Drd2 expression in the high alcohol-preferring and low alcohol-preferring mice

Unveiling the power of optimism: Exploring behavioral and neuromolecular correlates of alcohol seeking and drinking in rats with biased judgement

Alcohol use disorder (AUD) is a common psychiatric condition with substantial global mortality. Despite extensive research into its pathophysiology, the cognitive predispositions driving alcohol dependence are less understood. This study explores whether biased cognition, specifically traits of optimism and pessimism, predicts susceptibility to alcohol-seeking behaviors using an animal model. Rats were initially tested for judgement bias through Ambiguous Cue Interpretation tests. Those identified as 'optimistic' or 'pessimistic' were further examined for their tendency to escalate alcohol intake using the intermittent access 2-bottle choice (2BC) paradigm. Additionally, we assessed how judgement bias influenced the development of compulsive alcohol-seeking behavior in a Seeking-Taking (ST) and Seeking-Taking Punishment tasks, alcohol-seeking motivation in the Progressive Ratio Schedule of Reinforcement paradigm, the speed of extinction, and reinstatement after abstinence. Neurochemical analyses were conducted to investigate trait-specific differences in neurotransmitter-related gene expression and receptor densities in the brain. We used TaqMan Gene Expression Array Cards to analyze expression levels of genes linked to serotonergic, dopaminergic, glutamatergic, and GABAergic pathways, and alcohol metabolism in various brain regions. Receptor densities for 5-HT1A, 5-HT2A, and D2 were measured using autoradiography analysis. Behaviorally, 'optimistic' rats showed significantly lower alcohol consumption in the 2BC paradigm compared to 'pessimistic' rats. This lowered intake correlated with decreased monoamine oxidase-A (Maoa) expression in the medial prefrontal cortex (mPFC) and increased metabotropic glutamate receptor 2 (Grm2) expression in the amygdala (Amy). Additionally, we observed significant interactions between judgement bias and alcohol intake in the expression of several genes in the mPFC, nucleus accumbens (Nacc), orbitofrontal cortex (OFC), and Amy, as well as in 5-HT2A receptor binding in the Nacc. Overall, these results suggest that optimism is linked to lower alcohol consumption and related neurochemical changes, indicating a potential cognitive mechanism in AUD risk.

Identification of the Risk Genes Associated With Vulnerability to Addiction: Major Findings From Transgenic Animals

Understanding risk factors for substance use disorders (SUD) can facilitate medication development for SUD treatment. While a rich literature exists discussing environmental factors that influence SUD, fewer articles have focused on genetic factors that convey vulnerability to drug use. Methods to identify SUD risk genes include Genome-Wide Association Studies (GWAS) and transgenic approaches. GWAS have identified hundreds of gene variants or single nucleotide polymorphisms (SNPs). However, few genes identified by GWAS have been verified by clinical or preclinical studies. In contrast, significant progress has been made in transgenic approaches to identify risk genes for SUD. In this article, we review recent progress in identifying candidate genes contributing to drug use and addiction using transgenic approaches. A central hypothesis is if a particular gene variant (e.g., resulting in reduction or deletion of a protein) is associated with increases in drug self-administration or relapse to drug seeking, this gene variant may be considered a risk factor for drug use and addiction. Accordingly, we identified several candidate genes such as those that encode dopamine D₂ and D₃ receptors, mGluR₂, M₄ muscarinic acetylcholine receptors, and α₅ nicotinic acetylcholine receptors, which appear to meet the risk-gene criteria when their expression is decreased. Here, we describe the role of these receptors in drug reward and addiction, and then summarize major findings from the gene-knockout mice or rats in animal models of addiction. Lastly, we briefly discuss future research directions in identifying addiction-related risk genes and in risk gene-based medication development for the treatment of addiction.

Disentangling the diverse roles of dopamine D2 receptors in striatal function and behavior

Dopamine D2 receptors (D2Rs) mediate many of the actions of dopamine in the striatum, ranging from movement to the effortful pursuit of reward. Yet despite significant advances in linking D2Rs to striatal functions with pharmacological and genetic strategies in animals, how dopamine orchestrates its myriad actions on different cell populations -each expressing D2Rs- remains unclear. Furthermore, brain imaging and genetic studies in humans have consistently associated striatal D2R alterations with various neurological and neuropsychiatric disorders, but how and which D2Rs are involved in each case is poorly understood. Therefore, a critical first step is to engage in a refined and systematic investigation of the impact of D2R function on specific striatal cells, circuits, and behaviors. Here, I will review recent efforts, primarily in animal models, aimed at unlocking the complex and heterogeneous roles of D2Rs in striatum.

Rodent models and mechanisms of voluntary binge-like ethanol consumption: Examples, opportunities, and strategies for preclinical research

Binge ethanol consumption has widespread negative consequences for global public health. Rodent models offer exceptional power to explore the neurobiology underlying and affected by binge-like drinking as well as target potential prevention, intervention, and treatment strategies. An important characteristic of these models is their ability to consistently produce pharmacologically-relevant blood ethanol concentration. This review examines the current available rodent models of voluntary, pre-dependent binge-like ethanol consumption and their utility in various research strategies. Studies have demonstrated that a diverse array of neurotransmitters regulate binge-like drinking, resembling some findings from other drinking models. Furthermore, repeated binge-like drinking recruits neuroadaptive mechanisms in mesolimbocortical reward circuitry. New opportunities that these models offer in the current context of mechanistic research are also discussed.

Frizzled3 Controls Axonal Polarity and Intermediate Target Entry during Striatal Pathway Development

The striatum is a large brain nucleus with an important role in the control of movement and emotions. Medium spiny neurons (MSNs) are striatal output neurons forming prominent descending axon tracts that target different brain nuclei. However, how MSN axon tracts in the forebrain develop remains poorly understood. Here, we implicate the Wnt binding receptor Frizzled3 in several uncharacterized aspects of MSN pathway formation [i.e., anterior-posterior guidance of MSN axons in the striatum and their subsequent growth into the globus pallidus (GP), an important (intermediate) target]. In Frizzled3 knock-out mice, MSN axons fail to extend along the anterior-posterior axis of the striatum, and many do not reach the GP. Wnt5a acts as an attractant for MSN axons in vitro, is expressed in a posterior high, anterior low gradient in the striatum, and Wnt5a knock-out mice phenocopy striatal anterior-posterior defects observed in Frizzled3 mutants. This suggests that Wnt5a controls anterior-posterior guidance of MSN axons through Frizzled3. Axons that reach the GP in Frizzled3 knock-out mice fail to enter this structure. Surprisingly, entry of MSN axons into the GP non-cell-autonomously requires Frizzled3, and our data suggest that GP entry may be contingent on the correct positioning of "corridor" guidepost cells for thalamocortical axons by Frizzled3. Together, these data dissect MSN pathway development and reveal (non)cell-autonomous roles for Frizzled3 in MSN axon guidance. Further, they are the first to identify a gene that provides anterior-posterior axon guidance in a large brain nucleus and link Frizzled3 to corridor cell development.

SIGNIFICANCE STATEMENT

Striatal axon pathways mediate complex physiological functions and are an important therapeutic target, underscoring the need to define how these connections are established. Remarkably, the molecular programs regulating striatal pathway development remain poorly characterized. Here, we determine the embryonic ontogeny of the two main striatal pathways (striatonigral and striatopallidal) and identify novel (non)cell-autonomous roles for the axon guidance receptor Frizzled3 in uncharacterized aspects of striatal pathway formation (i.e., anterior-posterior axon guidance in the striatum and axon entry into the globus pallidus). Further, our results link Frizzled3 to corridor guidepost cell development and suggest that an abnormal distribution of these cells has unexpected, widespread effects on the development of different axon tracts (i.e., striatal and thalamocortical axons).

Dopamine receptor agonists modulate voluntary alcohol intake independently of individual levels of alcohol intake in rats

RATIONALE

Individual susceptibility to alcohol use disorder has been related to functional changes in dopaminergic neurotransmission.

OBJECTIVES

The aim of the current work was to assess the effects of selective dopamine D1 and D2 receptor agonists and antagonists on alcohol consumption in rats that differ in individual levels of alcohol intake.

METHODS

The effects of the dopamine D1 receptor agonist SKF 82958, the dopamine D1 receptor antagonist SCH 23390, the dopamine D2 receptor agonist sumanirole and the dopamine D2 receptor antagonist L741,626 on alcohol consumption and preference were assessed at different time points after treatment in subgroups of low and high alcohol drinking rats (LD and HD) using an intermittent alcohol access paradigm.

RESULTS

SKF 82958 decreased alcohol intake and alcohol preference throughout the 24-h session. Sumanirole decreased alcohol intake during the first 2 h, but increased alcohol intake during the remainder of the session. The effects of SKF 82958 and sumanirole on alcohol intake and alcohol preference were comparable in LD and HD. By contrast, the dopamine receptor antagonists SCH 23390 and L741,626 did not alter alcohol consumption in either group at any time point.

CONCLUSIONS

These data indicate that stimulation of dopamine D1 receptors reduces alcohol intake, but that endogenous dopamine does not play a primary role in alcohol consumption. Moreover, the difference in alcohol consumption between LD and HD does not involve altered dopamine signaling.

Upregulation of dopamine D2 receptors in the nucleus accumbens indirect pathway increases locomotion but does not reduce alcohol consumption

Brain imaging studies performed in humans have associated low striatal dopamine release and D2R binding with alcohol dependence. Conversely, high striatal D2R binding has been observed in unaffected members of alcoholic families suggesting that high D2R function may protect against alcohol dependence. A possible protective role of increased D2R levels in the striatum is further supported by preclinical studies in non-human primates and rodents. Here, we determined whether there is a causal relationship between D2R levels and alcohol intake. To this end, we upregulated D2R expression levels in the nucleus accumbens of the adult mouse, but selectively restricted the upregulation to the indirect striatal output pathway, which endogenously expresses D2Rs. After overexpression was established, mice were tested in two models of free-choice alcohol drinking: the continuous and intermittent access two-bottle choice models. As anticipated, we found that D2R upregulation leads to hyperactivity in the open field. Contrary to our expectation, D2R upregulation did not reduce alcohol intake during continuous or intermittent access or when alcohol drinking was tested in the context of aversive outcomes. These data argue against a protective role of accumbal indirect pathway D2Rs in alcohol consumption but emphasize their importance in promoting locomotor activity.

Chronic alcohol disrupts dopamine receptor activity and the cognitive function of the medial prefrontal cortex

Dopamine (DA) receptors in the medial prefrontal cortex (mPFC) exert powerful effects on cognition by modulating the balance between excitatory and inhibitory neurotransmission. The present study examined the impact of chronic intermittent ethanol (CIE) exposure on cognitive function and DA receptor-mediated neurotransmission in the rat mPFC. Consistent with alterations in executive function in alcoholics, CIE-exposed rats exhibited deficits in behavioral flexibility in an operant set-shifting task. Since alterations in dopaminergic neurotransmission in the mPFC have been implicated in a number of behavioral disorders including addiction, studies were then performed in the adult acute slice preparation to examine changes in DA receptor function in the mPFC following CIE exposure. In slices obtained from control rats, DA receptor stimulation was observed to exert complex actions on neuronal firing and synaptic neurotransmission that were not only dependent upon the particular receptor subtype but also whether it was a pyramidal cell or a fast-spiking interneuron. In contrast to slices from control rats, there was a near complete loss of the modulatory actions of D2/D4 receptors on cell firing and neurotransmission in slices obtained immediately, 1 and 4 weeks after the last day of CIE exposure. This loss did not appear to be associated with changes in receptor expression. In contrast, CIE exposure did not alter D1 receptor function or mGluR1 modulation of firing. These studies are consistent with the suggestion that chronic alcohol exposure disrupts cognitive function at least in part through disruption of D2 and D4 receptor signaling in mPFC.

Alcohol-preferring rats show decreased corticotropin-releasing hormone-2 receptor expression and differences in HPA activation compared to alcohol-nonpreferring rats

BACKGROUND

Corticotropin-releasing hormone (CRH) and urocortins (UCNs) bind to corticotropin-releasing hormone type 2 receptor (CRF2 receptor ), a Gs protein-coupled receptor that plays an important role in modulation of anxiety and stress responses. The Crhr2 gene maps to a quantitative trait locus (QTL) for alcohol preference on chromosome 4 previously identified in inbred alcohol-preferring (iP) and-nonpreferring (iNP) F2 rats.

METHODS

Real-time polymerase chain reaction was utilized to screen for differences in Crhr2 mRNA expression in the central nervous system (CNS) of male iP and iNP rats. DNA sequence analysis was then performed to screen for polymorphism in Crhr2 in order to identify genetic variation, and luciferase reporter assays were then applied to test their functional significance. Next, binding assays were used to determine whether this polymorphism affected CRF2 receptor binding affinity as well as CRF2 receptor density in the CNS. Finally, social interaction and corticosterone levels were measured in the P and NP rats before and after 30-minute restraint stress.

RESULTS

Crhr2 mRNA expression studies found lower levels of Crhr2 mRNA in iP rats compared to iNP rats. In addition, DNA sequencing identified polymorphisms in the promoter region, coding region, and 3'-untranslated region between the iP and iNP rats. A 7 bp insertion in the Crhr2 promoter of iP rats altered expression in vitro as measured by reporter assays, and we found that CRF2 receptor density was lower in the amygdala of iP as compared to iNP rats. Male P rats displayed decreased social interaction and significantly higher corticosterone levels directly following 30-minute restraint when compared to male NP rats.

CONCLUSIONS

This study identified Crhr2 as a candidate gene of interest underlying the chromosome 4 QTL for alcohol consumption that was previously identified in the P and NP model. Crhr2 promoter polymorphism is associated with reduced mRNA expression in certain brain regions, particularly the amygdala, and lowered the density of CRF2 receptor in the amygdala of iP compared to iNP rats. Together, these differences between the animals may contribute to the drinking disparity as well as the anxiety differences of the P and NP rats.

Differential role of D1 and D2 receptors in the perifornical lateral hypothalamus in controlling ethanol drinking and food intake: possible interaction with local orexin neurons

BACKGROUND

The neurotransmitter dopamine (DA), acting in various mesolimbic brain regions, is well known for its role in promoting motivated behaviors, including ethanol (EtOH) drinking. Indirect evidence, however, suggests that DA in the perifornical lateral hypothalamus (PF/LH) has differential effects on EtOH consumption, depending on whether it acts on the DA 1 (D1) or DA 2 (D2) receptor subtype, and that these effects are mediated in part by local peptide systems, such as orexin/hypocretin (OX) and melanin-concentrating hormone (MCH), known to stimulate the consumption of EtOH.

METHODS

The present study in brain-cannulated Sprague-Dawley rats measured the effects of dopaminergic compounds in the PF/LH on drinking behavior in animals trained to consume 7% EtOH and also on local peptide mRNA expression using digoxigenin-labeled in situ hybridization in EtOH-naïve animals.

RESULTS

Experiments 1 and 2 showed that the D1 agonist SKF81297 (10.8 nmol/side) in the PF/LH significantly increased food intake, while tending to increase EtOH intake, and the D1 antagonist SCH23390 significantly decreased EtOH intake without affecting food intake. In contrast, the D2 agonist quinelorane (6.2 nmol/side) in the PF/LH significantly reduced EtOH consumption, while the D2 antagonist sulpiride increased it. Experiments 3 and 4 revealed differential effects of PF/LH injection of the DA agonists on local OX mRNA, which was increased by the D1 agonist and decreased by the D2 agonist. These DA agonists had no impact on MCH expression.

CONCLUSIONS

These results support a stimulatory role of the PF/LH D1 receptor in promoting the consumption of both EtOH and food, in contrast to a suppressive effect of the D2 receptor on EtOH drinking. They further suggest that these receptors affect consumption, in part, through local OX-expressing neurons. These findings provide new evidence for the function of PF/LH DA receptor subtypes in controlling EtOH and food intake.

Mesolimbic transcriptional response to hedonic substitution of voluntary exercise and voluntary ethanol consumption

The mesolimbic dopaminergic pathway has been implicated in many rewarding behaviors, including the consumption of ethanol and voluntary exercise. It has become apparent that different rewarding stimuli activate this pathway, and therefore it is possible for these behaviors to influence each other, i.e. hedonic substitution. Using adult female C57BL/6J mice, we demonstrate that voluntary access to a running wheel substantially reduces the consumption and preference of ethanol. Furthermore, we examined gene expression of several genes involved in regulating the mesolimbic dopaminergic pathway, which we hypothesized to be the main pathway involved in hedonic substitution. In the striatum, we observed a reduction in mRNA expression of Drd1a due to exercise. Hippocampal Bdnf mRNA increased in response to exercise and decreased in response to ethanol. Furthermore, there was an interaction effect of exercise and ethanol on the expression of Slc18a2 in the midbrain. These data suggest an important role for this pathway, and especially for Bdnf and Slc18a2 in regulating hedonic substitution.

Expression, covariation, and genetic regulation of miRNA Biogenesis genes in brain supports their role in addiction, psychiatric disorders, and disease

The role of miRNA and miRNA biogenesis genes in the adult brain is just beginning to be explored. In this study we have performed a comprehensive analysis of the expression, genetic regulation, and co-expression of major components of the miRNA biogenesis pathway using human and mouse data sets and resources available on the GeneNetwork web site (genenetwork.org). We found a wide range of variation in expression in both species for key components of the pathway—Drosha, Pasha, and Dicer. Across species, tissues, and expression platforms all three genes are generally well-correlated. No single genetic locus exerts a strong and consistent influence on the expression of these key genes across murine brain regions. However, in mouse striatum, many members of the miRNA pathway are correlated—including Dicer, Drosha, Pasha, Ars2 (Srrt), Eif2c1 (Ago1), Eif2c2 (Ago2), Zcchc11, and Snip1. The expression of these genes may be partly influenced by a locus on Chromosome 9 (105.67–106.32 Mb). We explored ~1500 brain phenotypes available for the C57BL/6J × DBA/2J (BXD) genetic mouse population in order to identify miRNA biogenesis genes correlated with traits related to addiction and psychiatric disorders. We found a significant association between expression of Dicer and Drosha in several brain regions and the response to many drugs of abuse, including ethanol, cocaine, and methamphetamine. Expression of Dicer, Drosha, and Pasha in most of the brain regions explored is strongly correlated with the expression of key members of the dopamine system. Drosha, Pasha, and Dicer expression is also correlated with the expression of behavioral traits measuring depression and sensorimotor gating, impulsivity, and anxiety, respectively. Our study provides a global survey of the expression and regulation of key miRNA biogenesis genes in brain and provides preliminary support for the involvement of these genes and their product miRNAs in addiction and psychiatric disease processes.

Glucocorticoid receptor antagonism blocks ethanol-induced place preference learning in mice and attenuates dopamine D2 receptor adaptation in the frontal cortex

The glucocorticoid receptor (GR) plays an important role in alcohol (EtOH) self-administration behaviour by its interaction with the dopaminergic (DA) system in the brain. Here we asked whether the GR is also involved in the establishment of EtOH-induced conditioned place preference (CPP) by an interaction with the DA systems in terminal projection areas. We found that the establishment of an EtOH (2 g/kg, i.p.)-induced CPP was paralleled by a decrease in frontal cortex DA D2 receptor mRNA expression, but not in local D2 gene promoter methylation rate. No effect in other brain areas, nor on DA transporter or DA receptor regulating factor mRNA was found. The GR antagonist, RU486 (20 mg/kg, i.p.) blocked the establishment of EtOH CPP and prevented DA D2 receptor adaptations. These data may suggest a role of glucocorticoid receptor mediated D2 adaptations in the establishment of the reinforcing effects of EtOH.

Increased consumption of ethanol and sugar water in mice lacking the dopamine D2 long receptor

Individual differences in dopamine D2 receptor (D2R) expression in the brain are thought to influence motivation and reinforcement for ethanol and other rewards. D2R exists in two isoforms, D2 long (D2LR) and D2 short (D2SR), produced by alternative splicing of the same gene. The relative contributions of D2LR versus D2SR to ethanol and sugar water drinking are not known. Genetic engineering was used to produce a line of knockout (KO) mice that lack D2LR and consequently have increased expression of D2SR. KO and wild-type (WT) mice of both sexes were tested for intake of 20% ethanol, 10% sugar water and plain tap water using established drinking-in-the-dark procedures. Mice were also tested for effects of the D2 antagonist eticlopride on intake of ethanol to determine whether KO responses were caused by lack of D2LR or overrepresentation of D2SR. Locomotor activity on running wheels and in cages without wheels was also measured for comparison. D2L KO mice drank significantly more ethanol than WT in both sexes. KO mice drank more sugar water than WT in females but not in males. Eticlopride dose dependently decreased ethanol intake in all groups except male KO. KO mice were less physically active than WT in cages with or without running wheels. Results suggest that overrepresentation of D2SR contributes to increased intake of ethanol in the KO mice. Decreasing wheel running and general levels of physical activity in the KO mice rules out the possibility that higher intake results from higher motor activity. Results extend the literature implicating altered expression of D2R in risk for addiction by delineating the contribution of individual D2R isoforms. These findings suggest that D2LR and D2SR play differential roles in consumption of alcohol and sugar rewards.

Chronic ethanol exposure changes dopamine D2 receptor splicing during retinoic acid-induced differentiation of human SH-SY5Y cells

There is evidence for ethanol-induced impairment of the dopaminergic system in the brain during development. The dopamine D2 receptor (DRD2) and the dopamine transporter (DAT) are decisively involved in dopaminergic signaling. Two splice variants of DRD2 are known, with the short one (DRD2s) representing the autoreceptor and the long one (DRD2l) the postsynaptic receptor. We searched for a model to investigate the impact of chronic ethanol exposure and withdrawal on the expression of these proteins during neuronal differentiation. RA-induced differentiation of human neuroblastoma SH-SY5Y cells seems to represent such a model. Our real-time RT-PCR, Western blot, and immunocytochemistry analyses of undifferentiated and RA-differentiated cells have demonstrated the enhanced expression of both splice variants of DRD2, with the short one being stronger enhanced than the long one under RA-treatment, and the DRD2 distribution on cell bodies and neurites under both conditions. In contrast, DAT was down-regulated by RA. The DAT is functional both in undifferentiated and RA-differentiated cells as demonstrated by [(3)H]dopamine uptake. Chronic ethanol exposure during differentiation for up to 4 weeks resulted in a delayed up-regulation of DRD2s. Ethanol withdrawal caused an increased expression of DRD2l and a normalization of DRD2s. Thus the DRD2s/DRD2l ratio was still disturbed. The dopamine level was increased by RA-differentiation compared to controls and was diminished under RA/ethanol treatment and ethanol withdrawal compared to RA-only treated cells. In conclusion, chronic ethanol exposure impairs differentiation-dependent adaptation of dopaminergic proteins, specifically of DRD2s. RA-differentiating SH-SY5Y cells are suited to study the impact of chronic ethanol exposure and withdrawal on expression of dopaminergic proteins during neuronal differentiation.

Upregulation of cannabinoid type 1 receptors in dopamine D2 receptor knockout mice is reversed by chronic forced ethanol consumption

BACKGROUND

The anatomical proximity of the cannabinoid type 1 (CNR1/CB1R) and the dopamine D2 receptors (DRD2), their ability to form CB1R-DRD2 heteromers, their opposing roles in locomotion, and their involvement in ethanol's reinforcing and addictive properties prompted us to study the levels and distribution of CB1R after chronic ethanol intake, in the presence and absence of DRD2.

METHODS

We monitored the drinking patterns and locomotor activity of Drd2+/+ and Drd2-/- mice consuming either water or a 20% (v/v) ethanol solution (forced ethanol intake) for 6 months and used the selective CB1 receptor antagonist [³H]SR141716A to quantify CB1R levels in different brain regions with in vitro receptor autoradiography.

RESULTS

We found that the lack of DRD2 leads to a marked upregulation (approximately 2-fold increase) of CB1R in the cerebral cortex, the caudate-putamen, and the nucleus accumbens, which was reversed by chronic ethanol intake.

CONCLUSIONS

The results suggest that DRD2-mediated dopaminergic neurotransmission and chronic ethanol intake exert an inhibitory effect on cannabinoid receptor expression in cortical and striatal regions implicated in the reinforcing and addictive properties of ethanol.

Fine mapping and expression of candidate genes within the chromosome 10 QTL region of the high and low alcohol-drinking rats

The high and low alcohol-drinking (HAD and LAD) rats were selectively bred for differences in alcohol intake. The HAD/LAD rats originated from the N/Nih heterogeneous stock developed from intercrossing eight inbred rat strains. The HAD×LAD F2 were genotyped, and a powerful analytical approach, using ancestral recombination and F2 recombination, was used to narrow a quantitative trait loci (QTL) for alcohol drinking to a 2-cM region on distal chromosome 10 that was in common in the HAD1/LAD1 and HAD2/LAD2 analyses. Quantitative real-time PCR was used to examine mRNA expression of six candidate genes (Crebbp, Trap1, Gnptg, Clcn7, Fahd1, and Mapk8ip3) located within the narrowed QTL region in the HAD1/LAD1 rats. Expression was examined in five brain regions, including the nucleus accumbens, amygdala, caudate putamen, hippocampus, and prefrontal cortex. All six genes showed differential expression in at least one brain region. Of the genes tested in this study, Crebbp and Mapk8ip3 may be the most promising candidates with regard to alcohol drinking.

Event-related oscillations as risk markers in genetic mouse models of high alcohol preference

Mouse models have been developed to simulate several relevant human traits associated with alcohol use and dependence. However, the neurophysiological substrates regulating these traits remain to be completely elucidated. We have previously demonstrated that differences in the event-related potential (ERP) responses can be found that distinguish high-alcohol preferring from low alcohol preferring mice that resemble differences seen in human studies of individuals with high and low risk for alcohol dependence. Recently, evidence of genes that affect event-related oscillations (EROs) and the risk for alcohol dependence has emerged, however, to date EROs have not been evaluated in genetic mouse models of high and low alcohol preference. Therefore, the objective of the present study was to characterize EROs in mouse models of high (C57BL/6 [B6] and high alcohol preference 1 [HAP-1] mice) and low (DBA/2J [D2] and low alcohol preference-1 [LAP-1] mice) alcohol preference. A time-frequency representation method was used to determine delta, theta and alpha/beta ERO energy and the degree of phase variation in these mouse models. The present results suggest that the decrease in P3 amplitudes previously shown in B6 mice, compared to D2 mice, is related to reductions in evoked delta ERO energy and delta and theta phase locking. In contrast, the increase in P1 amplitudes reported in HAP-1 mice, compared to LAP-1 mice, is associated with increases in evoked theta ERO energy. These studies suggest that differences in delta and theta ERO measures in mice mirror changes observed between groups at high- and low-risk for alcoholism where changes in EROs were found to be more significant than group differences in P3 amplitudes, further suggesting that ERO measures are more stable endophenotypes in the study of alcohol dependence. Further studies are needed to determine the relationship between expression of these neurophysiological endophenotypes and the genetic profile of these mouse models.

Ethanol-responsive genes (Crtam, Zbtb16, and Mobp) located in the alcohol-QTL region of chromosome 9 are associated with alcohol preference in mice

BACKGROUND

Previously, our group identified cytotoxic and regulatory T-cell molecule (Crtam), zinc finger and BTB domain containing 16 (Zbtb16), and myelin-associated oligodendrocytic basic protein (Mobp) as ethanol-responsive genes in the mouse brain by gene expression profiling. In this study, we used a genetic co-segregation analysis to assess the association of Crtam, Zbtb16, and Mobp with the alcohol preference (AP) phenotype in the alcohol-preferring C57BL/6J (B6) and alcohol avoiding DBA/2J (D2) strains of mice.

METHODS

Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to confirm previous microarray analysis results that Crtam, Zbtb16, and Mobp brain mRNA levels in the B6 and D2 strains are altered by ethanol treatment. The association of the 3 genes with AP was assessed in a F(2) population (n = 427) derived from the reciprocal crosses involving the B6 and D2 strains. Each F(2) individual was assessed for their AP using the 2 bottle choice test and genotyped for Crtam, Zbtb16, and Mobp single nucleotide polymorphisms (SNPs) that differ between B6 and D2 mice.

RESULTS

Semi-quantitative RT-PCR analysis confirmed that Crtam, Zbtb16, and Mobp are ethanol-responsive genes. The SNP analyses show that alleles of the 3 genes co-segregate with the AP phenotype in F(2) mice, where individuals homozygous for the B6 allele have higher AP than those homozygous for the D2 allele. Also, the Crtam-Zbtb16 loci that are tightly linked and the Mobp locus act in an additive fashion in determining the relative AP phenotype.

CONCLUSION

Our results are consistent with the hypothesis that Crtam, Zbtb16, and Mobp may be involved in AP in mice. The nature of this association remains to be established and may reflect a direct effect of these genes or an indirect effect caused by linked genes on mouse chromosome 9.