Chronic alcohol drinking alters neuronal dendritic spines in the brain reward center nucleus accumbens

The Matricellular Protein Hevin Is Involved in Alcohol Use Disorder

Astrocytic-secreted matricellular proteins have been shown to influence various aspects of synaptic function. More recently, they have been found altered in animal models of psychiatric disorders such as drug addiction. Hevin (also known as Sparc-like 1) is a matricellular protein highly expressed in the adult brain that has been implicated in resilience to stress, suggesting a role in motivated behaviors. To address the possible role of hevin in drug addiction, we quantified its expression in human postmortem brains and in animal models of alcohol abuse. Hevin mRNA and protein expression were analyzed in the postmortem human brain of subjects with an antemortem diagnosis of alcohol use disorder (AUD, n = 25) and controls (n = 25). All the studied brain regions (prefrontal cortex, hippocampus, caudate nucleus and cerebellum) in AUD subjects showed an increase in hevin levels either at mRNA or/and protein levels. To test if this alteration was the result of alcohol exposure or indicative of a susceptibility factor to alcohol consumption, mice were exposed to different regimens of intraperitoneal alcohol administration. Hevin protein expression was increased in the nucleus accumbens after withdrawal followed by a ethanol challenge. The role of hevin in AUD was determined using an RNA interference strategy to downregulate hevin expression in nucleus accumbens astrocytes, which led to increased ethanol consumption. Additionally, ethanol challenge after withdrawal increased hevin levels in blood plasma. Altogether, these results support a novel role for hevin in the neurobiology of AUD.

Bmal1 in the striatum influences alcohol intake in a sexually dimorphic manner

Alcohol consumption has been strongly associated with circadian clock gene expression in mammals. Analysis of clock genes revealed a potential role of Bmal1 in the control of alcohol drinking behavior. However, a causal role of Bmal1 and neural pathways through which it may influence alcohol intake have not yet been established. Here we show that selective ablation of Bmal1 (Cre/loxP system) from medium spiny neurons of the striatum induces sexual dimorphic alterations in alcohol consumption in mice, resulting in augmentation of voluntary alcohol intake in males and repression of intake in females. Per2mRNA expression, quantified by qPCR, decreases in the striatum after the deletion of Bmal1. To address the possibility that the effect of striatal Bmal1 deletion on alcohol intake and preference involves changes in the local expression of Per2, voluntary alcohol intake (two-bottle, free-choice paradigm) was studied in mice with a selective ablation of Per2 from medium spiny neurons of the striatum. Striatal ablation of Per2 increases voluntary alcohol intake in males but has no effect in females. Striatal Bmal1 and Per2 expression thus may contribute to the propensity to consume alcohol in a sex -specific manner in mice.

Effect of chronic ethanol consumption in rhesus macaques on the nucleus accumbens core transcriptome

The nucleus accumbens core (NAcc) has been repeatedly demonstrated to be a key component of the circuitry associated with excessive ethanol consumption. Previous studies have illustrated that in a nonhuman primate (NHP) model of chronic ethanol consumption, there is significant epigenetic remodeling of the NAcc. In the current study, RNA-Seq was used to examine genome-wide gene expression in eight each of control, low/binge (LD*), and high/very high (HD*) rhesus macaque drinkers. Using an FDR < 0.05, zero genes were significantly differentially expressed (DE) between LD* and controls, six genes between HD* and LD*, and 734 genes between HD* and controls. Focusing on HD* versus control DE genes, the upregulated genes (N = 366) were enriched in genes with annotations associated with signal recognition particle (SRP)-dependent co-translational protein targeting to membrane (FDR < 3 × 10-59 ), structural constituent of ribosome (FDR < 3 × 10-47 ), and ribosomal subunit (FDR < 5 × 10-48 ). Downregulated genes (N = 363) were enriched in annotations associated with behavior (FDR < 2 × 10-4 ), membrane organization (FDR < 1 × 10-4 ), inorganic cation transmembrane transporter activity (FDR < 2 × 10-3 ), synapse part (FDR < 4 × 10-10 ), glutamatergic synapse (FDR < 1 × 10-6 ), and GABAergic synapse (FDR < 6 × 10-4 ). Ingenuity Pathway Analysis (IPA) revealed that EIF2 signaling and mTOR pathways were significantly upregulated in HD* animals (FDR < 3 × 10-33 and <2 × 10-16 , respectively). Overall, the data supported our working hypothesis; excessive consumption would be associated with transcriptional differences in GABA/glutamate-related genes.

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.

Effects of chemogenetic manipulation of the nucleus accumbens core in male C57BL/6J mice

Binge drinking is a widespread public health concern with limited effective treatment options. To better select pharmaceutical targets, it is imperative to expand our knowledge of the underlying neural mechanisms involved in binge drinking. Our previous experiments in C57BL/6J female mice found that increasing activity in the nucleus accumbens (NAc) core using excitatory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) reduced binge-like drinking. These results differed from what has been found in males; however, it is unclear whether differences in experimental procedures or sex underlie these discrepancies. We matched the conditions used in our female study and asked whether bidirectional manipulation of NAc core activity has different effects on binge-like drinking in males. Male C57BL/6J mice were stereotaxically injected with AAV2 hSyn-HA hM3Dq (excitatory), -hM4Di (inhibitory), or -eGFP bilaterally into the NAc core. We tested the effects of altering NAc activity on binge-like ethanol intake using Drinking in the Dark (DID). During the first week, mice were pre-treated with vehicle to establish baseline ethanol intake. In week 2, mice were treated with 1 mg/kg CNO prior to DID to determine the effects of DREADD-induced changes in NAc core activity on ethanol intake. Decreasing activity via CNO/hM4Di significantly decreased binge-like drinking in male mice relative to eGFP and hM4Di groups. We also measured intake of sucrose, quinine, and water after CNO treatment and found that increasing NAc core activity via CNO/hM3Dq increased quinine intake, and increased water intake over time. We did not observe significant differences in the GFP or hM4Di groups. This work suggests there exist apparent sex-related differences in NAc core contributions to binge-like alcohol drinking, thus demonstrating the need for inclusion of both sexes in future work.

Maternal Exposure to Di-(2-ethylhexyl) Phthalate Impairs Hippocampal Synaptic Plasticity in Male Offspring: Involvement of Damage to Dendritic Spine Development

Exposure to di-(2-ethylhexyl) phthalate (DEHP), a widely used kind of plasticizer, can result in neurodevelopment impairments and learning and memory disorders. We studied the effects and possible mechanisms of maternal DEHP treatment on hippocampal synaptic plasticity in offspring. Pregnant Wistar rats were randomly divided into four groups and received 0, 30, 300, 750 (mg/kg)/d DEHP by gavage from gestational day (GD) 0 to postnatal day (PN) 21. Our data showed that DEHP exposure impaired hippocampal synaptic plasticity, damaged synaptic ultrastructure, and decreased synaptic protein levels in male pups. Furthermore, DEHP decreased the density of dendritic spines, affected F-actin polymerization, and downregulated the Rac1/PAK/LIMK1/cofilin signaling pathway in male offspring. However, the alterations in the hippocampi of female offspring were not observed. These results illustrate that maternal DEHP exposure could impair hippocampal synaptic plasticity by affecting synaptic structure and dendritic spine development in male offspring, which may be attributed to altered cytoskeleton construction induced by downregulation of the Rac1/PAK/LIMK1/cofilin signaling pathway.

One Is Not Enough: Understanding and Modeling Polysubstance Use

Substance use disorder (SUD) is a chronic, relapsing disease with a highly multifaceted pathology that includes (but is not limited to) sensitivity to drug-associated cues, negative affect, and motivation to maintain drug consumption. SUDs are highly prevalent, with 35 million people meeting criteria for SUD. While drug use and addiction are highly studied, most investigations of SUDs examine drug use in isolation, rather than in the more prevalent context of comorbid substance histories. Indeed, 11.3% of individuals diagnosed with a SUD have concurrent alcohol and illicit drug use disorders. Furthermore, having a SUD with one substance increases susceptibility to developing dependence on additional substances. For example, the increased risk of developing heroin dependence is twofold for alcohol misusers, threefold for cannabis users, 15-fold for cocaine users, and 40-fold for prescription misusers. Given the prevalence and risk associated with polysubstance use and current public health crises, examining these disorders through the lens of co-use is essential for translatability and improved treatment efficacy. The escalating economic and social costs and continued rise in drug use has spurred interest in developing preclinical models that effectively model this phenomenon. Here, we review the current state of the field in understanding the behavioral and neural circuitry in the context of co-use with common pairings of alcohol, nicotine, cannabis, and other addictive substances. Moreover, we outline key considerations when developing polysubstance models, including challenges to developing preclinical models to provide insights and improve treatment outcomes.

Chronic Chemogenetic Stimulation of the Nucleus Accumbens Produces Lasting Reductions in Binge Drinking and Ameliorates Alcohol-Related Morphological and Transcriptional Changes

Binge drinking is a dangerous pattern of behavior. We tested whether chronically manipulating nucleus accumbens (NAc) activity (via clozapine-N-oxide (CNO) and Designer Receptors Exclusively Activated by Designer Drugs (DREADD)) could produce lasting effects on ethanol binge-like drinking in mice selectively bred to drink to intoxication. We found chronically increasing NAc activity (4 weeks, via CNO and the excitatory DREADD, hM3Dq) decreased binge-like drinking, but did not observe CNO-induced changes in drinking with the inhibitory DREADD, hM4Di. The CNO/hM3Dq-induced reduction in ethanol drinking persisted for at least one week, suggesting adaptive neuroplasticity via transcriptional and epigenetic mechanisms. Therefore, we defined this plasticity at the morphological and transcriptomic levels. We found that chronic binge drinking (6 weeks) altered neuronal morphology in the NAc, an effect that was ameliorated with CNO/hM3Dq. Moreover, we detected significant changes in expression of several plasticity-related genes with binge drinking that were ameliorated with CNO treatment (e.g., Hdac4). Lastly, we found that LMK235, an HDAC4/5 inhibitor, reduced binge-like drinking. Thus, we were able to target specific molecular pathways using pharmacology to mimic the behavioral effects of DREADDs.

Evidence for incentive salience sensitization as a pathway to alcohol use disorder

The incentive salience sensitization (ISS) theory of addiction holds that addictive behavior stems from the ability of drugs to progressively sensitize the brain circuitry that mediates attribution of incentive salience (IS) to reward-predictive cues and its behavioral manifestations. In this article, we establish the plausibility of ISS as an etiological pathway to alcohol use disorder (AUD). We provide a comprehensive and critical review of evidence for: (1) the ability of alcohol to sensitize the brain circuitry of IS attribution and expression; and (2) attribution of IS to alcohol-predictive cues and its sensitization in humans and non-human animals. We point out gaps in the literature and how these might be addressed. We also highlight how individuals with different alcohol subjective response phenotypes may differ in susceptibility to ISS as a pathway to AUD. Finally, we discuss important implications of this neuropsychological mechanism in AUD for psychological and pharmacological interventions attempting to attenuate alcohol craving and cue reactivity.

Effects of Ethanol Exposure and Withdrawal on Neuronal Morphology in the Agranular Insular and Prelimbic Cortices: Relationship with Withdrawal-Related Structural Plasticity in the Nucleus Accumbens

The present study investigated the effects of chronic intermittent ethanol exposure and withdrawal on dendritic morphology and spine density in the agranular insular and prelimbic cortices. Adult male Sprague–Dawley rats were passively exposed to vaporized ethanol (~37 mg/L; 12 h/day) or air (control) for ten consecutive days. Dendritic length, branching, and spine density were quantified in layer II/III pyramidal neurons 24 hours or seven days following the final ethanol exposure. Compared to unexposed control animals there were structural alterations on neurons in the prelimbic cortex, and to a lesser extent the agranular insular cortex. The most prominent ethanol-related differences were the transient increases in dendritic length and branching in prelimbic neurons at 24 h post-cessation, and increased mushroom-shaped spines at seven days post-cessation. The results obtained in the prelimbic cortex are the opposite of those previously reported in the nucleus accumbens core (Peterson, et al. 2015), suggesting that these regions undergo distinct functional adaptations following ethanol exposure and withdrawal.

Fish oil treatment reduces chronic alcohol exposure induced synaptic changes

Alcohol addiction is a chronic neuropsychiatric disorder that represents one of the most serious global public health problems. Yet, currently there still lacks an effective pharmacotherapy. Omega-3 polyunsaturated fatty acids (N-3 PUFAs) have exhibited beneficial effects in a variety of neurological disorders, particularly in reversing behavioral deficits and neurotoxicity induced by prenatal alcohol exposure and binge drinking. In the present study, we investigated if fish oil, which is rich in N-3 PUFAs, had beneficial effects on preventing relapse and alleviating withdrawal symptoms after chronic alcohol exposure. Our results demonstrated that fish oil significantly reduced the chronic alcohol exposure-induced aberrant dendritic morphologic changes of the medium-sized spiny neurons in the core and the shell of nucleus accumbens. This inhibited the expression of AMPAR2-lacking AMPARs and their accumulation on the post synaptic membranes of medium-sized spiny neurons and eventually alleviated withdrawal symptoms and alcohol dependence. Our study therefore suggests that N-3 PUFAs are promising for treating withdrawal symptoms and alcohol dependence.

Glucagon-Like Peptide-1 Receptor Agonist Treatment Does Not Reduce Abuse-Related Effects of Opioid Drugs

Dependence on opioids and the number of opioid overdose deaths are serious and escalating public health problems, but medication-assisted treatments for opioid addiction remain inadequate for many patients. Glucagon-like pepide-1 (GLP-1) is a gut hormone and neuropeptide with actions in peripheral tissues and in the brain, including regulation of blood glucose and food intake. GLP-1 analogs, which are approved diabetes medications, can reduce the reinforcing and rewarding effects of alcohol, cocaine, amphetamine, and nicotine in rodents. Investigations on effects of GLP-1 analogs on opioid reward and reinforcement have not been reported. We assessed the effects of the GLP-1 receptor agonist Exendin-4 (Ex4) on opioid-related behaviors in male mice, i.e., morphine-conditioned place preference (CPP), intravenous self-administration (IVSA) of the short-acting synthetic opioid remifentanil, naltrexone-precipitated morphine withdrawal, morphine analgesia (male and female mice), and locomotor activity. Ex4 treatment had no effect on morphine-induced CPP, withdrawal, or hyperlocomotion. Ex4 failed to decrease remifentanil self-administration, if anything reinforcing effects of remifentanil appeared increased in Ex4-treated mice relative to saline. Ex4 did not significantly affect analgesia. In contrast, Ex4 dose dependently decreased oral alcohol self-administration, and suppressed spontaneous locomotor activity. Taken together, Ex4 did not attenuate the addiction-related behavioral effects of opioids, indicating that GLP-1 analogs would not be useful medications in the treatment of opioid addiction. This difference between opioids and other drug classes investigated to date may shed light on the mechanism of action of GLP-1 receptor treatment in the addictive effects of alcohol, central stimulants, and nicotine.

Increased Nucleus Accumbens Volume in College Binge Drinkers - Preliminary Evidence From Manually Segmented MRI Analysis

INTRODUCTION

Binge drinking (BD) is characterized by high alcohol intake in a short time followed by periods of withdrawal. This pattern is very common during adolescence and early adulthood, a developmental stage marked by the maturation of the fronto-striatal networks. The basal ganglia, specifically the nucleus accumbens (NAcc) and the caudate nucleus (CN), are part of the fronto-striatal limbic circuit involved in reward processes underlying addictive behaviors. Abnormal NAcc and CN morphometry has been noted in alcoholics and other drug abusers, however the effects of BD on these subcortical regions have been poorly explored. Accordingly, the main goal of the present study was to address potential morphological alterations in the NAcc and CN in a sample of college binge drinkers (BDs).

METHOD

Manual segmentation of the NAcc and the CN was performed in Magnetic Resonance Imaging (MRI) of 20 college BDs and 16 age-matched alcohol abstainers (18-23 years-old).

RESULTS

A two-way mixed ANOVA revealed no group differences in the volumetry of the CN, whereas increased NAcc volume was observed in the BD group when compared to their abstinent control peers.

DISCUSSION

These findings are in line with previous automatically segmented MRI reports highlighting abnormalities in a key region involved in drug rewarding processes in BDs.

Dopamine and addiction: what have we learned from 40 years of research

Among the neurotransmitters involved in addiction, dopamine (DA) is clearly the best known. The critical role of DA in addiction is supported by converging evidence that has been accumulated in the last 40 years. In the present review, first we describe the dopaminergic system in terms of connectivity, functioning and involvement in reward processes. Second, we describe the functional, structural, and molecular changes induced by drugs within the DA system in terms of neuronal activity, synaptic plasticity and transcriptional and molecular adaptations. Third, we describe how genetic mouse models have helped characterizing the role of DA in addiction. Fourth, we describe the involvement of the DA system in the vulnerability to addiction and the interesting case of addiction DA replacement therapy in Parkinson's disease. Finally, we describe how the DA system has been targeted to treat patients suffering from addiction and the result obtained in clinical settings and we discuss how these different lines of evidence have been instrumental in shaping our understanding of the physiopathology of drug addiction.

Dopamine Restores Limbic Memory Loss, Dendritic Spine Structure, and NMDAR-Dependent LTD in the Nucleus Accumbens of Alcohol-Withdrawn Rats

Alcohol abuse leads to aberrant forms of emotionally salient memory, i.e., limbic memory, that promote escalated alcohol consumption and relapse. Accordingly, activity-dependent structural abnormalities are likely to contribute to synaptic dysfunctions that occur from suddenly ceasing chronic alcohol consumption. Here we show that alcohol-dependent male rats fail to perform an emotional-learning task during abstinence but recover their functioning by l-3,4-dihydroxyphenylalanin (l-DOPA) administration during early withdrawal. l-DOPA also reverses the selective loss of dendritic "long thin" spines observed in medium spiny neurons of the nucleus accumbens (NAc) shell of alcohol-dependent rats during abstinence, as well as the reduction in tyrosine hydroxylase immunostaining and postsynaptic density-95-positive elements. Patch-clamp experiments in NAc slices reveal that both in vivo systemic l-DOPA administration and in vitro exposure to dopamine can restore the loss of long-term depression (LTD) formation, counteract the reduction in NMDAR-mediated synaptic currents and rectify the altered NMDAR/AMPAR ratio observed in alcohol-withdrawn rats. Further, in vivo microdialysis experiments show that blunted dopaminergic signaling is revived after l-DOPA treatment during early withdrawal. These results suggest a key role of an efficient dopamine signaling for maintaining, and restore, neural trophism, NMDA-dependent LTD, and ultimately optimal learning.SIGNIFICANCE STATEMENT Blunted dopamine signaling and altered glutamate connectivity in the nucleus accumbens represent the neuroanatomical basis for the impairment in aversive limbic memory observed during withdrawal in alcohol dependence. Supplying l-DOPA during withdrawal re-establishes synaptic morphology and functional neuroadaptations, suggesting a complete recovery of nucleus accumbens glutamatergic synaptic plasticity when dopamine is revived. Importantly, restoring dopamine transmission allows those synapses to encode emotionally relevant information and rescue flexibility in the neuronal circuits that process limbic memory formation. Under these conditions, drugs capable of selectively boosting the dopaminergic function during the "fluid" and still responsive state of the early withdrawn maladaptive synapses may help in the treatment of alcohol addiction.

Ethanol-Induced Behavioral Sensitization Alters the Synaptic Transcriptome and Exon Utilization in DBA/2J Mice

Alcoholism is a complex behavioral disorder characterized by loss of control in limiting intake, and progressive compulsion to seek and consume ethanol. Prior studies have suggested that the characteristic behaviors associated with escalation of drug use are caused, at least in part, by ethanol-evoked changes in gene expression affecting synaptic plasticity. Implicit in this hypothesis is a dependence on new protein synthesis and remodeling at the synapse. It is well established that mRNA can be transported to distal dendritic processes, where it can undergo localized translation. It is unknown whether such modulation of the synaptic transcriptome might contribute to ethanol-induced synaptic plasticity. Using ethanol-induced behavioral sensitization as a model of neuroplasticity, we investigated whether repeated exposure to ethanol altered the synaptic transcriptome, contributing to mechanisms underlying subsequent increases in ethanol-evoked locomotor activity. RNAseq profiling of DBA/2J mice subjected to acute ethanol or ethanol-induced behavioral sensitization was performed on frontal pole synaptoneurosomes to enrich for synaptic mRNA. Genomic profiling showed distinct functional classes of mRNA enriched in the synaptic vs. cytosolic fractions, consistent with their role in synaptic function. Ethanol sensitization regulated more than twice the number of synaptic localized genes compared to acute ethanol exposure. Synaptic biological processes selectively perturbed by ethanol sensitization included protein folding and modification as well as and mitochondrial respiratory function, suggesting repeated ethanol exposure alters synaptic energy production and the processing of newly translated proteins. Additionally, marked differential exon usage followed ethanol sensitization in both synaptic and non-synaptic cellular fractions, with little to no perturbation following acute ethanol exposure. Altered synaptic exon usage following ethanol sensitization strongly affected genes related to RNA processing and stability, translational regulation, and synaptic function. These genes were also enriched for targets of the FMRP RNA-binding protein and contained consensus sequence motifs related to other known RNA binding proteins, suggesting that ethanol sensitization altered selective mRNA trafficking mechanisms. This study provides a foundation for investigating the role of ethanol in modifying the synaptic transcriptome and inducing changes in synaptic plasticity.

EFhd2/Swiprosin-1 is a common genetic determinator for sensation-seeking/low anxiety and alcohol addiction

In many societies, the majority of adults regularly consume alcohol. However, only a small proportion develops alcohol addiction. Individuals at risk often show a high sensation-seeking/low-anxiety behavioural phenotype. Here we asked which role EF hand domain containing 2 (EFhd2; Swiprosin-1) plays in the control of alcohol addiction-associated behaviours. EFhd2 knockout (KO) mice drink more alcohol than controls and spontaneously escalate their consumption. This coincided with a sensation-seeking and low-anxiety phenotype. A reversal of the behavioural phenotype with β-carboline, an anxiogenic inverse benzodiazepine receptor agonist, normalized alcohol preference in EFhd2 KO mice, demonstrating an EFhd2-driven relationship between personality traits and alcohol preference. These findings were confirmed in a human sample where we observed a positive association of the EFhd2 single-nucleotide polymorphism rs112146896 with lifetime drinking and a negative association with anxiety in healthy adolescents. The lack of EFhd2 reduced extracellular dopamine levels in the brain, but enhanced responses to alcohol. In confirmation, gene expression analysis revealed reduced tyrosine hydroxylase expression and the regulation of genes involved in cortex development, Eomes and Pax6, in EFhd2 KO cortices. These findings were corroborated in Xenopus tadpoles by EFhd2 knockdown. Magnetic resonance imaging (MRI) in mice showed that a lack of EFhd2 reduces cortical volume in adults. Moreover, human MRI confirmed the negative association between lifetime alcohol drinking and superior frontal gyrus volume. We propose that EFhd2 is a conserved resilience factor against alcohol consumption and its escalation, working through Pax6/Eomes. Reduced EFhd2 function induces high-risk personality traits of sensation-seeking/low anxiety associated with enhanced alcohol consumption, which may be related to cortex function.

Donepezil Reverses Dendritic Spine Morphology Adaptations and Fmr1 Epigenetic Modifications in Hippocampus of Adult Rats After Adolescent Alcohol Exposure

BACKGROUND

Adolescent intermittent ethanol (AIE) exposure produces persistent impairments in cholinergic and epigenetic signaling and alters markers of synapses in the hippocampal formation, effects that are thought to drive hippocampal dysfunction in adult rodents. Donepezil (Aricept), a cholinesterase inhibitor, is used clinically to ameliorate memory-related cognitive deficits. Given that donepezil also prevents morphological impairment in preclinical models of neuropsychiatric disorders, we investigated the ability of donepezil to reverse morphological and epigenetic adaptations in the hippocampus of adult rats exposed to AIE. Because of the known relationship between dendritic spine density and morphology with the fragile X mental retardation 1 (Fmr1) gene, we also assessed Fmr1 expression and its epigenetic regulation in hippocampus after AIE and donepezil pretreatment.

METHODS

Adolescent rats were administered intermittent ethanol for 16 days starting on postnatal day 30. Rats were treated with donepezil (2.5 mg/kg) once a day for 4 days starting 20 days after the completion of AIE exposure. Brains were dissected out after the fourth donepezil dose, and spine analysis was completed in dentate gyrus granule neurons. A separate cohort of rats, treated identically, was used for molecular studies.

RESULTS

AIE exposure significantly reduced dendritic spine density and altered morphological characteristics of subclasses of dendritic spines. AIE exposure also increased mRNA levels and H3-K27 acetylation occupancy of the Fmr1 gene in hippocampus. Treatment of AIE-exposed adult rats with donepezil reversed both the dendritic spine adaptations and epigenetic modifications and expression of Fmr1.

CONCLUSIONS

These findings indicate that AIE produces long-lasting decreases in dendritic spine density and changes in Fmr1 gene expression in the hippocampal formation, suggesting morphological and epigenetic mechanisms underlying previously reported behavioral deficits after AIE. The reversal of these effects by subchronic, post-AIE donepezil treatment indicates that these AIE effects can be reversed by up-regulating cholinergic function.

Adolescent alcohol exposure alters lysine demethylase 1 (LSD1) expression and histone methylation in the amygdala during adulthood

Alcohol exposure in adolescence is an important risk factor for the development of alcoholism in adulthood. Epigenetic processes are implicated in the persistence of adolescent alcohol exposure-related changes, specifically in the amygdala. We investigated the role of histone methylation mechanisms in the persistent effects of adolescent intermittent ethanol (AIE) exposure in adulthood. Adolescent rats were exposed to 2 g/kg ethanol (2 days on/off) or intermittent n-saline (AIS) during postnatal days (PND) 28-41 and used for behavioral and epigenetic studies. We found that AIE exposure caused a long-lasting decrease in mRNA and protein levels of lysine demethylase 1(Lsd1) and mRNA levels of Lsd1 + 8a (a neuron-specific splice variant) in specific amygdaloid structures compared with AIS-exposed rats when measured at adulthood. Interestingly, AIE increased histone H3 lysine 9 dimethylation (H3K9me2) levels in the central nucleus of the amygdala (CeA) and medial nucleus of the amygdala (MeA) in adulthood without producing any change in H3K4me2 protein levels. Acute ethanol challenge (2 g/kg) in adulthood attenuated anxiety-like behaviors and the decrease in Lsd1 + 8a mRNA levels in the amygdala induced by AIE. AIE caused an increase in H3K9me2 occupancy at the brain-derived neurotrophic factor exon IV promoter in the amygdala that returned to baseline after acute ethanol challenge in adulthood. These results indicate that AIE specifically modulates epizymes involved in H3K9 dimethylation in the amygdala in adulthood, which are possibly responsible for AIE-induced chromatin remodeling and adult psychopathology such as anxiety.

Genome-wide analysis of the nucleus accumbens identifies DNA methylation signals differentiating low/binge from heavy alcohol drinking

Alcohol-use disorders encompass a range of drinking levels and behaviors, including low, binge, and heavy drinking. In this regard, investigating the neural state of individuals who chronically self-administer lower doses of alcohol may provide insight into mechanisms that prevent the escalation of alcohol use. DNA methylation is one of the epigenetic mechanisms that stabilizes adaptations in gene expression and has been associated with alcohol use. Thus, we investigated DNA methylation, gene expression, and the predicted neural effects in the nucleus accumbens core (NAcc) of male rhesus macaques categorized as "low" or "binge" drinkers, compared to "alcohol-naïve" and "heavy" drinkers based on drinking patterns during a 12-month alcohol self-administration protocol. Using genome-wide CpG-rich region enrichment and bisulfite sequencing, the methylation levels of 2.6 million CpGs were compared between alcohol-naïve (AN), low/binge (L/BD), and heavy/very heavy (H/VHD) drinking subjects (n = 24). Through regional clustering analysis, we identified nine significant differential methylation regions (DMRs) that specifically distinguished ANs and L/BDs, and then compared those DMRs among H/VHDs. The DMRs mapped to genes encoding ion channels, receptors, cell adhesion molecules, and cAMP, NF-κβ and Wnt signaling pathway proteins. Two of the DMRs, linked to PDE10A and PKD2L2, were also differentially methylated in H/VHDs, suggesting an alcohol-dose independent effect. However, two other DMRs, linked to the CCBE1 and FZD5 genes, had L/BD methylation levels that significantly differed from both ANs and H/VHDs. The remaining five DMRs also differentiated L/BDs and ANs. However, H/VHDs methylation levels were not distinguishable from either of the two groups. Functional validation of two DMRs, linked to FZD5 and PDE10A, support their role in regulating gene expression and exon usage, respectively. In summary, the findings demonstrate that L/BD is associated with unique DNA methylation signatures in the primate NAcc, and that the methylation signatures identify synaptic genes that may play a role in preventing the escalation of alcohol use.

Alignment of the transcriptome with individual variation in animals selectively bred for High Drinking-In-the-Dark (HDID)

Among animals at risk for excessive ethanol consumption such as the HDID selected mouse lines, there is considerable individual variation in the amount of ethanol consumed and the associated blood ethanol concentrations (BECs). For the HDID lines, this variation occurs even though the residual genetic variation associated with the DID phenotype has been largely exhausted and thus is most likely associated with epigenetic factors. Here we focus on the question of whether the genes associated with individual variation in HDID-1 mice are different from those associated with selection (risk) (Iancu et al., 2013). Thirty-three HDID-1 mice were phenotyped for their BECs at the end of a standard DID trial, were sacrificed 3 weeks later, and RNA-Seq was used to analyze the striatal transcriptome. The data obtained illustrate that there is considerable overlap of the risk and variation gene sets, both focused on the fine-tuning of synaptic plasticity.

Alcohol-dose-dependent DNA methylation and expression in the nucleus accumbens identifies coordinated regulation of synaptic genes

Alterations in DNA methylation have been associated with alcohol exposure and proposed to contribute to continued alcohol use; however, the molecular mechanisms involved remain obscure. We investigated the escalating effects of alcohol use on DNA methylation, gene expression and predicted neural effects in the nucleus accumbens of rhesus macaques that self-administered 4% alcohol for over 12 months. Using an exploratory approach to identify CpG-rich regions, followed by bisulfite sequencing, the methylation levels of 2.7 million CpGs were compared between seven low-binge drinkers and nine heavy-very heavy drinking subjects. We identified 17 significant differential methylation regions (DMRs), including 14 with methylation levels that were correlated with average daily alcohol consumption. The size of the DMRs ranged from 29 to 158 bp (mean=63.7), included 4-19 CpGs per DMR (mean=8.06) and spanned a range of average methylation values from 5 to 34%. Eight of the DMRs mapped to genes implicated in modulating synaptic plasticity. Six of the synaptic genes have not previously been linked to alcohol use. Validation studies of these eight DMRs using bisulfite amplicon sequencing and an expanded set of 30 subjects confirmed the significant alcohol-dose-associated methylation of the DMRs. Expression analysis of three of the DMR-associated genes, LRP5, GPR39 and JAKMIP1, revealed significant correlations between DMR methylation and whole-gene or alternative transcript expression, supporting a functional role in regulating gene expression. Together, these studies suggest that alcohol-associated synaptic remodeling may be regulated and coordinated at the level of DNA methylation.

Acquisition of morphine conditioned place preference increases the dendritic complexity of nucleus accumbens core neurons

Contexts associated with opioid reward trigger craving and relapse in opioid addiction. Effects of reward-context associative learning on nucleus accumbens (NAc) dendritic morphology were studied using morphine conditioned place preference (CPP). Morphine-conditioned mice received saline and morphine 10 mg/kg subcutaneous (s.c.) on alternate days. Saline-conditioned mice received saline s.c. each day. Morphine-conditioned and saline-conditioned groups received injections immediately before each of eight daily conditioning sessions. Morphine homecage controls had no CPP training, but received saline and morphine in the homecage concomitantly with the morphine-conditioned group. Morphine conditioning produced greater place preference than saline conditioning. Mice were sacrificed 1 day after CPP expression. Dendritic changes were studied using Golgi-Cox staining and digital tracing of NAc core and shell neurons. In the NAc core, morphine homecage administration increased spine density, while morphine conditioning increased dendritic complexity, as defined by increased dendritic count, length and intersections. Place preference positively correlated with dendritic length and intersections in the NAc core. The core may mediate reward consolidation and determine how context-related signals from the shell lead to motor behavior. The combination of drug and conditioning in the morphine-conditioned group produced unique morphological effects different from the effects of drug or conditioning procedures by themselves. An additional study found no differences in neuron morphology between saline-conditioned mice, trained as described earlier, and mice that were not conditioned, but received saline in the homecage. The unique effect of morphine reward learning on NAc core dendrites reflects a brain substrate that could be targeted for therapeutic intervention in addiction.

Adolescent Alcohol Exposure: Burden of Epigenetic Reprogramming, Synaptic Remodeling, and Adult Psychopathology

Adolescence represents a crucial phase of synaptic maturation characterized by molecular changes in the developing brain that shape normal behavioral patterns. Epigenetic mechanisms play an important role in these neuromaturation processes. Perturbations of normal epigenetic programming during adolescence by ethanol can disrupt these molecular events, leading to synaptic remodeling and abnormal adult behaviors. Repeated exposure to binge levels of alcohol increases the risk for alcohol use disorder (AUD) and comorbid psychopathology including anxiety in adulthood. Recent studies in the field clearly suggest that adolescent alcohol exposure causes widespread and persistent changes in epigenetic, neurotrophic, and neuroimmune pathways in the brain. These changes are manifested by altered synaptic remodeling and neurogenesis in key brain regions leading to adult psychopathology such as anxiety and alcoholism. This review details the molecular mechanisms underlying adolescent alcohol exposure-induced changes in synaptic plasticity and the development of alcohol addiction-related phenotypes in adulthood.

Chronic intermittent ethanol exposure and withdrawal leads to adaptations in nucleus accumbens core postsynaptic density proteome and dendritic spines

Alcohol use disorder is a chronic relapsing brain disease characterized by the loss of ability to control alcohol (ethanol) intake despite knowledge of detrimental health or personal consequences. Clinical and pre-clinical models provide strong evidence for chronic ethanol-associated alterations in glutamatergic signaling and impaired synaptic plasticity in the nucleus accumbens (NAc). However, the neural mechanisms that contribute to aberrant glutamatergic signaling in ethanol-dependent individuals in this critical brain structure remain unknown. Using an unbiased proteomic approach, we investigated the effects of chronic intermittent ethanol (CIE) exposure on neuroadaptations in postsynaptic density (PSD)-enriched proteins in the NAc of ethanol-dependent mice. Compared with controls, CIE exposure significantly changed expression levels of 50 proteins in the PSD-enriched fraction. Systems biology and functional annotation analyses demonstrated that the dysregulated proteins are expressed at tetrapartite synapses and critically regulate cellular morphology. To confirm this latter finding, the density and morphology of dendritic spines were examined in the NAc core of ethanol-dependent mice. We found that CIE exposure and withdrawal differentially altered dendrite diameter and dendritic spine density and morphology. Through the use of quantitative proteomics and functional annotation, these series of experiments demonstrate that ethanol dependence produces neuroadaptations in proteins that modify dendritic spine morphology. In addition, these studies identified novel PSD-related proteins that contribute to the neurobiological mechanisms of ethanol dependence that drive maladaptive structural plasticity of NAc neurons.

Mouse and Human Genetic Analyses Associate Kalirin with Ventral Striatal Activation during Impulsivity and with Alcohol Misuse

Impulsivity is associated with a spectrum of psychiatric disorders including drug addiction. To investigate genetic associations with impulsivity and initiation of drug taking, we took a two-step approach. First, we identified genes whose expression level in prefrontal cortex, striatum and accumbens were associated with impulsive behavior in the 5-choice serial reaction time task across 10 BXD recombinant inbred (BXD RI) mouse strains and their progenitor C57BL/6J and DBA2/J strains. Behavioral data were correlated with regional gene expression using GeneNetwork (www.genenetwork.org), to identify 44 genes whose probability of association with impulsivity exceeded a false discovery rate of < 0.05. We then interrogated the IMAGEN database of 1423 adolescents for potential associations of SNPs in human homologs of those genes identified in the mouse study, with brain activation during impulsive performance in the Monetary Incentive Delay task, and with novelty seeking scores from the Temperament and Character Inventory, as well as alcohol experience. There was a significant overall association between the human homologs of impulsivity-related genes and percentage of premature responses in the MID task and with fMRI BOLD-response in ventral striatum (VS) during reward anticipation. In contrast, no significant association was found between the polygenic scores and anterior cingulate cortex activation. Univariate association analyses revealed that the G allele (major) of the intronic SNP rs6438839 in the KALRN gene was significantly associated with increased VS activation. Additionally, the A-allele (minor) of KALRN intronic SNP rs4634050, belonging to the same haplotype block, was associated with increased frequency of binge drinking.

Stereological analyses of reward system nuclei in maternally deprived/separated alcohol drinking rats

The experience of early life stress can trigger complex neurochemical cascades that influence emotional and addictive behaviors later in life in both adolescents and adults. Recent evidence suggests that excessive alcohol drinking and drug-seeking behavior, in general, are co-morbid with depressive-like behavior. Both behaviors are reported in humans exposed to early life adversity, and are prominent features recapitulated in animal models of early life stress (ELS) exposure. Currently, little is known about whether or how ELS modulates reward system nuclei. In this study we use operant conditioning of rats to show that the maternal separation stress (MS) model of ELS consumes up to 3-fold greater quantities of 10% vol/vol EtOH in 1-h, consistently over a 3-week period. This was correlated with a significant 22% reduction in the number of dopaminergic-like neurons in the VTA of naïve MS rats, similar to genetically alcohol-preferring (P) rats which show a 35% reduction in tyrosine hydroxylase (TH)-positive dopaminergic neurons in the VTA. MS rats had a significantly higher 2-fold immobility time in the forced swim test (FST) and reduced sucrose drinking compared to controls, indicative of depressive-like symptomology and anhedonia. Consistent with this finding, stereological analysis revealed that amygdala neurons were 25% greater in number at P70 following MS exposure. Our previous examination of the dentate gyrus of hippocampus, a region involved in encoding emotional memory, revealed fewer dentate gyrus neurons after MS, but we now report this reduction in neurons occurs without effect on the number of astrocytes or length of astrocytic fibers. These data indicate that MS animals exhibit neuroanatomical changes in reward centers similar to those reported for high alcohol drinking rats, but aspects of astrocyte morphometry remained unchanged. These data are of high relevance to understand the breadth of neuronal pathology that ensues in reward loci following ELS.

DNA co-methylation modules in postmortem prefrontal cortex tissues of European Australians with alcohol use disorders

DNA methylome alterations in the prefrontal cortex (PFC) may contribute to risk for alcohol use disorders (AUDs). We examined postmortem PFC DNA methylomes of 16 male and seven female pairs of AUD and control subjects using Illumina's HumanMethylation450 BeadChip assays. In male AUD subjects, 1,812 CpGs (1,099 genes) were differentially methylated (9.5 × 10(-9) ≤ Pnominal ≤ 7.2 × 10(-4), q < 0.05). In females, no CpGs were associated with AUDs after multiple testing correction (q > 0.05). Twenty-one AUD-associated co-methylation modules were identified in males by co-methylation analysis. The 1,812 CpGs were over-presented by two AUD-associated co-methylation modules (Mturquoise: 1,048 CpGs/683 genes; Mblue: 429 CpGs/304 genes) (Phyper ≤ 0.001). Biological processes enriched for genes in these two modules included neural development and transcriptional regulation. Genes mapped by CpGs in these two modules were enriched in genome-wide association study-identified genes with variants associated with four substance dependence phenotypes or five psychiatric disorders. Additionally, 106 of the 1,812 CpGs were mapped to 93 genes (e.g., AUD-associated genes GRIK3, GRIN2C, and GABRA1) with differential expression in postmortem PFC of male AUD subjects. Our study demonstrates that DNA methylation alterations in the PFC are associated with (and might result in) increased risk of AUDs, and there was a complex DNA methylation-gene expression relationship.

Applying the new genomics to alcohol dependence

This review summarizes the proceedings of a symposium presented at the "Alcoholism and Stress: A Framework for Future Treatment Strategies" conference held in Volterra, Italy on May 6-9, 2014. The overall goal of the symposium titled "Applying the New Genomics to Alcohol Dependence", chaired by Dr. Adron Harris, was to highlight recent genomic discoveries and applications for profiling alcohol use disorder (AUD). Dr. Sean Farris discussed the gene expression networks related to lifetime consumption of alcohol within human prefrontal cortex. Dr. Andrzej Pietrzykowski presented the effects of alcohol on microRNAs in humans and animal models. Alcohol-induced alterations in the synaptic transcriptome were discussed by Dr. Michael Miles. Dr. Pietro Sanna examined methods to probe the gene regulatory networks that drive excessive alcohol drinking, and Dr. Samir Zakhari served as a panel discussant and summarized the proceedings. Collectively, the presentations emphasized the power of integrating multiple levels of genetics and transcriptomics with convergent biological processes and phenotypic behaviors to determine causal factors of AUD. The combined use of diverse data types demonstrates how unique approaches and applications can help categorize genetic complexities into relevant biological networks using a systems-level model of disease.

Neuroplasticity of A-type potassium channel complexes induced by chronic alcohol exposure enhances dendritic calcium transients in hippocampus

RATIONALE

Chronic alcohol-induced cognitive impairments and maladaptive plasticity of glutamatergic synapses are well-documented. However, it is unknown if prolonged alcohol exposure affects dendritic signaling that may underlie hippocampal dysfunction in alcoholics. Back-propagation of action potentials (bAPs) into apical dendrites of hippocampal neurons provides distance-dependent signals that modulate dendritic and synaptic plasticity. The amplitude of bAPs decreases with distance from the soma that is thought to reflect an increase in the density of Kv4.2 channels toward distal dendrites.

OBJECTIVE

The aim of this study was to quantify changes in hippocampal Kv4.2 channel function and expression using electrophysiology, Ca(2+) imaging, and western blot analyses in a well-characterized in vitro model of chronic alcohol exposure.

RESULTS

Chronic alcohol exposure significantly decreased expression of Kv4.2 channels and KChIP3 in hippocampus. This reduction was associated with an attenuation of macroscopic A-type K(+) currents in CA1 neurons. Chronic alcohol exposure increased bAP-evoked Ca(2+) transients in the distal apical dendrites of CA1 pyramidal neurons. The enhanced bAP-evoked Ca(2+) transients induced by chronic alcohol exposure were not related to synaptic targeting of N-methyl-D-aspartate (NMDA) receptors or morphological adaptations in apical dendritic arborization.

CONCLUSIONS

These data suggest that chronic alcohol-induced decreases in Kv4.2 channel function possibly mediated by a downregulation of KChIP3 drive the elevated bAP-associated Ca(2+) transients in distal apical dendrites. Alcohol-induced enhancement of bAPs may affect metaplasticity and signal integration in apical dendrites of hippocampal neurons leading to alterations in hippocampal function.

Deep TMS on alcoholics: effects on cortisolemia and dopamine pathway modulation. A pilot study

The hypothalamic pituitary adrenal axis and dopamine have a key role in transition from alcohol social use to addiction. The medial prefrontal cortex was shown to modulate dopaminergic activity and cortisol releasing factor (CRF) release in hypothalamic and extra-hypothalamic systems. The recent advancements in non-invasive neurostimulation technologies has enabled stimulation of deeper brain regions using H-coil transcranial magnetic stimulation (TMS) in humans. This randomized double-blind placebo-controlled pilot study aims to evaluate H-coil efficacy in stimulating the medial prefrontal cortex. Cortisolemia and prolactinemia were evaluated as effectiveness markers. Alcohol intake and craving were considered as secondary outcomes. Eighteen alcoholics were recruited and randomized into 2 homogeneous groups: 9 in the real stimulation group and 9 in the sham stimulation group. Repetitive TMS (rTMS) was administered through a magnetic stimulator over 10 sessions at 20 Hz, directed to the medial prefrontal cortex. rTMS significantly reduced blood cortisol levels and decreased prolactinemia, thus suggesting dopamine increase. Craving visual analogic scale (VAS) in treated patients decreased, as well as mean number of alcoholic drinks/day and drinks on days of maximum alcohol intake (DMAI). In the sham group there was no significant effect observed on cortisolemia, prolactinemia, mean number of alcoholic drinks/day, or drinks/DMAI. Thus, deep rTMS could be considered a potential new treatment for alcoholism.

Homer2 deletion alters dendritic spine morphology but not alcohol-associated adaptations in GluN2B-containing N-methyl-D-aspartate receptors in the nucleus accumbens

Repeated exposure to ethanol followed by withdrawal leads to alterations in glutamatergic signaling and impaired synaptic plasticity in the nucleus accumbens (NAc) in both clinical and preclinical models of ethanol exposure. Homer2 is a member of a family of postsynaptic density (PSD) scaffolding proteins that functions in part to cluster N-methyl-D-aspartate (NMDA) signaling complexes in the PSD, and has been shown to be critically important for plasticity in multiple models of drug and alcohol abuse. Here we used Homer2 knockout (KO) mice and a chronic intermittent intraperitoneal (IP) ethanol injection model to investigate a potential role for the protein in ethanol-induced adaptations in dendritic spine morphology and PSD protein expression. While deletion of Homer2 was associated with increased density of long spines on medium spiny neurons of the NAc core of saline treated mice, ethanol exposure had no effect on dendritic spine morphology in either wild-type (WT) or Homer2 KO mice. Western blot analysis of tissue samples from the NAc enriched for PSD proteins revealed a main effect of ethanol treatment on the expression of GluN2B, but there was no effect of genotype or treatment on the expression other glutamate receptor subunits or PSD95. These data indicate that the global deletion of Homer2 leads to aberrant regulation of dendritic spine morphology in the NAc core that is associated with an increased density of long, thin spines. Unexpectedly, intermittent IP ethanol did not affect spine morphology in either WT or KO mice. Together these data implicate Homer2 in the formation of long, thin spines and further supports its role in neuronal structure.

Molecular mechanisms of synaptic remodeling in alcoholism

Alcohol use and alcohol addiction represent dysfunctional brain circuits resulting from neuroadaptive changes during protracted alcohol exposure and its withdrawal. Alcohol exerts a potent effect on synaptic plasticity and dendritic spine formation in specific brain regions, providing a neuroanatomical substrate for the pathophysiology of alcoholism. Epigenetics has recently emerged as a critical regulator of gene expression and synaptic plasticity-related events in the brain. Alcohol exposure and withdrawal induce changes in crucial epigenetic processes in the emotional brain circuitry (amygdala) that may be relevant to the negative affective state defined as the "dark side" of addiction. Here, we review the literature concerning synaptic plasticity and epigenetics, with a particular focus on molecular events related to dendritic remodeling during alcohol abuse and alcoholism. Targeting epigenetic processes that modulate synaptic plasticity may yield novel treatments for alcoholism.

Effects of ethanol exposure and withdrawal on dendritic morphology and spine density in the nucleus accumbens core and shell

Exposure to drugs of abuse can result in profound structural modifications on neurons in circuits involved in addiction that may contribute to drug dependence, withdrawal and related processes. Structural alterations on medium spiny neurons (MSNs) of the nucleus accumbens (NAc) have been observed following exposure to and withdrawal from a variety of drugs; however, relatively little is known about the effects of alcohol exposure and withdrawal on structural alterations of NAc MSNs. In the present study male rats were chronically exposed to vaporized ethanol for 10 days and underwent 1 or 7 days of withdrawal after which the brains were processed for Golgi-Cox staining and analysis of dendritic length, branching and spine density. MSNs of the NAc shell and core underwent different patterns of changes following ethanol exposure and withdrawal. At 1 day of withdrawal there were modest reductions in the dendritic length and branching of MSNs in both the core and the shell compared to control animals exposed only to air. At 7 days of withdrawal the length and branching of shell MSNs was reduced, whereas the length and branching of core MSNs were increased relative to the shell. The density of mature spines was increased in the core at 1 day of withdrawal, whereas the density of less mature spines was increased in both regions at 7 days of withdrawal. Collectively, these observations indicate that MSNs of the NAc core and shell undergo distinct patterns of structural modifications following ethanol exposure and withdrawal suggesting that modifications in dendritic structure in these regions may contribute differentially to ethanol withdrawal.

The "addicted" spine

Units of dendritic branches called dendritic spines represent more than simply decorative appendages of the neuron and actively participate in integrative functions of “spinous” nerve cells thereby contributing to the general phenomenon of synaptic plasticity. In animal models of drug addiction, spines are profoundly affected by treatments with drugs of abuse and represent important sub cellular markers which interfere deeply into the physiology of the neuron thereby providing an example of the burgeoning and rapidly increasing interest in “structural plasticity”. Medium Spiny Neurons (MSNs) of the Nucleus Accumbens (Nacc) show a reduced number of dendritic spines and a decrease in TH-positive terminals upon withdrawal from opiates, cannabinoids and alcohol. The reduction is localized “strictly” to second order dendritic branches where dopamine (DA)-containing terminals, impinging upon spines, make synaptic contacts. In addition, long-thin spines seems preferentially affected raising the possibility that cellular learning of these neurons may be selectively hampered. These findings suggest that dendritic spines are affected by drugs widely abused by humans and provide yet another example of drug-induced aberrant neural plasticity with marked reflections on the physiology of synapses, system structural organization, and neuronal circuitry remodeling.

Matrix metalloproteinase-9 involvement in the structural plasticity of dendritic spines

Dendritic spines are the locus for excitatory synaptic transmission in the brain and thus play a major role in neuronal plasticity. The ability to alter synaptic connections includes volumetric changes in dendritic spines that are driven by scaffolds created by the extracellular matrix (ECM). Here, we review the effects of the proteolytic activity of ECM proteases in physiological and pathological structural plasticity. We use matrix metalloproteinase-9 (MMP-9) as an example of an ECM modifier that has recently emerged as a key molecule in regulating the morphology and dysmorphology of dendritic spines that underlie synaptic plasticity and neurological disorders, respectively. We summarize the influence of MMP-9 on the dynamic remodeling of the ECM via the cleavage of extracellular substrates. We discuss its role in the formation, modification, and maintenance of dendritic spines in learning and memory. Finally, we review research that implicates MMP-9 in aberrant synaptic plasticity and spine dysmorphology in neurological disorders, with a focus on morphological abnormalities of dendritic protrusions that are associated with epilepsy.

Abnormal kalirin signaling in neuropsychiatric disorders

Changes in dendritic spines structure and function play a critical role in a number of physiological processes, including synaptic transmission and plasticity, and are intimately linked to cognitive function. Alterations in dendritic spine morphogenesis occur in a number of neuropsychiatric disorders and likely underlie the cognitive and behavioral changes associated with these disorders. The neuronal guanine nucleotide exchange factor (GEF) kalirin is emerging as a key regulator of structural and functional plasticity at dendritic spines. Moreover, a series of recent studies have genetically and functionally linked kalirin signaling to several disorders, including schizophrenia and Alzheimer's disease. Kalirin signaling may thus represent a disease mechanism and provide a novel therapeutic target.

Postnatal ethanol exposure simplifies the dendritic morphology of medium spiny neurons independently of adenylyl cyclase 1 and 8 activity in mice

BACKGROUND

Fetal exposure to alcohol can have multiple deleterious effects, including learning disorders and behavioral and executive functioning abnormalities, collectively termed fetal alcohol spectrum disorders. Neonatal mice lacking both calcium-/calmodulin-stimulated adenylyl cyclases (ACs) 1 and 8 demonstrate increased vulnerability to ethanol (EtOH)-induced neurotoxicity in the striatum compared with wild-type (WT) controls. However, the developmental impact on surviving neurons is still unclear.

METHODS

WT and AC1/8 double knockout (DKO) mice were administered 1 dose of EtOH (2.5 g/kg) between postnatal days 5 to 7 (P5-7). At P30, brains were removed and processed for Golgi-Cox staining. Medium spiny neurons (MSNs) from the caudate putamen were analyzed for changes in dendritic complexity; number of branches, branch points and terminals, total and average dendritic length; spine density and soma size.

RESULTS

EtOH significantly reduced the dendritic complexity and soma size in surviving MSNs regardless of genotype without affecting spine density. In the absence of EtOH, genetic deletion of AC1/8 reduced the dendritic complexity, number of branch points, spine density, and soma size of MSNs compared with WT controls.

CONCLUSIONS

These data indicate that neonatal exposure to a single dose of EtOH is sufficient to cause long-term alterations in the dendritic complexity of MSNs and that this outcome is not altered by the functional status of AC1 and AC8. Therefore, although deletion of AC1/8 demonstrates a role for the ACs in normal morphologic development and EtOH-induced neurodegeneration, loss of AC1/8 activity does not exacerbate the effects of EtOH on dendritic morphology or spine density.

Differential striatal spine pathology in Parkinson's disease and cocaine addiction: a key role of dopamine?

In the striatum, the dendritic tree of the two main populations of projection neurons, called "medium spiny neurons (MSNs)", are covered with spines that receive glutamatergic inputs from the cerebral cortex and thalamus. In Parkinson's disease (PD), striatal MSNs undergo an important loss of dendritic spines, whereas aberrant overgrowth of striatal spines occurs following chronic cocaine exposure. This review examines the possibility that opposite dopamine dysregulation is one of the key factors that underlies these structural changes. In PD, nigrostriatal dopamine degeneration results in a significant loss of dendritic spines in the dorsal striatum, while rodents chronically exposed to cocaine and other psychostimulants, display an increase in the density of "thin and immature" spines in the nucleus accumbens (NAc). In rodent models of PD, there is evidence that D2 dopamine receptor-containing MSNs are preferentially affected, while D1-positive cells are the main targets of increased spine density in models of addiction. However, such specificity remains to be established in primates. Although the link between the extent of striatal spine changes and the behavioral deficits associated with these disorders remains controversial, there is unequivocal evidence that glutamatergic synaptic transmission is significantly altered in both diseased conditions. Recent studies have suggested that opposite calcium-mediated regulation of the transcription factor myocyte enhancer factor 2 (MEF2) function induces these structural defects. In conclusion, there is strong evidence that dopamine is a major, but not the sole, regulator of striatal spine pathology in PD and addiction to psychostimulants. Further studies of the role of glutamate and other genes associated with spine plasticity in mediating these effects are warranted.

Chronic alcohol alters dendritic spine development in neurons in primary culture

Dendritic spines are specialised membrane protrusions of neuronal dendrites that receive the majority of excitatory synaptic inputs. Abnormal changes in their density, size and morphology have been associated with various neurological and psychiatric disorders, including those deriving from drug addiction. Dendritic spine formation, morphology and synaptic functions are governed by the actin cytoskeleton. Previous in vivo studies have shown that ethanol alters the number and morphology of spines, although the mechanisms underlying these alterations remain unknown. It has also been described how chronic ethanol exposure affects the levels, assembly and cellular organisation of the actin cytoskeleton in hippocampal neurons in primary culture. Therefore, we hypothesised that the ethanol-induced alterations in the number and shape of dendritic spines are due to alterations in the mechanisms regulating actin cytoskeleton integrity. The results presented herein show that chronic exposure to moderate levels of alcohol (30 mM) during the first 2 weeks of culture reduces dendritic spine density and alters the proportion of the different morphologies of these structures in hippocampal neurons, which affects the formation of mature spines. Apparently, these effects are associated with an increase in the G-actin/F-actin ratio due to a reduction of the F-actin fraction, leading to changes in the levels of the different factors regulating the organisation of this cytoskeletal component. The data presented herein indicate that these effects occur between weeks 1 and 2 of culture, an important period in dendritic spines development. These changes may be related to the dysfunction in the memory and learning processes present in children prenatally exposed to ethanol.

Craving in alcohol-dependent patients after detoxification is related to glutamatergic dysfunction in the nucleus accumbens and the anterior cingulate cortex

The upregulation of glutamatergic excitatory neurotransmission is thought to be partly responsible for the acute withdrawal symptoms and craving experienced by alcohol-dependent patients. Most physiological evidence supporting this hypothesis is based on data from animal studies. In addition, clinical data show that GABAergic and anti-glutamatergic drugs ameliorate withdrawal symptoms, offering indirect evidence indicative of glutamatergic hyperexcitability in alcohol-dependent subjects. We used proton magnetic resonance spectroscopy to quantify the glutamate (Glu) levels in healthy control subjects and in alcohol-dependent patients immediately after detoxification. The volumes of interest were located in the nucleus accumbens (NAcc) and the anterior cingulate cortex (ACC), which are two brain areas that have important functions in reward circuitry. In addition to Glu, we quantified the levels of combined Glu and glutamine (Gln), N-acetylaspartate, choline-containing compounds, and creatine. The Glu levels in the NAcc were significantly higher in patients than in controls. Craving, which was measured using the Obsessive Compulsive Drinking Scale, correlated positively with levels of combined Glu and Gln in the NAcc and in the ACC. The levels of all other metabolites were not significantly different between patients and controls. The increased Glu levels in the NAcc in alcohol-dependent patients shortly after detoxification confirm the animal data and suggest that striatal glutamatergic dysfunction is related to ethanol withdrawal. The positive correlation between craving and glutamatergic metabolism in both key reward circuitry areas support the hypothesis that the glutamatergic system has an important role in the later course of alcohol dependence with respect to abstinence and relapse.

Varenicline and neuronal nicotinic acetylcholine receptors: a new approach to the treatment of co-occurring alcohol and nicotine addiction?

BACKGROUND AND OBJECTIVES

Alcohol and nicotine dependence are serious public health problems worldwide. They are associated with substantial morbidity and mortality, as well as adverse social effects and increased healthcare costs. Although efficacious treatments are available for these disorders, additional therapeutic options are required to ensure greater treatment utilization. In this paper, we describe the empirical basis on which varenicline, a nicotinic partial agonist approved for smoking cessation, may also have utility in the treatment of alcohol addiction.

METHODS

We sought to identify papers examining nicotine dependence, alcohol dependence, smoking, alcohol, and varenicline for possible inclusion in the present review. We identified over 600 papers through Pubmed/Medline, PsychINFO, and Google Scholar. We found 12 papers taking into consideration the following criteria: original language English, varenicline effect on alcohol consumption.

RESULTS

Animal studies have shown that varenicline reduces alcohol consumption. Two recent studies showed that varenicline also reduces alcohol consumption in humans. Both nicotine and alcohol interact with α4β2 and α3β4 nicotinic acetylcholine (ACh) receptors located in the ventral tegmental area of the brain, inducing dopamine (DA) release at the nucleus accumbens. Varenicline binds to nicotinic ACh receptors, where it has partial agonist effects, producing a moderate and constant level of DA release both in the mesolimbic pathway and in the prefrontal cortex.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Through these effects, varenicline may reduce alcohol craving, seeking, and consumption, in addition to promoting smoking cessation. Additional studies are needed to confirm the efficacy of varenicline in the treatment of alcohol dependence.

Locomotor sensitization to ethanol impairs NMDA receptor-dependent synaptic plasticity in the nucleus accumbens and increases ethanol self-administration

Although alcoholism is a worldwide problem resulting in millions of deaths, only a small percentage of alcohol users become addicted. The specific neural substrates responsible for individual differences in vulnerability to alcohol addiction are not known. In this study, we used rodent models to study behavioral and synaptic correlates related to individual differences in the development of ethanol locomotor sensitization, a form of drug-dependent behavioral plasticity associated with addiction vulnerability. Male Swiss Webster mice were treated daily with saline or 1.8 g/kg ethanol for 21 d. Locomotor activity tests were performed once a week for 15 min immediately after saline or ethanol injections. After at least 11 d of withdrawal, cohorts of saline- or ethanol-treated mice were used to characterize the relationships between locomotor sensitization, ethanol drinking, and glutamatergic synaptic transmission in the nucleus accumbens. Ethanol-treated mice that expressed locomotor sensitization to ethanol drank significantly more ethanol than saline-treated subjects and ethanol-treated animals resilient to this form of behavioral plasticity. Moreover, ethanol-sensitized mice also had reduced accumbal NMDA receptor function and expression, as well as deficits in NMDA receptor-dependent long-term depression in the nucleus accumbens core after a protracted withdrawal. These findings suggest that disruption of accumbal core NMDA receptor-dependent plasticity may represent a synaptic correlate associated with ethanol-induced locomotor sensitization and increased propensity to consume ethanol.

Selection for drinking in the dark alters brain gene coexpression networks

BACKGROUND

Heterogeneous stock (HS/NPT) mice have been used to create lines selectively bred in replicate for elevated drinking in the dark (DID). Both selected lines routinely reach a blood ethanol (EtOH) concentration (BEC) of 1.00 mg/ml or greater at the end of the 4-hour period of access in Day 2. The mechanisms through which genetic differences influence DID are currently unclear. Therefore, the current study examines the transcriptome, the first stage at which genetic variability affects neurobiology. Rather than focusing solely on differential expression (DE), we also examine changes in the ways that gene transcripts collectively interact with each other, as revealed by changes in coexpression patterns.

METHODS

Naïve mice (N = 48/group) were genotyped using the Mouse Universal Genotyping Array, which provided 3,683 informative markers. Quantitative trait locus (QTL) analysis used a marker-by-marker strategy with the threshold for a significant logarithm of odds (LOD) set at 10.6. Gene expression in the ventral striatum was measured using the Illumina Mouse 8.2 array. Differential gene expression and the weighted gene coexpression network analysis (WGCNA) were implemented largely as described elsewhere.

RESULTS

Significant QTLs for elevated BECs after DID were detected on chromosomes 4, 14, and 16; the latter 2 were associated with gene-poor regions. None of the QTLs overlapped with known QTLs for EtOH preference drinking. Ninety-four transcripts were detected as being differentially expressed in both selected lines versus HS controls; there was no overlap with known preference genes. The WGCNA revealed 2 modules as showing significant effects of both selections on intramodular connectivity. A number of genes known to be associated with EtOH phenotypes (e.g., Gabrg1, Glra2, Grik1, Npy2r, and Nts) showed significant changes in connectivity.

CONCLUSIONS

We found marked and consistent effects of selection on coexpression patterns; DE changes were more modest and less concordant. The QTLs and differentially expressed genes detected here are distinct from the preference phenotype. This is consistent with behavioral data and suggests that the DID and preference phenotypes are markedly different genetically.

Emerging roles of actin cytoskeleton regulating enzymes in drug addiction: actin or reactin'?

Neurons rely on their cytoskeleton to give them shape and stability, and on cytoskeletal dynamics for growth and synaptic plasticity. Because drug addiction is increasingly seen as the inappropriate learning of strongly reinforcing stimuli, the role of the cytoskeleton in shaping drug memories has been of increasing interest in recent years. Does the cytoskeleton have an active role in shaping these memories, and to what extent do alterations in the cytoskeleton reflect the acute actions of drug exposure, or homeostatic reactions to the chronic exposure to drugs of abuse? Here we will review recent advances in understanding the role of the cytoskeleton in the development of drug addiction, with a focus on actin filaments, as they have been studied in greater detail.

Differential phosphorylation of GluN1-MAPKs in rat brain reward circuits following long-term alcohol exposure

The effects of long-term alcohol consumption on the mitogen-activated protein kinases (MAPKs) pathway and N-methyl-D-aspartate-type glutamate receptor 1 (GluN1) subunits in the mesocorticolimbic system remain unclear. In the present study, rats were allowed to consume 6% (v/v) alcohol solution for 28 consecutive days. Locomotor activity and behavioral signs of withdrawal were observed. Phosphorylation and expression of extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38 protein kinase and GluN1 in the nucleus accumbens, caudate putamen, amygdala, hippocampus and prefrontal cortex of these rats were also measured. Phosphorylation of ERK, but not JNK or p38, was decreased in all five brain regions studied in alcohol-drinking rats. The ratio of phospho/total-GluN1 subunit was reduced in all five brain regions studied. Those results suggest that the long-term alcohol consumption can inhibits GluN1 and ERK phosphorylation, but not JNK or p38 in the mesocorticolimbic system, and these changes may be relevant to alcohol dependence. To differentiate alcohol-induced changes in ERK and GluN1 between acute and chronic alcohol exposure, we have determined levels of phospho-ERK, phospho-GluN1 and total levels of GluN1 after acute alcohol exposure. Our data show that 30 min following a 2.5 g/kg dose of alcohol (administered intragastrically), levels of phospho-ERK are decreased while those of phospho-GluN1 are elevated with no change in total GluN1 levels. At 24 h following the single alcohol dose, levels of phospho-ERK are elevated in several brain regions while there are no differences between controls and alcohol treated animals in phospho-GluN1 or total GluN1. Those results suggest that alcohol may differentially regulate GluN1 function and ERK activation depending on alcohol dose and exposure time in the central nervous system.