavy alcohol use had less dynamic and complex brain activity, and through leveraging network control theory, had increased control energy to complete transitions between activation states. Furthermore, using separately acquired positron emission tomography data, we deployed an in silico evaluation demonstrating that decreased D2 receptor levels, as found previously in individuals with alcohol use disorder, may relate to our observed findings.

CONCLUSIONS

This work demonstrates that whole-brain, multimodal imaging information can be combined under a network control framework to identify and evaluate neurobiological correlates and mechanisms of heavy alcohol use.

Synchrony between midbrain gene transcription and dopamine terminal regulation is modulated by chronic alcohol drinking

Alcohol use disorder is marked by disrupted behavioral and emotional states which persist into abstinence. The enduring synaptic alterations that remain despite the absence of alcohol are of interest for interventions to prevent relapse. Here, 28 male rhesus macaques underwent over 20 months of alcohol drinking interspersed with three 30-day forced abstinence periods. After the last abstinence period, we paired direct sub-second dopamine monitoring via ex vivo voltammetry in nucleus accumbens slices with RNA-sequencing of the ventral tegmental area. We found persistent augmentation of dopamine transporter function, kappa opioid receptor sensitivity, and dynorphin release - all inhibitory regulators which act to decrease extracellular dopamine. Surprisingly, though transcript expression was not altered, the relationship between gene expression and functional readouts of these encoded proteins was highly dynamic and altered by drinking history. These results outline the long-lasting synaptic impact of alcohol use and suggest that assessment of transcript-function relationships is critical for the rational design of precision therapeutics.

Altered structural connectivity and functional brain dynamics in individuals with heavy alcohol use

Heavy alcohol use and its associated conditions, such as alcohol use disorder (AUD), impact millions of individuals worldwide. While our understanding of the neurobiological correlates of AUD has evolved substantially, we still lack models incorporating whole-brain neuroanatomical, functional, and pharmacological information under one framework. Here, we utilize diffusion and functional magnetic resonance imaging to investigate alterations to brain dynamics in N = 130 individuals with a high amount of current alcohol use. We compared these alcohol using individuals to N = 308 individuals with minimal use of any substances. We find that individuals with heavy alcohol use had less dynamic and complex brain activity, and through leveraging network control theory, had increased control energy to complete transitions between activation states. Further, using separately acquired positron emission tomography (PET) data, we deploy an in silico evaluation demonstrating that decreased D2 receptor levels, as found previously in individuals with AUD, may relate to our observed findings. This work demonstrates that whole-brain, multimodal imaging information can be combined under a network control framework to identify and evaluate neurobiological correlates and mechanisms of AUD.

Dopamine D2 receptors in the bed nucleus of the stria terminalis modulate alcohol-related behaviors

Dysregulation of the dopamine (DA) system is a hallmark of substance abuse disorders, including alcohol use disorder (AUD). Of the DA receptor subtypes, the DA D2 receptors (D2Rs) play a key role in the reinforcing effects of alcohol. D2Rs are expressed in numerous brain regions associated with the regulation of appetitive behaviors. One such region is the bed nucleus of the stria terminalis (BNST), which has been linked to the development and maintenance of AUD. Recently, we identified alcohol withdrawal-related neuroadaptations in the periaqueductal gray/dorsal raphe to BNST DA circuit in male mice. However, the role of D2R-expressing BNST neurons in voluntary alcohol consumption is not well characterized. In this study, we used a CRISPR-Cas9-based viral approach, to selectively reduce the expression of D2Rs in BNST VGAT neurons and interrogated the impact of BNST D2Rs in alcohol-related behaviors. In male mice, reduced D2R expression potentiated the stimulatory effects of alcohol and increased voluntary consumption of 20% w/v alcohol in a two-bottle choice intermittent access paradigm. This effect was not specific to alcohol, as D2R deletion also increased sucrose intake in male mice. Interestingly, cell-specific deletion of BNST D2Rs in female mice did not alter alcohol-related behaviors but lowered the threshold for mechanical pain sensitivity. Collectively, our findings suggest a role for postsynaptic BNST D2Rs in the modulation of sex-specific behavioral responses to alcohol and sucrose.

Cannabidiol as a Modulator of the Development of Alcohol Tolerance in Rats

The study aimed to explore in vivo the influence of cannabidiol (CBD) on the development of alcohol tolerance in rats. Rats were treated with ethanol (3.0 g/kg, i.p.) and CBD (20 mg/kg, p.o.) for nine successive days, and rectal body temperature, sedation (sleeping time), and blood alcohol concentration (BAC) were measured. In the prefrontal cortex, hippocampus, and striatum, the cannabinoid (CB1R and CB2R) and dopaminergic (DRD1, DRD2, DRD4, DRD5) receptors’ mRNA level changes were analyzed using the quantitative RT-PCR method. CBD inhibited the development of tolerance to the hypothermic and sedative action of alcohol, coupled with BAC elevation. On a molecular level, the most pronounced effects of the CBD + ethanol interaction in the striatum were observed, where CBD reversed the downregulation of CB2R gene transcription caused by ethanol. For CB1R, DRD1, and DRD2 mRNAs, the CBD + ethanol interaction produced opposite effects than for CB2R ones. In turn, for the transcription of genes encoding dopaminergic receptors, the most potent effect of alcohol as CBD occurred in the hippocampus. However, the combined CBD and alcohol administration showed the same effect for each substance administered separately. Since tolerance is considered a prelude to drug addiction, obtained results allow us to emphasize the thesis that CBD can inhibit the development of alcohol dependence in rats.

Transient equilibrium determination of dopamine D2/D3 receptor densities and affinities in brain

Long-term alteration of dopaminergic neurotransmission is known to modulate the D₂/D₃ receptor expression in the brain. The modulation can occur as a response to pathological processes or pharmacological intervention. The receptor density can be monitored by in vivo positron emission tomography (PET) of [¹¹C] raclopride. To obtain accurate measurements of receptor-ligand interaction, it is essential to estimate binding parameters at true (if transient) equilibrium of bound and unbound ligand quantities. We designed this study as a comparison of two quantitative approaches to transient equilibrium, the TRansient EquilibriuM BoLus Estimation (TREMBLE) method and the Transient Equilibrium Model (TEM) method, to determine binding parameters at transient equilibrium with bolus injection of the radioligand. The data demonstrates that TREMBLE unlike TEM identified the time at which equilibrium existed. TREMBLE revealed that equilibrium prevailed at one or more times after bolus injection and identified differences of receptor density among regions such as putamen and caudate nucleus. We demonstrated that TREMBLE is a quantitative approach suitable for the study of pathophysiological conditions of certain types of neurotransmission the brain.

Effects of chronic cocaine and ethanol self‐administration on brain dopamine receptors in a rhesus monkey model of polysubstance abuse

Most individuals with cocaine use disorder also use alcohol; however, little is known about the behavioural and pharmacological mechanisms that promote co‐abuse. For example, although studies in humans and animals have documented that chronic use of either alcohol or cocaine alone decreases D2‐like receptor (D2R) availability, effects of co‐abuse of these substances on dopamine receptor function have not been characterized. These studies examined the effects of long‐term cocaine self‐administration in 12 male rhesus monkeys who also consumed either ethanol or an ethanol‐free solution each day (n = 6 per group). Specifically, all monkeys self‐administered cocaine (0.1 mg/kg per injection) 5 days per week in the morning. In the afternoon, six monkeys consumed 2.0 g/kg ethanol over 1 h to model binge drinking and six monkeys drank an ethanol‐free solution. Assessment of D2R availability using positron emission tomography (PET) and [¹¹C]raclopride occurred when monkeys were drug‐naïve and again when monkeys had self‐administered approximately 400‐mg/kg cocaine. D₃R function was assessed at the same time points by determining the potency of the D₃R‐preferring agonist quinpirole to elicit yawns. Chronic cocaine self‐administration decreased D2R availability in subregions of the basal ganglia in control monkeys, but not those that also drank ethanol. In contrast, D₃R sensitivity increased significantly after chronic cocaine self‐administration in ethanol‐drinking monkeys but not controls. These results suggest that co‐use of ethanol substantially changes the effects of chronic cocaine self‐administration on dopamine receptors, specifically implicating D₃R as a target for medications in these individuals.

D2 receptor antagonism enhances cocaine-induced behavioral sensitization in female, but not male Japanese quail ( Coturnix japonica )

Sex differences in cocaine-induced behaviors are well established. In rodents, females show enhanced locomotion to cocaine over multiple trials compared with males, a behavioral response known as sensitization. Estradiol enhances cocaine-induced sensitization in female rats by agonizing dopaminergic activity within the brain. In female quail, cocaine does not increase locomotion regardless of increased estradiol. A higher D2:D1 dopamine receptor ratio in quail compared with rodents may explain this sex and species difference. The goal of the present work was to investigate the role of D2 receptors in cocaine-induced locomotion and sensitization in Japanese quail and to determine whether a greater D2 receptor availability contributed to the lack of cocaine-induced sensitization in female quail found in previous studies. Male and female quail were administered 0, 0.03, 0.05, or 0.07 mg/kg of eticlopride (Eti) followed by 10 mg/kg of cocaine or saline then immediately placed in open-field chambers. Distance traveled was recorded for 30 min daily for 7 days. In female quail, cocaine-induced sensitization was observed with 0.03 or 0.05 mg/kg Eti, but not in cocaine-only females. In male quail, cocaine-induced sensitization was observed similar to previous research. However, Eti did not enhance cocaine-induced locomotion or produce sensitization in male quail. The D2 receptor likely mediates cocaine's motor stimulating effects in quail. In females, this effect is more pronounced. Since high D2 availability is protective against stimulant abuse, Japanese quail may be a useful model for investigating the role of the D2 receptor in cocaine addiction, but further research is needed.

Role of the striatal dopamine, GABA and opioid systems in mediating feeding and fat intake

Food intake, which is a highly reinforcing behavior, provides nutrients required for survival in all animals. However, when fat and sugar consumption goes beyond the daily needs, it can favor obesity. The prevalence and severity of this health problem has been increasing with time. Besides covering nutrient and energy needs, food and in particular its highly palatable components, such as fats, also induce feelings of joy and pleasure. Experimental evidence supports a role of the striatal complex and of the mesolimbic dopamine system in both feeding and food-related reward processing, with the nucleus accumbens as a key target for reward or reinforcing-associated signaling during food intake behavior. In this review, we provide insights concerning the impact of feeding, including fat intake, on different types of receptors and neurotransmitters present in the striatal complex. Reciprocally, we also cover the evidence for a modulation of palatable food intake by different neurochemical systems in the striatal complex and in particular the nucleus accumbens, with a focus on dopamine, GABA and the opioid system.

Linking Ethanol-Addictive Behaviors With Brain Catecholamines: Release Pattern Matters

Using a variety of animal models that simulate key features of the alcohol use disorder (AUD), remarkable progress has been made in identifying neurochemical targets that may contribute to the development of alcohol addiction. In this search, the dopamine (DA) and norepinephrine (NE) systems have been long thought to play a leading role in comparison with other brain systems. However, just recent development and application of optogenetic approaches into the alcohol research field provided opportunity to identify neuronal circuits and specific patterns of neurotransmission that govern the key components of ethanol-addictive behaviors. This critical review summarizes earlier findings, which initially disclosed catecholamine substrates of ethanol actions in the brain and shows how the latest methodologies help us to reveal the significance of DA and NE release changes. Specifically, we focused on recent optogenetic investigations aimed to reveal cause-effect relationships between ethanol-drinking (seeking and taking) behaviors and catecholamine dynamics in distinct brain pathways. These studies gain the knowledge that is needed for the better understanding addiction mechanisms and, therefore, for development of more effective AUD treatments. Based on the reviewed findings, new messages for researches were indicated, which may have broad applications beyond the field of alcohol addiction.

Neurobiological mechanisms of control in alcohol use disorder - moving towards mechanism-based non-invasive brain stimulation treatments

Alcohol use disorder (AUD) is characterized by excessive habitual drinking and loss of control over alcohol intake despite negative consequences. Both of these aspects foster uncontrolled drinking and high relapse rates in AUD patients. Yet, common interventions mostly focus on the phenomenological level, and prioritize the reduction of craving and withdrawal symptoms. Our review provides a mechanistic understanding of AUD and suggests alternative therapeutic approaches targeting the mechanisms underlying dysfunctional alcohol-related behaviours. Specifically, we explain how repeated drinking fosters the development of rigid drinking habits and is associated with diminished cognitive control. These behavioural and cognitive effects are then functionally related to the neurobiochemical effects of alcohol abuse. We further explain how alterations in fronto-striatal network activity may constitute the neurobiological correlates of these alcohol-related dysfunctions. Finally, we discuss limitations in current pharmacological AUD therapies and suggest non-invasive brain stimulation (like TMS and tDCS interventions) as a potential addition/alternative for modulating the activation of both cortical and subcortical areas to help re-establish the functional balance between controlled and automatic behaviour.

A Review of DNA Risk Alleles to Determine Epigenetic Repair of mRNA Expression to Prove Therapeutic Effectiveness in Reward Deficiency Syndrome (RDS): Embracing "Precision Behavioral Management"

This is a review of research on "Precision Behavioral Management" of substance use disorder (SUD). America is experiencing a high prevalence of substance use disorder, primarily involving legal and illegal opioid use. A 3000% increase in treatment for substance abuse has occurred between 2000 and 2016. Unfortunately, present day treatment of opioid abuse involves providing replacement therapy with powerful opioids to, at best, induce harm reduction, not prophylaxis. These interventions do not enhance gene expression and restore the balance of the brain reward system's neurotransmitters. We are proposing a generalized approach called "Precision Behavioral Management". This approach includes 1) using the Genetic Addiction Risk Severity (GARS, a 10 candidate polymorphic gene panel shown to predict ASI-alcohol and drug severity) to assess early pre-disposition to substance use disorder; 2) using a validated reward deficiency syndrome (RDS) questionnaire; 3) utilization of the Comprehensive Analysis of Reported Drugs (CARD™) to assess treatment compliance and abstinence from illicit drugs during treatment, and, importantly; 4) utilization of a "Pro-dopamine regulator (KB220)" (via IV or oral [KB220Z] delivery systems) to optimize gene expression, restore the balance of the Brain Reward Cascade's neurotransmitter systems and prevent relapse by induction of dopamine homeostasis, and; 5) utilization of targeted DNA polymorphic reward genes to direct mRNA genetic expression profiling during the treatment process. Incorporation of these events can be applied to not only the under-considered African-American RDS community, but all victims of RDS, as a demonstration of a paradigm shift that uniquely provides a novel putative "standard of care" based on DNA guided precision nutrition therapy to induce "dopamine homeostasis" and rebalance neurotransmitters in the Brain Reward Cascade. We are also developing a Reward Deficiency Syndrome Diagnostic Criteria (RDSDC) to assist in potential tertiary treatment.

Disruption of the PDZ domain-binding motif of the dopamine transporter uniquely alters nanoscale distribution, dopamine homeostasis, and reward motivation

The dopamine (DA) transporter (DAT) is part of a presynaptic multiprotein network involving interactions with scaffold proteins via its C-terminal PDZ domain-binding sequence. Using a mouse model expressing DAT with mutated PDZ-binding sequence (DAT-AAA), we previously demonstrated the importance of this binding sequence for striatal expression of DAT. Here, we show by application of direct stochastic reconstruction microscopy not only that the striatal level of transporter is reduced in DAT-AAA mice but also that the nanoscale distribution of this transporter is altered with a higher propensity of DAT-AAA to localize to irregular nanodomains in dopaminergic terminals. In parallel, we observe mesostriatal DA adaptations and changes in DA-related behaviors distinct from those seen in other genetic DAT mouse models. DA levels in the striatum are reduced to ∼45% of that of WT, accompanied by elevated DA turnover. Nonetheless, fast-scan cyclic voltammetry recordings on striatal slices reveal a larger amplitude and prolonged clearance rate of evoked DA release in DAT-AAA mice compared with WT mice. Autoradiography and radioligand binding show reduced DA D2 receptor levels, whereas immunohistochemistry and autoradiography show unchanged DA D1 receptor levels. In behavioral experiments, we observe enhanced self-administration of liquid food under both a fixed ratio of one and progressive ratio schedule of reinforcement but a reduction compared with WT when using cocaine as reinforcer. In summary, our data demonstrate how disruption of PDZ domain interactions causes changes in DAT expression and its nanoscopic distribution that in turn alter DA clearance dynamics and related behaviors.

Exploring regulation and function of dopamine D3 receptors in alcohol use disorder. A PET [11C]-(+)-PHNO study

Preclinical studies support an important role of dopamine D3 receptors (DRD3s) in alcohol use disorder (AUD). In animals, voluntary alcohol consumption increases DRD3 expression, and pharmacological blockade of DRD3s attenuates alcohol self-administration and reinstatement of alcohol seeking. However, these findings have yet to be translated in humans. This study used positron emission tomography (PET) and [11C]-(+)-PHNO to compare receptor levels in several dopamine D2 receptor (DRD2) and DRD3 regions of interest between AUD subjects in early abstinence (n = 17; 6.59 ± 4.14 days of abstinence) and healthy controls (n = 18). We recruited non-treatment seeking subjects meeting DSM-5 criteria for AUD. We examined the relationship between DRD2/3 levels and both alcohol craving and alcohol motivation/wanting, using a cue reactivity procedure and an intravenous alcohol self-administration (IVASA) paradigm, respectively. [11C]-(+)-PHNO binding levels in AUD subjects were significantly lower than binding in HCs when looking at all DRD2/3 ROIs jointly (Wilk's Λ = .58, F(6,28) =3.33, p = 0.013, η2p = 0.42), however there were no region-specific differences. Binding values demonstrate -12.3% and -16.1% lower [11C]-(+)-PHNO binding in the SMST and SN respectively, though these differences did not withstand Bonferroni corrections. There was a positive association between [11C]-(+)-PHNO binding in the SN (almost exclusively reflective of DRD3) and alpha (lower values reflect higher alcohol demand) in the APT after Bonferroni corrections (r = 0.66, p = 0.0080). This demonstrates that AUD subjects with lower DRD3 levels in the SN exhibit increased demand for alcohol. These results replicate previous findings demonstrating reduced DRD2/3 levels while also supporting a lack of DRD3 upregulation and potential downregulation in early abstinent AUD. Furthermore, the finding that binding in the SN is associated with alcohol demand warrants further examination.

No evidence for decreased D2/3 receptor availability and frontal hypoperfusion in subjects with compulsive pornography use

Pornographic addiction refers to an addiction model associated with compulsive and repeated use of pornographic material. Whether the use of pornography may indeed become addictive remains a matter of debate. The current study investigated whether compulsive pornography use (CPU) is accompanied by reduced D2/3 receptor availability in the striatum and frontal hypofunctionality. Male subjects between 18 and 50 years of age with and without CPU were recruited using online and newspaper advertisements. Questionnaires were used to the assess the severity of compulsive pornography use (CIUS) and symptoms of depression, impulsivity and sensation seeking. Dopaminergic imaging was performed using [11C]-raclopride PET. Striatal binding potentials (BPND) and regional frontal cerebral influx values (R1) of [11C]-raclopride were calculated. Arterial Spin Labeling (ASL) MRI was performed to assess regional cerebral blood flow. No group differences between striatal BPND's of [11C]-raclopride in subjects with (n = 15) and without (n = 10) CPU were detected. In CPU subjects, no correlation was found between the CIUS score and striatal BPND's. Cerebral R1 values in frontal brain regions and cerebral blood flow measurements did not differ between groups. The current study fails to provide imaging support for sharing similar neurobiological alterations as previously has been reported in other addictive modalities.

Factors associated with the level of prolactin in patients under remission from Alcohol Use Disorder: A gender perspective

BACKGROUND

Prolactin mirrors the dopaminergic activity in the brain which is key to understanding alcohol use disorders (AUD). Still, patients with AUD are a heterogenous group and there seem to be gender differences in the relationship between alcohol use and the level of prolactin. In this study, we examined gender-wise relationship of alcohol use trait- and state-related factors with the level of prolactin among AUD inpatients in remission.

METHODS

This cross-sectional study examined the level of prolactin along with general patient characteristics and alcohol use trait- and state-related factors that could influence the level of prolactin in 112 AUD inpatients at three rehabilitation clinics in Norway. Logistic regression was performed to identify the gender-specific predictors of level of prolactin.

RESULTS

Male and female AUD patients had similar level of prolactin. Among females, younger age, early alcohol debut, and absence of parental drinking problem predicted higher level of prolactin. In males, presence of other substance dependence predicted a lower level of prolactin.

CONCLUSIONS

There were gender differences in the factors associated with the level of prolactin among the AUD patients. Especially in the female AUD patients under remission, alcohol use trait-related factors were better predictors of the level of prolactin than the alcohol use state-related factors, indicating that individuals might characteristically have varying degree of dopamine reactivity.

Body mass index and serum levels of soluble leptin receptor are sex-specifically related to alcohol binge drinking behavior

OBJECTIVE

Binge drinking is a highly prevalent behavior in adolescents and young adults and a risk factor to develop alcohol use disorder. Body mass index (BMI) and blood levels of leptin peptide and its soluble receptor have been implicated in alcohol use disorder; however, their role in binge drinking remains to be investigated.

METHOD

We studied associations of BMI, serum levels of soluble leptin receptor (ObRe) and leptin as well as the free leptin index with binge drinking in 93 male and 99 female young adults.

RESULTS

In men, binge drinkers showed significantly higher BMI (kg/m²) than non-binge drinkers (23.67 vs. 22.08) and higher BMI correlated significantly with more severe binge drinking episodes (ρ = 0.251). In women, we found significantly higher ObRe (ng/ml) / BMI (kg/m²) values in binge drinkers than in non-binge drinkers (0.52 vs. 0.44) and ObRe/BMI values correlated significantly with more severe binge drinking episodes (ρ = 0.210).

CONCLUSION

This study confirms that higher BMI associates with binge drinking in men and shows for the first time a role of ObRe/BMI in binge drinking in women. Our data emphasize the importance of further research in the field of metabolic markers and implications in neurobiological processes of binge drinking.

Alcohol Induced Brain and Liver Damage: Advantages of a Porcine Alcohol Use Disorder Model

Alcohol is one of the most commonly abused intoxicants with 1 in 6 adults at risk for alcohol use disorder (AUD) in the United States. As such, animal models have been extensively investigated with rodent AUD models being the most widely studied. However, inherent anatomical and physiological differences between rodents and humans pose a number of limitations in studying the complex nature of human AUD. For example, rodents differ from humans in that rodents metabolize alcohol rapidly and do not innately demonstrate voluntary alcohol consumption. Comparatively, pigs exhibit similar patterns observed in human AUD including voluntary alcohol consumption and intoxication behaviors, which are instrumental in establishing a more representative AUD model that could in turn delineate the risk factors involved in the development of this disorder. Pigs and humans also share anatomical similarities in the two major target organs of alcohol- the brain and liver. Pigs possess gyrencephalic brains with comparable cerebral white matter volumes to humans, thus enabling more representative evaluations of susceptibility and neural tissue damage in response to AUD. Furthermore, similarities in the liver result in a comparable rate of alcohol elimination as humans, thus enabling a more accurate extrapolation of dosage and intoxication level to humans. A porcine model of AUD possesses great translational potential that can significantly advance our current understanding of the complex development and continuance of AUD in humans.

Dopamine Receptor DRD2 Gene rs1076560, Personality Traits and Anxiety in the Polysubstance Use Disorder

Development of an addiction is conditioned by many factors. The dopaminergic system has been shown to be the key element in this process. In this paper, we analyzed the influence of dopamine receptor 2 polymorphism rs1076560 in two groups—polysubstance-dependent male patients (n = 299) and the controls matched for age (n = 301). In both groups, we applied the same questionnaires for testing—Mini-international neuropsychiatric interview, the NEO Five-Factor Inventory, and the State–Trait Anxiety Inventory. The real-time PCR method was used for genotyping. When we compared the controls with the case group subjects, we observed significantly higher scores in the second group on both the state and trait scales of anxiety, as well as on the Neuroticism and Openness scales of the NEO-FFI; and lower scores on the scales of Extraversion and Agreeability of the NEO-FFI. The model 2 × 3 factorial ANOVA of the addicted subjects and controls was performed, and the DRD2 rs1076560 variant interaction was found for the anxiety state and trait scales, and for the NEO-FFI Neuroticism scale. The observed associations allow noticing that analysis of psychological factors in combination with genetic data opens new possibilities in addiction research.

The Human Laboratory and Drug Development in Alcohol Use Disorder: Recent Updates

Despite a number of approved medications for alcohol use disorder (AUD), this chronic relapsing disease still produces a considerable global burden, with both health-related and financial consequences. While clinical trials are a critical step in drug development, human laboratory studies provide the field with means of screening pharmacotherapy for more nuanced aspects of AUD. Specifically, studies employing alcohol administration techniques (e.g., alcohol challenge and self-administration) are able to investigate potential drugs with respect to their ability to alter various responses to alcohol administration or alter alcohol consumption in laboratory settings. This chapter reviews methodological designs and provides updates from alcohol administration studies used to screen for potential AUD pharmacotherapy over the past decade. These recent studies have supported the efficacy of approved drugs, identified some promising novel drugs, and investigated other drugs that appear ineffective in AUD treatment. Yet, few drugs are explored using the different variants of alcohol administration methods, and using the different methods has provided inconsistent results for the same drug. Future research would aid advancement in the field by testing medication with various methodologies and refining recently developed techniques.

Binge alcohol use is not associated with alterations in striatal dopamine receptor binding or dopamine release

BACKGROUND

Previous imaging studies using Positron Emission Tomography (PET) have shown that alcohol use disorder (AUD) is associated with a decrease in dopamine type 2/3 receptor (D_2/3) binding and dopamine transmission. Although binge drinking is a risk factor for future AUD, little is known about the neurobiology of binge drinking in young adults. This study measured D_2/3 receptor binding and stimulant-induced dopamine release using PET and [¹¹C]raclopride in binge drinkers without an AUD.

METHODS

This study included 14 healthy controls (HC) and 14 young adult binge drinkers (BD), aged 18-25. The BD met National Institute on Alcohol Abuse and Alcoholism (NIAAA) criteria for binge drinking and the HC subjects were social drinkers. The subjects were scanned with [¹¹C]raclopride before and after the administration of oral methylphenidate (60 mg) to measure D_2/3 binding and dopamine release.

RESULTS

There was no significant difference in the PET measures of D_2/3 binding or methylphenidate-induced dopamine release between the two groups. There was no significant association between Alcohol Use Disorders Identification Test (AUDIT) scores or 30-day drinking history and the imaging data.

CONCLUSION

In this sample of 18-25-year-old binge drinkers without a diagnosis of a substance use disorder, there were no significant differences in D_2/3 receptor binding potential or methylphenidate-induced dopamine release relative to healthy controls.

Evaluation of the dopaminergic system with positron-emission tomography in alcohol abuse: A systematic review

OBJECTIVE

Performed a systematic review to evaluated the dopaminergic system in alcohol abuse in a systematic review in humans.

METHOD

A search of the electronic databases was proceeded, on MEDLINE, EMBASE, Cochrane Library, Insight and Gray literature (Google Scholar and the British Library) for studies published until August 2018. A search strategy was developed using the terms: "dopamine" and "ethanol" or ""alcohol"," and "positron-emission tomography" as text words and Medical Subject Headings (i.e., MeSH and EMTREE) and searched.

RESULTS

We found 293 studies. After reading titles and abstracts 235 were considered irrelevant, as they did not meet the inclusion criteria. For the reading of the full text, 50 studies were analyzed. Of these 41 were excluded with reasons by study design, patient population, intervention and outcomes. Nine studies were included in our qualitative synthesis. Four studies have resulted in a reduction in availability only at the D2 receptor in different brain regions. Concerning the D3 receptor alone only one study reported this finding and four studies reported a decrease in both receptors.

CONCLUSION

Changes in D2 receptors in several brain regions in human alcoholics were found in a systematic review.

A Mechanism Linking Two Known Vulnerability Factors for Alcohol Abuse: Heightened Alcohol Stimulation and Low Striatal Dopamine D2 Receptors

Alcohol produces both stimulant and sedative effects in humans and rodents. In humans, alcohol abuse disorder is associated with a higher stimulant and lower sedative responses to alcohol. Here, we show that this association is conserved in mice and demonstrate a causal link with another liability factor: low expression of striatal dopamine D2 receptors (D2Rs). Using transgenic mouse lines, we find that the selective loss of D2Rs on striatal medium spiny neurons enhances sensitivity to ethanol stimulation and generates resilience to ethanol sedation. These mice also display higher preference and escalation of ethanol drinking, which continues despite adverse outcomes. We find that striatal D1R activation is required for ethanol stimulation and that this signaling is enhanced in mice with low striatal D2Rs. These data demonstrate a link between two vulnerability factors for alcohol abuse and offer evidence for a mechanism in which low striatal D2Rs trigger D1R hypersensitivity, ultimately leading to compulsive-like drinking.

phMRI, neurochemical and behavioral responses to psychostimulants distinguishing genetically selected alcohol-preferring from genetically heterogenous rats

Alcoholism is often associated with other forms of drug abuse, suggesting that innate predisposing factors may confer vulnerability to addiction to diverse substances. However, the neurobiological bases of these factors remain unknown. Here, we have used a combination of imaging, neurochemistry and behavioral techniques to investigate responses to the psychostimulant amphetamine in Marchigian Sardinian (msP) alcohol-preferring rats, a model of vulnerability to alcoholism. Specifically, we employed pharmacological magnetic resonance imaging to investigate the neural circuits engaged by amphetamine challenge, and to relate functional reactivity to neurochemical and behavioral responses. Moreover, we studied self-administration of cocaine in the msP rats. We found stronger functional responses in the extended amygdala, alongside with increased release of dopamine in the nucleus accumbens shell and augmented vertical locomotor activity compared with controls. Wistar and msP rats did not differ in operant cocaine self-administration under short access (2 hours) conditions, but msP rats exhibited a higher propensity to escalate drug intake following long access (6 hours). Our findings suggest that neurobiological and genetic mechanisms that convey vulnerability to excessive alcohol drinking also facilitate the transition from psychostimulants use to abuse.

Computational modelling reveals contrasting effects on reinforcement learning and cognitive flexibility in stimulant use disorder and obsessive-compulsive disorder: remediating effects of dopaminergic D2/3 receptor agents

RATIONALE

Disorders of compulsivity such as stimulant use disorder (SUD) and obsessive-compulsive disorder (OCD) are characterised by deficits in behavioural flexibility, some of which have been captured using probabilistic reversal learning (PRL) paradigms.

OBJECTIVES

This study used computational modelling to characterise the reinforcement learning processes underlying patterns of PRL behaviour observed in SUD and OCD and to show how the dopamine D2/3 receptor agonist pramipexole and the D2/3 antagonist amisulpride affected these responses.

METHODS

We applied a hierarchical Bayesian method to PRL data across three groups: individuals with SUD, OCD, and healthy controls. Participants completed three sessions where they received placebo, pramipexole, and amisulpride, in a double-blind placebo-controlled, randomised design. We compared seven models using a bridge sampling estimate of the marginal likelihood.

RESULTS

Stimulus-bound perseveration, a measure of the degree to which participants responded to the same stimulus as before irrespective of outcome, was significantly increased in SUD, but decreased in OCD, compared to controls (on placebo). Individuals with SUD also exhibited reduced reward-driven learning, whilst both the SUD and OCD groups showed increased learning from punishment (nonreward). Pramipexole and amisulpride had similar effects on the control and OCD groups; both increased punishment-driven learning. These D2/3-modulating drugs affected the SUD group differently, remediating reward-driven learning and reducing aspects of perseverative behaviour, amongst other effects.

CONCLUSIONS

We provide a parsimonious computational account of how perseverative tendencies and reward- and punishment-driven learning differentially contribute to PRL in SUD and OCD. D2/3 agents modulated these processes and remediated deficits in SUD in particular, which may inform therapeutic effects.

Body mass index and craving predict 24-month hospital readmissions of alcohol-dependent in-patients following withdrawal

OBJECTIVE

Addictive alcohol drinking, craving, and overeating share common etiopathological mechanisms. We investigated whether body mass index (BMI) and craving predict outcome of alcohol-dependent in-patients.

METHOD

The prospective study included 101 male and 72 female early-abstinent alcohol-dependent in-patients. Craving was quantified by Obsessive-Compulsive Drinking Scale (OCDS) scores. We documented alcohol-related readmissions over 24 months.

RESULTS

In males, a higher BMI was associated with alcohol-related hospital readmission (median 26.1 vs. 23.1 kg/m², P = .007) and correlated with more (ρ = 0.286, P = .004) and earlier readmissions (ρ = -0.256, P = .010). These associations were stronger in the subgroup of active smokers (n = 79; median 25.9 vs. 22.3 kg/m², P = .005; ρ = 0.350, P = .002; ρ = -0.340, P = .002). BMI did not significantly predict outcome in females. Males with at least one readmission reported higher OCDS scores than those without (OCDS-total, OCDS-obsessive, OCDS-compulsive, P < .040), and the OCDS scores correlated with more readmissions (males: OCDS-total, OCDS-obsessive, OCDS-compulsive, ρ > 0.244, P < .014; females: OCDS-compulsive, ρ = 0.341, P = .003) and fewer days to first readmission (males: OCDS-total, OCDS-compulsive, ρ < -0.195, P < .050; females: OCDS-compulsive, ρ = -0.335, P = .004). The OCDS scores explained 9 to 19% of the relationship between BMI and outcome in males.

CONCLUSION

BMI and craving are easily accessible outcome predictors of alcohol-related readmission following in-patient withdrawal treatment. They might be used to individualize relapse prevention in the future.

NOP Receptor Agonist Ro 64-6198 Decreases Escalation of Cocaine Self-Administration in Rats Genetically Selected for Alcohol Preference

Cocaine dependence is a psychiatric condition for which effective medications are still lacking. Published data indicate that an increase in nociceptin/orphanin FQ (N/OFQ) transmission by NOP receptor activation attenuates cocaine-induced place conditioning and the locomotor sensitization effects of cocaine. This suggests that the activation of the N/OFQ receptor (NOP) may attenuate the motivation for psychostimulants. To further explore this possibility, we investigated the effect of the potent and selective NOP receptor agonist Ro 64-6198 on cocaine intake under 1 h short access (ShA) and 6 h long access (LgA) operant self-administration conditions in rats. We used Marchigian Sardinian alcohol-preferring (msP) rats and Wistar control rats. msP rats were used because we recently found that this rat line, originally selected for excessive alcohol drinking and preference, exhibits a greater propensity to escalate cocaine self-administration following LgA training. msP rats are also characterized by innate overexpression of the N/OFQ-NOP system compared with Wistar rats. Wistar and msP rats both exhibited an increase in cocaine self-administration under LgA conditions, with a higher trend toward escalation in msP rats. In Wistar rats, the intraperitoneal administration of Ro 64-6198 (0. 1 and 3 mg/kg) significantly decreased ShA cocaine self-administration. In Wistar rats that underwent LgA cocaine self-administration training, Ro 64-6198 induced no significant effect either during the first hour of self-administration or after the entire 6 h session. In msP rats, Ro 64-6198 significantly reduced cocaine self-administration both under ShA conditions and in the first hour of the LgA session. At the end of the 6 h session, the effect of Ro 64-6198 was no longer observed in msP rats. The highest dose of Ro 64-6198 (3 mg/kg) did not affect saccharin self-administration in msP rats but reduced saccharin self-administration in Wistar rats. Altogether, these data suggest that NOP receptor activation attenuates cocaine self-administration, and this effect tends to be more pronounced in a rat line with innately higher NOP receptor expression and that more robustly escalates cocaine intake.

A potential link between gambling addiction severity and central dopamine levels: Evidence from spontaneous eye blink rates

Accumulating evidence points at similarities between substance use disorders (SUD) and gambling disorder on the behavioral and neural level. In SUD, attenuation of striatal D2/3-receptor availability is a consistent finding, at least for stimulating substances. For gambling disorder, no clear association with striatal D2/3-receptor availability has been unveiled so far. With its presumably negligible dopaminergic toxicity, possible differences in receptor availability in gambling disorder might constitute a vulnerability marker. Spontaneous eye blink rate (sEBR) is discussed as a potential proxy measure for striatal dopamine D2/3-receptor availability. Here we examined sEBR in 21 male problem gamblers and 20 healthy control participants. In addition, participants completed a screening questionnaire for overall psychopathology and self-reported measures of alcohol and nicotine consumption. We found no significant difference in sEBR between gamblers and controls. However, in gamblers, sEBR was negatively associated with gambling severity and positively associated with psychopathology. A final exploratory analysis revealed that healthy controls with low sEBR displayed higher alcohol and nicotine consumption than healthy participants with high sEBR. Although the exact association between dopamine transmission and sEBR is still debated, our findings reveal that sEBR is sensitive to inter-individual differences in gambling disorder severity in problem gamblers.

Effects of Long-Term Alcohol Drinking on the Dopamine D2 Receptor: Gene Expression and Heteroreceptor Complexes in the Striatum in Rats

BACKGROUND

Reduced dopamine D2 receptor (D2R) ligand binding has repeatedly been demonstrated in the striatum of humans with alcohol use disorder (AUD). The attenuated D2R binding has been suggested to reflect a reduced D2R density, which in turn has been proposed to drive craving and relapse. However, results from rodent studies addressing the effects of alcohol drinking on D2R density have been inconsistent.

METHODS

A validated alcohol drinking model (intermittent access to 20% alcohol) in Wistar rats was used to study the effects of voluntary alcohol drinking (at least 12 weeks) on the D2R in the striatum compared to age-matched alcohol-naïve control rats. Reverse transcriptase quantitative PCR was used to quantify isoform-specific Drd2 gene expression levels. Using bisulfite pyrosequencing, DNA methylation levels of a regulatory region of the Drd2 gene were determined. In situ proximity ligation assay was used to measure densities of D2R receptor complexes: D2R-D2R, adenosine A2A receptor (A2AR)-D2R, and sigma1 receptor (sigma1R)-D2R.

RESULTS

Long-term voluntary alcohol drinking significantly reduced mRNA levels of the long D2R isoform in the nucleus accumbens (NAc) but did not alter CpG methylation levels in the analyzed sequence of the Drd2 gene. Alcohol drinking also reduced the striatal density of D2R-D2R homoreceptor complexes, increased the density of A2AR-D2R heteroreceptor complexes in the NAc shell and the dorsal striatum, and decreased the density of sigma1R-D2R heteroreceptor complexes in the dorsal striatum.

CONCLUSIONS

The present results on long-term alcohol drinking might reflect reduced D2R levels through reductions in D2R-D2R homoreceptor complexes and gene expression. Furthermore, based on antagonistic interactions between A2AR and D2R, an increased density of A2AR-D2R heteroreceptor complexes might indicate a reduced affinity and signaling of the D2R population within the complex. Hence, both reduced striatal D2R levels and reduced D2R protomer affinity within the striatal A2AR-D2R complex might underlie reduced D2R radioligand binding in humans with AUD. This supports the hypothesis of a hypodopaminergic system in AUD and suggests the A2AR-D2R heteroreceptor complex as a potential novel treatment target.

Genome-wide analysis of the nucleus accumbens identifies DNA methylation signals differentiating low/binge from heavy alcohol drinking

Alcohol-use disorders encompass a range of drinking levels and behaviors, including low, binge, and heavy drinking. In this regard, investigating the neural state of individuals who chronically self-administer lower doses of alcohol may provide insight into mechanisms that prevent the escalation of alcohol use. DNA methylation is one of the epigenetic mechanisms that stabilizes adaptations in gene expression and has been associated with alcohol use. Thus, we investigated DNA methylation, gene expression, and the predicted neural effects in the nucleus accumbens core (NAcc) of male rhesus macaques categorized as "low" or "binge" drinkers, compared to "alcohol-naïve" and "heavy" drinkers based on drinking patterns during a 12-month alcohol self-administration protocol. Using genome-wide CpG-rich region enrichment and bisulfite sequencing, the methylation levels of 2.6 million CpGs were compared between alcohol-naïve (AN), low/binge (L/BD), and heavy/very heavy (H/VHD) drinking subjects (n = 24). Through regional clustering analysis, we identified nine significant differential methylation regions (DMRs) that specifically distinguished ANs and L/BDs, and then compared those DMRs among H/VHDs. The DMRs mapped to genes encoding ion channels, receptors, cell adhesion molecules, and cAMP, NF-κβ and Wnt signaling pathway proteins. Two of the DMRs, linked to PDE10A and PKD2L2, were also differentially methylated in H/VHDs, suggesting an alcohol-dose independent effect. However, two other DMRs, linked to the CCBE1 and FZD5 genes, had L/BD methylation levels that significantly differed from both ANs and H/VHDs. The remaining five DMRs also differentiated L/BDs and ANs. However, H/VHDs methylation levels were not distinguishable from either of the two groups. Functional validation of two DMRs, linked to FZD5 and PDE10A, support their role in regulating gene expression and exon usage, respectively. In summary, the findings demonstrate that L/BD is associated with unique DNA methylation signatures in the primate NAcc, and that the methylation signatures identify synaptic genes that may play a role in preventing the escalation of alcohol use.

Neurochemical and metabolic effects of acute and chronic alcohol in the human brain: Studies with positron emission tomography

The use of Positron emission tomography (PET) to study the effects of acute and chronic alcohol on the human brain has enhanced our understanding of the mechanisms underlying alcohol's rewarding effects, the neuroadaptations from chronic exposure that contribute to tolerance and withdrawal, and the changes in fronto-striatal circuits that lead to loss of control and enhanced motivation to drink that characterize alcohol use disorders (AUD). These include studies showing that alcohol's reinforcing effects may result not only from its enhancement of dopaminergic, GABAergic and opioid signaling but also from its caloric properties. Studies in those suffering from an AUD have revealed significant alterations in dopamine (DA), GABA, cannabinoids, opioid and serotonin neurotransmission and in brain energy utilization (glucose and acetate metabolism) that are likely to contribute to compulsive alcohol taking, dysphoria/depression, and to alcohol-associated neurotoxicity. Studies have also evaluated the effects of abstinence on recovery of brain metabolism and neurotransmitter function and the potential value of some of these measures to predict clinical outcomes. Finally, PET studies have started to provide insights about the neuronal mechanisms by which certain genes contribute to the vulnerability to AUD. These findings have helped identify new strategies for prevention and treatment of AUD. This article is part of the Special Issue entitled "Alcoholism".

Family history of alcoholism is related to increased D2 /D3 receptor binding potential: a marker of resilience or risk?

The aim of this study was to examine the relationship between family history of alcohol use disorder and striatal dopamine using positron emission tomography imaging. Participants were 84 healthy, 18- to 30-year-old, social drinkers recruited via fliers and newspaper advertisements. At assessment, participants completed measures of lifetime personal and family substance use and psychiatric symptoms. Participants underwent two consecutive positron emission tomography scans using the D₂ /D₃ dopamine receptor radioligand [¹¹ C]raclopride. Scans were preceded by intravenous saline and amphetamine 0.3 mg/kg, providing measures of baseline [¹¹ C]raclopride binding potential (BP_ND ) and change in [¹¹ C]raclopride (ΔBP_ND ). Subjective ratings of stimulant drug effects were collected during scans. Subjects were classified as family history positive (FHP) if they reported any first-degree relative with alcohol use disorder (AUD) and family history negative (FHN) if no first-degree relatives had history of AUD. Participants were predominantly White (69.0 percent) and male (62.1 percent). Baseline [¹¹ C]raclopride BP_ND was generally higher in FHP compared with FHN subjects across striatal subdivisions. There were no differences in ΔBP_ND across regions. Negative subjective drug effects were more pronounced in FHP than in FHN subjects. While FHN subjects evidenced the expected positive relationship between ΔBP_ND and positive subjective drug effects, this relationship was disrupted in FHP subjects. There are key differences in dopamine status and subjective stimulant drug experiences as a function of family AUD history. These findings have important implications for understanding risk for AUD development in FHP offspring.

Similarities and Differences in Neurobiology

Substance addiction is a chronic, relapsing brain disease characterized by compulsive drug seeking and use despite harmful consequences. Non-substance addiction is defined recently that people may compulsively engage in an activity despite any negative consequences to their lives. Despite differences with respect to their addictive object, substance addiction and non-substance addiction may share similarities with respect to biological, epidemiological, clinical, genetic and other features. Here we review the similarities and differences in neurobiology between these two addictions with a focus on dopamine, serotonin, opioid, glutamate and norepinephrine systems. Studies suggest the involvement of all these systems in both substance addiction and non-substance addiction while differences may exist with respect to their contributions.

The 2D:4D Marker and Different Forms of Internet Use Disorder

Internet use disorder (IUD) presents a growing problem worldwide. Among others, it manifests in loss of control over Internet usage and social problems due to problematic Internet use. Although IUD currently is not an official diagnosis in DSM-5 or ICD-10, mounting evidence suggests that IUD indeed could be categorized as a behavioral addiction. On a systemic neuroscientific level, IUD is well characterized and dysfunctions in the fronto-striatal-limbic loop have been observed in persons being afflicted with IUD. On a molecular level underlying these neural dysfunctions less is known. Therefore, the present research investigates the influence of prenatal testosterone as measured via the 2D:4D marker of the hand on IUD. Testosterone represents an interesting hormonal marker, because sex differences in IUD have been observed, e.g., males show higher tendencies toward Internet gaming disorder (IGD) or females toward overusage of online social networks (both compared to the contrary sex). In N = 217 participants associations between the 2D:4D marker of the hand and both unspecified IUD and specific forms of IUD were investigated. It appeared that more female hands (right side; characterized by higher digit ratio of the index to the ring finger, i.e., >1, meaning lower prenatal testosterone) were associated with lower IGD (rho = -0.17, p = 0.01, N = 211). This effect was driven by the facet of loss of control of Internet Gaming in the whole sample (rho = -0.20, p < 0.01, N = 211) and the female subsample (rho = -0.20, p = 0.02, N(f) = 137). Aside from this, a negative association appeared between the facet of loss of control of generalized IUD and the right digit ratio in males underlining earlier work. In sum, the present work demonstrates that the 2D:4D marker is an interesting marker for Internet addiction and can be easily included as a biomarker to understand the biological underpinnings of Internet (over-)usage.

Alcohol-dose-dependent DNA methylation and expression in the nucleus accumbens identifies coordinated regulation of synaptic genes

Alterations in DNA methylation have been associated with alcohol exposure and proposed to contribute to continued alcohol use; however, the molecular mechanisms involved remain obscure. We investigated the escalating effects of alcohol use on DNA methylation, gene expression and predicted neural effects in the nucleus accumbens of rhesus macaques that self-administered 4% alcohol for over 12 months. Using an exploratory approach to identify CpG-rich regions, followed by bisulfite sequencing, the methylation levels of 2.7 million CpGs were compared between seven low-binge drinkers and nine heavy-very heavy drinking subjects. We identified 17 significant differential methylation regions (DMRs), including 14 with methylation levels that were correlated with average daily alcohol consumption. The size of the DMRs ranged from 29 to 158 bp (mean=63.7), included 4-19 CpGs per DMR (mean=8.06) and spanned a range of average methylation values from 5 to 34%. Eight of the DMRs mapped to genes implicated in modulating synaptic plasticity. Six of the synaptic genes have not previously been linked to alcohol use. Validation studies of these eight DMRs using bisulfite amplicon sequencing and an expanded set of 30 subjects confirmed the significant alcohol-dose-associated methylation of the DMRs. Expression analysis of three of the DMR-associated genes, LRP5, GPR39 and JAKMIP1, revealed significant correlations between DMR methylation and whole-gene or alternative transcript expression, supporting a functional role in regulating gene expression. Together, these studies suggest that alcohol-associated synaptic remodeling may be regulated and coordinated at the level of DNA methylation.

Blunted Dopamine Transmission in Addiction: Potential Mechanisms and Implications for Behavior

Positron emission tomography (PET) imaging consistently shows blunted striatal dopamine release and decreased dopamine D2 receptor availability in addiction. Here, we review the preclinical and clinical studies indicating that this neurobiological phenotype is likely to be both a consequence of chronic drug consumption and a vulnerability factor in the development of addiction. We propose that, behaviorally, blunted striatal dopamine transmission could reflect the increased impulsivity and altered cost/benefit computations that are associated with addiction. The factors that influence blunted striatal dopamine transmission in addiction are unknown. Herein, we give an overview of various factors, genetic, environmental, and social, that are known to affect dopamine transmission and that have been associated with the vulnerability to develop addiction. Altogether, these data suggest that blunted dopamine transmission and decreased D2 receptor availability are biomarkers both for the development of addiction and resistance to treatment. These findings support the view that blunted dopamine reflects impulsive behavior and deficits in motivation, which lead to the escalation of drug use.

The metabolic syndrome in patients with alcohol dependency: Current research and clinical implications

The relationship between alcohol dependency and disorders such as liver disease and cancer has been thoroughly researched. However, the effects of alcohol on cardiometabolic health remain controversial. Several reports found low to moderate alcohol consumption to be associated with a lower risk for cardiometabolic disorders. In contrast, excessive alcohol consumption has been related to an increased risk. Most of these studies were performed in non-clinical populations, therefore limiting the explanatory power to non-dependent patients. Only a few studies examined cardiovascular disorders and cardiovascular risk factors, in particular the metabolic syndrome (MetS), in alcohol dependent patients. We here present a narrative review of studies performed so far on the MetS in alcohol dependency, and provide current hypotheses on the association of alcohol dependency, appetite regulation and the development of the MetS.

Impaired Ethanol-Induced Sensitization and Decreased Cannabinoid Receptor-1 in a Model of Posttraumatic Stress Disorder

BACKGROUND AND PURPOSE

Impaired striatal neuroplasticity may underlie increased alcoholism documented in those with posttraumatic stress disorder (PTSD). Cannabinoid receptor-1 (CB1) is sensitive to the effects of ethanol (EtOH) and traumatic stress, and is a critical regulator of striatal plasticity. To investigate CB1 involvement in the PTSD-alcohol interaction, this study measured the effects of traumatic stress using a model of PTSD, mouse single-prolonged stress (mSPS), on EtOH-induced locomotor sensitization and striatal CB1 levels.

METHODS

Mice were exposed to mSPS, which includes: 2-h restraint, 10-min group forced swim, 15-min exposure to rat bedding odor, and diethyl ether exposure until unconsciousness or control conditions. Seven days following mSPS exposure, the locomotor sensitizing effects of EtOH were assessed. CB1, post-synaptic density-95 (PSD95), and dopamine-2 receptor (D2) protein levels were then quantified in the dorsal striatum using standard immunoblotting techniques.

RESULTS

Mice exposed to mSPS-EtOH demonstrated impaired EtOH-induced locomotor sensitization compared to Control-EtOH mice, which was accompanied by reduced striatal CB1 levels. EtOH increased striatal PSD95 in control and mSPS-exposed mice. Additionally, mSPS-Saline exposure increased striatal PSD95 and decreased D2 protein expression, with mSPS-EtOH exposure alleviating these changes.

CONCLUSIONS

These data indicate that the mSPS model of PTSD blunts the behavioral sensitizing effects of EtOH, a response that suggests impaired striatal neuroplasticity. Additionally, this study demonstrates that mice exposed to mSPS and repeated EtOH exposure decreases CB1 in the striatum, providing a mechanism of interest for understanding the effects of EtOH following severe, multimodal stress exposure.

The monoamine stabilizer (-)-OSU6162 counteracts downregulated dopamine output in the nucleus accumbens of long-term drinking Wistar rats

We recently established that the monoamine stabilizer (−)‐OSU6162 (OSU6162) decreased voluntary alcohol‐mediated behaviors, including alcohol intake and cue/priming‐induced reinstatement, in long‐term drinking rats, while blunting alcohol‐induced dopamine output in the nucleus accumbens (NAc) of alcohol‐naïve rats. Therefore, we hypothesized that OSU6162 attenuates alcohol‐mediated behaviors by blunting alcohol's rewarding effects. Here, we evaluated the effects of long‐term drinking and OSU6162 treatment (30 mg/kg, sc) on basal and alcohol‐induced (2.5 g/kg, ip) NAc dopamine outputs in Wistar rats after 10 months of intermittent access to 20% alcohol. The results showed that basal and alcohol‐induced NAc dopamine outputs were significantly lower in long‐term drinking rats, compared with alcohol‐naïve rats. In the long‐term drinking rats, OSU6162 slowly increased and maintained the dopamine output significantly elevated compared with baseline for at least 4 hours. Furthermore, OSU6162 pre‐treatment did not blunt the alcohol‐induced output in the long‐term drinking rats, a finding that contrasted with our previous results in alcohol‐naïve rats. Finally, OSU6162 did not induce conditioned place preference (CPP) in either long‐term drinking or alcohol‐naïve rats, indicating that OSU6162 has no reinforcing properties. To verify that the CPP results were not due to memory acquisition impairment, we demonstrated that OSU6162 did not affect novel object recognition. In conclusion, these results indicate that OSU6162 attenuates alcohol‐mediated behaviors by counteracting NAc dopamine deficits in long‐term drinking rats and that OSU6162 is not rewarding on its own. Together with OSU6162's beneficial side‐effect profile, the present study merits evaluation of OSU6162's clinical efficacy to attenuate alcohol use in alcohol‐dependent patients.

Convergent evidence from alcohol-dependent humans and rats for a hyperdopaminergic state in protracted abstinence

A major hypothesis in addiction research is that alcohol induces neuroadaptations in the mesolimbic dopamine (DA) system and that these neuroadaptations represent a key neurochemical event in compulsive drug use and relapse. Whether these neuroadaptations lead to a hypo- or hyperdopaminergic state during abstinence is a long-standing, unresolved debate among addiction researchers. The answer is of critical importance for understanding the neurobiological mechanism of addictive behavior. Here we set out to study systematically the neuroadaptive changes in the DA system during the addiction cycle in alcohol-dependent patients and rats. In postmortem brain samples from human alcoholics we found a strong down-regulation of the D1 receptor- and DA transporter (DAT)-binding sites, but D2-like receptor binding was unaffected. To gain insight into the time course of these neuroadaptations, we compared the human data with that from alcohol-dependent rats at several time points during abstinence. We found a dynamic regulation of D1 and DAT during 3 wk of abstinence. After the third week the rat data mirrored our human data. This time point was characterized by elevated extracellular DA levels, lack of synaptic response to D1 stimulation, and augmented motor activity. Further functional evidence is given by a genetic rat model for hyperdopaminergia that resembles a phenocopy of alcohol-dependent rats during protracted abstinence. In summary, we provide a new dynamic model of abstinence-related changes in the striatal DA system; in this model a hyperdopaminergic state during protracted abstinence is associated with vulnerability for relapse.

Dopamine receptor agonists modulate voluntary alcohol intake independently of individual levels of alcohol intake in rats

RATIONALE

Individual susceptibility to alcohol use disorder has been related to functional changes in dopaminergic neurotransmission.

OBJECTIVES

The aim of the current work was to assess the effects of selective dopamine D1 and D2 receptor agonists and antagonists on alcohol consumption in rats that differ in individual levels of alcohol intake.

METHODS

The effects of the dopamine D1 receptor agonist SKF 82958, the dopamine D1 receptor antagonist SCH 23390, the dopamine D2 receptor agonist sumanirole and the dopamine D2 receptor antagonist L741,626 on alcohol consumption and preference were assessed at different time points after treatment in subgroups of low and high alcohol drinking rats (LD and HD) using an intermittent alcohol access paradigm.

RESULTS

SKF 82958 decreased alcohol intake and alcohol preference throughout the 24-h session. Sumanirole decreased alcohol intake during the first 2 h, but increased alcohol intake during the remainder of the session. The effects of SKF 82958 and sumanirole on alcohol intake and alcohol preference were comparable in LD and HD. By contrast, the dopamine receptor antagonists SCH 23390 and L741,626 did not alter alcohol consumption in either group at any time point.

CONCLUSIONS

These data indicate that stimulation of dopamine D1 receptors reduces alcohol intake, but that endogenous dopamine does not play a primary role in alcohol consumption. Moreover, the difference in alcohol consumption between LD and HD does not involve altered dopamine signaling.

How Imaging Glutamate, γ-Aminobutyric Acid, and Dopamine Can Inform the Clinical Treatment of Alcohol Dependence and Withdrawal

Neuroimaging studies have dramatically advanced our understanding of the neurochemical basis of alcohol dependence, a major public health issue. In this paper, we review the research generated from neurochemical specific imaging modalities including magnetic resonance spectroscopy, positron emission tomography, and single-photon emission computed tomography in studies of alcohol dependence and withdrawal. We focus on studies interrogating γ-aminobutyric acid (GABA), glutamate, and dopamine, as these are prominent neurotransmitter systems implicated in alcohol dependence. Highlighted findings include diminished dopaminergic functioning and modulation of the GABA system by tobacco smoking during alcohol withdrawal. Then, we consider how these findings impact the clinical treatment of alcohol dependence and discuss directions for future experiments to address existing gaps in the literature, for example, sex differences and smoking comorbidity. These and other considerations provide opportunities to build upon the current neurochemistry imaging literature of alcohol dependence and withdrawal, which may usher in improved therapeutic and relapse prevention strategies.

The Molecular Neurobiology of Twelve Steps Program & Fellowship: Connecting the Dots for Recovery

There are some who suggest that alcoholism and drug abuse are not diseases at all and that they are not consequences of a brain disorder as espoused recently by the American Society of Addiction Medicine (ASAM). Some would argue that addicts can quit on their own and moderate their alcohol and drug intake. When they present to a treatment program or enter the 12 Step Program & Fellowship, many addicts finally achieve complete abstinence. However, when controlled drinking fails, there may be successful alternatives that fit particular groups of individuals. In this expert opinion, we attempt to identify personal differences in recovery, by clarifying the molecular neurobiological basis of each step of the 12 Step Program. We explore the impact that the molecular neurobiological basis of the 12 steps can have on Reward Deficiency Syndrome (RDS) despite addiction risk gene polymorphisms. This exploration has already been accomplished in part by Blum and others in a 2013 Springer Neuroscience Brief. The purpose of this expert opinion is to briefly, outline the molecular neurobiological and genetic links, especially as they relate to the role of epigenetic changes that are possible in individuals who regularly attend AA meetings. It begs the question as to whether "12 steps programs and fellowship" does induce neuroplasticity and continued dopamine D2 receptor proliferation despite carrying hypodopaminergic type polymorphisms such as DRD2 A1 allele. "Like-minded" doctors of ASAM are cognizant that patients in treatment without the "psycho-social-spiritual trio," may not be obtaining the important benefits afforded by adopting 12-step doctrines. Are we better off with coupling medical assisted treatment (MAT) that favors combining dopamine agonist modalities (DAM) as possible histone-deacetylase activators with the 12 steps followed by a program that embraces either one or the other? While there are many unanswered questions, at least we have reached a time when "science meets recovery," and in doing so, can further redeem joy in recovery.

Aberrant mesolimbic dopamine-opiate interaction in obesity

Dopamine and opioid neurotransmitter systems share many functions such as regulation of reward and pleasure. μ-Opioid receptors (MOR) modulate the mesolimbic dopamine system in ventral tegmental area and striatum, key areas implicated in reward. We hypothesized that dopamine and opioid receptor availabilities correlate in vivo and that this correlation is altered in obesity, a disease with altered reward processing. Twenty lean females (mean BMI 22) and 25 non-binge eating morbidly obese females (mean BMI 41) underwent two positron emission tomography scans with [(11)C]carfentanil and [(11)C]raclopride to measure the MOR and dopamine D2 receptor (DRD2) availability, respectively. In lean subjects, the MOR and DRD2 availabilities were positively associated in the ventral striatum (r=0.62, p=0.003) and dorsal caudate nucleus (r=0.62, p=0.004). Moreover, DRD2 availability in the ventral striatum was associated with MOR availability in other regions of the reward circuitry, particularly in the ventral tegmental area. In morbidly obese subjects, this receptor interaction was significantly weaker in ventral striatum but unaltered in the caudate nucleus. Finally, the association between DRD2 availability in the ventral striatum and MOR availability in the ventral tegmental area was abolished in the morbidly obese. The study demonstrates a link between DRD2 and MOR availabilities in living human brain. This interaction is selectively disrupted in mesolimbic dopamine system in morbid obesity. We propose that interaction between the dopamine and opioid systems is a prerequisite for normal reward processing and that disrupted cross-talk may underlie altered reward processing in obesity.

Upregulation of dopamine D2 receptors in the nucleus accumbens indirect pathway increases locomotion but does not reduce alcohol consumption

Brain imaging studies performed in humans have associated low striatal dopamine release and D2R binding with alcohol dependence. Conversely, high striatal D2R binding has been observed in unaffected members of alcoholic families suggesting that high D2R function may protect against alcohol dependence. A possible protective role of increased D2R levels in the striatum is further supported by preclinical studies in non-human primates and rodents. Here, we determined whether there is a causal relationship between D2R levels and alcohol intake. To this end, we upregulated D2R expression levels in the nucleus accumbens of the adult mouse, but selectively restricted the upregulation to the indirect striatal output pathway, which endogenously expresses D2Rs. After overexpression was established, mice were tested in two models of free-choice alcohol drinking: the continuous and intermittent access two-bottle choice models. As anticipated, we found that D2R upregulation leads to hyperactivity in the open field. Contrary to our expectation, D2R upregulation did not reduce alcohol intake during continuous or intermittent access or when alcohol drinking was tested in the context of aversive outcomes. These data argue against a protective role of accumbal indirect pathway D2Rs in alcohol consumption but emphasize their importance in promoting locomotor activity.