Overview of mouse assays of ethanol intoxication

Early-life inflammation increases ethanol consumption in adolescent male mice

Recent studies have demonstrated that stress during the critical windows of development can evoke a cascade of neurological changes that can result in neuropsychiatric disorders later in life. In this study, we examined the effect of early-life inflammation on ethanol consumption in adolescent mice. C57BL/6J mice were assigned to either the control or Lipopolysaccharide (LPS) group on postnatal day 14 (P14). In the latter group, LPS at a dose of 50 μg/kg was injected intraperitoneally. The mice were weaned at P21, and behavior tests were performed at P45. Ethanol consumption was assessed using a two-bottle choice drinking paradigm. Anxiety-like behaviors were assessed by marble burying test (MBT), open field (OF), and elevated plus maze (EPM). Ethanol-induced loss of righting reflex (LORR), hypothermia and ethanol metabolism were assessed to evaluate ethanol intoxication. P14 LPS-injected adolescent male mice exhibited significantly increased ethanol preference and consumption, with a similar taste preference for saccharin and avoidance of quinine. The adolescent male mice showed increased anxiety-like behaviors in the OF and EPM tests, and an increased duration of LORR, without affecting the hypothermic effects of ethanol and ethanol metabolism. Interestingly, these behavioral changes were not obvious in female mice. In conclusion, our data indicate that early-life inflammation may be a risk factor for ethanol consumption in adolescents with greater changes observed in male mice. SIGNIFICANCE STATEMENT: Our study is the first preclinical model to report the enhancement effect of early-life inflammation on ethanol consumption in adolescent male mice and our findings provide a valuable mouse model to examine the neurobiological mechanisms mediating the long-lasting effects of early-life inflammation on alcohol use disorders vulnerability.

Genome-wide association mapping of ethanol sensitivity in the Diversity Outbred mouse population

BACKGROUND

A strong predictor for the development of alcohol use disorder (AUD) is altered sensitivity to the intoxicating effects of alcohol. Individual differences in the initial sensitivity to alcohol are controlled in part by genetic factors. Mice offer a powerful tool to elucidate the genetic basis of behavioral and physiological traits relevant to AUD, but conventional experimental crosses have only been able to identify large chromosomal regions rather than specific genes. Genetically diverse, highly recombinant mouse populations make it possible to observe a wider range of phenotypic variation, offer greater mapping precision, and thus increase the potential for efficient gene identification.

METHODS

We have taken advantage of the Diversity Outbred (DO) mouse population to identify and precisely map quantitative trait loci (QTL) associated with ethanol sensitivity. We phenotyped 798 male J:DO mice for three measures of ethanol sensitivity: ataxia, hypothermia, and loss of the righting response. We used high-density MegaMUGA and GigaMUGA to obtain genotypes ranging from 77,808 to 143,259 SNPs. We also performed RNA sequencing in striatum to map expression QTLs and identify gene expression-trait correlations. We then applied a systems genetic strategy to identify narrow QTLs and construct the network of correlations that exists between DNA sequence, gene expression values, and ethanol-related phenotypes to prioritize our list of positional candidate genes.

RESULTS

We observed large amounts of phenotypic variation with the DO population and identified suggestive and significant QTLs associated with ethanol sensitivity on chromosomes 1, 2, and 16. The implicated regions were narrow (4.5-6.9 Mb in size) and each QTL explained ~4-5% of the variance.

CONCLUSIONS

Our results can be used to identify alleles that contribute to AUD in humans, elucidate causative biological mechanisms, or assist in the development of novel therapeutic interventions.

Ethanol-Related Behaviors in Mouse Lines Selectively Bred for Drinking to Intoxication

Alcohol use disorder (AUD) is a devastating psychiatric disorder that has significant wide-reaching effects on individuals and society. Selectively bred mouse lines are an effective means of exploring the genetic and neuronal mechanisms underlying AUD and such studies are translationally important for identifying treatment options. Here, we report on behavioral characterization of two replicate lines of mice that drink to intoxication, the High Drinking in the Dark (HDID)-1 and -2 mice, which have been selectively bred (20+ generations) for the primary phenotype of reaching high blood alcohol levels (BALs) during the drinking in the dark (DID) task, a binge-like drinking assay. Along with their genetically heterogenous progenitor line, Hs/Npt, we tested these mice on: DID and drinking in the light (DIL); temporal drinking patterns; ethanol sensitivity, through loss of righting reflex (LORR); and operant self-administration, including fixed ratio (FR1), fixed ratio 3:1 (FR3), extinction/reinstatement, and progressive ratio (PR). All mice consumed more ethanol during the dark than the light and both HDID lines consumed more ethanol than Hs/Npt during DIL and DID. In the dark, we found that the HDID lines achieved high blood alcohol levels early into a drinking session, suggesting that they exhibit front loading like drinking behavior in the absence of the chronicity usually required for such behavior. Surprisingly, HDID-1 (female and male) and HDID-2 (male) mice were more sensitive to the intoxicating effects of ethanol during the dark (as determined by LORR), while Hs/Npt (female and male) and HDID-2 (female) mice appeared less sensitive. We observed lower HDID-1 ethanol intake compared to either HDID-2 or Hs/Npt during operant ethanol self-administration. There were no genotype differences for either progressive ratio responding, or cue-induced ethanol reinstatement, though the latter is complicated by a lack of extinguished responding behavior. Taken together, these findings suggest that genes affecting one AUD-related behavior do not necessarily affect other AUD-related behaviors. Moreover, these findings highlight that alcohol-related behaviors can also differ between lines selectively bred for the same phenotype, and even between sexes within those same line.

Alcohol Sensitivity as an Endophenotype of Alcohol Use Disorder: Exploring Its Translational Utility between Rodents and Humans

Alcohol use disorder (AUD) is a complex, chronic, relapsing disorder with multiple interacting genetic and environmental influences. Numerous studies have verified the influence of genetics on AUD, yet the underlying biological pathways remain unknown. One strategy to interrogate complex diseases is the use of endophenotypes, which deconstruct current diagnostic categories into component traits that may be more amenable to genetic research. In this review, we explore how an endophenotype such as sensitivity to alcohol can be used in conjunction with rodent models to provide mechanistic insights into AUD. We evaluate three alcohol sensitivity endophenotypes (stimulation, intoxication, and aversion) for their translatability across human and rodent research by examining the underlying neurobiology and its relationship to consumption and AUD. We show examples in which results gleaned from rodents are successfully integrated with information from human studies to gain insight in the genetic underpinnings of AUD and AUD-related endophenotypes. Finally, we identify areas for future translational research that could greatly expand our knowledge of the biological and molecular aspects of the transition to AUD with the broad hope of finding better ways to treat this devastating disorder.

Rapid reacquisition of contextual fear following extinction in mice: effects of amount of extinction, acute ethanol withdrawal, and ethanol intoxication

RATIONALE

Many studies have found that ethanol intoxication and withdrawal impair initial acquisition or extinction of learned behaviors. Rapid reconditioning following extinction is a form of post-extinction re-emergence of conditioned behavior that has not been studied for its interaction with ethanol intoxication or withdrawal.

OBJECTIVES

The goals of this paper were to define the parameters that allow rapid post-extinction reacquisition of fear in mice and investigate the effect of acute ethanol withdrawal and intoxication on acquisition, extinction, and post-extinction reconditioning.

METHODS

We examined acquisition, extinction, and post-extinction reconditioning of contextual fear in male C57BL/6 mice. Acute ethanol withdrawal occurred 6 h following a 4 g/kg injection of 20% ethanol and acute ethanol intoxication occurred 5 min following a 1.5 g/kg injection of 20% ethanol.

RESULTS

A weak context-shock pairing caused rapid reacquisition of conditioned freezing following moderate, but not extensive extinction. Acute ethanol intoxication impaired initial conditioning and acute ethanol withdrawal impaired rapid reacquisition after extinction, but not reconditioning or extinction itself.

CONCLUSIONS

These findings show that rapid reconditioning occurs following moderate but not extensive extinction in C57BL/6J mice. Additionally, acute ethanol withdrawal and intoxication may differentially affect different phases of conditioning. Results are discussed in terms of current ideas about post-extinction behavior and ethanol's effects on memory.

Spatial and Sex-Dependent Responses of Adult Endogenous Neural Stem Cells to Alcohol Consumption

Chronic alcohol abuse results in alcohol-related neurodegeneration, and critical gaps in our knowledge hinder therapeutic development. Neural stem cells (NSCs) are a subpopulation of cells within the adult brain that contribute to brain maintenance and recovery. While it is known that alcohol alters NSCs, little is known about how NSC response to alcohol is related to sex, brain region, and stage of differentiation. Understanding these relationships will aid in therapeutic development. Here, we used an inducible transgenic mouse model to track the stages of differentiation of adult endogenous NSCs and observed distinct NSC behaviors in three brain regions (subventricular zone, subgranular zone, and tanycyte layer) after long-term alcohol consumption. Particularly, chronic alcohol consumption profoundly affected the survival of NSCs in the subventricular zone and altered NSC differentiation in all three regions. Significant differences between male and female mice were further discovered.

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Alcohol alters neural stem cell differentiation in a region-dependent manner

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Sex plays a role in neural stem cell response to alcohol consumption

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Sex contributes to regional differences of neural stem cell response to alcohol

Sex differences and hormonal modulation of ethanol-enhanced risk taking in rats

BACKGROUND

Ethanol (EtOH) intake correlates with increased risk-taking, and sex differences exist in both EtOH use and risk-taking in humans and rats. However, the interaction of sex and gonadal hormones to affect risk-taking under the influence of EtOH has not been determined. This was the focus of the current study.

METHODS

Adult Long-Evans rats (n=18 males and females) were gonadectomized and received hormone replacement at physiologic levels or blank implants (n=7-9/group). Risk-taking was assessed with probability discounting, requiring rats to choose between a small/certain reward and a large/uncertain reward delivered with decreasing probability throughout each daily session. Before testing, rats received saline or EtOH (0.5 or 1.0g/kg) ip.

RESULTS

In males, EtOH increased preference for the large/uncertain reward lever (F_2,28=10.462, p<0.05). However, there was no effect of EtOH on lever preference in females (F_1,30=0.914, p>0.05). At baseline, ORCHX+T males showed a greater preference for the large/uncertain reward lever then ORCHX males (F_1,14=13.805, p<0.05). In females only, EtOH decreased choice latency relative to baseline (F_1,10=7.25, p<0.05). EtOH decreased loss sensitivity in both sexes, with all rats exhibiting decreased lose-shift ratios (males: F_2,18=5.10, p<0.05; females F_2,10=4.37, p<0.05).

CONCLUSIONS

These results show that EtOH, sex, and hormones interact to influence decision making. EtOH increases risk taking in males, but not in females. However, EtOH selectively decreases choice latency in females, and decreases loss sensitivity in both sexes. These findings are relevant to understanding human behavior, particularly in adolescents who experience increased hormone levels and often drink EtOH and engage in risky behavior.

Social housing conditions and oxytocin and vasopressin receptors contribute to ethanol conditioned social preference in female mice

Social behavior modulates response to alcohol. Because oxytocin (OXT) and vasopressin (AVP) contribute to rewarding social behavior, the present study utilized a genetic strategy to determine whether OXT and AVP receptors (OXTR, AVPR1a) are essential for female mice to demonstrate a conditioned social preference for ethanol. The study compared wild-type (WT) and knock-out (KO) females lacking either Oxtr or Avpr1a in a conditioned social preference (CSP) test. KO females and WT females from Het-Het crosses were pair-housed: KO and WT(ko). WT females from Het-WT crosses were pair-housed: WT(wt). Test mice received 2g/kg ethanol or saline ip, and were paired four times each with one stimulus female (CS-) after saline, and with another female (CS+) following ethanol. After pairing, the time spent with CS+ and CS- females was measured. WT(wt) females showed conditioned preference for the CS+ female paired with ethanol, demonstrated by greater interaction time (p<0.05). In both KO lines, ethanol significantly reduced interaction with the CS+ female (p<0.05), and there was no change in interaction for WT(ko) females. Response to odors by habituation-dishabituation was unaffected in both KO lines, and the response to a hypnotic dose of ethanol also was the same as in WT mice. However, anxiety, measured as time on the open arms of the elevated plus maze, was reduced in KO(Oxtr) females compared with WT(wt). The results suggest that Oxtr and Avpr1a are required for conditioned effects of an ethanol-associated social stimulus. The lack of CSP in WT(ko) females suggests that the quality of social interactions during postnatal and postweaning life may modulate development and expression of normal social responses.

"Drinking in the Dark" (DID): a simple mouse model of binge-like alcohol intake

One of the greatest challenges that scientists face when studying the neurobiology and/or genetics of alcohol (ethanol) consumption is that most preclinical animal models do not voluntarily consume enough ethanol to achieve pharmacologically meaningful blood ethanol concentrations (BECs). Recent rodent models have been developed that promote binge-like levels of ethanol consumption associated with high BECs (i.e., ≥100 mg/dl). This unit describes procedures for an animal model of binge-like ethanol drinking which has come to be called "drinking in the dark" (DID). The "basic" variation of DID involves replacing the water bottle with a bottle containing 20% ethanol for 2 to 4 hr, beginning 3 hr into the dark cycle, on cages of singly-housed C57BL/6J mice. Using this procedure, mice typically consume enough ethanol to achieve BECs >100 mg/dl and to exhibit behavioral evidence of intoxication. An alternative two-bottle (ethanol and water) procedure is also described.

Ethanol induces conditioned social preference in male mice

BACKGROUND

Affiliative social interactions promote alcohol consumption, and alcohol also promotes affiliative behavior. Furthermore, for most species, moderate doses of ethanol (EtOH) and social affiliation are each rewarding. However, animal studies of drug and EtOH reward typically test individuals in isolation. To address social dimensions of EtOH reward, this study tested EtOH-induced conditioned social preference in male C57BL/6 mice with (ORCHX+T) and without (ORCHX) testosterone.

METHODS

ORCHX+T males received EtOH (0, 1, 2, or 3 g/kg) intraperitoneally and were paired 4× for 30 minutes each with 1 of 2 stimulus males: with the CS- stimulus male after saline injection and with the CS+ male following EtOH. After pairing, time spent with CS+ and CS- males was measured in a 10-minute test.

RESULTS

ORCHX+T test males showed conditioned preference for the CS+ male in response to 3 g/kg EtOH (change in preference: +71.3 ± 30.0 s/10 min, p < 0.05), but not for 0, 1, or 2 g/kg. By contrast, ORCHX males did not demonstrate conditioned preference for 3 g/kg EtOH (+16.0 ± 24.3 s/10 min, p > 0.05). In separate groups of mice, stimulus males (IS+) received EtOH during pairing to determine whether test mice prefer another intoxicated mouse. Both ORCHX+T and ORCHX test mice showed an increase in preference score for the IS+ mouse (ORCHX+T: +68.1 ± 24.0 seconds; ORCHX: +58.9 ± 19.6 seconds, p < 0.05).

CONCLUSIONS

These data demonstrate that EtOH promotes social preference in male mice, as it does in females. Testosterone enhances this effect.

Novel test of motor and other dysfunctions in mouse neurological disease models

BACKGROUND

Just like human neurological disorders, corresponding mouse models present multiple deficiencies. Estimating disease progression or potential treatment effectiveness in such models necessitates the use of time consuming and multiple tests usually requiring a large number of scarcely available genetically modified animals.

NEW METHOD

Here we present a novel and simple single camera arrangement and analysis software for detailed motor function evaluation in mice walking on a wire mesh that provides complex 3D information (instantaneous position, speed, distance traveled, foot fault depth, duration, location, relationship to speed of movement, etc.).

RESULTS

We investigated 3 groups of mice with various neurological deficits: (1) unilateral motor cortical stroke; (2) effects of moderate ethanol doses; and (3) aging (96-99 weeks old). We show that post stroke recovery can be divided into separate stages based on strikingly different characteristics of motor function deficits, some resembling the human motor neglect syndrome. Mice treated with moderate dose of alcohol and aged mice showed specific motor and exploratory deficits.

COMPARISON WITH EXISTING METHODS

Other tests rely either partially or entirely on manual video analysis introducing a significant subjective component into the analysis, and analyze a single aspect of motor function.

CONCLUSIONS

Our novel experimental approach provides qualitatively new, complex information about motor impairments and locomotor/exploratory activity. It should be useful for the detailed characterization of a broad range of human neurological disease models in mice, and for the more accurate assessment of disease progression or treatment effectiveness.

Probing the modulation of acute ethanol intoxication by pharmacological manipulation of the NMDAR glycine co-agonist site

BACKGROUND

Stimulating the glycine(B) binding site on the N-methyl-d-aspartate ionotropic glutamate receptor (NMDAR) has been proposed as a novel mechanism for modulating behavioral effects of ethanol (EtOH) that are mediated via the NMDAR, including acute intoxication. Here, we pharmacologically interrogated this hypothesis in mice.

METHODS

Effects of systemic injection of the glycine(B) agonist, d-serine, the GlyT-1 glycine transporter inhibitor, ALX-5407, and the glycine(B) antagonist, L-701,324, were tested for the effects on EtOH-induced ataxia, hypothermia, and loss of righting reflex (LORR) duration in C57BL/6J (B6) and 129S1/SvImJ (S1) inbred mice. Effects of the glycine(B) partial agonist, d-cycloserine (DCS), the GlyT-1 inhibitor, N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine (NFPS), and the glycine(B) antagonist, 5,7-dichlorokynurenic (DCKA), on EtOH-induced LORR duration were also tested. Interaction effects on EtOH-induced LORR duration were examined via combined treatment with d-serine and ALX-5407, d-serine and MK-801, d-serine and L-701,324, as well as L-701,324 and ALX-5407, in B6 mice, and d-serine in GluN2A and PSD-95 knockout mice. The effect of dietary depletion of magnesium (Mg), an element that interacts with the glycine(B) site, was also tested.

RESULTS

Neither d-serine, DCS, ALX-5407, nor NFPS significantly affected EtOH intoxication on any of the measures or strains studied. L-701,324, but not DCKA, dose-dependently potentiated the ataxia-inducing effects of EtOH and increased EtOH-induced (but not pentobarbital-induced) LORR duration. d-serine did not have interactive effects on EtOH-induced LORR duration when combined with ALX-5407. The EtOH-potentiating effects of L-701,324, but not MK-801, on LORR duration were prevented by d-serine, but not ALX-5407. Mg depletion potentiated LORR duration in B6 mice and was lethal in a large proportion of S1 mice.

CONCLUSIONS

Glycine(B) site activation failed to produce the hypothesized reduction in EtOH intoxication across a range of measures and genetic strains, but blockade of the glycine(B) site potentiated EtOH intoxication. These data suggest endogenous activity at the glycine(B) opposes EtOH intoxication, but it may be difficult to pharmacologically augment this action, at least in nondependent subjects, perhaps because of physiological saturation of the glycine(B) site.

Ethanol-induced conditioned partner preference in female mice

Drinking behavior and social context are intimately intertwined. Peer relations can promote drinking. Conversely, alcohol promotes social interaction. The present study tested female mice for ethanol-induced conditioned partner preference. Ovariectomized (OVX) C57Bl/6 females with chronic estradiol replacement (OVX+E) received saline or ethanol (1, 2 or 4 g/kg) ip and were paired 4 × for 30 min each with 1 of 2 stimulus females. The test female was paired with the CS- stimulus female following saline, and was paired with the CS+ female following ethanol. After pairing, we measured proximity of the test female to the CS+ and CS- females in a 10' test. In a second study, OVX and OVX+E females were tested for conditioned partner preference (CS+ vs. CS-) in response to 2.5 g/kg ethanol. In separate groups of mice, both test and stimulus females (IS+) received ethanol during pairing to determine if test mice develop conditioned partner preference for another intoxicated mouse. OVX+E test females showed conditioned partner preference for the CS+ female in response to ethanol at 2g/kg (change in preference score for CS+: +86.6 ± 30.0 s/10 min), but not at 0, 1 or 4 g/kg. At 2.5 g/kg ethanol, OVX+E females developed conditioned partner preference for either IS+ (+63.6 ± 24.0 s) or CS+ females (+93.8 ± 27.1 s). OVX test females demonstrated ethanol-induced conditioned partner preference only for the IS+ female (+153.8 ± 32.0 s). These data demonstrate that ethanol promotes social preference in female mice, and that estradiol enhances this effect.

Response to ethanol induced ataxia between C57BL/6J and 129X1/SvJ mouse strains using a treadmill based assay

More sensitive assays of mouse motor ataxia may provide a better understanding of the pathological profile. Treadmill gait analysis using ventral imaging allows for unhindered access to the ambulating mouse. In contrast to genetic mutations or exogenous brain injury, ethanol (EtOH) allows for the detection of dose dependent changes in motor behavior, which can be used to assess an assay's detection sensitivity. EtOH induced ataxia was assessed in C57BL/6J (B6) and 129X1/SvJ (129) mice using the DigiGait imaging system. Gait was analyzed across EtOH dosage (1.75, 2.25 and 2.75 g/kg) in each strain using a linear mixed effects model. Overall, 129 mice displayed greater susceptibility to EtOH ataxia than their B6 counterparts. In both strains, hind paws exhibited greater sensitivity to EtOH dosage than fore paws. Across most variables analyzed, only a modest EtOH-induced change in motor behavior was observed in each strain with the 1.75 g/kg EtOH doses failing to elicit significant change. These data indicate the ability to detect motor differences between strains, yet only moderate ability to detect change across EtOH dosage using the automated treadmill. Rotarod assays, however, were able to detect motor impairment at lower doses of EtOH. The significant, but opposite changes in paw placement with increasing EtOH doses highlight strain-specific differences in biophysical adaptations in response to acute EtOH intoxication.

Ethanol withdrawal-induced motor impairment in mice

RATIONALE

Human ethanol withdrawal manifests as multiple behavioral deficits with distinct time courses. Most studies with mice index ethanol withdrawal severity with the handling-induced convulsion (HIC). Using the accelerating rotarod (ARR), we recently showed that ethanol withdrawal produced motor impairment.

OBJECTIVES

This study aimed (a) to characterize further the ARR withdrawal trait, (b) to assess generalizability across additional behavioral assays, and (c) to test the genetic correlation between ethanol withdrawal ARR impairment and HICs.

RESULTS

The severity of the ARR performance deficit depends on ethanol vapor dose and exposure duration, and lasts 1-4 days. Fatigue could not explain the deficits, which were also evident after intermittent exposure to ethanol vapor. Withdrawing mice were also impaired on a balance beam, but not on a static dowel or in foot slip errors per distance traveled in the parallel rod floor test, where they showed reduced locomotor activity. To assess genetic influences, we compared Withdrawal Seizure-Prone and -Resistant mice, genetically selected to express severe vs. mild withdrawal HICs, respectively. The ARR scores were approximately equivalent in all groups treated with ethanol vapor, though Withdrawal Seizure-Prone (WSP) mice may have displayed a slightly more severe deficit as control-treated WSP mice performed better than control-treated Withdrawal Seizure-Resistant mice.

CONCLUSIONS

These studies show that ethanol withdrawal motor impairment is sensitive to a range of ethanol doses and lasts for several days. Multiple assays of behavioral impairment are affected, but the effects depend on the assay employed. Genetic contributions to withdrawal-induced ARR impairment appear largely distinct from those leading to severe or mild HICs.

Quantitative trait loci for sensitivity to ethanol intoxication in a C57BL/6J×129S1/SvImJ inbred mouse cross

Individual variation in sensitivity to acute ethanol (EtOH) challenge is associated with alcohol drinking and is a predictor of alcohol abuse. Previous studies have shown that the C57BL/6J (B6) and 129S1/SvImJ (S1) inbred mouse strains differ in responses on certain measures of acute EtOH intoxication. To gain insight into genetic factors contributing to these differences, we performed quantitative trait locus (QTL) analysis of measures of EtOH-induced ataxia (accelerating rotarod), hypothermia, and loss of righting reflex (LORR) duration in a B6 × S1 F2 population. We confirmed that S1 showed greater EtOH-induced hypothermia (specifically at a high dose) and longer LORR compared to B6. QTL analysis revealed several additive and interacting loci for various phenotypes, as well as examples of genotype interactions with sex. QTLs for different EtOH phenotypes were largely non-overlapping, suggesting separable genetic influences on these behaviors. The most compelling main-effect QTLs were for hypothermia on chromosome 16 and for LORR on chromosomes 4 and 6. Several QTLs overlapped with loci repeatedly linked to EtOH drinking in previous mouse studies. The architecture of the traits we examined was complex but clearly amenable to dissection in future studies. Using integrative genomics strategies, plausible functional and positional candidates may be found. Uncovering candidate genes associated with variation in these phenotypes in this population could ultimately shed light on genetic factors underlying sensitivity to EtOH intoxication and risk for alcoholism in humans.

Reduced alcohol intake and reward associated with impaired endocannabinoid signaling in mice with a deletion of the glutamate transporter GLAST

A hyperglutamatergic state has been hypothesized to drive escalation of alcohol intake. This hypothesis predicts that an impairment of glutamate clearance through inactivation of the astrocytic glutamate transporter, GLAST (EAAT1), will result in escalation of alcohol consumption. Here, we used mice with a deletion of GLAST to test this prediction. WT and GLAST KO mice were tested for alcohol consumption using two-bottle free-choice drinking. Alcohol reward was evaluated using conditioned place preference (CPP). Sensitivity to depressant alcohol effects was tested using the accelerating rotarod, alcohol-induced hypothermia, and loss of righting reflex. Extracellular glutamate was measured using microdialysis, and striatal slice electrophysiology was carried out to examine plasticity of the cortico-striatal pathway as a model system in which adaptations to the constitutive GLAST deletion can be studied. Contrary to our hypothesis, GLAST KO mice showed markedly decreased alcohol consumption, and lacked CPP for alcohol, despite a higher locomotor response to this drug. Alcohol-induced ataxia, hypothermia, and sedation were unaffected. In striatal slices from GLAST KO mice, long-term depression (LTD) induced by high frequency stimulation, or by post-synaptic depolarization combined with the l-type calcium channel activator FPL 64176 was absent. In contrast, normal synaptic depression was observed after application of the cannabinoid 1 (CB1) receptor agonist WIN55,212-2. Constitutive deletion of GLAST unexpectedly results in markedly reduced alcohol consumption and preference, associated with markedly reduced alcohol reward. Endocannabinoid signaling appears to be down-regulated upstream of the CB1 receptor as a result of the GLAST deletion, and is a candidate mechanism behind the reduction of alcohol reward observed.

Dependence induced increases in intragastric alcohol consumption in mice

Three experiments used the intragastric alcohol consumption (IGAC) procedure to examine the effects of variations in passive ethanol exposure on withdrawal and voluntary ethanol intake in two inbred mouse strains, C57BL/6J (B6) and DBA/2J (D2). Experimental treatments were selected to induce quantitative differences in ethanol dependence and withdrawal severity by: (1) varying the periodicity of passive ethanol exposure (three, six or nine infusions/day); (2) varying the dose per infusion (low, medium or high); and (3) varying the duration of passive exposure (3, 5 or 10 days). All experiments included control groups passively exposed to water. B6 mice generally self-infused more ethanol than D2 mice, but passive ethanol exposure increased IGAC in both strains, with D2 mice showing larger relative increases during the first few days of ethanol access. Bout data supported the characterization of B6 mice as sippers and D2 mice as gulpers. Three larger infusions per day produced a stronger effect on IGAC than six or nine smaller infusions, especially in D2 mice. Increased IGAC was strongly predicted by cumulative ethanol dose and intoxication during passive exposure in both strains. Withdrawal during the passive exposure phase was also a strong predictor of increased IGAC in D2 mice. However, B6 mice showed little withdrawal, precluding analysis of its potential role. Overall, these data support the hypothesis that dependence-induced increases in IGAC are jointly determined by two processes that might vary across genotypes: (1) tolerance to aversive postabsorptive ethanol effects and (2) negative reinforcement (i.e. alleviation of withdrawal by self-administered ethanol).

Oral Nicotine Self-Administration in Rodents

Nicotine addiction is a complex process that begins with self-administration. Consequently, this process has been studied extensively using animal models. A person is usually not called "smoker" if s/he has smoked for a week or a month in a lifetime; in general, a smoker has been smoking for many years. Furthermore, a smoker has free access to cigarettes and can smoke whenever she/he wants, provided there are no social/legal restraints. Subsequently, in an animal model of tobacco addiction, it will be desirable to expose the animal to free access nicotine for 24 hours/day for many weeks, starting at different stages of development.

A novel role for PSD-95 in mediating ethanol intoxication, drinking and place preference

The synaptic signaling mechanisms mediating the behavioral effects of ethanol (EtOH) remain poorly understood. Post-synaptic density 95 (PSD-95, SAP-90, Dlg4) is a key orchestrator of N-methyl-D-aspartate receptors (NMDAR) and glutamatergic synapses, which are known to be major sites of EtOH's behavioral actions. However, the potential contribution of PSD-95 to EtOH-related behaviors has not been established. Here, we evaluated knockout (KO) mice lacking PSD-95 for multiple measures of sensitivity to the acute intoxicating effects of EtOH (ataxia, hypothermia, sedation/hypnosis), EtOH drinking under conditions of free access and following deprivation, acquisition and long-term retention of EtOH conditioned place preference (CPP) (and lithium chloride-induced conditioned taste aversion), and intoxication-potentiating responses to NMDAR antagonism. PSD-95 KO exhibited increased sensitivity to the sedative/hypnotic, but not ataxic or hypothermic, effects of acute EtOH relative to wild-type controls (WT). PSD-95 KO consumed less EtOH than WT, particularly at higher EtOH concentrations, although increases in KO drinking could be induced by concentration-fading and deprivation. PSD-95 KO showed normal EtOH CPP 1 day after conditioning, but showed significant aversion 2 weeks later. Lithium chloride-induced taste aversion was impaired in PSD-95 KO at both time points. Finally, the EtOH-potentiating effects of the NMDAR antagonist MK-801 were intact in PSD-95 KO at the dose tested. These data reveal a major, novel role for PSD-95 in mediating EtOH behaviors, and add to growing evidence that PSD-95 is a key mediator of the effects of multiple abused drugs.

The complexity of alcohol drinking: studies in rodent genetic models

Risk for alcohol dependence in humans has substantial genetic contributions. Successful rodent models generally attempt to address only selected features of the human diagnosis. Most such models target the phenotype of oral administration of alcohol solutions, usually consumption of or preference for an alcohol solution versus water. Data from rats and mice for more than 50 years have shown genetic influences on preference drinking and related phenotypes. This paper summarizes some key findings from that extensive literature. Much has been learned, including the genomic location and possible identity of several genes influencing preference drinking. We report new information from congenic lines confirming QTLs for drinking on mouse chromosomes 2 and 9. There are many strengths of the various phenotypic assays used to study drinking, but there are also some weaknesses. One major weakness, the lack of drinking excessively enough to become intoxicated, has recently been addressed with a new genetic animal model, mouse lines selectively bred for their high and intoxicating blood alcohol levels after a limited period of drinking in the circadian dark. We report here results from a second replicate of that selection and compare them with the first replicate.

Effects of topiramate and other anti-glutamatergic drugs on the acute intoxicating actions of ethanol in mice: modulation by genetic strain and stress

Compounds with anti-glutamatergic properties currently in clinical use for various indications (eg Alzheimer's disease, epilepsy, psychosis, mood disorders) have potential utility as novel treatments for alcoholism. Enhanced sensitivity to certain acute intoxicating effects (ataxia, sedative) of alcohol may be one mechanism by which anti-glutamatergic drugs modulate alcohol use. We examined the effects of six compounds (memantine, dextromethorphan, haloperidol, lamotrigine, oxcarbazepine, and topiramate) on sensitivity to acute intoxicating effects of ethanol (ataxia, hypothermia, sedation/hypnosis) in C57BL/6J mice. Analysis of topiramate was extended to determine the influence of genetic background (by comparison of the 129S1, BALB/cJ, C57BL/6J, DBA/2J inbred strains) and prior stress history (by chronic exposure of C57BL/6J to swim stress) on topiramate's effects on ethanol-induced sedation/hypnosis. Results showed that one N-methyl-D-aspartate receptor (NMDAR) antagonist, memantine, but not another, dextromethorphan, potentiated the ataxic but not hypothermic or sedative/hypnotic effects of ethanol. Haloperidol increased ethanol-induced ataxia and sedation/hypnosis to a similar extent as the prototypical NMDAR antagonist MK-801. Of the anticonvulsants tested, lamotrigine accentuated ethanol-induced sedation/hypnosis, whereas oxcarbazepine was without effect. Topiramate was without effect per se under baseline conditions in C57BL/6J, but had a synergistic effect with MK-801 on ethanol-induced sedation/hypnosis. Comparing inbred strains, topiramate was found to significantly potentiate ethanol's sedative/hypnotic effects in BALB/cJ, but not 129S1, C57BL/6J, or DBA/2J strains. Topiramate also increased ethanol-induced sedation/hypnosis in C57BL/6J after exposure to chronic stress exposure. Current data demonstrate that with the exception of MK-801 and haloperidol, the compounds tested had either no significant or assay-selective effects on sensitivity to acute ethanol under baseline conditions in C57BL/6J. However, significant effects of topiramate were revealed as a function of co-treatment with an NMDAR blocker, genetic background, or prior stress history. These findings raise the possibility that topiramate and possibly other anti-glutamatergic drugs could promote the acute intoxicating effects of ethanol in specific subpopulations defined by genetics or life history.

A line of mice selected for high blood ethanol concentrations shows drinking in the dark to intoxication

BACKGROUND

Many animal models of alcoholism have targeted aspects of excessive alcohol intake (abuse) and dependence. In the rodent, models aimed at increasing alcohol self-administration have used genetic or environmental manipulations, or their combination. Strictly genetic manipulations (e.g., comparison of inbred strains or targeted mutants, selective breeding) have not yielded rat or mouse genotypes that will regularly and voluntarily drink alcohol to the point of intoxication. Although some behavioral manipulations (e.g., scheduling or limiting access to alcohol, adding a sweetener) will induce mice or rats to drink enough alcohol to become intoxicated, these typically require significant food or water restriction or a long time to develop. We report progress toward the development of a new genetic animal model for high levels of alcohol drinking.

METHODS

High Drinking in the Dark (HDID-1) mice have been selectively bred for high blood ethanol concentrations (BEC, ideally exceeding 100 mg%) resulting from the ingestion of a 20% alcohol solution.

RESULTS

After 11 generations of selection, more than 56% of the population now exceeds this BEC after a 4-hour drinking session in which a single bottle containing 20% ethanol is available. The dose of ethanol consumed also produced quantifiable signs of intoxication.

CONCLUSIONS

These mice will be useful for mechanistic studies of the biological and genetic contributions to excessive drinking.

Role of major NMDA or AMPA receptor subunits in MK-801 potentiation of ethanol intoxication

BACKGROUND

The glutamate system plays a major role in mediating EtOH's effects on brain and behavior, and is implicated in the pathophysiology of alcohol-related disorders. N-methyl-D-aspartate receptor (NMDAR) antagonists such as MK-801 (dizocilpine) interact with EtOH at the behavioral level, but the molecular basis of this interaction is unclear.

METHODS

We first characterized the effects of MK-801 treatment on responses to the ataxic (accelerating rotarod), hypothermic and sedative/hypnotic effects of acute EtOH administration in C57BL/6J and 129/SvImJ inbred mice. Effects of another NMDAR antagonist, phencyclidine, on EtOH-induced sedation/hypnosis were also assessed. Gene knockout of the NMDAR subunit NR2A or l-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate GluR1 or pharmacological antagonism of the NMDAR subunit NR2B (via Ro 25-6981) was employed to examine whether inactivating any one of these glutamate signaling molecules modified MK-801's effect on EtOH-related behaviors.

RESULTS

MK-801 markedly potentiated the ataxic effects of 1.75 g/kg EtOH and the sedative/hypnotic effects of 3.0 g/kg EtOH, but not the hypothermic effects of 3.0 g/kg EtOH, in C57BL/6J and 129/SvImJ mice. Phencyclidine potentiated EtOH-induced sedation/hypnosis in both inbred strains. Neither NR2A nor GluR1 KO significantly altered basal EtOH-induced ataxia, hypothermia, or sedation/hypnosis. Ro 25-6981 modestly increased EtOH-induced sedation/hypnosis. The ability of MK-801 to potentiate EtOH-induced ataxia and sedation/hypnosis was unaffected by GluR1 KO or NR2B antagonism. NR2A KO partially reduced MK-801 + EtOH-induced sedation/hypnosis, but not ataxia or hypothermia.

CONCLUSIONS

Data confirm a robust and response-specific potentiating effect of MK-801 on sensitivity to EtOH's intoxicating effects. Inactivation of three major components of glutamate signaling had no or only partial impact on the ability of MK-801 to potentiate behavioral sensitivity to EtOH. Further work to elucidate the mechanisms underlying NMDAR x EtOH interactions could ultimately provide novel insight into the role of NMDARs in alcoholism and its treatment.