Tolerance to alcohol: A critical yet understudied factor in alcohol addiction

Behavioral changes and transcriptional regulation of mesolimbic dopaminergic genes in a mouse model of binge eating disorder by diet intermittent access

Binge Eating Disorder (BED) is among the most prevalent eating disorders worldwide. It is characterized by recurrent episodes of excessive consumption of palatable foods in short periods, accompanied by a sense of loss of control and distress around the episode, which tends to worsen over time. The mesolimbic dopaminergic system influences on reinforcement and reward-seeking behaviors is implicated in the disorder's pathogenesis. Animal models that replicate the clinical conditions observed in humans, including the disorder progression, are essential for understanding the underlying physiological mechanisms of BED. This study aimed to evaluate binge eating behavior induced by intermittent High Sugar and Butter (HSB) diet access in mice, their phenotypes, transcriptional regulation of mesolimbic dopaminergic system genes, and behavior. Thus, mice were subdivided into three groups: CHOW (maintenance diet only), HSB-i (maintenance diet with thrice-weekly access to HSB), and HSB (continuous access to HSB). Animals were subjected to marble-burying and light-dark box behavioral tests, and transcriptional regulation was evaluated by RT-qPCR. The results indicated that the HSB-i group established a feeding pattern of significantly more kilocalories on days when HSB was available and reduced intake on non-HSB days similar to human binge eating. Over time, binge episodes intensified, potentially indicating a tolerance effect. Additionally, these animals behave differently towards preferring the HSB diet and exhibited altered transcriptional regulation of the Drd1, Slc6a3, and Lrrk2 genes. Our study provides a mouse model that reflects human BED, showing a progression in binge episodes and mesolimbic dopamine pathway involvement, suggesting targets for future therapeutic interventions.

Exploratory analysis of blood alcohol concentration-related technology use and drinking outcomes among young adults

BACKGROUND

Mobile health (mHealth) technology use may reduce alcohol use and related negative consequences; however, little is known about its efficacy without prompting from researchers or pay-per-use. This exploratory analysis assessed relationships between mHealth technology use frequency and alcohol-use outcomes.

METHODS

Young adults who drink heavily (N = 97, Mage = 23, 51% male, 64% non-Hispanic White, Mdrinks/week = 21) had the option to use three mHealth technologies (breathalyzer device/app, blood alcohol content estimator app, drink counting via text message) while drinking for 2 weeks. Relationships between alcohol-related outcomes and any, multiple, and specific mHealth technology use across study days and drinking days were evaluated via bivariate correlations and multiple regressions.

RESULTS

Participants used one or more mHealth technologies on approximately 68% of drinking days (33% of field days), with multiple technologies used on 34% of drinking days. Bivariate correlations revealed that a higher percentage of study days with any mHealth technology use was related to higher mean weekly drinks. However, a higher percentage of drinking days with any mHealth technology use was related to lower mean weekly drinks, percent of heavy and high-intensity drinking days, and negative consequences. There were several significant, inverse correlations between alcohol variables and using the mHealth technologies that provided personalized feedback. Multiple regression analyses (holding sex and baseline alcohol variables constant) indicated that a higher percentage of drinking days with any mHealth technology use was related to lower mean weekly drinks and lower percentage of heavy drinking days.

CONCLUSIONS

Using mHealth technologies to moderate drinking without direct prompting from the research team or per-use incentives was related to less overall alcohol use and heavy drinking. This indicates potential real-world engagement with mHealth apps to assist with in-the-moment drinking. Normalizing mHealth technology use during drinking could help curb the public health crisis around harmful alcohol use in young adult populations.

The role of nitric oxide and hormone signaling in chronic stress, anxiety, depression and post-traumatic stress disorder

This paper provides a summary of the role of nitric oxide (NO) and hormones in the development of chronic stress, anxiety, depression, and post-traumatic stress disorder (PTSD). These mental health conditions are prevalent globally and involve complex molecular interactions. Although there is a significant amount of research and therapeutic options available, the underlying mechanisms of these disorders are still not fully understood. The primary pathophysiologic processes involved in chronic stress, anxiety, depression, and PTSD include dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, the intracellular influence of neuronal nitric oxide synthase (nNOS) on transcription factors, an inflammatory response with the formation of nitrergic oxidative species, and reduced serotonergic transmission in the dorsal raphe nucleus. Despite the extensive literature on this topic, there is a great need for further research to clarify the complexities inherent in these pathways, with the primary aim of improving psychiatric care.

Does tolerance to ethanol-induced ataxia explain the sensitized response to ethanol?

Under conditions of repeated exposure to ethanol, a sensitized locomotor stimulant response develops in some strains of mice. It has been hypothesized that the sensitized response is a consequence of tolerance development to the sedative/incoordinating effects of ethanol. Conversely, ethanol-induced sensitization and tolerance may be independent effects of repeated ethanol exposure. A published study in C57BL/6J by DBA/2J recombinant inbred strains concluded that the two phenomena are not genetically related and thus perhaps mechanistically distinct. To extend evaluation beyond the genetic variance found in C57BL/6J and DBA/2J mice and examine phenotypic associations, we simultaneously measured ethanol-induced sensitization and tolerance in a genetically diverse panel of 15 standard inbred mouse strains and a genetically heterogeneous stock that was produced by the intercrossing of eight inbred mouse strains. Changes in activity counts and ataxia ratio across repeated ethanol treatments indexed sensitization and tolerance, respectively. Photocell beam breaks provided the measure of activity, and foot slip errors corrected for activity in a grid test provided a measure of coordination. The results were strain and individual dependent. The genetic correlation between magnitude of sensitization and tolerance was not significant in the panel of inbred strains, but when individual data were correlated, without regard to strain, there was a significant correlation. This relationship was also significant in the genetically heterogeneous population of mice. However, magnitude of tolerance explained only 10% of the variance in sensitization among individuals of the inbred strain population, whereas it explained 44% of the variance among individuals of the eight-strain cross. When repeated exposures to ethanol were disassociated from the test apparatus, this relationship in the eight-strain cross disappeared. Furthermore, days to peak sensitization and tolerance across days did not perfectly mirror each other. Overall, our data do not support shared genetic mechanisms in sensitization and tolerance development but suggest a partial relationship among individuals that could be related to drug-environment associations.

Sex-dependent, lateralized engagement of anterior insular cortex inputs to the dorsolateral striatum in binge alcohol drinking

How does alcohol consumption alter synaptic transmission across time, and do these alcohol-induced neuroadaptations occur similarly in both male and female mice? Previously we identified that anterior insular cortex (AIC) projections to the dorsolateral striatum (DLS) are uniquely sensitive to alcohol-induced neuroadaptations in male, but not female mice, and play a role in governing binge alcohol consumption in male mice (Haggerty et al., 2022). Here, by using high-resolution behavior data paired with in-vivo fiber photometry, we show how similar levels of alcohol intake are achieved via different behavioral strategies across sexes, and how inter-drinking session thirst states predict future alcohol intakes in females, but not males. Furthermore, we show how presynaptic calcium activity recorded from AIC synaptic inputs in the DLS across 3 weeks of water consumption followed by 3 weeks of binge alcohol consumption changes across, fluid, time, sex, and brain circuit lateralization. By time-locking presynaptic calcium activity from AIC inputs to the DLS to peri-initiation of drinking events we also show that AIC inputs into the left DLS robustly encode binge alcohol intake behaviors relative to water consumption. These findings suggest a fluid-, sex-, and lateralization-dependent role for the engagement of AIC inputs into the DLS that encode binge alcohol consumption behaviors and further contextualize alcohol-induced neuroadaptations at AIC inputs to the DLS.

Alcohol sipping patterns, personality, and psychopathology in Children: Moderating effects of dorsal anterior cingulate cortex (dACC) activation

BACKGROUND

Alcohol, the most consumed drug in the United States, is associated with various psychological disorders and abnormal personality traits. Despite extensive research on adolescent alcohol consumption, the impact of early alcohol sipping patterns on changes in personality and mental health over time remains unclear. There is also limited information on the latent trajectory of early alcohol sipping, beginning as young as 9-10 years old. The dorsal anterior cingulate cortex (dACC) is crucial for cognitive control and response inhibition. However, the role of the dACC remains unclear in the relationship between early alcohol sipping and mental health outcomes and personality traits over time.

METHODS

Utilizing the large data from the Adolescent Brain Cognitive Development study (N = 11,686, 52% males, 52% white, mean [SD] age 119 [7.5] months, 9807 unique families, 22 sites), we aim to comprehensively examine the longitudinal impact of early alcohol sipping patterns on psychopathological measures and personality traits in adolescents, filling crucial gaps in the literature.

RESULTS

We identified three latent alcohol sipping groups, each demonstrating distinct personality traits and depression score trajectories. Bilateral dACC activation during the stop-signal task moderated the effect of early alcohol sipping on personality and depression over time. Additionally, bidirectional effects were observed between alcohol sipping and personality traits.

CONCLUSIONS

This study provides insights into the impact of early alcohol consumption on adolescent development. The key finding of our analysis is that poor response inhibition at baseline, along with increased alcohol sipping behaviors may accelerate the changes in personality traits and depression scores over time as individuals transition from childhood into adolescence.

Retrospective self-reports of sensitivity to the effects of alcohol: Trait-like stability and concomitant changes with alcohol involvement

OBJECTIVE

Lower sensitivity to the acute effects of alcohol is known to confer risk for the development of alcohol use disorder. Alcohol sensitivity, or level of response to alcohol's subjective effects, is heritable but also can change as a result of persistent alcohol exposure (i.e., acquired tolerance). Here, we examined how changes over time in four indices of alcohol involvement affected scores on two validated, retrospective self-report measures of alcohol response-the Self-Rating of the Effects of Alcohol (SRE) form and the Alcohol Sensitivity Questionnaire (ASQ)-in a sample of emerging adult drinkers.

METHOD

Participants (N = 173; Mage = 19.5 years; 60% assigned female at birth) completed the ASQ, SRE, and measures of alcohol use and problems at two time points separated by a median of 0.77 years (range: 0.30-2.54 years).

RESULTS

Multiple linear regression showed that increases in drinking over this period accounted for increases in SRE and ASQ scores (i.e., in reported numbers of drinks needed to experience subjective effects of alcohol). Increased drinking accounted for more variance in the number of drinks needed to experience lighter drinking versus heavier drinking effects, and increases in the number of drinks consumed per occasion had a larger effect than did changes in total numbers of drinks consumed, number of binge-drinking occasions, or drinking-related problems.

CONCLUSIONS

Findings suggest that both SRE and ASQ capture some stable, trait-like variability in alcohol response as well as some state-dependent, within-person variability in alcohol response acquired through increases in alcohol involvement. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Sex-dependent, lateralized engagement of anterior insular cortex inputs to the dorsolateral striatum in binge alcohol drinking

How does alcohol consumption alter synaptic transmission across time, and do these alcohol-induced neuroadaptations occur similarly in both male and female mice? Previous work shows that anterior insular cortex (AIC) projections to the dorsolateral striatum (DLS) are uniquely sensitive to alcohol-induced neuroadaptations in male, but not female mice, and play a role in governing binge alcohol consumption in male mice. Here, by using high-resolution behavior data paired with in-vivo fiber photometry, we show how similar levels of alcohol intake are achieved via different behavioral strategies across sex, and how inter-drinking session thirst states predict future alcohol intakes in females, but not males. Further, we show how presynaptic calcium activity recorded from AIC synaptic inputs in the DLS across 3 weeks of water consumption followed by 3 weeks of binge alcohol consumption change across, fluid, time, sex, and brain circuit lateralization. By time-locking presynaptic calcium activity from AIC inputs to the DLS to peri-initiation of drinking events we also show that AIC inputs into the left DLS robustly encode binge alcohol intake behaviors relative to water consumption and AIC inputs into the right DLS in males, but not females. These findings suggest a fluid-, sex- and lateralization-dependent role for the engagement of AIC inputs into the DLS that encode binge alcohol consumption behaviors and further contextualize alcohol-induced neuroadaptations at AIC inputs to the DLS.

Synaptic Mechanisms of Ethanol Tolerance and Neuroplasticity: Insights from Invertebrate Models

Alcohol tolerance is a neuroadaptive response that leads to a reduction in the effects of alcohol caused by previous exposure. Tolerance plays a critical role in the development of alcohol use disorder (AUD) because it leads to the escalation of drinking and dependence. Understanding the molecular mechanisms underlying alcohol tolerance is therefore important for the development of effective therapeutics and for understanding addiction in general. This review explores the molecular basis of alcohol tolerance in invertebrate models, Drosophila and C. elegans, focusing on synaptic transmission. Both organisms exhibit biphasic responses to ethanol and develop tolerance similar to that of mammals. Furthermore, the availability of several genetic tools makes them a great candidate to study the molecular basis of ethanol response. Studies in invertebrate models show that tolerance involves conserved changes in the neurotransmitter systems, ion channels, and synaptic proteins. These neuroadaptive changes lead to a change in neuronal excitability, most likely to compensate for the enhanced inhibition by ethanol.

Understanding How Acute Alcohol Impacts Neural Encoding in the Rodent Brain

Alcohol impacts neural circuitry throughout the brain and has wide-ranging effects on the biophysical properties of neurons in these circuits. Articulating how these wide-ranging effects might eventually result in altered computational properties has the potential to provide a tractable working model of how alcohol alters neural encoding. This chapter reviews what is currently known about how acute alcohol influences neural activity in cortical, hippocampal, and dopaminergic circuits as these have been the primary focus of understanding how alcohol alters neural computation. While other neural systems have been the focus of exhaustive work on this topic, these brain regions are the ones where in vivo neural recordings are available, thus optimally suited to make the link between changes in neural activity and behavior. Rodent models have been key in developing an understanding of how alcohol impacts the function of these circuits, and this chapter therefore focuses on work from mice and rats. While progress has been made, it is critical to understand the challenges and caveats associated with experimental procedures, especially when performed in vivo, which are designed to answer this question and if/how to translate these data to humans. The hypothesis is discussed that alcohol impairs the ability of neural circuits to acquire states of neural activity that are transiently elevated and characterized by increased complexity. It is hypothesized that these changes are distinct from the traditional view of alcohol being a depressant of neural activity in the forebrain.

Animal Models of Excessive Alcohol Consumption in Rodents

The development of animal models that demonstrate excessive levels of alcohol consumption has played an important role in advancing our knowledge about neurobiological underpinnings and environmental circumstances that engender such maladaptive behavior. The use of these preclinical models has also provided valuable opportunities for discovering new and novel therapeutic targets that may be useful in the treatment of alcohol use disorder (AUD). While no single model can fully capture the complexities of AUD, the goal is to develop animal models that closely approximate characteristics of heavy alcohol drinking in humans to enhance their translational value and utility. A variety of experimental approaches have been employed to produce the desired phenotype of interest-robust and reliable excessive levels of alcohol drinking. Here we provide an updated review of five animal models that are commonly used. The models entail procedural manipulations of scheduled access to alcohol (time of day, duration, frequency), periods of time when access to alcohol is withheld, and history of alcohol exposure. Specially, the models involve (a) scheduled access to alcohol, (b) scheduled periods of alcohol deprivation, (c) scheduled intermittent access to alcohol, (d) scheduled-induced polydipsia, and (e) chronic alcohol (dependence) and withdrawal experience. Each of the animal models possesses unique experimental features that engender excessive levels of alcohol consumption. Both advantages and disadvantages of each model are described along with discussion of future work to be considered in developing more optimal models. Ultimately, the validity and utility of these models will lie in their ability to aid in the discovery of new and novel potential therapeutic targets as well as serve as a platform to evaluate treatment strategies that effectively reduce excessive levels of alcohol consumption associated with AUD.

Large analysis of genetic manipulations reveals an inverse correlation between initial alcohol resistance and rapid tolerance phenotypes

Tolerance occurs when, following an initial experience with a substance, more of the substance is required subsequently to induce identical behavioral effects. Tolerance is not well-understood, and numerous researchers have turned to model organisms, particularly Drosophila melanogaster, to unravel its mechanisms. Flies have high translational relevance for human alcohol responses, and there is substantial overlap in disease-causing genes between flies and humans, including those associated with Alcohol Use Disorder. Numerous Drosophila tolerance mutants have been described; however, approaches used to identify and characterize these mutants have varied across time and labs and have mostly disregarded any impact of initial resistance/sensitivity to ethanol on subsequent tolerance development. Here, we analyzed our own, as well as data published by other labs to uncover an inverse correlation between initial ethanol resistance and tolerance phenotypes. This inverse correlation suggests that initial resistance phenotypes can explain many 'perceived' tolerance phenotypes, thus classifying such mutants as 'secondary' tolerance mutants. Additionally, we show that tolerance should be measured as a relative increase in time to sedation between an initial and second exposure rather than an absolute change in time to sedation. Finally, based on our analysis, we provide a method for using a linear regression equation to assess the residuals of potential tolerance mutants. These residuals provide predictive insight into the likelihood of a mutant being a 'primary' tolerance mutant, where a tolerance phenotype is not solely a consequence of initial resistance, and we offer a framework for understanding the relationship between initial resistance and tolerance.

A multicomponent ethanol response battery across a cumulative dose ethanol challenge reveals diminished adolescent rat ethanol responsivity relative to adults

Adolescence is a conserved developmental period associated with low alcohol responsivity, which can contribute to heavy drinking and development of an alcohol use disorder (AUD) later in life. To investigate ethanol responsivity between adolescent and adult rats, we developed an ethanol response battery (ERB) to assess acute ethanol responses across cumulative doses of ethanol during the rising phase of the blood ethanol curve. We tested the hypothesis that adolescent male and female rats would exhibit lower ethanol responsivity to a cumulative ethanol challenge relative to adults. Male and female adolescent (postnatal day [P]40) and adult (P85) Wistar rats underwent ERB assessment following consecutive doses of ethanol (i.e., 1.0, 1.0, and 1.0 g/kg) to produce cumulative ethanol doses of 0.0, 1.0, 2.0, and 3.0 g/kg. The ERB consisted of (1) the 6-point behavioral intoxication rating scale, (2) body temperature assessment, (3) tail blood collection, (4) accelerating rotarod assessment, (5) tilting plane assessment, and (6) loss of righting reflex (LORR) assessment. Across cumulative ethanol doses, adolescent and adult rats evidenced progressive changes in ERB measures. On the ERB, adolescent rats of both sexes evidenced (1) lower intoxication rating, (2) blunted hypothermic responses, particularly in females, (3) longer latencies to fall from the accelerating rotarod, and (4) less tilting plane impairment relative to adults despite comparable BECs. All adult rats, regardless of sex, displayed a LORR at the 3.0 g/kg cumulative ethanol dose while among the adolescent rats, only one male rat and no females showed the LORR. These data reveal decreased adolescent ethanol responsivity across body temperature, intoxication, balance, and coordination responses to a cumulative ethanol challenge as assessed using the novel ERB relative to adults. The results of this study suggest that adolescent-specific low ethanol responsivity may contribute to adolescent binge drinking and increased risk for development of an AUD.

Post-translational modifications of histone and non-histone proteins in epigenetic regulation and translational applications in alcohol-associated liver disease: Challenges and research opportunities

Epigenetic regulation is a process that takes place through adaptive cellular pathways influenced by environmental factors and metabolic changes to modulate gene activity with heritable phenotypic variations without altering the DNA sequences of many target genes. Epigenetic regulation can be facilitated by diverse mechanisms: many different types of post-translational modifications (PTMs) of histone and non-histone nuclear proteins, DNA methylation, altered levels of noncoding RNAs, incorporation of histone variants, nucleosomal positioning, chromatin remodeling, etc. These factors modulate chromatin structure and stability with or without the involvement of metabolic products, depending on the cellular context of target cells or environmental stimuli, such as intake of alcohol (ethanol) or Western-style high-fat diets. Alterations of epigenetics have been actively studied, since they are frequently associated with multiple disease states. Consequently, explorations of epigenetic regulation have recently shed light on the pathogenesis and progression of alcohol-associated disorders. In this review, we highlight the roles of various types of PTMs, including less-characterized modifications of nuclear histone and non-histone proteins, in the epigenetic regulation of alcohol-associated liver disease (ALD) and other disorders. We also describe challenges in characterizing specific PTMs and suggest future opportunities for basic and translational research to prevent or treat ALD and many other disease states.

New insights into the molecular basis of alcohol abstinence and relapse in alcohol-associated liver disease

Alcohol use disorder remains a significant public health concern, affecting around 5% of adults worldwide. Novel pathways of damage have been described during the last years, providing insight into the mechanism of injury due to alcohol misuse beyond the direct effect of ethanol byproducts on the liver parenchyma and neurobehavioral mechanisms. Thus, the gut-liver-brain axis and immune system involvement could be therapeutic targets for alcohol use disorder. In particular, changes in gut microbiota composition and function, and bile acid homeostasis, have been shown with alcohol consumption and cessation. Alcohol can also directly disrupt intestinal and blood-brain barriers. Activation of the immune system can be triggered by intestinal barrier dysfunction and translocation of bacteria, pathogen-associated molecular patterns (such as lipopolysaccharide), cytokines, and damage-associated molecular patterns. These factors, in turn, promote liver and brain inflammation and the progression of liver fibrosis. Other involved mechanisms include oxidative stress, apoptosis, autophagy, and the release of extracellular vesicles and miRNA from hepatocytes. Potential therapeutic targets include gut microbiota (probiotics and fecal microbiota transplantation), neuroinflammatory pathways, as well as neuroendocrine pathways, for example, the ghrelin system (ghrelin receptor blockade), incretin mimetics (glucagon-like peptide-1 analogs), and the mineralocorticoid receptor system (spironolactone). In addition, support with psychological and behavioral treatments is essential to address the multiple dimensions of alcohol use disorder. In the future, a personalized approach considering these novel targets can contribute to significantly decreasing the alcohol-associated burden of disease.

Large genetic analysis of alcohol resistance and tolerance reveals an inverse correlation and suggests 'true' tolerance mutants

Tolerance occurs when, following an initial experience with a substance, more of the substance is required subsequently to induce the same behavioral effects. Tolerance is historically not well-understood, and numerous researchers have turned to model organisms, particularly Drosophila melanogaster, to unravel its mechanisms. Flies have high translational relevance for human alcohol responses, and there is substantial overlap in disease-causing genes between flies and humans, including those associated with Alcohol Use Disorder. Numerous Drosophila tolerance mutants have been described; however, approaches used to identify and characterize these mutants have varied across time and between labs and have mostly disregarded any impact of initial resistance/sensitivity to ethanol on subsequent tolerance development. Here, we have analyzed a large amount of data - our own published and unpublished data and data published by other labs - to uncover an inverse correlation between initial ethanol resistance and tolerance phenotypes. This inverse correlation suggests that initial resistance phenotypes can explain many 'perceived' tolerance phenotypes. Additionally, we show that tolerance should be measured as a relative increase in time to sedation between an initial and second exposure rather than an absolute change in time to sedation. Finally, based on our analysis, we provide a method for using a linear regression equation to assess the residuals of potential tolerance mutants. We show that these residuals provide predictive insight into the likelihood of a mutant being a 'true' tolerance mutant, and we offer a framework for understanding the relationship between initial resistance and tolerance.

Individual differences in response to alcohol and nicotine in zebrafish: Gene expression and behavior

Alcohol and nicotine are psychoactive substances responsible for serious health consequences. Although the biological mechanisms of alcohol and nicotine have been studied extensively, individual differences in the response to these drugs have received little attention. Here we evaluated gene expression and behavior of bold and shy individuals after acute exposure to alcohol and nicotine. For this, zebrafish were classified as bold and shy individuals based on emergence tests, and then fish were exposed to 0.00, 0.10, and 0.50% alcohol or 0.00, 1.00, and 5.00 mg/L nicotine and their anxiety-like and locomotor behavior was observed. After behavioral assessment, brain mRNA expression (ache, bdnf, gaba1, gad1b, th1, and tph1) was evaluated. Locomotion patterns differed between profiles depending on alcohol and nicotine concentration. Anxiety increased in shy fish and decreased in bold fish after exposure to both drugs. Alcohol exposure induced an increase in tph1 mRNA expression in bold fish, while bdnf mRNA expression was increased in shy fish. Nicotine increased ache, bdnf, and tph1 mRNA levels in both profiles, but at higher levels in bold fish. Based on our research, we found that alcohol induces anxiogenic effects in both bold and shy zebrafish. Additionally, shy individuals exposed to a low concentration of nicotine exhibited stronger anxiety-like responses than their bold counterparts. These findings further support the validity of using zebrafish as a dependable tool for studying the effects of drugs and uncovering the underlying mechanisms associated with individual variations.

Alcohol sensitivity and tolerance encoding in sleep regulatory circadian neurons in Drosophila

Alcohol tolerance is a simple form of behavioural and neural plasticity that occurs with the first drink. Neural plasticity in tolerance is likely a substrate for longer term adaptations that can lead to alcohol use disorder. Drosophila develop tolerance with characteristics similar to vertebrates, and it is a useful model for determining the molecular and circuit encoding mechanisms in detail. Rapid tolerance, measured after the first alcohol exposure is completely metabolized, is localized to specific brain regions that are not interconnected in an obvious way. We used a forward neuroanatomical screen to identify three new neural sites for rapid tolerance encoding. One of these was composed of two groups of neurons, the DN1a and DN1p glutamatergic neurons, that are part of the Drosophila circadian clock. We localized rapid tolerance to the two DN1a neurons that regulate arousal by light at night, temperature-dependent sleep timing, and night-time sleep. Two clock neurons that regulate evening activity, LNd6 and the 5th LNv, are postsynaptic to the DN1as, and they promote rapid tolerance via the metabotropic glutamate receptor. Thus, rapid tolerance to alcohol overlaps with sleep regulatory neural circuitry, suggesting a mechanistic link.

Theoretical Frameworks and Mechanistic Aspects of Alcohol Addiction: Alcohol Addiction as a Reward Deficit/Stress Surfeit Disorder

Alcohol use disorder (AUD) can be defined by a compulsion to seek and take alcohol, the loss of control in limiting intake, and the emergence of a negative emotional state when access to alcohol is prevented. Alcohol use disorder impacts multiple motivational mechanisms and can be conceptualized as a disorder that includes a progression from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). Compulsive drug seeking that is associated with AUD can be derived from multiple neuroadaptations, but the thesis argued herein is that a key component involves the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from the dysregulation of specific neurochemical elements that are involved in reward and stress within basal forebrain structures that involve the ventral striatum and extended amygdala, respectively. Specific neurochemical elements in these structures include decreases in reward neurotransmission (e.g., decreases in dopamine and opioid peptide function in the ventral striatum) and the recruitment of brain stress systems (e.g., corticotropin-releasing factor [CRF]) in the extended amygdala, which contributes to hyperkatifeia and greater alcohol intake that is associated with dependence. Glucocorticoids and mineralocorticoids may play a role in sensitizing the extended amygdala CRF system. Other components of brain stress systems in the extended amygdala that may contribute to the negative motivational state of withdrawal include norepinephrine in the bed nucleus of the stria terminalis, dynorphin in the nucleus accumbens, hypocretin and vasopressin in the central nucleus of the amygdala, and neuroimmune modulation. Decreases in the activity of neuropeptide Y, nociception, endocannabinoids, and oxytocin in the extended amygdala may also contribute to hyperkatifeia that is associated with alcohol withdrawal. Such dysregulation of emotional processing may also significantly contribute to pain that is associated with alcohol withdrawal and negative urgency (i.e., impulsivity that is associated with hyperkatifeia during hyperkatifeia). Thus, an overactive brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of AUD. The combination of the loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement that at least partially drives the compulsivity of AUD.

Sex-specific biobehavioral regulation of persistent inflammatory pain by alcohol

BACKGROUND

Although a large percentage of chronic pain patients consume alcohol to manage their pain, there is a significant gap in knowledge regarding the mechanisms underlying the antinociceptive effects of alcohol.

METHODS

To determine the longitudinal analgesic effects of alcohol, we utilized the complete Freund's adjuvant (CFA) model of inflammatory pain in adult female and male Wistar rats. Both somatic and negative motivational aspects of pain were measured using the electronic von Frey (mechanical nociception) system, thermal probe test (thermal nociception), and mechanical conflict avoidance task (pain avoidance-like behavior). Tests were conducted at baseline and 1 and 3 weeks following intraplantar CFA or saline administration. At both time points post-CFA, animals were treated with each of three doses of alcohol (intraperitoneal; 0, 0.5, and 1.0 g/kg) over separate days in a Latin square design.

RESULTS

Alcohol produced dose-dependent mechanical analgesia and antihyperalgesia in females but only antihyperalgesia in males. Although alcohol continued to attenuate CFA-induced decreases in both thermal and mechanical nociceptive thresholds between 1 and 3 weeks post-CFA, it appeared less effective at increasing thresholds 3 weeks after CFA induction.

CONCLUSIONS

These data suggest that individuals may develop tolerance to alcohol's ability to alleviate both somatic and negative motivational symptoms of chronic pain over time. We also discovered sex-specific neuroadaptations in protein kinase A-dependent phosphorylation of GluR1 subunits and extracellular signal-regulated kinase (ERK 1/2) phosphorylation in nociceptive brain centers of animals receiving an alcohol challenge 1 week post-CFA. Together, these findings illustrate a sex-specific regulation of behavioral and neurobiological indices of persistent pain by alcohol.

Holding your liquor: Comparison of alcohol-induced psychomotor impairment in drinkers with and without alcohol use disorder

BACKGROUND

Behavioral tolerance to alcohol underscores the widely accepted notion that individuals who regularly drink alcohol become less sensitive to its impairing effects. However, previous research assessing alcohol-induced impairment in humans has primarily focused on social drinkers. This has limited our understanding of the nature and extent of behavioral tolerance among heavier drinkers, such as those with alcohol use disorder (AUD).

METHODS

Data from three cohorts of the Chicago Social Drinking Project were evaluated to examine the acute effects of alcohol on psychomotor performance across the breath alcohol curve in light drinkers (LDs; n = 86), heavy drinkers (HDs; n = 208), and individuals with AUD (AUDs; n = 103). Before and at several intervals after ingesting either alcohol (0.8 g/kg, peak BrAC = 0.09 g/dL) or placebo in two random-order laboratory sessions, participants completed a test of fine motor coordination (Grooved Pegboard), a test of perceptual-motor processing (Digit Symbol Substitution Task), and a self-reported survey of perceived impairment. Sixty individuals with AUD completed a third session with a very high dose of alcohol (1.2 g/kg, peak BrAC = 0.13 g/dL).

RESULTS

The AUD and HD groups, relative to the LD group, perceived less impairment and demonstrated greater behavioral tolerance to an intoxicating dose of alcohol, exhibited by reduced peak impairment and a quicker return to baseline performance on psychomotor measures. Among individuals with AUD who consumed the very high dose, impairment was more than double that following the usual high dose, and it exceeded the impairment among LDs following the usual high dose.

CONCLUSIONS

In this sample of young adult drinkers, relative to the LD group, those with heavier drinking patterns (AUD and HD groups) showed greater behavioral tolerance to 0.8 g/kg alcohol, a dose typically associated with a binge drinking episode. However, when challenged with a very high alcohol dose commensurate with high-intensity drinking, individuals with AUD showed substantial psychomotor impairment.

Shared Mechanisms of GABAergic and Opioidergic Transmission Regulate Corticolimbic Reward Systems and Cognitive Aspects of Motivational Behaviors

The functional interplay between the corticolimbic GABAergic and opioidergic systems plays a crucial role in regulating the reward system and cognitive aspects of motivational behaviors leading to the development of addictive behaviors and disorders. This review provides a summary of the shared mechanisms of GABAergic and opioidergic transmission, which modulate the activity of dopaminergic neurons located in the ventral tegmental area (VTA), the central hub of the reward mechanisms. This review comprehensively covers the neuroanatomical and neurobiological aspects of corticolimbic inhibitory neurons that express opioid receptors, which act as modulators of corticolimbic GABAergic transmission. The presence of opioid and GABA receptors on the same neurons allows for the modulation of the activity of dopaminergic neurons in the ventral tegmental area, which plays a key role in the reward mechanisms of the brain. This colocalization of receptors and their immunochemical markers can provide a comprehensive understanding for clinicians and researchers, revealing the neuronal circuits that contribute to the reward system. Moreover, this review highlights the importance of GABAergic transmission-induced neuroplasticity under the modulation of opioid receptors. It discusses their interactive role in reinforcement learning, network oscillation, aversive behaviors, and local feedback or feedforward inhibitions in reward mechanisms. Understanding the shared mechanisms of these systems may lead to the development of new therapeutic approaches for addiction, reward-related disorders, and drug-induced cognitive impairment.

Using animal models to identify clinical risk factors in the older population due to alcohol use and misuse

The number of people over the age of 65 years old is increasing and understanding health risks associated with the aged population is important. Recent research has revealed that alcohol (ethanol) consumption levels in older demographics remains elevated and often occurs in a dangerous binge pattern. Given ethical constraints on investigating high level or binge pattern alcohol consumption in humans, animal models are often used to study the effects of ethanol. The current review highlights ongoing work revealing that aged rats are often more sensitive to the effects of acute ethanol compared to younger rats. Specifically, aged rats are more sensitive to the motor impairing, hypnotic, hypothermic, and often the cognitive effects of ethanol compared to younger rats. In addition, the development of ethanol tolerance following chronic exposure may have a different temporal pattern in aged rats compared to younger rats. However, the neurobiological mechanisms that cause the increased sensitivity to ethanol in aged animals have yet to be identified. Furthermore, the differential age effects of ethanol highlight clinical risk factors for alcohol misuse in the older human population. Future work is needed to determine underlying CNS mechanisms producing altered effects of ethanol in aged subjects and also the development of educational material concerning ethanol's effects across ages for health care providers working with the aged population.

The BDNF Val68Met polymorphism causes a sex specific alcohol preference over social interaction and also acute tolerance to the anxiolytic effects of alcohol, a phenotype driven by malfunction of BDNF in the ventral hippocampus of male mice

BACKGROUND

The brain-derived neurotrophic factor (BDNF) Valine 66 to Methionine human polymorphism results in impaired activity-dependent BDNF release and has been linked to psychiatric disorders including depression and anxiety. We previously showed that male knock-in mice carrying the mouse Methionine homolog (Met68BDNF) exhibit excessive and compulsive alcohol drinking behaviors as compared to the wild-type Val68BDNF mice.

OBJECTIVE

Here, we set out to determine the potential mechanism for the heightened and compulsive alcohol drinking phenotypes detected in Met68BDNF mice.

RESULTS

We found that male, but not female Met68BDNF mice exhibit social anxiety-like behaviors. We further show that male Met68BDNF mice exhibit a preference for alcohol over social interaction. In contrast, alcohol place preference without an alternative social reward, is similar in male Met68BDNF and Val68BDNF mice. Since the Met68BDNF mice show social anxiety phenotypes, we tested whether alcohol reliefs anxiety similarly in Met68BDNF and Val68BDNF mice and found that male, but not female Met68BDNF mice are insensitive to the acute anxiolytic action of alcohol. Finally, we show that this acute tolerance to alcohol-dependent anxiolysis can be restored by overexpressing wild-type Val68BDNF in the ventral hippocampus (vHC) of Met68BDNF mice.

CONCLUSIONS

Together, our results suggest that excessive alcohol drinking in the Met68BDNF may be attributed, in part, to heighted social anxiety and a lack of alcohol-dependent anxiolysis, a phenotype that is associated with malfunction of BDNF signaling in the vHC of male Met68BDNF mice.

Alcohol dependence and the ventral hippocampal influence on alcohol drinking in male mice

Examining neural circuits underlying persistent, heavy drinking provides insight into the neurobiological mechanisms driving alcohol use disorder. Facilitated by its connectivity with other parts of the brain such as the nucleus accumbens (NAc), the ventral hippocampus (vHC) supports many behaviors, including those related to reward seeking and addiction. These studies used a well-established mouse model of alcohol (ethanol) dependence. After surgery to infuse DREADD-expressing viruses (hM4Di, hM3Dq, or mCherry-only) into the vHC and position guide cannula above the NAc, male C57BL/6J mice were treated in the CIE drinking model that involved repeated cycles of chronic intermittent alcohol (CIE) vapor or air (CTL) exposure alternating with weekly test drinking cycles in which mice were offered alcohol (15% v/v) 2 h/day. Additionally, smaller groups of mice were evaluated for either cFos expression or glutamate release using microdialysis procedures. In CIE mice expressing inhibitory (hM4Di) DREADDs in the vHC, drinking increased as expected, but CNO (3 mg/kg intraperitoneally [i.p.]) given 30 min before testing did not alter alcohol intake. However, in CTL mice expressing hM4Di, CNO significantly increased alcohol drinking (∼30%; p < 0.05) to levels similar to the CIE mice. The vHC-NAc pathway was targeted by infusing CNO into the NAc (3 or 10 μM/side) 30 min before testing. CNO activation of the pathway in mice expressing excitatory (hM3Dq) DREADDs selectively reduced consumption in CIE mice back to CTL levels (∼35-45%; p < 0.05) without affecting CTL alcohol intake. Lastly, activating the vHC-NAc pathway increased cFos expression and evoked significant glutamate release from the vHC terminals in the NAc. These data indicate that reduced activity of the vHC increases alcohol consumption and that targeted, increased activity of the vHC-NAc pathway attenuates excessive drinking associated with alcohol dependence. Thus, these findings indicate that the vHC and its glutamatergic projections to the NAc are involved in excessive alcohol drinking.

Acute Administration of Ethanol and of a D1-Receptor Antagonist Affects the Behavior and Neurochemistry of Adult Zebrafish

Alcohol abuse represents major societal problems, an unmet medical need resulting from our incomplete understanding of the mechanisms underlying alcohol’s actions in the brain. To uncover these mechanisms, animal models have been proposed. Here, we explore the effects of acute alcohol administration in zebrafish, a promising animal model in alcohol research. One mechanism via which alcohol may influence behavior is the dopaminergic neurotransmitter system. As a proof-of-concept analysis, we study how D1 dopamine-receptor antagonism may alter the effects of acute alcohol on the behavior of adult zebrafish and on whole brain levels of neurochemicals. We conduct these analyses using a quasi-inbred strain, AB, and a genetically heterogeneous population SFWT. Our results uncover significant alcohol x D1-R antagonist interaction and main effects of these factors in shoaling, but only additive effects of these factors in measures of exploratory behavior. We also find interacting and main effects of alcohol and the D1-R antagonist on dopamine and DOPAC levels, but only alcohol effects on serotonin. We also uncover several strain dependent effects. These results demonstrate that acute alcohol may act through dopaminergic mechanisms for some but not all behavioral phenotypes, a novel discovery, and also suggest that strain differences may, in the future, help us identify molecular mechanisms underlying acute alcohol effects.

Definition matters: assessment of tolerance to the effects of alcohol in a prospective cohort study of emerging adults

BACKGROUND AND AIMS

Tolerance to the effects of alcohol is an important element in the diagnosis of alcohol use disorders (AUD); however, there is ongoing debate about its utility in the diagnosis AUD in adolescents and young adults. This study aimed to refine the assessment of tolerance in young adults by testing different definitions of tolerance and their associations with longitudinal AUD outcomes.

DESIGN

Prospective cohort study.

SETTINGS

Australia.

PARTICIPANTS

A contemporary cohort of emerging adults across Australia (n = 565, mean age = 18.9, range = 18-21 at baseline).

MEASUREMENTS

Clinician-administered Structured Clinical Interview for DSM-IV Research Version (SCID-IV-RV) assessed for AUD criteria across five interviews, at 6-month intervals over 2.5 years. Tolerance definitions were operationalized using survey-type response (yes/no), clinician judgement (SCID-IV-RV), different initial drinking quantity and percentage increase thresholds and average heavy consumption metrics. AUD persistence was operationalized by the number of times AUD was present across the 2.5-year study period (n = 491), and new-onset AUD was operationalized as any new incidence of AUD during the follow-up period (n = 461).

FINDINGS

The (i) SCID-IV-RV clinician judgement [odds ratio (OR) = 2.50, P = 0.005], (ii) an initial drinking quantity threshold of four to five drinks and 50% minimum increase (OR = 2.48, P = 0.007) and (iii) 50% increase only (OR = 2.40, P = 0.005) were the tolerance definitions more strongly associated with any new onset of AUD throughout the four follow-up time-points than other definitions. However, these definitions were not associated with persistent AUD (Ps > 0.05). Average heavy consumption definitions of tolerance were most strongly associated with persistent AUD (OR = 6.66, P = 0.001; OR = 4.65, P = 0.004) but not associated with new-onset AUD (Ps > 0.05).

CONCLUSIONS

Initial drink and percentage change thresholds appear to improve the efficacy of change-based tolerance as an indicator for new-onset alcohol use disorder diagnosis in self-report surveys of young adults. When predicting persistent alcohol use disorder, average heavy consumption-based indicators appear to be a better way to measure tolerance than self-reported change-based definitions.

A critical review of front-loading: A maladaptive drinking pattern driven by alcohol's rewarding effects

Front-loading is a drinking pattern in which alcohol intake is skewed toward the onset of reward access. This phenomenon has been reported across several different alcohol self-administration protocols in a wide variety of species, including humans. The hypothesis of the current review is that front-loading emerges in response to the rewarding effects of alcohol and can be used to measure the motivation to consume alcohol. Alternative or additional hypotheses that we consider and contrast with the main hypothesis are that: (1) front-loading is directed at overcoming behavioral and/or metabolic tolerance and (2) front-loading is driven by negative reinforcement. Evidence for each of these explanations is reviewed. We also consider how front-loading has been evaluated statistically in previous research and make recommendations for defining this intake pattern in future studies. Because front-loading may predict long-term maladaptive alcohol drinking patterns leading to the development of alcohol use disorder (AUD), several future directions are proposed to elucidate the relationship between front-loading and AUD.

Subregional Differences in Alcohol Modulation of Central Amygdala Neurocircuitry

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

Multiple diverse drinking trajectories among sexual minority women: Unique and joint prediction by minority stress and social influence risk factors

BACKGROUND

Sexual minority populations are at heightened risk for alcohol use disorders compared to heterosexual populations, and these disparities are particularly pronounced for sexual minority women (SMW). Little research has examined the diversity of drinking trajectories among sexual minorities, despite evidence that such trajectories have high predictive utility and are useful in understanding how risk factors may be uniquely associated with specific trajectories.

METHOD

We utilized four waves of data (12 months between waves) from a sample of 1,057 SMW ages 18-25 at Wave 1. The goals were to (a) identify multiple distinct trajectories of alcohol use; (b) examine the predictive utility of these trajectories; and (c) test associations between minority stress (e.g., discrimination) and social influence (e.g., sexual minority community involvement) risk factors and alcohol trajectories.

RESULTS

Using growth mixture modeling, we identified five classes based on drinking patterns at Wave 1 and change over time (stable low, stable high drinking, stable high HED, low increasing, and high decreasing). These classes were differentially associated with Wave 1 levels and changes in alcohol consequences. Minority stressors uniquely predicted a low increasing trajectory, while social influences uniquely predicted a stable high trajectory. Both minority stress and social risk factors predicted high decreasing and stable high HED trajectories.

CONCLUSIONS

Findings indicate that some drinking trajectories among SMW appear similar to those found in the general population, while others appear unique. Results provide insight into how minority stress and social influence risk factors may uniquely and jointly contribute to disparities affecting this population.