Alcohol and the Brain: Neuronal Molecular Targets, Synapses, and Circuits

Brain ethanol metabolism and mitochondria

Alcohol abuse and dependence in humans causes an extreme shift in metabolism for which the human brain is not evolutionarily prepared. Oxidation of ethanol and acetaldehyde are not regulated, making ethanol a dominating metabolic substrate that prevents the activity of enzymes from oxidizing their usual endogenous substrates. The enzymes required to oxidize ethanol across the variety of affected tissues all produce acetaldehyde which is then converted to acetate by aldehyde dehydrogenases (ALDHs). ALDHs are NAD+-dependent enzymes, and mitochondrial ALDH2 is likely the primary contributor to ethanol-derived acetaldehyde clearance in cells. Metabolism of alcohol has several adverse effects on mitochondria including increased free radical levels, hyperacetylation of mitochondrial proteins, and excessive mitochondrial fragmentation. This review discusses the role of astrocytic and neuronal mitochondria in ethanol metabolism that contributes to the acute and chronic changes in mitochondrial function and morphology, that might promote tolerance, dependence and withdrawal. We also propose potential modes of therapeutic intervention to reduce the toxicity of chronic alcohol consumption.

Corticotropin Releasing Factor Binding Protein as a Novel Target to Restore Brain Homeostasis: Lessons Learned From Alcohol Use Disorder Research

Stress is well-known to contribute to the development of many psychiatric illnesses including alcohol and substance use disorder (AUD and SUD). The deleterious effects of stress have also been implicated in the acceleration of biological age, and age-related neurodegenerative disease. The physio-pathology of stress is regulated by the corticotropin-releasing factor (CRF) system, the upstream component of the hypothalamic-pituitary-adrenal (HPA) axis. Extensive literature has shown that dysregulation of the CRF neuroendocrine system contributes to escalation of alcohol consumption and, similarly, chronic alcohol consumption contributes to disruption of the stress system. The CRF system also represents the central switchboard for regulating homeostasis, and more recent studies have found that stress and aberrations in the CRF pathway are implicated in accelerated aging and age-related neurodegenerative disease. Corticotropin releasing factor binding protein (CRFBP) is a secreted glycoprotein distributed in peripheral tissues and in specific brain regions. It neutralizes the effects of CRF by sequestering free CRF, but may also possess excitatory function by interacting with CRF receptors. CRFBP’s dual role in influencing CRF bioavailability and CRF receptor signaling has been shown to have a major part in the HPA axis response. Therefore, CRFBP may represent a valuable target to treat stress-related illness, including: development of novel medications to treat AUD and restore homeostasis in the aging brain. This narrative review focuses on molecular mechanisms related to the role of CRFBP in the progression of addictive and psychiatric disorders, biological aging, and age-related neurodegenerative disease. We provide an overview of recent studies investigating modulation of this pathway as a potential therapeutic target for AUD and age-related neurodegenerative disease.

Chronic ethanol exposure during adolescence impairs simple spike activity of cerebellar Purkinje cells in vivo in mice

Cerebellar Purkinje cells (PCs) play critical roles in motor coordination and motor learning through their simple spike (SS) activity. Previous studies have shown that chronic ethanol exposure (CEE) in adolescents impairs learning, attention, and behavior, at least in part by impairing the activity of cerebellar PCs. In this study, we investigated the effect of CEE on the SS activity in urethane-anesthetized adolescent mice by in vivo electrophysiological recordings and pharmacological methods. Our results showed that the cerebellar PCs in CEE adolescent mice expressed a significant decrease in the frequency and an increase in the coefficient of variation (CV) of SS than control group. Blockade of ɤ-aminobutyric acid A (GABA_A) receptor did not change the frequency and CV of SS firing in control group but produced a significant increase in the frequency and a decrease in the CV of SS firing in CEE mice. The CEE-induced decrease in SS firing rate and increase in CV were abolished by application of an N-methyl-D-aspartate (NMDA) receptor blocker, D-APV, but not by anα-amino-3-hydroxy-5-methyl -4-isoxazolepropionic acid (AMPA) receptor antagonist, NBQX. Notably, the spontaneous spike rate of molecular layer interneurons (MLIs) in CEE mice was significantly higher than control group, which was also abolished by application of D-APV. These results indicate that adolescent CEE enhances the spontaneous spike firing rate of MLIs through activation of NMDA receptor, resulting in a depression in the SS activity of cerebellar PCs in vivo in mice.

Methylmercury plus Ethanol Exposure: How Much Does This Combination Affect Emotionality?

Mercury is a heavy metal found in organic and inorganic forms that represents an important toxicant with impact on human health. Mercury can be released in the environment by natural phenoms (i.e., volcanic eruptions), industrial products, waste, or anthropogenic actions (i.e., mining activity). Evidence has pointed to mercury exposure inducing neurological damages related to emotional disturbance, such as anxiety, depression, and insomnia. The mechanisms that underlie these emotional disorders remain poorly understood, although an important role of glutamatergic pathways, alterations in HPA axis, and disturbance in activity of monoamines have been suggested. Ethanol (EtOH) is a psychoactive substance consumed worldwide that induces emotional alterations that have been strongly investigated, and shares common pathophysiological mechanisms with mercury. Concomitant mercury and EtOH intoxication occur in several regions of the world, specially by communities that consume seafood and fish as the principal product of nutrition (i.e., Amazon region). Such affront appears to be more deleterious in critical periods of life, such as the prenatal and adolescence period. Thus, this review aimed to discuss the cellular and behavioral changes displayed by the mercury plus EtOH exposure during adolescence, focused on emotional disorders, to answer the question of whether mercury plus EtOH exposure intensifies depression, anxiety, and insomnia observed by the toxicants in isolation.

Sex differences in the development of conditioned place preference induced by intragastric alcohol administration in mice

BACKGROUND

The present study aimed to identify for the first time sex differences in the development of CPP induced by intragastric alcohol administration in mice.

METHODS

Male and female adult Swiss mice were submitted to 16 days of conditioning with alcohol (0.5-3.0 g/kg, N = 8/dose/sex), with 2 post-conditioning tests (after 8 and 16 sessions) during the protocol.

RESULTS

8 days of conditioning (4 alcohol sessions, 4 saline sessions) with intragastric alcohol administration were sufficient to induce CPP in male mice at the doses of 1.0, 1.5 and 2.0 g/kg. However, only higher doses (2.0, 2.5 and 3.0 g/kg) induced CPP in female mice using an 8-day conditioning protocol, while a 16-day conditioning protocol was necessary for the development of intragastric alcohol-induced CPP at the doses of 1.0 and 1.5 g/kg. Regardless of the conditioning protocol, higher doses or alcohol that had rewarding effects in females (2.5 and 3.0 g/kg) did not induce CPP in males, with a significant difference between males and females at those doses. Analysis of the potency (EC₅₀) and efficacy (E_max) of alcohol in inducing CPP when administered intragastrically in male and female mice showed significant sex differences with 8 conditioning sessions.

CONCLUSIONS

Our data show a clear protocol (8 vs 16 days) and dose difference between male and female Swiss mice regarding the development of CPP induced by intragastric alcohol administration. Intragastric alcohol administration is closer to human drinking, and our protocol provides a more translational approach to studying the rewarding effects of alcohol in mice.

Effect of ketamine on binge drinking patterns in crossed high alcohol-preferring (cHAP) mice

BACKGROUND

Previous research has demonstrated the utility of subanesthetic doses of ketamine in decreasing binge (Drinking-in-the-Dark, or DID) 20% alcohol intake in female inbred (C57BL/6J) mice when administered 12 hours prior to alcohol access (Crowley et al., 2019). In the current study, we assess the efficacy of a similar ketamine pretreatment using male and female selectively bred, crossed High Alcohol Preferring (cHAP) mice, which also drink to intoxication, but are not inbred. We hypothesized that ketamine would decrease binge alcohol intake without impacting locomotor activity.

METHODS AND RESULTS

Subjects were 28 adult cHAP mice. Mice first received a 2-week DID drinking history using 2-h/day alcohol access. On day 12, prior to ketamine treatment, the average blood ethanol concentration (BEC) was 130 mg/dL, confirming that mice reliably reached intoxicating BECs. On day 15, mice were given 0, 3, or 10 mg/kg of ketamine 12 hours prior to the DID session. Ketamine did not decrease total (2-h) alcohol consumption or locomotion. Interestingly, the 10 mg/kg dose of ketamine did alter the drinking pattern in male mice, decreasing front-loading for a single day. We opted to then increase the doses to 32 or 100 mg/kg (i.e., an anesthetic dose) two days after the initial treatment, keeping the saline control. Mice of both sexes decreased total binge alcohol intake at the 100 mg/kg dose only, but again, the effect only lasted one day.

CONCLUSIONS

The current study found that cHAP mice reached more than double the BECs observed in C57BL/6J mice during DID, but did not respond to subanesthetic ketamine. Modest efficacy was found for ketamine pretreatment at anesthetic doses. Differences in findings may be due to differential intake during DID, or genetic differences between C57Bl/6J mice and cHAP mice. Drug efficacy in multiple models is important for discovering reliable pharmacotherapies for alcoholism.

Adolescent neuroimmune function and its interaction with alcohol

Adolescence is an evolutionarily conserved developmental period associated with behavioral change, including increased risk-taking and alcohol use. Experimentation with alcohol typically begins in adolescence and transitions to binge-like patterns of consumption. Alcohol exposure during adolescence can alter normative changes in brain structure and function. Understanding mechanisms by which ethanol impacts neurodevelopmental processes is important for preventing and ameliorating the deleterious consequences of adolescent alcohol abuse. This review focuses on the neuroimmune system as a key contributor to ethanol-induced changes in adolescent brain and behavior. After brief review of neuroimmune system development, acute and chronic effects of ethanol on adolescent neuroimmune functioning are addressed. Comparisons between stress/immunological challenges and ethanol on adolescent neuroimmunity are reviewed, as cross-sensitization is relevant during adolescence. The mechanisms by which ethanol alters neuroimmune functioning are then discussed, as they may portend development of neuropathological consequences and thus increase vulnerability to subsequent challenges and potentiate addictive behaviors.

Changes in the metabolic profile of human male postmortem frontal cortex and cerebrospinal fluid samples associated with heavy alcohol use

Heavy alcohol use is one of the top causes of disease and death in the world. The brain is a key organ affected by heavy alcohol use. Here, our aim was to measure changes caused by heavy alcohol use in the human brain metabolic profile. We analyzed human postmortem frontal cortex and cerebrospinal fluid (CSF) samples from males with a history of heavy alcohol use (n = 74) and controls (n = 74) of the Tampere Sudden Death Series cohort. We used a nontargeted liquid chromatography mass spectrometry-based metabolomics method. We observed differences between the study groups in the metabolite levels of both frontal cortex and CSF samples, for example, in amino acids and derivatives, and acylcarnitines. There were more significant alterations in the metabolites of frontal cortex than in CSF. In the frontal cortex, significant alterations were seen in the levels of neurotransmitters (e.g., decreased levels of GABA and acetylcholine), acylcarnitines (e.g., increased levels of acylcarnitine 4:0), and in some metabolites associated with alcohol metabolizing enzymes (e.g., increased levels of 2-piperidone). Some of these changes were also significant in the CSF samples (e.g., elevated 2-piperidone levels). Overall, these results show the metabolites associated with neurotransmitters, energy metabolism and alcohol metabolism, were altered in human postmortem frontal cortex and CSF samples of persons with a history of heavy alcohol use.

Acute alcohol intoxication modulates the temporal dynamics of resting electroencephalography networks

This study aimed to provide a currently missing link between general intoxication-induced changes in overall brain activity and the multiple cognitive control deficits typically observed during acute alcohol intoxication. For that purpose, we analyzed the effects of acute alcohol intoxication (1.1‰) on the four archetypal electroencephalography (EEG) resting networks (i.e., microstates A-D) and their temporal dynamics (e.g., coverage and transitions from one microstate to another), as well as on self-reported resting-state cognition in n = 22 healthy young males using a counterbalanced within-subject design. Our microstate analyses indicated that alcohol increased the coverage of the visual processing-related microstate B at the expense of the autonomic processing-related microstate C. Add-on exploratory analyses revealed that alcohol increased transitions from microstate C to microstate B and decreased bidirectional transitions between microstate C and the attention-related microstate D. In line with the observed alcohol-induced decrease of the autonomic processing-related microstate C, participants reported decreases of their somatic awareness during intoxication, which were positively associated with more transitions from microstate C to microstate B. In sum, the observed effects provide mechanistic insights into how alcohol might hamper cognitive processing by generally prioritizing the bottom-up processing of visual stimuli over top-down internal information processing. The fact that this was found during the resting state further proves that alcohol-induced changes in brain activity are continuously present and do not only emerge during demanding situations or tasks.

Subjective executive function deficits in hazardous alcohol drinkers

BACKGROUND

Dependent alcohol drinkers exhibit differences in the structure and function of the brain, and impairments in cognitive function, including executive functions (EFs). Less is known about the impact of non-dependent but hazardous use (that which raises the risk of harm), and it is also unclear to what extent executive impairments in this cohort affect real-world function. The current study examines the relationship between alcohol use, EF and alcohol-related problems, in the general population.

METHODS

A between-groups cross-sectional design assessed EF across two levels of drinking; hazardous (Alcohol Use Disorders Identification Test (AUDIT) score of ⩾8) and non-hazardous. Alcohol drinkers (n = 666; 136 male; 524 female; six not disclosed; aged 28.02 ± 10.40 years) completed validated questionnaires online assessing subjective EF, alcohol use and alcohol-related problems.

RESULTS

Organisation, Strategic Planning, Impulse Control and overall function were significantly impaired in hazardous drinkers. Furthermore, the effect of alcohol on EF, partially mediated the relationship between alcohol use and alcohol-related problems.

CONCLUSION

Hazardous drinking was associated with lower subjective EF, and this mediated the effect of alcohol on alcohol-related problems. This may be due to changes in prefrontal brain regions, which could indicate greater risk for the development of alcohol dependence (AD). Future research should use additional means to assess EF in hazardous drinkers, including recovery of function, development of AD and the relationship between cognition and alcohol-related daily problems.

Alcohol and the brain: from genes to circuits

Alcohol use produces wide-ranging and diverse effects on the central nervous system. It influences intracellular signaling mechanisms, leading to changes in gene expression, chromatin remodeling, and translation. As a result of these molecular alterations, alcohol affects the activity of neuronal circuits. Together, these mechanisms produce long-lasting cellular adaptations in the brain that in turn can drive the development and maintenance of alcohol use disorder (AUD). We provide an update on alcohol research, focusing on multiple levels of alcohol-induced adaptations, from intracellular changes to changes in neural circuits. A better understanding of how alcohol affects these diverse and interlinked mechanisms may lead to the identification of novel therapeutic targets and to the development of much-needed novel and efficacious treatment options.

Research Needs for Inpatient Management of Severe Alcohol Withdrawal Syndrome: An Official American Thoracic Society Research Statement

Background: Severe alcohol withdrawal syndrome (SAWS) is highly morbid, costly, and common among hospitalized patients, yet minimal evidence exists to guide inpatient management. Research needs in this field are broad, spanning the translational science spectrum. Goals: This research statement aims to describe what is known about SAWS, identify knowledge gaps, and offer recommendations for research in each domain of the Institute of Medicine T0-T4 continuum to advance the care of hospitalized patients who experience SAWS. Methods: Clinicians and researchers with unique and complementary expertise in basic, clinical, and implementation research related to unhealthy alcohol consumption and alcohol withdrawal were invited to participate in a workshop at the American Thoracic Society 2019 International Conference. The committee was subdivided into four groups on the basis of interest and expertise: T0-T1 (basic science research with translation to humans), T2 (research translating to patients), T3 (research translating to clinical practice), and T4 (research translating to communities). A medical librarian conducted a pragmatic literature search to facilitate this work, and committee members reviewed and supplemented the resulting evidence, identifying key knowledge gaps. Results: The committee identified several investigative opportunities to advance the care of patients with SAWS in each domain of the translational science spectrum. Major themes included 1) the need to investigate non-γ-aminobutyric acid pathways for alcohol withdrawal syndrome treatment; 2) harnessing retrospective and electronic health record data to identify risk factors and create objective severity scoring systems, particularly for acutely ill patients with SAWS; 3) the need for more robust comparative-effectiveness data to identify optimal SAWS treatment strategies; and 4) recommendations to accelerate implementation of effective treatments into practice. Conclusions: The dearth of evidence supporting management decisions for hospitalized patients with SAWS, many of whom require critical care, represents both a call to action and an opportunity for the American Thoracic Society and larger scientific communities to improve care for a vulnerable patient population. This report highlights basic, clinical, and implementation research that diverse experts agree will have the greatest impact on improving care for hospitalized patients with SAWS.

Dietary, Cultural and Pathogens-Related Selective Pressures Shaped Differential Adaptive Evolution Among Native Mexican Populations

Native American genetic ancestry has been remarkably implicated with increased risk of diverse health issues in several Mexican populations, especially in relation to the dramatic changes in environmental, dietary, and cultural settings they have recently undergone. In particular, the effects of these ecological transitions and Westernization of lifestyles have been investigated so far predominantly on Mestizo individuals. Nevertheless, indigenous groups, rather than admixed Mexicans, have plausibly retained the highest proportions of genetic components shaped by natural selection in response to the ancient milieu experienced by Mexican ancestors during their pre-Columbian evolutionary history. These formerly adaptive variants have the potential to represent the genetic determinants of some biological traits that are peculiar to Mexican people, as well as a reservoir of loci with possible biomedical relevance. To test such a hypothesis, we used genome-wide genotype data to infer the unique adaptive evolution of Native Mexican groups selected as reasonable descendants of the main pre-Columbian Mexican civilizations. A combination of haplotype-based and gene-network analyses enabled us to detect genomic signatures ascribable to polygenic adaptive traits plausibly evolved by the main genetic clusters of Mexican indigenous populations to cope with local environmental and/or cultural conditions. Some of these adaptations were found to play a role in modulating the susceptibility/resistance of these groups to certain pathological conditions, thus providing new evidence that diverse selective pressures have contributed to shape the current biological and disease-risk patterns of present-day Native and Mestizo Mexican populations.

Somatostatin neurons control an alcohol binge drinking prelimbic microcircuit in mice

Somatostatin (SST) neurons have been implicated in a variety of neuropsychiatric disorders such as depression and anxiety, but their role in substance use disorders, including alcohol use disorder (AUD), is not fully characterized. Here, we found that repeated cycles of alcohol binge drinking via the Drinking-in-the-Dark (DID) model led to hypoactivity of SST neurons in the prelimbic (PL) cortex by diminishing their action potential firing capacity and excitatory/inhibitory transmission dynamic. We examined their role in regulating alcohol consumption via bidirectional chemogenetic manipulation. Both hM3Dq-induced excitation and KORD-induced silencing of PL SST neurons reduced alcohol binge drinking in males and females, with no effect on sucrose consumption. Alcohol binge drinking disinhibited pyramidal neurons by augmenting SST neurons-mediated GABA release and synaptic strength onto other GABAergic populations and reducing spontaneous inhibitory transmission onto pyramidal neurons. Pyramidal neurons additionally displayed increased intrinsic excitability. Direct inhibition of PL pyramidal neurons via hM4Di was sufficient to reduce alcohol binge drinking. Together these data revealed an SST-mediated microcircuit in the PL that modulates the inhibitory dynamics of pyramidal neurons, a major source of output to subcortical targets to drive reward-seeking behaviors and emotional response.

Using the Drosophila Transcriptional Reporter of Intracellular Calcium (TRIC) to examine lasting ethanol-induced changes in neuroexcitability

The Drosophila transcriptional reporter of intracellular calcium (TRIC) is a genetic tool used to measure lasting changes in neuroexcitability. Both pan-neuronal and dopaminergic cells were examined with TRIC to test the hypothesis that ethanol exposure causes lasting changes in adult brain neuroexcitability. We found little to no impact on TRIC signal following acute and repeated ethanol vapor exposures. This work shows that TRIC may be useful in future investigations such as developmental or chronic drug exposure paradigms.

Electroencephalographic neurofeedback as a tool for reducing harm and risk associated with alcohol use disorder: A critical review

ISSUES

Alcohol use disorder (AUD) causes the highest harms around the world. Many people use alcohol to reduce stress and anxiety, considered as risk factors for AUD. Chronic alcohol use leads to changes in the reward system and the high level of stress may exacerbate neuroendocrine responses. Electroencephalographic (EEG) neurofeedback shows reduction of stress, anxiety and alcohol abuse and it could be an important tool for reducing harm and risk associated with AUD. The aim of this paper is to review the studies that investigated the effects of EEG neurofeedback in subjects with AUD and it proposes to discuss this intervention as a tool for reducing harm and risk in AUD.

APPROACH

Medline, PsycINFO and LILACS databases were searched and appropriated terms were used. Inclusion criterion was adopted. The year of publication was not limited because of the scarce number of studies. Eighty-two papers returned and eight were included. A critical review was conducted.

KEY FINDINGS

Most of the papers analysed used the alpha/theta protocol to reduce the 'hyperexcitation' of the nervous system. This protocol provides relaxation, decreases anxiety or stress, prevents alcohol relapse, maintains abstinence and increases the feeling of well-being.

IMPLICATIONS

EEG neurofeedback has important effects on AUD and anxiety or stress. Studies reinforce the use of EEG neurofeedback as an alternative tool for reducing harm and risk in AUD.

CONCLUSION

EEG neurofeedback is an intervention to treat AUD, specifically, to reduce harm and risk. However, more randomised studies are necessary to consolidate the effectiveness of the technique.

Chronic Exposure to Alcohol Inhibits New Myelin Generation in Adult Mouse Brain

Chronic alcohol consumption causes cognitive impairments accompanying with white matter atrophy. Recent evidence has shown that myelin dynamics remain active and are important for brain functions in adulthood. For example, new myelin generation is required for learning and memory functions. However, it remains undetermined whether alcohol exposure can alter myelin dynamics in adulthood. In this study, we examine the effect of chronic alcohol exposure on myelin dynamics by using genetic approaches to label newly generated myelin (NG2-CreERt; mT/mG). Our results indicated that alcohol exposure (either 5% or 10% in drinking water) for 3 weeks remarkably reduced mGFP + /NG2- new myelin and mGFP + /CC1 + new oligodendrocytes in the prefrontal cortex and corpus callosum of 6-month-old NG2-CreERt; mT/mG mice as compared to controls without changing the mGFP + /NG2 + oligodendrocyte precursor cells (OPCs) density, suggesting that alcohol exposure may inhibit oligodendrocyte differentiation. In support with these findings, the alcohol exposure did not significantly alter apoptotic cell number or overall MBP expression in the brains. Further, the alcohol exposure decreased the histone deacetylase1 (HDAC1) expression in mGFP + /NG2 + OPCs, implying epigenetic mechanisms were involved in the arrested OPC differentiation. Together, our results indicate that chronic exposure to alcohol can inhibit myelinogenesis in the adult mouse brain and that may contribute to alcohol-related cognitive impairments.

The Interaction of Single Nucleotide Polymorphisms on Fibroblast Growth Factor 19 Superfamily Genes Is Associated With Alcohol Dependence-Related Aggression

Alcohol dependence (AD) is characterized by compulsive alcohol consumption, which involves behavioral impairments such as aggression. Members of fibroblast growth factor (FGF) 19 superfamily, including FGF19, FGF21, and FGF23, are major endocrine mediators that play an important role in alcohol metabolism and alcohol related disorders. The objective of the present study is to explore the possible associations among the interaction of single nucleotide polymorphisms (SNPs) of the FGF 19 superfamily, AD occurrence, and aggression in patients with AD. A total of 956 subjects were enrolled in this study, including 482 AD patients and 474 healthy controls (HCs). Michigan alcoholism screening test (MAST) was used to measure the level of AD, a Chinese version of the Buss–Perry Aggression Questionnaire was used to evaluate the aggressive behavior of subjects, and MassARRAY^@ system was used to genotype rs948992 of FGF19, rs11665841 and rs11665896 of FGF21, rs7955866 and rs11063118 of FGF23. The results showed that AD patients presented a significantly higher level of aggression compared to HCs, and MAST scores were significantly positively associated Buss–Perry aggression scores (r = 0.402, p < 0.001) in AD patients. The interaction of FGF19 rs948992 TC × FGF21 rs11665896 GG presented the high-risk genotype combination predicting the high level of AD. In addition, the interaction of FGF19 rs948992 TC × FGF21 rs11665896 TG × FGF23 rs11063118 TT presented the high-risk genotype combination predicting the high level of aggression in AD patients. Our results added evidence linking the combination of rs948992 TC × rs11665896 TG × rs11063118 TT to aggressive behavior in AD patients and pointed out the potential usefulness of the SNPs of FGF19 superfamily as a predictor for the aggression in AD patients.

Current View on the Mechanisms of Alcohol-Mediated Toxicity

Alcohol is a psychoactive substance that is widely used and, unfortunately, often abused. In addition to acute effects such as intoxication, it may cause many chronic pathological conditions. Some of the effects are very well described and explained, but there are still gaps in the explanation of empirically co-founded dysfunction in many alcohol-related conditions. This work focuses on reviewing actual knowledge about the toxic effects of ethanol and its degradation products.

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.

Isolation, Characterization and Neuroprotective Activity of Folecitin: An In Vivo Study

Neurodegenerative diseases (NDs) extend the global health burden. Consumption of alcohol as well as maternal exposure to ethanol can damage several neuronal functions and cause cognition and behavioral abnormalities. Ethanol induces oxidative stress that is linked to the development of NDs. Treatment options for NDs are yet scarce, and natural product-based treatments could facilitate ND management since plants possess plenty of bioactive metabolites, including flavonoids, which typically demonstrate antioxidant and anti-inflammatory properties. Hypericum oblongifolium is an important traditional medicinal plant used for hepatitis, gastric ulcer, external wounds, and other gastrointestinal disorders. However, it also possesses multiple bioactive compounds and antioxidant properties, but the evaluation of isolated pure compounds for neuroprotective efficacy has not been done yet. Therefore, in the current study, we aim to isolate and characterize the bioactive flavonoid folecitin and evaluate its neuroprotective activity against ethanol-induced oxidative-stress-mediated neurodegeneration in the hippocampus of postnatal day 7 (PND-7) rat pups. A single dose of ethanol (5 g/kg body weight) was intraperitoneally administered after the birth of rat pups on PND-7. This caused oxidative stress accompanied by the activation of phosphorylated-c-Jun N-terminal kinase (p-JNK), nod-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), and cysteine-aspartic acid protease-1 (caspase-1) proteins to form a complex called the NLRP3-inflammasome, which converts pro-interleukin 1 beta (IL-1B) to activate IL-1B and induce widespread neuroinflammation and neurodegeneration. In contrast, co-administration of folecitin (30 mg/kg body weight) reduced ethanol-induced oxidative stress, inhibited p-JNK, and deactivated the NLRP3-inflammasome complex. Furthermore, folecitin administration reduced neuroinflammatory and neurodegenerative protein markers, including decreased caspase-3, BCL-2-associated X protein (BAX), B cell CLL/lymphoma 2 (BCL-2), and poly (ADP-ribose) polymerase-1 (PARP-1) expression in the immature rat brain. These findings conclude that folecitin is a flavone compound, and it might be a novel, natural and safe agent to curb oxidative stress and its downstream harmful effects, including inflammasome activation, neuroinflammation, and neurodegeneration. Further evaluation in a dose-dependent manner would be worth it in order to find a suitable dose regimen for NDs.

Isolation, Characterization and Neuroprotective Activity of Folecitin: An In Vivo Study

Neurodegenerative diseases (NDs) extend the global health burden. Consumption of alcohol as well as maternal exposure to ethanol can damage several neuronal functions and cause cognition and behavioral abnormalities. Ethanol induces oxidative stress that is linked to the development of NDs. Treatment options for NDs are yet scarce, and natural product-based treatments could facilitate ND management since plants possess plenty of bioactive metabolites, including flavonoids, which typically demonstrate antioxidant and anti-inflammatory properties. Hypericum oblongifolium is an important traditional medicinal plant used for hepatitis, gastric ulcer, external wounds, and other gastrointestinal disorders. However, it also possesses multiple bioactive compounds and antioxidant properties, but the evaluation of isolated pure compounds for neuroprotective efficacy has not been done yet. Therefore, in the current study, we aim to isolate and characterize the bioactive flavonoid folecitin and evaluate its neuroprotective activity against ethanol-induced oxidative-stress-mediated neurodegeneration in the hippocampus of postnatal day 7 (PND-7) rat pups. A single dose of ethanol (5 g/kg body weight) was intraperitoneally administered after the birth of rat pups on PND-7. This caused oxidative stress accompanied by the activation of phosphorylated-c-Jun N-terminal kinase (p-JNK), nod-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), and cysteine-aspartic acid protease-1 (caspase-1) proteins to form a complex called the NLRP3-inflammasome, which converts pro-interleukin 1 beta (IL-1B) to activate IL-1B and induce widespread neuroinflammation and neurodegeneration. In contrast, co-administration of folecitin (30 mg/kg body weight) reduced ethanol-induced oxidative stress, inhibited p-JNK, and deactivated the NLRP3-inflammasome complex. Furthermore, folecitin administration reduced neuroinflammatory and neurodegenerative protein markers, including decreased caspase-3, BCL-2-associated X protein (BAX), B cell CLL/lymphoma 2 (BCL-2), and poly (ADP-ribose) polymerase-1 (PARP-1) expression in the immature rat brain. These findings conclude that folecitin is a flavone compound, and it might be a novel, natural and safe agent to curb oxidative stress and its downstream harmful effects, including inflammasome activation, neuroinflammation, and neurodegeneration. Further evaluation in a dose-dependent manner would be worth it in order to find a suitable dose regimen for NDs.

Changes in Alcohol Consumption Pattern Based on Gender during COVID-19 Confinement in Spain

(1) The goal of this study was to analyze the prevalence and pattern of alcohol consumption (frequency of consumption, average daily consumption, and risky consumption) before and during confinement due to the coronavirus disease (COVID-19) in the adult population and based on gender. (2) Methods: Data from 3779 individuals were collected via a set of online surveys. The AUDIT alcohol consumption questions (AUDIT-C) were used to measure the frequency of consumption, the average daily consumption, intensive consumption, risky consumption, and standard drink units. (3) Results: During confinement, the prevalence of alcohol consumption declined in both males and females, but only intensive consumption showed significant differences, with a greater reduction in males. The number of females who consumed alcohol four or more times per week doubled, whereas the number of males who did so was multiplied by a factor of 1.5; in both females and males, the percentage who presented intensive consumption doubled. The percentage of females with risky consumption was higher than that of males both before and during confinement. In addition to gender, the interaction between age and the employment situation explain consumption before and during confinement. (4) Conclusions: During confinement due to COVID-19, alcohol consumption declined in both sexes, but alcohol-risk consumers increased their frequency of use. The interaction between gender, age, and employment situation was related to these changes. These findings are relevant for guiding public health and health-risk management policies related to alcohol consumption in environmental situations similar to COVID-19.

Sodium Leak Channel in the Nucleus Accumbens Modulates Ethanol-Induced Acute Stimulant Responses and Locomotor Sensitization in Mice: A Brief Research Report

Ethanol can induce acute stimulant responses in animals and human beings. Moreover, repeated exposure to ethanol may produce increased sensitivity to its acute locomotor stimulant actions, a process referred to as locomotor sensitization. The molecular mechanism of the development of acute stimulant responses and locomotor sensitization by ethanol is not fully understood. Sodium leak channel (NALCN) is widely expressed in central nervous system and controls the basal excitability of neurons. The present study aims to determine whether NALCN is implicated in the ethanol-induced acute responses and locomotor sensitization in mice. Here, our results showed that ethanol caused acute stimulant responses in DBA/2 mice. Locomotor sensitization was successfully induced following the sensitization procedure. Accordingly, the expression levels of NALCN mRNA and protein in the nucleus accumbens (NAc) were markedly increased in the sensitization mice compared to the control mice. Knockdown the expression levels of NALCN in the NAc alleviated both the ethanol-induced acute responses and locomotor sensitization. Our findings indicate that upregulation of NALCN expression in the NAc contributes to the ethanol-induced acute stimulant responses and locomotor sensitization in DBA/2 mice.

Moderate Alcohol Intake Changes Visual Perception by Enhancing V1 Inhibitory Surround Interactions

Moderate alcohol consumption is considered to enhance the cortical GABA-ergic inhibitory system and it also variously affects visual perception. However, little behavioral evidence indicates changes of visual perception due to V1 modulated by alcohol intoxication. In this study, we investigated this issue by using center-surround tilt illusion (TI) as a probe of V1 inhibitory interactions, by taking into account possible higher-order effects. Participants conducted TI measures under sober, moderate alcohol intoxication, and placebo states. We found alcohol significantly increased repulsive TI effect and weakened orientation discrimination performance, which is consistent with the increase of lateral inhibition between orientation sensitive V1 neurons caused by alcohol intoxication. We also observed no visible changes in the data for global orientation processing but a presence of global attentional modulation. Thus, our results provide psychophysics evidence that alcohol changed V1 processing, which affects visual perception of contextual stimuli.

Negative allosteric modulation of metabotropic glutamate receptor 5 attenuates alcohol self-administration in baboons

Many of the behavioral symptoms that define alcohol use disorder (AUD) are thought to be mediated by amplified glutamatergic activity. As a result, previous preclinical studies have investigated glutamate receptor inhibition as a potential pharmacotherapy for AUD, particularly the metabotropic glutamate receptor 5 (mGlu5). In rodents, mGlu5 negative allosteric modulators (NAMs) have been shown to decrease alcohol self-administration. However, their effect on non-human primates has not previously been explored. To bridge this gap, the effects of mGlu5 NAM pretreatment on sweetened alcohol (8% w/v in diluted KoolAid) self-administration in female baboons were evaluated. Two different mGlu5 NAMs were tested: 1) 3-2((-Methyl-4-thiazolyl) ethynyl) pyridine (MTEP) which was administered at a dose of 2 mg/kg IM; and 2) auglurant (N-(5-fluoropyridin-2-yl)-6-methyl-4-(pyrimidin-5-yloxy)picolinamide), a newly developed NAM, which was tested under two different routes (0.001, 0.01, 0.03, 0.1 mg/kg IM and 0.1, 0.3, 1.0 mg/kg PO). MTEP decreased both fixed ratio and progressive ratio responding for sweetened alcohol. Auglurant, administered IM, decreased alcohol self-administration at doses that did not affect self-administration of an alcohol-free sweet liquid reward (0.01 to 0.1 mg/kg). Oral administration of auglurant was not effective in decreasing alcohol self-administration. Our results extend positive findings from rodent studies on mGlu5 regulation of alcohol drinking to female baboons and further strengthen the rationale for targeting mGlu5 in clinical trials for AUD.

Long-term alcohol consumption alters dorsal striatal dopamine release and regulation by D2 dopamine receptors in rhesus macaques

The dorsal striatum (DS) is implicated in behavioral and neural processes including action control and reinforcement. Alcohol alters these processes in rodents, and it is believed that the development of alcohol use disorder involves changes in DS dopamine signaling. In nonhuman primates, the DS can be divided into caudate and putamen subregions. As part of a collaborative effort examining the effects of long-term alcohol self-administration in rhesus macaques, we examined DS dopamine signaling using fast-scan cyclic voltammetry. We found that chronic alcohol self-administration resulted in several dopamine system adaptations. Most notably, dopamine release was altered in a sex- and region-dependent manner. Following long-term alcohol consumption, male macaques, regardless of abstinence status, had reduced dopamine release in putamen, while only male macaques in abstinence had reduced dopamine release in caudate. In contrast, female macaques had enhanced dopamine release in the caudate, but not putamen. Dopamine uptake was also enhanced in females, but not males (regardless of abstinence state). We also found that dopamine D2/3 autoreceptor function was reduced in male, but not female, alcohol drinkers relative to control groups. Finally, we found that blockade of nicotinic acetylcholine receptors inhibited evoked dopamine release in nonhuman primates. Altogether, our findings demonstrate that long-term alcohol consumption can sex-dependently alter dopamine release, as well as its feedback control mechanisms in both DS subregions.

Ethanol-Dependent Synthesis of Salsolinol in the Posterior Ventral Tegmental Area as Key Mechanism of Ethanol's Action on Mesolimbic Dopamine

Abnormal consumption of ethanol, the ingredient responsible for alcoholic drinks' addictive liability, causes millions of deaths yearly. Ethanol's addictive potential is triggered through activation, by a still unknown mechanism, of the mesolimbic dopamine (DA) system, part of a key motivation circuit, DA neurons in the posterior ventral tegmental area (pVTA) projecting to the ipsilateral nucleus accumbens shell (AcbSh). The present in vivo brain microdialysis study, in dually-implanted rats with one probe in the pVTA and another in the ipsilateral or contralateral AcbSh, demonstrates this mechanism. As a consequence of the oral administration of a pharmacologically relevant dose of ethanol, we simultaneously detect a) in the pVTA, a substance, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), untraceable under control conditions, product of condensation between DA and ethanol's first by-product, acetaldehyde; and b) in the AcbSh, a significant increase of DA release. Moreover, such newly generated salsolinol in the pVTA is responsible for increasing AcbSh DA release via μ opioid receptor (μOR) stimulation. In fact, inhibition of salsolinol's generation in the pVTA or blockade of pVTA μORs prevents ethanol-increased ipsilateral, but not contralateral, AcbSh DA release. This evidence discloses the long-sought key mechanism of ethanol's addictive potential and suggests the grounds for developing preventive and therapeutic strategies against abnormal consumption.

Identification of a G-Protein-Independent Activator of GIRK Channels

G-protein-gated inwardly rectifying K⁺ (GIRK) channels are essential effectors of inhibitory neurotransmission in the brain. GIRK channels have been implicated in diseases with abnormal neuronal excitability, including epilepsy and addiction. GIRK channels are tetramers composed of either the same subunit (e.g., homotetramers) or different subunits (e.g., heterotetramers). Compounds that specifically target subsets of GIRK channels in vivo are lacking. Previous studies have shown that alcohol directly activates GIRK channels through a hydrophobic pocket located in the cytoplasmic domain of the channel. Here, we report the identification and functional characterization of a GIRK1-selective activator, termed GiGA1, that targets the alcohol pocket. GiGA1 activates GIRK1/GIRK2 both in vitro and in vivo and, in turn, mitigates the effects of a convulsant in an acute epilepsy mouse model. These results shed light on the structure-based development of subunit-specific GIRK modulators that could provide potential treatments for brain disorders.

Altered excitatory transmission in striatal neurons after chronic ethanol consumption in selectively bred crossed high alcohol-preferring mice

Genetic predisposition to heavy drinking is a risk factor for alcohol misuse. We used selectively bred crossed high alcohol-preferring (cHAP) mice to study sex differences in alcohol drinking and its effect on glutamatergic activity in dorsolateral (DLS) and dorsomedial (DMS) striatum. We performed whole-cell patch-clamp recording in neurons from male and female cHAP mice with 5-week alcohol drinking history and alcohol-naïve controls. In DMS, alcohol-naïve males' neurons displayed lower cell capacitance and higher membrane resistance than females' neurons, both effects reversed by drinking. Conversely, in DLS neurons, drinking history increased capacitance only in males and changed membrane resistance only in females. Altered biophysical membrane properties were accompanied by disrupted glutamatergic transmission. Drinking history increased spontaneous excitatory postsynaptic current (sEPSC) amplitude in DMS and frequency in DLS female neurons, compared to alcohol-naïve females, without effect in males. Acute ethanol differentially impacted DMS and DLS neurons by sex and drinking history. In DMS, acute alcohol significantly increased sEPSC frequency only in neurons from alcohol-naïve females, an effect that disappeared after drinking history. In DLS, acute alcohol had opposing effects in males and females based on drinking history. Estrous cycle also impacted DMS and DLS neurons differently: sEPSC amplitudes were higher in DMS cells from drinking history than alcohol-naïve females, whereas estrous cycle, not drinking history, modified DLS firing rate. Our data show sex differences in cHAP ethanol consumption and neurophysiology, suggesting differential dysregulation of glutamatergic drive onto DMS and DLS after chronic ethanol consumption.

Similarities in alcohol and opioid withdrawal syndromes suggest common negative reinforcement mechanisms involving the interoceptive antireward pathway

Alcohol and opioids are two major contributors to so-called deaths of despair. Though the effects of these substances on mammalian systems are distinct, commonalities in their withdrawal syndromes suggest a shared pathophysiology. For example, both are characterized by marked autonomic dysregulation and are treated with alpha-2 agonists. Moreover, alcohol and opioids rapidly induce dependence motivated by withdrawal avoidance. Resemblances observed in withdrawal syndromes and abuse behavior may indicate common addiction mechanisms. We argue that neurovisceral feedback influences autonomic and emotional circuits generating antireward similarly for both substances. Amygdala is central to this hypothesis as it is principally responsible for negative emotion, prominent in addiction and motivated behavior, and processes autonomic inputs while generating autonomic outputs. The solitary nucleus (NTS) has strong bidirectional connections to the amygdala and receives interoceptive inputs communicating visceral states via vagal afferents. These visceral-emotional hubs are strongly influenced by the periphery including gut microbiota. We propose that gut dysbiosis contributes to alcohol and opioid withdrawal syndromes by contributing to peripheral and neuroinflammation that stimulates these antireward pathways and motivates substance dependence.

Associations between lifestyle and amyotrophic lateral sclerosis stratified by C9orf72 genotype: a longitudinal, population-based, case-control study

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is considered to be caused by both genetic and environmental factors. The causal cascade is, however, not known. We aimed to assess lifestyle during the presymptomatic phase of ALS, stratified by C9orf72 mutation, and examine evidence supporting causality of lifestyle factors.

METHODS

This study was a longitudinal, population-based, case-control study that used data from the Prospective ALS study the Netherlands. We included patients with a C9orf72 mutation (C9+ group), patients without a C9orf72 mutation (C9- group), and controls. Patients fulfilled the revised El Escorial criteria and were recruited through neurologists and rehabilitation physicians in the Netherlands as well as the Dutch Neuromuscular Patient Association and ALS Centrum website. 1322 population-based controls, matched for age and sex, were enrolled via the patients' general practitioners. Blood relatives or spouses of patients were not eligible as controls. We studied the relationship between ALS risk and smoking, alcohol, physical activity, body-mass index (BMI), and energy intake by the use of structured questionnaires. Smoking, physical activity, and BMI were longitudinally assessed up to 50 years before onset (defined as the period before onset of muscle weakness or bulbar symptoms for cases, or age at completing the questionnaire for controls). We calculated posterior probabilities (P(θ|x)) for causal effects of smoking, alcohol, and BMI, using Bayesian instrumental variable analyses.

FINDINGS

Between Jan 1, 2006 and Jan 27, 2016, we included 143 patients in the C9+ group, 1322 patients in the C9- group, and 1322 controls. Compared with controls, cigarette pack-years (C9+ group mean difference from control 3·15, 95% CI 0·36 to 5·93, p=0·027; C9- group 3·20, 2·02 to 4·39, p<0·0001) and daily energy intake at symptom onset (C9+ group 712 kJ, 95% CI 212 to 1213, p=0·0053; C9- group 497, 295 to 700, p<0·0001) were higher in the C9+ and C9- groups, whereas current BMI (C9+ group -2·01 kg/m², 95% CI -2·73 to -1·29, p<0·0001; C9- group -1·35, -1·64 to -1·06, p<0·0001) and lifetime alcohol consumption (C9+ group -5388 units, 95% CI -9113 to -1663, p=0·0046; C9- group -2185, -3748 to -622, p=0·0062) were lower in the C9+ and C9- groups. Median BMI during the presymptomatic phase for the C9+ group was lower (-0·69 kg/m², 95% CI -1·24 to -0·13, p=0·015) and physical activity was similar (-348 metabolic equivalent of task [MET], 95% CI -966 to 270, p=0·27) to controls, whereas both the median BMI during the presymptomatic phase (0·27 kg/m², 95% CI 0·04 to 0·50, p=0·022) and physical activity (585 MET, 291 to 878, p=0·0001) were higher in the C9- group than controls. Longitudinal analyses showed more cigarette pack-years in the C9- (starting 47 years pre-onset) and C9+ (starting 24 years pre-onset) groups, and higher physical activity over time in the C9- group (starting >30 years pre-onset). BMI of the C9+ group increased more slowly and was significantly lower (starting at 36 years pre-onset) than in controls, whereas the BMI of the C9- group was higher than controls (23-49 years pre-onset, becoming lower 10 years pre-onset). Instrumental variable analyses supported causal effects of alcohol consumption (P(θ|x)=0·9347) and smoking (P(θ|x)=0·9859) on ALS in the C9- group. We found evidence supporting a causal effect of increased BMI at younger age (mean 33·8 years, SD 11·7) in the C9- group (P[θ|x]=0·9272), but not at older ages.

INTERPRETATION

Lifestyle during the presymptomatic phase differs between patients with ALS and controls decades before onset, depends on C9- status, and is probably part of the presymptomatic causal cascade. Identification of modifiable disease-causing lifestyle factors offers opportunities to lower risk of developing neurodegenerative disease.

FUNDING

Netherlands ALS Foundation.

Yeast volatiles double starvation survival in Drosophila

Organisms make decisions based on the information they gather from their environment, the effects of which affect their fitness. Understanding how these interactions affect physiology may generate interventions that improve the length and quality of life. Here, we provide evidence that exposure to live yeast volatiles during starvation significantly extends survival, increases activity, and slows the rate of triacylglyceride (TAG) decline independent of canonical sensory perception. We demonstrate that ethanol (EtOH) is one of the active components in yeast volatiles that influences these phenotypes and that EtOH metabolites mediate dynamic mechanisms to promote Drosophila survival. Silencing R4d neurons reverses the ability of high EtOH concentrations to promote starvation survival, and their activation promotes EtOH metabolism. The transcription factor foxo promotes EtOH resistance, likely by protection from EtOH toxicity. Our results suggest that food-related cues recruit neural circuits and modulate stress signaling pathways to promote survival during starvation.

Cortical copper transporter expression in schizophrenia: interactions of risk gene dysbindin-1

Schizophrenia susceptibility factor dysbindin-1 is associated with cognitive processes. Downregulated dysbindin-1 expression is associated with lower expression of copper transporters ATP7A and CTR1, required for copper transport to the central nervous system. We measured dysbindin-1 isoforms-1A and -1BC, CTR1, and ATP7A via Western blots of the postmortem dorsolateral prefrontal cortex (DLPFC) of schizophrenia subjects (n = 28) and matched controls (n = 14). In addition, we subdivided the schizophrenia group by treatment status and comorbidity of alcohol use disorder (AUD) and assessed the relationships between proteins. Schizophrenia subjects exhibited similar protein levels to that of controls, with no effect of antipsychotic treatment. We observed a shift towards more dysbindin-1A expression in schizophrenia, as revealed by the ratio of dysbindin-1 isoforms. Dysbindin-1A expression was negatively correlated with ATP7A in schizophrenia, with no correlation present in controls. AUD subjects exhibited less dysbindin-1BC and CTR1 than those without AUD. Our results, taken together with previous data, suggest that alterations in dysbindin-1 and copper transporters are brain-region specific. For example, protein levels of ATP7A, dysbindin 1BC, and CTR1 are lower in the substantia nigra in schizophrenia subjects. AUD in the DLPFC was associated with lower protein levels of dysbindin-1 and CTR1. Changes in dysbindin-1 isoform ratio and relationships appear to be prevalent in the disease, potentially impacting symptomology.

Astrocytes promote ethanol-induced enhancement of intracellular Ca2+ signals through intercellular communication with neurons

Ethanol (EtOH) abuse induces significant mortality and morbidity worldwide because of detrimental effects on brain function. Defining the contribution of astrocytes to this malfunction is imperative to understanding the overall EtOH effects due to their role in homeostasis and EtOH-seeking behaviors. Using a highly controllable in vitro system, we identify chemical signaling mechanisms through which acute EtOH exposure induces a modulatory feedback loop between neurons and astrocytes. Neuronally-derived purinergic signaling primed a subpopulation of astrocytes to respond to subsequent acute EtOH exposures (^SEastrocytes: signal enhanced astrocytes) with greater calcium signal strength. Generation of ^SEastrocytes arose from astrocytic hemichannel-derived ATP and accumulation of its metabolite adenosine within the astrocyte microenvironment to modulate adenylyl cyclase and phospholipase C activity. These results highlight an important role of astrocytes in shaping the overall physiological responsiveness to EtOH and emphasize the unique plasticity of astrocytes to adapt to single and multiple exposures of EtOH.

Effect of alcohol on the central nervous system to develop neurological disorder: pathophysiological and lifestyle modulation can be potential therapeutic options for alcohol-induced neurotoxication

The central nervous system (CNS) is the major target for adverse effects of alcohol and extensively promotes the development of a significant number of neurological diseases such as stroke, brain tumor, multiple sclerosis (MS), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Excessive alcohol consumption causes severe neuro-immunological changes in the internal organs including irreversible brain injury and it also reacts with the defense mechanism of the blood-brain barrier (BBB) which in turn leads to changes in the configuration of the tight junction of endothelial cells and white matter thickness of the brain. Neuronal injury associated with malnutrition and oxidative stress-related BBB dysfunction may cause neuronal degeneration and demyelination in patients with alcohol use disorder (AUD); however, the underlying mechanism still remains unknown. To address this question, studies need to be performed on the contributing mechanisms of alcohol on pathological relationships of neurodegeneration that cause permanent neuronal damage. Moreover, alcohol-induced molecular changes of white matter with conduction disturbance in neurotransmission are a likely cause of myelin defect or axonal loss which correlates with cognitive dysfunctions in AUD. To extend our current knowledge in developing a neuroprotective environment, we need to explore the pathophysiology of ethanol (EtOH) metabolism and its effect on the CNS. Recent epidemiological studies and experimental animal research have revealed the association between excessive alcohol consumption and neurodegeneration. This review supports an interdisciplinary treatment protocol to protect the nervous system and to improve the cognitive outcomes of patients who suffer from alcohol-related neurodegeneration as well as clarify the pathological involvement of alcohol in causing other major neurological disorders.

Chronic Alcohol Use Induces Molecular Genetic Changes in the Dorsomedial Thalamus of People with Alcohol-Related Disorders

The Mediodorsal (MD) thalamus that represents a fundamental subcortical relay has been underrepresented in the studies focusing on the molecular changes in the brains of subjects with alcohol use disorder (AUD). In the current study, MD thalamic regions from AUD subjects and controls were analyzed with Affymetrix Clariom S human microarray. Long-term alcohol use induced a significant (FDR ≤ 0.05) upregulation of 2802 transcripts and downregulation of 1893 genes in the MD thalamus of AUD subjects. A significant upregulation of GRIN1 (glutamate receptor NMDA type 1) and FTO (alpha-ketoglutarate dependent dioxygenase) was confirmed in western blot analysis. Immunohistochemical staining revealed similar heterogenous distribution of GRIN1 in the thalamic nuclei of both AUD and control subjects. The most prevalent functional categories of upregulated genes were related to glutamatergic and GABAergic neurotransmission, cellular metabolism, and neurodevelopment. The prevalent gene cluster among down-regulated genes was immune system mediators. Forty-two differentially expressed genes, including FTO, ADH1B, DRD2, CADM2, TCF4, GCKR, DPP6, MAPT and CHRH1, have been shown to have strong associations (FDR p < 10-8) with AUD or/and alcohol use phenotypes in recent GWA studies. Despite a small number of subjects, we were able to detect robust molecular changes in the mediodorsal thalamus caused by alcohol emphasizing the importance of deeper brain structures such as diencephalon, in the development of AUD-related dysregulation of neurocircuitry.

Plasticity in the Hippocampus, Neurogenesis and Drugs of Abuse

Synaptic plasticity in the hippocampus assists with consolidation and storage of long-lasting memories. Decades of research has provided substantial information on the cellular and molecular mechanisms underlying synaptic plasticity in the hippocampus, and this review discusses these mechanisms in brief. Addiction is a chronic relapsing disorder with loss of control over drug taking and drug seeking that is caused by long-lasting memories of drug experience. Relapse to drug use is caused by exposure to context and cues associated with the drug experience, and is a major clinical problem that contributes to the persistence of addiction. This review also briefly discusses some evidence that drugs of abuse alter plasticity in the hippocampus, and that development of novel treatment strategies that reverse or prevent drug-induced synaptic alterations in the hippocampus may reduce relapse behaviors associated with addiction.

Mechanism for differential recruitment of orbitostriatal transmission during actions and outcomes following chronic alcohol exposure

Psychiatric disease often produces symptoms that have divergent effects on neural activity. For example, in drug dependence, dysfunctional value-based decision-making and compulsive-like actions have been linked to hypo- and hyperactivity of orbital frontal cortex (OFC)-basal ganglia circuits, respectively; however, the underlying mechanisms are unknown. Here we show that alcohol-exposed mice have enhanced activity in OFC terminals in dorsal striatum (OFC-DS) associated with actions, but reduced activity of the same terminals during periods of outcome retrieval, corresponding with a loss of outcome control over decision-making. Disrupted OFC-DS terminal activity was due to a dysfunction of dopamine-type 1 receptors on spiny projection neurons (D1R SPNs) that resulted in increased retrograde endocannabinoid signaling at OFC-D1R SPN synapses reducing OFC-DS transmission. Blocking CB1 receptors restored OFC-DS activity in vivo and rescued outcome-based control over decision-making. These findings demonstrate a circuit-, synapse-, and computation-specific mechanism gating OFC activity in alcohol-exposed mice.

Ventral striatum regulates behavioral response to ethanol and MDMA combination

Our previous studies consistently showed that MDMA-induced locomotor hyperactivity is dramatically increased by coadministration of ethanol (EtOH) in rats, indicating possible potentiation of MDMA abuse liability. Thus, we aimed to identify the brain region(s) and neuropharmacological substrates involved in the pharmacodynamics of this potentiation. We first showed that potentiation of locomotor activity by the combination of ip administration of EtOH (1.5 g/kg) and MDMA (6.6 mg/kg) is delay sensitive and maximal when both drugs are injected simultaneously. Then, we used the 2-deoxyglucose quantitative autoradiography technique to assess the impact of EtOH, MDMA, or their combination on local cerebral metabolic rates for glucose (CMRglcs). We showed a specific metabolic activation in the ventral striatum (VS) under MDMA + EtOH versus MDMA or EtOH alone. We next tested if reversible (tetrodotoxin, TTX) or permanent (6-hydrodoxyopamine, 6-OHDA) lesion of the VS could affect locomotor response to MDMA and MDMA + EtOH. Finally, we blocked dopamine D1 or glutamate NMDA receptors in the VS and measured the effects of MDMA and MDMA + EtOH on locomotor activity. We showed that bilateral reversible inactivation (TTX) or permanent lesion (6-OHDA) of the VS prevented the potentiation by EtOH of MDMA-induced locomotor hyperactivity. Likewise, blockade of D1 or NMDA receptors in the VS also reduced the potentiation of MDMA locomotor activity by EtOH. These data indicate that dopamine D1 and glutamate NMDA receptor-driven mechanisms in the VS play a key role in the pharmacodynamics of EtOH-induced potentiation of the locomotor effects of MDMA.

Brain ethanol metabolism by astrocytic ALDH2 drives the behavioural effects of ethanol intoxication

Alcohol is among the most widely used psychoactive substances worldwide. Ethanol metabolites such as acetate, thought to be primarily the result of ethanol breakdown by hepatic aldehyde dehydrogenase 2 (ALDH2), contribute to alcohol's behavioural effects and alcoholism. Here, we show that ALDH2 is expressed in astrocytes in the mouse cerebellum and that ethanol metabolism by astrocytic ALDH2 mediates behavioural effects associated with ethanol intoxication. We show that ALDH2 is expressed in astrocytes in specific brain regions and that astrocytic, but not hepatocytic, ALDH2 is required to produce ethanol-derived acetate in the mouse cerebellum. Cerebellar astrocytic ALDH2 mediates low-dose ethanol-induced elevation of GABA levels, enhancement of tonic inhibition and impairment of balance and coordination skills. Thus, astrocytic ALDH2 controls the production, cellular and behavioural effects of alcohol metabolites in a brain-region-specific manner. Our data indicate that astrocytic ALDH2 is an important, but previously under-recognized, target in the brain to alter alcohol pharmacokinetics and potentially treat alcohol use disorder.

Oxytocin and Addiction: Potential Glutamatergic Mechanisms

Recently, oxytocin (OXT) has been investigated for its potential therapeutic role in addiction. OXT has been found to diminish various drug-seeking and drug-induced behaviors. Although its behavioral effects are well-established, there is not much consensus on how this neuropeptide exerts its effects. Previous research has given thought to how dopamine (DA) may be involved in oxytocinergic mechanisms, but there has not been as strong of a focus on the role that glutamate (Glu) has. The glutamatergic system is critical for the processing of rewards and the disruption of glutamatergic projections produces the behaviors seen in drug addicts. We introduce the idea that OXT has direct effects on Glu transmission within the reward processing pathway. Thus, OXT may reduce addictive behaviors by restoring abnormal drug-induced changes in the glutamatergic system and in its interactions with other neurotransmitters. This review offers insight into the mechanisms through which a potentially viable therapeutic target, OXT, could be used to reduce addiction-related behaviors.

Ethanol-induced locomotor sensitization: Neuronal activation in the nucleus accumbens and medial prefrontal cortex

Ethanol consumption may promote neuroplasticity and alterations in synapses, resulting in modifications in neuronal activity. Here, we treated male Swiss mice with ethanol (2.2 g/kg) or saline once per day for 21 consecutive days. Nine days after the last ethanol administration, they received a challenge injection of ethanol or saline, and we assessed locomotor activity. After the behavioral analysis, we evaluated neuronal activation in the medial Prefrontal Cortex (Cingulate, Prelimbic, and Infralimbic) and the Nucleus Accumbens (Shell and Core) using Fos/DAB immunohistochemistry. In another group of animals, we performed the quantitative analysis of the ARC and PSD-95 protein levels by Western blotting in the medial prefrontal cortex and nucleus accumbens brain areas. Repeated ethanol administration produced locomotor sensitization, accompanied by an increase in the nucleus accumbens shell's activation but not core. Furthermore, the ethanol pretreatment reduced ARC expression in the nucleus accumbens and medial prefrontal cortex. Our results suggest the participation of the nucleus accumbens shell in ethanol behavioral sensitization and add new pieces of evidence that neuroplasticity in synapses may contribute to the mechanism underlying this behavior.

Ethanol induces persistent potentiation of 5-HT3 receptor-stimulated GABA release at synapses on rat hippocampal CA1 neurons

Several studies have shown that ethanol (EtOH) can enhance the activity of GABAergic synapses via presynaptic mechanisms, including in hippocampal CA1 neurons. The serotonin type 3 receptor (5-HT3-R) has been implicated in the neural actions of ethanol (EtOH) and in modulation of GABA release from presynaptic terminals. In the present study, we investigated EtOH modulation of GABA release induced by 5-HT3-R activation using the mechanically isolated neuron/bouton preparation from the rat CA1 hippocampal subregion. EtOH application before and during exposure to the selective 5-HT3 receptor agonist, m-chlorophenylbiguanide (mCPBG) potentiated the mCPBG-induced increases in the peak frequency and charge transfer of spontaneous GABAergic inhibitory postsynaptic currents. Interestingly, the potentiation was maintained even after EtOH was removed from the preparation. A protein kinase A inhibitor reduced the magnitude of EtOH potentiation. Fluorescent Ca2+ imaging showed that Ca2+ transients in the presynaptic terminals increased during EtOH exposure. These findings indicate that EtOH produces long-lasting potentiation of 5-HT3-induced GABA release by modulating calcium levels, via a process involving cAMP-mediated signaling in presynaptic terminals.

Voluntary intake of psychoactive substances is regulated by the dopamine receptor Dop1R1 in Drosophila

Dysregulated motivation to consume psychoactive substances leads to addictive behaviors that often result in serious health consequences. Understanding the neuronal mechanisms that drive drug consumption is crucial for developing new therapeutic strategies. The fruit fly Drosophila melanogaster offers a unique opportunity to approach this problem with a battery of sophisticated neurogenetic tools available, but how they consume these drugs remains largely unknown. Here, we examined drug self-administration behavior of Drosophila and the underlying neuronal mechanisms. We measured the preference of flies for five different psychoactive substances using a two-choice feeding assay and monitored its long-term changes. We found that flies show acute preference for ethanol and methamphetamine, but not for cocaine, caffeine or morphine. Repeated intake of ethanol, but not methamphetamine, increased over time. Preference for methamphetamine and the long-term escalation of ethanol preference required the dopamine receptor Dop1R1 in the mushroom body. The protein level of Dop1R1 increased after repeated intake of ethanol, but not methamphetamine, which correlates with the acquired preference. Genetic overexpression of Dop1R1 enhanced ethanol preference. These results reveal a striking diversity of response to individual drugs in the fly and the role of dopamine signaling and its plastic changes in controlling voluntary intake of drugs.