Repeated alcohol administration during adolescence causes changes in the mesolimbic dopaminergic and glutamatergic systems and promotes alcohol intake in the adult rat

The interplay between gut microbiome, epigenetics, and substance use disorders: from molecular to clinical perspectives

Substance use disorders (SUDs) involve a complex series of central and peripheral pathologies, leading to impairments in cognitive, behavioral, and physiological processes. Emerging evidence indicates a more significant role for the microbiome-gut-brain axis (MGBA) in SUDs than previously recognized. The MGBA is interconnected with various body systems by producing numerous metabolites, most importantly short-chain fatty acids (SCFAs), cytokines, and neurotransmitters. These mediators influence the human body's epigenome and transcriptome. While numerous epigenetic alterations in different brain regions have been reported in SUD models, the intricate relationship between SUDs and the MGBA suggests that the gut microbiome may partially contribute to the underlying mechanisms of SUDs. Promising results have been observed with gut microbiome-directed interventions in patients with SUDs, including prebiotics, probiotics, antibiotics, and fecal microbiota transplantation. Nonetheless, the long-term epigenetic effects of these interventions remain unexplored. Moreover, various confounding factors and study limitations have hindered the identification of molecular mechanisms and clinical applications of gut microbiome interventions in SUDs. In the present review, we will (i) provide a comprehensive discussion on how the gut microbiome influences SUDs, with an emphasis on epigenetic alterations; (ii) discuss the current evidence on the bidirectional relationship of gut microbiome and SUDs, highlighting potential targets for intervention; and (iii) review recent advances in gut microbiome-directed therapies, along with their limitations and future directions.

Adolescent binge drinking in male Wistar rats increases ethanol consumption and reduces intoxication sensitivity in early adulthood without affecting withdrawal

Background: Early adolescent ethanol exposure increases the risk of developing an alcohol use disorder. The mechanisms underlying this relationship may involve early ethanol exposure influencing anxiety or altering ethanol sensitivity.Objectives: To examine how adolescent binge drinking impacts sensitivity to ethanol intoxication, withdrawal symptoms, anxiety, compulsive behaviors, and ethanol intake in adulthood.Methods: Thirty-seven male Wistar rats self-administered ethanol during adolescence [postnatal days (PD) 27-45] or were housed under control conditions. In adulthood, the rats received intragastric intubations to simulate heavy alcohol (PDs 61-65, 3 daily doses of 0.0 or 1.5 g/kg) exposure. Intoxication and withdrawal symptoms were assessed (PDs 61-70), along with compulsive behaviors (marble burying test, PD68) and anxiety-related behaviors (light-dark box and elevated plus maze tests, PDs 69-70). Two-bottle choice tests provided measures of ethanol intake (PDs 75-87).Results: Adolescent binge exposure increased ethanol consumption in adulthood (p < .001; η2 = 0.51), with binge-exposed rats drinking 4.5-6.5 g/kg/day vs. 2 g/kg/day in controls. Binge-exposed rats exhibited reduced sensitivity to ethanol intoxication (p < .05; η2 = 0.17). Withdrawal symptoms were significantly greater (p < .005; η2 = 0.36) in rats exposed to alcohol during adulthood compared to controls, regardless of binge ethanol exposure. Anxiety or compulsive behaviors were unaffected by binge ethanol.Conclusions: Adolescent binge drinking led, in male rats, to significant increases in ethanol intake and reduced sensitivity to intoxication in adulthood. These findings suggest that early ethanol exposure results in decreased ethanol sensitivity, potentially increasing the likelihood of ethanol use. Adolescent binge drinking is a key vulnerability factor, and interventions should target this behavior.

Elucidating the molecular symphony: unweaving the transcriptional & epigenetic pathways underlying neuroplasticity in opioid dependence and withdrawal

The persistent use of opioids leads to profound changes in neuroplasticity of the brain, contributing to the emergence and persistence of addiction. However, chronic opioid use disrupts the delicate balance of the reward system in the brain, leading to neuroadaptations that underlie addiction. Chronic cocaine usage leads to synchronized alterations in gene expression, causing modifications in the Nucleus Accumbens (NAc), a vital part of the reward system of the brain. These modifications assist in the development of maladaptive behaviors that resemble addiction. Neuroplasticity in the context of addiction involves changes in synaptic connectivity, neuronal morphology, and molecular signaling pathways. Drug-evoked neuroplasticity in opioid addiction and withdrawal represents a complicated interaction between environmental, genetic, and epigenetic factors. Identifying specific transcriptional and epigenetic targets that can be modulated to restore normal neuroplasticity without disrupting essential physiological processes is a critical consideration. The discussion in this article focuses on the transcriptional aspects of drug-evoked neuroplasticity, emphasizing the role of key transcription factors, including cAMP response element-binding protein (CREB), ΔFosB, NF-kB, Myocyte-enhancing factor 2 (MEF2), Methyl-CpG binding protein 2 (MeCP2), E2F3a, and FOXO3a. These factors regulate gene expression and lead to the neuroadaptive changes observed in addiction and withdrawal. Epigenetic regulation, which involves modifying gene accessibility by controlling these structures, has been identified as a critical component of addiction development. By unraveling these complex molecular processes, this study provides valuable insights that may pave the way for future therapeutic interventions targeting the mechanisms underlying addiction and withdrawal.

Effects of isolation stress and voluntary ethanol exposure during adolescence on ethanol and nicotine co-use in adulthood using male rats

Background

Alcohol use in adolescence may increase susceptibility to substance use disorders (SUDs) in adulthood. This study determined if voluntary ethanol (EtOH) consumption during adolescence, combined with social isolation, alters the trajectory of EtOH and nicotine intake during adulthood, as well as activating brain neuroinflammation.

Methods

Adolescent male isolate- and group-housed rats were given 0.2 % saccharin/20 % EtOH (Sacc/EtOH) or water using intermittent 2-bottle choice; controls were given water in both bottles (n=17-20 per group). Some rats from each group (n=5-6) were euthanized one week later to measure autoradiographic [3H]PK-11195 binding, an indicator of microglial reactivity, and the remainder (n=11-14 per group) were tested in adulthood in 2-bottle choice, followed by nicotine self-administration using an incremental fixed ratio (FR) schedule with Sacc/EtOH and water concurrently available.

Results

Isolation housing increased adolescent intake of Sacc/EtOH, but the increase did not produce an observable neuroimmunological response in brain. Adolescent EtOH exposure decreased adult intake of both Sacc/EtOH and unsweetened EtOH, with isolate-housed rats showing a greater effect than group-housed rats. In the co-use model, a cross-price economic demand analysis revealed a substitutional relationship between Sacc/EtOH and nicotine, but no effect of adolescent Sacc/EtOH exposure. Compared to group-housed rats, isolate-housed rats were more sensitive to the changing price of nicotine and showed greater substitutability of Sacc/EtOH for nicotine.

Conclusion

The current results suggest that adolescent EtOH exposure per se, with or without isolation stress, does not likely explain the enhanced risk for either alcohol or nicotine use later in life.

Adolescent alcohol exposure persistently alters orbitofrontal cortical encoding of Pavlovian conditional stimulus components in female rats

Exposure to alcohol during adolescence impacts cortical and limbic brain regions undergoing maturation. In rodent models, long-term effects on behavior and neurophysiology have been described after adolescent intermittent ethanol (AIE), especially in males. We hypothesized that AIE in female rats increases conditional approach to a reward-predictive cue and corresponding neuronal activity in the orbitofrontal cortex (OFC) and nucleus accumbens (NAc). We evaluated behavior and neuronal firing after AIE (5 g/kg intragastric) or water (CON) in adult female rats. Both AIE and CON groups expressed a ST phenotype, and AIE marginally increased sign-tracking (ST) and decreased goal-tracking (GT) metrics. NAc neurons exhibited phasic firing patterns to the conditional stimulus (CS), with no differences between groups. In contrast, neuronal firing in the OFC of AIE animals was greater at CS onset and offset than in CON animals. During reward omission, OFC responses to CS offset normalized to CON levels, but enhanced OFC firing to CS onset persisted in AIE. We suggest that the enhanced OFC neural activity observed in AIE rats to the CS could contribute to behavioral inflexibility. Ultimately, AIE persistently impacts the neurocircuitry of reward-motivated behavior in female rats.

Adolescent binge ethanol impacts H3K9me3-occupancy at synaptic genes and the regulation of oligodendrocyte development

Introduction

Binge drinking in adolescence can disrupt myelination and cause brain structural changes that persist into adulthood. Alcohol consumption at a younger age increases the susceptibility of these changes. Animal models to understand ethanol's actions on myelin and white matter show that adolescent binge ethanol can alter the developmental trajectory of oligodendrocytes, myelin structure, and myelin fiber density. Oligodendrocyte differentiation is epigenetically regulated by H3K9 trimethylation (H3K9me3). Prior studies have shown that adolescent binge ethanol dysregulates H3K9 methylation and decreases H3K9-related gene expression in the PFC.

Methods

Here, we assessed ethanol-induced changes to H3K9me3 occupancy at genomic loci in the developing adolescent PFC. We further assessed ethanol-induced changes at the transcription level with qPCR time course approaches in oligodendrocyte-enriched cells to assess changes in oligodendrocyte progenitor and oligodendrocytes specifically.

Results

Adolescent binge ethanol altered H3K9me3 regulation of synaptic-related genes and genes specific for glutamate and potassium channels in a sex-specific manner. In PFC tissue, we found an early change in gene expression in transcription factors associated with oligodendrocyte differentiation that may lead to the later significant decrease in myelin-related gene expression. This effect appeared stronger in males.

Conclusion

Further exploration in oligodendrocyte cell enrichment time course and dose response studies could suggest lasting dysregulation of oligodendrocyte maturation at the transcriptional level. Overall, these studies suggest that binge ethanol may impede oligodendrocyte differentiation required for ongoing myelin development in the PFC by altering H3K9me3 occupancy at synaptic-related genes. We identify potential genes that may be contributing to adolescent binge ethanol-related myelin loss.

Epigenetic regulation of microglia and neurons by proinflammatory signaling following adolescent intermittent ethanol (AIE) exposure and in human AUD

Adolescent alcohol drinking is linked to high rates of adult alcohol problems and alcohol use disorder (AUD). The Neurobiology of Alcohol Drinking in Adulthood (NADIA) consortium adolescent intermittent ethanol (AIE) models adolescent binge drinking, followed by abstinent maturation to adulthood to determine the persistent AIE changes in neurobiology and behavior. AIE increases adult alcohol drinking and preference, increases anxiety and reward seeking, and disrupts sleep and cognition, all risks for AUD. In addition, AIE induces changes in neuroimmune gene expression in neurons and glia that alter neurocircuitry and behavior. HMGB1 is a unique neuroimmune signal released from neurons and glia by ethanol that activates multiple proinflammatory receptors, including Toll-like receptors (TLRs), that spread proinflammatory gene induction. HMGB1 expression is increased by AIE in rat brain and in post-mortem human AUD brain, where it correlates with lifetime alcohol consumption. HMGB1 activation of TLR increase TLR expression. Human AUD brain and rat brain following AIE show increases in multiple TLRs. Brain regional differences in neurotransmitters and cell types impact ethanol responses and neuroimmune gene induction. Microglia are monocyte-like cells that provide trophic and synaptic functions, that ethanol proinflammatory signals sensitize or "prime" during repeated drinking cycles, impacting neurocircuitry. Neurocircuits are differently impacted dependent upon neuronal-glial signaling. Acetylcholine is an anti-inflammatory neurotransmitter. AIE increases HMGB1-TLR4 signaling in forebrain, reducing cholinergic neurons by silencing multiple cholinergic defining genes through upregulation of RE-1 silencing factor (REST), a transcription inhibitor known to regulate neuronal differentiation. HMGB1 REST induction reduces cholinergic neurons in basal forebrain and cholinergic innervation of hippocampus. Adult brain hippocampal neurogenesis is regulated by a neurogenic niche formed from multiple cells. In vivo AIE and in vitro studies find ethanol increases HMGB1-TLR4 signaling and other proinflammatory signaling as well as reducing trophic factors, NGF, and BDNF, coincident with loss of the cholinergic synapse marker vChAT. These changes in gene expression-transcriptomes result in reduced adult neurogenesis. Excitingly, HMGB1 antagonists, anti-inflammatories, and epigenetic modifiers like histone deacetylase inhibitors restore trophic the neurogenesis. These findings suggest anti-inflammatory and epigenetic drugs should be considered for AUD therapy and may provide long-lasting reversal of psychopathology.

The Impact of Alcohol-Induced Epigenetic Modifications in the Treatment of Alcohol use Disorders

Alcohol use disorders are responsible for 5.9% of all death annually and 5.1% of the global disease burden. It has been suggested that alcohol abuse can modify gene expression through epigenetic processes, namely DNA and histone methylation, histone acetylation, and microRNA expression. The alcohol influence on epigenetic mechanisms leads to molecular adaptation of a wide number of brain circuits, including the hypothalamus-hypophysis-adrenal axis, the prefrontal cortex, the mesolimbic-dopamine pathways and the endogenous opioid pathways. Epigenetic regulation represents an important level of alcohol-induced molecular adaptation in the brain. It has been demonstrated that acute and chronic alcohol exposure can induce opposite modifications in epigenetic mechanisms: acute alcohol exposure increases histone acetylation, decreases histone methylation and inhibits DNA methyltransferase activity, while chronic alcohol exposure induces hypermethylation of DNA. Some studies investigated the chromatin status during the withdrawal period and the craving period and showed that craving was associated with low methylation status, while the withdrawal period was associated with elevated activity of histone deacetylase and decreased histone acetylation. Given the effects exerted by ethanol consumption on epigenetic mechanisms, chromatin structure modifiers, such as histone deacetylase inhibitors and DNA methyltransferase inhibitors, might represent a new potential strategy to treat alcohol use disorder. Further investigations on molecular modifications induced by ethanol might be helpful to develop new therapies for alcoholism and drug addiction targeting epigenetic processes.

Abuse-like toluene exposure during early adolescence alters subsequent ethanol and cocaine behavioral effects and brain monoamines in male mice

Currently, there is a gap in understanding the neurobiological impact early adolescent toluene exposure has on subsequent actions of other drugs. Adolescent (PND 28-32) male Swiss-Webster mice (N = 210) were exposed to 0, 2000, or 4000 ppm of toluene vapor for 30 min/day for 5 days. Immediately following the last toluene exposure (PND 32; n = 15) or after a short delay (PND 35; n = 15), a subset of subjects' brains was collected for monoamine analysis. Remaining mice were assigned to one of two abstinence periods: a short 4-day (PND 36) or long 12-day (PND 44) delay after toluene exposure. Mice were then subjected to a cumulative dose response assessment of either cocaine (0, 2.5, 5, 10, 20 mg/kg; n = 60), ethanol (0, 0.5, 1, 2, 4 g/kg; n = 60), or saline (5 control injections; n = 60). Toluene concentration-dependently increased locomotor activity during exposure. When later challenged, mice exposed previously to toluene were significantly less active after cocaine (10 and 20 mg/kg) compared to air-exposed controls. Animals were also less active at the highest dose of alcohol (4 g/kg) following prior exposure to 4000 ppm when compared to air-exposed controls. Analysis of monoamines and their metabolites using High Pressure Liquid Chromatography (HPLC) within the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and ventral tegmental area (VTA) revealed subtle effects on monoamine or metabolite levels following cumulative dosing that varied by drug (cocaine and ethanol) and abstinence duration. Our results suggest that early adolescent toluene exposure produces behavioral desensitization to subsequent cocaine-induced locomotor activity with subtle enhancement of ethanol's depressive effects and less clear impacts on levels of monoamines.

Adolescent alcohol and nicotine exposure alters the adult response to alcohol use

Adolescence through young adulthood is a unique period of neuronal development and maturation. Numerous agents can alter this process, resulting in long-term neurological and biological consequences. In the clinical literature, it is frequently reported that adolescent alcohol consumption increases the propensity to develop addictions, including alcohol use disorder (AUD), during adulthood. A general limitation of both clinical and human pre-clinical adolescent alcohol research is the high rate of co-using/abusing more than one drug during adolescence, such as co-using/abusing alcohol with nicotine. A primary goal of basic research is elucidating neuroadaptations produced by adolescent alcohol exposure/consumption that promote alcohol and other drug self-administration in adulthood. The long-term goal is to develop pharmacotherapeutics for the prevention or amelioration of these neuroadaptations. This review will focus on studies that have examined the effects of adolescent alcohol and nicotine exposure on adult alcohol consumption, the hypersensitivity of the mesolimbic dopaminergic system, and enhanced responses not only to alcohol but also to nicotine during adulthood. Again, the long-term goal is to identify potential cholinergic agents to prevent or ameliorate the consequences of, peri-adolescent alcohol abuse.

Adolescent Intermittent Ethanol Drives Modest Neuroinflammation but Does Not Escalate Drinking in Male Rats

During adolescence, the brain is highly susceptible to alcohol-induced damage and subsequent neuroimmune responses, effects which may enhance development of an alcohol use disorder (AUD). Neuroimmune reactions are implicated in adolescent alcohol exposure escalating adulthood drinking. Therefore, we investigated whether intermittent alcohol exposure in male, adolescent rats (AIE) escalated adult drinking via two-bottle choice (2BC). We also examined the influence of housing environment across three groups: standard (group-housed with enrichment during 2BC), impoverished (group-housed without enrichment during 2BC), or isolation (single-housed without bedding or enrichment throughout). In the standard group immediately after AIE/saline and after 2BC, we also examined the expression of microglial marker, Iba1, reactive astrocyte marker, vimentin, and neuronal cell death dye, FluoroJade B (FJB). We did not observe an escalation of adulthood drinking following AIE, regardless of housing condition. Further, only a modest neuroimmune response occurred after AIE in the standard group: no significant microglial reactivity or neuronal cell death was apparent using this model, although some astrocyte reactivity was detected in adolescence following AIE that resolved by adulthood. These data suggest that the lack of neuroimmune response in adolescence in this model may underlie the lack of escalation of alcohol drinking, which could not be modified through isolation stress.

Cannabidiol tempers alcohol intake and neuroendocrine and behavioural correlates in alcohol binge drinking adolescent rats. Focus on calcitonin gene-related peptide's brain levels

Alcohol binge drinking is common among adolescents and may challenge the signalling systems that process affective stimuli, including calcitonin gene-related peptide (CGRP) signalling. Here, we employed a rat model of adolescent binge drinking to evaluate reward-, social- and aversion-related behaviour, glucocorticoid output and CGRP levels in affect-related brain regions. As a potential rescue, the effect of the phytocannabinoid cannabidiol was explored. Adolescent male rats underwent the intermittent 20% alcohol two-bottle choice paradigm; at the binge day (BD) and the 24 h withdrawal day (WD), we assessed CGRP expression in medial prefrontal cortex (mPFC), nucleus accumbens (NAc), amygdala, hypothalamus and brainstem; in addition, we evaluated sucrose preference, social motivation and drive, nociceptive response, and serum corticosterone levels. Cannabidiol (40 mg/kg, i.p.) was administered before each drinking session, and its effect was measured on the above-mentioned readouts. At BD and WD, rats displayed decreased CGRP expression in mPFC, NAc and amygdala; increased CGRP levels in the brainstem; increased response to rewarding- and nociceptive stimuli and decreased social drive; reduced serum corticosterone levels. Cannabidiol reduced alcohol consumption and preference; normalised the abnormal corticolimbic CGRP expression, and the reward and aversion-related hyper-responsivity, as well as glucocorticoid levels in alcohol binge-like drinking rats. Overall, CGRP can represent both a mediator and a target of alcohol binge-like drinking and provides a further piece in the intricate puzzle of alcohol-induced behavioural and neuroendocrine sequelae. CBD shows promising effects in limiting adolescent alcohol binge drinking and rebalancing the bio-behavioural abnormalities.

Differential consumption of alcohol, caffeine, and caffeinated alcohol by adolescent rats, and effects on post-adolescent gene expression signatures in the nucleus accumbens and orbitofrontal cortex

Caffeinated alcoholic beverages (CABs) are widely consumed despite little known about their behavioral and biological effects. Furthermore, CABs are also popular among adolescents, a particularly vulnerable and maturing demographic. In this preliminary study, we compared levels of daily adolescent voluntary consumption of caffeine (0.03%), alcohol (10%), caffeinated alcohol (0.03% + 10%), or vehicle and evaluated the effects of this on mRNA expression in brain regions associated with addiction and known to be affected by each drug. Beginning on postnatal day 30, rats were allowed unrestricted access to gelatin combined with one, both, or neither drug for twenty days. Compared to vehicle-consuming animals, consumption of gelatin was significantly attenuated when alcohol was included. The addition of caffeine to alcohol increased alcohol consumption in the early days of access compared to alcohol alone; however, after two weeks, alcohol consumption between these groups reached comparable levels. Compared to animals consuming caffeine alone, combining caffeine with alcohol significantly reduced caffeine intake. Targeted mRNA analysis of tissue collected from the nucleus accumbens and orbitofrontal cortex after the consumption period identified unique patterns of differentially expressed genes between treatment groups, across a broad array of neurotransmitter systems. Of particular note were genes related to a number of solute transporters and serotonergic functions. This preliminary work suggests unique pharmacological and behavioral effects from consuming caffeinated alcohol during adolescence. Since CABs are widely consumed by adolescents, these results suggest that more research into the pharmacological and behavioral effects elicited by CABs is warranted.

A review on the reciprocal interactions between neuroinflammatory processes and substance use and misuse, with a focus on alcohol misuse

Background: The last decade has witnessed a surge of findings implicating neuroinflammatory processes as pivotal players in substance use disorders. The directionality of effects began with the expectation that the neuroinflammation associated with prolonged substance misuse contributes to long-term neuropathological consequences. As the literature grew, however, it became evident that the interactions between neuroinflammatory processes and alcohol and drug intake were reciprocal and part of a pernicious cycle in which disease-relevant signaling pathways contributed to an escalation of drug intake, provoking further inflammation-signaling and thereby exacerbating the neuropathological effects of drug misuse.Objectives: The goal of this review and its associated special issue is to provide an overview of the emergent findings relevant to understanding these reciprocal interactions. The review highlights the importance of preclinical and clinical studies in testing and validation of immunotherapeutics as viable targets for curtailing substance use and misuse, with a focus on alcohol misuse.Methods: A narrative review of the literature on drug and neuroinflammation was conducted, as well as articles published in this Special Issue on Alcohol- and Drug-induced Neuroinflammation: Insights from Pre-clinical Models and Clinical Research.Results: We argue that (a) demographic variables and genetic background contribute unique sensitivity to drug-related neuroinflammation; (b) co-morbidities between substance use disorders and affect dysfunction may share common inflammation-related signatures that predict the efficacy of immunotherapeutic drugs; and (c) examination of polydrug interactions with neuroinflammation is a critical area where greater research emphasis is needed.Conclusions: This review provides an accessible and example-driven review of the relationship between drug misuse, neuroinflammatory processes, and their resultant neuropathological outcomes.

Negative and positive allosteric modulators of the α7 nicotinic acetylcholine receptor regulates the ability of adolescent binge alcohol exposure to enhance adult alcohol consumption

Rationale and Objectives: Ethanol acts directly on the α7 Nicotinic acetylcholine receptor (α7). Adolescent-binge alcohol exposure (ABAE) produces deleterious consequences during adulthood, and data indicate that the α7 receptor regulates these damaging events. Administration of an α7 Negative Allosteric Modulator (NAM) or the cholinesterase inhibitor galantamine can prophylactically prevent adult consequences of ABAE. The goals of the experiments were to determine the effects of co-administration of ethanol and a α7 agonist in the mesolimbic dopamine system and to determine if administration of an α7 NAM or positive allosteric modulator (PAM) modulates the enhancement of adult alcohol drinking produced by ABAE. Methods: In adult rats, ethanol and the α7 agonist AR-R17779 (AR) were microinjected into the posterior ventral tegmental area (VTA), and dopamine levels were measured in the nucleus accumbens shell (AcbSh). In adolescence, rats were treated with the α7 NAM SB-277011-A (SB) or PNU-120596 (PAM) 2 h before administration of EtOH (ABAE). Ethanol consumption (acquisition, maintenance, and relapse) during adulthood was characterized. Results: Ethanol and AR co-administered into the posterior VTA stimulated dopamine release in the AcbSh in a synergistic manner. The increase in alcohol consumption during the acquisition and relapse drinking during adulthood following ABAE was prevented by administration of SB, or enhanced by administration of PNU, prior to EtOH exposure during adolescence. Discussion: Ethanol acts on the α7 receptor, and the α7 receptor regulates the critical effects of ethanol in the brain. The data replicate the findings that cholinergic agents (α7 NAMs) can act prophylactically to reduce the alterations in adult alcohol consumption following ABAE.

Longitudinal associations between age 20 problematic substance use and opioid use disorder incidence at age 30 - findings from an urban cohort

This study used data from a longitudinal prevention study in an urban cohort to examine associations between nicotine dependence, alcohol, and cannabis use disorder and disorder criteria at age 20, with opioid use disorder (OUD) incidence or criteria onset by age 30. The study sample included 1408 participants (57.5% female, 72.5% African American) drawn from two cohorts of participants in a mid-Atlantic region of the U.S. as part of a series of randomized controlled trials of elementary school-based universal prevention interventions. Lifetime cannabis use disorder (CUD), alcohol use disorder (AUD; both DSM-IV), and current nicotine dependence (Fagerstrom Test for Nicotine Dependence, FTND) assessed at age 20 were used to predict (1) DSM-IV lifetime OUD at age 30, and (2) OUD criteria between ages 20 and 30 in multivariable logistic regression models. Covariates for all analyses included sociodemographics (sex, race, and free/reduced-priced lunch status), community disadvantage, and intervention status. Nicotine dependence (FTND≥3) at age 20 predicted age 30 DSM-IV lifetime OUD (aOR = 2.37; 95% CI 1.02,5.54). The number of CUD criteria (aOR = 1.30; 95% CI 1.09,1.57) and nicotine dependence severity scores (aOR = 1.22; 95% CI = 1.05,1.41) at age 20 predicted any OUD criteria between the ages of 20 and 30. Findings are consistent with previous research on opioid use behavior in young adulthood and suggest that nicotine dependence and CUD criteria among urban young people predict onset of OUD and OUD criteria in young adulthood.

Targeting Persistent Changes in Neuroimmune and Epigenetic Signaling in Adolescent Drinking to Treat Alcohol Use Disorder in Adulthood

Studies universally find early age of drinking onset is linked to lifelong risks of alcohol problems and alcohol use disorder (AUD). Assessment of the lasting effect of drinking during adolescent development in humans is confounded by the diversity of environmental and genetic factors that affect adolescent development, including emerging personality disorders and progressive increases in drinking trajectories into adulthood. Preclinical studies using an adolescent intermittent ethanol (AIE) exposure rat model of underage binge drinking avoid the human confounds and support lifelong changes that increase risks. AIE increases adult alcohol drinking, risky decision-making, reward-seeking, and anxiety as well as reductions in executive function that all increase risks for the development of an AUD. AIE causes persistent increases in brain neuroimmune signaling high-mobility group box 1 (HMGB1), Toll-like receptor, receptor for advanced glycation end products, and innate immune genes that are also found to be increased in human AUD brain. HMGB1 is released from cells by ethanol, both free and within extracellular vesicles, that act on neurons and glia, shifting transcription and cellular phenotype. AIE-induced decreases in adult hippocampal neurogenesis and loss of basal forebrain cholinergic neurons are reviewed as examples of persistent AIE-induced pathology. Both are prevented and reversed by anti-inflammatory and epigenetic drugs. Findings suggest AIE-increased HMGB1 signaling induces the RE-1 silencing transcript blunting cholinergic gene expression, shifting neuronal phenotype. Inhibition of HMGB1 neuroimmune signaling, histone methylation enzymes, and galantamine, the cholinesterase inhibitor, both prevent and reverse AIE pathology. These findings provide new targets that may reverse AUD neuropathology as well as other brain diseases linked to neuroimmune signaling. SIGNIFICANCE STATEMENT: Adolescent underage binge drinking studies find that earlier adolescent drinking is associated with lifelong alcohol problems including high levels of lifetime alcohol use disorder (AUD). Preclinical studies find the underage binge drinking adolescent intermittent ethanol (AIE) model causes lasting changes in adults that increase risks of developing adult alcohol problems. Loss of hippocampal neurogenesis and loss of basal forebrain cholinergic neurons provide examples of how AIE-induced epigenetic and neuroimmune signaling provide novel therapeutic targets for adult AUD.

Binge eating promotes ethanol self-administration in female rats with a history of intermittent ethanol exposure at adolescence

BACKGROUND

Ethanol drinking begins during adolescence and, particularly when occurs in a binge-like pattern, exerts lingering adverse consequences. Pre-clinical studies indicate that intermittent ethanol exposure (IEA, a model of repeated ethanol intoxication), or binge eating (BE) can increase subsequent ethanol consumption. It is unknown if the promoting effects of BE upon ethanol drinking are found in female rats and are modulated by IEA at adolescence. This study assessed interactive effects between IEA and BE, upon ethanol drinking.

METHODS

Female Wistar rats were given 4.0 g/kg ethanol, every other day from postnatal day 25-45. At adulthood, they were exposed to sessions in which a brief offering of a sizeable portion of highly palatable sugary pills was followed by a 120-min exposure to an ethanol bottle.

RESULTS

Exploratory activity and recognition memory was not affected by the IEA. Glutathione peroxidase and catalase activity, and lipid peroxidation (measured in blood and brain at the end of the procedure) were not significantly affected by IEA or BE exposure. BE alone had a mild promoting effect on ethanol ingestion. Those rats that underwent IEA and BE, however, exhibited heightened and sustained ethanol self-administration (average of 2.12 g/kg/120 min, vs 1.15 g/kg/120 min of the other groups), that persisted throughout the BE sessions. IEA and a history of BE also promoted ethanol intake or preference in a two-bottle endpoint test.

CONCLUSION

The study suggests that exposure to IEA exerts, when followed by BE at adulthood, promoting effects upon ethanol intake, particularly at concentrations ≥ 6%.

The Dopamine System in Mediating Alcohol Effects in Humans

Brain-imaging studies show that the development and maintenance of alcohol use disorder (AUD) is determined by a complex interaction of different neurotransmitter systems and multiple psychological factors. In this context, the dopaminergic reinforcement system appears to be of fundamental importance. We focus on the excitatory and depressant effects of acute versus chronic alcohol intake and its impact on dopaminergic neurotransmission. Furthermore, we describe alterations in dopaminergic neurotransmission as associated with symptoms of alcohol dependence. We specifically focus on neuroadaptations to chronic alcohol consumption and their effect on central processing of alcohol-associated and reward-related stimuli. Altered reward processing, complex conditioning processes, impaired reinforcement learning, and increased salience attribution to alcohol-associated stimuli enable alcohol cues to drive alcohol seeking and consumption. Finally, we will discuss how the neurobiological and neurochemical mechanisms of alcohol-associated alterations in reward processing and learning can interact with stress, cognition, and emotion processing.

Sex-specific decision-making impairments and striatal dopaminergic changes after binge drinking history in rats

Binge drinking (BD) is a harmful behavior for health and is a predictive factor for the development of alcohol addiction. Weak decision-making (DM) capacities could play a role in the vulnerability to BD which in turn would lead to DM impairments, thus perpetuating BD. Longitudinal preclinical studies are however lacking and necessary to understand this complex relationship. Both DM and BD are influenced by sex and involve dopamine release in the core of the nucleus accumbens, a central mechanism regulated by dopamine D2/3 autoreceptors. In this context, we used an operant self-administration procedure of BD in male and female rats, and longitudinally assessed DM capacity, memory and anxiety-like behavior. To better understand the mechanisms potentially involved in the relationship between DM and BD, ex vivo dopamine transmission was assessed short term after the end of the binge exposure in the core of the nucleus accumbens (NAc) using the fast-scan cyclic voltammetry (FSCV) technique and the D2/3 agonist quinpirole. We found important basal sex differences in DM, with female rats showing better performances at baseline. Choice processes were impaired exclusively in males after BD history, associated with a decrease in impulse control in both sexes, while memory and anxiety-like behavior were not affected. Our neurobiological results demonstrate that BD did not affect basal dopamine signaling in the NAc core, regardless of the sex, but reveal changes in the sensitivity to the inhibitory effects of quinpirole in females. DM impairments were neither associated with changes in basal dopamine signaling nor pre-synaptic D2 activity. Overall, our findings show that BD affects both DM processes and dopamine transmission in the core of the NAc in a sex-related manner, further suggesting that these effects may play a role in the vicious cycle leading to BD perpetuation and the early onset of AUD. Our results may inform novel strategies for therapeutic and prevention interventions.

Folate administration ameliorates neurobehavioral effects of prenatal ethanol exposure

Background: Prenatal ethanol exposure (PEE) induces heightened ethanol intake at adolescence in preclinical studies. Ethanol intake alters the absorption of folate, a methyl-group donor critical for numerous cellular functions. The prenatal administration of folate is, therefore, a promising approach to reduce the effects of PEE.Objectives: Experiment 1 determined if prenatal folate modulated the effects of PEE on ethanol intake, anxiety-like response, and exploratory behaviors (Experiment 1) in Wistar rats. Experiment 2 assessed, in rats not given PEE, if postnatal folate reversed effects of ethanol exposure at postnatal days 28-42. Experiment 3 assessed if folate altered blood ethanol levels (BELs).Methods: Experiment 1 involved 242 (125 male) adolescent Wistar rats derived from dams given folate (20 mg/kg, gestational days - GD- 13-20) + ethanol (2.0 g/kg, GD 17-20), ethanol, or vehicle only at pregnancy. Experiment 2 involved 29 male adolescents administered vehicle or ethanol doses co-administered or not with folate. In Experiment 3 twelve adult females were tested for BELs after folate administration. These tests were applied: intake tests, light dark box (LDB), elevated plus maze, open field and concentric square field.Results: PEE heightened ethanol intake (η² ps = 0.06-07) and induced hyperactivity and a reduced latency to exit the white area of the LDB (η² ps = 0.12-17). These effects were partially inhibited by folate (p > .05). Rats exposed to ethanol exposure at adolescence exhibited reduced motor activity (η² p = .17), regardless of folate treatment. Folate did not affect BELs.Conclusion: Folate administration should be considered as a preventive or acute treatment to attenuate the neurobehavioral effects of PEE.

Blood Vessels as a Key Mediator for Ethanol Toxicity: Implication for Neuronal Damage

Excessive intake of ethanol is associated with severe brain dysfunction, and the subsequent neurological and behavioral abnormalities are well-established social risks. Many research studies have addressed how ethanol induces neurological toxicity. However, the underlying mechanisms with which ethanol induces neurological toxicity are still obscure, perhaps due to the variety and complexity of these mechanisms. Epithelial cells are in direct contact with blood and can thus mediate ethanol neurotoxicity. Ethanol activates the endothelial cells of blood vessels, as well as lymphatic vessels, in a concentration-dependent manner. Among various signaling mediators, nitric oxide plays important roles in response to ethanol. Endothelial and inducible nitric oxide synthases (eNOS and iNOS) are upregulated and activated by ethanol and enhance neuroinflammation. On the other hand, angiogenesis and blood vessel remodeling are both affected by ethanol intake, altering blood supply and releasing angiocrine factors to regulate neuronal functions. Thus, ethanol directly acts on endothelial cells, yet the molecular target(s) on endothelial cells remain unknown. Previous studies on neurons and glial cells have validated the potential contribution of membrane lipids and some specific proteins as ethanol targets, which may also be the case in endothelial cells. Future studies, based on current knowledge, will allow for a greater understanding of the contribution and underlying mechanisms of endothelial cells in ethanol-induced neurological toxicity, protecting neurological health against ethanol toxicity.

Effects of voluntary adolescent intermittent alcohol exposure and social isolation on adult alcohol intake in male rats

Initiating alcohol use in adolescence significantly increases the likelihood of developing adult alcohol use disorder (AUD). However, it has been difficult to replicate adolescent alcohol exposure leading to increased adult alcohol intake across differing preclinical models. In the present study, differentially housed male rats (group vs. single cages) were used to determine the effects of voluntary intermittent exposure of saccharin-sweetened ethanol during adolescence on adult intake of unsweetened 20% ethanol. Adolescent male rats were assigned to group- or isolated-housing conditions and underwent an intermittent 2-bottle choice in adolescence (water only or water vs. 0.2% saccharin/20% ethanol), and again in adulthood (water vs. 20% ethanol). Intermittent 2-bottle choice sessions lasted for 24 h, and occurred three days per week, for five weeks. Rats were moved from group or isolated housing to single-housing cages for 2-bottle choice tests and returned to their original housing condition on off days. During adolescence, rats raised in isolated-housing conditions consumed significantly more sweetened ethanol than rats raised in group-housing conditions, an effect that was enhanced across repeated exposures. In adulthood, rats raised in isolated-housing conditions and exposed to sweetened ethanol during adolescence also consumed significantly higher levels of unsweetened 20% ethanol compared to group-housed rats. The effect was most pronounced over the first five re-exposure sessions. Housing conditions alone had little effect on adult ethanol intake. These preclinical results suggest that social isolation stress, combined with adolescent ethanol exposure, may play a key role in adult AUD risk.

The Role of the Adenosine System on Emotional and Cognitive Disturbances Induced by Ethanol Binge Drinking in the Immature Brain and the Beneficial Effects of Caffeine

Binge drinking intake is the most common pattern of ethanol consumption by adolescents, which elicits emotional disturbances, mainly anxiety and depressive symptoms, as well as cognitive alterations. Ethanol exposure may act on the adenosine neuromodulation system by increasing adenosine levels, consequently increasing the activation of adenosine receptors in the brain. The adenosine modulation system is involved in the control of mood and memory behavior. However, there is a gap in the knowledge about the exact mechanisms related to ethanol exposure’s hazardous effects on the immature brain (i.e., during adolescence) and the role of the adenosine system thereupon. The present review attempts to provide a comprehensive picture of the role of the adenosinergic system on emotional and cognitive disturbances induced by ethanol during adolescence, exploring the potential benefits of caffeine administration in view of its action as a non-selective antagonist of adenosine receptors.

Repeated Cycles of Binge-Like Ethanol Exposure Induces Neurobehavioral Changes During Short- and Long-Term Withdrawal in Adolescent Female Rats

Alcohol consumption is spread worldwide and can lead to an abuse profile associated with severe health problems. Adolescents are more susceptible to addiction and usually consume ethanol in a binge drinking pattern. This form of consumption can lead to cognitive and emotional disorders, however scarce studies have focused on long-term hazardous effects following withdrawal periods after binge drinking in adolescents. Thus, the present study aims at investigating whether behavioral and cognitive changes persist until mid and late adulthood. Female Wistar rats (9-10 animals/group) received intragastric administration of four cycles of ethanol binge-like pattern (3.0 g/kg/day, 20% w/v; 3 days-on/4 days-off) from 35^th to 58^th days old, followed withdrawal checkpoints 1 day, 30 days, and 60 days. At each checkpoint period, behavioral tests of open field, object recognition test, elevated plus maze, and forced swimming test were performed, and blood and hippocampus were collected for oxidative biochemistry and brain-derived neurotrophic factor (BDNF) levels analysis, respectively. The results demonstrated that adolescent rats exposed to binge drinking displayed anxiogenic- and depressive-like phenotype in early and midadulthood, however, anxiety-like profile persisted until late adulthood. Similarly, short-term memory was impaired in all withdrawal periods analysed, including late adult life. These behavioral data were associated with oxidative damage in midadulthood but not BDNF alterations. Taken together, the present work highlights the long-lasting emotional and cognitive alterations induced by ethanol binge drinking during adolescence, even after a long period of abstinence, which might impact adult life.

Age-related differences in the effect of chronic alcohol on cognition and the brain: a systematic review

Adolescence is an important developmental period associated with increased risk for excessive alcohol use, but also high rates of recovery from alcohol use-related problems, suggesting potential resilience to long-term effects compared to adults. The aim of this systematic review is to evaluate the current evidence for a moderating role of age on the impact of chronic alcohol exposure on the brain and cognition. We searched Medline, PsycInfo, and Cochrane Library databases up to February 3, 2021. All human and animal studies that directly tested whether the relationship between chronic alcohol exposure and neurocognitive outcomes differs between adolescents and adults were included. Study characteristics and results of age-related analyses were extracted into reference tables and results were separately narratively synthesized for each cognitive and brain-related outcome. The evidence strength for age-related differences varies across outcomes. Human evidence is largely missing, but animal research provides limited but consistent evidence of heightened adolescent sensitivity to chronic alcohol's effects on several outcomes, including conditioned aversion, dopaminergic transmission in reward-related regions, neurodegeneration, and neurogenesis. At the same time, there is limited evidence for adolescent resilience to chronic alcohol-induced impairments in the domain of cognitive flexibility, warranting future studies investigating the potential mechanisms underlying adolescent risk and resilience to the effects of alcohol. The available evidence from mostly animal studies indicates adolescents are both more vulnerable and potentially more resilient to chronic alcohol effects on specific brain and cognitive outcomes. More human research directly comparing adolescents and adults is needed despite the methodological constraints. Parallel translational animal models can aid in the causal interpretation of observed effects. To improve their translational value, future animal studies should aim to use voluntary self-administration paradigms and incorporate individual differences and environmental context to better model human drinking behavior.

Maternal immune activation and adolescent alcohol exposure increase alcohol drinking and disrupt cortical-striatal-hippocampal oscillations in adult offspring

Maternal immune activation (MIA) is strongly associated with an increased risk of developing mental illness in adulthood, which often co-occurs with alcohol misuse. The current study aimed to begin to determine whether MIA, combined with adolescent alcohol exposure (AE), could be used as a model with which we could study the neurobiological mechanisms behind such co-occurring disorders. Pregnant Sprague-Dawley rats were treated with polyI:C or saline on gestational day 15. Half of the offspring were given continuous access to alcohol during adolescence, leading to four experimental groups: controls, MIA, AE, and Dual (MIA + AE). We then evaluated whether MIA and/or AE alter: (1) alcohol consumption; (2) locomotor behavior; and (3) cortical-striatal-hippocampal local field potentials (LFPs) in adult offspring. Dual rats, particularly females, drank significantly more alcohol in adulthood compared to all other groups. MIA led to reduced locomotor behavior in males only. Using machine learning to build predictive models from LFPs, we were able to differentiate Dual rats from control rats and AE rats in both sexes, and Dual rats from MIA rats in females. These data suggest that Dual "hits" (MIA + AE) increases substance use behavior and disrupts activity in reward-related circuits, and that this may be a valuable heuristic model we can use to study the neurobiological underpinnings of co-occurring disorders. Our future work aims to extend these findings to other addictive substances to enhance the translational relevance of this model, as well as determine whether amelioration of these circuit disruptions can reduce substance use behavior.

Epigenetic Effects of Addictive Drugs in the Nucleus Accumbens

Substance use induces long-lasting behavioral changes and drug craving. Increasing evidence suggests that epigenetic gene regulation contributes to the development and expression of these long-lasting behavioral alterations. Here we systematically review extensive evidence from rodent models of drug-induced changes in epigenetic regulation and epigenetic regulator proteins. We focus on histone acetylation and histone methylation in a brain region important for drug-related behaviors: the nucleus accumbens. We also discuss how experimentally altering these epigenetic regulators via systemically administered compounds or nucleus accumbens-specific manipulations demonstrate the importance of these proteins in the behavioral effects of drugs and suggest potential therapeutic value to treat people with substance use disorder. Finally, we discuss limitations and future directions for the field of epigenetic studies in the behavioral effects of addictive drugs and suggest how to use these insights to develop efficacious treatments.

Early-Life Sleep Deprivation Enhanced Alcohol Consumption in Adolescent Rats

Evidence in the literature suggests that sleep deprivation during early-life developmental stages, by impacting important processes such as the reward circuit maturation, may increase the vulnerability for alcohol and substance use. The mechanisms involved are not fully understood. In this study, utilizing our previously established model, we examined the impact of early-life sleep deprivation on alcohol consumption in adolescent rats. Male Sprague Dawley rats served as either the control (CON) or sleep-deprived (SD) group. Sleep deprivation was induced using a Pinnacle automated sleep deprivation apparatus. The SD group of rats was sleep deprived for 6–8 h/day for 14 days from postnatal day (PND)19 to PND32. At PND33, anxiety- and depression-like behaviors were assessed in rats using elevated plus maze and sucrose splash test, respectively. At PND39, alcohol consumption was assessed in rats for five consecutive days using the two-bottle choice paradigm, water versus 5% ethanol. SD rats exhibited significant anxiety- and depression-like behaviors as compared to CON rats. Interestingly, SD rats consumed a larger volume of alcohol when compared to CON rats, which was significantly higher at day 5 (mean of alcohol consumption (ml) ± SD; CON = 6.67 ± 3.42; SD = 19.00 ± 6.05, p = 0.0126). SD rats also showed high preference for alcohol over water, which was significantly higher at day 5 (mean of alcohol preference (%) ± SD; CON = 26.85 ± 14.97; SD = 57.69 ± 5.61, p = 0.014). Our data suggest that early-life sleep deprivation enhanced alcohol consumption in adolescent rats.

Astroglia in the Vulnerability and Maintenance of Alcohol Use Disorders

Changes induced in the morphology and the multiplicity of functional roles played by astrocytes in brain regions critical to the establishment and maintenance of alcohol abuse suggest that they make an important contribution to the vulnerability to alcohol use disorders. The understanding of the relevant mechanisms accounting for that contribution is complicated by the fact that alcohol itself acts directly on astrocytes altering their metabolism, gene expression, and plasticity, so that the ultimate result is a complex interaction of various cellular pathways, including intracellular calcium regulation, neuroimmune responses, and regulation of neurotransmitter and gliotransmitter release and uptake. The recent years have seen a steady increase in the characterization of several of the relevant mechanisms, but much remains to be done for a full understanding of the astrocytes' contribution to the vulnerability to alcohol dependence and abuse and for using that knowledge in designing effective therapies for AUDs.

Adolescent Intermittent Ethanol (AIE) Enhances the Dopaminergic Response to Ethanol within the Mesolimbic Pathway during Adulthood: Alterations in Cholinergic/Dopaminergic Genes Expression in the Nucleus Accumbens Shell

A consistent preclinical finding is that exposure to alcohol during adolescence produces a persistent hyperdopaminergic state during adulthood. The current experiments determine that effects of Adolescent Intermittent Ethanol (AIE) on the adult neurochemical response to EtOH administered directly into the mesolimbic dopamine system, alterations in dendritic spine and gene expression within the nucleus accumbens shell (AcbSh), and if treatment with the HDACII inhibitor TSA could normalize the consequences of AIE. Rats were exposed to the AIE (4 g/kg ig; 3 days a week) or water (CON) during adolescence, and all testing occurred during adulthood. CON and AIE rats were microinjected with EtOH directly into the posterior VTA and dopamine and glutamate levels were recorded in the AcbSh. Separate groups of AIE and CON rats were sacrificed during adulthood and Taqman arrays and dendritic spine morphology assessments were performed. The data indicated that exposure to AIE resulted in a significant leftward and upward shift in the dose-response curve for an increase in dopamine in the AcbSh following EtOH microinjection into the posterior VTA. Taqman array indicated that AIE exposure affected the expression of target genes (Chrna7, Impact, Chrna5). The data indicated no alterations in dendritic spine morphology in the AcbSh or any alteration in AIE effects by TSA administration. Binge-like EtOH exposure during adolescence enhances the response to acute ethanol challenge in adulthood, demonstrating that AIE produces a hyperdopaminergic mesolimbic system in both male and female Wistar rats. The neuroadaptations induced by AIE in the AcbSh could be part of the biological basis of the observed negative consequences of adolescent binge-like alcohol exposure on adult drug self-administration behaviors.

The persistent impact of adolescent binge alcohol on adult brain structural, cellular, and behavioral pathology: A role for the neuroimmune system and epigenetics

Adolescence is a critical neurodevelopmental window for maturation of brain structure, neurocircuitry, and glia. This development is sculpted by an individual's unique experiences and genetic background to establish adult level cognitive function and behavioral makeup. Alcohol abuse during adolescence is associated with an increased lifetime risk for developing an alcohol use disorder (AUD). Adolescents participate in heavy, episodic binge drinking that causes persistent changes in neurocircuitry and behavior. These changes may underlie the increased risk for AUD and might also promote cognitive deficits later in life. In this chapter, we have examined research on the persistent effects of adolescent binge-drinking both in humans and in rodent models. These studies implicate roles for neuroimmune signaling as well as epigenetic reprogramming of neurons and glia, which create a vulnerable neuroenvironment. Some of these changes are reversible, giving hope for future treatments to prevent many of the long-term consequences of adolescent alcohol abuse.

Exploration of alcohol use disorder-associated brain miRNA-mRNA regulatory networks

Transcriptomic changes in specific brain regions can influence the risk of alcohol use disorder (AUD), but the underlying mechanism is not fully understood. We investigated AUD-associated miRNA-mRNA regulatory networks in multiple brain regions by analyzing transcriptomic changes in two sets of postmortem brain tissue samples and ethanol-exposed human embryonic stem cell (hESC)-derived cortical interneurons. miRNA and mRNA transcriptomes were profiled in 192 tissue samples (Set 1) from eight brain regions (amygdala, caudate nucleus, cerebellum, hippocampus, nucleus accumbens, prefrontal cortex, putamen, and ventral tegmental area) of 12 AUD and 12 control European Australians. Nineteen differentially expressed miRNAs (fold-change>2.0 & P < 0.05) and 97 differentially expressed mRNAs (fold-change>2.0 & P < 0.001) were identified in one or multiple brain regions of AUD subjects. AUD-associated miRNA-mRNA regulatory networks in each brain region were constructed using differentially expressed and negatively correlated miRNA-mRNA pairs. AUD-relevant pathways (including CREB Signaling, IL-8 Signaling, and Axonal Guidance Signaling) were potentially regulated by AUD-associated brain miRNA-mRNA pairs. Moreover, miRNA and mRNA transcriptomes were mapped in additional 96 tissue samples (Set 2) from six of the above eight brain regions of eight AUD and eight control European Australians. Some of the AUD-associated miRNA-mRNA regulatory networks were confirmed. In addition, miRNA and mRNA transcriptomes were analyzed in hESC-derived cortical interneurons with or without ethanol exposure, and ethanol-influenced miRNA-mRNA regulatory networks were constructed. This study provided evidence that alcohol could induce concerted miRNA and mRNA expression changes in reward-related or alcohol-responsive brain regions. We concluded that altered brain miRNA-mRNA regulatory networks might contribute to AUD development.

Binge ethanol consumption-associated behavioral impairments in male mice using a gelatin-based drinking-in-the dark model

BACKGROUND

Acute intoxication caused by binge ethanol drinking is linked to widespread impairments in brain functions. Various alcohol administration paradigms have been used in animals to model the heterogeneous clinical manifestation of intoxication in people. It is challenging to model a procedure that produces "visible intoxication" in rodents; however, manipulation of variables such as route of alcohol administration, time of availability, frequency, and duration and amount of ethanol exposure has achieved some success. In the current study, we employed a modified drinking-in-the-dark model to assess the validity of this model in producing "post-ethanol consumption intoxication" impairments following prolonged repeated daily voluntary "binge" ethanol consumption.

METHODS

Adult male C57BL/6J mice were allowed a daily 3-h access to non-alcoholic plain or ethanol-containing gel during the dark cycle for a total of 83 days. After the initial 2-month daily DID, ethanol intake patterns were intensely characterized during the next 3 weeks. Immediately following the last DID session (day 83), plain and ethanol gel-consuming mice were then subjected to behavioral tests of locomotor ability and/or anxiety (cylinder, wire grip, open field) followed by blood ethanol concentration measurement.

RESULT

Mice exhibited a relatively consistent ethanol consumption pattern during and across daily access periods. Ethanol intake of individual mice positively correlated with blood ethanol concentration that averaged 61.64 ± 2.84 mg/dL (n = 12). Compared to the plain gel-consuming control mice, ethanol gel mice exhibited significant locomotor impairment as well as anxiety-like behavior, with the magnitude of impairments of key indices well correlated with blood ethanol levels.

CONCLUSION

The gelatin vehicle-based voluntary ethanol drinking-in-the-dark model reliably produced post consumption acute movement impairments as well as anxiety-like behaviors even after 2 months of daily binge ethanol consumption in male mice. Taken together, this mouse binge ethanol model should facilitate the investigation of mechanisms of binge drinking in subjects chronically abusing ethanol and the search for effective novel treatment strategies.

The effects of peri-adolescent alcohol use on the developing hippocampus

Adolescence is a period of continued brain development. Regions of the brain, such as the hippocampus, continue to undergo refinement and maturation throughout adolescence and into early adulthood. Adolescence is also a time of heightened sensitivity to novelty and reward, which contribute to an increase in risk-taking behaviors including the use of drugs and alcohol. Importantly, binge drinking is highly prevalent among adolescents and emerging adults. The hippocampus which is important for the integration of emotion, reward, homeostasis, and memory is particularly vulnerable to the neurotoxic effects of alcohol. In this chapter, we cover the fundamentals of hippocampal neuroanatomy and the current state of knowledge of the acute and chronic effects of ethanol in adolescent humans and adolescent rodent models. We focus on the hippocampal-dependent behavioral, structural, and neurochemical changes and identify knowledge gaps in our understanding of age-dependent neurobiological effects of alcohol use.

Voluntary Adolescent-Onset Alcohol Drinking Fails to Influence Alcohol Consumption or Anxiety-Like Behaviour in Adulthood in Female Alcohol-Preferring Rats

AIMS

Alcohol exposure during adolescence is associated with both increased risk for alcohol use disorders and anxiety in adulthood. Our present experiments examined this association using alcohol-preferring AA (Alko Alcohol) rats selected for high voluntary alcohol drinking.

METHODS

Two groups of female AA rats acquired alcohol drinking at different ages. We gave the adolescent-onset group free choice to 10% alcohol and water for seven weeks, starting on post-natal day 42 (PND 42), whereas the adult-onset group started drinking alcohol on PND 112. After the 7-week drinking, we withdrew the adolescent group from alcohol for two weeks, followed by another voluntary 7-week drinking period, started at the same age as the adult-onset group. We assessed anxiety-like behaviour repeatedly during alcohol drinking with open field and elevated plus maze tests. At the end of alcohol drinking, we also tested the rats using the light/dark box, stress-induced body temperature test and social dominance test.

RESULTS

During the first 7-week alcohol drinking, adolescent rats exhibited significantly slower acquisition of alcohol drinking and lower alcohol preference than the adult-onset group. However, when tested at the same age as the adult-onset rats, they displayed identical alcohol intake and preference. We found no alcohol-induced effects on anxiety- or stress-related behaviour in the experimental groups at any time points.

CONCLUSIONS

These data show that the genetically determined phenotype of high alcohol drinking of the female alcohol-preferring AA rats is not associated with a predisposition to develop anxiety-like behaviour following voluntary alcohol exposure, even when initiated during adolescence.

The role of sex in the persistent effects of adolescent alcohol exposure on behavior and neurobiology in rodents

Alcohol drinking is often initiated during adolescence, and this frequently escalates to binge drinking. As adolescence is also a period of dynamic neurodevelopment, preclinical evidence has highlighted that some of the consequences of binge drinking can be long lasting with deficits persisting into adulthood in a variety of cognitive-behavioral tasks. However, while the majority of preclinical work to date has been performed in male rodents, the rapid increase in binge drinking in adolescent female humans has re-emphasized the importance of addressing alcohol effects in the context of sex as a biological variable. Here we review several of the consequences of adolescent ethanol exposure in light of sex as a critical biological variable. While some alcohol-induced outcomes, such as non-social approach/avoidance behavior and sleep disruption, are generally consistent across sex, others are variable across sex, such as alcohol drinking, sensitivity to ethanol, social anxiety-like behavior, and induction of proinflammatory markers.

Adolescent oxycodone exposure inhibits withdrawal-induced expression of genes associated with the dopamine transmission

Prescription opioid misuse is a major public health concern among children and adolescents in the United States. Opioids are the most commonly abused drugs and are the fastest growing drug problem among adolescents. In humans and animals, adolescence is a particularly sensitive period associated with an increased response to drugs of abuse. Our previous studies indicate that oxycodone exposure during adolescence increases morphine reward in adulthood. How early drug exposure mediates long-term changes in the brain and behavior is not known, but epigenetic regulation is a likely mechanism. To address this question, we exposed mice to oxycodone or saline during adolescence and examined epigenetic modifications at genes associated with dopamine activity during adulthood at early and late withdrawal, in the ventral tegmental area (VTA). We then compared these with alterations in the VTA of adult-treated mice following an equivalent duration of exposure and withdrawal to determine if the effects of oxycodone are age dependent. We observed persistence of adolescent-like gene expression following adolescent oxycodone exposure relative to age-matched saline exposed controls, although dopamine-related gene expression was transiently activated at 1 day of withdrawal. Following prolonged withdrawal enrichment of the repressive histone mark, H3K27me3, was maintained, consistent with inhibition of gene regulation following adolescent exposure. By contrast, mice exposed to oxycodone as adults showed loss of the repressive mark and increased gene expression following 28 days of withdrawal following oxycodone exposure. Together, our findings provide evidence that adolescent oxycodone exposure has long-term epigenetic consequences in VTA of the developing brain.

Acute depletion of dopamine precursors in the human brain: effects on functional connectivity and alcohol attentional bias

Individuals who abuse alcohol often show exaggerated attentional bias (AB) towards alcohol-related cues, which is thought to reflect reward conditioning processes. Rodent studies indicate that dopaminergic pathways play a key role in conditioned responses to reward- and alcohol-associated cues. However, investigation of the dopaminergic circuitry mediating this process in humans remains limited. We hypothesized that depletion of central dopamine levels in adult alcohol drinkers would attenuate AB and that these effects would be mediated by altered function in frontolimbic circuitry. Thirty-four male participants (22-38 years, including both social and heavy drinkers) underwent a two-session, placebo-controlled, double-blind dopamine precursor depletion procedure. At each visit, participants consumed either a balanced amino acid (control) beverage or an amino acid beverage lacking dopamine precursors (order counterbalanced), underwent resting-state fMRI, and completed behavioral testing on three AB tasks: an alcohol dot-probe task, an alcohol attentional blink task, and a task measuring AB to a reward-conditioned cue. Dopamine depletion significantly diminished AB in each behavioral task, with larger effects among subjects reporting higher levels of binge drinking. The depletion procedure significantly decreased resting-state functional connectivity among ventral tegmental area, striatum, amygdala, and prefrontal regions. Beverage-related AB decreases were mediated by decreases in functional connectivity between the fronto-insular cortex and striatum and, for alcohol AB only, between anterior cingulate cortex and amygdala. The results support a substantial role for dopamine in AB, and suggest specific dopamine-modulated functional connections between frontal, limbic, striatal, and brainstem regions mediate general reward AB versus alcohol AB.

The effects of voluntary adolescent alcohol consumption on alcohol taste reactivity in Long Evans rats

RATIONALE

The relationship between age, ethanol intake, and the hedonic value of ethanol is key to understanding the motivation to consume ethanol.

OBJECTIVE

It is uncertain whether ethanol drinking during adolescence changes ethanol's hedonic value into adulthood.

METHODS

The current study compared voluntary intermittent ethanol consumption (IAE; 2-bottle choice; 20%v/v) among adolescent and adult Long-Evans rats to examine the effects of age and IAE on taste reactivity in adulthood. For taste reactivity, orally infused fluids included water, ethanol (5, 20, and 40%v/v), and sucrose (0.01, 0.1, 1M).

RESULTS

IAE results indicate that adolescents drank more ethanol during IAE but had a lower rate of change in ethanol consumption across time than adults due to initially high adolescent drinking. During taste reactivity testing for ethanol, IAE rats had greater hedonic responding, less aversive responding, and a more positive relationship between hedonic responses and ethanol concentration than water-receiving control rats. Hedonic responses had positive, while aversive responses had negative relationships with ethanol concentration and total ethanol consumed during IAE. Adolescent+IAE rats displayed less hedonic and more aversive responses to ethanol than Adult+IAE rats. Sucrose responding was unrelated to ethanol consumption.

CONCLUSIONS

These results suggest that ethanol consumption influences the future hedonic and aversive value of ethanol in a way that makes ethanol more palatable with greater prior consumption. However, it appears that those drinking ethanol as adolescents may be more resistant to this palatability shift than those first drinking as adults, suggesting different mechanisms of vulnerability to consumption escalation for adolescents and adults.

Pairing Binge Drinking and a High-Fat Diet in Adolescence Modulates the Inflammatory Effects of Subsequent Alcohol Consumption in Mice

Alcohol binge drinking (BD) and poor nutritional habits are two frequent behaviors among many adolescents that alter gut microbiota in a pro-inflammatory direction. Dysbiotic changes in the gut microbiome are observed after alcohol and high-fat diet (HFD) consumption, even before obesity onset. In this study, we investigate the neuroinflammatory response of adolescent BD when combined with a continuous or intermittent HFD and its effects on adult ethanol consumption by using a self-administration (SA) paradigm in mice. The inflammatory biomarkers IL-6 and CX3CL1 were measured in the striatum 24 h after BD, 3 weeks later and after the ethanol (EtOH) SA. Adolescent BD increased alcohol consumption in the oral SA and caused a greater motivation to seek the substance. Likewise, mice with intermittent access to HFD exhibited higher EtOH consumption, while the opposite effect was found in mice with continuous HFD access. Biochemical analyses showed that after BD and three weeks later, striatal levels of IL-6 and CX3CL1 were increased. In addition, in saline-treated mice, CX3CL1 was increased after continuous access to HFD. After oral SA procedure, striatal IL-6 was increased only in animals exposed to BD and HFD. In addition, striatal CX3CL1 levels were increased in all BD- and HFD-exposed groups. Overall, our findings show that adolescent BD and intermittent HFD increase adult alcohol intake and point to neuroinflammation as an important mechanism modulating this interaction.

The role of the orbitofrontal cortex and the nucleus accumbens for craving in alcohol use disorder

This study aimed to investigate structural and functional alterations of the reward system and the neurobiology of craving in alcohol use disorder (AUD). We hypothesized reduced volume of the nucleus accumbens (NAcc), reduced structural connectivity of the segment of the supero-lateral medial forebrain bundle connecting the orbitofrontal cortex (OFC) with the NAcc (OFC-NAcc), and reduced resting-state OFC-NAcc functional connectivity (FC). Furthermore, we hypothesized that craving is related to an increase of OFC-NAcc FC. Thirty-nine recently abstinent patients with AUD and 18 healthy controls (HC) underwent structural (T1w-MP2RAGE, diffusion-weighted imaging (DWI)) and functional (resting-state fMRI) MRI-scans. Gray matter volume of the NAcc, white matter microstructure (fractional anisotropy (FA)) and macrostructure (tract length) of the OFC-NAcc connection and OFC-NAcc FC were compared between AUD and HC using a mixed model MANCOVA controlling for age and gender. Craving was assessed using the thoughts subscale of the obsessive-compulsive drinking scale (OCDS) scale and was correlated with OFC-NAcc FC. There was a significant main effect of group. Results were driven by a volume reduction of bilateral NAcc, reduced FA in the left hemisphere, and reduced tract length of bilateral OFC-NAcc connections in AUD patients. OFC-NAcc FC did not differ between groups. Craving was associated with increased bilateral OFC-NAcc FC. In conclusion, reduced volume of the NAcc and reduced FA and tract length of the OFC-NAcc network suggest structural alterations of the reward network in AUD. Increased OFC-NAcc FC is associated with craving in AUD, and may contribute to situational alcohol-seeking behavior in AUD.

The Molecular Basis of Alcohol Use Disorder (AUD). Genetics, Epigenetics, and Nutrition in AUD: An Amazing Triangle

Alcohol use disorder (AUD) is a very common and complex disease, as alcohol is the most widely used addictive drug in the world. This disorder has an enormous impact on public health and social and private life, and it generates a huge number of social costs. Alcohol use stimulates hypothalamic-pituitary-adrenal (HPA) axis responses and is the cause of many physical and social problems (especially liver disease and cancer), accidental injury, and risky sexual behavior. For years, researchers have been trying to identify the genetic basis of alcohol use disorder, the molecular mechanisms responsible for its development, and an effective form of therapy. Genetic and environmental factors are known to contribute to the development of AUD, and the expression of genes is a complicated process that depends on epigenetic modulations. Dietary nutrients, such as vitamins, may serve as one these modulators, as they have a direct impact on epigenomes. In this review, we connect gathered knowledge from three emerging fields-genetics, epigenetics, and nutrition-to form an amazing triangle relating to alcohol use disorder.

Adolescent intermittent ethanol exposure induces sex-dependent divergent changes in ethanol drinking and motor activity in adulthood in C57BL/6J mice

With alcohol readily accessible to adolescents, its consumption leads to many adverse effects, including impaired learning, attention, and behavior. Adolescents report higher rates of binge drinking compared to adults. They are also more prone to substance use disorder in adulthood due to physiological changes during the adolescent developmental period. We used C57BL/6J male and female mice to investigate the long-lasting impact of binge ethanol exposure during adolescence on voluntary ethanol intake and open field behavior during later adolescence (Experiment 1) and during emerging adulthood (Experiment 2). The present set of experiments were divided into four stages: (1) adolescent intermittent vapor inhalation exposure, (2) abstinence, (3) voluntary ethanol intake, and (4) open field behavioral testing. During adolescence, male and female mice were exposed to air or ethanol using intermittent vapor inhalation from postnatal day (PND) 28-42. Following this, mice underwent short-term abstinence from PND 43-49 (Experiment 1) or protracted abstinence from PND 43-69 (Experiment 2). Beginning on PND 50-76 or PND 70-97, mice were assessed for intermittent voluntary ethanol consumption using a two-bottle choice drinking procedure over 28 days. Male adolescent ethanol-exposed mice showed increased ethanol consumption following short-term abstinence and following protracted abstinence. In contrast, female mice showed no changes in ethanol consumption following short-term abstinence and decreased ethanol consumption following protracted abstinence. There were modest changes in open field behavior following voluntary ethanol consumption in both experiments. These data demonstrate a sexually divergent shift in ethanol consumption following binge ethanol exposure during adolescence and differences in open field behavior. These results highlight sex-dependent vulnerability to developing substance use disorders in adulthood.

Effects of vapourized THC and voluntary alcohol drinking during adolescence on cognition, reward, and anxiety-like behaviours in rats

Cannabis and alcohol co-use is prevalent in adolescence, but the long-term behavioural effects of this co-use remain largely unexplored. The aim of this study is to investigate the effects of adolescent alcohol and Δ⁹-tetrahydracannabinol (THC) vapour co-exposure on cognitive- and reward-related behaviours. Male Sprague-Dawley rats received vapourized THC (10 mg vapourized THC/four adolescent rats) or vehicle every other day (from post-natal day (PND) 28-42) and had continuous voluntary access to ethanol (10% volume/volume) in adolescence. Alcohol intake was measured during the exposure period to assess the acute effects of THC on alcohol consumption. In adulthood (PND 56+), rats underwent behavioural testing. Adolescent rats showed higher alcohol preference, assessed using the two-bottle choice test, on days on which they were not exposed to THC vapour. In adulthood, rats that drank alcohol as adolescents exhibited short-term memory deficits and showed decreased alcohol preference; on the other hand, rats exposed to THC vapour showed learning impairments in the delay-discounting task. Vapourized THC, alcohol or their combination had no effect on anxiety-like behaviours in adulthood. Our results show that although adolescent THC exposure acutely affects alcohol drinking, adolescent alcohol and cannabis co-use may not produce long-term additive effects.

CXCR4 inhibition with AMD3100 attenuates amphetamine induced locomotor activity in adolescent Long Evans male rats

Adolescent psychostimulant abuse has been on the rise over the past decade. This trend has demonstrable ramifications on adolescent behavior and brain morphology, increasing risk for development of addiction during adolescence and in later adulthood. Neuroimmune substrates are implicated in the etiology of substance use disorders. To add to this body of work, the current study was developed to explore the role of a chemokine receptor, CXC Chemokine Receptor 4 (CXCR4), in the development of amphetamine (AMPH) sensitization. We targeted CXCR4 as it is implicated in developmental processes, dopaminergic transmission, neuroimmune responses, and the potentiation of psychostimulant abuse pathology. To evaluate the role of CXCR4 activity on the development of AMPH sensitization, a CXCR4 antagonist (Plerixafor; AMD3100) was administered to rats as a pretreatment variable. Specifically, adolescent Long Evans male rats (N = 37) were divided into four groups: (1) AMD3100 (IP, 4.0 mg/kg) + AMPH (IP, 4.0 mg/kg), (2) saline (SAL; 0.9% NaCl) + AMPH, (3) AMD3100 + SAL, and (4) SAL + SAL. Animals were first habituated to locomotor activity (LMA) chambers, then injected with a pretreatment drug (AMD3100 or SAL) followed by AMPH or SAL every other for four days. After a one-week withdrawal period, all animals were administered a low challenge dose of AMPH (IP, 1.0 mg/kg). AMPH-injected rats displayed significantly more locomotor activity compared to controls across all testing days. CXCR4 antagonism significantly attenuated AMPH-induced locomotor activity. On challenge day, AMD3100 pre-treated animals exhibited diminutive AMPH-induced locomotor activity compared to SAL pre-treated animals. Postmortem analyses of brain tissue revealed elevated CXCR4 protein levels in the striatum of all experimental groups. Our results implicate CXCR4 signaling in the development of AMPH sensitization and may represent an important therapeutic target for future research in psychostimulant abuse.

Resilience in the age of COVID-19

Resilience is broadly defined as the ability to bounce back from adversity or trauma. Recent advances in resilience research have shifted away from merely describing individual characteristics towards focusing on the complex interactions between individuals and their dynamic personal, community and cultural contexts. It is clear that resilience involves both neurobiological and cultural processes. Neurobiological contributions include genes, epigenetics, stress-response systems, the immune system and neural circuitry. Culture helps to elucidate collective systems of belief and accepted positive adaptations. Importantly, resilience can also be affected by evidence-based interventions and deliberate practice on the part of the individual. This review seeks to understand resilience as a complex and active process that is shaped by neurobiological profiles, developmental experiences, cultural and temporal contexts, and practical training. It uses the COVID-19 pandemic as a case example to better understand individual and group responses to tragedy. We suggest practical recommendations to help populations around the world cope and recover from the global threat of COVID-19.

Adolescent intermittent ethanol exposure does not alter responsiveness to ifenprodil or expression of vesicular GABA and glutamate transporters

Adolescent intermittent ethanol (AIE) exposure in the rat results in a retention of adolescent-like responsiveness to ethanol into adulthood characterized by enhanced sensitivity to socially facilitating and decreased sensitivity to socially suppressing and aversive effects. Similar pattern of responsiveness to social and aversive effects of the selective glutamate NMDA NR2B receptor antagonist ifenprodil is evident in adolescent rats, suggesting that AIE would also retain this pattern of ifenprodil sensitivity into adulthood. Social (Experiment 1) and aversive (measured via conditioned taste aversion; Experiment 2) effects of ifenprodil were assessed in adult male and female rats following AIE exposure. Sensitivity to the social and aversive effects of ifenprodil was not affected by AIE exposure. Experiment 3 assessed protein expression of vesicular transporters of GABA (vGAT) and glutamate (vGlut2) within the prelimbic cortex and nucleus accumbens in adolescents versus adults and in AIE adults versus controls. vGlut2 expression was higher in adolescents relative to adults within the PrL, but lower in the NAc. AIE adults did not retain these adolescent-typical ratios. These findings suggest that AIE is not associated with the retention of adolescent-typical sensitivity to NR2B receptor antagonism, along with no AIE-induced shift in vGlut2 to vGAT ratios.

Impact of High Fat Diet and Ethanol Consumption on Neurocircuitry Regulating Emotional Processing and Metabolic Function

The prevalence of psychiatry disorders such as anxiety and depression has steadily increased in recent years in the United States. This increased risk for anxiety and depression is associated with excess weight gain, which is often due to over-consumption of western diets that are typically high in fat, as well as with binge eating disorders, which often overlap with overweight and obesity outcomes. This finding suggests that diet, particularly diets high in fat, may have important consequences on the neurocircuitry regulating emotional processing as well as metabolic functions. Depression and anxiety disorders are also often comorbid with alcohol and substance use disorders. It is well-characterized that many of the neurocircuits that become dysregulated by overconsumption of high fat foods are also involved in drug and alcohol use disorders, suggesting overlapping central dysfunction may be involved. Emerging preclinical data suggest that high fat diets may be an important contributor to increased susceptibility of binge drug and ethanol intake in animal models, suggesting diet could be an important aspect in the etiology of substance use disorders. Neuroinflammation in pivotal brain regions modulating metabolic function, food intake, and binge-like behaviors, such as the hypothalamus, mesolimbic dopamine circuits, and amygdala, may be a critical link between diet, ethanol, metabolic dysfunction, and neuropsychiatric conditions. This brief review will provide an overview of behavioral and physiological changes elicited by both diets high in fat and ethanol consumption, as well as some of their potential effects on neurocircuitry regulating emotional processing and metabolic function.