Cross-species epigenetic regulation of nucleus accumbens KCNN3 transcripts by excessive ethanol drinking

The underlying genetic and epigenetic mechanisms driving functional adaptations in neuronal excitability and excessive alcohol intake are poorly understood. Small-conductance Ca2+-activated K+ (KCa2 or SK) channels encoded by the KCNN family of genes have emerged from preclinical studies as a key contributor to alcohol-induced functional neuroadaptations in alcohol-drinking monkeys and alcohol-dependent mice. Here, this cross-species analysis focused on KCNN3 DNA methylation, gene expression, and single nucleotide polymorphisms, including alternative promoters in KCNN3, that could influence surface trafficking and function of KCa2 channels. Bisulfite sequencing analysis of the nucleus accumbens tissue from alcohol-drinking monkeys and alcohol-dependent mice revealed a differentially methylated region in exon 1A of KCNN3 that overlaps with a predicted promoter sequence. The hypermethylation of KCNN3 in the accumbens paralleled an increase in the expression of alternative transcripts that encode apamin-insensitive and dominant-negative KCa2 channel isoforms. A polymorphic repeat in macaque KCNN3 encoded by exon 1 did not correlate with alcohol drinking. At the protein level, KCa2.3 channel expression in the accumbens was significantly reduced in very heavy-drinking monkeys. Together, our cross-species findings on epigenetic dysregulation of KCNN3 represent a complex mechanism that utilizes alternative promoters to potentially impact the firing of accumbens neurons. Thus, these results provide support for hypermethylation of KCNN3 as a possible key molecular mechanism underlying harmful alcohol intake and alcohol use disorder.

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.

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.

Assessing negative affect in mice during abstinence from alcohol drinking: Limitations and future challenges

Alcohol use disorder (AUD) is frequently comorbid with mood disorders, and these co-occurring neuropsychiatric disorders contribute to the development and maintenance of alcohol dependence and relapse. In preclinical models, mice chronically exposed to alcohol display anxiety-like and depressive-like behaviors during acute withdrawal and protracted abstinence. However, in total, results from studies using voluntary alcohol-drinking paradigms show variable behavioral outcomes in assays measuring negative affective behaviors. Thus, the main objective of this review is to summarize the literature on the variability of negative affective behaviors in mice after chronic alcohol exposure. We compare the behavioral phenotypes that emerge during abstinence across different exposure models, including models of alcohol and stress interactions. The complicated outcomes from these studies highlight the difficulties of assessing negative affective behaviors in mouse models designed for the study of AUD. We discuss new behavioral assays, comprehensive platforms, and unbiased machine-learning algorithms as promising approaches to better understand the interaction between alcohol and negative affect in mice. New data-driven approaches in the understanding of mouse behavior hold promise for improving the identification of mechanisms, cell subtypes, and neurocircuits that mediate negative affect. In turn, improving our understanding of the neurobehavioral basis of alcohol-associated negative affect will provide a platform to test hypotheses in mouse models that aim to improve the development of more effective strategies for treating individuals with AUD and co-occurring mood disorders.

The histone methyltransferase G9a mediates stress-regulated alcohol drinking

The epigenetic enzyme G9a is a histone methyltransferase that dimethylates lysine 9 on histone H3 (H3K9me2), and in the adult nucleus accumbens (NAc), G9a regulates multiple behaviors associated with substance use disorder. We show here that chronic intermittent ethanol (CIE) exposure in male mice reduced both G9a and H3K9me2 levels in the adult NAc, but not dorsal striatum. Viral-mediated reduction of G9a in the NAc had no effects on baseline volitional ethanol drinking or escalated alcohol drinking produced by CIE exposure; however, NAc G9a was required for stress-regulated changes in ethanol drinking, including potentiated alcohol drinking produced by activation of the kappa-opioid receptor. In addition, we observed that chronic systemic administration of a G9a inhibitor, UNC0642, also blocked stress-potentiated alcohol drinking. Together, our findings suggest that chronic alcohol use, similar to other abused substances, produces a NAc-selective reduction in G9a levels that serves to limit stress-regulated alcohol drinking. Moreover, our findings suggest that pharmacological inhibition of G9a might provide a novel therapeutic approach to treat stress-induced alcohol drinking, which is a major trigger of relapse in individuals suffering from AUD.

Chronic intermittent ethanol during adolescence and adulthood alters dendritic spines in the primary motor and visual cortex in rats

Prolonged adolescent binge drinking can disrupt sleep quality and increase the likelihood of alcohol-induced sleep disruptions in young adulthood in rodents and in humans. Striking changes in spine density and morphology have been seen in many cortical and subcortical regions after adolescent alcohol exposure in rats. However, there is little known about the impact of alcohol exposure on dendritic spines in the same motor and sensory cortices that EEG sleep is typically recorded from in rats. The aim of this study is to investigate whether an established model of chronic intermittent ethanol vapor in rats that has been demonstrated to disrupt sleep during adolescence or adulthood, also significantly alters cortical dendritic spine density and morphology. To this end, adolescent and adult Wistar rats were exposed to 5 weeks of ethanol vapor or control air exposure. After a 13-day withdrawal, primary motor cortex (M1) and primary/secondary visual cortex (V1/V2) layer V dendrites were analyzed for differences in spine density and morphology. Spines were classified into four categories (stubby, long, filopodia, and mushroom) based on the spine length and the width of the spine head and neck. The main results indicate an age-specific effect of adolescent intermittent ethanol exposure decreasing spine density in the M1 cortex compared to age-matched controls. Reductions in the density of M1 long-shaped spine subclassifications were seen in adolescent ethanol-exposed rats, but not adult-exposed rats, compared to their air-controls. Irrespective of age, there was an overall reduction produced by ethanol exposure on the density of filopodia and the length of long-shaped spines in V1/V2 cortex as compared to their air-exposed controls. Together, these data add to growing evidence that some cortical circuits are vulnerable to the effects of alcohol during adolescence and begin to elucidate potential mechanisms that may influence brain plasticity following early alcohol use.

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

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

Interaction of chronic intermittent ethanol and repeated stress on structural and functional plasticity in the mouse medial prefrontal cortex

Stress is a risk factor that plays a considerable role in the development and maintenance of alcohol (ethanol) abuse and relapse. Preclinical studies examining ethanol-stress interactions have demonstrated elevated ethanol drinking, cognitive deficits, and negative affective behaviors in mice. However, the neural adaptations in prefrontal cortical regions that drive these aberrant behaviors produced by ethanol-stress interactions are unknown. In this study, male C57BL/6J mice were exposed to chronic intermittent ethanol (CIE) and repeated forced swim stress (FSS). After two cycles of CIE x FSS, brain slices containing the prelimbic (PrL) and infralimbic (IfL) cortex were prepared for analysis of adaptations in dendritic spines and synaptic plasticity. In the PrL cortex, total spine density was increased in mice exposed to CIE. Immediately following induction of long-term potentiation (LTP), the fEPSP slope was increased in the PrL of CIE x FSS treated mice, indicative of a presynaptic adaptation on post-tetanic potentiation (PTP). In the IfL cortex, CIE exposure regardless of FSS experience resulted in an increase in spine density. FSS alone or when combined with CIE exposure increased PTP following LTP induction. Repeated FSS episodes increased IfL cortical paired-pulse facilitation, a second measure of presynaptic plasticity. In summary, CIE exposure resulted in structural adaptations while repeated stress exposure drove metaplastic changes in presynaptic function, demonstrating distinct morphological and functional changes in PrL and IfL cortical neurons. Thus, the structural and functional adaptations may be one mechanism underlying the development of excessive drinking and cognitive deficits associated with ethanol-stress interactions.

Bioinformatics identification and pharmacological validation of Kcnn3/KCa2 channels as a mediator of negative affective behaviors and excessive alcohol drinking in mice

Mood disorders are often comorbid with alcohol use disorder (AUD) and play a considerable role in the development and maintenance of alcohol dependence and relapse. Because of this high comorbidity, it is necessary to determine shared and unique genetic factors driving heavy drinking and negative affective behaviors. In order to identify novel pharmacogenetic targets, a bioinformatics analysis was used to quantify the expression of amygdala K+ channel genes that covary with anxiety-related phenotypes in the well-phenotyped and fully sequenced family of BXD strains. We used a model of stress-induced escalation of drinking in alcohol-dependent mice to measure negative affective behaviors during abstinence. A pharmacological approach was used to validate the key bioinformatics findings in alcohol-dependent, stressed mice. Amygdalar expression of Kcnn3 correlated significantly with 40 anxiety-associated phenotypes. Further examination of Kcnn3 expression revealed a strong eigentrait for anxiety-like behaviors and negative correlations with binge-like and voluntary alcohol drinking. Mice treated with chronic intermittent alcohol exposure and repeated swim stress consumed more alcohol in their home cages and showed hypophagia on the novelty-suppressed feeding test during abstinence. Pharmacologically targeting Kcnn gene products with the KCa2 (SK) channel-positive modulator 1-EBIO decreased drinking and reduced feeding latency in alcohol-dependent, stressed mice. Collectively, these validation studies provide central nervous system links into the covariance of stress, negative affective behaviors, and AUD in the BXD strains. Further, the bioinformatics discovery tool is effective in identifying promising targets (i.e., KCa2 channels) for treating alcohol dependence exacerbated by comorbid mood disorders.

Absence of effects of intermittent access to alcohol on negative affective and anxiety-like behaviors in male and female C57BL/6J mice

Alcohol use disorder is highly comorbid with other neuropsychiatric disorders such as depression and anxiety. Importantly, women and men are affected differentially by heavy drinking, with women experiencing longer negative affective states after intoxication and increased likelihood to present with comorbid mood or anxiety disorders. In rodents, several studies using different alcohol administration models have shown the development of depressive-like or anxiety-like phenotypes that emerge during abstinence. In this study, we compared the emergence of negative affective behaviors during abstinence from 7 weeks of two-bottle choice intermittent access to 20% alcohol in male and female C57BL/6J mice, a drinking paradigm little studied in this context. Half of the mice were tested 24 hours into abstinence on the elevated zero maze and 19-20 days into abstinence in a novel object in the home cage encounter test. The other half of the mice were tested 27-28 days into abstinence with the novelty-suppressed feeding test. As expected, females drank more than males across the 7 weeks of access to alcohol. Drinking history did not affect performance on these tasks, with the exception of increasing the number of open arm entries on the elevated zero maze. Interestingly, in alcohol-naïve mice, females showed fewer anxiety-like behaviors than males in the elevated zero maze and the novelty-suppressed feeding test. Our results suggest that the intermittent access model does not reliably induce negative affective behaviors on these tasks, and that behavior in female and male mice differs across these tests. Rather, intermittent alcohol drinking may induce a mild form of behavioral disinhibition. Thus, the model of alcohol access is a critical factor in determining the appearance of behavioral disturbances that emerge during abstinence.

Dynamic c-Fos changes in mouse brain during acute and protracted withdrawal from chronic intermittent ethanol exposure and relapse drinking

Alcohol dependence promotes neuroadaptations in numerous brain areas, leading to escalated drinking and enhanced relapse vulnerability. We previously developed a mouse model of ethanol dependence and relapse drinking in which repeated cycles of chronic intermittent ethanol (CIE) vapor exposure drive a significant escalation of voluntary ethanol drinking. In the current study, we used this model to evaluate changes in neuronal activity (as indexed by c‐Fos expression) throughout acute and protracted withdrawal from CIE (combined with or without a history of ethanol drinking). We analyzed c‐Fos protein expression in 29 brain regions in mice sacrificed 2, 10, 26, and 74 hours or 7 days after withdrawal from 5 cycles of CIE. Results revealed dynamic time‐ and brain region‐dependent changes in c‐Fos activity over the time course of withdrawal from CIE exposure, as compared with nondependent air‐exposed control mice, beginning with markedly low expression levels upon removal from the ethanol vapor chambers (2 hours), reflecting intoxication. c‐Fos expression was enhanced during acute CIE withdrawal (10 and 26 hours), followed by widespread reductions at the beginning of protracted withdrawal (74 hours) in several brain areas. Persistent reductions in c‐Fos expression were observed during prolonged withdrawal (7 days) in prelimbic cortex, nucleus accumbens shell, dorsomedial striatum, paraventricular nucleus of thalamus, and ventral subiculum. A history of ethanol drinking altered acute CIE withdrawal effects and caused widespread reductions in c‐Fos that persisted during extended abstinence even without CIE exposure. These data indicate that ethanol dependence and relapse drinking drive long‐lasting neuroadaptations in several brain regions.

Distinct Region- and Time-Dependent Functional Cortical Adaptations in C57BL/6J Mice after Short and Prolonged Alcohol Drinking

Alcohol (ethanol) use disorder is associated with changes in frontal cortical areas including the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) that contribute to cognitive deficits, uncontrolled drinking, and relapse. Acute ethanol exposure reduces intrinsic excitability of lateral OFC (lOFC) neurons, while chronic exposure and long-term drinking influence plasticity of intrinsic excitability and function of glutamatergic synapses. However, the time course that these adaptations occur across a history of ethanol drinking is unknown. The current study examined whether short-term and long-term voluntary ethanol consumption using an intermittent access paradigm would alter the biophysical properties of deep-layer pyramidal neurons in the ACC and lOFC. Neuronal spiking varied in the ACC with an initial increase in evoked firing after 1 d of drinking followed by a decrease in firing in mice that consumed ethanol for one week. No difference in lOFC spike number was observed between water controls and 1-d ethanol drinking mice, but mice that consumed ethanol for one week or more showed a significant increase in evoked firing. Voluntary ethanol drinking for 4 weeks also produced a total loss of ethanol inhibition of lOFC neurons. There was no effect of drinking on excitatory or inhibitory synaptic events in ACC or lOFC neurons across all time points in this model. Overall, these results demonstrate that voluntary drinking alters neuronal excitability in the ACC and lOFC in distinct ways and on a different time scale that may contribute to the impairment of prefrontal cortex-dependent behaviors observed in individuals with alcohol use disorder (AUD).

Mechanisms of Persistent Neurobiological Changes Following Adolescent Alcohol Exposure: NADIA Consortium Findings

The Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium has focused on the impact of adolescent binge drinking on brain development, particularly on effects that persist into adulthood. Adolescent binge drinking is common, and while many factors contribute to human brain development and alcohol use during adolescence, animal models are critical for understanding the specific consequences of alcohol exposure during this developmental period and the underlying mechanisms. Using adolescent intermittent ethanol (AIE) exposure models, NADIA investigators identified long-lasting AIE-induced changes in adult behavior that are consistent with observations in humans, such as increased alcohol drinking, increased anxiety (particularly social anxiety), increased impulsivity, reduced behavioral flexibility, impaired memory, disrupted sleep, and altered responses to alcohol. These behavioral changes are associated with multiple molecular, cellular, and physiological alterations in the brain that persist long after AIE exposure. At the molecular level, AIE results in long-lasting changes in neuroimmune/trophic factor balance and epigenetic-microRNA (miRNA) signaling across glia and neurons. At the cellular level, AIE history is associated in adulthood with reduced expression of cholinergic, serotonergic, and dopaminergic neuron markers, attenuated cortical thickness, decreased neurogenesis, and altered dendritic spine and glial morphology. This constellation of molecular and cellular adaptations to AIE likely contributes to observed alterations in neurophysiology, measured by synaptic physiology, EEG patterns, and functional connectivity. Many of these AIE-induced brain changes replicate findings seen in postmortem brains of humans with alcohol use disorder (AUD). NADIA researchers are now elucidating mechanisms of these adaptations. Emerging data demonstrate that exercise, antiinflammatory drugs, anticholinesterases, histone deacetylase inhibitors, and other pharmacological compounds are able to prevent (administered during AIE) and/or reverse (given after AIE) AIE-induced pathology in adulthood. These studies support hypotheses that adolescent binge drinking increases risk of adult hazardous drinking and influences brain development, and may provide insight into novel therapeutic targets for AIE-induced neuropathology and AUDs.

Identification and validation of midbrain Kcnq4 regulation of heavy alcohol consumption in rodents

Currently available pharmacotherapies for treating alcohol use disorder (AUD) suffer from deleterious side effects and are not efficacious in diverse populations. Clinical and preclinical studies provide evidence that the Kcnq family of genes that encode K_V7 channels influence alcohol intake and dependence. K_V7 channels are a class of slowly activating voltage-dependent K⁺ channels that regulate neuronal excitability. Studies indicate that the K_V7 channel positive modulator retigabine can decrease dopaminergic neuron firing, alter dopamine (DA) release, and reduce alcohol intake in heavy drinking rodents. Given the critical nature of ventral tegmental area (VTA) DA to the addiction process and predominant expression of Kcnq4 in DA neurons, we investigated the role of midbrain Kcnq genes and K_V7 channels in the VTA of genetically diverse mice and long-term heavy drinking rats, respectively. Integrative bioinformatics analysis identified negative correlations between midbrain Kcnq4 expression and alcohol intake and seeking behaviors. Kcnq4 expression levels were also correlated with dopaminergic-related phenotypes in BXD strains, and Kcnq4 was present in support intervals for alcohol sensitivity and alcohol withdrawal severity QTLs in rodents. Pharmacological validation studies revealed that VTA K_V7 channels regulate excessive alcohol intake in rats with a high-drinking phenotype. Administration of a novel and selective K_V7.2/4 channel positive modulator also reduced alcohol drinking in rats. Together, these findings indicate that midbrain Kcnq4 expression regulates alcohol-related behaviors in genetically diverse mice and provide evidence that K_V7.4 channels are a critical mediator of excessive alcohol drinking.

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.

Chronic Alcohol, Intrinsic Excitability, and Potassium Channels: Neuroadaptations and Drinking Behavior

Neural mechanisms underlying alcohol use disorder remain elusive, and this lack of understanding has slowed the development of efficacious treatment strategies for reducing relapse rates and prolonging abstinence. While synaptic adaptations produced by chronic alcohol exposure have been extensively characterized in a variety of brain regions, changes in intrinsic excitability of critical projection neurons are understudied. Accumulating evidence suggests that prolonged alcohol drinking and alcohol dependence produce plasticity of intrinsic excitability as measured by changes in evoked action potential firing and after-hyperpolarization amplitude. In this chapter, we describe functional changes in cell firing of projection neurons after long-term alcohol exposure that occur across species and in multiple brain regions. Adaptations in calcium-activated (K_Ca2), voltage-dependent (K_V7), and G protein-coupled inwardly rectifying (K_ir3 or GIRK) potassium channels that regulate the evoked firing and after-hyperpolarization parallel functional changes in intrinsic excitability induced by chronic alcohol. Moreover, there are strong genetic links between alcohol-related behaviors and genes encoding K_Ca2, K_V7, and GIRK channels, and pharmacologically targeting these channels reduces alcohol consumption and alcohol-related behaviors. Together, these studies demonstrate that chronic alcohol drinking produces adaptations in K_Ca2, K_V7, and GIRK channels leading to impaired regulation of the after-hyperpolarization and aberrant cell firing. Correcting the deficit in the after-hyperpolarization with positive modulators of K_Ca2 and K_V7 channels and altering the GIRK channel binding pocket to block the access of alcohol represent a potentially highly effective pharmacological approach that can restore changes in intrinsic excitability and reduce alcohol consumption in affected individuals.

Persistent cognitive and morphological alterations induced by repeated exposure of adolescent rats to the abused inhalant toluene

While thepsychoactive inhalant toluene causes behavioral effects similarto those produced by other drugs of abuse, the persistent behavioral and anatomical abnormalities induced by toluene exposure are not well known. To mimic human "binge-like" inhalant intoxication, adolescent, male Sprague-Dawley rats were exposed to toluene vapor (5700ppm) twice daily for five consecutive days. These rats remained in their home cages until adulthood (P60), when they were trained in operant boxes to respond to a palatable food reward and then challenged with several different cognitive tasks. Rats that experienced chronic exposure to toluene plus abstinence ("CTA") showed enhanced performance in a strategy set-shifting task using a between-session, but not a within-session test design. CTA also blunted operant and classical conditioning without affecting responding during a progressive ratio task. While CTA rats displayed normal latent inhibition, previous exposure to a non-reinforced cue enhanced extinction of classically conditioned approach behavior of these animals compared to air controls. To determine whether CTA alters the structural plasticity of brain areas involved in set-shifting and appetitive behaviors, we quantified basal dendritic spine morphology in DiI-labeled pyramidal neurons in layer 5 of the medial prefrontal cortex (mPFC) and medium spiny neurons in the nucleus accumbens (NAc). There were no changes in dendritic spine density or subtype in the mPFC of CTA rats while NAc spine density was significantly increased due to an enhanced prevalence of long-thin spines. Together, these findings suggest that the persistent effects of CTA on cognition are related to learning and memory consolidation/recall, but not mPFC-dependent behavioral flexibility.

Ethanol Dependence Abolishes Monoamine and GIRK (Kir3) Channel Inhibition of Orbitofrontal Cortex Excitability

Alcohol abuse disorders are associated with dysfunction of frontal cortical areas including the orbitofrontal cortex (OFC). The OFC is extensively innervated by monoamines, and drugs that target monoamine receptors have been used to treat a number of neuropsychiatric diseases, including alcoholism. However, little is known regarding how monoamines affect OFC neuron excitability or whether this modulation is altered by chronic exposure to ethanol. In this study, we examined the effect of dopamine, norepinephrine, and serotonin on lOFC neuronal excitability in naive mice and in those exposed to chronic intermittent ethanol (CIE) treatment. All three monoamines decreased current-evoked spike firing of lOFC neurons and this action required G_iα-coupled D2, α2-adrenergic, and 5HT_1A receptors, respectively. Inhibition of firing by dopamine or the D2 agonist quinpirole, but not norepinephrine or serotonin, was prevented by the GABA_A receptor antagonist picrotoxin. GABA-mediated tonic current was enhanced by dopamine or the D1 agonist SKF81297 but not quinpirole, whereas the amplitude of spontaneous IPSCs was increased by quinpirole but not dopamine. Spiking was also inhibited by the direct GIRK channel activator ML297, whereas blocking these channels with barium increased firing and eliminated the inhibitory actions of monoamines. In the presence of ML297 or the G-protein blocker GDP-β-S, DA induced a further decrease in spike firing, suggesting the involvement of a non-GIRK channel mechanism. In neurons from CIE-treated mice, spike frequency was nearly doubled and inhibition of firing by monoamines or ML297 was lost. These effects occurred in the absence of significant changes in expression of G_i/o or GIRK channel proteins. Together, these findings show that monoamines are important modulators of lOFC excitability and suggest that disruption of this process could contribute to various deficits associated with alcohol dependence.

Prefrontal Cortex KCa2 Channels Regulate mGlu5-Dependent Plasticity and Extinction of Alcohol-Seeking Behavior

Identifying novel treatments that facilitate extinction learning could enhance cue-exposure therapy and reduce high relapse rates in alcoholics. Activation of mGlu5 receptors in the infralimbic prefrontal cortex (IL-PFC) facilitates learning during extinction of cue-conditioned alcohol-seeking behavior. Small-conductance calcium-activated potassium (KCa2) channels have also been implicated in extinction learning of fear memories, and mGlu5 receptor activation can reduce KCa2 channel function. Using a combination of electrophysiological, pharmacological, and behavioral approaches, this study examined KCa2 channels as a novel target to facilitate extinction of alcohol-seeking behavior in rats. This study also explored related neuronal and synaptic mechanisms within the IL-PFC that underlie mGlu5-dependent enhancement of extinction learning. Using whole-cell patch-clamp electrophysiology, activation of mGlu5 in ex vivo slices significantly reduced KCa2 channel currents in layer V IL-PFC pyramidal neurons, confirming functional downregulation of KCa2 channel activity by mGlu5 receptors. Additionally, positive modulation of KCa2 channels prevented mGlu5 receptor-dependent facilitation of long-term potentiation in the IL-PFC. Systemic and intra-IL-PFC treatment with apamin (KCa2 channel allosteric inhibitor) significantly enhanced extinction of alcohol-seeking behavior across multiple extinction sessions, an effect that persisted for 3 weeks, but was not observed after apamin microinfusions into the prelimbic PFC. Positive modulation of IL-PFC KCa2 channels significantly attenuated mGlu5-dependent facilitation of alcohol cue-conditioned extinction learning. These data suggest that mGlu5-dependent facilitation of extinction learning and synaptic plasticity in the IL-PFC involves functional inhibition of KCa2 channels. Moreover, these findings demonstrate that KCa2 channels are a novel target to facilitate long-lasting extinction of alcohol-seeking behavior.SIGNIFICANCE STATEMENT Alcohol use disorder is a chronic relapsing disorder that is associated with compulsive alcohol-seeking behavior. One of the main causes of alcohol relapse is the craving caused by environmental cues that are associated with alcohol. These cues are formed by normal learning and memory principles, and the understanding of the brain mechanisms that help form these associations can lead to the development of drugs and/or behavior therapies that reduce the impact that these cues have on relapse in alcoholics.

Promising pharmacogenetic targets for treating alcohol use disorder: evidence from preclinical models

Inherited genetic variants contribute to risk factors for developing an alcohol use disorder, and polymorphisms may inform precision medicine strategies for treating alcohol addiction. Targeting genetic mutations linked to alcohol phenotypes has provided promising initial evidence for reducing relapse rates in alcoholics. Although successful in some studies, there are conflicting findings and the reports of adverse effects may ultimately limit their clinical utility, suggesting that novel pharmacogenetic targets are necessary to advance precision medicine approaches. Here, we describe promising novel genetic variants derived from preclinical models of alcohol consumption and dependence that may uncover disease mechanisms that drive uncontrolled drinking and identify novel pharmacogenetic targets that facilitate therapeutic intervention for the treatment of alcohol use disorder.

Effects of Repeated Ethanol Exposures on NMDA Receptor Expression and Locomotor Sensitization in Mice Expressing Ethanol Resistant NMDA Receptors

Evidence from a large number of preclinical studies suggests that chronic exposure to drugs of abuse, such as psychostimulants or ethanol induces changes in glutamatergic transmission in key brain areas associated with reward and control of behavior. These changes include alterations in the expression of ionotropic glutamate receptors including N-methyl-D-aspartate receptors (NMDAR) that are important for regulating neuronal activity and synaptic plasticity. NMDA receptors are inhibited by ethanol and reductions in NMDA-mediated signaling are thought to trigger homestatic responses that limit ethanol's effects on glutamatergic transmission. Following repeated exposures to ethanol, these homeostatic responses may become unstable leading to an altered glutamatergic state that contributes to the escalations in drinking and cognitive deficits observed in alcohol-dependent subjects. An important unanswered question is whether ethanol-induced changes in NMDAR expression are modulated by the intrinsic sensitivity of the receptor to ethanol. In this study, we examined the effects of ethanol on NMDAR subunit expression in cortical (orbitofrontal, medial prefrontal), striatal (dorsal and ventral striatum) and limbic (dorsal hippocampus, basolateral amygdala) areas in mice genetically modified to express ethanol-resistant receptors (F639A mice). These mice have been previously shown to drink more ethanol than their wild-type counterparts and have altered behavioral responses to certain actions of ethanol. Following long-term voluntary drinking, F639A mice showed elevations in GluN2A but not GluN1 or GluN2B expression as compared to wild-type mice. Mice treated with repeated injections with ethanol (2-3.5 g/kg; i.p.) showed changes in NMDAR expression that varied in a complex manner with genotype, brain region, subunit type and exposure protocol all contributing to the observed response. F639A mice, but not wild-type mice, showed enhanced motor activity following repeated ethanol injections and this was associated with differences in NMDAR subunit expression across brain regions thought to be involved in drug sensitization. Overall, while the results of the study suggest that NMDARs with reduced sensitivity to ethanol favor the development of locomotor sensitization, they also show that intrinsic ethanol sensitivity is not the sole determinant underlying changes in NMDAR expression following repeated exposures to ethanol.

Differential potassium channel gene regulation in BXD mice reveals novel targets for pharmacogenetic therapies to reduce heavy alcohol drinking

Alcohol (ethanol) dependence is a chronic relapsing brain disorder partially influenced by genetics and characterized by an inability to regulate harmful levels of drinking. Emerging evidence has linked genes that encode K_V7, K_IR, and K_Ca2 K⁺ channels with variation in alcohol-related behaviors in rodents and humans. This led us to experimentally test relations between K⁺ channel genes and escalation of drinking in a chronic-intermittent ethanol (CIE) exposure model of dependence in BXD recombinant inbred strains of mice. Transcript levels for K⁺ channel genes in the prefrontal cortex (PFC) and nucleus accumbens (NAc) covary with voluntary ethanol drinking in a non-dependent cohort. Transcripts that encode K_V7 channels covary negatively with drinking in non-dependent BXD strains. Using a pharmacological approach to validate the genetic findings, C57BL/6J mice were allowed intermittent access to ethanol to establish baseline consumption before they were treated with retigabine, an FDA-approved K_V7 channel positive modulator. Systemic administration significantly reduced drinking, and consistent with previous evidence, retigabine was more effective at reducing voluntary consumption in high-drinking than low-drinking subjects. We evaluated the specific K⁺ channel genes that were most sensitive to CIE exposure and identified a gene subset in the NAc and PFC that were dysregulated in the alcohol-dependent BXD cohort. CIE-induced modulation of nine genes in the NAc and six genes in the PFC covaried well with the changes in drinking induced by ethanol dependence. Here we identified novel candidate genes in the NAc and PFC that are regulated by ethanol dependence and correlate with voluntary drinking in non-dependent and dependent BXD mice. The findings that Kcnq expression correlates with drinking and that retigabine reduces consumption suggest that K_V7 channels could be pharmacogenetic targets to treat individuals with alcohol addiction.

Kv7 channels in the nucleus accumbens are altered by chronic drinking and are targets for reducing alcohol consumption

Alcohol use disorders (AUDs) are a major public health issue and produce enormous societal and economic burdens. Current Food and Drug Administration (FDA)-approved pharmacotherapies for treating AUDs suffer from deleterious side effects and are only effective in a subset of individuals. It is therefore essential to find improved medications for the management of AUDs. Emerging evidence suggests that anticonvulsants are a promising class of drugs for treating individuals with AUDs. In these studies, we used integrative functional genomics to demonstrate that genes that encode Kv7 channels (i.e. Kcnq2/3) are related to alcohol (ethanol) consumption, preference and acceptance in rodents. We then tested the ability of the FDA-approved anticonvulsant retigabine, a Kv7 channel opener, to reduce voluntary ethanol consumption of Wistar rats in a two-bottle choice intermittent alcohol access paradigm. Systemic administration and microinjections of retigabine into the nucleus accumbens significantly reduced alcohol drinking, and retigabine was more effective at reducing intake in high- versus low-drinking populations of Wistar rats. Prolonged voluntary drinking increased the sensitivity to the proconvulsant effects of pharmacological blockade of Kv7 channels and altered surface trafficking and SUMOylation patterns of Kv7.2 channels in the nucleus accumbens. These data implicate Kcnq2/3 in the regulation of ethanol drinking and demonstrate that long-term drinking produces neuroadaptations in Kv7 channels. In addition, these results have identified retigabine as a potential pharmacotherapy for treating AUDs and Kv7 channels as a novel therapeutic target for reducing heavy drinking.

Signals from the Fourth Dimension Regulate Drug Relapse

Despite the enormous societal burden of alcohol and drug addiction and abundant research describing drug-induced maladaptive synaptic plasticity, there are few effective strategies for treating substance use disorders. Recent awareness that synaptic plasticity involves astroglia and the extracellular matrix is revealing new possibilities for understanding and treating addiction. We first review constitutive corticostriatal adaptations that are elicited by and shared between all abused drugs from the perspective of tetrapartite synapses, and integrate recent discoveries regarding cell type-specificity in striatal neurons. Next, we describe recent discoveries that drug-seeking is associated with transient synaptic plasticity that requires all four synaptic elements and is shared across drug classes. Finally, we prognosticate how considering tetrapartite synapses can provide new treatment strategies for addiction.

FMRP Mediates Chronic Ethanol-Induced Changes in NMDA, Kv4.2, and KChIP3 Expression in the Hippocampus

BACKGROUND

Exposure to chronic ethanol (EtOH) results in changes in the expression of proteins that regulate neuronal excitability. This study examined whether chronic EtOH alters the hippocampal expression and function of fragile X mental retardation protein (FMRP) and the role of FMRP in the modulation of chronic EtOH-induced changes in the expression of NMDA receptors and Kv4.2 channels.

METHODS

For in vivo studies, C57BL/6J mice underwent a chronic intermittent EtOH (CIE) vapor exposure procedure. After CIE, hippocampal tissue was collected and subjected to immunoblot blot analysis of NMDA receptor subunits (GluN1, GluN2B), Kv4.2, and its accessory protein KChIP3. For in vitro studies, hippocampal slice cultures were exposed to 75 mM EtOH for 8 days. Following EtOH exposure, mRNAs bound to FMRP was measured. In a separate set of studies, cultures were exposed to an inhibitor of S6K1 (PF-4708671 [PF], 6 μM) in order to assess whether EtOH-induced homeostatic changes in protein expression depend upon changes in FMRP activity.

RESULTS

Immunoblot blot analysis revealed increases in GluN1 and GluN2B but reductions in Kv4.2 and KChIP3. Analysis of mRNAs bound to FMRP revealed a similar bidirectional change observed as reduction of GluN2B and increase in Kv4.2 and KChIP3 mRNA transcripts. Analysis of FMRP further revealed that while chronic EtOH did not alter the expression of FMRP, it significantly increased phosphorylation of FMRP at the S499 residue that is known to critically regulate its activity. Inhibition of S6K1 prevented the chronic EtOH-induced increase in phospho-FMRP and changes in NMDA subunits, Kv4.2, and KChIP3. In contrast, PF had no effect in the absence of alcohol, indicating it was specific for the chronic EtOH-induced changes.

CONCLUSIONS

These findings demonstrate that chronic EtOH exposure enhances translational control of plasticity-related proteins by FMRP, and that S6K1 and FMRP activities are required for expression of chronic EtOH-induced homeostatic plasticity at glutamatergic synapses in the hippocampus.

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.

Chronic Intermittent Ethanol Exposure Enhances the Excitability and Synaptic Plasticity of Lateral Orbitofrontal Cortex Neurons and Induces a Tolerance to the Acute Inhibitory Actions of Ethanol

Alcoholism is associated with changes in brain reward and control systems, including the prefrontal cortex. In prefrontal areas, the orbitofrontal cortex (OFC) has been suggested to have an important role in the development of alcohol-abuse disorders and studies from this laboratory demonstrate that OFC-mediated behaviors are impaired in alcohol-dependent animals. However, it is not known whether chronic alcohol (ethanol) exposure alters the fundamental properties of OFC neurons. In this study, mice were exposed to repeated cycles of chronic intermittent ethanol (CIE) exposure to induce dependence and whole-cell patch-clamp electrophysiology was used to examine the effects of CIE treatment on lateral OFC (lOFC) neuron excitability, synaptic transmission, and plasticity. Repeated cycles of CIE exposure and withdrawal enhanced current-evoked action potential (AP) spiking and this was accompanied by a reduction in the after-hyperpolarization and a decrease in the functional activity of SK channels. CIE mice also showed an increase in the AMPA/NMDA ratio, and this was associated with an increase in GluA1/GluA2 AMPA receptor expression and a decrease in GluN2B NMDA receptor subunits. Following CIE treatment, lOFC neurons displayed a persistent long-term potentiation of glutamatergic synaptic transmission following a spike-timing-dependent protocol. Lastly, CIE treatment diminished the inhibitory effect of acute ethanol on AP spiking of lOFC neurons and reduced expression of the GlyT1 transporter. Taken together, these results suggest that chronic exposure to ethanol leads to enhanced intrinsic excitability and glutamatergic synaptic signaling of lOFC neurons. These alterations may contribute to the impairment of OFC-dependent behaviors in alcohol-dependent individuals.

Adolescent alcohol exposure alters GABAA receptor subunit expression in adult hippocampus

BACKGROUND

The long-term consequences of adolescent alcohol abuse that persist into adulthood are poorly understood and have not been widely investigated. We have shown that intermittent exposure to alcohol during adolescence decreased the amplitude of GABAA receptor (GABAA R)-mediated tonic currents in hippocampal dentate granule cells in adulthood. The aim of this study was to investigate the enduring effects of chronic intermittent alcohol exposure during adolescence or adulthood on the expression of hippocampal GABAA Rs.

METHODS

We used a previously characterized tissue fractionation method to isolate detergent resistant membranes and soluble fractions, followed by Western blots to measure GABAA R protein expression. We also measured mRNA levels of GABAA R subunits using quantitative real-time polymerase chain reaction.

RESULTS

Although the protein levels of α1-, α4-, and δ-GABAA R subunits remained stable between postnatal day (PD) 30 (early adolescence) and PD71 (adulthood), the α5-GABAA R subunit was reduced across that period. In rats that were subjected to adolescent intermittent ethanol (AIE) exposure between PD30 and PD46, there was a significant reduction in the protein levels of the δ-GABAA R, in the absence of any changes in mRNA levels, at 48 hours and 26 days after the last ethanol (EtOH) exposure. Protein levels of the α4-GABAA R subunit were significantly reduced, but mRNA levels were increased, 26 days (but not 48 hours) after the last AIE exposure. Protein levels of α5-GABAA R were not changed by AIE, but mRNA levels were reduced at 48 hours but normalized 26 days after AIE. In contrast to the effects of AIE, chronic intermittent ethanol (CIE) exposure during adulthood had no effect on expression of any of the GABAA R subunits examined.

CONCLUSIONS

AIE produced both short- and long-term alterations of GABAA R subunits mRNA and protein expression in the hippocampus, whereas CIE produced no long-lasting effects on those measures. The observed reduction of protein levels of the δ-GABAA R, specifically, is consistent with previously reported altered hippocampal GABAA R-mediated electrophysiological responses after AIE. The absence of effects of CIE underscores the emerging view of adolescence as a time of distinctive vulnerability to the enduring effects of repeated EtOH exposure.

Chronic intermittent ethanol induced axon and myelin degeneration is attenuated by calpain inhibition

Chronic alcohol consumption causes multifaceted damage to the central nervous system (CNS), underlying mechanisms of which are gradually being unraveled. In our previous studies, activation of calpain, a calcium-activated neutral protease has been found to cause detrimental alterations in spinal motor neurons following ethanol (EtOH) exposure in vitro. However, it is not known whether calpain plays a pivotal role in chronic EtOH exposure-induced structural damage to CNS in vivo. To test the possible involvement of calpain in EtOH-associated neurodegenerative mechanisms the present investigation was conducted in a well-established mouse model of alcohol dependence - chronic intermittent EtOH (CIE) exposure and withdrawal. Our studies indicated significant loss of axonal proteins (neurofilament light and heavy, 50-60%), myelin proteins (myelin basic protein, 20-40% proteolipid protein, 25%) and enzyme (2', 3'-cyclic-nucleotide 3'-phosphodiesterase, 21-55%) following CIE in multiple regions of brain including hippocampus, corpus callosum, cerebellum, and importantly in spinal cord. These CIE-induced deleterious effects escalated after withdrawal in each CNS region tested. Increased expression and activity of calpain along with enhanced ratio of active calpain to calpastatin (sole endogenous inhibitor) was observed after withdrawal compared to EtOH exposure. Pharmacological inhibition of calpain with calpeptin (25 μg/kg) prior to each EtOH vapor inhalation significantly attenuated damage to axons and myelin as demonstrated by immuno-profiles of axonal and myelin proteins, and Luxol Fast Blue staining. Calpain inhibition significantly protected the ultrastructural integrity of axons and myelin compared to control as confirmed by electron microscopy. Together, these findings confirm CIE exposure and withdrawal induced structural alterations in axons and myelin, predominantly after withdrawal and corroborate calpain inhibition as a potential protective strategy against EtOH associated CNS degeneration.

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.

Withdrawal from chronic intermittent alcohol exposure increases dendritic spine density in the lateral orbitofrontal cortex of mice

Alcohol use disorders (AUDs) are associated with functional and morphological changes in subfields of the prefrontal cortex. Clinical and preclinical evidence indicates that the orbitofrontal cortex (OFC) is critical for controlling impulsive behaviors, representing the value of a predicted outcome, and reversing learned associations. Individuals with AUDs often demonstrate deficits in OFC-dependent tasks, and rodent models of alcohol exposure show that OFC-dependent behaviors are impaired by chronic alcohol exposure. To explore the mechanisms that underlie these impairments, we examined dendritic spine density and morphology, and NMDA-type glutamate receptor expression in the lateral OFC of C57BL/6J mice following chronic intermittent ethanol (CIE) exposure. Western blot analysis demonstrated that NMDA receptors were not altered immediately following CIE exposure or after 7 days of withdrawal. Morphological analysis of basal dendrites of layer II/III pyramidal neurons revealed that dendritic spine density was also not affected immediately after CIE exposure. However, the total density of dendritic spines was significantly increased after a 7-day withdrawal from CIE exposure. The effect of withdrawal on spine density was mediated by an increase in the density of long, thin spines with no change in either stubby or mushroom spines. These data suggest that morphological neuroadaptations in lateral OFC neurons develop during alcohol withdrawal and occur in the absence of changes in the expression of NMDA-type glutamate receptors. The enhanced spine density that follows alcohol withdrawal may contribute to the impairments in OFC-dependent behaviors observed in CIE-treated mice.

Technical and implementation issues in using next-generation sequencing of cancers in clinical practice

Next-generation sequencing (NGS) of cancer genomes promises to revolutionise oncology, with the ability to design and use targeted drugs, to predict outcome and response, and to classify tumours. It is continually becoming cheaper, faster and more reliable, with the capability to identify rare yet clinically important somatic mutations. Technical challenges include sequencing samples of low quality and/or quantity, reliable identification of structural and copy number variation, and assessment of intratumour heterogeneity. Once these problems are overcome, the use of the data to guide clinical decision making is not straightforward, and there is a risk of premature use of molecular changes to guide patient management in the absence of supporting evidence. Paradoxically, NGS may simply move the bottleneck of personalised medicine from data acquisition to the identification of reliable biomarkers. Standardised cancer NGS data collection on an international scale would be a significant step towards optimising patient care.

Novel anticonvulsants for reducing alcohol consumption: A review of evidence from preclinical rodent drinking models

Alcohol use disorders (AUDs) are a major public health issue and have an enormous social and economic burden in developed, developing, and third-world countries. Current pharmacotherapies for treating AUDs suffer from deleterious side effects and are only effective in preventing relapse in a subset of individuals. This signifies an essential need for improved medications to reduce heavy episodic drinking and alcohol-related problems. Growing literature has provided support for the use of anticonvulsants in suppressing symptoms induced by alcohol withdrawal. Emerging clinical and preclinical evidence suggests that a number of well-tolerated anticonvulsants may also decrease alcohol drinking. This review will focus on recent evidence supporting the efficacy of novel anticonvulsants in reducing voluntary alcohol consumption in rodent models. The data demonstrate that anticonvulsants reduce drinking in standard home cage two-bottle choice paradigms, self-administration of alcohol in operant chambers, and cue- and stress-induced reinstatement of alcohol seeking behaviors in rats and mice. This review also highlights evidence that some anticonvulsants were only moderately effective in reducing drinking in select strains of rodents or models. This suggests that genetics, possible neuroadaptations, or the pharmacological target affect the ability of anticonvulsants to attenuate alcohol consumption. Nonetheless, anticonvulsants are relatively safe, have little abuse potential, and can work in combination with other drugs. The results from these preclinical and clinical studies provide compelling evidence that anticonvulsants are a promising class of medication for the treatment of AUDs.

Constitutive knockout of the membrane cytoskeleton protein beta adducin decreases mushroom spine density in the nucleus accumbens but does not prevent spine remodeling in response to cocaine

The adducin family of proteins associates with the actin cytoskeleton in a calcium-dependent manner. Beta adducin (βAdd) is involved in synaptic plasticity in the hippocampus; however, the role of βAdd in synaptic plasticity in other brain areas is unknown. Using diolistic labeling with the lipophilic dye DiI, we found that the density of mature mushroom-shaped spines was significantly decreased in the nucleus accumbens (NAc) in brain slices from βAdd-knockout (KO) mice as compared to their wildtype (WT) siblings. The effect of 10 days of daily cocaine (15 mg/kg) administration on NAc spine number and locomotor behavior was also measured in βAdd WT and KO mice. As expected, there was a significant increase in overall spine density in NAc slices from cocaine-treated WT mice at this time-point; however, there was a greater increase in the density of mushroom spines in βAdd-KO animals following chronic cocaine administration than in WT. In addition, βAdd-KO mice showed elevated locomotor activity in response to cocaine treatment compared to WT siblings. These results indicate that βAdd is required for stabilising mature spines under basal conditions in the NAc, but that lack of this protein does not prevent synaptic remodeling following repeated cocaine administration. In addition, these data are consistent with previous studies suggesting that βAdd may normally be involved in stabilising spines once drug- or experience-dependent remodeling has occurred.

Chronic ethanol up-regulates the synaptic expression of the nuclear translational regulatory protein AIDA-1 in primary hippocampal neurons

Recent studies have identified synaptic proteins that undergo synapse-to-nucleus translocation in response to neuronal activity that modulate protein synthesis. One such translational regulatory protein of the postsynaptic density (PSD) is AIDA-1d, which binds to PSD-95 via its C-terminus. Activation of synaptic NMDA receptors induces the cleavage of AIDA-1d, and the N-terminus is then shuttled to nuclear Cajal bodies where it plays a role in regulating global protein synthesis. Chronic ethanol exposure has been shown to increase the synaptic clustering of NMDA receptors and PSD-95. Here, we tested the hypothesis that AIDA-1d regulates chronic ethanol-induced increases in synaptic NMDA receptor expression. As reported, we found that AIDA-1 was highly enriched in dendritic spines and co-localized with PSD-95. Acute NMDA treatment increased AIDA-1 colocalization with p80 coilin, a marker of Cajal bodies. Chronic treatment (4 day) of cultures with ethanol (25-100 mM) or with the NMDA receptor antagonist AP-V (50 μM) enhanced the clustering of AIDA-1 at synaptic sites. However, chronic ethanol treatment (50 mM) in the presence of the NMDA receptor agonist NMDA (2.5 μM) prevented this increase. Surprisingly, PSD-95 did not seem to play a role in the synaptic distribution of AIDA-1 as this distribution was not affected by declustering PSD-95 from synapses in response to inhibition of palmitoylation. We found that lentiviral knockdown of AIDA-1d did not affect protein expression levels of NMDA receptor subunits GluN1, GluN1 C2', or GluN2B. The results of this study demonstrate that synaptic AIDA-1 expression is enhanced by chronic ethanol exposure that can be prevented by concurrent stimulation of NMDA receptors. In addition, we found that the association of AIDA-1 with PSD-95 is not required for its localization to the PSD. Moreover, we found that AIDA-1 does not regulate protein expression levels or alternative splicing of the GluN1 subunit of NMDA receptors.

K(Ca)2 channels: novel therapeutic targets for treating alcohol withdrawal and escalation of alcohol consumption

Small-conductance, calcium-activated potassium (K(Ca)2) channels influence neuronal firing properties, intrinsic excitability, and NMDA receptor-dependent synaptic responses and plasticity. In this mini-review, we discuss new evidence that chronic alcohol-associated plasticity critically involves K(Ca)2 channels in hippocampus, ventral tegmental area, and nucleus accumbens. K(Ca)2 channel activity can modulate the magnitude of excitation of midbrain dopamine neurons induced by acute alcohol exposure. Emerging evidence indicates that K(Ca)2 channels regulate neuroadaptations to chronic alcohol that contribute to withdrawal hyperexcitability and escalation of voluntary alcohol consumption. Restoring K(Ca)2 channel activity can attenuate the severity of the alcohol withdrawal syndrome in vivo and withdrawal-associated neurotoxicity in vitro. Pharmacological modulation of K(Ca)2 channels can bi-directionally influence drinking behavior in rat and mouse models of voluntary alcohol consumption. Collectively, these studies using various rodent models have clearly indicated a central role for K(Ca)2 channels in the neuroplasticity of chronic alcohol exposure. In addition, accumulating evidence suggests that K(Ca)2 channels are a novel therapeutic target to alleviate the symptoms of alcohol withdrawal and reduce high amounts of alcohol drinking.

Glucocorticoid and polyamine interactions in the plasticity of glutamatergic synapses that contribute to ethanol-associated dependence and neuronal injury

Stress contributes to the development of ethanol dependence and is also a consequence of dependence. However, the complexity of physiological interactions between activation of the hypothalamic-pituitary-adrenal (HPA) axis and ethanol itself is not well delineated. Emerging evidence derived from examination of corticotropin-releasing factor systems and glucocorticoid receptor systems in ethanol dependence suggests a role for pharmacological manipulation of the HPA axis in attenuating ethanol intake, though it is not clear how activation of the HPA axis may promote ethanol dependence or contribute to the neuroadaptative changes that accompany the development of dependence and the severity of ethanol withdrawal. This review examines the role that glucocorticoids, in particular, have in promoting ethanol-associated plasticity of glutamatergic synapses by influencing expression of endogenous linear polyamines and polyamine-sensitive polypeptide subunits of N-methyl-D-aspartate (NMDA)-type glutamate receptors. We provide evidence that interactions among glucocorticoid systems, polyamines and NMDA receptors are highly relevant to both the development of ethanol dependence and to behavioral and neuropathological sequelae associated with ethanol withdrawal. Examination of these issues is likely to be of critical importance not only in further elucidating the neurobiology of HPA axis dysregulation in ethanol dependence, but also with regard to identification of novel therapeutic targets that may be exploited in the treatment of ethanol dependence.

Tolerance to cannabinoid-induced behaviors in mice treated chronically with ethanol

RATIONALE

Chronic ethanol (EtOH) treatment decreases the motor-impairing effects of cannabinoids and downregulates the cannabinoid type 1 (CB1) receptor. However, these studies have been limited to measures of ataxia and analysis of CB1 expression from whole-brain or hippocampal preparations.

OBJECTIVE

To more fully assess the interactions between ethanol and cannabinoids, a tetrad of four well-characterized cannabinoid-induced behaviors (hypolocomotion, antinociception, hypothermia, and catalepsy) was measured in mice following EtOH treatment. Additionally, immunoblotting assessed CB1 protein in tissue from nine brain regions associated with these behaviors and the addiction neurocircuitry.

MATERIALS AND METHODS

Male C57Bl/6J mice were administered EtOH (0, 2, or 4 g/kg; intraperitoneally (i.p.)) twice daily for 10 days. Tetrad behaviors induced by the CB1 agonist WIN 55212-2 (3 mg/kg, i.p.) were measured in subjects 1 or 10 days following the last EtOH injection. In a separate group of animals, tissue was collected at the same time points for immunoblot analysis.

RESULTS

EtOH-treated mice were less sensitive to the hypothermic, hypolocomotive, and antinociceptive effects of WIN, and this effect reversed to control levels over a 10-day abstinence period. EtOH treatment did not affect WIN-induced catalepsy. CB1 protein expression was significantly altered in several brain areas including the hypothalamus, periaqueductal gray, ventral tegmental area, and cerebellum.

CONCLUSIONS

These results show that chronic EtOH treatment significantly affects the behavioral sensitivity to cannabinoid drugs and alters CB1 expression in several brain regions. Furthermore, these effects are selective as some behaviors and brain regions display an altered response while others do not.

NR2B-deficient mice are more sensitive to the locomotor stimulant and depressant effects of ethanol

The NR2B subunit of N-methyl d-aspartate glutamate receptors influences pharmacological properties and confers greater sensitivity to the modulatory effects of ethanol. This study examined behavioral responses to acute ethanol in a conditional knockout mouse model that allowed for a delayed genetic deletion of the NR2B subunit to avoid mouse lethality. Mice lacking the NR2B gene (knockout) were produced by mating NR2B[f/f] mice with CAMKIIa-driven tTA transgenic mice and the tetO-CRE transgenic mice. Adult male and female offspring representing each of the resultant genotypes (knockout, CAM, CRE and wildtype mice) were tested for open-field locomotor activity following acute low- and high-dose ethanol challenge as well as loss of righting reflex. Findings indicate that male and female mice lacking the NR2B subunit exhibited greater overall activity in comparison to other genotypes during the baseline locomotor activity test. NR2B knockout mice exhibited an exaggerated stimulant response to 1.5 g/kg (i.p.) and an exaggerated depressant response to 3.0 g/kg (i.p.) ethanol challenge. In addition, NR2B knockout mice slept longer following a high dose of ethanol (4.0 g/kg, i.p.). To evaluate pharmacokinetics, clearance rates of ethanol (1.5, 4.0 g/kg, i.p.) were measured and showed that female NR2B knockouts had a faster rate of metabolism only at the higher ethanol dose. Western blot analyses confirmed significant reduction in NR2B expression in the forebrain of knockout mice. Collectively, these data indicate that the NR2B subunit of the N-methyl d-aspartate glutamate receptor is involved in regulating low-dose stimulant effects of ethanol and the depressant/hypnotic effects of ethanol.

The glutamatergic component of the mesocortical pathway emanating from different subregions of the ventral midbrain

The mesocortical pathway projecting from the ventral tegmental area (VTA) to the prefrontal cortex (PFC) plays a critical role in a number of cognitive and emotional processes. While this pathway has been traditionally viewed as dopaminergic, recent data indicate that a considerable proportion of rostromedial VTA neurons possess markers for glutamate transmission. However, the relative density of the glutamatergic projection to the PFC from these rostromedial regions is unknown. In the present study, anterograde tracer injections into 4 ventral midbrain subregions were coupled with immunohistochemical analysis of labeled axons in PFC for markers of dopamine (DA; tyrosine hydroxylase [TH]) and glutamate (vesicular glutamate transporter 2; VGLUT2). We found that while tracer injections into the interfascicular nucleus produced labeled fibers in the PFC that were mainly TH positive, tracer injections into the rostral linear nucleus, rostral VTA, and parabrachial pigmented nucleus produced labeled fibers in PFC that contained mainly VGLUT2-positive rather than TH-positive varicosities. When viewed in the light of the previously documented strong γ-aminobutyric acidergic component, it would seem that the rostromedial mesocortical projection is actually an amino acid pathway that in addition has a DA component.

Small conductance calcium-activated potassium type 2 channels regulate alcohol-associated plasticity of glutamatergic synapses

BACKGROUND

Small conductance calcium-activated potassium type 2 channels (SK2) control excitability and contribute to plasticity by reducing excitatory postsynaptic potentials. Recent evidence suggests that SK2 channels form a calcium-dependent negative-feedback loop with synaptic N-methyl-D-aspartate (NMDA) receptors. Addiction to alcohol and other drugs of abuse induces plastic changes in glutamatergic synapses that include the targeting of NMDA receptors to synaptic sites; however, the role of SK2 channels in alcohol-associated homeostatic plasticity is unknown.

METHODS

Electrophysiology, Western blot, and behavioral analyses were used to quantify changes in hippocampal small conductance calcium-activated potassium (SK) channel function and expression using well-characterized in vitro and in vivo models of chronic alcohol exposure.

RESULTS

Chronic ethanol reduced apamin-sensitive SK currents in cornu ammonis 1 pyramidal neurons that were associated with a downregulation of surface SK2 channels. Blocking SK channels with apamin potentiated excitatory postsynaptic potentials in control but not ethanol-treated cornu ammonis 1 pyramidal neurons, suggesting that chronic ethanol disrupts the SK channel-NMDA receptor feedback loop. Alcohol reduced expression of SK2 channels and increased expression of NMDA receptors at synaptic sites in a mouse model. Positive modulation of SK function by 1-EBIO decreased alcohol withdrawal hyperexcitability and attenuated ethanol withdrawal neurotoxicity in hippocampus. The 1-EBIO also reduced seizure activity in mice undergoing withdrawal.

CONCLUSIONS

These results provide evidence that SK2 channels contribute to alcohol-associated adaptive plasticity of glutamatergic synapses and that positive modulation of SK channels reduces the severity of withdrawal-related hyperexcitability. Therefore, SK2 channels appear to be critical regulators of alcohol-associated plasticity and may be novel therapeutic targets for the treatment of addiction.

Inhibition of glutamate transporters couples to Kv4.2 dephosphorylation through activation of extrasynaptic NMDA receptors

Activation of glutamate receptors is known to modulate K(+) channel surface trafficking, phosphorylation, and function, and increasing evidence has implicated K(+) channels in plastic changes in glutamatergic synapses. Kv4.2 channels control the amplitude of back-propagating action potentials and shape postsynaptic responses in hippocampus, and synaptic glutamate receptor activation leads to increased phosphorylation of Kv4.2 channels that is associated with enhanced synaptic plasticity. Thus, we investigated the possibility that activation of extrasynaptic NMDA-type glutamate receptors couples to Kv4.2 channel dephosphorylation. In hippocampal neurons, we found that selective activation of extrasynaptic NMDA receptors dephosphorylates Kv4.2 channels, and driving synaptic activity increases phosphorylation of Kv4.2. We also observed that Ca(2+) entry through NMDA receptors is necessary for dephosphorylation of Kv4.2 channels. Consistent with a synaptic and extrasynaptic localization at hippocampal synapses, a fraction of Kv4.2 channel clusters was found to localize outside of pre- and postsynaptic markers. Excitatory amino acid transporters (EAATs) regulate ambient extracellular glutamate levels that active extrasynaptic NMDA receptors, and inhibition of glutamate uptake by blocking EAATs with the non-selective transporter inhibitor dl-threo-beta-benzyloxyaspartic acid (TBOA) or the EAAT1/3 selective inhibitor l-serine O-sulfate (SOS) dephosphorylates Kv4.2 channels. These findings in conjunction with previous reports support the interesting possibility that synaptic and extrasynaptic NMDA receptors bi-directionally regulate phosphorylation levels of Kv4.2 channels in hippocampus. Moreover, we observed that EAAT activity controls extrasynaptic NMDA receptor modulation of Kv4.2 channel dephosphorylation.

Sizing up ethanol-induced plasticity: the role of small and large conductance calcium-activated potassium channels

Small (SK) and large conductance (BK) Ca(2+)-activated K(+) channels contribute to action potential repolarization, shape dendritic Ca(2+)spikes and postsynaptic responses, modulate the release of hormones and neurotransmitters, and contribute to hippocampal-dependent synaptic plasticity. Over the last decade, SK and BK channels have emerged as important targets for the development of acute ethanol tolerance and for altering neuronal excitability following chronic ethanol consumption. In this mini-review, we discuss new evidence implicating SK and BK channels in ethanol tolerance and ethanol-associated homeostatic plasticity. Findings from recent reports demonstrate that chronic ethanol produces a reduction in the function of SK channels in VTA dopaminergic and CA1 pyramidal neurons. It is hypothesized that the reduction in SK channel function increases the propensity for burst firing in VTA neurons and increases the likelihood for aberrant hyperexcitability during ethanol withdrawal in hippocampus. There is also increasing evidence supporting the idea that ethanol sensitivity of native BK channel results from differences in BK subunit composition, the proteolipid microenvironment, and molecular determinants of the channel-forming subunit itself. Moreover, these molecular entities play a substantial role in controlling the temporal component of ethanol-associated neuroadaptations in BK channels. Taken together, these studies suggest that SK and BK channels contribute to ethanol tolerance and adaptive plasticity.

Ethanol disrupts NMDA receptor and astroglial EAAT2 modulation of Kv2.1 potassium channels in hippocampus

Delayed-rectifier Kv2.1 channels are the principal component of voltage-sensitive K+ currents (I(K)) in hippocampal neurons and are critical regulators of somatodendritic excitability. In a recent study, we demonstrated that surface trafficking and phosphorylation of Kv2.1 channels is modulated by NMDA-type glutamate receptors and that astroglial excitatory amino acid transporters 2 (EAAT2) regulate the coupling of NMDA receptors and Kv2.1 channels. Because ethanol is known to acutely inhibit NMDA receptors, we sought to determine if NMDA receptor and astroglial EAAT2 modulation of Kv2.1 channels is impaired by ethanol in the rodent hippocampus. As expected, bath application of NMDA to hippocampal cultures reduced the size of Kv2.1 clusters and produced a hyperpolarizing shift in the voltage-dependent activation of I(K) that was associated with dephosphorylated Kv2.1 channels. Ethanol, applied acutely, prevented the hyperpolarizing shift in activation of I(K) induced by NMDA and restored Kv2.1 clustering and phosphorylation to near control levels. Ethanol also attenuated the dephosphorylation of Kv2.1 channels produced by the EAAT2 selective inhibitor dihydrokainic acid. These data demonstrate that acute ethanol disrupts changes in Kv2.1 channels that follow NMDA receptor activation and impairs astroglial regulation of the functional coupling between NMDA receptors and Kv2.1 channels.