Moderate Alcohol Drinking and the Amygdala Proteome: Identification and Validation of Calcium/Calmodulin Dependent Kinase II and AMPA Receptor Activity as Novel Molecular Mechanisms of the Positive Reinforcing Effects of Alcohol

Differential regulation of G protein-coupled receptor-associated proteins in the caudate and the putamen of cynomolgus macaques following chronic ethanol drinking

The dorsal striatum is composed of the caudate nucleus and the putamen in human and non-human primates. These two regions receive different cortical projections and are functionally distinct. The caudate is involved in the control of goal-directed behaviors, while the putamen is implicated in habit learning and formation. Previous reports indicate that ethanol differentially influences neurotransmission in these two regions. Because neurotransmitters primarily signal through G protein-coupled receptors (GPCRs) to modulate neuronal activity, the present study aimed to determine whether ethanol had a region-dependent impact on the expression of proteins that are involved in the trafficking and function of GPCRs, including G protein subunits and their effectors, protein kinases, and elements of the cytoskeleton. Western blotting was performed to examine protein levels in the caudate and the putamen of male cynomolgus macaques that self-administered ethanol for 1 year under free access conditions, along with control animals that self-administered an isocaloric sweetened solution under identical operant conditions. Among the 18 proteins studied, we found that the levels of one protein (PKCβ) were increased, and 13 proteins (Gαi1/3, Gαi2, Gαo, Gβ1γ, PKCα, PKCε, CaMKII, GSK3β, β-actin, cofilin, α-tubulin, and tubulin polymerization promoting protein) were reduced in the caudate of alcohol-drinking macaques. However, ethanol did not alter the expression of any proteins examined in the putamen. These observations underscore the unique vulnerability of the caudate nucleus to changes in protein expression induced by chronic ethanol exposure. Whether these alterations are associated with ethanol-induced dysregulation of GPCR function and neurotransmission warrants future investigation.

Prefrontal cortex glutamatergic adaptations in a mouse model of alcohol use disorder

Alcohol use disorder (AUD) produces cognitive deficits, indicating a shift in prefrontal cortex (PFC) function. PFC glutamate neurotransmission is mostly mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type ionotropic receptors (AMPARs); however preclinical studies have mostly focused on other receptor subtypes. Here we examined the impact of early withdrawal from chronic ethanol on AMPAR function in the mouse medial PFC (mPFC). Dependent male C57BL/6J mice were generated using the chronic intermittent ethanol vapor-two bottle choice (CIE-2BC) paradigm. Non-dependent mice had access to water and ethanol bottles but did not receive ethanol vapor. Naïve mice had no ethanol exposure. We used patch-clamp electrophysiology to measure glutamate neurotransmission in layer 2/3 prelimbic mPFC pyramidal neurons. Since AMPAR function can be impacted by subunit composition or plasticity-related proteins, we probed their mPFC expression levels. Dependent mice had higher spontaneous excitatory postsynaptic current (sEPSC) amplitude and kinetics compared to the Naïve/Non-dependent mice. These effects were seen during intoxication and after 3-8 days withdrawal, and were action potential-independent, suggesting direct enhancement of AMPAR function. Surprisingly, 3 days withdrawal decreased expression of genes encoding AMPAR subunits (Gria1/2) and synaptic plasticity proteins (Dlg4 and Grip1) in Dependent mice. Further analysis within the Dependent group revealed a negative correlation between Gria1 mRNA levels and ethanol intake. Collectively, these data establish a role for mPFC AMPAR adaptations in the glutamatergic dysfunction associated with ethanol dependence. Future studies on the underlying AMPAR plasticity mechanisms that promote alcohol reinforcement, seeking, drinking and relapse behavior may help identify new targets for AUD treatment.

LPA1 receptors in the lateral habenula regulate negative affective states associated with alcohol withdrawal

The role of lysophosphatidic acid (LPA) signaling in psychiatric disorders and drug abuse is significant. LPA receptors are widely expressed in the central nervous system, including the lateral habenula (LHb). Recent studies suggest that LHb is involved in a negative emotional state during alcohol withdrawal, which can lead to relapse. The current study examines the role of LHb LPA signaling in the negative affective state associated with alcohol withdrawal. Adult male Long-Evans rats were trained to consume either alcohol or water for eight weeks. At 48 h of withdrawal, alcohol-drinking rats showed anxiety- and depression-like symptoms, along with a significant increase in LPA signaling and related neuronal activation molecules, including autotaxin (ATX, Enpp2), LPA receptor 1/3 (LPA1/3), βCaMKII, and c-Fos. However, there was a decrease in lipid phosphate phosphatase-related protein type 4 (LPPR4) in the LHb. Intra-LHb infusion of the LPA1/3 receptor antagonist ki-16425 or PKC-γ inhibitor Go-6983 reduced the abnormal behaviors and elevated relapse-like ethanol drinking. It also normalized high LPA1/3 receptors and enhanced AMPA GluA1 phosphorylation in Ser831 and GluA1/GluA2 ratio. Conversely, selective activation of LPA1/3 receptors by intra-LHb infusion of 18:1 LPA induced negative affective states and upregulated βCaMKII-AMPA receptor phosphorylation in Naive rats, which were reversed by pretreatment with intra-LHb Go-6983. Our findings suggest that disturbances in LPA signaling contribute to adverse affective disorders during alcohol withdrawal, likely through PKC-γ/βCaMKII-linked glutamate signaling. Targeting LPA may therefore be beneficial for individuals suffering from alcohol use disorders.

Alcohol-drinking during later life by C57BL/6J mice induces sex- and age-dependent changes in hippocampal and prefrontal cortex expression of glutamate receptors and neuropathology markers

Heavy drinking can induce early-onset dementia and increase the likelihood of the progression and severity of Alzheimer's Disease and related dementias (ADRD). Recently, we showed that alcohol-drinking by mature adult C57BL/6J mice induces more signs of cognitive impairment in females versus males without worsening age-related cognitive decline in aged mice. Here, we immunoblotted for glutamate receptors and protein markers of ADRD-related neuropathology within the hippocampus and prefrontal cortex (PFC) of these mice after three weeks of alcohol withdrawal to determine protein correlates of alcohol-induced cognitive decline. Irrespective of alcohol history, age-related changes in protein expression included a male-specific decline in hippocampal glutamate receptors and an increase in the expression of a beta-site amyloid precursor protein cleaving enzyme (BACE) isoform in the PFC as well as a sex-independent increase in hippocampal amyloid precursor protein. Alcohol-drinking was associated with altered expression of glutamate receptors in the hippocampus in a sex-dependent manner, while all glutamate receptor proteins exhibited significant alcohol-related increases in the PFC of both sexes. Expression of BACE isoforms and phosphorylated tau varied in the PFC and hippocampus based on age, sex, and drinking history. The results of this study indicate that withdrawal from a history of alcohol-drinking during later life induces sex- and age-selective effects on glutamate receptor expression and protein markers of ADRD-related neuropathology within the hippocampus and PFC of potential relevance to the etiology, treatment and prevention of alcohol-induced dementia and Alzheimer's Disease.

A subchronic history of binge-drinking elicits mild, age- and sex-selective, affective, and cognitive anomalies in C57BL/6J mice

Introduction

Alcohol abuse is a risk factor for affective and cognitive disorders, with evidence indicating that adolescent-onset excessive drinking can result in long-term deficiencies in emotional regulation and cognition, with females more susceptible to the negative emotional and cognitive consequences of excessive alcohol consumption. However, our prior examination of the interactions between sex and the age of drinking-onset indicated minimal signs of anxiety-like behavior during alcohol withdrawal, which may have related to the concurrent anxiety testing of male and female subjects.

Methods

The present study addressed this potential confound by assaying for alcohol withdrawal-induced negative affect separately in males and females and expanded our investigation to include measures of spatial and working memory.

Results

Following 14 days of drinking under modified Drinking-in-the-Dark procedures (10, 20, and 40% alcohol v/v; 2 h/day), adolescent and adult binge-drinking mice of both sexes exhibited, respectively, fewer and more signs of negative affect in the light-dark shuttle-box and forced swim tests than their water-drinking counterparts. Adolescent-onset binge-drinking mice also exhibited signs of impaired working memory early during radial arm maze training during early alcohol withdrawal. When tested in late (30 days) withdrawal, only adult female binge-drinking mice buried more marbles than their water-drinking counterparts. However, adolescent-onset binge-drinking mice exhibited poorer spatial memory recall in a Morris water maze.

Discussion

These findings indicate that a subchronic (14-day) binge-drinking history induces mild, age- and sex-selective, changes in negative affect and cognition of potential relevance to understanding individual variability in the etiology and treatment of alcohol abuse and alcohol use disorder.

Negative modulation of AMPA receptors bound to transmembrane AMPA receptor regulatory protein γ-8 blunts the positive reinforcing properties of alcohol and sucrose in a brain region-dependent manner in male mice

RATIONALE

The development and progression of alcohol use disorder (AUD) are widely viewed as maladaptive neuroplasticity. The transmembrane alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) regulatory protein γ8 (TARP γ-8) is a molecular mechanism of neuroplasticity that has not been evaluated in AUD or other addictions.

OBJECTIVE

To address this gap in knowledge, we evaluated the mechanistic role of TARP γ-8 bound AMPAR activity in the basolateral amygdala (BLA) and ventral hippocampus (vHPC) in the positive reinforcing effects of alcohol, which drive repetitive alcohol use throughout the course of AUD, in male C57BL/6 J mice. These brain regions were selected because they exhibit high levels of TARP γ-8 expression and send glutamate projections to the nucleus accumbens (NAc), which is a key nucleus in the brain reward pathway.

METHODS AND RESULTS

Site-specific pharmacological inhibition of AMPARs bound to TARP γ-8 in the BLA via bilateral infusion of the selective negative modulator JNJ-55511118 (0-2 µg/µl/side) significantly decreased operant alcohol self-administration with no effect on sucrose self-administration in behavior-matched controls. Temporal analysis showed that reductions in alcohol-reinforced response rate occurred > 25 min after the onset of responding, consistent with a blunting of the positive reinforcing effects of alcohol in the absence of nonspecific behavioral effects. In contrast, inhibition of TARP γ-8 bound AMPARs in the vHPC selectively decreased sucrose self-administration with no effect on alcohol.

CONCLUSIONS

This study reveals a novel brain region-specific role of TARP γ-8 bound AMPARs as a molecular mechanism of the positive reinforcing effects of alcohol and non-drug rewards.

Autophosphorylation of αCaMKII regulates alcohol consumption by controlling sedative effects of alcohol and alcohol-induced loss of excitatory synapses

Calcium/calmodulin-dependent kinase II (CaMKII) is a key enzyme at the glutamatergic synapses. CAMK2A gene variants have been linked with alcohol use disorder (AUD) by an unknown mechanism. Here, we looked for the link between αCaMKII autophosphorylation and the AUD aetiology. Autophosphorylation-deficient heterozygous αCaMKII mutant mice (T286A^+/- ) were trained in the IntelliCages to test the role of αCaMKII activity in AUD-related behaviours. The glutamatergic synapses morphology in CeA was studied in the animals drinking alcohol using 3D electron microscopy. We found that T286A^+/- mutants consumed less alcohol and were more sensitive to sedating effects of alcohol, as compared to wild-type littermates (WT). After voluntary alcohol drinking, T286A^+/- mice had less excitatory synapses in the CeA, as compared to alcohol-naive animals. This change correlated with alcohol consumption was not reversed after alcohol withdrawal and not observed in WT mice. Our study suggests that αCaMKII autophosphorylation affects alcohol consumption by controlling sedative effects of alcohol and preventing synaptic loss in the individuals drinking alcohol. This finding advances our understanding of the molecular processes that regulate alcohol dependence.

Arc controls alcohol cue relapse by a central amygdala mechanism

Alcohol use disorder (AUD) is a chronic and fatal disease. The main impediment of the AUD therapy is a high probability of relapse to alcohol abuse even after prolonged abstinence. The molecular mechanisms of cue-induced relapse are not well established, despite the fact that they may offer new targets for the treatment of AUD. Using a comprehensive animal model of AUD, virally-mediated and amygdala-targeted genetic manipulations by CRISPR/Cas9 technology and ex vivo electrophysiology, we identify a mechanism that selectively controls cue-induced alcohol relapse and AUD symptom severity. This mechanism is based on activity-regulated cytoskeleton-associated protein (Arc)/ARG3.1-dependent plasticity of the amygdala synapses. In humans, we identified single nucleotide polymorphisms in the ARC gene and their methylation predicting not only amygdala size, but also frequency of alcohol use, even at the onset of regular consumption. Targeting Arc during alcohol cue exposure may thus be a selective new mechanism for relapse prevention.

β-hydroxybutyrate reduces reinstatement of cocaine conditioned place preference through hippocampal CaMKII-α β-hydroxybutyrylation

Studies have shown the therapeutic effects of a ketogenic diet (KD) on epilepsy, but the effect of a KD on drug reinstatement is largely unclear. This study aims to investigate whether KD consumption possesses therapeutic potential for cocaine reinstatement and the molecular mechanism. We find that a KD significantly reduces cocaine-induced reinstatement in mice, which is accompanied by a markedly elevated level of β-hydroxybutyrate (β-OHB), the most abundant ketone body, in the hippocampus. The underlying mechanism is that β-OHB posttranslationally modifies CaMKII-α with β-hydroxybutyrylation, resulting in significant inhibition of T286 autophosphorylation and downregulation of CaMKII activity. Collectively, our results reveal that β-hydroxybutyrylation is a posttranslational modification of CaMKII-α that plays a critical role in mediating the effect of KD consumption in reducing cocaine reinstatement.

Postsynaptic signaling at glutamatergic synapses as therapeutic targets

Dysregulation of glutamatergic synapses plays an important role in the pathogenesis of neurological diseases. In addition to mediating excitatory synaptic transmission, postsynaptic glutamate receptors interact with various membrane and intracellular proteins. They form structural and/or signaling synaptic protein complexes and thereby play diverse postsynaptic functions. Recently, several postsynaptic protein complexes have been associated with various neurological diseases and hence, have been characterized as important therapeutic targets. Moreover, novel small molecules and therapeutic peptides targeting and modulating the activities of these protein complexes have been discovered, some of which have advanced through preclinical translational research and/or clinical studies. This article describes the recent investigation of eight key protein complexes associated with the postsynaptic ionotropic and metabotropic glutamate receptors as therapeutic targets for central nervous system diseases.

Neuroligin Plays a Role in Ethanol-Induced Disruption of Memory and Corresponding Modulation of Glutamate Receptor Expression

Exposure to alcohol causes deficits in long-term memory formation across species. Using a long-term habituation memory assay in Caenorhabditis elegans, the effects of ethanol on long-term memory (> 24 h) for habituation were investigated. An impairment in long-term memory was observed when animals were trained in the presence of ethanol. Cues of internal state or training context during testing did not restore memory. Ethanol exposure during training also interfered with the downregulation of AMPA/KA-type glutamate receptor subunit (GLR-1) punctal expression previously associated with long-term memory for habituation in C. elegans. Interestingly, ethanol exposure alone had the opposite effect, increasing GLR-1::GFP punctal expression. Worms with a mutation in the C. elegans ortholog of vertebrate neuroligins (nlg-1) were resistant to the effects of ethanol on memory, as they displayed both GLR-1::GFP downregulation and long-term memory for habituation after training in the presence of ethanol. These findings provide insights into the molecular mechanisms through which alcohol consumption impacts memory.

Alcohol-Drinking Under Limited-Access Procedures During Mature Adulthood Accelerates the Onset of Cognitive Impairment in Mice

A history of heavy drinking increases vulnerability to, and the severity of, Alzheimer’s disease (AD) and related dementias, with alcohol use disorder identified as the strongest modifiable risk factor for early-onset dementia. Heavy drinking has increased markedly in women over the past 10 years, particularly in mature adult women during the coronavirus (COVID-19) pandemic. This is concerning as women are more sensitive to many alcohol-related disease states, including AD and related dementias. Herein, we conducted two studies to determine if a 1-month period of binge drinking during mature adulthood (i.e., 5–9 months of age) impairs spatial and working memory to a greater extent in female vs. male C57BL/6J (B6J) mice. The anxiogenic and cognitive-impairing effects of binge drinking were also compared between mature adult and old B6J mice (18 months of age) in a third study. Throughout, females consumed more alcohol than males, indicating that a sex difference in binge drinking persists into old age. Despite the sex difference in intake, we detected no consistent sex difference in our measures of alcohol withdrawal-induced anxiety during a behavioral test battery. Although mature adult females exhibited more cognitive deficits than males, the precise outcome exhibiting a female-selective effect varied across studies. Old mice drank lower amounts of alcohol than mature adult mice, yet their blood ethanol concentrations (BECs) were within error of the 80 mg/dl criterion for binge drinking, indicative of an age-related slowing of alcohol metabolism. As expected, 18-month-old controls exhibited more signs of cognitive impairment than their 6-month-old counterparts, and binge drinking history impaired the Morris water maze performance of mice of both ages. In contrast, binge drinking history impaired the radial arm maze performance of 6-month-old mice only, and the extent of the impairment was comparable to the behavior exhibited by the older mice. We conclude from our studies that: (1) both biological sex and the age of drinking onset are subject factors that impact voluntary alcohol consumption by mice into old age; (2) binge drinking during later life elicits a negative affective state that is relatively sex-independent; (3) binge drinking during both mature adulthood and old age impairs spatial learning and memory; (4) binge drinking during mature adulthood accelerates deficits in working memory; and (5) mature adult females tend to exhibit more alcohol-induced cognitive impairments than males. If relevant to humans, these findings suggest that binge-like drinking by older adult men and women induces a negative affective state and cognitive decline, but that mature adult women, in particular, may be more sensitive to both the immediate and persistent cognitive-impairing effects of heavy drinking.

Prevention of glutamate excitotoxicity in lateral habenula alleviates ethanol withdrawal-induced somatic and behavioral effects in ethanol dependent mice

Ethanol withdrawal commonly leads to anxiety-related disorder, a central factor toward negative reinforcement leading to relapse. The lateral habenula (LHb), an epithalamic nucleus, has emerged to be critical for both reward and aversion processing. Recent studies have also implicated the hyperactivity of LHb, adding to the emergence of negative emotional states during withdrawal from addictive drugs. Herein, we have studied the effects of glutamate transporter inhibitor (PDC), GluN2B-containing NMDAR antagonist (Ro25-6981), and intracellular calcium chelator (BAPTA-AM) injection in LHb on ethanol withdrawal symptoms. We found that ethanol 4 g/kg 20 % w/v intragastric (i.g.) for 10 days followed by 24 h of withdrawal showed a significant increase in somatic signs characterized by vocalization, shaking, and scratching. It also increased locomotor activity and anxiety-like behavior, collectively showing expression of ethanol withdrawal symptoms. The intra-LHb administration of PDC (0.5 ng) worsened the effect of ethanol withdrawal, whereas Ro25-6981 (2 and 4 ng) and BAPTA-AM (6.5 and 13 ng) significantly reversed ethanol withdrawal-induced behavior evident by a decrease in somatic signs, locomotor activity, and anxiety-like behavior. Further, pretreatment of Ro25-6981 and BAPTA-AM reduced the neuronal loss, whereas PDC increased it compared to the vehicle-treated group, as evidenced by NeuN staining. Altogether, our results suggest that increased glutamate, GluN2B activation, and likely calcium increase indicative of glutamate excitotoxicity-induced neuronal loss in LHb possibly endorse the emergence of ethanol withdrawal symptoms, while their inhibition might help in alleviating the ethanol withdrawal symptoms.

Sex-specific plasticity in CRF regulation of inhibitory control in central amygdala CRF1 neurons after chronic voluntary alcohol drinking

Despite strong preclinical evidence for the ability of corticotropin releasing factor 1 (CRF1) antagonists to regulate alcohol consumption, clinical trials have not yet demonstrated therapeutic effects of these compounds in alcohol use disorder (AUD) patients. Several confounding factors may limit the translation of preclinical CRF1 research to patients, including reliance on experimenter-administered alcohol instead of voluntary consumption, a preponderance of evidence collected in male subjects only and an inability to assess the effects of alcohol on specific brain circuits. A population of particular interest is the CRF1-containing neurons of the central amygdala (CeA). CRF1 CeA neurons are sensitive to ethanol, but the effects of alcohol drinking on CRF signalling within this population are unknown. In the present study, we assessed the effects of voluntary alcohol drinking on inhibitory control of CRF1+ CeA neurons from male and female CRF1:GFP mice using ex vivo electrophysiology and determined the contributions of CRF1 signalling to inhibitory control and voluntary alcohol drinking. Chronic alcohol drinking produced neuroadaptations in CRF1+ neurons that increased the sensitivity of GABA_A receptor-mediated sIPSCs to the acute effects of alcohol, CRF and the CRF1 antagonist R121919, but these adaptations were more pronounced in male versus female mice. The CRF1 antagonist CP-154,526 reduced voluntary alcohol drinking in both sexes and abolished sex differences in alcohol drinking. The lack of alcohol-induced adaptation in the female CRF1 system may be related to the elevated alcohol intake exhibited by female mice and could contribute to the ineffectiveness of CRF1 antagonists in female AUD patients.

Calcium-permeable AMPA receptor activity and GluA1 trafficking in the basolateral amygdala regulate operant alcohol self-administration

Addiction is viewed as maladaptive glutamate-mediated neuroplasticity that is regulated, in part, by calcium-permeable AMPA receptor (CP-AMPAR) activity. However, the contribution of CP-AMPARs to alcohol-seeking behavior remains to be elucidated. We evaluated CP-AMPAR activity in the basolateral amygdala (BLA) as a potential target of alcohol that also regulates alcohol self-administration in C57BL/6J mice. Operant self-administration of sweetened alcohol increased spontaneous EPSC frequency in BLA neurons that project to the nucleus accumbens as compared with behavior-matched sucrose controls indicating an alcohol-specific upregulation of synaptic activity. Bath application of the CP-AMPAR antagonist NASPM decreased evoked EPSC amplitude only in alcohol self-administering mice indicating alcohol-induced synaptic insertion of CP-AMPARs in BLA projection neurons. Moreover, NASPM infusion in the BLA dose-dependently decreased the rate of operant alcohol self-administration providing direct evidence for CP-AMPAR regulation of alcohol reinforcement. As most CP-AMPARs are GluA1-containing, we asked if alcohol alters the activation state of GluA1-containing AMPARs. Immunocytochemistry results showed elevated GluA1-S831 phosphorylation in the BLA of alcohol as compared with sucrose mice. To investigate mechanistic regulation of alcohol self-administration by GluA1-containing AMPARs, we evaluated the necessity of GluA1 trafficking using a TET-ON AAV encoding a dominant-negative GluA1 c-terminus (GluA1ct) that blocks activity-dependent synaptic delivery of native GluA1-containing AMPARs. GluA1ct expression in the BLA reduced alcohol self-administration with no effect on sucrose controls. These results show that CP-AMPAR activity and GluA1 trafficking in the BLA mechanistically regulate the reinforcing effects of sweetened alcohol. Pharmacotherapeutic targeting these mechanisms of maladaptive neuroplasticity may aid medical management of alcohol use disorder.

Alcohol dependence activates ventral tegmental area projections to central amygdala in male mice and rats

The neural adaptations that occur during the transition to alcohol dependence are not entirely understood but may include a gradual recruitment of brain stress circuitry by mesolimbic reward circuitry that is activated during early stages of alcohol use. Here, we focused on dopaminergic and nondopaminergic projections from the ventral tegmental area (VTA), important for mediating acute alcohol reinforcement, to the central nucleus of the amygdala (CeA), important for alcohol dependence-related negative affect and escalated alcohol drinking. The VTA projects directly to the CeA, but the functional relevance of this circuit is not fully established. Therefore, we combined retrograde and anterograde tracing, anatomical, and electrophysiological experiments in mice and rats to demonstrate that the CeA receives input from both dopaminergic and nondopaminergic projection neurons primarily from the lateral VTA. We then used slice electrophysiology and fos immunohistochemistry to test the effects of alcohol dependence on activity and activation profiles of CeA-projecting neurons in the VTA. Our data indicate that alcohol dependence activates midbrain projections to the central amygdala, suggesting that VTA projections may trigger plasticity in the CeA during the transition to alcohol dependence and that this circuit may be involved in mediating behavioral dysregulation associated with alcohol dependence.

Reduced exploratory behavior in neuronal nucleoredoxin knockout mice

Nucleoredoxin is a thioredoxin-like redoxin that has been recognized as redox modulator of WNT signaling. Using a Yeast-2-Hybrid screen, we identified calcium calmodulin kinase 2a, Camk2a, as a prominent prey in a brain library. Camk2a is crucial for nitric oxide dependent processes of neuronal plasticity of learning and memory. Therefore, the present study assessed functions of NXN in neuronal Nestin-NXN^-/- deficient mice. The NXN-Camk2a interaction was confirmed by coimmunoprecipitation, and by colocalization in neuropil and dendritic spines. Functionally, Camk2a activity was reduced in NXN deficient neurons and restored with recombinant NXN. Proteomics revealed reduced oxidation in the hippocampus of Nestin-NXN^-/- deficient mice, including Camk2a, further synaptic and mitochondrial proteins, and was associated with a reduction of mitochondrial respiration. Nestin-NXN^-/- mice were healthy and behaved normally in behavioral tests of anxiety, activity and sociability. They had no cognitive deficits in touchscreen based learning & memory tasks, but omitted more trials showing a lower interest in the reward. They also engaged less in rewarding voluntary wheel running, and in exploratory behavior in IntelliCages. Accuracy was enhanced owing to the loss of exploration. The data suggested that NXN maintained the oxidative state of Camk2a and thereby its activity. In addition, it supported oxidation of other synaptic and mitochondrial proteins, and mitochondrial respiration. The loss of NXN-dependent pro-oxidative functions manifested in a loss of exploratory drive and reduced interest in reward in behaving mice.

Inhibition of AMPA receptors (AMPARs) containing transmembrane AMPAR regulatory protein γ-8 with JNJ-55511118 shows preclinical efficacy in reducing chronic repetitive alcohol self-administration

BACKGROUND

A prominent therapeutic indication for alcohol use disorder (AUD) is reduction in chronic repetitive alcohol use. Glutamate α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPARs) regulate chronic alcohol self-administration in preclinical models. Recent evidence indicates that the expression and function of AMPARs require the transmembrane AMPAR regulatory protein γ-8 (TARP γ-8). This study evaluated the preclinical efficacy of JNJ-55511118, a novel, selective, high-affinity inhibitor of TARP γ-8-bound AMPARs, in reducing chronic operant alcohol self-administration.

METHODS

Separate groups of male and female C57BL/6J mice (n = 8/sex/group) were trained to lever press for sweetened alcohol (9% v/v + sucrose 2% w/v) or sucrose only (2% w/v) in operant conditioning chambers using an FR-4 schedule of reinforcement. After a 40-day baseline, JNJ-55511118 (0, 1, and 10 mg/kg, p.o.) was administered in randomized order 1 h before self-administration sessions. Parameters of operant behavior including response rate, total reinforcers, and head entries in the drinking troughs were computer recorded.

RESULTS

During baseline, responding to alcohol, but not sucrose, was greater in female than male mice. In male mice, both doses of JNJ-55511118 decreased multiple parameters of alcohol self-administration but did not reduce behavior-matched sucrose-only self-administration. JNJ-55511118 had no effect on sweetened alcohol or sucrose self-administration in female mice. Subsequent tests of motor function showed that the lowest effective dose of JNJ-55511118 (1 mg/kg) had no effect on open-field activity in male mice.

CONCLUSIONS

This study shows for the first time that TARP γ-8-bound AMPARs regulate a behavioral pathology associated with addiction. The preclinical efficacy of JNJ-55511118 in reducing alcohol self-administration in male mice suggests that inhibition of TARP γ-8-bound AMPARs is a novel and highly significant neural target for developing medications to treat AUD and other forms of addiction.

Proteomic insights into synaptic signaling in the brain: the past, present and future

Chemical synapses in the brain connect neurons to form neural circuits, providing the structural and functional bases for neural communication. Disrupted synaptic signaling is closely related to a variety of neurological and psychiatric disorders. In the past two decades, proteomics has blossomed as a versatile tool in biological and biomedical research, rendering a wealth of information toward decoding the molecular machinery of life. There is enormous interest in employing proteomic approaches for the study of synapses, and substantial progress has been made. Here, we review the findings of proteomic studies of chemical synapses in the brain, with special attention paid to the key players in synaptic signaling, i.e., the synaptic protein complexes and their post-translational modifications. Looking toward the future, we discuss the technological advances in proteomics such as data-independent acquisition mass spectrometry (DIA-MS), cross-linking in combination with mass spectrometry (CXMS), and proximity proteomics, along with their potential to untangle the mystery of how the brain functions at the molecular level. Last but not least, we introduce the newly developed synaptomic methods. These methods and their successful applications marked the beginnings of the synaptomics era.

Proteomic Signatures of Lifestyle Risk Factors for Cardiovascular Disease: A Cross-Sectional Analysis of the Plasma Proteome in the Framingham Heart Study

Background Proteomic biomarkers related to cardiovascular disease risk factors may offer insights into the pathogenesis of cardiovascular disease. We investigated whether modifiable lifestyle risk factors for cardiovascular disease are associated with distinctive proteomic signatures. Methods and Results We analyzed 1305 circulating plasma proteomic biomarkers (assayed using the SomaLogic platform) in 897 FHS (Framingham Heart Study) Generation 3 participants (mean age 46±8 years; 56% women; discovery sample) and 1121 FOS (Framingham Offspring Study) participants (mean age 52 years; 54% women; validation sample). Participants were free of hypertension, diabetes mellitus, and clinical cardiovascular disease. We used linear mixed effects models (adjusting for age, sex, body mass index, and family structure) to relate levels of each inverse-log transformed protein to 3 lifestyle factors (ie, smoking, alcohol consumption, and physical activity). A Bonferroni-adjusted P value indicated statistical significance (based on number of proteins and traits tested, P<4.2×10-6 in the discovery sample; P<6.85×10-4 in the validation sample). We observed statistically significant associations of 60 proteins with smoking (37/40 top proteins validated in FOS), 30 proteins with alcohol consumption (23/30 proteins validated), and 5 proteins with physical activity (2/3 proteins associated with the physical activity index validated). We assessed the associations of protein concentrations with previously identified genetic variants (protein quantitative trait loci) linked to lifestyle-related disease traits in the genome-wide-association study catalogue. The protein quantitative trait loci were associated with coronary artery disease, inflammation, and age-related mortality. Conclusions Our cross-sectional study from a community-based sample elucidated distinctive sets of proteins associated with 3 key lifestyle factors.

Cannabinoid Receptor Interacting Protein 1a (CRIP1a) in Health and Disease

Endocannabinoid signaling depends upon the CB₁ and CB₂ cannabinoid receptors, their endogenous ligands anandamide and 2-arachidonoylglycerol, and intracellular proteins that mediate responses via the C-terminal and other intracellular receptor domains. The CB₁ receptor regulates and is regulated by associated G proteins predominantly of the Gi/o subtypes, β-arrestins 1 and 2, and the cannabinoid receptor-interacting protein 1a (CRIP1a). Evidence for a physiological role for CRIP1a is emerging as data regarding the cellular localization and function of CRIP1a are generated. Here we summarize the neuronal distribution and role of CRIP1a in endocannabinoid signaling, as well as discuss investigations linking CRIP1a to development, vision and hearing sensory systems, hippocampus and seizure regulation, and psychiatric disorders including schizophrenia. We also examine the genetic and epigenetic association of CRIP1a within a variety of cancer subtypes. This review provides evidence upon which to base future investigations on the function of CRIP1a in health and disease.

The Emerging Role of LHb CaMKII in the Comorbidity of Depressive and Alcohol Use Disorders

Depressive disorders and alcohol use disorders are widespread among the general population and are significant public health and economic burdens. Alcohol use disorders often co-occur with other psychiatric conditions and this dual diagnosis is called comorbidity. Depressive disorders invariably contribute to the development and worsening of alcohol use disorders, and vice versa. The mechanisms underlying these disorders and their comorbidities remain unclear. Recently, interest in the lateral habenula, a small epithalamic brain structure, has increased because it becomes hyperactive in depression and alcohol use disorders, and can inhibit dopamine and serotonin neurons in the midbrain reward center, the hypofunction of which is believed to be a critical contributor to the etiology of depressive disorders and alcohol use disorders as well as their comorbidities. Additionally, calcium/calmodulin-dependent protein kinase II (CaMKII) in the lateral habenula has emerged as a critical player in the etiology of these comorbidities. This review analyzes the interplay of CaMKII signaling in the lateral habenula associated with depressive disorders and alcohol use disorders, in addition to the often-comorbid nature of these disorders. Although most of the CaMKII signaling pathway's core components have been discovered, much remains to be learned about the biochemical events that propagate and link between depression and alcohol abuse. As the field rapidly advances, it is expected that further understanding of the pathology involved will allow for targeted treatments.

Pharmacological inhibition of glycogen synthase kinase 3 increases operant alcohol self-administration in a manner associated with altered pGSK-3β, protein interacting with C kinase and GluA2 protein expression in the reward pathway of male C57BL/6J mice

Glycogen synthase kinase 3 (GSK-3) is a constitutively active serine-threonine kinase that regulates numerous signaling pathways and has been implicated in neurodegenerative and neuropsychiatric diseases. Alcohol exposure increases GSK-3β (ser9) phosphorylation (pGSK-3β); however, few studies have investigated whether GSK-3 regulates the positive reinforcing effects of alcohol, which drive repetitive drug use. To address this goal, male C57BL/6J mice were trained to lever press on a fixed-ratio 4 schedule of sweetened alcohol or sucrose-only reinforcement in operant conditioning chambers. The GSK-3 inhibitor CHIR 99021 (0-10 mg/kg, i.p.) was injected 45 minutes prior to self-administration sessions. After completion of the self-administration dose-effect curve, potential locomotor effects of the GSK-3 inhibitor were assessed. To determine molecular efficacy, CHIR 99021 (10 mg/kg, i.p.) was evaluated on pGSK-3β, GSK-3β, protein interacting with C kinase (PICK1), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA2 subunit protein expression in amygdala, nucleus accumbens (NAcb), and frontal cortex. Results showed that CHIR 99021 (10 mg/kg) dose-dependently increased alcohol reinforced responding with no effect on sucrose self-administration or locomotor activity. CHIR 99021 (10 mg/kg) significantly decreased pGSK-3β expression in all brain regions tested, reduced PICK1 and increased GluA2 total expression only in the NAcb. We conclude that GSK-3 inhibition increased the reinforcing effects of alcohol in mice. This was associated with reduced pGSK-3β and PICK1, and increased GluA2 expression. Given prior results showing that AMPA receptor activity regulates alcohol self-administration, we propose that signaling through the GSK-3/PICK1/GluA2 molecular pathway drives the positive reinforcing effects of the drug, which are required for abuse liability.

Alcohol Use Disorder, Neurodegeneration, Alzheimer's and Parkinson's Disease: Interplay Between Oxidative Stress, Neuroimmune Response and Excitotoxicity

Alcohol use disorder (AUD) has been associated with neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. Prolonged excessive alcohol intake contributes to increased production of reactive oxygen species that triggers neuroimmune response and cellular apoptosis and necrosis via lipid peroxidation, mitochondrial, protein or DNA damage. Long term binge alcohol consumption also upregulates glutamate receptors, glucocorticoids and reduces reuptake of glutamate in the central nervous system, resulting in glutamate excitotoxicity, and eventually mitochondrial injury and cell death. In this review, we delineate the following principles in alcohol-induced neurodegeneration: (1) alcohol-induced oxidative stress, (2) neuroimmune response toward increased oxidants and lipopolysaccharide, (3) glutamate excitotoxicity and cell injury, and (4) interplay between oxidative stress, neuroimmune response and excitotoxicity leading to neurodegeneration and (5) potential chronic alcohol intake-induced development of neurodegenerative diseases, including Alzheimer’s and Parkinson’s disease.

Ultrasound stress compromises the correlates of emotional-like states and brain AMPAR expression in mice: effects of antioxidant and anti-inflammatory herbal treatment

The modern lifestyle is associated with exposure to "psychological" or "emotional" stress. A growing portion of the population is exposed to emotional stress that results in a high incidence of anxiety disorders, a serious social problem. With this rise, there is a need for understanding the neurobiological causes of stress-induced anxiety and to offer safe remedies for this condition. Side effects of existing pharmaceuticals necessitate the search for alternatives. Having fewer adverse effects than classic remedies, natural extract-based therapies can be a promising solution. Here, we applied a model of emotional stress in BALB/c mice using ultrasound exposure to evoke the signs of anxiety-like behavior. We examined the behavioral and molecular impact of ultrasound and administration of herbal antioxidant/anti-inflammatory treatment (HAT) on AMPA receptor expression, markers of plasticity, inflammation and oxidative stress. A 3-week ultrasound exposure increased scores of anxiety-like behaviors in the standard tests and altered hippocampal expression as well as internalization of AMPA receptor subunits GluA1-A3. Concomitant treatment with HAT has prevented increases of anxiety-like behaviors and other behavioral changes, normalized hippocampal malondialdehyde content, GSK3β and pro-inflammatory cytokines Il-1β and Il-6, and the number of Ki67-positive cells. Levels of malondialdehyde, a common measure of oxidative stress, significantly correlated with the investigated end-points in stressed, but not in non-stressed animals. Our results emphasize the role of oxidative stress in neurobiological abnormalities associated with experimentally induced condition mimicking emotional stress in rodents and highlight the potential therapeutic use of anti-oxidants like herbal compositions for management of stress-related emotional disturbances within the community.

Modulation of responses to visual stimulus onset and offset by chronic alcohol consumption and withdrawal in the rat visual cortex and lateral geniculate nucleus

In the visual system, chronic alcohol consumption and subsequent abstinence strongly modulate processing of sensory information, which could interfere with the actions in our daily lives. Although previous studies showed histological and electrophysiological changes in the retina and visual cortex during chronic alcohol consumption and abstinence, there is still a lack of information related to the effect of alcohol on: 1) different stages of visual information processing; and 2) responses of stimulus onset (ON) and offset (OFF). In order to answer these questions, we recorded visual evoked potentials (VEPs), elicited by onset and offset of a 500-ms stimulus, following long-term alcohol consumption (8 weeks) and abstinence (3 weeks) in freely moving Wistar rats. Latency and amplitude of five components in the visual cortex (N1_VC, P2_VC, N2_VC, P3_VC, N3_VC) and three components in the lateral geniculate nucleus (P1_LGN, N1_LGN, P2_LGN) were analyzed. The results showed that long-term chronic alcohol consumption and abstinence have a strong long-term and, in some cases, irreversible impact on visual information processing. Both of these conditions modulate only the last stage of stimulus onset processing at the level of the visual cortex, but not at the level of the lateral geniculate body. Response to the stimulus offset is more susceptible to the effect of alcohol consumption and/or abstinence and is modulated at both the visual cortex and lateral geniculate nucleus levels. This modulation at different stages of the information processing chain can result in inaccurate processing of visual stimuli parameters and can lead to changes in perception of stimulus duration and intensity.

Manipulations of Central Amygdala Neurotensin Neurons Alter the Consumption of Ethanol and Sweet Fluids in Mice

The central nucleus of the amygdala plays a significant role in alcohol use and other affective disorders; however, the genetically-defined neuronal subtypes and projections that govern these behaviors are not well known. Here we show that neurotensin neurons in the central nucleus of the amygdala of male mice are activated by in vivo ethanol consumption and that genetic ablation of these neurons decreases ethanol consumption and preference in non-ethanol-dependent animals. This ablation did not impact preference for sucrose, saccharin, or quinine. We found that the most robust projection of the central amygdala neurotensin neurons was to the parabrachial nucleus, a brain region known to be important in feeding behaviors, conditioned taste aversion, and alarm. Optogenetic stimulation of projections from these neurons to the parabrachial nucleus is reinforcing, and increases ethanol drinking as well as consumption of sucrose and saccharin solutions. These data suggest that this central amygdala to parabrachial nucleus projection influences the expression of reward-related phenotypes and is a novel circuit promoting consumption of ethanol and palatable fluids.SIGNIFICANCE STATEMENT Alcohol use disorder (AUD) is a major health burden worldwide. Although ethanol consumption is required for the development of AUD, much remains unknown regarding the underlying neural circuits that govern initial ethanol intake. Here we show that ablation of a population of neurotensin-expressing neurons in the central amygdala decreases intake of and preference for ethanol in non-dependent animals, whereas the projection of these neurons to the parabrachial nucleus promotes consumption of ethanol as well as other palatable fluids.

Alcohol drinking exacerbates neural and behavioral pathology in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that represents the most common cause of dementia in the United States. Although the link between alcohol use and AD has been studied, preclinical research has potential to elucidate neurobiological mechanisms that underlie this interaction. This study was designed to test the hypothesis that nondependent alcohol drinking exacerbates the onset and magnitude of AD-like neural and behavioral pathology. We first evaluated the impact of voluntary 24-h, two-bottle choice home-cage alcohol drinking on the prefrontal cortex and amygdala neuroproteome in C57BL/6J mice and found a striking association between alcohol drinking and AD-like pathology. Bioinformatics identified the AD-associated proteins MAPT (Tau), amyloid beta precursor protein (APP), and presenilin-1 (PSEN-1) as the main modulators of alcohol-sensitive protein networks that included AD-related proteins that regulate energy metabolism (ATP5D, HK1, AK1, PGAM1, CKB), cytoskeletal development (BASP1, CAP1, DPYSL2 [CRMP2], ALDOA, TUBA1A, CFL2, ACTG1), cellular/oxidative stress (HSPA5, HSPA8, ENO1, ENO2), and DNA regulation (PURA, YWHAZ). To address the impact of alcohol drinking on AD, studies were conducted using 3xTg-AD mice that express human MAPT, APP, and PSEN-1 transgenes and develop AD-like brain and behavioral pathology. 3xTg-AD and wild-type mice consumed alcohol or saccharin for 4 months. Behavioral tests were administered during a 1-month alcohol-free period. Alcohol intake induced AD-like behavioral pathologies in 3xTg-AD mice including impaired spatial memory in the Morris Water Maze, diminished sensorimotor gating as measured by prepulse inhibition, and exacerbated conditioned fear. Multiplex immunoassay conducted on brain lysates showed that alcohol drinking upregulated primary markers of AD pathology in 3xTg-AD mice: Aβ 42/40 ratio in the lateral entorhinal and prefrontal cortex and total Tau expression in the lateral entorhinal cortex, medial prefrontal cortex, and amygdala at 1-month post alcohol exposure. Immunocytochemistry showed that alcohol use upregulated expression of pTau (Ser199/Ser202) in the hippocampus, which is consistent with late-stage AD. According to the NIA-AA Research Framework, these results suggest that alcohol use is associated with Alzheimer's pathology. Results also showed that alcohol use was associated with a general reduction in Akt/mTOR signaling via several phosphoproteins (IR, IRS1, IGF1R, PTEN, ERK, mTOR, p70S6K, RPS6) in multiple brain regions including hippocampus and entorhinal cortex. Dysregulation of Akt/mTOR phosphoproteins suggests alcohol may target this pathway in AD progression. These results suggest that nondependent alcohol drinking increases the onset and magnitude of AD-like neural and behavioral pathology in 3xTg-AD mice.

Adaptation in 5-HT2 receptors-CaMKII signaling in lateral habenula underlies increased nociceptive-sensitivity in ethanol-withdrawn rats

Alcoholics often experience hyperalgesia, especially during abstinence, yet the underlying cellular and molecular bases are unclear. Recent evidence suggests that 5-HT type 2 receptors (5-HT₂Rs) at glutamatergic synapses on lateral habenula (LHb) neurons may play a critical role. We, therefore, measured paw withdrawal responses to thermal and mechanical stimuli, and alcohol intake in a rat model of intermittent drinking paradigm, as well as spontaneous glutamatergic transmission (sEPSCs), and firing of LHb neurons in brain slices. Here, we report that nociceptive sensitivity was higher in rats at 24 h withdrawal from chronic alcohol consumption than that of alcohol-naive counterparts. The basal frequency of sEPSCs and firings was higher in slices of withdrawn rats than that of Naïve rats, and 5-HT2R antagonists attenuated the enhancement. Also, an acute ethanol-induced increase of sEPSCs and firings was smaller in withdrawal than in Naïve rats; it was attenuated by 5-HT₂R antagonists but mimicked by 5-HT₂R agonists. Importantly, intra-LHb infusion of 5-HT₂R agonists increased nociceptive sensitivity in Naïve rats, while antagonists or 5-HT reuptake blocker decreased nociceptive sensitivity and alcohol intake in withdrawn rats. Additionally, KN-62, a CaMKII inhibitor, attenuated the enhancement of EPSCs and firing induced by acute alcohol and by 5-HT₂R agonist. Furthermore, intra-LHb KN-62 reduced nociceptive sensitivity and alcohol intake. Quantitative real-time PCR assay detected mRNA of 5-HT2A and 2C in the LHb. Thus adaptation in 5-HT₂R-CaMKII signaling pathway contributes to the hyper-glutamatergic state, the hyperactivity of LHb neurons as well as the higher nociceptive sensitivity in rats withdrawn from chronic alcohol consumption.

Cross-Species Co-analysis of Prefrontal Cortex Chronic Ethanol Transcriptome Responses in Mice and Monkeys

Despite recent extensive genomic and genetic studies on behavioral responses to ethanol, relatively few new therapeutic targets for the treatment of alcohol use disorder have been validated. Here, we describe a cross-species genomic approach focused on identifying gene networks associated with chronic ethanol consumption. To identify brain mechanisms underlying a chronic ethanol consumption phenotype highly relevant to human alcohol use disorder, and to elucidate potential future therapeutic targets, we conducted a genomic study in a non-human primate model of chronic open-access ethanol consumption. Microarray analysis of RNA expression in anterior cingulate and subgenual cortices from rhesus macaques was performed across multiple cohorts of animals. Gene networks correlating with ethanol consumption or showing enrichment for ethanol-regulated genes were identified, as were major ethanol-related hub genes within these networks. A subsequent consensus module analysis was used to co-analyze monkey data with expression data from a chronic intermittent ethanol vapor-exposure and consumption model in C57BL/6J mice. Ethanol-related gene networks conserved between primates and rodents were enriched for genes involved in discrete biological functions, including; myelination, synaptic transmission, chromatin modification, Golgi apparatus function, translation, cellular respiration, and RNA processing. The myelin-related network, in particular, showed strong correlations with ethanol consumption behavior and displayed marked network reorganization between control and ethanol-drinking animals. Further bioinformatics analysis revealed that these networks also showed highly significant overlap with other ethanol-regulated gene sets. Altogether, these studies provide robust primate and rodent cross-species validation of gene networks associated with chronic ethanol consumption. Our results also suggest potential novel focal points for future therapeutic interventions in alcohol use disorder.

Sequential Changes in Brain Glutamate and Adenosine A1 Receptors May Explain Severity of Adolescent Alcohol Withdrawal after Consumption of High Levels of Alcohol

There is an excellent correlation between the age when alcohol consumption begins and the likelihood of lifelong problems with alcohol abuse. Alcohol use often begins in adolescence, a time marked by brain development and maturation of numerous brain systems. Rats are an important model, wherein the emergence of alcohol withdrawal symptoms serves as a gauge of dependency following chronic alcohol consumption. Previous work has shown that adolescent Long-Evans rats consume high levels of alcohol and develop a severe alcohol withdrawal syndrome when fed alcohol as part of a liquid diet. Acutely, alcohol inhibits two important excitatory receptors for glutamate (NMDA and AMPA) and may further decrease glutamate activity through modulatory adenosine receptors. The present study focuses on potential adaptive changes in expression of these receptors that may create a receptor imbalance during chronic alcohol consumption and lead to severe overexcitation of the adolescent brain during alcohol withdrawal. Levels of brain expression of NMDA, AMPA, and adenosine A1 and A2a receptors were determined by Western blotting after adolescent rats consumed an alcohol-containing liquid diet for 4, 11, or 18 days. Severity of alcohol withdrawal was also assessed at these time points. Levels increased for both AMPA and NMDA receptors, significant and approaching maximal by day 11. In contrast, A1 receptor density showed a slow decline reaching significance at 18 days. There were no changes in expression of adenosine A2a receptor. The most severe withdrawal symptoms appear to coincide with the later downregulation of adenosine A1 receptors coming on top of maximal upregulation of excitatory AMPA and NMDA glutamate receptors. Thus, loss of adenosine "brakes" on glutamate excitation may punctuate receptor imbalance in alcohol-consuming adolescents by allowing the upregulation of the excitatory receptors to have full impact during early alcohol withdrawal.

MGluR5 activity is required for the induction of ethanol behavioral sensitization and associated changes in ERK MAP kinase phosphorylation in the nucleus accumbens shell and lateral habenula

Metabotropic glutamate receptor subtype-5 (mGluR5) activity regulates a variety of behavioral pathologies associated with alcohol addiction. The main goal of this study was to determine if mGluR5 regulates the induction of ethanol-induced locomotor sensitization, which is a model of experience-dependent plasticity following initial exposure to drugs of abuse. The extracellular signal-regulated kinase (ERK_1/2) pathway is downstream of mGluR5 and implicated in alcohol addiction; however, its role in sensitization remains unexplored. We sought to determine if mGluR5-mediated changes in ethanol-induced sensitization are associated with changes in ERK_1/2 phosphorylation (pERK_1/2) in specific brain regions. Adult male DBA/2 J mice were tested for acute locomotor response to ethanol (0 or 2 g/kg, IP) followed by a 9-day induction period in which the mGluR5 antagonist MPEP (0 or 30 mg/kg, IP) was administered prior to ethanol (0 or 2.5 g/kg, IP). One day later, ethanol (2 g/kg) produced a robust within- and between-group increase in locomotor activity, indicating sensitization in mice that received MPEP (0 mg/kg) during induction. MPEP (30 mg/kg) treatment during induction resulted in locomotor response to ethanol (2 g/kg) challenge that was equivalent to an acute response, indicating full blockade of sensitization. Sensitization was associated with increased pERK_1/2 immunoreactivity (IR) in nucleus accumbens shell (AcbSh) and a reduction in lateral habenula (LHb), both of which were blocked by MPEP treatment during induction. Sensitization was also associated with mGluR5-independent increases in pERK_1/2 IR in the nucleus accumbens core and decreases in the dentate gyrus and lateral septum. These data indicate that mGluR5 activity is required for the induction of ethanol locomotor sensitization and associated changes in ERK_1/2 phosphorylation in the AcbSh and LHb, which raises the hypothesis that mGluR5-mediated cell signaling in these brain regions may mediate the induction of sensitization. Elucidating mechanisms of sensitization may increase understanding of how ethanol hijacks behavioral functions during the development of addiction.

From Synapse to Function: A Perspective on the Role of Neuroproteomics in Elucidating Mechanisms of Drug Addiction

Drug addiction is a complex disorder driven by dysregulation in molecular signaling across several different brain regions. Limited therapeutic options currently exist for treating drug addiction and related psychiatric disorders in clinical populations, largely due to our incomplete understanding of the molecular pathways that influence addiction pathology. Recent work provides strong evidence that addiction-related behaviors emerge from the convergence of many subtle changes in molecular signaling networks that include neuropeptides (neuropeptidome), protein-protein interactions (interactome) and post-translational modifications such as protein phosphorylation (phosphoproteome). Advancements in mass spectrometry methodology are well positioned to identify these novel molecular underpinnings of addiction and further translate these findings into druggable targets for therapeutic development. In this review, we provide a general perspective of the utility of novel mass spectrometry-based approaches for addressing critical questions in addiction neuroscience, highlighting recent innovative studies that exemplify how functional assessments of the neuroproteome can provide insight into the mechanisms of drug addiction.

The center of the emotional universe: Alcohol, stress, and CRF1 amygdala circuitry

The commonalities between different phases of stress and alcohol use as well as the high comorbidity between alcohol use disorders (AUDs) and anxiety disorders suggest common underlying cellular mechanisms governing the rewarding and aversive aspects of these related conditions. As an integrative center that assigns emotional salience to a wide variety of internal and external stimuli, the amygdala complex plays a major role in how alcohol and stress influence cellular physiology to produce disordered behavior. Previous work has illustrated the broad role of the amygdala in alcohol, stress, and anxiety. However, the challenge of current and future studies is to identify the specific dysregulations that occur within distinct amygdala circuits and subpopulations and the commonalities between these alterations in each disorder, with the long-term goal of identifying potential targets for therapeutic intervention. Specific intra-amygdala circuits and cell type-specific subpopulations are emerging as critical targets for stress- and alcohol-induced plasticity, chief among them the corticotropin releasing factor (CRF) and CRF receptor 1 (CRF1) system. CRF and CRF1 have been implicated in the effects of alcohol in several amygdala nuclei, including the basolateral (BLA) and central amygdala (CeA); however, the precise circuitry involved in these effects and the role of these circuits in stress and anxiety are only beginning to be understood.

Phosphorylation of calcium/calmodulin-dependent protein kinase II in the rat dorsal medial prefrontal cortex is associated with alcohol-induced cognitive inflexibility

Repeated cycles of alcohol [ethanol (EtOH)] intoxication and withdrawal dysregulate excitatory glutamatergic systems in the brain and induce neuroadaptations in the medial prefrontal cortex (mPFC) that contribute to cognitive dysfunction. The mPFC is composed of subdivisions that are functionally distinct, with dorsal regions facilitating drug-cue associations and ventral regions modulating new learning in the absence of drug. A key modulator of glutamatergic activity is the holoenzyme calcium/calmodulin-dependent protein kinase II (CaMKII) that phosphorylates ionotropic glutamate receptors. Here, we examined the hypothesis that abstinence from chronic intermittent EtOH (CIE) exposure dysregulates CaMKII activity in the mPFC to impair cognitive flexibility. We used an operant model of strategy set shifting in male Long-Evans rats demonstrating reduced susceptibility to trial omissions during performance in a visual cue-guided task versus albino strains. Relative to naïve controls, rats experiencing approximately 10 days of abstinence from CIE vapor exposure demonstrated impaired performance during a procedural shift from visual cue to spatial location discrimination. Phosphorylation of CaMKII subtype α was upregulated in the dorsal, but not ventral mPFC of CIE-exposed rats, and was positively correlated with perseverative-like responding during the set shift. The findings suggest that abstinence from CIE exposure induces an undercurrent of kinase activity (e.g. CaMKII), which may promote aberrant glutamatergic responses in select regions of the mPFC. Given the role of the mPFC in modulating executive control of behavior, we propose that increased CaMKII subtype α activity reflects a dysregulated 'top-down' circuit that interferes with adaptive behavioral performance under changing environmental demands.

Alcohol Consumption during Adolescence in a Mouse Model of Binge Drinking Alters the Intrinsic Excitability and Function of the Prefrontal Cortex through a Reduction in the Hyperpolarization-Activated Cation Current

Periodic episodes of excessive alcohol consumption ("binge drinking") occur frequently among adolescents, and early binge drinking is associated with an increased risk of alcohol use disorders later in life. The PFC undergoes significant development during adolescence and hence may be especially susceptible to the effects of binge drinking. In humans and in animal models, adolescent alcohol exposure is known to alter PFC neuronal activity and produce deficits in PFC-dependent behaviors, such as decision making, response inhibition, and working memory. Using a voluntary intermittent access to alcohol (IA EtOH) procedure in male mice, we demonstrate that binge-level alcohol consumption during adolescence leads to altered drinking patterns and working memory deficits in young adulthood, two outcomes that suggest medial PFC dysfunction. We recorded from pyramidal neurons (PNs) in the prelimbic subregion of the medial PFC in slices obtained from mice that had IA EtOH and found that they display altered excitability, including a hyperpolarization of the resting membrane potential and reductions in the hyperpolarization-activated cation current (I_h) and in intrinsic persistent activity (a mode of neuronal firing that is dependent on I_h). Many of these effects on intrinsic excitability were sustained following abstinence and observed in mice that showed working memory deficits. In addition, we found that resting membrane potential and the I_h-dependent voltage "sag" in prelimbic PFC PNs are developmentally regulated during adolescence, suggesting that adolescent alcohol exposure may compromise PFC function by arresting the normal developmental trajectory of PN intrinsic excitability.SIGNIFICANCE STATEMENT Binge alcohol drinking during adolescence has negative consequences for the function of the developing PFC. Using a mouse model of voluntary binge drinking during adolescence, we found that this behavior leads to working memory deficits and altered drinking behavior in adulthood. In addition, we found that adolescent drinking is associated with specific changes to the intrinsic excitability of pyramidal neurons in the PFC, reducing the ability of these neurons to generate intrinsic persistent activity, a phenomenon thought to be important for working memory. These findings may help explain why human adolescent binge drinkers show performance deficits on tasks mediated by the PFC.

Targeted overexpression of CRH receptor subtype 1 in central amygdala neurons: effect on alcohol-seeking behavior

RATIONALE

The corticotropin-releasing hormone (CRH) system is a key mediator of stress-induced responses in alcohol-seeking behavior. Recent research has identified the central nucleus of the amygdala (CeA), a brain region involved in the regulation of fear and stress-induced responses that is especially rich in CRH-positive neurons, as a key player in mediating excessive alcohol seeking. However, detailed characterization of the specific influences that local neuronal populations exert in mediating alcohol responses is hampered by current limitations in pharmacological and immunohistochemical tools for targeting CRH receptor subtype 1 (CRHR1).

OBJECTIVE

In this study, we investigated the effect of cell- and region-specific overexpression of CRHR1 in the CeA using a novel transgenic tool.

METHODS

Co-expression of CRHR1 in calcium-calmodulin-dependent kinase II (αCaMKII) neurons of the amygdala was demonstrated by double immunohistochemistry using a Crhr1-GFP reporter mouse line. A Cre-inducible Crhr1-expressing adeno-associated virus (AAV) was site-specifically injected into the CeA of αCaMKII-Cre^ERT2 transgenic rats to analyze the role of CRHR1 in αCaMKII neurons on alcohol self-administration and reinstatement behavior.

RESULTS

Forty-eight percent of CRHR1-containing cells showed co-expression of αCaMKII in the CeA. AAV-mediated gene transfer in αCaMKII neurons induced a 24-fold increase of Crhr1 mRNA in the CeA which had no effect on locomotor activity, alcohol self-administration, or cue-induced reinstatement. However, rats overexpressing Crhr1 in the CeA increased responding in the stress-induced reinstatement task with yohimbine serving as a pharmacological stressor.

CONCLUSION

We demonstrate that CRHR1 overexpression in CeA-αCaMKII neurons is sufficient to mediate increased vulnerability to stress-triggered relapse into alcohol seeking.

Mining the nucleus accumbens proteome for novel targets of alcohol self-administration in male C57BL/6J mice

RATIONALE

There is a clear need for discovery of effective medications to treat behavioral pathologies associated with alcohol addiction, such as chronic drinking.

OBJECTIVE

The goal of this preclinical study was to assess effects of chronic alcohol drinking on the nucleus accumbens (NAcb) proteome to identify and validate novel targets for medications development.

MATERIALS AND METHODS

Two-dimensional difference in-gel electrophoresis (2D-DIGE) with matrix-assisted laser desorption ionization tandem time-of-flight (MALDI-TOF/TOF) was used to assess effects of chronic voluntary home-cage (24-h access) alcohol drinking on the NAcb proteome of C57BL/6J mice. To extend these findings to a model of alcohol self-administration and reinforcement, we investigated potential regulation of the positive reinforcing effects of alcohol by the target protein glutathione S-transferase Pi 1 (GSTP1) using a pharmacological inhibition strategy in mice trained to self-administer alcohol or sucrose.

RESULTS

Expression of 52 unique proteins in the NAcb was changed by chronic alcohol drinking relative to water control (23 upregulated, 29 downregulated). Ingenuity Pathway Analysis showed that alcohol drinking altered an array of protein networks associated with neurological and psychological disorders, molecular and cellular functions, and physiological systems and development. DAVID functional annotation analysis identified 9 proteins (SNCA, GSTP1, PRDX3, PPP3R1, EIF5A, PHB, PEBP1/RKIP, GAPDH, AND SOD1) that were significantly overrepresented in a functional cluster that included the Gene Ontology categories "response to alcohol" and "aging." Immunoblots confirmed changes in Pebp1 (RKIP) and GSTP1 in NAcb with no change in amygdala or frontal cortex, suggesting anatomical specificity. Systemic inhibition of GSTP1 with Ezatiostat (0-30 mg/kg, i.p.) dose-dependently reduced the reinforcing effects of alcohol as measured by operant self-administration, in the absence of motor effects. Sucrose self-administration was also reduced but in a manner associated with nonspecific motor inhibition.

CONCLUSIONS

Protein expression profiling identified an array of proteins and networks in the NAcb, including GSTP1, that are novel molecular targets of chronic alcohol drinking. Pharmacological inhibition of GSTP1 significantly reduced the positive reinforcing effects of alcohol, which regulate repetitive use and abuse liability. The observation that this protein was both upregulated after chronic drinking and that its inhibition could modulate the reinforcing properties of alcohol suggests that it is a key target for alcohol-related pathologies. Proteomic strategies combined with specific preclinical models has potential to identify and validate novel targets of alcohol that may be useful in the medical management of alcohol addiction.

Proanthocyanidins prevent ethanol-induced cognitive impairment by suppressing oxidative and inflammatory stress in adult rat brain

Excessive chronic alcohol consumption enhances brain oxidative and inflammatory stress, resulting in cognitive deficit. This study investigated the potential alleviating effects of proanthocyanidins (PACs) on ethanol-induced cognitive impairment and stress in brain regions including the prefrontal cortex, hippocampus, and amygdala. Adult male rats were administered saline, PACs, ethanol, or combinations of ethanol with different doses of PACs for 8 weeks. Then, the Morris water-maze test was performed. Thiobarbituric acid-reactive substances, superoxide dismutase activity, total antioxidant capacity, and nitric oxide were chosen as parameters of oxidative stress, whereas tumor necrosis factor-α and interleukin-1β chosen as parameters of inflammatory stress. The results indicated that ethanol led to cognitive impairment along with enhanced oxidative and inflammatory stress in brain regions, whereas PACs per se had no significant effects. Moreover, coadministration with PACs in ethanol-treated rats dose dependently rescued cognitive impairment accompanied by suppressed oxidative and inflammatory stress in brain regions. Thus, the protective effects of PACs on ethanol-induced cognitive impairments may be because of their antioxidant and anti-inflammatory activities.

Integrating Genetic and Gene Co-expression Analysis Identifies Gene Networks Involved in Alcohol and Stress Responses

Although the link between stress and alcohol is well recognized, the underlying mechanisms of how they interplay at the molecular level remain unclear. The purpose of this study is to identify molecular networks underlying the effects of alcohol and stress responses, as well as their interaction on anxiety behaviors in the hippocampus of mice using a systems genetics approach. Here, we applied a gene co-expression network approach to transcriptomes of 41 BXD mouse strains under four conditions: stress, alcohol, stress-induced alcohol and control. The co-expression analysis identified 14 modules and characterized four expression patterns across the four conditions. The four expression patterns include up-regulation in no restraint stress and given an ethanol injection (NOE) but restoration in restraint stress followed by an ethanol injection (RSE; pattern 1), down-regulation in NOE but rescue in RSE (pattern 2), up-regulation in both restraint stress followed by a saline injection (RSS) and NOE, and further amplification in RSE (pattern 3), and up-regulation in RSS but reduction in both NOE and RSE (pattern 4). We further identified four functional subnetworks by superimposing protein-protein interactions (PPIs) to the 14 co-expression modules, including γ-aminobutyric acid receptor (GABA) signaling, glutamate signaling, neuropeptide signaling, cAMP-dependent signaling. We further performed module specificity analysis to identify modules that are specific to stress, alcohol, or stress-induced alcohol responses. Finally, we conducted causality analysis to link genetic variation to these identified modules, and anxiety behaviors after stress and alcohol treatments. This study underscores the importance of integrative analysis and offers new insights into the molecular networks underlying stress and alcohol responses.

Do Alcohol-Related AMPA-Type Glutamate Receptor Adaptations Promote Intake?

Ionotropic glutamate receptors (AMPA, NMDA, and kainate receptors) play a central role in excitatory glutamatergic signaling throughout the brain. As a result, functional changes, especially long-lasting forms of plasticity, have the potential to profoundly alter neuronal function and the expression of adaptive and pathological behaviors. Thus, alcohol-related adaptations in ionotropic glutamate receptors are of great interest, since they could promote excessive alcohol consumption, even after long-term abstinence. Alcohol- and drug-related adaptations in NMDARs have been recently reviewed, while less is known about kainate receptor adaptations. Thus, we focus here on functional changes in AMPARs, tetramers composed of GluA1-4 subunits. Long-lasting increases or decreases in AMPAR function, the so-called long-term potentiation or depression, have widely been considered to contribute to normal and pathological memory states. In addition, a great deal has been learned about the acute regulation of AMPARs by signaling pathways, scaffolding and auxiliary proteins, intracellular trafficking, and other mechanisms. One important common adaptation is a shift in AMPAR subunit composition from GluA2-containing, calcium-impermeable AMPARs (CIARs) to GluA2-lacking, calcium-permeable AMPARs (CPARs), which is observed under a broad range of conditions including intoxicant exposure or intake, stress, novelty, food deprivation, and ischemia. This shift has the potential to facilitate AMPAR currents, since CPARs have much greater single-channel currents than CIARs, as well as faster AMPAR activation kinetics (although with faster inactivation) and calcium-related activity. Many tools have been developed to interrogate particular aspects of AMPAR signaling, including compounds that selectively inhibit CPARs, raising exciting translational possibilities. In addition, recent studies have used transgenic animals and/or optogenetics to identify AMPAR adaptations in particular cell types and glutamatergic projections, which will provide critical information about the specific circuits that CPARs act within. Also, less is known about the specific nature of alcohol-related AMPAR adaptations, and thus we use other examples that illustrate more fully how particular AMPAR changes might influence intoxicant-related behavior. Thus, by identifying alcohol-related AMPAR adaptations, the specific molecular events that underlie them, and the cells and projections in which they occur, we hope to better inform the development of new therapeutic interventions for addiction.

Targeting the intracellular signaling "STOP" and "GO" pathways for the treatment of alcohol use disorders

In recent years, research has identified the molecular and neural substrates underlying the transition of moderate "social" consumption of alcohol to the characteristic alcohol use disorder (AUD) phenotypes including excessive and compulsive alcohol use which we define in the review as the GO signaling pathways. In addition, growing evidence points to the existence of molecular mechanisms that keep alcohol consumption in check and that confer resilience for the development of AUD which we define herein as the STOP signaling pathways. In this review, we focus on examples of the GO and the STOP intracellular signaling pathways and discuss our current knowledge of how manipulations of these pathways may be used for the treatment of AUD.

Cue-induced reinstatement of alcohol-seeking behavior is associated with increased CaMKII T286 phosphorylation in the reward pathway of mice

Cue-induced reinstatement of alcohol-seeking is a hallmark behavioral pathology of addiction. Evidence suggests that reinstatement (e.g., relapse), may be regulated by cell signaling systems that underlie neuroplasticity. A variety of plasticity events require activation of calcium calmodulin-dependent protein kinase II (CaMKII) in components of the reward pathway, such as the nucleus accumbens and amygdala. We sought to determine if cue-induced reinstatement of alcohol-seeking behavior is associated with changes in the activation state (e.g., phosphorylation) of CaMKII-T286. Male C57BL/6J mice (n=14) were trained to lever press on a fixed-ratio-4 schedule of sweetened alcohol (2% sucrose+9% EtOH) reinforcement. After 14-d of extinction (no cues or reinforcers), mice underwent a response-contingent reinstatement (n=7) vs. an additional day of extinction (n=7). Brains were removed immediately after the test and processed for evaluation of pCaMKII-T286 immunoreactivity (IR). Number of pCaMKII-T286 positive cells/mm² was quantified from coronal brain sections using Bioquant Image Analysis software. Mice emitted significantly more responses on the alcohol vs. the inactive lever throughout the baseline phase with average alcohol intake of 1.1±0.03g/kg/1-h. During extinction, responses on the alcohol lever decreased to inactive lever levels by day 7. Significant cue-induced reinstatement of alcohol-seeking was observed during a single test with no effects on the inactive lever. Reinstatement was associated with increased pCaMKII-T286 IR specifically in amygdala (LA and BLA), nucleus accumbens (AcbSh), lateral septum, mediodorsal thalamus, and piriform cortex as compared to extinction control. Brain regions showing no change included the dorsal striatum, medial septum, cingulate cortex, habenula, paraventricular thalamus, and ventral hypothalamus. These results show response contingent cue-induced reinstatement of alcohol-seeking behavior is associated with selective increases in pCaMKII-T286 in specific reward- and memory-related brain regions of male C57BL/6J mice. Primary molecular mechanisms of associative learning and memory may regulate relapse in alcohol addiction.

Ketamine Self-Administration Elevates αCaMKII Autophosphorylation in Mood and Reward-Related Brain Regions in Rats

Modulation of αCaMKII expression and phosphorylation is a feature shared by drugs of abuse with different mechanisms of action. Accordingly, we investigated whether αCaMKII expression and activation could be altered by self-administration of ketamine, a non-competitive antagonist of the NMDA glutamate receptor, with antidepressant and psychotomimetic as well as reinforcing properties. Rats self-administered ketamine at a sub-anesthetic dose for 43 days and were sacrificed 24 h after the last drug exposure; reward-related brain regions, such as medial prefrontal cortex (PFC), ventral striatum (vS), and hippocampus (Hip), were used for the measurement of αCaMKII-mediated signaling. αCaMKII phosphorylation was increased in these brain regions suggesting that ketamine, similarly to other reinforcers, activates this kinase. We next measured the two main targets of αCaMKII, i.e., GluN2B (S1303) and GluA1 (S831), and found increased activation of GluN2B (S1303) together with reduced phosphorylation of GluA1 (S831). Since GluN2B, via inhibition of ERK, regulates the membrane expression of GluA1, we measured ERK2 phosphorylation in the crude synaptosomal fraction of these brain regions, which was significantly reduced suggesting that ketamine-induced phosphorylation of αCaMKII promotes GluN2B (S1303) phosphorylation that, in turn, inhibits ERK 2 signaling, an effect that results in reduced membrane expression and phosphorylation of GluA1. Taken together, our findings point to αCaMKII autophosphorylation as a critical signature of ketamine self-administration providing an intracellular mechanism to explain the different effects caused by αCaMKII autophosphorylation on the post-synaptic GluN2B- and GluA1-mediated functions. These data add ketamine to the list of drugs of abuse converging on αCaMKII to sustain their addictive properties.

Molecular and synaptic mechanisms regulating drug-associated memories: Towards a bidirectional treatment strategy

The successful treatment of substance use disorders is dependent on the establishment of a long-term abstinent state. Relapse can be suppressed by interfering with memories of drug use that are evoked by re-exposure to drug-associated contexts and cues. Two strategies for accomplishing this goal are either to prevent drug-memory reconsolidation or to induce the formation of a competing, extinction memory. However, clinical attempts to prolong abstinence by behavioral modification of drug-related memories have had limited success. One approach to improve behavioral treatment strategies is to identify the molecular mechanisms that regulate these memory processes and then use pharmacological tools as supplements to improve efficacy. Still, due to the involvement of several overlapping signaling cascades in both reconsolidation and extinction, it is difficult to specifically modify one of the two processes. For example, attempting to elicit extinction may instead initiate reconsolidation, resulting in the unintentional strengthening of drug-related memories. A better approach is to identify diverging components of the two processes, whereby a single medication would simultaneously weaken reconsolidation and enhance extinction. This review will provide an overview of the neural substrates that are involved in the regulation of drug-associated memories, and will discuss emerging approaches to pharmacologically weaken these memories, including recent efforts to precisely and bidirectionally target reconsolidation and extinction. Ultimately, pharmacologically-enhanced memory-based approaches have the potential to produce more informed relapse-prevention therapies.

Down-regulation of dorsal striatal αCaMKII causes striatum-related cognitive and synaptic disorders

Alpha calcium/calmodulin dependent protein kinase II (αCaMKII) is a serine/threonine protein kinase which is expressed abundantly in dorsal striatum and is highly involved in the corticostriatal synaptic plasticity. Nevertheless, it currently remains unclear whether and how αCaMKII plays a in the striatum-related neural disorders. To address the above issue, lentivirus-mediated short hairpin RNA (shRNA) was used to silence the expression of αCaMKII gene in the dorsal striatum of mice. As a consequence of down-regulation of dorsal striatal αCaMKII expression, we observed defective motor skill learning in accelerating rotarod and response learning in water cross maze. Furthermore, impaired corticostriatal basal transmission and long-term potentiation (LTP), which correlated with the deficits in dorsal striatum-related cognition, were also detected in the αCaMKII-shRNA mice. Consistent with the above results, αCaMKII-shRNA mice exhibited a remarkable decline in GluA1-Ser831 and GluA1-Ser845 phosphorylation levels of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), and a decline in the expression levels of N-methyl-d-aspartic acid receptor (NMDAR) subunits NR1, NR2A and NR2B. Taken together, αCaMKII down-regulation caused dorsal striatum-related cognitive disorders by inhibiting corticostriatal synaptic plasticity, which resulted from dysfunction of AMPARs and NMDARs. Our findings demonstrate for the first time an important role of αCaMKII in striatum-related neural disorders and provide further evidence for the proposition that corticostriatal LTP underlies aspects of dorsal striatum-related cognition.

Inhibition of AMPA receptor and CaMKII activity in the lateral habenula reduces depressive-like behavior and alcohol intake in rats

Depression is a well-known risk factor for developing relapse drinking, but the neuronal mechanisms underlying the interactions between depression and alcohol use disorders remain elusive. Accumulating evidence has associated depression with hyperactivity of the lateral habenula (LHb), an epithalamic structure in the brain that encodes aversive signals. Glutamate receptors contribute substantially to the excitability of LHb neurons. Glutamatergic synapses in LHb neurons largely express GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) that can be modulated by Ca²⁺/calmodulin-dependent protein II (CaMKII). In the current study, we tested the hypothesis that withdrawal from repeated cycles of ethanol drinking triggers an increase in LHb AMPAR and CaMKII activity concomitant with depression-like symptoms, and their inhibitions bring a reduction in depressive-like behaviors and alcohol consumption. Western blotting revealed a higher level of phosphorylated AMPAR GluA1 subunit at a CaMKII locus (GluA1-Ser831) in the LHb of ethanol-withdrawn rats than that of age-matched naïve counterparts. In ethanol-withdrawn rats, pharmacological inhibition of LHb AMPAR activity significantly mitigated the depressive-like behavior and ethanol drinking and seeking behaviors, but affected neither sucrose intake nor locomotor activity; and inhibition of LHb CaMKII activity, or chemogenetic inhibition of LHb activity produced similar effects. Conversely, activation of LHb AMPARs induced depressive-like behaviors in ethanol-naïve rats. These results demonstrate that CaMKII-AMPAR signaling in the LHb exemplifies a molecular basis for depressive-like symptoms during ethanol withdrawal and that inhibition of this signaling pathway may offer a new therapeutic approach to address the comorbidity of alcohol abuse and depression.

Loss of control over the ethanol consumption: differential transcriptional regulation in prefrontal cortex

Alcohol use disorder (AUD) is a complex multifactorial disease with heritability of ∼50% and corresponds to the state in which the body triggers a reinforcement or reward compulsive behavior due to ethanol consumption, even when faced with negative consequences. Although several studies have shown the impact of high ethanol intake on the prefrontal cortex (PFC) gene expression, few have addressed the relationship between the patterns of gene expression underlying the compulsive behaviour associated with relapsing. In this study, we used a chronic three-bottle free-choice mouse model to investigate the PFC transcriptome in three different groups of mice drinkers: 'Light drinkers' (preference for water throughout the experiment); 'Heavy drinkers' (preference for ethanol with a non-compulsive intake), and 'Inflexible drinkers' (preference for ethanol with a compulsive drinking component). Our aim was to correlate the intake patterns observed in this model with gene expression changes in the PFC, a brain region critical for the development and maintenance of alcohol addiction. We found that the Camk2a gene showed a downregulated profile only in the Inflexible when compared to the Light drinkers group, the Camk2n1 and Pkp2 genes showed an upregulated profile only in the Inflexible drinkers when compared to the Control group, and the Gja1 gene showed an upregulated profile in the Light and Inflexible drinkers when compared to the Control group. These different transcription patterns have been associated to the presence of alcohol, in the Camk2n1 and Gja1 genes; to the amount of ethanol consumed, in the Camk2a gene; and to the loss of control in the alcohol consumption, in the Pkp2 gene. Here, we provide, for the first time, the potential involvement of the Pkp2 gene in the compulsivity and loss of control over the voluntary ethanol consumption.

Phosphoproteomic Analysis Reveals a Novel Mechanism of CaMKIIα Regulation Inversely Induced by Cocaine Memory Extinction versus Reconsolidation

Successful addiction treatment depends on maintaining long-term abstinence, making relapse prevention an essential therapeutic goal. However, exposure to environmental cues associated with drug use often thwarts abstinence efforts by triggering drug using memories that drive craving and relapse. We sought to develop a dual approach for weakening cocaine memories through phosphoproteomic identification of targets regulated in opposite directions by memory extinction compared with reconsolidation in male Sprague-Dawley rats that had been trained to self-administer cocaine paired with an audiovisual cue. We discovered a novel, inversely regulated, memory-dependent phosphorylation event on calcium-calmodulin-dependent kinase II α (CaMKIIα) at serine (S)331. Correspondingly, extinction-associated S331 phosphorylation inhibited CaMKIIα activity. Intra-basolateral amygdala inhibition of CaMKII promoted memory extinction and disrupted reconsolidation, leading to a reduction in subsequent cue-induced reinstatement. CaMKII inhibition had no effect if the memory was neither retrieved nor extinguished. Therefore, inhibition of CaMKII represents a novel mechanism for memory-based addiction treatment that leverages both extinction enhancement and reconsolidation disruption to reduce relapse-like behavior.

SIGNIFICANCE STATEMENT

Preventing relapse to drug use is an important goal for the successful treatment of addictive disorders. Relapse-prevention therapies attempt to interfere with drug-associated memories, but are often hindered by unintentional memory strengthening. In this study, we identify phosphorylation events that are bidirectionally regulated by the reconsolidation versus extinction of a cocaine-associated memory, including a novel site on CaMKIIα. Additionally, using a rodent model of addiction, we show that CaMKII inhibition in the amygdala can reduce relapse-like behavior. Together, our data supports the existence of mechanisms that can be used to enhance current strategies for addiction treatment.

The lateral habenula and alcohol: Role of glutamate and M-type potassium channels

Alcohol use disorder (AUD) or alcoholism is a chronic relapsing disorder. Our knowledge of alcoholism hinges on our understanding of its effects on the brain. This review will center on the effects of alcohol in the lateral habenula (LHb), an epithalamic structure that connects the forebrain with the midbrain and encodes aversive signaling. Like many addictive drugs, alcohol has both rewarding and aversive properties. While alcohol's euphoric property is believed to be important for the initiation of drinking, increasing evidence suggests that alcohol's negative affect plays a critical role in excessive drinking and alcohol dependence. During withdrawal and abstinence, alcoholics often experience anxiety and depressions, both of which have been implicated in relapse drinking. This review focuses on the recent accumulation of knowledge about the effects of acute and chronic alcohol exposure on the activity of and synaptic transmissions on LHb neurons, as well as the effects of manipulation of LHb function on alcohol consumption and related behaviors. Recent evidence highlights a critical role for the LHb in AUD and related psychiatric ailments. Multidisciplinary work in animals collectively suggests that LHb function and activity, including M-type potassium channels and glutamatergic transmission are altered by acute and repeated chronic alcohol exposure. We will also discuss how functional, pharmacological, and chemogenetic manipulation of the LHb affects ethanol drinking and psychiatric disorders occurring in animals withdrawn from chronic alcohol exposure. Conceivable mechanisms behind these effects and their potential as targets for therapies will also be discussed.