Presynaptic Ethanol Actions: Potential Roles in Ethanol Seeking

Adaptor protein complex 2 in the orbitofrontal cortex predicts alcohol use disorder

Alcohol use disorder (AUD) is a life-threatening disease characterized by compulsive drinking, cognitive deficits, and social impairment that continue despite negative consequences. The inability of individuals with AUD to regulate drinking may involve functional deficits in cortical areas that normally balance actions that have aspects of both reward and risk. Among these, the orbitofrontal cortex (OFC) is critically involved in goal-directed behavior and is thought to maintain a representation of reward value that guides decision making. In the present study, we analyzed post-mortem OFC brain samples collected from age- and sex-matched control subjects and those with AUD using proteomics, bioinformatics, machine learning, and reverse genetics approaches. Of the 4,500+ total unique proteins identified in the proteomics screen, there were 47 proteins that differed significantly by sex that were enriched in processes regulating extracellular matrix and axonal structure. Gene ontology enrichment analysis revealed that proteins differentially expressed in AUD cases were involved in synaptic and mitochondrial function, as well as transmembrane transporter activity. Alcohol-sensitive OFC proteins also mapped to abnormal social behaviors and social interactions. Machine learning analysis of the post-mortem OFC proteome revealed dysregulation of presynaptic (e.g., AP2A1) and mitochondrial proteins that predicted the occurrence and severity of AUD. Using a reverse genetics approach to validate a target protein, we found that prefrontal Ap2a1 expression significantly correlated with voluntary alcohol drinking in male and female genetically diverse mouse strains. Moreover, recombinant inbred strains that inherited the C57BL/6J allele at the Ap2a1 interval consumed higher amounts of alcohol than those that inherited the DBA/2J allele. Together, these findings highlight the impact of excessive alcohol consumption on the human OFC proteome and identify important cross-species cortical mechanisms and proteins that control drinking in individuals with AUD.

5. Collaborative Study on the Genetics of Alcoholism: Functional genomics

Alcohol Use Disorder is a complex genetic disorder, involving genetic, neural, and environmental factors, and their interactions. The Collaborative Study on the Genetics of Alcoholism (COGA) has been investigating these factors and identified putative alcohol use disorder risk genes through genome-wide association studies. In this review, we describe advances made by COGA in elucidating the functional changes induced by alcohol use disorder risk genes using multimodal approaches with human cell lines and brain tissue. These studies involve investigating gene regulation in lymphoblastoid cells from COGA participants and in post-mortem brain tissues. High throughput reporter assays are being used to identify single nucleotide polymorphisms in which alternate alleles differ in driving gene expression. Specific single nucleotide polymorphisms (both coding or noncoding) have been modeled using induced pluripotent stem cells derived from COGA participants to evaluate the effects of genetic variants on transcriptomics, neuronal excitability, synaptic physiology, and the response to ethanol in human neurons from individuals with and without alcohol use disorder. We provide a perspective on future studies, such as using polygenic risk scores and populations of induced pluripotent stem cell-derived neurons to identify signaling pathways related with responses to alcohol. Starting with genes or loci associated with alcohol use disorder, COGA has demonstrated that integration of multimodal data within COGA participants and functional studies can reveal mechanisms linking genomic variants with alcohol use disorder, and potential targets for future treatments.

Adaptor protein complex 2 in the orbitofrontal cortex predicts alcohol use disorder

Alcohol use disorder (AUD) is a life-threatening disease characterized by compulsive drinking, cognitive deficits, and social impairment that continue despite negative consequences. The inability of individuals with AUD to regulate drinking may involve functional deficits in cortical areas that normally balance actions that have aspects of both reward and risk. Among these, the orbitofrontal cortex (OFC) is critically involved in goal-directed behavior and is thought to maintain a representation of reward value that guides decision making. In the present study, we analyzed post-mortem OFC brain samples collected from age- and sex-matched control subjects and those with AUD using proteomics, bioinformatics, machine learning, and reverse genetics approaches. Of the 4,500+ total unique proteins identified in the proteomics screen, there were 47 proteins that differed significantly by sex that were enriched in processes regulating extracellular matrix and axonal structure. Gene ontology enrichment analysis revealed that proteins differentially expressed in AUD cases were involved in synaptic and mitochondrial function, as well as transmembrane transporter activity. Alcohol-sensitive OFC proteins also mapped to abnormal social behaviors and social interactions. Machine learning analysis of the post-mortem OFC proteome revealed dysregulation of presynaptic (e.g., AP2A1) and mitochondrial proteins that predicted the occurrence and severity of AUD. Using a reverse genetics approach to validate a target protein, we found that prefrontal Ap2a1 expression significantly correlated with voluntary alcohol drinking in male and female genetically diverse mouse strains. Moreover, recombinant inbred strains that inherited the C57BL/6J allele at the Ap2a1 interval consumed higher amounts of alcohol than those that inherited the DBA/2J allele. Together, these findings highlight the impact of excessive alcohol consumption on the human OFC proteome and identify important cross-species cortical mechanisms and proteins that control drinking in individuals with AUD.

Precocious emergence of cognitive and synaptic dysfunction in 3xTg-AD mice exposed prenatally to ethanol

Alzheimer's disease (AD) is the most common cause of dementia, affecting approximately 50 million people worldwide. Early life risk factors for AD, including prenatal exposures, remain underexplored. Exposure of the fetus to alcohol (ethanol) is not uncommon during pregnancy, and may result in physical, behavioral, and cognitive changes that are first detected during childhood but result in lifelong challenges. Whether or not prenatal ethanol exposure may contribute to Alzheimer's disease risk is not yet known. Here we exposed a mouse model of Alzheimer's disease (3xTg-AD), bearing three dementia-associated transgenes, presenilin1 (PS1M146V), human amyloid precursor protein (APPSwe), and human tau (TauP301S), to ethanol on gestational days 13.5-16.5 using an established binge-type maternal ethanol exposure paradigm. We sought to investigate whether prenatal ethanol exposure resulted in a precocious onset or increased severity of AD progression, or both. We found that a brief binge-type gestational exposure to ethanol during a period of peak neuronal migration to the developing cortex resulted in an earlier onset of spatial memory deficits and behavioral inflexibility in the progeny, as assessed by performance on the modified Barnes maze task. The observed cognitive changes coincided with alterations to both GABAergic and glutamatergic synaptic transmission in layer V/VI neurons, diminished GABAergic interneurons, and increased β-amyloid accumulation in the medial prefrontal cortex. These findings provide the first preclinical evidence for prenatal ethanol exposure as a potential factor for modifying the onset of AD-like behavioral dysfunction and set the groundwork for more comprehensive investigations into the underpinnings of AD-like cognitive changes in individuals with fetal alcohol spectrum disorders.

Male mice exposed to chronic intermittent ethanol exposure exhibit significant upregulation or downregulation of circular RNAs

B a ckground: Circular RNAs (circRNAs) have been crucially implicated in various diseases, however, their involvement in chronic intermittent ethanol (CIE) exposure remains unclear.O bjective: The present study was conducted to evaluate the circular RNA expression alteration in brain samples and to identify the molecular mechanisms underlying chronic intermittent ethanol exposure.M ethods: Male C57BL/6J mice (10 for each group) were given 4 weeks of chronic intermittent ethanol exposure. Whole brain samples were collected for high-throughput sequencing and circRNA bioinformatic analysis. Real-time quantitative PCR (RI-qPCR) and agarose electrophoresis were used to validate the differentially expressed circRNAs. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) analysis were performed. A p level < 0.05 was considered statistically significant.R esults: Compared with the control group and baseline values, the CIE group showed a significant increase in ethanol intake. High-throughput sequencing revealed 399 significantly different circRNAs in CIE mice, including 150 up-regulated circRNAs and 249 down-regulated circRNAs. GO analysis showed that the most significantly enriched term for biological process, cellular component, and molecular function were GO:0050885, GO:0016020 and GO:0005515, respectively. The most enriched pathways in KEGG analysis were GABAergic synapse (mmu04727), followed by retrograde endocannabinoid (eCB) signaling (mmu04723) and morphine addiction (mmu05032). Among the circRNAs, RT-qPCR confirmed 14 upregulated and 13 downregulated circRNAs in the brain tissues with 9 upregulated and 10 downregulated circRNAs being observed in blood samples.C onclusions: Our study suggests that chronic ethanol exposure upregulates or downregulates circRNAs in the brain, which, in turn, could alter neurotransmitter release and signal transduction.

Differential sensitivity of human neurons carrying μ opioid receptor (MOR) N40D variants in response to ethanol

The acute and chronic effects of alcohol on the brain and behavior are linked to alterations in inhibitory synaptic transmission. Alcohol's most consistent effect at the synaptic level is probably a facilitation of γ-aminobutyric acid (GABA) release, as seen from several rodent studies. The impact of alcohol on GABAergic neurotransmission in human neurons is unknown, due to a lack of a suitable experimental model. Human neurons can also be used to model effects of genetic variants linked with alcohol use disorders (AUDs). The A118G single nucleotide polymorphism (SNP rs1799971) of the OPRM1 gene encoding the N40D (D40 minor allele) mu-opioid receptor (MOR) variant has been linked with individuals who have an AUD. However, while N40D is clearly associated with other drugs of abuse, involvement with AUDs is controversial. In this study, we employed Ascl1-and Dlx2-induced inhibitory neuronal cells (AD-iNs) generated from human iPS cell lines carrying N40D variants, and investigated the impact of ethanol acutely and chronically on GABAergic synaptic transmission. We found that N40 AD-iNs display a stronger facilitation (versus D40) of spontaneous and miniature inhibitory postsynaptic current frequency in response to acute ethanol application. Quantitative immunocytochemistry of Synapsin 1+ synaptic puncta revealed a similar synapse number between N40 and D40 iNs, suggesting an ethanol modulation of presynaptic GABA release without affecting synapse density. Interestingly, D40 iNs exposed to chronic intermittent ethanol application caused a significant increase in mIPSC frequency, with only a modest enhancement observed in N40 iNs. These data suggest that the MOR genotype may confer differential sensitivity to synaptic output, which depends on ethanol exposure time and concentration for AD-iNs and may help explain alcohol dependence in individuals who carry the MOR D40 SNPs. Furthermore, this study supports the use of human neuronal cells carrying risk-associated genetic variants linked to disease, as in vitro models to assay the synaptic actions of alcohol on human neuronal cells.

Cannabinoid 1 Receptor Antagonists Play a Neuroprotective Role in Chronic Alcoholic Hippocampal Injury Related to Pyroptosis Pathway

BACKGROUND

Alcohol use disorders affect millions of people worldwide, and there is growing evidence that excessive alcohol intake causes severe damage to the brain of both humans and animals. Numerous studies on chronic alcohol exposure in animal models have identified that many functional impairments are associated with the hippocampus, which is a structure exhibiting substantial vulnerability to alcohol exposure. However, the precise mechanisms that lead to structural and functional impairments of the hippocampus are poorly understood. Herein, we report a novel cell death type, namely pyroptosis, which accounts for alcohol neurotoxicity in mice.

METHODS

For this study, we used an in vivo model to induce alcohol-related neurotoxicity in the hippocampus. Adult male C57BL/6 mice were treated with 95% alcohol vapor either alone or in combination with selective cannabinoid receptor antagonists or agonists, and VX765 (Belnacasan), which is a selective caspase-1 inhibitor.

RESULTS

Alcohol-induced in vivo pyroptosis occurs because of an increase in the levels of pyroptotic proteins such as nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3), caspase-1, gasdermin D (GSDMD), and amplified inflammatory response. Our results indicated that VX765 suppressed the expression of caspase-1 and inhibited the maturation of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. Additionally, chronic alcohol intake created an imbalance in the endocannabinoid system and regulated 2 cannabinoid receptors (CB1R and CB2R) in the hippocampus. Specific antagonists of CB1R (AM251 and AM281) significantly ameliorated alcohol-induced pyroptosis signaling and inactivated the inflammatory response.

CONCLUSIONS

Alcohol induces hippocampal pyroptosis, which leads to neurotoxicity, thereby indicating that pyroptosis may be an essential pathway involved in chronic alcohol-induced hippocampal neurotoxicity. Furthermore, cannabinoid receptors are regulated during this process, which suggests promising therapeutic strategies against alcohol-induced neurotoxicity through pharmacologic inhibition of CB1R.

Alcohol Enhances Responses to High Frequency Stimulation in Hippocampus from Transgenic Mice with Increased Astrocyte Expression of IL-6

Recent studies show that alcohol exposure can induce glial production of neuroimmune factors in the CNS. Of these, IL-6 has gained attention because it is involved in a number of important physiological and pathophysiological processes that could be affected by alcohol-induced CNS production of IL-6, particularly under conditions of excessive alcohol use. For example, IL-6 has been shown to play a role in hippocampal behaviors and synaptic plasticity (long-term potentiation; LTP) associated with memory and learning. Surprisingly, in our in vitro studies of LTP at the Schaffer collateral to CA1 pyramidal neuron synapse in hippocampus from transgenic mice that express elevated levels of astrocyte produced IL-6 (TG), LTP was not altered by the increased levels of IL-6. However, exposure to acute alcohol revealed neuroadaptive changes that served to protect LTP against the alcohol-induced reduction of LTP observed in hippocampus from non-transgenic control mice (WT). Here we examined the induction phase of LTP to assess if presynaptic neuroadaptive changes occurred in the hippocampus of TG mice that contributed to the resistance of LTP to alcohol. Results are consistent with a role for IL-6-induced neuroadaptive effects on presynaptic mechanisms involved in transmitter release in the resistance of LTP to alcohol in hippocampus from the TG mice. These actions are important with respect to a role for IL-6 in physiological and pathophysiological processes in the CNS and in CNS actions of alcohol, especially when excessive alcohol used is comorbid with conditions associated with elevated levels of IL-6 in the CNS.

Intermittent ethanol exposure during adolescence impairs cannabinoid type 1 receptor-dependent long-term depression and recognition memory in adult mice

Binge drinking is a significant problem in adolescent populations, and because of the reciprocal interactions between ethanol (EtOH) consumption and the endocannabinoid (eCB) system, we sought to determine if adolescent EtOH intake altered the localization and function of the cannabinoid 1 (CB1) receptors in the adult brain. Adolescent mice were exposed to a 4-day-per week drinking in the dark (DID) procedure for a total of 4 weeks and then tested after a 2-week withdrawal period. Field excitatory postsynaptic potentials (fEPSPs), evoked by medial perforant path (MPP) stimulation in the dentate gyrus molecular layer (DGML), were significantly smaller. Furthermore, unlike control animals, CB1 receptor activation did not depress fEPSPs in the EtOH-exposed animals. We also examined a form of excitatory long-term depression that is dependent on CB1 receptors (eCB-eLTD) and found that it was completely lacking in the animals that consumed EtOH during adolescence. Histological analyses indicated that adolescent EtOH intake significantly reduced the CB1 receptor distribution and proportion of immunopositive excitatory synaptic terminals in the medial DGML. Furthermore, there was decreased binding of [35S]guanosine-5*-O-(3-thiotriphosphate) ([35S] GTPγS) and the guanine nucleotide-binding (G) protein Gαi2 subunit in the EtOH-exposed animals. Associated with this, there was a significant increase in monoacylglycerol lipase (MAGL) mRNA and protein in the hippocampus of EtOH-exposed animals. Conversely, deficits in eCB-eLTD and recognition memory could be rescued by inhibiting MAGL with JZL184. These findings indicate that repeated exposure to EtOH during adolescence leads to long-term deficits in CB1 receptor expression, eCB-eLTD, and reduced recognition memory, but that these functional deficits can be restored by treatments that increase endogenous 2-arachidonoylglycerol.

Female-specific decreases in alcohol binge-like drinking resulting from GABAA receptor delta-subunit knockdown in the VTA

Binge drinking is short-term drinking that achieves blood alcohol levels of 0.08 g/dl or above. It exhibits well-established sex differences in GABAergic inhibitory neurotransmission, including extrasynaptic δ subunit-containing GABAA receptors (δ-GABAARs) that mediate tonic inhibition, or synaptic γ2-containing GABAARs which underlie fast, synaptic, phasic inhibition have been implicated in sex differences in binge drinking. Ovarian hormones regulate δ-GABAARs, further implicating these receptors in potential sex differences. Here, we explored the contribution of extrasynaptic δ-GABAARs to male and female binge-like drinking in a critical area of mesolimbic circuitry-the ventral tegmental area (VTA). Quantitative PCR revealed higher Gabrd transcript levels and larger tonic currents in the VTA of females compared to males. In contrast, male and female Gabrg2 transcript levels and measures of phasic inhibition were equivalent. Intra-VTA infusion of AAV-Cre-GFP in floxed Gabrd mice downregulated δ-GABAARs and decreased binge-like drinking in females. There was no significant difference in either male or female mice after GABAAR γ2 subunit reduction in the VTA following AAV-Cre-GFP infusion in floxed Gabrg2 mice. Collectively, these findings suggest sex differences and GABAAR subunit specificity in alcohol intake.

Synaptic plasticity mechanisms common to learning and alcohol use disorder

Alcohol use disorders include drinking problems that span a range from binge drinking to alcohol abuse and dependence. Plastic changes in synaptic efficacy, such as long-term depression and long-term potentiation are widely recognized as mechanisms involved in learning and memory, responses to drugs of abuse, and addiction. In this review, we focus on the effects of chronic ethanol (EtOH) exposure on the induction of synaptic plasticity in different brain regions. We also review findings indicating that synaptic plasticity occurs in vivo during EtOH exposure, with a focus on ex vivo electrophysiological indices of plasticity. Evidence for effects of EtOH-induced or altered synaptic plasticity on learning and memory and EtOH-related behaviors is also reviewed. As this review indicates, there is much work needed to provide more information about the molecular, cellular, circuit, and behavioral consequences of EtOH interactions with synaptic plasticity mechanisms.

GABA and Glutamate Synaptic Coadaptations to Chronic Ethanol in the Striatum

Alcohol (ethanol) is a widely used and abused drug with approximately 90% of adults over the age of 18 consuming alcohol at some point in their lifetime. Alcohol exerts its actions through multiple neurotransmitter systems within the brain, most notably the GABAergic and glutamatergic systems. Alcohol's actions on GABAergic and glutamatergic neurotransmission have been suggested to underlie the acute behavioral effects of ethanol. The striatum is the primary input nucleus of the basal ganglia that plays a role in motor and reward systems. The effect of ethanol on GABAergic and glutamatergic neurotransmission within striatal circuitry has been thought to underlie ethanol taking, seeking, withdrawal and relapse. This chapter reviews the effects of ethanol on GABAergic and glutamatergic transmission, highlighting the dynamic changes in striatal circuitry from acute to chronic exposure and withdrawal.