Acute functional tolerance to ethanol mediated by protein kinase Cepsilon

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.

JNK Signaling Positively Regulates Acute Ethanol Tolerance in C. elegans

Alcohol use disorder (AUD) is a chronic neurobehavioral condition characterized by a cycle of tolerance development, increased consumption, and reinstated craving and seeking behaviors during withdrawal. Understanding the intricate mechanisms of AUD necessitates reliable animal models reflecting its key features. Caenorhabditis elegans (C. elegans), with its conserved nervous system and genetic tractability, has emerged as a valuable model organism to study AUD. Here, we employ an ethanol vapor exposure model in Caenorhabditis elegans, recapitulating AUD features while maintaining high-throughput scalability. We demonstrate that ethanol vapor exposure induces intoxication-like behaviors, acute tolerance, and ethanol preference, akin to mammalian AUD traits. Leveraging this model, we elucidate the conserved role of c-jun N-terminal kinase (JNK) signaling in mediating acute ethanol tolerance. Mutants lacking JNK signaling components exhibit impaired tolerance development, highlighting JNK's positive regulation. Furthermore, we detect ethanol-induced JNK activation in C. elegans. Our findings underscore the utility of C. elegans with ethanol vapor exposure for studying AUD and offer novel insights into the molecular mechanisms underlying acute ethanol tolerance through JNK signaling.

Natural variation in protein kinase D modifies alcohol sensitivity in Caenorhabditis elegans

Differences in naïve alcohol sensitivity between individuals are a strong predictor of later life alcohol use disorders (AUD). However, the genetic bases for alcohol sensitivity (beyond ethanol metabolism) and pharmacological approaches to modulate alcohol sensitivity remain poorly understood. We used a high-throughput behavioral screen to measure acute behavioral sensitivity to alcohol, a model of intoxication, in a genetically diverse set of over 150 wild strains of the nematode Caenorhabditis elegans. We performed a genome-wide association study to identify loci that underlie natural variation in alcohol sensitivity. We identified five quantitative trait loci (QTL) and further show that variants in the C. elegans ortholog of protein kinase D, dkf-2, likely underlie the chromosome V QTL. We found that resistance to intoxication was conferred by dkf-2 loss-of-function mutations as well as partly by a PKD inhibitor in a dkf-2-dependent manner. Protein kinase D might represent a conserved, druggable target to modify alcohol sensitivity with application towards AUD.

Brain-specific serine/threonine-protein kinase 1 is a substrate of protein kinase C epsilon involved in sex-specific ethanol and anxiety phenotypes

Protein kinase C epsilon (PKCε) regulates behavioural responses to ethanol and plays a role in anxiety-like behaviour, but knowledge is limited on downstream substrates of PKCε that contribute to these behaviours. We recently identified brain-specific serine/threonine-protein kinase 1 (BRSK1) as a substrate of PKCε. Here, we test the hypothesis that BRSK1 mediates responses to ethanol and anxiety-like behaviours that are also PKCε dependent. We used in vitro kinase assays to further validate BRSK1 as a substrate of PKCε and used Brsk1-/- mice to assess the role of BRSK1 in ethanol- and anxiety-related behaviours and in physiological responses to ethanol. We found that BRSK1 is phosphorylated by PKCε at a residue identified in a chemical genetic screen of PKCε substrates in mouse brain. Like Prkce-/- mice, male and female Brsk1-/- mice were more sensitive than wild-type to the acute sedative-hypnotic effect of alcohol. Unlike Prkce-/- mice, Brsk1-/- mice responded like wild-type to ataxic doses of ethanol. Although in Prkce-/- mice ethanol consumption and reward are reduced in both sexes, they were reduced only in female Brsk1-/- mice. Ex vivo slice electrophysiology revealed that ethanol-induced facilitation of GABA release in the central amygdala was absent in male Brsk1-/- mice similar to findings in male Prkce-/- mice. Collectively, these results indicate that BRSK1 is a target of PKCε that mediates some PKCε-dependent responses to ethanol in a sex-specific manner and plays a role distinct from PKCε in anxiety-like behaviour.

Large analysis of genetic manipulations reveals an inverse correlation between initial alcohol resistance and rapid tolerance phenotypes

Tolerance occurs when, following an initial experience with a substance, more of the substance is required subsequently to induce identical behavioral effects. Tolerance is not well-understood, and numerous researchers have turned to model organisms, particularly Drosophila melanogaster, to unravel its mechanisms. Flies have high translational relevance for human alcohol responses, and there is substantial overlap in disease-causing genes between flies and humans, including those associated with Alcohol Use Disorder. Numerous Drosophila tolerance mutants have been described; however, approaches used to identify and characterize these mutants have varied across time and labs and have mostly disregarded any impact of initial resistance/sensitivity to ethanol on subsequent tolerance development. Here, we analyzed our own, as well as data published by other labs to uncover an inverse correlation between initial ethanol resistance and tolerance phenotypes. This inverse correlation suggests that initial resistance phenotypes can explain many 'perceived' tolerance phenotypes, thus classifying such mutants as 'secondary' tolerance mutants. Additionally, we show that tolerance should be measured as a relative increase in time to sedation between an initial and second exposure rather than an absolute change in time to sedation. Finally, based on our analysis, we provide a method for using a linear regression equation to assess the residuals of potential tolerance mutants. These residuals provide predictive insight into the likelihood of a mutant being a 'primary' tolerance mutant, where a tolerance phenotype is not solely a consequence of initial resistance, and we offer a framework for understanding the relationship between initial resistance and tolerance.

The neurobiological markers of acute alcohol's subjective effects in humans

The ingestion of alcohol yields acute biphasic subjective effects: stimulation before sedation. Despite their predictive relevance to the development of alcohol use disorders (AUD), the neurobiological markers accounting for the biphasic effects of alcohol remain poorly understood in humans. Informed by converging lines of evidence, this study tested the hypothesis that alcohol ingestion acutely increases gamma-aminobutyric acid (GABA)-mediated inhibition, which would positively and negatively predict the feeling of stimulation and sedation, respectively. To do so, healthy participants (n = 20) ingested a single dose of 94% ABV alcohol (males: 1.0 ml/kg; females: 0.85 ml/kg) in a randomized placebo-controlled cross-over design. The alcohol's biphasic effects were assessed with the Brief-Biphasic Alcohol Effects Scale, and non-invasive neurobiological markers were measured with transcranial magnetic stimulation, before and every 30 min (up to 120 min) after the complete ingestion of the beverage. Results showed that acute alcohol ingestion selectively increased the duration of the cortical silent period (CSP) as compared to placebo, suggesting that alcohol increases non-specific GABAergic inhibition. Importantly, CSP duration positively and negatively predicted increases in the feeling of stimulation and sedation, respectively, suggesting that stimulation emerges as GABAergic inhibition increases and that sedation emerges as GABAergic inhibition returns to baseline values. Overall, these results suggest that modulations of GABAergic inhibition are central to the acute biphasic subjective effects of alcohol, providing a potential preventive target to curb the progression of at-risk individuals to AUD.

Neuropeptidergic regulation of compulsive ethanol seeking in C. elegans

Despite the catastrophic consequences of alcohol abuse, alcohol use disorders (AUD) and comorbidities continue to strain the healthcare system, largely due to the effects of alcohol-seeking behavior. An improved understanding of the molecular basis of alcohol seeking will lead to enriched treatments for these disorders. Compulsive alcohol seeking is characterized by an imbalance between the superior drive to consume alcohol and the disruption or erosion in control of alcohol use. To model the development of compulsive engagement in alcohol seeking, we simultaneously exploited two distinct and conflicting Caenorhabditis elegans behavioral programs, ethanol preference and avoidance of aversive stimulus. We demonstrate that the C. elegans model recapitulated the pivotal features of compulsive alcohol seeking in mammals, specifically repeated attempts, endurance, and finally aversion-resistant alcohol seeking. We found that neuropeptide signaling via SEB-3, a CRF receptor-like GPCR, facilitates the development of ethanol preference and compels animals to seek ethanol compulsively. Furthermore, our functional genomic approach and behavioral elucidation suggest that the SEB-3 regulates another neuropeptidergic signaling, the neurokinin receptor orthologue TKR-1, to facilitate compulsive ethanol-seeking behavior.

Acute alcohol and cognition: Remembering what it causes us to forget

Addiction has been conceptualized as a specific form of memory that appropriates typically adaptive neural mechanisms of learning to produce the progressive spiral of drug-seeking and drug-taking behavior, perpetuating the path to addiction through aberrant processes of drug-related learning and memory. From that perspective, to understand the development of alcohol use disorders, it is critical to identify how a single exposure to alcohol enters into or alters the processes of learning and memory, so that involvement of and changes in neuroplasticity processes responsible for learning and memory can be identified early. This review characterizes the effects produced by acute alcohol intoxication as a function of brain region and memory neurocircuitry. In general, exposure to ethanol doses that produce intoxicating effects causes consistent impairments in learning and memory processes mediated by specific brain circuitry, whereas lower doses either have no effect or produce a facilitation of memory under certain task conditions. Therefore, acute ethanol does not produce a global impairment of learning and memory, and can actually facilitate particular types of memory, perhaps particular types of memory that facilitate the development of excessive alcohol use. In addition, the effects on cognition are dependent on brain region, task demands, dose received, pharmacokinetics, and tolerance. Additionally, we explore the underlying alterations in neurophysiology produced by acute alcohol exposure that help to explain these changes in cognition and highlight future directions for research. Through understanding the impact that acute alcohol intoxication has on cognition, the preliminary changes potentially causing a problematic addiction memory can better be identified.

Novel Small-Molecule Inhibitors of Protein Kinase C Epsilon Reduce Ethanol Consumption in Mice

BACKGROUND

Despite the high cost and widespread prevalence of alcohol use disorders, treatment options are limited, underscoring the need for new, effective medications. Previous results using protein kinase C epsilon (PKCε) knockout mice, RNA interference against PKCε, and peptide inhibitors of PKCε predict that small-molecule inhibitors of PKCε should reduce alcohol consumption in humans.

METHODS

We designed a new class of PKCε inhibitors based on the Rho-associated protein kinase (ROCK) inhibitor Y-27632. In vitro kinase and binding assays were used to identify the most potent compounds. Their effects on ethanol-stimulated synaptic transmission; ethanol, sucrose, and quinine consumption; ethanol-induced loss of righting; and ethanol clearance were studied in mice.

RESULTS

We identified two compounds that inhibited PKCε with Ki <20 nM, showed selectivity for PKCε over other kinases, crossed the blood-brain barrier, achieved effective concentrations in mouse brain, prevented ethanol-stimulated gamma-aminobutyric acid release in the central amygdala, and reduced ethanol consumption when administered intraperitoneally at 40 mg/kg in wild-type but not in Prkce^-/- mice. One compound also reduced sucrose and saccharin consumption, while the other was selective for ethanol. Both transiently impaired locomotion through an off-target effect that did not interfere with their ability to reduce ethanol intake. One compound prolonged recovery from ethanol-induced loss of righting but this was also due to an off-target effect since it was present in Prkce^-/- mice. Neither altered ethanol clearance.

CONCLUSIONS

These results identify lead compounds for development of PKCε inhibitors that reduce alcohol consumption.

Ethanol-Induced Changes in PKCε: From Cell to Behavior

The long-term binge intake of ethanol causes neuroadaptive changes that lead to drinkers requiring higher amounts of ethanol to experience its effects. This neuroadaptation can be partly attributed to the modulation of numerous neurotransmitter receptors by the various protein kinases C (PKCs). PKCs are enzymes that control cellular activities by regulating other proteins via phosphorylation. Among the various isoforms of PKC, PKCε is the most implicated in ethanol-induced biochemical and behavioral changes. Ethanol exposure causes changes to PKCε expression and localization in various brain regions that mediate addiction-favoring plasticity. Ethanol works in conjunction with numerous upstream kinases and second messenger activators to affect cellular PKCε expression. Chauffeur proteins, such as receptors for activated C kinase (RACKs), cause the translocation of PKCε to aberrant sites and mediate ethanol-induced changes. In this article, we aim to review the following: the general structure and function of PKCε, ethanol-induced changes in PKCε expression, the regulation of ethanol-induced PKCε activities in DAG-dependent and DAG-independent environments, the mechanisms underlying PKCε-RACKε translocation in the presence of ethanol, and the existing literature on the role of PKCε in ethanol-induced neurobehavioral changes, with the goal of creating a working model upon which further research can build.

Mutation of the inhibitory ethanol site in GABAA ρ1 receptors promotes tolerance to ethanol-induced motor incoordination

Genes encoding the ρ1/2 subunits of GABA_A receptors have been associated with alcohol (ethanol) dependence in humans, and ρ1 was also shown to regulate some of the behavioral effects of ethanol in animal models. Ethanol inhibits GABA-mediated responses in wild-type (WT) ρ1, but not ρ1(T6'Y) mutant receptors expressed in Xenopus laevis oocytes, indicating the presence of an inhibitory site for ethanol in the second transmembrane helix. In this study, we found that ρ1(T6'Y) receptors expressed in oocytes display overall normal responses to GABA, the endogenous GABA modulator (zinc), and partial agonists (β-alanine and taurine). We generated ρ1 (T6'Y) knockin (KI) mice using CRISPR/Cas9 to test the behavioral importance of the inhibitory actions of ethanol on this receptor. Both ρ1 KI and knockout (KO) mice showed faster recovery from acute ethanol-induced motor incoordination compared to WT mice. Both KI and KO mutant strains also showed increased tolerance to motor impairment produced by ethanol. The KI mice did not differ from WT mice in other behavioral actions, including ethanol intake and preference, conditioned taste aversion to ethanol, and duration of ethanol-induced loss of righting reflex. WT and KI mice did not differ in levels of ρ1 or ρ2 mRNA in cerebellum or in ethanol clearance. Our findings indicate that the inhibitory site for ethanol in GABA_A ρ1 receptors regulates acute functional tolerance to moderate ethanol intoxication. We note that low sensitivity to alcohol intoxication has been linked to risk for development of alcohol dependence in humans.

Selective chemical genetic inhibition of protein kinase C epsilon reduces ethanol consumption in mice

Reducing expression or inhibiting translocation of protein kinase C epsilon (PKCε) prolongs ethanol intoxication and decreases ethanol consumption in mice. However, we do not know if this phenotype is due to reduced PKCε kinase activity or to impairment of kinase-independent functions. In this study, we used a chemical-genetic strategy to determine whether a potent and highly selective inhibitor of PKCε catalytic activity reduces ethanol consumption. We generated ATP analog-specific PKCε (AS-PKCε) knock-in mice harboring a point mutation in the ATP binding site of PKCε that renders the mutant kinase highly sensitive to inhibition by 1-tert-butyl-3-naphthalen-1-ylpyrazolo[3,4-d]pyrimidin-4-amine (1-NA-PP1). Systemically administered 1-NA-PP1 readily crossed the blood brain barrier and inhibited PKCε-mediated phosphorylation. 1-NA-PP1 reversibly reduced ethanol consumption by AS-PKCε mice but not by wild type mice lacking the AS-PKCε mutation. These results support the development of inhibitors of PKCε catalytic activity as a strategy to reduce ethanol consumption, and they demonstrate that the AS- PKCε mouse is a useful tool to study the role of PKCε in behavior.

Genes and Alcohol Consumption: Studies with Mutant Mice

In this chapter, we review the effects of global null mutant and overexpressing transgenic mouse lines on voluntary self-administration of alcohol. We examine approximately 200 publications pertaining to the effects of 155 mouse genes on alcohol consumption in different drinking models. The targeted genes vary in function and include neurotransmitter, ion channel, neuroimmune, and neuropeptide signaling systems. The alcohol self-administration models include operant conditioning, two- and four-bottle choice continuous and intermittent access, drinking in the dark limited access, chronic intermittent ethanol, and scheduled high alcohol consumption tests. Comparisons of different drinking models using the same mutant mice are potentially the most informative, and we will highlight those examples. More mutants have been tested for continuous two-bottle choice consumption than any other test; of the 137 mouse genes examined using this model, 97 (72%) altered drinking in at least one sex. Overall, the effects of genetic manipulations on alcohol drinking often depend on the sex of the mice, alcohol concentration and time of access, genetic background, as well as the drinking test.

Evidence revealing deregulation of the KLF11-MAO A pathway in association with chronic stress and depressive disorders

The biochemical pathways underlying major depressive disorder (MDD) and chronic stress are not well understood. However, it has been reported that monoamine oxidase A (MAO A, a major neurotransmitter-degrading enzyme) is significantly increased in the brains of human subjects affected with MDD and rats exposed to chronic social defeat (CSD) stress, which is used to model depression. In the current study, we compared the protein levels of a MAO A-transcriptional activator, Kruppel-like factor 11 (KLF11 , also recognized as transforming growth factor-beta-inducible early gene 2) between the brains of 18 human subjects with MDD and 18 control subjects. We found that, indeed, the expression of KLF11 is increased by 36% (p<0.02) in the postmortem prefrontal cortex of human subjects with MDD compared with controls. We also observed a positive correlation between KLF11 levels and those of its target gene, MAO A, both in association with MDD. KLF11 protein expression was also increased by 44% (p<0.02) in the frontal cortex of KLF11 wild-type mice (Klf11(+/+)) vs Klf11(-/-) when both exposed to CSD stress. In contrast, locomotor activities, central box duration and sucrose preference were significantly reduced in the stressed Klf11(+/+) mice, suggesting that Klf11(+/+) mice are more severely affected by the stress model compared with Klf11(-/-) mice. These results serve to assign an important role of KLF11 in upregulating MAO A in MDD and chronic social stress, suggesting that inhibition of the pathways regulated by this transcription factor may aid in the therapeutics of neuropsychiatric illnesses. Thus, the new knowledge derived from the current study extends our understanding of transcriptional mechanisms that are operational in the pathophysiology of common human diseases and thus bears significant biomedical relevance.

Regulation of GABAARs by phosphorylation

γ-Aminobutyric acid type A receptors (GABAARs) are the principal mediators of fast synaptic inhibition in the brain as well as the low persistent extrasynaptic inhibition, both of which are fundamental to proper brain function. Thus unsurprisingly, deficits in GABAARs are implicated in a number of neurological disorders and diseases. The complexity of GABAAR regulation is determined not only by the heterogeneity of these receptors but also by its posttranslational modifications, the foremost, and best characterized of which is phosphorylation. This review will explore the details of this dynamic process, our understanding of which has barely scratched the surface. GABAARs are regulated by a number of kinases and phosphatases, and its phosphorylation plays an important role in governing its trafficking, expression, and interaction partners. Here, we summarize the progress in understanding the role phosphorylation plays in the regulation of GABAARs. This includes how phosphorylation can affect the allosteric modulation of GABAARs, as well as signaling pathways that affect GABAAR phosphorylation. Finally, we discuss the dysregulation of GABAAR phosphorylation and its implication in disease processes.

MeCP2 regulates ethanol sensitivity and intake

We have investigated the expression of chromatin-regulating genes in the prefrontal cortex and in the shell subdivision of the nucleus accumbens during protracted withdrawal in mice with increased ethanol drinking after chronic intermittent ethanol (CIE) vapor exposure and in mice with a history of non-dependent drinking. We observed that the methyl-CpG binding protein 2 (MeCP2) was one of the few chromatin-regulating genes to be differentially regulated by a history of dependence. As MeCP2 has the potential of acting as a broad gene regulator, we investigated sensitivity to ethanol and ethanol drinking in MeCP2(308/) (Y) mice, which harbor a truncated MeCP2 allele but have a milder phenotype than MeCP2 null mice. We observed that MeCP2(308/) (Y) mice were more sensitive to ethanol's stimulatory and sedative effects than wild-type (WT) mice, drank less ethanol in a limited access 2 bottle choice paradigm and did not show increased drinking after induction of dependence with exposure to CIE vapors. Alcohol metabolism did not differ in MeCP2(308/) (Y) and WT mice. Additionally, MeCP2(308/) (Y) mice did not differ from WT mice in ethanol preference in a 24-hour paradigm nor in their intake of graded solutions of saccharin or quinine, suggesting that the MeCP2(308/) (Y) mutation did not alter taste function. Lastly, using the Gene Set Enrichment Analysis algorithm, we found a significant overlap in the genes regulated by alcohol and by MeCP2. Together, these results suggest that MeCP2 contributes to the regulation of ethanol sensitivity and drinking.

The expression of KLF11 (TIEG2), a monoamine oxidase B transcriptional activator in the prefrontal cortex of human alcohol dependence

BACKGROUND

The biochemical pathways underlying alcohol abuse and dependence are not well understood, although brain cell loss and neurotoxicity have been reported in subjects with alcohol dependence. Monoamine oxidase B (MAO B; an enzyme that catabolizes neurotransmitters such as dopamine) is consistently increased in this psychiatric illness. MAO B has been implicated in the pathogenesis of alcohol dependence and alcohol-induced brain neurotoxicity. Recently, the cell growth inhibitor protein, Kruppel-like factor 11 (KLF11), has been reported to be an MAO transcriptional activator. KLF11 is also known as TIEG2 (transforming growth factor-beta-inducible early gene 2) and mediates apoptotic cell death. This study investigates the protein expression of KLF11 and its relationship with MAO B using human postmortem prefrontal cortex from subjects with alcohol dependence.

METHODS

Twelve subjects with alcohol dependence and the respective psychiatrically normal control subjects were investigated. Expression of KLF11 and MAO B proteins in the prefrontal cortex was measured by Western blot analysis. Correlation studies involving KLF11 and MAO B protein expression were performed. Localization of KLF11 in the human prefrontal cortex was also determined by immunohistochemistry.

RESULTS

Levels of KLF11 protein were significantly increased by 44% (p < 0.03) in the postmortem prefrontal cortex of subjects with alcohol dependence as compared to age- and gender-matched, psychiatrically normal control subjects. Furthermore, KLF11 levels were significantly and positively correlated with both the increased MAO B protein levels and blood alcohol content in alcohol-dependent subjects. In addition, KLF11 protein expression was visualized in both neuronal and glial cells.

CONCLUSIONS

This novel study shows the important role of KLF11, an MAO transcriptional activator, in human alcohol dependence. It further supports that the KLF11-MAO B cell death cascade may contribute to chronic alcohol-induced brain damage. This argues a case for KLF11-MAO B inhibition as a novel therapeutic strategy that may impact this highly prevalent illness.

Signaling pathways mediating alcohol effects

Ethanol's effects on intracellular signaling pathways contribute to acute effects of ethanol as well as to neuroadaptive responses to repeated ethanol exposure. In this chapter we review recent discoveries that demonstrate how ethanol alters signaling pathways involving several receptor tyrosine kinases and intracellular tyrosine and serine-threonine kinases, with consequences for regulation of cell surface receptor function, gene expression, protein translation, neuronal excitability and animal behavior. We also describe recent work that demonstrates a key role for ethanol in regulating the function of scaffolding proteins that organize signaling complexes into functional units. Finally, we review recent exciting studies demonstrating ethanol modulation of DNA and histone modification and the expression of microRNAs, indicating epigenetic mechanisms by which ethanol regulates neuronal gene expression and addictive behaviors.

The biology of protein kinase C

This review gives a basic introduction to the biology of protein kinase C, one of the first calcium-dependent kinases to be discovered. We review the structure and function of protein kinase C, along with some of the substrates of individual isoforms. We then review strategies for inhibiting PKC in experimental systems and finally discuss the therapeutic potential of targeting PKC. Each aspect is covered in summary, with links to detailed resources where appropriate.

SEB-3, a CRF receptor-like GPCR, regulates locomotor activity states, stress responses and ethanol tolerance in Caenorhabditis elegans

The CRF (corticotropin-releasing factor) system is a key mediator of the stress response. Alterations in CRF signaling have been implicated in drug craving and ethanol consumption. The development of negative reinforcement via activation of brain stress systems has been proposed as a mechanism that contributes to alcohol dependence. Here, we isolated a gain-of-function allele of seb-3, a CRF receptor-like GPCR in Caenorhabditis elegans, providing an in vivo model of a constitutively activated stress system. We also characterized a loss-of-function allele of seb-3 and showed that SEB-3 positively regulates a stress response that leads to an enhanced active state of locomotion, behavioral arousal and tremor. SEB-3 also contributed to acute tolerance to ethanol and to the development of tremor during ethanol withdrawal. Furthermore, we found that a specific CRF(1) receptor antagonist reduced acute functional tolerance to ethanol in mice. These findings demonstrate functional conservation of the CRF system in responses to stress and ethanol in vertebrates and invertebrates.

Selection for high alcohol preference drinking in mice results in heightened sensitivity and rapid development of acute functional tolerance to alcohol's ataxic effects

Propensity to develop acute functional (or within session) tolerance to alcohol (ethanol) may influence the amount of alcohol consumed, with higher drinking associated with greater acute functional tolerance (AFT). The goal of this study was to assess this potential correlated response between alcohol preference and AFT in second and third replicate lines of mice selectively bred for high (HAP2 and HAP3) and low (LAP2 and LAP3) alcohol preference drinking. Male and female mice were tested for development of AFT on a static dowel task, which requires that animals maintain balance on a wooden dowel in order to prevent falling. On test day, each mouse received one (1.75 g/kg; Experiment 1) or two (1.75 and 2.0 g/kg; Experiment 2) injections of ethanol; an initial administration before being placed on the dowel and in Experiment 2, an additional administration after the first regain of balance on the dowel. Blood samples were taken immediately after loss of balance [when blood ethanol concentrations (BECs) were rising] and at recovery (during falling BECs) in Experiment 1, and after first and second recovery in Experiment 2. It was found that HAP mice fell from the dowel significantly earlier and at lower BECs than LAP mice following the initial injection of ethanol and were therefore more sensitive to its early effects. Furthermore, Experiment 1 detected significantly greater AFT development (BECfalling--BECrising) in HAP mice when compared with LAP mice, which occurred within ~30 min, supporting our hypothesis. However, AFT was not different between lines in Experiment 2, indicating that ~30-60 min following alcohol administration, AFT development was similar in both lines. These data show that high alcohol drinking genetically associates with both high initial sensitivity and very early tolerance to the ataxic effects of ethanol.

Lipid environment modulates the development of acute tolerance to ethanol in Caenorhabditis elegans

The development of tolerance to a drug at the level of the neuron reflects a homeostatic mechanism by which neurons respond to perturbations of their function by external stimuli. Acute functional tolerance (AFT) to ethanol is a fast compensatory response that develops within a single drug session and normalizes neuronal function despite the continued presence of the drug. We performed a genetic screen to identify genes required for the development of acute functional tolerance to ethanol in the nematode C. elegans. We identified mutations affecting multiple genes in a genetic pathway known to regulate levels of triacylglycerols (TAGs) via the lipase LIPS-7, indicating that there is an important role for TAGs in the development of tolerance. Genetic manipulation of lips-7 expression, up or down, produced opposing effects on ethanol sensitivity and on the rate of development of AFT. Further, decreasing cholesterol levels through environmental manipulation mirrored the effects of decreased TAG levels. Finally, we found that genetic alterations in the levels of the TAG lipase LIPS-7 can modify the phenotype of gain-of-function mutations in the ethanol-inducible ion channel SLO-1, the voltage- and calcium-sensitive BK channel. This study demonstrates that the lipid milieu modulates neuronal responses to ethanol that include initial sensitivity and the development of acute tolerance. These results lend new insight into studies of alcohol dependence, and suggest a model in which TAG levels are important for the development of AFT through alterations of the action of ethanol on membrane proteins.

Advancing addiction treatment: what can we learn from animal studies?

Substance addiction is a maladaptive behavior characterized by compulsive and uncontrolled self-administration of a substance (drug). Years of research indicate that addictive behavior is the result of complex interactions between the drug, the user, and the environment in which the drug is used; therefore, addiction cannot simply be attributed to the neurobiological actions of a drug. However, despite the obvious complexity of addictive behavior, animal models have both advanced understanding of addiction and contributed importantly to the development of medications to treat this disease. We briefly review recent animal models used to study drug addiction and the contribution of data generated by these animal models for the clinical treatment of addictive disorders.

Responses to ethanol in C57BL/6 versus C57BL/6 × 129 hybrid mice

Although genetic background alters responses to ethanol, there has not yet been a methodical quantification of differences in ethanol-related behaviors between inbred and hybrid mice commonly used in gene-targeting studies. Here, we compared C57BL/6NTac × 129S6/SvEvTac F1 hybrid mice (B6129S6) with C57BL/6NTac inbred mice (B6NT), and C57BL/6J × 129X1/SvJ (B6129X1) and C57BL/6J × 129S4/SvJae F1 hybrids (B6129S4) with C57BL/6J mice (B6J), in five commonly used tests: continuous access two-bottle choice drinking, intermittent limited-access binge drinking, ethanol clearance, ethanol-induced loss of the righting reflex, and conditioned place preference (CPP) for ethanol. We found that inbred B6J and B6NT mice showed greater ethanol preference and consumption than their respective hybrids when ethanol was continuously available. Within the intermittent limited-access drinking procedure, though all lines showed similar intake over eight drinking sessions, the average of all sessions showed that B6NT mice drank significantly more ethanol than B6129S6 mice. In addition, B6J mice consumed more ethanol than B6129X1 mice, although they drank less than B6129S4 mice. No differences in ethanol LORR duration were observed between inbred and hybrid mice. Although ethanol clearance was similar among B6J mice and their respective hybrids, B6NT mice cleared ethanol more rapidly than B6129S6 mice. All lines developed CPP for ethanol. Our findings indicate that it may not be necessary to backcross hybrids to an inbred B6 background to study many ethanol-related behaviors in gene-targeted mice.

The genetic relationships between ethanol preference, acute ethanol sensitivity, and ethanol tolerance in Drosophila melanogaster

The relationship between alcohol consumption, sensitivity, and tolerance is an important question that has been addressed in humans and rodent models. Studies have shown that alcohol consumption and risk of abuse may correlate with (1) increased sensitivity to the stimulant effects of alcohol, (2) decreased sensitivity to the depressant effects of alcohol, and (3) increased alcohol tolerance. However, many conflicting results have been observed. To complement these studies, we utilized a different organism and approach to analyze the relationship between ethanol consumption and other ethanol responses. Using a set of 20 Drosophila melanogaster mutants that were isolated for altered ethanol sensitivity, we measured ethanol-induced hyperactivity, ethanol sedation, sedation tolerance, and ethanol consumption preference. Ethanol preference showed a strong positive correlation with ethanol tolerance, consistent with some rodent and human studies, but not with ethanol hyperactivity or sedation. No pairwise correlations were observed between ethanol hyperactivity, sedation, and tolerance. The evolutionary conservation of the relationship between tolerance and ethanol consumption in flies, rodents, and humans indicates that there are fundamental biological mechanisms linking specific ethanol responses.

Upregulation of Kupffer cell α2A-Adrenoceptors and downregulation of MKP-1 mediate hepatic injury in chronic alcohol exposure

Alcohol-induced liver disease is associated with unacceptable morbidity and mortality. When activated, Kupffer cells (KCs), the resident macrophages in the liver, release proinflammatory cytokine TNF-α, a key mediator of hepatic damage. Although chronic alcohol causes increase in norepinephrine (NE) release leading to hepatic dysfunction, the mechanism of NE-induced hepatic injury in chronic alcohol exposure has not been elucidated. This study was conducted to determine whether chronic alcohol exposure increases NE and upregulates KC α(2A)-adrenoceptors (α(2A)-AR) to cause TNF-α release. We also examined the role of mitogen activated protein kinase (MAPK) phosphatase-1 (MKP-1) in this process. Male adult rats were fed the Lieber-DeCarli liquid diet containing alcohol as 36% of total calories. The animals were sacrificed after 6 weeks and blood and liver samples were harvested for further analysis. KCs from healthy male rats were cultured with alcohol for 7 days, and cells then harvested for RNA and protein analyses. Chronic alcohol exposure resulted in hepatic damage. Alcohol caused a 276% increase in circulating NE and 86% increase in TNF-α in the liver. There was a 75% and 62% decrease in MKP-1 mRNA and protein levels, respectively in the liver. In-vitro experiments revealed 121% and 98% increase in TNF-α and α(2A)-AR mRNA levels with alcohol exposure, respectively, and a 32% decrease in MKP-1 mRNA compared to controls. In summary, chronic alcohol exposure elevates NE and upregulates KC α(2A)-AR to release TNF-α. Alcohol induced downregulation of MKP-1 leads to further release of TNF-α and hepatic injury.

Molecular profiles of drinking alcohol to intoxication in C57BL/6J mice

BACKGROUND

Alcohol addiction develops through a series of stages, and mechanistic studies are needed to understand the transition from initial drug use to sustained controlled alcohol consumption followed by abuse and physical dependence. The focus of this study was to examine the effects of voluntary alcohol consumption on brain gene expression profiles using a mouse model of binge drinking. The main goal was to identify alcohol-responsive genes and functional categories after a single episode of drinking to intoxication.

METHODS

We used a modification of a "Drinking In the Dark" (DID) procedure (Rhodes et al., 2005) that allows mice to experience physiologically relevant amounts of alcohol in a non-stressful environment and also allows for detection of alcohol-sensitive molecular changes in a dose-dependent manner. C57BL/6J male mice were exposed to either 20% ethanol solution or water (single bottle) starting 3 hours after lights off for 4 hours and brains were harvested immediately after the drinking session. cDNA microarrays were used to assess the effects of voluntary drinking on global gene expression in 6 brain regions. We employed three statistical approaches to analyze microarray data.

RESULTS

A commonly used approach that applies a strict statistical threshold identified the eight top statistically significant genes whose expression was significantly correlated with blood ethanol concentration (BEC) in one of the brain regions. We then used a systems network approach to examine brain region-specific transcriptomes and identify modules of co-expressed (correlated) genes. In each brain region, we identified alcohol-responsive modules, i.e., modules significantly enriched for genes whose expression was correlated with BEC. A functional over-representation analysis was then applied to examine the organizing principles of alcohol-responsive modules. Genes were clustered into modules according to their roles in different physiological processes, functional groups, and cell types, including blood circulation, signal transduction, cell-cell communication, and striatal neurons. Finally, a meta-analysis across all brain regions suggested a global role of increasing alcohol dose in coordination of brain blood circulation and reaction of astrocytes.

CONCLUSIONS

This study showed that acute drinking resulted in small but consistent changes in brain gene expression which occurred in a dose-dependent manner. We identified both general and region-specific changes, some of which represent adaptive changes in response to increasing alcohol dose, which may play a role in alcohol-related behaviours, such as tolerance and consumption. Our systems approach allowed us to estimate the functional values of individual genes in the context of their genetic networks and formulate new refined hypotheses. An integrative analysis including other alcohol studies suggested several top candidates for functional validation, including Mt2, Gstm1, Scn4b, Prkcz, and Park7.

Tolerance to allopregnanolone with focus on the GABA-A receptor

Many studies have suggested a relationship between stress, sex steroids, and negative mental and mood changes in humans. The progesterone metabolite allopregnanolone is a potent endogenous ligand of the γ-amino butyric acid -A (GABA-A) receptor, and the most discussed neuroactive steroid. Variations in the levels of neuroactive steroids that influence the activity of the GABA-A receptor cause a vulnerability to mental and emotional pathology. There are physiological conditions in which allopregnanolone production increases acutely (e.g. stress) or chronically (e.g. menstrual cycle, pregnancy), thus exposing the GABA-A receptor to high and continuous allopregnanolone concentrations. In such conditions, tolerance to allopregnanolone may develop. We have shown that both acute and chronic tolerances can develop to the effects of allopregnanolone. Following the development of acute allopregnanolone tolerance, there is a decrease in the abundance of the GABA-A receptor α4 subunit and the expression of the α4 subunit mRNA in the ventral-posteriomedial nucleus of the thalamus. Little is known about the mechanism behind allopregnanolone tolerance and its effects on assembly of the GABA-A receptor composition. The exact mechanism of the allopregnanolone tolerance phenomena remains unclear. The purpose of this review is to summarize certain aspects of current knowledge concerning allopregnanolone tolerance and changes in the GABA-A receptors.

Protein kinase C isozymes as regulators of sensitivity to and self-administration of drugs of abuse-studies with genetically modified mice

Studies using targeted gene deletion in mice have revealed distinct roles for individual isozymes of the protein kinase C (PKC) family of enzymes in regulating sensitivity to various drugs of abuse. These changes in drug sensitivity are associated with altered patterns of drug self-administration. The purpose of this review is to summarize behavioral studies conducted on mice carrying targeted deletions of genes encoding specific PKC isozymes (namely the beta, gamma, delta, and epsilon isozymes), and to critically evaluate the possibility of using pharmacological inhibitors of specific PKC isozymes as modulators of the sensitivity to various drugs of abuse, as well as potential aids in the treatment of substance use disorders.

The substrates and binding partners of protein kinase Cepsilon

The epsilon isoform of protein kinase C (PKCepsilon) has important roles in the function of the cardiac, immune and nervous systems. As a result of its diverse actions, PKCepsilon is the target of active drug-discovery programmes. A major research focus is to identify signalling cascades that include PKCepsilon and the substrates that PKCepsilon regulates. In the present review, we identify and discuss those proteins that have been conclusively shown to be direct substrates of PKCepsilon by the best currently available means. We will also describe binding partners that anchor PKCepsilon near its substrates. We review the consequences of substrate phosphorylation and discuss cellular mechanisms by which target specificity is achieved. We begin with a brief overview of the biology of PKCepsilon and methods for substrate identification, and proceed with a discussion of substrate categories to identify common themes that emerge and how these may be used to guide future studies.

Altered glutamatergic neurotransmission in the striatum regulates ethanol sensitivity and intake in mice lacking ENT1

Alcohol-sensitive type 1 equilibrative nucleoside transporter (ENT1) regulates adenosine-mediated glutamate neurotransmission in the brain. Our behavioral studies suggest that the diminished aversive effects of ethanol and the increased resistance to acute ethanol intoxication in mice lacking ENT1, could be related to increased voluntary ethanol self-seeking behavior. In addition, we found that ENT1 null mice were resistant to the ataxic effects of glutamate antagonists when tested on a rotarod. Using microdialysis experiments, we examined glutamate levels in the dorsal and ventral striatum in response to ethanol. In the dorsal striatum of ENT1 null mice, a low intoxicating dose of ethanol (1.5 g/kg) induced a greater increase of glutamate levels, while a higher hypnotic dose of ethanol (3.0 g/kg) decreased to a lesser degree the glutamate levels, compared with that of wild-type mice. In the ventral striatum, however, the low (1.5 g/kg) and the high (3.0 g/kg) ethanol doses altered glutamate levels similarly in both genotypes. Our results suggest that adenosine-regulated glutamatergic signaling contributes to a reduced level of alcohol response, which might be associated with a higher susceptibility for alcoholism in humans.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Amygdala protein kinase C epsilon controls alcohol consumption

Alcoholism is a progressive disorder that involves the amygdala. Mice lacking protein kinase C epsilon (PKCepsilon) show reduced ethanol consumption, sensitivity and reward. We therefore investigated whether PKCepsilon signaling in the amygdala is involved in ethanol consumption. Local knockdown of PKCepsilon in the amygdala reduced ethanol consumption and preference in a limited-access paradigm. Further, mice that are heterozygous for the PKCepsilon allele consume less ethanol compared with wild-type mice in this paradigm. These mice have a >50% reduction in the abundance of PKCepsilon in the amygdala compared with wild-type mice. We conclude that amygdala PKCepsilon is important for ethanol consumption in mice.

Protein kinases and addiction

Although drugs of abuse have different chemical structures and interact with different protein targets, all appear to usurp common neuronal systems that regulate reward and motivation. Addiction is a complex disease that is thought to involve drug-induced changes in synaptic plasticity due to alterations in cell signaling, gene transcription, and protein synthesis. Recent evidence suggests that drugs of abuse interact with and change a common network of signaling pathways that include a subset of specific protein kinases. The best studied of these kinases are reviewed here and include extracellular signal-regulated kinase, cAMP-dependent protein kinase, cyclin-dependent protein kinase 5, protein kinase C, calcium/calmodulin-dependent protein kinase II, and Fyn tyrosine kinase. These kinases have been implicated in various aspects of drug addiction including acute drug effects, drug self-administration, withdrawal, reinforcement, sensitization, and tolerance. Identifying protein kinase substrates and signaling pathways that contribute to the addicted state may provide novel approaches for new pharmacotherapies to treat drug addiction.

Overview of mouse assays of ethanol intoxication

There are many behavioral assays to assess sensitivity to ethanol intoxication in mice. Most are simple to implement, and are sensitive to a particular dose range of ethanol. Most reflect genetic influences, and each test appears to reflect the contribution of a relatively distinct collection of genes. This genetic heterogeneity implies that no single test can claim to capture the construct "ethanol intoxication" completely. Depending on the test, and when measurements are made, acute functional tolerance to even a single dose of ethanol must be considered as a contributing factor. Whether or not a test is conducted in naïve mice or as part of a test battery can influence sensitivity, and do so in a strain-dependent manner. This unit reviews existing tests and recommends several.

The role of multiple hydrogen-bonding groups in specific alcohol binding sites in proteins: insights from structural studies of LUSH

It is now generally accepted that many of the physiological effects of alcohol consumption are a direct result of binding to specific sites in neuronal proteins such as ion channels or other components of neuronal signaling cascades. Binding to these targets generally occurs in water-filled pockets and leads to alterations in protein structure and dynamics. However, the precise interactions required to confer alcohol sensitivity to a particular protein remain undefined. Using information from the previously solved crystal structures of the Drosophila melanogaster protein LUSH in complexes with short-chain alcohols, we have designed and tested the effects of specific amino acid substitutions on alcohol binding. The effects of these substitutions, specifically S52A, T57S, and T57A, were examined using a combination of molecular dynamics, X-ray crystallography, fluorescence spectroscopy, and thermal unfolding. These studies reveal that the binding of ethanol is highly sensitive to small changes in the composition of the alcohol binding site. We find that T57 is the most critical residue for binding alcohols; the T57A substitution completely abolishes binding, while the T57S substitution differentially affects ethanol binding compared to longer-chain alcohols. The additional requirement for a potential hydrogen-bond acceptor at position 52 suggests that both the presence of multiple hydrogen-bonding groups and the identity of the hydrogen-bonding residues are critical for defining an ethanol binding site. These results provide new insights into the detailed chemistry of alcohol's interactions with proteins.

Nociceptive and behavioural sensitisation by protein kinase Cepsilon signalling in the CNS

Despite the apparent homology in the protein kinase C (PKC) family, it has become clear that slight structural differences are sufficient to have unique signalling properties for each individual isoform. For PKCepsilon in depth investigation of these aspects revealed unique actions in the CNS and lead to development of specific modulators with clinical perspective. In this review, we describe to which extent PKCepsilon is distinct from other isoforms on the level of tissue expression and protein structure. As this kinase is highly expressed in the brain, we outline three main aspects of PKCepsilon signalling in the CNS. First, its ability to alter the permeability of N-type Ca2+ channels in dorsal root ganglia has been shown to enhance nociception. Secondly, PKCepsilon increases anxiety by diminishing GABA(A)R-induced inhibitory post-synaptic currents in the prefrontal cortex. Another important aspect of the latter inhibition is the reduced sensitivity of GABA(A) receptors to ethanol, a mechanism potentially contributing to abuse. A third signalling cascade improves cognitive functions by facilitating cholinergic signalling in the hippocampus. Collectively, these findings point to a physical and behavioural sensitising role for this kinase.

Protein kinase C epsilon regulates gamma-aminobutyrate type A receptor sensitivity to ethanol and benzodiazepines through phosphorylation of gamma2 subunits

Ethanol enhances gamma-aminobutyrate (GABA) signaling in the brain, but its actions are inconsistent at GABA(A) receptors, especially at low concentrations achieved during social drinking. We postulated that the epsilon isoform of protein kinase C (PKCepsilon) regulates the ethanol sensitivity of GABA(A) receptors, as mice lacking PKCepsilon show an increased behavioral response to ethanol. Here we developed an ATP analog-sensitive PKCepsilon mutant to selectively inhibit the catalytic activity of PKCepsilon. We used this mutant and PKCepsilon(-/-) mice to determine that PKCepsilon phosphorylates gamma2 subunits at serine 327 and that reduced phosphorylation of this site enhances the actions of ethanol and benzodiazepines at alpha1beta2gamma2 receptors, which is the most abundant GABA(A) receptor subtype in the brain. Our findings indicate that PKCepsilon phosphorylation of gamma2 regulates the response of GABA(A) receptors to specific allosteric modulators, and, in particular, PKCepsilon inhibition renders these receptors sensitive to low intoxicating concentrations of ethanol.

GABAA receptor subtypes: the "one glass of wine" receptors

This review discusses evidence for and apparent controversy about, gamma-aminobutyric acid type A (GABAA) receptor (GABAAR) subtypes that mediate alcohol effects experienced during social drinking. GABAARs that contain the beta3 and delta subunits were shown to be enhanced by alcohol concentrations that mirror the concentration dependence of alcohol responses in humans. A mutation (alpha6R100Q) previously found in alcohol nontolerant rats in the cerebellar GABAAR alpha6 subunit is sufficient for increased alcohol-induced ataxia in rats homozygous for this mutation (alpha6-100QQ) and further increases alcohol sensitivity of tonic GABA currents (mediated by alpha6betadelta receptors) in cerebellar granule cells of alpha6-100QQ rats and in recombinant alpha6R100Qbeta3delta receptors. This provided the first direct evidence that these types of receptors mediate behavioral effects of ethanol. Furthermore, the behavioral alcohol antagonist Ro15-4513 specifically reverses ethanol enhancement on alpha4/6beta3delta receptors. Unexpectedly, native and recombinant alpha4/6beta3delta receptors bind the behavioral alcohol antagonist Ro15-4513 with high affinity and this binding is competitive with EtOH, suggesting a specific and mutually exclusive (competitive) ethanol/Ro15-4513 site, which explains the puzzling activity of Ro15-4513 as a behavioral alcohol antagonist. Our conclusion from these findings is that alcohol/Ro15-4513-sensitive GABAAR subtypes are important alcohol targets and that alcohol at relevant concentrations is more specific than previously thought. In this review, we discuss technical difficulties in expressing recombinant delta subunit-containing receptors in oocytes and mammalian cells that may have contributed to negative results and confusion. Not only because we have reproduced detailed positive results numerous times, and we and many others have built extensively on basic findings, but also because we explain and combine many previously puzzling results into a coherent and highly plausible paradigm on how alcohol exerts an important part of its action in the brain, we are confident about our findings and conclusions. However, many important open questions remain to be answered.

Differential effects of systemic ethanol administration on protein kinase cepsilon, gamma, and beta isoform expression, membrane translocation, and target phosphorylation: reversal by chronic ethanol exposure

Systemic ethanol administration alters protein kinase C (PKC) activity in brain, but the effects of ethanol on the expression and translocation of specific isoforms are unknown. Rats were administered ethanol (2 g/kg i.p.) or saline and PKC levels were measured in the cytosolic and membrane fractions by Western blot analysis. PKCepsilon expression was increased in the cytosol and decreased in the membrane (P2) fraction of cerebral cortex at 10 min. At 60 min, expression of PKCepsilon in the P2 fraction was increased by 42.2 +/- 12%, but cytosolic levels were unchanged. In contrast, PKCgamma in the P2 fraction was decreased 32.7 +/- 7% at 60 min but not at 10 min post-ethanol administration. PKCgamma levels in the cytosol were reduced at 10 min post-ethanol administration and unchanged at 60 min. PKCbeta expression was increased 36 +/- 10 and 144 +/- 52% in the P2 fraction both at 10 and 60 min post-ethanol administration, whereas cytosolic levels were unchanged. Serine phosphorylation of GABA(A) receptor beta-chain was reduced, and phosphorylation of N-methyl-d-aspartate receptor NR1 subunit was increased 60 min following ethanol administration. There was no effect of acute ethanol administration on PKC isoform levels in the hippocampus. Ethanol challenge did not alter PKC isoform expression in the P2 fraction of cerebral cortex following chronic ethanol administration. These findings suggest that acute ethanol administration alters PKC synthesis and translocation in an isoform and brain region specific manner that leads to alterations in serine phosphorylation of receptors. Furthermore, chronic ethanol administration prevents ethanol-induced alterations in PKC expression in the P2 fraction, where PKC interacts with ethanol-responsive ion channels.

Immature hippocampal neuronal networks do not develop tolerance to the excitatory actions of ethanol

Ethanol (EtOH) damages the hippocampus, a brain region that is involved in learning and memory processes. The mechanisms responsible for this effect of EtOH are not fully understood. We recently demonstrated that acute EtOH exposure potently stimulates oscillatory activity driven by the excitatory actions of GABA in the CA3 region of the neonatal rat hippocampus. This activity can be recorded during the growth spurt period as giant depolarizing potentials (GDPs). Here, we characterized the effects of prolonged EtOH exposure on GDPs. In the first study, we prepared hippocampal coronal slices from neonatal rats and exposed these to control artificial cerebrospinal fluid (ACSF) or ACSF plus 50 mM EtOH for 3-4 h. We then performed whole-cell patch-clamp electrophysiological recordings from CA3 pyramidal neurons, which revealed that tolerance to the GDP stimulating effects of EtOH did not occur after continuous exposure. In the second study, we exposed neonatal rats to air or air plus 1.9 g/dl EtOH in vapor chambers for 4h/day for 1 or 3 days (neonatal peak blood EtOH concentration = 40-45 mM). We then performed slice electrophysiological studies 24 h after the end of EtOH exposure and found that there was no statistically significant difference in the acute effect of 50 mM EtOH on GDP frequency in samples from neonates exposed to air or air plus EtOH. These findings indicate that EtOH persistently stimulates network-driven oscillatory activity in the developing hippocampus. We propose that the lack of adaptive response to continuous EtOH exposure could make immature neuronal networks particularly vulnerable to the actions of this agent.

Alcohol-related genes: contributions from studies with genetically engineered mice

Since 1996, nearly 100 genes have been studied for their effects related to ethanol in mice using genetic modifications including gene deletion, gene overexpression, gene knock-in, and occasionally by studying existing mutants. Nearly all such studies have concentrated on genes expressed in brain, and the targeted genes range widely in their function, including most of the principal neurotransmitter systems, several neurohormones, and a number of signaling molecules. We review 141 published reports of effects (or lack thereof) of 93 genes on responses to ethanol. While most studies have focused on ethanol self-administration and reward, and/or sedative effects, other responses studied include locomotor stimulation, anxiolytic effects, and neuroadaptation (tolerance, sensitization, withdrawal). About 1/4 of the engineered mutations increase self-administration, 1/3 decrease it, and about 40% have no significant effect. In many cases, the effects on self-administration are rather modest and/or depend on the specific experimental procedures. In some cases, genes in the background strains on which the mutant is placed are important for results. Not surprisingly, review of the systems affected further supports roles for serotonin, gamma-aminobutyric acid, opioids and dopamine, all of which have long been foci of alcohol research. Novel modulatory effects of protein kinase C and G protein-activated inwardly rectifying K+ (GIRK) channels are also suggested. Some newer research with cannabinoid systems is promising, and has led to ongoing clinical trials.