Overexpression of dopamine D2 receptors reduces alcohol self-administration

Role of antioxidants in the neurobiology of drug addiction: An update

Relationships between protective enzymatic and non-enzymatic pro-antioxidant mechanisms and addictive substances use disorders (SUDs) are analyzed here, based on the results of previous research, as well as on the basis of our current own studies. This review introduces new aspects of comparative analysis of associations of pro-antixidant and neurobiological effects in patients taking psychoactive substances and complements very limited knowledge about relationships with SUDs from different regions, mainly Europe. In view of the few studies on relations between antioxidants and neurobiological processes acting in patients taking psychoactive substances, this review is important from the point of view of showing the state of knowledge, directions of diagnosis and treatment, and further research needed explanation. We found significant correlations between chemical elements, pro-antioxidative mechanisms, and lipoperoxidation in the development of disorders associated with use of addictive substances, therefore elements that show most relations (Pr, Na, Mn, Y, Sc, La, Cr, Al, Ca, Sb, Cd, Pb, As, Hg, Ni) may be significant factors shaping SUDs. The action of pro-antioxidant defense and lipid peroxidation depends on the pro-antioxidative activity of ions. We explain the strongest correlations between Mg and Sb, and lipoperoxidation in addicts, which proves their stimulating effect on lipoperoxidation and on the induction of oxidative stress. We discussed which mechanisms and neurobiological processes change susceptibility to SUDs. The innovation of this review is to show that addicted people have lower activity of dismutases and peroxidases than healthy ones, which indicates disorders of antioxidant system and depletion of enzymes after long-term tolerance of stressors. We explain higher level of catalases, reductases, ceruloplasmin, bilirubin, retinol, α-tocopherol and uric acid of addicts. In view of poorly understood factors affecting addiction, analysis of interactions allows for more effective understanding of pathogenetic mechanisms leading to formation of addiction and development the initiation of directed, more effective treatment (pharmacological, hormonal) and may be helpful in the diagnosis of psychoactive changes.

Exercise Influences the Brain's Metabolic Response to Chronic Cocaine Exposure in Male Rats

Cocaine use is associated with negative health outcomes: cocaine use disorders, speedballing, and overdose deaths. Currently, treatments for cocaine use disorders and overdose are non-existent when compared to opioid use disorders, and current standard cocaine use disorder treatments have high dropout and recidivism rates. Physical exercise has been shown to attenuate addiction behavior as well as modulate brain activity. This study examined the differential effects of chronic cocaine use between exercised and sedentary rats. The effects of exercise on brain glucose metabolism (BGluM) following chronic cocaine exposure were assessed using Positron Emission Tomography (PET) and [18F]-Fluorodeoxyglucose (FDG). Compared to sedentary animals, exercise decreased metabolism in the SIBF primary somatosensory cortex. Activation occurred in the amygdalopiriform and piriform cortex, trigeminothalamic tract, rhinal and perirhinal cortex, and visual cortex. BGluM changes may help ameliorate various aspects of cocaine abuse and reinstatement. Further investigation is needed into the underlying neuronal circuits involved in BGluM changes and their association with addiction behaviors.

Role of glycogen synthase kinase-3β in dependence and abuse liability of alcohol

BACKGROUND

Alcohol is a major abused drug worldwide that contributes substantially to health and social problems. These problems result from acute alcohol overuse as well as chronic use, leading to alcohol use disorder (AUD). A major goal of this field is to establish a treatment for alcohol abuse and dependence in patients with AUD. The central molecular mechanisms of acute alcohol actions have been extensively investigated in rodent models.

AIMS

One of the central mechanisms that may be involved is glycogen synthase kinase-3β (GSK-3β) activity, a key enzyme involved in glycogen metabolism but which has crucial roles in numerous cellular processes. Although the exact mechanisms leading from acute alcohol actions to these chronic changes in GSK-3β function are not yet clear, GSK-3β nonetheless constitutes a potential therapeutic target for AUD by reducing its function using GSK-3β inhibitors. This review is focused on the correlation between GSK-3β activity and the degree of alcohol consumption.

METHODS

Research articles regarding investigation of effect of GSK-3β on alcohol consumption in rodents were searched on PubMed, Embase, and Scopus databases using keywords "glycogen synthase kinase," "alcohol (or ethanol)," "intake (or consumption)," and evaluated by changes in ratios of pGSK-3βSer9/pGSK-3β.

RESULTS

In animal experiments, GSK-3β activity decreases in the brain under forced and voluntary alcohol consumption while GSK-3β activity increases under alcohol-seeking behavior.

CONCLUSIONS

Several pieces of evidence suggest that alterations in GSK-3β function are important mediators of chronic ethanol actions, including those related to alcohol dependence and the adverse effects of chronic ethanol exposure.

High intensity interval training exercise increases dopamine D2 levels and modulates brain dopamine signaling

Background

Previous research has outlined the health benefits of exercise including its therapeutic potential for substance use disorders (SUD). These data have already been utilized and it is now common to find exercise as part of SUD treatment and relapse prevention programs. However, we need to better understand different exercise regimens and determine which would be the most beneficial for SUDs. Recently, high intensity interval training (HIIT) has gained attention in comparison with aerobic and resistance exercise. Little is known regarding the neurobiological mechanisms of HIIT, including its effects on dopamine signaling and receptor levels in the brain. The present study examined the effects of chronic HIIT exercise on dopamine signaling as measured by dopamine type 1-like receptor (D1R)-like, dopamine type 2-like receptor (D2R)-like, and tyrosine hydroxylase (TH) quantification in the brains of male and female rats as measured by [3H] SCH 23390 and [3H] spiperone autoradiography, and TH-immunoreactive optical density values.

Methods

Rats were separated in two groups: sedentary and HIIT exercise. Exercise was on a treadmill for 30 min daily (10 3 min cycles) for six weeks with progressive speed increased up to 0.8 mph (21.5 m/min).

Results

Results showed for D2R-like binding, a significant effect across the ventral caudate putamen (V CPU) between sexes, such that mean D2R-like binding was 14% greater for males than females. In the nucleus accumbens shell (Nac Shell), the HIIT Exercise rats showed 16% greater D2R-like binding as compared to the sedentary rats. No significant effects of HIIT exercise were found across groups for brain D1R-like binding levels or TH expression.

Conclusion

These results suggest that HIIT exercise can modulate dopamine signaling by way of increased D2R. These findings support the premise that HIIT exercise plays an important role in dopamine signaling and, may provide a potential mechanism for how HIIT exercise can impact the brain and behavior.

"TO BE OR NOT TO BE" GWAS Ends the Controversy about the DRD2 Gene as a Determinant of Reward Deficiency Syndrome (RDS)

Since 1990, there have been thousands of published studies on addiction psychiatry. Several from Blum et al showed the clinical relevance of the Genetic Addiction Risk Severity (GARS) test in identifying risk for reward deficiency behaviors in cohorts from polysubstance abuse and pain clinics, post-surgical bariatrics, and DWI offenders facing prison time. Since Blum et al first published in JAMA (1990) concerning the association of the DRD2 gene polymorphism and severe alcoholism, reactions have been mixed. More recently, however, a meta-analysis of 62 studies showed a significant association between DRD2 rs1800497 and Alcohol Use Disorder (AUD). Other studies from Yale University showed that a haplotype block of the DRD2 gene A1 allele was associated with AUD and heroin dependence. GWAS studies of depression and suicide in 1.2 million veterans confirmed the first psychiatric candidate gene study finding from Blum et al 1990; a significant association between the minor DRD2 allele, Taq A1 and severe alcoholism. Additionally, the DRD2 rs1800497 is robustly associated with suicidal behaviors. Furthermore, DNA polymorphic alleles underlying substance use disorder (SUD) with multiple substances were mapped via chromatin refolding, revealing that the DRD2 gene and associated polymorphism(s) as the top gene signal. Based on these investigations, we conclude that GWAS should end the controversy about the DRD2 gene being one determinant of Reward Deficiency Syndrome (RDS) first reported in 1996.

GDNF gene therapy for alcohol use disorder in male non-human primates

Alcohol use disorder (AUD) exacts enormous personal, social and economic costs globally. Return to alcohol use in treatment-seeking patients with AUD is common, engendered by a cycle of repeated abstinence-relapse episodes even with use of currently available pharmacotherapies. Repeated ethanol use induces dopaminergic signaling neuroadaptations in ventral tegmental area (VTA) neurons of the mesolimbic reward pathway, and sustained dysfunction of reward circuitry is associated with return to drinking behavior. We tested this hypothesis by infusing adeno-associated virus serotype 2 vector encoding human glial-derived neurotrophic factor (AAV2-hGDNF), a growth factor that enhances dopaminergic neuron function, into the VTA of four male rhesus monkeys, with another four receiving vehicle, following induction of chronic alcohol drinking. GDNF expression ablated the return to alcohol drinking behavior over a 12-month period of repeated abstinence-alcohol reintroduction challenges. This behavioral change was accompanied by neurophysiological modulations to dopamine signaling in the nucleus accumbens that countered the hypodopaminergic signaling state associated with chronic alcohol use, indicative of a therapeutic modulation of limbic circuits countering the effects of alcohol. These preclinical findings suggest gene therapy targeting relapse prevention may be a potential therapeutic strategy for AUD.

Overexpression of wild type glycine alpha 1 subunit rescues ethanol sensitivity in accumbal receptors and reduces binge drinking in mice

The nucleus accumbens (nAc) is a critical region in the brain reward system since it integrates abundant synaptic inputs contributing to the control of neuronal excitability in the circuit. The presence of inhibitory α1 glycine receptor (GlyRs) subunits, sensitive to ethanol, has been recently reported in accumbal neurons suggesting that they are protective against excessive binge consumption. In the present study, we used viral vectors (AAV) to overexpress mutant and WT α1 subunits in accumbal neurons in D1 Cre and α1 KI mice. Injection of a Cre-inducible AAV carrying an ethanol insensitive α1 subunit in D1 Cre neurons was unable to affect sensitivity to ethanol in GlyRs or affect ethanol drinking. On the other hand, using an AAV that transduced WT α1 GlyRs in GABAergic neurons in the nAc of high-ethanol consuming mice caused a reduction in ethanol intake as reflected by lowered drinking in the dark and reduced blood ethanol concentration. As expected, the AAV increased the glycine current density by 5-fold without changing the expression of GABAA receptors. Examination of the ethanol sensitivity in isolated accumbal neurons indicated that the GlyRs phenotype changed from an ethanol resistant to an ethanol sensitive type. These results support the conclusion that increased inhibition in the nAc can control excessive ethanol consumption and that selective targeting of GlyRs by pharmacotherapy might provide a mechanistic procedure to reduce ethanol binge.

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.

Prenatal Effects of Nicotine on Obesity Risks: A Narrative Review

Nicotine usage by mothers throughout pregnancy has been observed to relate to numerous deleterious effects in children, especially relating to obesity. Children who have prenatally been exposed to nicotine tend to have lower birth weights, with an elevated risk of becoming overweight throughout development and into their adolescent and adult life. There are numerous theories as to how this occurs: catch-up growth theory, thrifty phenotype theory, neurotransmitter or endocrine imbalances theory, and a more recent examination on the genetic factors relating to obesity risk. In addition to the negative effect on bodyweight and BMI, individuals with obesity may also suffer from numerous comorbidities involving metabolic disease. These may include type 1 and 2 diabetes, high cholesterol levels, and liver disease. Predisposition for obesity with nicotine usage may also be associated with genetic risk alleles for obesity, such as the DRD2 A1 variant. This is important for prenatally nicotine-exposed individuals as an opportunity to provide early prevention and intervention of obesity-related risks.

The Advent of Nutrigenomics: A Narrative Review with an Emphasis on Psychological Disorders

A new research field is emerging that combines nutrition and genetics at the molecular level, namely nutrigenomics. Several aspects of nutrigenomics are examined in this review, with a particular focus on psychological disorders. The origin of this field in the 20th century and its modern developments have been investigated. Various studies have reported the impact of genetic factors and diet on various chronic disorders, elucidating how the deficiency of several macronutrients results in significant ailments, including diabetes, cancer, cardiovascular disorders, and others. Furthermore, the application of nutrigenomics to diet and its impact on the global disease rate and quality of life have been discussed. The relationship between diet and gene expression can facilitate the classification of diet-gene interactions and the diagnosis of polymorphisms and anomalies. Numerous databases and research tools for the study of nutrigenomics are essential to the medical application of this field. The nutrition-gene interrelationships can be utilized to study brain development, impairment, and diseases, which could be a significant medical breakthrough. It has also been observed that psychological conditions are exacerbated by the interaction between gut microbes and the prevalence of malnutrition. This article focuses on the impact of nutrition on genes involved in various psychological disorders and the potential application of nutrigenomics as a revolutionary treatment method.

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.

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.

Reward Deficiency Syndrome (RDS): A Cytoarchitectural Common Neurobiological Trait of All Addictions

Alcohol and other substance use disorders share comorbidity with other RDS disorders, i.e., a reduction in dopamine signaling within the reward pathway. RDS is a term that connects addictive, obsessive, compulsive, and impulsive behavioral disorders. An estimated 2 million individuals in the United States have opioid use disorder related to prescription opioids. It is estimated that the overall cost of the illegal and legally prescribed opioid crisis exceeds one trillion dollars. Opioid Replacement Therapy is the most common treatment for addictions and other RDS disorders. Even after repeated relapses, patients are repeatedly prescribed the same opioid replacement treatments. A recent JAMA report indicates that non-opioid treatments fare better than chronic opioid treatments. Research demonstrates that over 50 percent of all suicides are related to alcohol or other drug use. In addition to effective fellowship programs and spirituality acceptance, nutrigenomic therapies (e.g., KB220Z) optimize gene expression, rebalance neurotransmitters, and restore neurotransmitter functional connectivity. KB220Z was shown to increase functional connectivity across specific brain regions involved in dopaminergic function. KB220/Z significantly reduces RDS behavioral disorders and relapse in human DUI offenders. Taking a Genetic Addiction Risk Severity (GARS) test combined with a the KB220Z semi-customized nutrigenomic supplement effectively restores dopamine homeostasis (WC 199).

A systems omics-based approach to decode substance use disorders and neuroadaptations

Substance use disorders (SUDs) are a group of neuropsychiatric conditions manifesting due to excessive dependence on potential drugs of abuse such as psychostimulants, opioids including prescription opioids, alcohol, inhalants, etc. Experimental studies have generated enormous data in the area of SUDs, but outcomes from such data have remained largely fragmented. In this review, we attempt to coalesce these data points providing an important first step towards our understanding of the etiology of SUDs. We propose and describe a 'core addictome' pathway that behaves central to all SUDs. Besides, we also have made some notable observations paving way for several hypotheses; MECP2 behaves as a master switch during substance use; five distinct gene clusters were identified based on respective substance addiction; a central cluster of genes serves as a hub of the addiction pathway connecting all other substance addiction clusters. In addition to describing these findings, we have emphasized the importance of some candidate genes that are of substantial interest for further investigation and serve as high-value targets for translational efforts.

Circuit selectivity in drug versus natural reward seeking behaviors

Substance use disorder (SUD) is characterized, in part by behavior biased toward drug use and away from natural sources of reward (e.g., social interaction, food, sex). The neurobiological underpinnings of SUDs reveal distinct brain regions where neuronal activity is necessary for the manifestation of SUD-characteristic behaviors. Studies that specifically examine how these regions are involved in behaviors motivated by drug versus natural reward allow determinations of which regions are necessary for regulating seeking of both reward types, and appraisals of novel SUD therapies for off-target effects on behaviors motivated by natural reward. Here, we evaluate studies directly comparing regulatory roles for specific brain regions in drug versus natural reward. While it is clear that many regions drive behaviors motivated by all reward types, based on the literature reviewed we propose a set of interconnected regions that become necessary for behaviors motivated by drug, but not natural rewards. The circuitry is selectively necessary for drug seeking includes an Action/Reward subcircuit, comprising nucleus accumbens, ventral pallidum, and ventral tegmental area, a Prefrontal subcircuit comprising prelimbic, infralimbic, and insular cortices, a Stress subcircuit comprising the central nucleus of the amygdala and the bed nucleus of the stria terminalis, and a Diencephalon circuit including lateral hypothalamus. Evidence was mixed for nucleus accumbens shell, insular cortex, and ventral pallidum. Studies for all other brain nuclei reviewed supported a necessary role in regulating both drug and natural reward seeking. Finally, we discuss emerging strategies to further disambiguate the necessity of brain regions in drug- versus natural reward-associated behaviors.

Receptors and Channels Associated with Alcohol Use: Contributions from Drosophila

Alcohol Use Disorder (AUD) is a debilitating disorder that manifests as problematic patterns of alcohol use. At the core of AUD's behavioral manifestations are the profound structural, physiological, cellular, and molecular effects of alcohol on the brain. While the field has made considerable progress in understanding the neuromolecular targets of alcohol we still lack a comprehensive understanding of alcohol's actions and effective treatment strategies. Drosophila melanogaster is a powerful model for investigating the neuromolecular targets of alcohol because flies model many of the core behavioral elements of AUD and offer a rich genetic toolkit to precisely reveal the in vivo molecular actions of alcohol. In this review, we focus on receptors and channels that are often targeted by alcohol within the brain. We discuss the general roles of these proteins, their role in alcohol-associated behaviors across species, and propose ways in which Drosophila models can help advance the field.

An autophagy-related protein Becn2 regulates cocaine reward behaviors in the dopaminergic system

Drug abuse is a foremost public health problem. Cocaine is a widely abused drug worldwide that produces various reward-related behaviors. The mechanisms that underlie cocaine-induced disorders are unresolved, and effective treatments are lacking. Here, we found that an autophagy-related protein Becn2 is a previously unidentified regulator of cocaine reward behaviors. Becn2 deletion protects mice from cocaine-stimulated locomotion and reward behaviors, as well as cocaine-induced dopamine accumulation and signaling, by increasing presynaptic dopamine receptor 2 (D2R) autoreceptors in dopamine neurons. Becn2 regulates D2R endolysosomal trafficking, degradation, and cocaine-induced behaviors via interacting with a D2R-bound adaptor GASP1. Inactivating Becn2 by upstream autophagy inhibitors stabilizes striatal presynaptic D2R, reduces dopamine release and signaling, and prevents cocaine reward in normal mice. Thus, the autophagy protein Becn2 is essential for cocaine psychomotor stimulation and reward through regulating dopamine neurotransmission, and targeting Becn2 by autophagy inhibitors is a potential strategy to prevent cocaine-induced behaviors.

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.

High Genetic Addiction Risk Score (GARS) in Chronically Prescribed Severe Chronic Opioid Probands Attending Multi-pain Clinics: an Open Clinical Pilot Trial

Millions of Americans experience pain daily. In 2017, opioid overdose claimed 64,000 lives increasing to 84,000 lives in 2020, resulting in a decrease in national life expectancy. Chronic opioid use results in dependency, drug tolerance, neuroadaptation, hyperalgesia, potential addictive behaviors, or Reward Deficiency Syndrome (RDS) caused by a hypodopaminergia. Evaluation of pain clinic patients with the Genetic Addiction Risk Score (GARS) test and the Addiction Severity Index (ASI- Media Version V) revealed that GARS scores equal to or greater than 4 and 7 alleles significantly predicted drug and alcohol severity, respectively. We utilized RT-PCR for SNP genotyping and multiplex PCR/capillary electrophoresis for fragment analysis of the role of eleven alleles in a ten-reward gene panel, reflecting the activity of brain reward circuitry in 121 chronic opioid users. The study consisted of 55 males and 66 females averaging ages 54 and 53 years of age, respectively. The patients included Caucasians, African Americans, Hispanics, and Asians. Inclusion criteria mandated that the Morphine Milligram Equivalent (MME) was 30-600 mg/day (males) and 20 to 180 mg/day (females) for treatment of chronic pain over 12 months. Ninety-six percent carried four or more risk alleles, and 73% carried seven or more risk alleles, suggesting a high predictive risk for opioid and alcohol dependence, respectively. These data indicate that chronic, legally prescribed opioid users attending a pain clinic possess high genetic risk for drug and alcohol addiction. Early identification of genetic risk, using the GARS test upon entry to treatment, may prevent iatrogenic induced opioid dependence.

Chemogenetic selective manipulation of nucleus accumbens medium spiny neurons bidirectionally controls alcohol intake in male and female rats

The nucleus accumbens (NAc), considered the hub of reward circuitry, is comprised of two medium spiny neuron (MSN) subtypes that are classified by their enrichment of dopamine 1 (D1) or 2 (D2) receptors. While reports indicate that alcohol increases excitatory neurotransmission exclusively on NAc D1-MSNs in male rats, it remains unknown how NAc MSNs control alcohol intake in either sex. Therefore, this study investigated how NAc MSNs mediate alcohol intake by using Drd1a-iCre and Drd2-iCre transgenic rats of both sexes. Intra-NAc infusions of Cre-inducible viral vectors containing stimulatory (hM3Dq) or inhibitory (hM4Di) designer receptors exclusively activated by designer drugs (DREADDs) were delivered after 4-weeks of alcohol intake, and clozapine-N-oxide (CNO) was administered to selectively manipulate NAc MSNs. Our results show that activation of NAc D1-MSNs increased alcohol intake 1-, 4-, and 24-h after the start of drinking while inhibition decreased it 1-h after the start of drinking, with no sex differences observed at any time point. Activation of NAc D2-MSNs had no impact on alcohol intake while inhibition increased alcohol intake in Drd2-iCre rats for 1-h in males and 4-h in females. These findings suggest opposing roles for how NAc D1- and D2-MSNs modulate alcohol intake in rats of both sexes.

Inhibition of Lrrk2 reduces ethanol preference in a model of acute exposure in zebrafish

Due to its multifactorial and yet to be fully understood origin, ethanol addiction is a field that still requires studies for the elucidation of novel genes and pathways that potentially influence the establishment and maintenance of addiction-like phenotypes. In this context, the present study aimed to evaluate the role of the LRRK2 pathway in the modulation of ethanol preference behavior in Zebrafish (Danio rerio). Using the behavioral Conditioned Place Preference (CPP) paradigm, we accessed the preference of animals for ethanol. Next, we evaluated the transcriptional regulation of the gene lrrk2 and the receptors drd1, drd2, grin1a, gria2a, and gabbr1b in the zebrafish brain. Additionally, we used a selective inhibitor of Lrrk2 (GNE-0877) to assess the role of this gene in the preference behavior. Our results revealed four distinct ethanol preference phenotypes (Light, Heavy, Negative Reinforcement, and Inflexible), each showing different transcriptional regulation patterns of the drd1, drd2, grin1a, gria2a, and gabbr1b receptors. We showed that the lrrk2 gene was hyperregulated only in the brains of the animals with the Inflexible phenotype. Most importantly, we showed, for the first time in the context of preference for ethanol, that treatment with the GNE-0877 inhibitor modulates the transcription of the target receptor genes and reduces the preference for ethanol in the animals of the Inflexible group. This result corroborates the hypothesis that the LRRK2 pathway is involved in the inflexible preference for ethanol behavior. Lastly, we identified a possible pharmacological target for the treatment of abusive preference behavior for ethanol.

Different dopamine tone in ethanol high- and low-consuming Wistar rats

Excessive alcohol use causes considerable morbidity and mortality worldwide. Changes in the mesolimbic dopamine system have been postulated as a neurobiological underpinning of excessive alcohol consumption, and recent research also suggests that the amino acid taurine plays a central role in ethanol-induced dopamine elevation. The aim of this study was to further outline the role of dopamine and taurine in regulating alcohol consumption. In this study, a choice between ethanol (20%) and water was administered to Wistar rats in an intermittent manner (three times/week) for seven consecutive weeks. In vivo microdialysis was used to explore baseline levels as well as ethanol-induced increases of extracellular dopamine and taurine, in the nucleus accumbens (nAc) of Wistar rats voluntarily consuming large or small amounts of ethanol. Basal levels of taurine were also measured in cerebrospinal fluid (CSF) and serum in a subset of rats. Ethanol-induced increases in nAc dopamine and taurine did not differ between alcohol-consuming and naïve rats. However, when categorized based on ethanol intake, rats consuming larger amounts of ethanol exhibited a lower dopamine tone in the nucleus accumbens and responded to ethanol with a slower elevation of extracellular taurine levels, as compared with low-consuming animals. Basal levels of taurine in nAc, CSF, or serum did not differ between ethanol high- and low-consuming rats. Our data support previous studies claiming an association between low endogenous dopamine levels and excessive alcohol intake.

Mechanisms of Shared Vulnerability to Post-traumatic Stress Disorder and Substance Use Disorders

Psychoactive substance use is a nearly universal human behavior, but a significant minority of people who use addictive substances will go on to develop an addictive disorder. Similarly, though ~90% of people experience traumatic events in their lifetime, only ~10% ever develop post-traumatic stress disorder (PTSD). Substance use disorders (SUD) and PTSD are highly comorbid, occurring in the same individual far more often than would be predicted by chance given the respective prevalence of each disorder. Some possible reasons that have been proposed for the relationship between PTSD and SUD are self-medication of anxiety with drugs or alcohol, increased exposure to traumatic events due to activities involved in acquiring illegal substances, or addictive substances altering the brain's stress response systems to make users more vulnerable to PTSD. Yet another possibility is that some people have an intrinsic vulnerability that predisposes them to both PTSD and SUD. In this review, we integrate clinical and animal data to explore these possible etiological links between SUD and PTSD, with an emphasis on interactions between dopaminergic, adrenocorticotropic, GABAergic, and glutamatergic neurobehavioral mechanisms that underlie different emotional learning styles.

Dopamine transporter gene expression within the nucleus accumbens plays important role in the acquisition and reinstatement of ethanol-seeking behavior in mice

Alcoholism and alcohol use disorders are chronically relapsing conditions which is a major problem in treating alcohol addiction. In a previous study we showed that the dopamine transporter (DAT) is implicated in voluntary intake and preference. However, its role in modulating ethanol-associated contextual memory remains largely unknown. In this study we have investigated the role of DAT in ethanol-induced conditioned place preference (EtOH-CPP) acquisition and reinstatement in adult male C57BL/6 mice. For this purpose, we used both loss- and gain-of-function approaches to test the effects of central DAT manipulation on EtOH-CPP. We developed a lentiviral-mediated gene transfer approach to examine whether DAT knockdown (shDAT) or overexpression in the nucleus accumbens (Nacc) is enough to impair EtOH-CPP acquisition and reinstatement. In the first experiment, results showed that DAT knockdown blocked, whereas DAT overexpression, exacerbated the acquisition of EtOH-CPP. In the second experiment and after the EtOH-CPP expression, the mice were subjected to a 14-day extinction trials before drug-induced EtOH-CPP reinstatement was induced by a priming injection of 1 g/kg EtOH. Results indicated that reinstatement of EtOH-CPP was considerably decreased after accumbal shDAT injection. However, DAT overexpression significantly increased EtOH-CPP reinstatement. Finally, and following DAT mRNA quantification using RT-PCR, Pearson's correlation showed a strong positive relationship between accumbal DAT mRNA and EtOH-CPP acquisition and reinstatement. These results suggest that DAT expression in the Nacc is involved in the acquisition and retrieval of EtOH contextual memory and that blockade of this transporter can decrease the rewarding properties of EtOH.

Personality Traits or Genetic Determinants-Which Strongly Influences E-Cigarette Users?

Presently, a growing popularity of electronic cigarettes may be observed. Used as a means of obtaining nicotine they allow to substitute traditional cigarettes. The origins of substance use disorders are conditioned by dopaminergic signaling which influences motivational processes being elementary factors conditioning the process of learning and exhibiting goal-directed behaviors. The study concentrated on analysis of three polymorphisms located in the dopamine receptor 2 (DRD2) gene—rs1076560, rs1799732 and rs1079597 using the PCR method, personality traits determined with the Big Five Questionnaire, and anxiety measured with the State Trait Anxiety Inventory. The study was conducted on a group of 394 volunteers, consisting e-cigarette users (n = 144) and controls (n = 250). Compared to the controls the case group subjects achieved significantly higher scores in regard to the STAI state and the trait scale, as well as the NEO-FFI Neuroticism and Openness scale. Likewise, in the case of the STAI state for DRD2 rs1076560 significant differences were found. Furthermore, while comparing the groups (e-cigarette users vs. controls) we noticed interactions for the NEO FFI Neuroticism and DRD2 rs1076560. The same was observed in the case of interactions significance while comparing groups (e-cigarette users vs. controls) for the STAI trait/scale and DRD2 rs1799732. Findings from this study demonstrate that psychological factors and genetic determinants should be analyzed simultaneously and comprehensively while considering groups of addicted patients. Since the use, and rapid increase in popularity, of electronic cigarettes has implications for public health, e-cigarette users should be studied holistically, especially younger groups of addicted and experimenting users.

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.

The Neuroscience of Drug Reward and Addiction

Drug consumption is driven by a drug's pharmacological effects, which are experienced as rewarding, and is influenced by genetic, developmental, and psychosocial factors that mediate drug accessibility, norms, and social support systems or lack thereof. The reinforcing effects of drugs mostly depend on dopamine signaling in the nucleus accumbens, and chronic drug exposure triggers glutamatergic-mediated neuroadaptations in dopamine striato-thalamo-cortical (predominantly in prefrontal cortical regions including orbitofrontal cortex and anterior cingulate cortex) and limbic pathways (amygdala and hippocampus) that, in vulnerable individuals, can result in addiction. In parallel, changes in the extended amygdala result in negative emotional states that perpetuate drug taking as an attempt to temporarily alleviate them. Counterintuitively, in the addicted person, the actual drug consumption is associated with an attenuated dopamine increase in brain reward regions, which might contribute to drug-taking behavior to compensate for the difference between the magnitude of the expected reward triggered by the conditioning to drug cues and the actual experience of it. Combined, these effects result in an enhanced motivation to "seek the drug" (energized by dopamine increases triggered by drug cues) and an impaired prefrontal top-down self-regulation that favors compulsive drug-taking against the backdrop of negative emotionality and an enhanced interoceptive awareness of "drug hunger." Treatment interventions intended to reverse these neuroadaptations show promise as therapeutic approaches for addiction.

Food Addiction: Implications for the Diagnosis and Treatment of Overeating

With the obesity epidemic being largely attributed to overeating, much research has been aimed at understanding the psychological causes of overeating and using this knowledge to develop targeted interventions. Here, we review this literature under a model of food addiction and present evidence according to the fifth edition of the Diagnostic and Statistical Manual (DSM-5) criteria for substance use disorders. We review several innovative treatments related to a food addiction model ranging from cognitive intervention tasks to neuromodulation techniques. We conclude that there is evidence to suggest that, for some individuals, food can induce addictive-type behaviours similar to those seen with other addictive substances. However, with several DSM-5 criteria having limited application to overeating, the term 'food addiction' is likely to apply only in a minority of cases. Nevertheless, research investigating the underlying psychological causes of overeating within the context of food addiction has led to some novel and potentially effective interventions. Understanding the similarities and differences between the addictive characteristics of food and illicit substances should prove fruitful in further developing these interventions.

The neurobiology of addiction

Substance and alcohol use disorders impose large health and economic burdens on individuals, families, communities, and society. Neither prevention nor treatment efforts are effective in all individuals. Results are often modest. Advances in neuroscience and addiction research have helped to describe the neurobiological changes that occur when a person transitions from recreational substance use to a substance use disorder or addiction. Understanding both the drivers and consequences of substance use in vulnerable populations, including those whose brains are still maturing, has revealed behavioral and biological characteristics that can increase risks of addiction. These findings are particularly timely, as law- and policymakers are tasked to reverse the ongoing opioid epidemic, as more states legalize marijuana, as new products including electronic cigarettes and newly designed abused substances enter the legal and illegal markets, and as "deaths of despair" from alcohol and drug misuse continue.

The Ankyrin Repeat and Kinase Domain Containing 1 Gene Polymorphism (ANKK1 Taq1A) and Personality Traits in Addicted Subjects

The Taq1A polymorphism located in the ANKK1 gene is one of the most widely studied polymorphisms in regards to the genetics of behavior and addiction. The aim of our study was to analyze this polymorphism with regard to personality characteristics and anxiety measured by means of the Personality Inventory—(NEO Five-Factor Inventory—NEO—FFI) and the State-Trait Anxiety Inventory (STAI) in polysubstance addicted subjects. The study group consisted of 600 male volunteers, including 299 addicted subjects and 301 controls. Psychiatrists recruited members for both groups. Addiction was diagnosed in the case group. In the control group mental illness was excluded. The same psychometric test and genotyping using the real-time PCR (polymerase chain reaction) method was performed for both groups. The results were investigated by means of multivariate analysis of the main effects Multi-factor ANOVA. Significantly higher scores on the scale of STAI state and Neuroticism and Openness traits, as well as lower scores on the scales of Extraversion, Agreeability, and Conscientiousness, were found in the case group subjects, compared to the controls. Differences in frequency of genotypes and alleles of Taq1A polymorphism between the studied groups were not found. Multi-factor ANOVA of addicted subjects and control subjects and the ANKK1 Taq1A variant interaction approximated the statistical significance for the STAI state. The main effects ANOVA of both subjects’ groups were found for the STAI state and trait, the Neuroticism scale, the Extraversion scale, and the Agreeability scale. The ANKK1 Taq1A main effects approximated the statistical significance of the STAI trait. Our study shows not only differences in personality traits between addicted and non-addicted subjects, but also the possible impact of ANKK1 on given traits and on addiction itself.

Stress changes amphetamine response, D2 receptor expression and epigenetic regulation in low-anxiety rats

The aim of this study was to assess the influence of chronic restraint stress on amphetamine (AMPH)-related appetitive 50-kHz ultrasonic vocalisations (USVs) in rats differing in freezing duration in a contextual fear test (CFT), i.e. HR (high-anxiety responsive) and LR (low-anxiety responsive) rats. The LR and the HR rats, previously exposed to an AMPH binge experience, differed in sensitivity to AMPH's rewarding effects, measured as appetitive vocalisations. Moreover, chronic restraint stress attenuated AMPH-related appetitive vocalisations in the LR rats but had no influence on the HR rats' behaviour. To specify, the restraint LR rats vocalised appetitively less in the AMPH-associated context and after an AMPH challenge than the control LR rats. This phenomenon was associated with a decrease in the mRNA level for D2 dopamine receptor in the amygdala and its protein expression in the basal amygdala (BA) and opposite changes in the nucleus accumbens (NAc) - an increase in the mRNA level for D2 dopamine receptor and its protein expression in the NAc shell, compared to control conditions. Moreover, we observed that chronic restraint stress influenced epigenetic regulation in the LR and the HR rats differently. The contrasting changes were observed in the dentate gyrus (DG) of the hippocampus - the LR rats presented a decrease, but the HR rats showed an increase in H3K9 trimethylation. The restraint LR rats also showed higher miR-494 and miR-34c levels in the NAc than the control LR group. Our study provides behavioural and biochemical data concerning the role of differences in fear-conditioned response in stress vulnerability and AMPH-associated appetitive behaviour. The LR rats were less sensitive to the rewarding effects of AMPH when previously exposed to chronic stress that was accompanied by changes in D2 dopamine receptor expression and epigenetic regulation in mesolimbic areas.

DRD2 promoter methylation and measures of alcohol reward: functional activation of reward circuits and clinical severity

Studies have identified strong associations between D2 receptor binding potential and neural responses to rewarding stimuli and substance use. Thus, D2 receptor perturbations are central to theoretical models of the pathophysiology of substance dependence, and epigenetic changes may represent one of the fundamental molecular mechanisms impacting the effects of alcohol exposure on the brain. We hypothesized that epigenetic alterations in the promoter region of the dopamine D2 receptor (DRD2) gene would be associated with cue-elicited activation of neural reward regions, as well as severity of alcohol use behavior. The current study leveraged functional neuroimaging (fMRI) during an alcohol reward paradigm (n = 383) to test associations among DRD2 promoter methylation in peripheral tissue, signal change in the striatum during the presentation of alcohol cues, and severity of alcohol use disorder (AUD). Controlling for age, DRD2 promoter methylation was positively associated with responses to alcohol cues in the right accumbens (partial r = 0.144, P = 0.005), left putamen (partial r = 0.133, P = 0.009), right putamen (partial r = 0.106, P = 0.039), left caudate (partial r = 0.117, P = 0.022), and right caudate (partial r = 0.133, P = 0.009), suggesting that DRD2 methylation was positively associated with robust activation in the striatum in response to reward cues. DRD2 methylation was also positively associated with clinical metrics of AUD severity. Specifically, controlling for age, DRD2 methylation was associated with Alcohol Use Disorders Identification Test total (partial r = 0.140, P = 0.002); Impaired Control Scale total (partial r = 0.097, P = 0.044) and Alcohol Dependence Scale total (partial r = 0.152, P = 0.001). Thus, DRD2 methylation may be a critical mechanism linking D2 receptors with functional striatal brain changes and clinical severity among alcohol users.

Overexpression of miR-9 in the Nucleus Accumbens Increases Oxycodone Self-Administration

BACKGROUND

There is an urgent need to identify factors that increase vulnerability to opioid addiction to help stem the opioid epidemic and develop more efficient pharmacotherapeutics. MicroRNAs are small non-coding RNAs that regulate gene expression at a posttranscriptional level and have been implicated in chronic drug-taking in humans and in rodent models. Recent evidence has shown that chronic opioid treatment regulates the microRNA miR-9. The present study was designed to test the hypothesis that miR-9 in the nucleus accumbens potentiates oxycodone addictive-like behavior.

METHODS

We utilized adeno-associated virus (AAV) to overexpress miR-9 in the nucleus accumbens of male rats and tested the effects on intravenous self-administration of the highly abused prescription opioid, oxycodone, in 1-hour short-access followed by 6-h long-access sessions, the latter of which leads to escalation of drug intake. In separate rats, we assessed the effects of nucleus accumbens miR-9 overexpression on mRNA targets including RE1-silencing transcription factor (REST) and dopamine D2 receptor (DRD2), which have been shown to be regulated by drugs of abuse.

RESULTS

Overexpression of miR-9 in the nucleus accumbens significantly increased oxycodone self-administration compared with rats expressing a control, scrambled microRNA. Analysis of the pattern of oxycodone intake revealed that miR-9 overexpression increased "burst" episodes of intake and decreased the inter-infusion interval. Furthermore, miR-9 overexpression decreased the expression of REST and increased DRD2 in the nucleus accumbens at time points that coincided with behavioral effects.

CONCLUSIONS

These results suggest that nucleus accumbens miR-9 regulates oxycodone addictive-like behavior as well as the expression of genes that are involved in drug addiction.

No effect of sex on ethanol intake and preference after dopamine transporter (DAT) knockdown in adult mice

RATIONALE

Dopamine levels are controlled in part by transport across the cell membrane by the dopamine transporter (DAT), and recent evidence showed that a polymorphism in the gene encoding DAT is associated with alcoholism. However, research in animal models using DAT knockout mice has yielded conflicting results.

OBJECTIVES

The present study was planned to evaluate the effects of DAT knockdown in the nucleus accumbens (Nacc) on voluntary ethanol consumption and preference in male and female C57BL/6J mice.

METHODS

For this purpose, animals were stereotaxically injected with DAT siRNA-expressing lentiviral vectors in the Nacc, and using a voluntary, continuous access two-bottle choice model of alcohol, we investigated the importance of accumbal DAT expression in voluntary alcohol intake and preference. We also investigated the effects of DAT knockdown on saccharin and quinine consumption and ethanol metabolism.

RESULTS

We show that females consumed more alcohol than males. Interestingly, DAT knockdown in the Nacc significantly decreased alcohol intake and preference in both groups, but no significant sex by group interaction was observed. Also, DAT knockdown did not alter total fluid consumption, saccharin or quinine consumption, or blood ethanol concentrations. Using Pearson correlation, results indicated a strong positive relationship between DAT mRNA expression and ethanol consumption and preference.

CONCLUSIONS

Taken together, these data provide further evidence that DAT plays an important role in controlling ethanol intake and that accumbal DAT contributes in the modulation of the reinforcing effects of ethanol. Overall, the results suggest that DAT inhibitors may be valuable in the pharmacotherapy of alcoholism.

Optogenetic investigation of neural mechanisms for alcohol-use disorder

Optogenetic techniques have been widely used in the study of neuropsychiatric diseases such as anxiety, depression, and drug addiction. Cell-type specific targeting of optogenetic tools to neurons has contributed to a tremendous understanding of the function of neural circuits for future treatment of neuropsychiatric disorders. Though optogenetics has been widely used in many research areas, the use of optogenetic tools to uncover and elucidate neural circuit mechanisms of alcohol's actions in the brain are still developing. Here in this review article, we will provide a basic introduction to optogenetics and discuss how these optogenetic experimental approaches can be used in alcohol studies to reveal neural circuit mechanisms of alcohol's actions in regions implicated in the development of alcohol addiction.

Disentangling the diverse roles of dopamine D2 receptors in striatal function and behavior

Dopamine D2 receptors (D2Rs) mediate many of the actions of dopamine in the striatum, ranging from movement to the effortful pursuit of reward. Yet despite significant advances in linking D2Rs to striatal functions with pharmacological and genetic strategies in animals, how dopamine orchestrates its myriad actions on different cell populations -each expressing D2Rs- remains unclear. Furthermore, brain imaging and genetic studies in humans have consistently associated striatal D2R alterations with various neurological and neuropsychiatric disorders, but how and which D2Rs are involved in each case is poorly understood. Therefore, a critical first step is to engage in a refined and systematic investigation of the impact of D2R function on specific striatal cells, circuits, and behaviors. Here, I will review recent efforts, primarily in animal models, aimed at unlocking the complex and heterogeneous roles of D2Rs in striatum.

Unmasking neurobiological commonalities between addictive disorders and impulse control disorders in Parkinson’s disease

Changes in reward circuitry have been studied extensively in substance and behavioural addictions. However, comparatively little is known about the neurobiology underlying impulse control disorders (ICDs) in Parkinson's disease, which show roughly similar risk factors and behavioural presentations to both stimulant and behavioural addictions. ICDs occur in a subset of susceptible patients with Parkinson's disease (PD) following intake of dopamine replacement therapy (DRT). These behavioural disorders often have debilitating effects on a patient's quality of life and increase caregiver burden. This comprehensive review examined findings of 40 neuroimaging studies of ICDs in PD to determine (a) whether there are putative neurobiological commonalities between traditional substance and behavioural addictions and DRT-induced ICD in PD and (b) opportunities for future studies to advance current neurobiological understanding of the phenomenon. Results revealed that strikingly similar (a) deficits in dopaminergic receptor expression, (b) connectivity changes in corticostriatal circuitry and (c) neural responses to cue exposure are observed in both ICDs in PD and addictive disorders. These findings point to the value of adopting a transdiagnostic approach when studying addicted populations and pave the way for demystifying this peculiar, often-devastating phenomenon in PD that has so far proven extremely difficult to treat and predict with any precision.

Addiction and Dopamine: Sex Differences and Insights from Studies of Smoking

Mesolimbic dopaminergic function influences addiction through effects on reinforcement learning, decision-making, and impulsivity. This review covers sex differences in dopaminergic neurochemistry, their hormonal and genetic determinants, and how differences in dopaminergic tone interact with sex and/or ovarian hormone status to affect cognitive functions. Findings from research on cigarette smoking reveal sex differences in striatal and midbrain dopamine D2-type receptor availability and striatal dopamine release that suggest mechanisms of nicotine dependence, and stronger subjective responses to nicotine and efficacy of nicotine replacement therapies in male smokers than in their female counterparts. Opportunities exist to extend such efforts in studies of how sex and hormone status influence other addictions.

Early life adversity and health-risk behaviors: proposed psychological and neural mechanisms

Early life adversity (ELA) is associated with poorer health in adulthood, an association explained, at least in part, by increased engagement in health-risk behaviors (HRBs). In this review, we make the case that ELA influences brain development in ways that increase the likelihood of engaging in HRBs. We argue that ELA alters neural circuitry underpinning cognitive control as well as emotional processing, including networks involved in processing threat and reward. These neural changes are associated psychologically and behaviorally with heightened emotional reactivity, blunted reward responsivity, poorer emotion regulation, and greater delay discounting. We then demonstrate that these adaptations to ELA are associated with an increased risk of smoking cigarettes, drinking alcohol, and eating high-fat, high-sugar foods. Furthermore, we explore how HRBs affect the brain in ways that reinforce addiction and further explain clustering of HRBs.

Co-Administration of Low-Dose Naltrexone and Bupropion Reduces Alcohol Drinking in Alcohol-Preferring (P) Rats

BACKGROUND

This study examined whether combining naltrexone (NTX) with bupropion (BUP) is more effective in reducing alcohol drinking in alcohol-preferring (P) rats with a genetic predisposition toward high voluntary alcohol intake than either drug alone.

METHODS

Alcohol-experienced, adult, male, P rats were fed NTX alone in a dose of 10.0 mg/kg BW, BUP alone in a dose of 10.0 mg/kg BW, BUP alone in a dose of 20.0 mg/kg BW, NTX (10.0 mg/kg BW) + BUP (10.0 mg/kg BW), or vehicle (VEH) at 1 hour prior to onset of a daily 2-hour alcohol access period for 5 consecutive days.

RESULTS

When administered alone, neither NTX (10.0 mg/kg BW) nor BUP, in either of 2 doses (10.0 mg/kg BW or 20.0 mg/kg BW), reduced voluntary alcohol intake in P rats. However, NTX combined with BUP (10.0 mg/kg NTX + 10.0 mg/kg BUP) and given as a single medication significantly reduced alcohol consumption throughout prolonged treatment.

CONCLUSIONS

Combining low doses of NTX and BUP, each of which is ineffective when given alone, increases the efficacy of the medication. Low drug doses circumvent the problem of negative side effects that can occur with higher doses of either drug. A reduction in side effects can facilitate patient compliance and improve clinical outcomes for alcoholics and heavy drinkers who want to reduce their alcohol intake. The results, together with those from our prior studies, demonstrate the strength of a combinatorial pharmacotherapeutic approach to the treatment of alcohol use disorder.

Midbrain circuit regulation of individual alcohol drinking behaviors in mice

Alcohol-use disorder (AUD) is the most prevalent substance-use disorder worldwide. There is substantial individual variability in alcohol drinking behaviors in the population, the neural circuit mechanisms of which remain elusive. Utilizing in vivo electrophysiological techniques, we find that low alcohol drinking (LAD) mice have dramatically higher ventral tegmental area (VTA) dopamine neuron firing and burst activity. Unexpectedly, VTA dopamine neuron activity in high alcohol drinking (HAD) mice does not differ from alcohol naive mice. Optogenetically enhancing VTA dopamine neuron burst activity in HAD mice decreases alcohol drinking behaviors. Circuit-specific recordings reveal that spontaneous activity of nucleus accumbens-projecting VTA (VTA-NAc) neurons is selectively higher in LAD mice. Specifically activating this projection is sufficient to reduce alcohol consumption in HAD mice. Furthermore, we uncover ionic and cellular mechanisms that suggest unique neuroadaptations between the alcohol drinking groups. Together, these data identify a neural circuit responsible for individual alcohol drinking behaviors.

Mice exposed to a two-bottle alcohol choice paradigm can be divided into high and low drinking groups. Here, the authors show that stimulating VTA neurons to induce higher phasic activity patterns that are observed in low alcohol drinking mice, suppresses alcohol drinking in mice that are high alcohol drinking.

Positron emission tomography in Parkinson's disease: insights into impulsivity

This study reviews previous studies that employ positron emission tomography (PET) imaging assessments in Parkinson's disease (PD) patients with and without Impulsive Compulsive Behaviours (ICB). This begins with a summary of the potential benefits and limitations of commonly utilized ligands, specifically D_2/3 receptor and dopamine transporter ligands. Since previous findings emphasize the role of the ventral striatum in the manifestation of ICBs, this study attempts to relate these imaging findings to changes in behaviour, especially emphasizing work performed in substance abuse and addiction. Next, it reviews how increasing disease duration in PD can influence dopamine receptor expression, with an emphasis on differential striatal and extra-striatal changes that occur along the course of PD. Finally, it focuses on how extra-striatal changes, particularly in the orbitofrontal cortex, amygdala, and anterior cingulate, may influence the proficiency of behavioural regulation in PD. The discussion emphasizes the interaction of disease and medication effects on network-wide changes that occur in PD, and how these changes may result in behavioural dysregulation.

The gut in the brain: the effects of bariatric surgery on alcohol consumption

Obesity represents a major medical and public health problem worldwide. Efforts have been made to develop novel treatments, and among them bariatric surgery is used as an effective treatment to achieve significant, long-term weight loss and alleviate medical problems related to obesity. Alcohol use disorder (AUD) is also a leading cause of morbidity and mortality worldwide. Recent clinical studies have revealed a concern for bariatric surgery patients developing an increased risk for alcohol consumption, and for AUD. A better understanding of the relationship between bariatric surgery and potential later development of AUD is important, given the critical need of identifying patients at high risk for AUD. This paper reviews current clinical and basic science research and discusses potential underlying mechanisms. Special emphasis in this review is given to recent work suggesting that, alterations in alcohol metabolism/pharmacokinetics resulting from bariatric surgery are unlikely to be the primary or at least the only explanation for increased alcohol use and development of AUD, as changes in brain reward processing are also likely to play an important role. Additional studies are needed to clarify the potential role and mechanisms of how bariatric surgery may increase alcohol use and lead to AUD development.

The genetic epidemiology of substance use disorder: A review

BACKGROUND

Substance use disorder (SUD) remains a significant public health issue. A greater understanding of how genes and environment interact to regulate phenotypes comprising SUD will facilitate directed treatments and prevention.

METHODS

The literature studying the neurobiological correlates of SUD with a focus on the genetic and environmental influences underlying these mechanisms was reviewed. Results from twin/family, human genetic association, gene-environment interaction, epigenetic literature, phenome-wide association studies are summarized for alcohol, nicotine, cannabinoids, cocaine, and opioids.

RESULTS

There are substantial genetic influences on SUD that are expected to influence multiple neurotransmission pathways, and these influences are particularly important within the dopaminergic system. Genetic influences involved in other aspects of SUD etiology including drug processing and metabolism are also identified. Studies of gene-environment interaction emphasize the importance of environmental context in SUD. Epigenetic studies indicate drug-specific changes in gene expression as well as differences in gene expression related to the use of multiple substances. Further, gene expression is expected to differ by stage of SUD such as substance initiation versus chronic substance use. While a substantial literature has developed for alcohol and nicotine use disorders, there is comparatively less information for other commonly abused substances.

CONCLUSIONS

A better understanding of genetically-mediated mechanisms involved in the neurobiology of SUD provides increased opportunity to develop behavioral and biologically based treatment and prevention of SUD.

Evaluation of the Abuse Potential of Novel Amphetamine Derivatives with Modifications on the Amine (NBNA) and Phenyl (EDA, PMEA, 2-APN) Sites

Recently, there has been a rise in the number of amphetamine derivatives that serve as substitutes for controlled substances (e.g. amphetamine and methamphetamine) on the global illegal drug market. These substances are capable of producing rewarding effects similar to their parent drug. In anticipation of the future rise of new and similar psychoactive substances, we designed and synthesized four novel amphetamine derivatives with N-benzyl, N-benzylamphetamine HCl (NBNA) substituent on the amine region, 1,4-dioxane ring, ethylenedioxy-amphetamine HCl (EDA), methyl, para-methylamphetamine HCl (PMEA), and naphthalene, 2-(aminopropyl) naphthalene HCl (2-APN) substituents on the phenyl site. Then, we evaluated their abuse potential in the conditioned place preference (CPP) test in mice and self-administration (SA) test in rats. We also investigated the psychostimulant properties of the novel drugs using the locomotor sensitization test in mice. Moreover, we performed qRT-PCR analyses to explore the effects of the novel drugs on the expression of D1 and D2 dopamine receptor genes in the striatum. NBNA, but not EDA, PMEA, and 2-APN, induced CPP and SA in rodents. None of the test drugs have produced locomotor sensitization. qRT-PCR analyses demonstrated that NBNA increased the expression of striatal D1 dopamine receptor genes. These data indicate that NBNA yields rewarding effects, suggesting potential for abuse. Continual observation for the rise of related substances is thus strongly encouraged.