Deletion of the fyn-kinase gene alters behavioral sensitivity to ethanol

FYN Tyrosine Kinase Gene Polymorphisms in Alcohol-Dependent Korean Patients

Background

Alcohol use disorder (AUD) is a common disease with a high economic cost. The glutamate cell signaling pathway associated with alcohol has been reported to be one of the main pathologies of AUD. Previous studies have suggested that FYN, which is known to control NMDA glutamate receptor function through phosphorylation, might be associated with AUD.

Method

The present study included 354 subjects in the alcohol-dependent group and 139 subjects in the control group. The alcohol-dependent group was recruited from five university hospitals and a psychiatric hospital, and the control group was recruited from people who visited the university hospital for routine medical checkups in Korea. FYN gene single nucleotide polymorphism (SNPs) were selected based on SNP databases and previous studies of the FYN gene. Ten SNPs were genotyped using polymerase chain reaction-restriction fragment length polymorphism techniques.

Results

GG genotypes and G allele frequencies of rs1058134 in male AUD patients were significantly lower than in controls (p = 0.003). AA genotypes and A allele frequencies of rs12191154 in female AUD patients were significantly lower than in controls (p < 0.001, p = 0.003). In female AUD patients, AA genotypes and A allele frequencies of rs9387025 were significantly higher than in controls (p = 0.003).

Conclusion

These findings suggest that the FYN gene may be a candidate gene for AUD. This may help for the planning of further studies to determine the function of each SNP and the exact relationship between the FYN gene and AUD.

Lentiviral-mediated up-regulation of let-7d microRNA decreases alcohol intake through down-regulating the dopamine D3 receptor

Recent studies have shown that Lethal-7 (let-7) microRNA (miRNA) is involved in a wide range of psychiatric disorders such as anxiety, depression, schizophrenia, and cocaine addiction. However, the exact role of let-7d miRNA in regulating ethanol intake and preference remains to be elucidated. The aim of the present study was to clarify the role of accumbal let-7d in controlling ethanol-related behaviors in adult rats. For this purpose, stereotaxic injections of let-7d-overexpressing lentiviral vectors (LV) were administered bilaterally into the nucleus accumbens (Nacc) of Wistar rats. The ethanol-related behaviors were investigated using the two-bottle choice (TBC) access paradigm, in which the rats had access to 2.5, 5, and 10% ethanol solutions, the grid hanging test (GHT) and ethanol-induced loss-of-righting-reflex (LORR) test. The results showed that intra-accumbally administered let-7d-overexpressing LV significantly decreased ethanol intake and preference without having significant effects on body weight, consumption or preference for tastants (saccharin and quinine) or ethanol metabolism. Furthermore, accumbal let-7d increased resistance to ethanol-induced sedation in the GHT and LORR test. Most importantly, the data showed that the dopamine D3 receptor (D3R) was a candidate target of let-7d In fact, and using real time PCR, let-7d was found to directly target D3R mRNA to decrease its expression. Further analyses proved that D3R expression was negatively correlated with the levels of let-7d and ethanol-related behaviors parameters. Taken together, the data indicating that let-7d impaired ethanol-related behaviors by targeting D3R will open up new exciting possibilities and might provide potential therapeutic evidence for alcoholism.

Fyn Tyrosine Kinase as Harmonizing Factor in Neuronal Functions and Dysfunctions

Fyn is a non-receptor or cytoplasmatic tyrosine kinase (TK) belonging to the Src family kinases (SFKs) involved in multiple transduction pathways in the central nervous system (CNS) including synaptic transmission, myelination, axon guidance, and oligodendrocyte formation. Almost one hundred years after the original description of Fyn, this protein continues to attract extreme interest because of its multiplicity of actions in the molecular signaling pathways underlying neurodevelopmental as well as neuropathologic events. This review highlights and summarizes the most relevant recent findings pertinent to the role that Fyn exerts in the brain, emphasizing aspects related to neurodevelopment and synaptic plasticity. Fyn is a common factor in healthy and diseased brains that targets different proteins and shapes different transduction signals according to the neurological conditions. We will primarily focus on Fyn-mediated signaling pathways involved in neuronal differentiation and plasticity that have been subjected to considerable attention lately, opening the fascinating scenario to target Fyn TK for the development of potential therapeutic interventions for the treatment of CNS injuries and certain neurodegenerative disorders like Alzheimer’s disease.

Genetic association between −93A/G polymorphism in the Fyn kinase gene and alcohol dependence in Spanish men

Background

Fyn tyrosine kinase is a member of the Scr family that phosphorylates the NR2A and NR2B subunits of the NMDA receptors reducing the inhibitory effects of ethanol and therefore may regulate the individual sensitivity to ethanol.

Objectives

To investigate whether there is any relationship between the polymorphism at position −93 of the Fyn kinase gene and the susceptibility to develop alcoholism.

Methods

We studied the distribution of genotypes and alleles of the polymorphism −93A/G (137346 T/C) in the 5′ UTR region of the fyn gene in 207 male heavy drinkers (119 with alcohol dependence and 88 with alcohol abuse) and 100 control subjects from Castilla y León (Spain).

Results

The frequency of G allele carriers was higher in alcohol dependents than in alcohol abusers (47.9% vs 30.6%; p = 0.015; OR = 2.077; 95% CI 1.165–3.704).

Conclusion

Our results show that the −93G allele of Fyn kinase gene is associated with higher risk to develop alcohol dependence in Spanish men.

Nonphosphorylatable Src Ser75 Mutation Increases Ethanol Preference and Consumption in Mice

Src is highly expressed in CNS neurons and contributes not only to developmental proliferation and differentiation but also to high-order brain functions, such as those contributing to alcohol consumption. Src knock-out mice exhibit no CNS abnormalities, presumably due to compensation by other Src family kinases (SFKs), but have a shortened lifespan and osteopetrosis-associated defects, impeding investigations of the role of Src on behavior in adult mice. However, the Unique domain of Src differs from those in other SFKs and is phosphorylated by cyclin-dependent kinase 1 (Cdk1) and Cdk5 at Ser75, which influences its postmitotic function in neurons. Therefore, ethanol consumption in mice harboring nonphosphorylatable (Ser75Ala) or phosphomimetic (Ser75Asp) Src mutants was investigated. Mice harboring the Ser75Ala Src mutant, but not the Ser75Asp mutant, had a higher preference for and consumption of solutions containing 5% and 10% ethanol than wild-type mice. However, plasma ethanol concentrations and sensitivities to the sedative effects of ethanol were not different among the groups. In mice harboring the Ser75Ala Src mutant, the activity of Rho-associated kinase (ROCK) in the striatum was significantly lower and Akt Ser473 phosphorylation was significantly higher than in wild-type mice. These results suggest that Src regulates voluntary ethanol drinking in a manner that depends on Ser75 phosphorylation.

Src-dependent phosphorylation of μ-opioid receptor at Tyr336 modulates opiate withdrawal

Opiate withdrawal/negative reinforcement has been implicated as one of the mechanisms for the progression from impulsive to compulsive drug use. Increase in the intracellular cAMP level and protein kinase A (PKA) activities within the neurocircuitry of addiction has been a leading hypothesis for opiate addiction. This increase requires the phosphorylation of μ‐opioid receptor (MOR) at Tyr³³⁶ by Src after prolonged opiate treatment in vitro. Here, we report that the Src‐mediated MOR phosphorylation at Tyr³³⁶ is a prerequisite for opiate withdrawal in mice. We observed the recruitment of Src in the vicinity of MOR and an increase in phosphorylated Tyr³³⁶ (pY336) levels during naloxone‐precipitated withdrawal. The intracerebroventricular or stereotaxic injection of a Src inhibitor (AZD0530), or Src shRNA viruses attenuated pY336 levels, and several somatic withdrawal signs. This was also observed in Fyn^−/− mice. The stereotaxic injection of wild‐type MOR, but not mutant (Y336F) MOR, lentiviruses into the locus coeruleus of MOR^−/− mice restored somatic withdrawal jumping. Regulating pY336 levels during withdrawal might be a future target for drug development to prevent opiate addictive behaviors.

Implication of Genes for the N-Methyl-D-Aspartate (NMDA) Receptor in Substance Addictions

Drug dependence is a chronic brain disease with harmful consequences for both individual users and society. Glutamate is a primary excitatory neurotransmitter in the brain, and both in vivo and in vitro experiments have implicated N-methyl-D-aspartate (NMDA) receptor, a glutamate receptor, as an element in various types of addiction. Recent findings from genetics-based approaches such as genome-wide linkage, candidate gene association, genome-wide association (GWA), and next-generation sequencing have demonstrated the significant association of NMDA receptor subunit genes such as GluN3A, GluN2B, and GluN2A with various addiction-related phenotypes. Of these genes, GluN3A has been the most studied, and it has been revealed to play crucial roles in the etiology of addictions. In this communication, we provide an updated view of the genetic effects of NMDA receptor subunit genes and their functions in the etiology of addictions based on the findings from investigation of both common and rare variants as well as SNP-SNP interactions. To better understand the molecular mechanisms underlying addiction-related behaviors and to promote the development of specific medicines for the prevention and treatment of addictions, current efforts aim not only to identify more causal variants in NMDA receptor subunits by using large independent samples but also to reveal the molecular functions of these variants in addictions.

Effects of selection for ethanol preference on gene expression in the nucleus accumbens of HS-CC mice

Previous studies on changes in murine brain gene expression associated with the selection for ethanol preference have used F₂ intercross or heterogeneous stock (HS) founders, derived from standard laboratory strains. However, these populations represent only a small proportion of the genetic variance available in Mus musculus. To investigate a wider range of genetic diversity, we selected mice for ethanol preference using an HS derived from the eight strains of the collaborative cross. These HS mice were selectively bred (four generations) for high and low ethanol preference. The nucleus accumbens shell of naive S₄ mice was interrogated using RNA sequencing (RNA-Seq). Gene networks were constructed using the weighted gene coexpression network analysis assessing both coexpression and cosplicing. Selection targeted one of the network coexpression modules (greenyellow) that was significantly enriched in genes associated with receptor signaling activity including Chrna7, Grin2a, Htr2a and Oprd1. Connectivity in the module as measured by changes in the hub nodes was significantly reduced in the low preference line. Of particular interest was the observation that selection had marked effects on a large number of cell adhesion molecules, including cadherins and protocadherins. In addition, the coexpression data showed that selection had marked effects on long non-coding RNA hub nodes. Analysis of the cosplicing network data showed a significant effect of selection on a large cluster of Ras GTPase-binding genes including Cdkl5, Cyfip1, Ndrg1, Sod1 and Stxbp5. These data in part support the earlier observation that preference is linked to Ras/Mapk pathways.

Alcohol-dependent molecular adaptations of the NMDA receptor system

Phenotypes such as motivation to consume alcohol, goal-directed alcohol seeking and habit formation take part in mechanisms underlying heavy alcohol use. Learning and memory processes greatly contribute to the establishment and maintenance of these behavioral phenotypes. The N-methyl-d-aspartate receptor (NMDAR) is a driving force of synaptic plasticity, a key cellular hallmark of learning and memory. Here, we describe data in rodents and humans linking signaling molecules that center around the NMDARs, and behaviors associated with the development and/or maintenance of alcohol use disorder (AUD). Specifically, we show that enzymes that participate in the regulation of NMDAR function including Fyn kinase as well as signaling cascades downstream of NMDAR including calcium/calmodulin-dependent protein kinase II (CamKII), the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and the mammalian target of rapamycin complex 1 (mTORC1) play a major role in mechanisms underlying alcohol drinking behaviors. Finally, we emphasize the brain region specificity of alcohol's actions on the above-mentioned signaling pathways and attempt to bridge the gap between the molecular signaling that drive learning and memory processes and alcohol-dependent behavioral phenotypes. Finally, we present data to suggest that genes related to NMDAR signaling may be AUD risk factors.

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.

Fyn-dependent gene networks in acute ethanol sensitivity

Studies in humans and animal models document that acute behavioral responses to ethanol are predisposing factor for the risk of long-term drinking behavior. Prior microarray data from our laboratory document strain- and brain region-specific variation in gene expression profile responses to acute ethanol that may be underlying regulators of ethanol behavioral phenotypes. The non-receptor tyrosine kinase Fyn has previously been mechanistically implicated in the sedative-hypnotic response to acute ethanol. To further understand how Fyn may modulate ethanol behaviors, we used whole-genome expression profiling. We characterized basal and acute ethanol-evoked (3 g/kg) gene expression patterns in nucleus accumbens (NAC), prefrontal cortex (PFC), and ventral midbrain (VMB) of control and Fyn knockout mice. Bioinformatics analysis identified a set of Fyn-related gene networks differently regulated by acute ethanol across the three brain regions. In particular, our analysis suggested a coordinate basal decrease in myelin-associated gene expression within NAC and PFC as an underlying factor in sensitivity of Fyn null animals to ethanol sedation. An in silico analysis across the BXD recombinant inbred (RI) strains of mice identified a significant correlation between Fyn expression and a previously published ethanol loss-of-righting-reflex (LORR) phenotype. By combining PFC gene expression correlates to Fyn and LORR across multiple genomic datasets, we identified robust Fyn-centric gene networks related to LORR. Our results thus suggest that multiple system-wide changes exist within specific brain regions of Fyn knockout mice, and that distinct Fyn-dependent expression networks within PFC may be important determinates of the LORR due to acute ethanol. These results add to the interpretation of acute ethanol behavioral sensitivity in Fyn kinase null animals, and identify Fyn-centric gene networks influencing variance in ethanol LORR. Such networks may also inform future design of pharmacotherapies for the treatment and prevention of alcohol use disorders.

The neurobiology of alcohol consumption and alcoholism: an integrative history

Studies of the neurobiological predisposition to consume alcohol (ethanol) and to transition to uncontrolled drinking behavior (alcoholism), as well as studies of the effects of alcohol on brain function, started a logarithmic growth phase after the repeal of the 18th Amendment to the United States Constitution. Although the early studies were primitive by current technological standards, they clearly demonstrated the effects of alcohol on brain structure and function, and by the end of the 20th century left little doubt that alcoholism is a "disease" of the brain. This review traces the history of developments in the understanding of ethanol's effects on the most prominent inhibitory and excitatory systems of brain (GABA and glutamate neurotransmission). This neurobiological information is integrated with knowledge of ethanol's actions on other neurotransmitter systems to produce an anatomical and functional map of ethanol's properties. Our intent is limited in scope, but is meant to provide context and integration of the actions of ethanol on the major neurobiologic systems which produce reinforcement for alcohol consumption and changes in brain chemistry that lead to addiction. The developmental history of neurobehavioral theories of the transition from alcohol drinking to alcohol addiction is presented and juxtaposed to the neurobiological findings. Depending on one's point of view, we may, at this point in history, know more, or less, than we think we know about the neurobiology of alcoholism.

Behavioral actions of alcohol: phenotypic relations from multivariate analysis of mutant mouse data

Behavioral studies on genetically diverse mice have proven powerful for determining relationships between phenotypes and have been widely used in alcohol research. Most of these studies rely on naturally occurring genetic polymorphisms among inbred strains and selected lines. Another approach is to introduce variation by engineering single-gene mutations in mice. We have tested 37 different mutant mice and their wild-type controls for a variety (31) of behaviors and have mined this data set by K-means clustering and analysis of correlations. We found a correlation between a stress-related response (activity in a novel environment) and alcohol consumption and preference for saccharin. We confirmed several relationships detected in earlier genetic studies, including positive correlation of alcohol consumption with saccharin consumption and negative correlations with conditioned taste aversion and alcohol withdrawal severity. Introduction of single-gene mutations either eliminated or greatly diminished these correlations. The three tests of alcohol consumption used (continuous two-bottle choice and two limited access tests: drinking in the dark and sustained high alcohol consumption) share a relationship with saccharin consumption, but differ from each other in their correlation networks. We suggest that alcohol consumption is controlled by multiple physiological systems where single-gene mutations can disrupt the networks of such systems.

Src family kinases: modulators of neurotransmitter receptor function and behavior

Src family kinases (SFKs) are non-receptor-type protein tyrosine kinases that were originally identified as the products of proto-oncogenes and were subsequently implicated in the regulation of cell proliferation and differentiation in the developing mammalian brain. Recent studies using transgenic mouse models have demonstrated that SFKs that are highly expressed in the adult brain regulate neuronal plasticity and behavior through tyrosine phosphorylation of key substrates such as neurotransmitter receptors. Here, we provide an overview of these recent studies, as well as discussing how modulation of the endocytosis of neurotransmitter receptors by SFKs contributes, in part, to this regulation. Deregulation of SFK-dependent tyrosine phosphorylation of such substrates might underlie certain brain disorders.

Ethanol-induced increase in Fyn kinase activity in the dorsomedial striatum is associated with subcellular redistribution of protein tyrosine phosphatase α

In vivo exposure of rodents to ethanol leads to a long-lasting increase in Fyn kinase activity in the dorsomedial striatum (DMS). In this study, we set out to identify a molecular mechanism that contributes to the enhancement of Fyn activity in response to ethanol in the DMS. Protein tyrosine phosphatase α (PTPα) positively regulates the activity of Fyn, and we found that repeated systemic administration or binge drinking of ethanol results in an increase in the synaptic localization of PTPα in the DMS, the same site where Fyn resides. We also demonstrate that binge drinking of ethanol leads to an increase in Fyn activity and to the co-localization of Fyn and PTPα in lipid rafts in the DMS. Finally, we show that the level of tyrosine phosphorylated (and thus active) PTPα in the synaptic fractions is increased in response to contingent or non-contingent exposure of rats to ethanol. Together, our results suggest that the redistribution of PTPα in the DMS into compartments where Fyn resides is a potential mechanism by which the activity of the kinase is increased upon ethanol exposure. Such neuroadaptations could be part of a mechanism that leads to the development of excessive ethanol consumption.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

BK channel and alcohol, a complicated affair

Alcohol is a fast acting molecule that alters behavior within a few minutes of absorption. Its rapid behavioral impact suggests early action on ion channels. Of all voltage-gated potassium ion channels, BK channels, a subcategory of potassium channels characterized by their large unitary conductance, and by their capacity of being activated synergistically by membrane potential and intracellular free calcium, are unique due to their high sensitivity to alcohol. In this review, we discuss BK channels structure and function, and how they help us understand the various ways BK channel mediates alcohol's effects on neuronal function and on behavior in the striatum.

Mice lacking Gad2 show altered behavioral effects of ethanol, flurazepam and gabaxadol

Gamma-aminobutyric acid (GABA) is synthesized in brain by two isoforms of glutamic acid decarboxylase (Gad), Gad1 and Gad2. Gad1 provides most of the GABA in brain, but Gad2 can be rapidly activated in times of high GABA demand. Mice lacking Gad2 are viable whereas deletion of Gad1 is lethal. We produced null mutant mice for Gad2 on three different genetic backgrounds: predominantly C57BL/6J and one or two generations of backcrossing to 129S1/SvimJ (129N1, 129N2). We used these mice to determine if actions of alcohol are regulated by synthesis of GABA from this isoform. We also studied behavioral responses to a benzodiazepine (flurazepam) and a GABAA receptor agonist (gabaxadol). Deletion of Gad2 increased ethanol palatability and intake and slightly reduced the severity of ethanol-induced withdrawal, but these effects depended strongly on genetic background. Mutant mice on the 129N2 background showed the above three ethanol behavioral phenotypes, but the C57BL/6J inbred background did not show any of these phenotypes. Effects on ethanol consumption also depended on the test as the mutation did not alter consumption in limited access models. Deletion of Gad2 reduced the effect of flurazepam on motor incoordination and increased the effect of extrasynaptic GABAA receptor agonist gabaxadol without changing the duration of loss of righting reflex produced by these drugs. These results are consistent with earlier proposals that deletion of Gad2 (on 129N2 background) reduces synaptic GABA but also suggest changes in extrasynaptic receptor function.

Sensitivity and tolerance to the hypnotic and ataxic effects of ethanol in adolescent and adult C57BL/6J and DBA/2J mice

BACKGROUND

There is considerable research examining differences in adolescent and adult sensitivity and tolerance to ethanol related behavioral phenotypes. However, the available published data has almost exclusively assessed these behaviors in outbred rats. The present study was conducted using the alcohol preferring inbred mouse strain C57BL/6J (B6) and the alcohol nonpreferring inbred mouse strain DBA/2J (D2) to determine if differences in the sedative and ataxic effects of ethanol exist between adolescents and adults, and to determine whether there are any genetic influences involved therein.

METHODS

Adolescent and adult mice of each sex and genotype were given intraperitoneal (i.p.) injections of ethanol (1.5, 1.75, or 4.0 g/kg) or saline and assessed for the loss of righting reflex (LORR) or hind footslips on the balance beam apparatus. These animals were then tested for the development of tolerance to these behaviors on subsequent days.

RESULTS

Despite evident pharmacokinetic differences, D2 adolescents were found to be relatively less sensitive to ethanol's hypnotic actions than their adult D2 counterparts. Adolescent and adult B6 animals did not differ. Furthermore, although adult animals appeared to develop significantly greater degrees of tolerance to ethanol-induced hypnosis compared with adolescents, these effects were likely in part related to differences in ethanol absorption/metabolism across time. Taking into account pharmacokinetic differences and the overall poor performance of male adults, adolescent animals were found to be equally if not more sensitive to the motor incoordinating (ataxic) effects of ethanol. Overall, tolerance to these effects varied by age and genotype but appeared to be related to changes in ethanol pharmacokinetics rather than strict behavioral sensitivity.

CONCLUSION

The current work suggests that adolescent B6 and D2 inbred mice exhibit ontogenetic differences in sensitivity to ethanol's hypnotic and ataxic effects. Importantly, in some cases age differences emerge as a function of differential ethanol pharmacokinetics. These results extend the current literature examining this critical developmental period in mice and illustrate the benefits of comparing ethanol related developmental differences in different genetic mouse populations.

Motor impairment: a new ethanol withdrawal phenotype in mice

Alcoholism is a complex disorder with genetic and environmental risk factors. The presence of withdrawal symptoms is one criterion for alcohol dependence. Genetic animal models have followed a reductionist approach by quantifying various effects of ethanol withdrawal separately. Different ethanol withdrawal symptoms may have distinct genetic etiologies, and therefore differentiating distinct neurobiological mechanisms related to separate signs of withdrawal would increase our understanding of various aspects of the complex phenotype. This study establishes motor incoordination as a new phenotype of alcohol withdrawal in mice. Mice were made physically dependent on ethanol by exposure to ethanol vapor for 72 h. The effects of ethanol withdrawal in mice from different genetic backgrounds were measured on the accelerating rotarod, a simple motor task. Ethanol withdrawal disrupted accelerating rotarod behavior in mice. The disruptive effects of withdrawal suggest a performance rather than a learning deficit. Inbred strain comparisons suggest genetic differences in magnitude of this withdrawal phenotype. The withdrawal-induced deficits were not correlated with the selection response difference in handling convulsion severity in selectively bred Withdrawal Seizure-Prone and Withdrawal Seizure-Resistant lines. The accelerating rotarod seems to be a simple behavioral measure of ethanol withdrawal that is suitable for comparing genotypes.

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.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.

Role of endocannabinoids in alcohol consumption and intoxication: studies of mice lacking fatty acid amide hydrolase

Endocannabinoid signaling plays the important role in regulation of ethanol intake. Fatty acid amide hydrolase (FAAH) is a key membrane protein for metabolism of endocannabinoids, including anandamide, and blockade of FAAH increases the level of anandamide in the brain. To determine if FAAH regulates ethanol consumption, we studied mutant mice with deletion of the FAAH gene. Null mutant mice showed higher preference for alcohol and voluntarily consumed more alcohol than wild-type littermates. There was no significant difference in consumption of sweet or bitter solutions. To determine the specificity of FAAH for ethanol intake, we studied additional ethanol-related behaviors. There were no differences between null mutant and wild-type mice in severity of ethanol-induced acute withdrawal, conditioned taste aversion to alcohol, conditioned place preference, or sensitivity to hypnotic effect of ethanol. However, null mutant mice showed shorter duration of loss of righting reflex induced by low doses of ethanol (3.2 and 3.4 g/kg) and faster recovery from motor incoordination induced by ethanol. All three behavioral phenotypes (increased preference for ethanol, decreased sensitivity to ethanol-induced sedation, and faster recovery from ethanol-induced motor incoordination) seen in mutant mice were reproduced in wild-type mice by injection of a specific inhibitor of FAAH activity--URB597. These data suggest that increased endocannabinoid signaling increased ethanol consumption owing to decreased acute ethanol intoxication.

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.

Candidate genes and their regulatory elements: alcohol preference and tolerance

QTL analysis of behavioral traits and mouse brain gene expression studies were combined to identify candidate genes involved in the traits of alcohol preference and acute functional alcohol tolerance. The systematic application of normalization and statistical analysis of differential gene expression, behavioral and expression QTL location, and informatics methodologies resulted in identification of 8 candidate genes for the trait of alcohol preference and 22 candidate genes for acute functional tolerance. Pathway analysis, combined with clustering by ontology, indicated the importance of transcriptional regulation and DNA and protein binding elements in the acute functional tolerance trait, and protein kinases and intracellular signal transduction elements in the alcohol preference trait. A rudimentary search for transcription control elements that could indicate coregulation of the panels of candidate genes produced modest results, implicating SMAD-3 in the regulation of four of the eight candidate genes for alcohol preference. However, the realization of the many caveats related to transcription factor binding site analysis, and attempts to correlate between transcription factor binding and function, forestalled any definitive global analysis of transcriptional control of differentially expressed candidate genes.

Complex Genetics of Interactions of Alcohol and CNS Function and Behavior

This work summarizes the proceedings of a symposium at the 2004 RSA Meeting in Vancouver, Canada. The organizers were R. W. Williams and D. B. Matthews; the Chair was M. F. Miles. The presentations were (1) WebQTL: A resource for analysis of gene expression variation and the genetic dissection of alcohol related phenotypes, by E. J. Chesler, (2) The marriage of microarray and qtl analyses: what's to gain, by J. K. Belknap, (3) Use of WebQTL to identify QTLs associated with footshock stress and ethanol related behaviors, by D. B. Matthews, (4) A high throughput strategy for the detection of quantitative trait genes, by R. J. Hitzemann, and (5) The use of gene arrays in conjunction with transgenic and selected animals to understand anxiety in alcoholism, by. B. Tabakoff.

Identifikation von Risikogenen für Alkoholabhängigkeit

Alcohol dependence is one of the most common addictive diseases and known to be in part genetically transmitted, based on an oligogenic background in which each gene involved contributes only little to the resulting phenotype. Besides influencing other signal transduction mechanisms, alcohol specifically inhibits the NMDA signaling cascade, which mediates the excitatory effects of glutamate in the brain. Target molecules, sensitive to ethanol, include the NMDA receptors as well as downstream molecules of the glutamatergic system, glutamate transporters, and associated regulatory proteins. Adaptive processes of the glutamatergic system during chronic alcohol consumption may play a major role for later development of reward symptoms. Candidate gene studies, including association studies and animal models, are powerful and sensitive for detecting oligogenic effects and thus important to alcoholism research.

Pharmacological manipulation of CB1 receptor function alters development of tolerance to alcohol

AIMS

The current study investigated the efficacy of CB1 receptor-targeted drugs on the development and expression of tolerance to alcohol (EtOH).

METHODS

An EtOH-inhalation model was used to induce tolerance, as measured by EtOH-induced sedation and hypothermia after a 24 h withdrawal period. Two drug treatment procedures, (i) co-treatment with EtOH and (ii) acute drug administration following chronic EtOH treatment, were used to test the efficacy of CB1 receptor manipulations on EtOH tolerance.

RESULTS

The effects of the CB1 receptor agonist CP-55,940 varied depending on paradigm and behavioural measure. Chronic CP-55,940 co-treatment blocked tolerance to EtOH-induced hypothermia but not to the sedative effect (sleep time) in EtOH-exposed mice. However, chronic CP-55,940 administration alone resulted in tolerance to the sedative effect of a challenge dose of EtOH in control mice. Acute CP-55,940 administration after chronic alcoholization blocked the development of tolerance to EtOH-induced sedation compared to the EtOH alone exposed group, but induced tolerance to the hypothermic effects of EtOH in control mice. Chronic blockade of CB1 receptor function by SR141716A resulted in tolerance to both the sedative and hypothermic effects of EtOH in control mice, but had no effect on EtOH-exposed mice.

CONCLUSIONS

The data support a role for the endocannabinoid (EC) system in EtOH tolerance/dependence and suggest that drugs targeted against EC system could be therapeutically useful in treating alcohol-related disorders.

Intracellular signaling pathways that regulate behavioral responses to ethanol

Recent evidence indicates that ethanol modulates the function of specific intracellular signaling cascades, including those that contain cyclic adenosine 3', 5'-monophosphate (cAMP)-dependent protein kinase A (PKA), protein kinase C (PKC), the tyrosine kinase Fyn, and phospholipase D (PLD). In some cases, the specific components of these cascades appear to mediate the effects of ethanol, whereas other components indirectly modify responses to ethanol. Studies utilizing selective inhibitors and genetically modified mice have identified specific isoforms of proteins involved in responses to ethanol. The effects of ethanol on neuronal signaling appear restricted to certain brain regions, partly due to the restricted distribution of these proteins. This likely contributes specificity to ethanol's actions on behavior. This review summarizes recent work on ethanol and intracellular signal transduction, emphasizing studies that have identified specific molecular events that underlie behavioral responses to ethanol.

Gene expression in animals with different acute responses to ethanol

The genetic and environmental contributions to differences in response to ethanol have been examined widely using inbred strains, selected lines and genetically engineered (transgenic and 'knock-out') animals. In addition, recombinant inbred strains have been used to identify QTLs (chromosomal regions) associated with particular responses to ethanol. If the polymorphism that underlies such a QTL is localized within the regulatory region of a gene, it could alter the level or stability of the gene product (transcript). This possibility can be addressed by measuring mRNA levels in brains (or other tissue) of inbred or selected lines of animals using DNA microarray technology. In this paper, we review microarray studies conducted in animals that differ in their responses to ethanol. The results of these studies point out the critical nature of the experimental design, statistical analyses and 'filtering' procedures for producing interpretable data and identifying candidate genes. In particular, the determination of differentially expressed genes between selected lines of animals, and the localization of the differentially expressed genes within QTLs for the selected phenotype, dramatically increases the probability of identifying genes that contribute to that phenotype through differential expression. Microarray analysis can also be used to assess changes in gene expression that accompany transgene introduction and/or gene 'knock-out', which may modulate the influence of the targeted gene on behaviour.

Over-expression of the fyn-kinase gene reduces hypnotic sensitivity to ethanol in mice

Our previous work indicated a role for fyn-kinase in mediating several ethanol- and GABA(A) agonist-mediated behaviors. In the present work we investigate behavioral sensitivity to ethanol and several GABA(A) compounds in mice that over-express fyn-kinase in forebrain to further characterize the role of this non-receptor tyrosine kinase in the mediation of ethanol sensitivity. Transgenic mice over-expressing fyn-kinase were tested for sensitivity to ethanol-induced loss of righting reflex and ethanol preference drinking using a two-bottle choice drinking paradigm. Loss of righting reflex induced by 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; GABA(A) agonist) and etomidate (GABA(A) positive allosteric modulator) were also assessed. Fyn over-expressing mice exhibited shorter durations of ethanol-induced loss of righting reflex in the absence of differences in the rate of blood ethanol clearance, and exhibited reduced ethanol preference drinking. The genotypes did not differ in initial sensitivity to ethanol-induced loss of righting reflex suggesting development of greater acute tolerance to this ethanol action. Fyn over-expressing and wild-type mice also did not differ in sensitivity to loss of righting reflex induced by THIP and etomidate. The present results suggest regional specificity for fyn-kinase in the modulation of ethanol and GABAergic behavioral sensitivity. Fyn-kinase over-expression in forebrain structures modulates ethanol's hypnotic actions, as well as ethanol preference and consumption. Moreover, fyn over-expression in forebrain does not alter hypnotic sensitivity to THIP or etomidate, supporting data from fyn null mutant mice suggesting that cerebellar structures mediate the hypnotic actions of these GABAergic compounds.

γ-Aminobutyric acid A receptor subunit mutant mice: new perspectives on alcohol actions

gamma-Aminobutyric acid A (GABA(A)) receptors are believed to mediate a number of alcohol's behavioral actions. Because the subunit composition of GABA(A) receptors determines receptor pharmacology, behavioral sensitivity to alcohol (ethanol) may depend on which subunits are present (or absent). A number of knock-out and/or transgenic mouse models have been developed (alpha1, alpha2, alpha5, alpha6, beta2, beta3, gamma2S, gamma2L, delta) and tested for behavioral sensitivity to ethanol. Here we review the current GABA(A) receptor subunit knock-out and transgenic literature for ethanol sensitivity, and integrate these results into those obtained using quantitative trait loci (QTL) analysis and gene expression assays. Converging evidence from these three approaches support the notion that different behavioral actions of ethanol are mediated by specific subunits, and suggest that new drugs that target specific GABA(A) subunits may selectively alter some behavioral actions of ethanol, without altering others. Current data sets provide strongest evidence for a role of alpha1-subunits in ethanol-induced loss of righting reflex, and alpha5-subunits in ethanol-stimulated locomotion. However, three-way validation is hampered by the incomplete behavioral characterization of many of the mutant mice, and additional subunits are likely to be linked to alcohol actions as behavioral testing progresses.

Fyn kinase and NR2B-containing NMDA receptors regulate acute ethanol sensitivity but not ethanol intake or conditioned reward

BACKGROUND

The tyrosine kinase Fyn previously has been shown to play a key role in mediating acute tolerance to ethanol. Recently, we found that the compartmentalization of Fyn to the NR2B subunit of the NMDA receptor (NMDAR) in the hippocampus regulates Fyn phosphorylation of NR2B in response to ethanol, which mediates the acute tolerance of NMDAR to ethanol inhibition in hippocampal slices. In this study we determined, first, whether acute tolerance to ethanol inhibition is mediated via NR2B-containing NMDARs in vivo and, second, whether the increase in acute sensitivity to ethanol in the Fyn-/- mice influences ethanol consumption or ethanol's conditioned rewarding effects.

METHODS

A loss of righting reflex test was used to study the acute/sedative effects of ethanol after intraperitoneal injections of sedative doses of ethanol. Conditioned place preference was used to study the rewarding properties of ethanol. The two-bottle choice protocol was used to measure oral ethanol self-administration and preference as described previously.

RESULTS

We found that systemic injection of the NR2B-containing NMDAR selective antagonist, ifenprodil, abolished the differences between Fyn+/+ and Fyn-/- mice in sensitivity to the acute sedative effects of ethanol. Moreover, we found that Fyn-/- and Fyn+/+ mice did not differ in their voluntary ethanol consumption or in the rewarding properties of ethanol.

CONCLUSIONS

Our results suggest that the interaction between Fyn and NR2B mediates the acute sedative effects of ethanol, and that alteration in acute ethanol sensitivity does not necessarily correlate with levels of ethanol consumption or the rewarding properties of ethanol.

Deletion of the fyn-kinase gene alters sensitivity to GABAergic drugs: dependence on beta2/beta3 GABAA receptor subunits

Tyrosine phosphorylation can modulate GABA(A) receptor function, and deletion of the fyn-kinase gene alters GABAergic function in olfactory bulb neurons, as reported by Kitazawa, Yagi, Miyakawa, Niki, and Kawai (J Neurophysiol 1998;79:137-142). Our goal was to determine whether fyn gene deletion altered behavioral and functional actions of compounds that act on GABA(A) receptors. Such evidence might suggest a role for fyn-kinase in modulating GABA(A) receptor function, possibly via direct interactions between the kinase and receptor. Using the loss of righting reflex test, we found that null mutants were less sensitive to the hypnotic effects of THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol), a GABA(A) receptor agonist. Subunit specificity was suggested by the observation that null mutants were also less sensitive to the hypnotic effects of etomidate, a GABAergic compound that is selective for receptors possessing beta2 and/or beta3 receptor subunits. The genotypes did not differ in sensitivity to zolpidem, an alpha1-selective GABAergic drug. GABA(A) receptor functional assays ((36)Cl(-) influx) supported our behavioral results; the actions of the GABA(A) agonists, THIP and muscimol, were reduced in the cerebellar membranes of fyn-null mutant mice. Importantly, similar results were seen with etomidate. Binding of [(3)H]flunitrazepam supported the idea that this is due to a decrease in functional GABA(A) receptor density. These data suggest that fyn-kinase may alter the function of GABA(A) receptors, perhaps via actions on beta2 and/or beta3 receptor subunits.