Observer-rated ataxia: rating scales for assessment of genetic differences in ethanol-induced intoxication in mice

GenomeMUSter mouse genetic variation service enables multitrait, multipopulation data integration and analysis

Hundreds of inbred mouse strains and intercross populations have been used to characterize the function of genetic variants that contribute to disease. Thousands of disease-relevant traits have been characterized in mice and made publicly available. New strains and populations including consomics, the collaborative cross, expanded BXD, and inbred wild-derived strains add to existing complex disease mouse models, mapping populations, and sensitized backgrounds for engineered mutations. The genome sequences of inbred strains, along with dense genotypes from others, enable integrated analysis of trait-variant associations across populations, but these analyses are hampered by the sparsity of genotypes available. Moreover, the data are not readily interoperable with other resources. To address these limitations, we created a uniformly dense variant resource by harmonizing multiple data sets. Missing genotypes were imputed using the Viterbi algorithm with a data-driven technique that incorporates local phylogenetic information, an approach that is extendable to other model organisms. The result is a web- and programmatically accessible data service called GenomeMUSter, comprising single-nucleotide variants covering 657 strains at 106.8 million segregating sites. Interoperation with phenotype databases, analytic tools, and other resources enable a wealth of applications, including multitrait, multipopulation meta-analysis. We show this in cross-species comparisons of type 2 diabetes and substance use disorder meta-analyses, leveraging mouse data to characterize the likely role of human variant effects in disease. Other applications include refinement of mapped loci and prioritization of strain backgrounds for disease modeling to further unlock extant mouse diversity for genetic and genomic studies in health and disease.

GenomeMUSter mouse genetic variation service enables multi-trait, multi-population data integration and analyses

Hundreds of inbred laboratory mouse strains and intercross populations have been used to functionalize genetic variants that contribute to disease. Thousands of disease relevant traits have been characterized in mice and made publicly available. New strains and populations including the Collaborative Cross, expanded BXD and inbred wild-derived strains add to set of complex disease mouse models, genetic mapping resources and sensitized backgrounds against which to evaluate engineered mutations. The genome sequences of many inbred strains, along with dense genotypes from others could allow integrated analysis of trait - variant associations across populations, but these analyses are not feasible due to the sparsity of genotypes available. Moreover, the data are not readily interoperable with other resources. To address these limitations, we created a uniformly dense data resource by harmonizing multiple variant datasets. Missing genotypes were imputed using the Viterbi algorithm with a data-driven technique that incorporates local phylogenetic information, an approach that is extensible to other model organism species. The result is a web- and programmatically-accessible data service called GenomeMUSter ( https://muster.jax.org ), comprising allelic data covering 657 strains at 106.8M segregating sites. Interoperation with phenotype databases, analytic tools and other resources enable a wealth of applications including multi-trait, multi-population meta-analysis. We demonstrate this in a cross-species comparison of the meta-analysis of Type 2 Diabetes and of substance use disorders, resulting in the more specific characterization of the role of human variant effects in light of mouse phenotype data. Other applications include refinement of mapped loci and prioritization of strain backgrounds for disease modeling to further unlock extant mouse diversity for genetic and genomic studies in health and disease.

Strawberry notch homolog 2 regulates the response to interleukin-6 in the central nervous system

BACKGROUND

The cytokine interleukin-6 (IL-6) modulates a variety of inflammatory processes and, context depending, can mediate either pro- or anti-inflammatory effects. Excessive IL-6 signalling in the brain is associated with chronic inflammation resulting in neurodegeneration. Strawberry notch homolog 2 (Sbno2) is an IL-6-regulated gene whose function is largely unknown. Here we aimed to address this issue by investigating the impact of Sbno2 disruption in mice with IL-6-mediated neuroinflammation.

METHODS

Mice with germline disruption of Sbno2 (Sbno2-/-) were generated and crossed with transgenic mice with chronic astrocyte production of IL-6 (GFAP-IL6). Phenotypic, molecular and transcriptomic analyses were performed on tissues and primary cell cultures to clarify the role of SBNO2 in IL-6-mediated neuroinflammation.

RESULTS

We found Sbno2-/- mice to be viable and overtly normal. By contrast GFAP-IL6 × Sbno2-/- mice had more severe disease compared with GFAP-IL6 mice. This was evidenced by exacerbated neuroinflammation and neurodegeneration and enhanced IL-6-responsive gene expression. Cell culture experiments on primary astrocytes from Sbno2-/- mice further showed elevated and sustained transcript levels of a number of IL-6 stimulated genes. Notably, despite enhanced disease in vivo and gene expression both in vivo and in vitro, IL-6-stimulated gp130 pathway activation was reduced when Sbno2 is disrupted.

CONCLUSION

Based on these results, we propose a role for SBNO2 as a novel negative feedback regulator of IL-6 that restrains the excessive inflammatory actions of this cytokine in the brain.

CNS-Specific Synthesis of Interleukin 23 Induces a Progressive Cerebellar Ataxia and the Accumulation of Both T and B Cells in the Brain: Characterization of a Novel Transgenic Mouse Model

Interleukin 23 (IL-23) is a key mediator in neuroinflammation in numerous autoimmune diseases including multiple sclerosis (MS). However, the pathophysiology of IL-23 and how it contributes to neuroinflammation is poorly defined. To further clarify the role of IL-23 in CNS inflammation, we generated a transgenic mouse model (GF-IL23) with astrocyte-targeted expression of both IL-23 subunits, IL-23p19, and IL-23p40. These GF-IL23 mice spontaneously develop a progressive ataxic phenotype, which corresponds to cerebellar tissue destruction, and inflammatory infiltrates most prominent in the subarachnoidal and perivascular space. The CNS-cytokine milieu was characterized by numerous inflammatory mediators such as IL-17a and IFNγ. However, the leukocytic infiltrates were surprisingly predominated by B cells. To further examine the impact of the CNS-specific IL-23 synthesis on an additional systemic inflammatory stimulus, we applied the LPS-induced endotoxemia model. Administration of LPS in GF-IL23 mice resulted in early and pronounced microglial activation, enhanced cytokine production and, in sharp contrast to control animals, in the formation of lymphocytic infiltrates. Our model confirms a critical role for IL-23 in the induction of inflammation in the CNS, in particular facilitating the accumulation of lymphocytes in and around the brain. Thereby, CNS-specific synthesis of IL-23 is able to induce a cascade of inflammatory cytokines leading to microglia activation, astrocytosis, and ultimately tissue damage. The presented transgenic model will be a useful tool to further dissect the role of IL-23 in neuroinflammation.

Glyoxalase 1 (GLO1) Inhibition or Genetic Overexpression Does Not Alter Ethanol's Locomotor Effects: Implications for GLO1 as a Therapeutic Target in Alcohol Use Disorders

BACKGROUND

Glyoxalase 1 (GLO1) is an enzyme that metabolizes methylglyoxal (MG), which is a competitive partial agonist at GABA_A receptors. Inhibition of GLO1 increases concentrations of MG in the brain and decreases binge-like ethanol (EtOH) drinking. This study assessed whether inhibition of GLO1, or genetic overexpression of Glo1, would also alter the locomotor effects of EtOH, which might explain reduced EtOH consumption following GLO1 inhibition. We used the prototypical GABA_A receptor agonist muscimol as a positive control.

METHODS

Male C57BL/6J mice were pretreated with either the GLO1 inhibitor S-bromobenzylglutathione cyclopentyl diester (pBBG; 7.5 mg/kg; Experiment 1) or muscimol (0.75 mg/kg; Experiment 2), or their corresponding vehicle. We then determined whether locomotor response to a range of EtOH doses (0, 0.5, 1.0, 1.5, 2.0, and 2.5) was altered by either pBBG or muscimol pretreatment. We also examined the locomotor response to a range of EtOH doses in FVB/NJ wild-type and transgenic Glo1 overexpressing mice (Experiment 3). Anxiety-like behavior (time spent in the center of the open field) was assessed in all 3 experiments.

RESULTS

The EtOH dose-response curve was not altered by pretreatment with pBBG or by transgenic overexpression of Glo1. In contrast, muscimol blunted locomotor stimulation at low EtOH doses and potentiated locomotor sedation at higher EtOH doses. No drug or genotype differences were seen in anxiety-like behavior after EtOH treatment.

CONCLUSIONS

The dose of pBBG used in this study is within the effective range shown previously to reduce EtOH drinking. Glo1 overexpression has been previously shown to increase EtOH drinking. However, neither manipulation altered the dose-response curve for EtOH's locomotor effects, whereas muscimol appeared to enhance the locomotor sedative effects of EtOH. The present data demonstrate that reduced EtOH drinking caused by GLO1 inhibition is not due to potentiation of EtOH's stimulant or depressant effects.

An experimental evaluation of a new designed apparatus (NDA) for the rapid measurement of impaired motor function in rats

BACKGROUND

Assessment of the ability of rat to balance by rotarod apparatus (ROTA) is frequently used as a measure of impaired motor system function. Most of these methods have some disadvantages, such as failing to sense motor coordination rather than endurance and as the sensitivity of the method is low, more animals are needed to obtain statistically significant results.

NEW METHOD

We have designed and tested a new designed apparatus (NDA) to measure motor system function in rats. Our system consists of a glass box containing 4 beams which placed with 1cm distance between them, two electrical motors for rotating the beams, and a camera to record the movements of the rats. The RPM of the beams is adjustable digitally between 0 and 50 rounds per minute.

RESULTS

We evaluated experimentally the capability of the NDA for the rapid measurement of impaired motor function in rats. Also we demonstrated that the sensitivity of the NDA increases by faster rotation speeds and may be more sensitive than ROTA for evaluating of impaired motor system function.

COMPARISON WITH EXISTING METHODS

Compared to a previous version of this task, our NDA provides a more efficient method to test rodents for studies of motor system function after impaired motor nervous system.

CONCLUSIONS

In summary, our NDA will allow high efficient monitoring of rat motor system function and may be more sensitive than ROTA for evaluating of impaired motor system function in rats.

Comparative studies of oral administration of marine collagen peptides from Chum Salmon (Oncorhynchus keta) pre- and post-acute ethanol intoxication in female Sprague-Dawley rats

The present study aimed to evaluate the effect of an oral administration of marine collagen peptides (MCPs) pre- and post-acute ethanol intoxication in female Sprague-Dawley (SD) rats. MCPs were orally administered to rats at doses of 0 g per kg bw, 2.25 g per kg bw, 4.5 g per kg bw and 9.0 g per kg bw, prior to or after the oral administration of ethanol. Thirty minutes after ethanol treatment, the effect of MCPs on motor incoordination and hypnosis induced by ethanol were investigated using a screen test, fixed speed rotarod test (5 g per kg bw ethanol) and loss of righting reflex (7 g per kg bw ethanol). In addition, the blood ethanol concentrations at 30, 60, 90, and 120 minutes after ethanol administration (5 g per kg bw ethanol) were measured. The results of the screen test and fixed speed rotarod test suggested that treatment with MCPs at 4.5 g per kg bw and 9.0 g per kg bw prior to ethanol could attenuate ethanol-induced loss of motor coordination. Moreover, MCP administered both pre- and post-ethanol treatment had significant potency to alleviate the acute ethanol induced hypnotic states in the loss of righting reflex test. At 30, 60, 90 and 120 minutes after ethanol ingestion at 5 g per kg bw, the blood ethanol concentration (BEC) of control rats significantly increased compared with that in the 4.5 g per kg bw and 9.0 g per kg bw MCP pre-treated groups. However, post-treatment with MCPs did not exert a significant inhibitory effect on the BEC of the post-treated groups until 120 minutes after ethanol administration. Therefore, the anti-inebriation effect of MCPs was verified in SD rats with the possible mechanisms related to inhibiting ethanol absorption and facilitating ethanol metabolism. Moreover, the efficiency was better when MCPs were administered prior to ethanol.

Adapting to alcohol: Dwarf hamster (Phodopus campbelli) ethanol consumption, sensitivity, and hoard fermentation

Ethanol consumption and sensitivity in many species are influenced by the frequency with which ethanol is encountered in their niches. In Experiment 1, dwarf hamsters (Phodopus campbelli) with ad libitum access to food and water consumed high amounts of unsweetened alcohol solutions. Their consumption of 15%, but not 30%, ethanol was reduced when they were fed a high-fat diet; a high carbohydrate diet did not affect ethanol consumption. In Experiment 2, intraperitoneal injections of ethanol caused significant dose-related motor impairment. Much larger doses administered orally, however, had no effect. In Experiment 3, ryegrass seeds, a common food source for wild dwarf hamsters, supported ethanol fermentation. Results of these experiments suggest that dwarf hamsters may have adapted to consume foods in which ethanol production naturally occurs.

T-cell TGF-β signaling abrogation restricts medulloblastoma progression

Cancer cell secretion of TGF-β is a potent mechanism for immune evasion. However, little is known about how central nervous system tumors guard against immune eradication. We sought to determine the impact of T-cell TGF-β signaling blockade on progression of medulloblastoma (MB), the most common pediatric brain tumor. Genetic abrogation of T-cell TGF-β signaling mitigated tumor progression in the smoothened A1 (SmoA1) transgenic MB mouse. T regulatory cells were nearly abolished and antitumor immunity was mediated by CD8 cytotoxic T lymphocytes. To define the CD8 T-cell subpopulation responsible, primed CD8 T cells were adoptively transferred into tumor-bearing immunocompromised SmoA1 recipients. This led to generation of CD8(+)/killer cell lectin-like receptor G1 high (KLRG1(hi))/IL-7R(lo) short-lived effector cells that expressed granzyme B at the tumor. These results identify a cellular immune mechanism whereby TGF-β signaling blockade licenses the T-cell repertoire to kill pediatric brain tumor cells.

Neurotoxic effects of ivermectin administration in genetically engineered mice with targeted insertion of the mutated canine ABCB1 gene

OBJECTIVE

To develop in genetically engineered mice an alternative screening method for evaluation of P-glycoprotein substrate toxicosis in ivermectin-sensitive Collies.

ANIMALS

14 wild-type C57BL/6J mice (controls) and 21 genetically engineered mice in which the abcb1a and abcb1b genes were disrupted and the mutated canine ABCB1 gene was inserted.

PROCEDURES

Mice were allocated to receive 10 mg of ivermectin/kg via SC injection (n = 30) or a vehicle-only formulation of propylene glycol and glycerol formal (5). Each was observed for clinical signs of toxic effects from 0 to 7 hours following drug administration.

RESULTS

After ivermectin administration, considerable differences were observed in drug sensitivity between the 2 types of mice. The genetically engineered mice with the mutated canine ABCB1 gene had signs of severe sensitivity to ivermectin, characterized by progressive lethargy, ataxia, and tremors, whereas the wild-type control mice developed no remarkable effects related to the ivermectin.

CONCLUSIONS AND CLINICAL RELEVANCE

The ivermectin sensitivity modeled in the transgenic mice closely resembled the lethargy, stupor, disorientation, and loss of coordination observed in ivermectin-sensitive Collies with the ABCB1-1Δ mutation. As such, the model has the potential to facilitate toxicity assessments of certain drugs for dogs that are P-glycoprotein substrates, and it may serve to reduce the use of dogs in avermectin derivative safety studies that are part of the new animal drug approval process.

Induction of atypical EAE mediated by transgenic production of IL-6 in astrocytes in the absence of systemic IL-6

Interleukin (IL)-6 is crucial for the induction of many murine models of autoimmunity including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. While IL-6-deficient mice (IL-6 KO) are resistant to EAE, we showed previously that in transgenic mice with astrocyte-targeted production of IL-6-restricted to the cerebellum (GFAP-IL6), EAE induced with MOG(35-55) was redirected away from the spinal cord to the cerebellum. To further establish the importance of IL-6 produced in the central nervous system, we have generated mice producing IL-6 essentially only in the brain by crossing the GFAP-IL6 mice with IL-6 KO mice. Interestingly, GFAP-IL6-IL-6 KO mice showed a milder but almost identical phenotype as the GFAP-IL6 mice, which correlated with a lower load of inflammatory cells and decreased microglial reactivity. These results indicate that not only is cerebellar IL-6 production and eventual leakage into the peripheral compartment the dominating factor controlling this type of EAE but that it can also facilitate induction of autoimmunity in the absence of normal systemic IL-6 production.

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.

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).

Reversed light-dark cycle and cage enrichment effects on ethanol-induced deficits in motor coordination assessed in inbred mouse strains with a compact battery of refined tests

The laboratory environment existing outside the test situation itself can have a substantial influence on results of some behavioral tests with mice, and the extent of these influences sometimes depends on genotype. For alcohol research, the principal issue is whether genotype-related ethanol effects will themselves be altered by common variations in the lab environment or instead will be essentially the same across a wide range of lab environments. Data from 20 inbred strains were used to reduce an original battery of seven tests of alcohol intoxication to a compact battery of four tests: the balance beam and grip strength with a 1.25 g/kg ethanol dose and the accelerating rotarod and open-field activation tests with 1.75 g/kg. The abbreviated battery was then used to study eight inbred strains housed under a normal or reversed light-dark cycle, or a standard or enriched home cage environment. The light-dark cycle had no discernable effects on any measure of behavior or response to alcohol. Cage enrichment markedly improved motor coordination in most strains. Ethanol-induced motor coordination deficits were robust; the well-documented strain-dependent effects of ethanol were not altered by cage enrichment.

Intragastric self-infusion of ethanol in high- and low-drinking mouse genotypes after passive ethanol exposure

Two experiments examined the effect of 5 days of passive exposure to ethanol (or water) on later self-infusion of ethanol or water via surgically implanted intragastric (IG) catheters in mouse genotypes previously shown to drink high (C57BL/6J, HAP2) or low (DBA/2J, LAP2) amounts of ethanol in home-cage continuous-access two-bottle choice procedures. Intragastric ethanol self-infusion was affected by both genotype and a history of passive ethanol exposure, with greater intakes in the high-drinking genotypes and in groups that received passive exposure to ethanol. Passive ethanol exposure also increased preference for the flavor that signaled ethanol infusion (S+), eliminating genetic differences in this measure. The increases in ethanol intake and S+ preference induced by ethanol exposure might have been mediated jointly by development of tolerance to aversive post-absorptive ethanol effects and negative reinforcement because of alleviation of withdrawal. Bout analyses indicated that ethanol exposure increased ethanol self-infusion by increasing the total number of daily bouts rather than by increasing bout size. These analyses also showed that DBA/2J mice infused larger ethanol bouts and a greater percentage of their total intakes in large bouts than C57BL/6J mice. Overall, these studies suggest that the IG self-infusion procedure is a potentially useful new tool for studying genetic and environmental influences on excessive ethanol intake and preference in mice.

Site-specific production of IL-6 in the central nervous system retargets and enhances the inflammatory response in experimental autoimmune encephalomyelitis

IL-6 is crucial for the induction of many murine models of autoimmunity including experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. To establish the role of site-specific production of IL-6 in autoimmunity, we examined myelin oligodendrocyte glycoprotein immunization-induced EAE in transgenic mice (GFAP-IL6) with IL-6 production restricted to the cerebellum. Myelin oligodendrocyte glycoprotein-immunized (Mi-) GFAP-IL6 mice developed severe ataxia but no physical signs of spinal cord involvement, which was in sharp contrast to Mi-wild type (WT) animals that developed classical EAE with ascending paralysis. Immune pathology and demyelination were nearly absent from the spinal cord, but significantly increased in the cerebellum of Mi-GFAP-IL6 mice. Tissue damage in the cerebellum in the Mi-GFAP-IL6 mice was accompanied by increased total numbers of infiltrating leukocytes and increased proportions of both neutrophils and B-cells. With the exception of IL-17 mRNA, which was elevated in both control immunized and Mi-GFAP-IL6 cerebellum, the level of other cytokine and chemokine mRNAs were comparable with Mi-WT cerebellum whereas significantly higher levels of IFN-gamma and TNF-alpha mRNA were found in Mi-WT spinal cord. Thus, site-specific production of IL-6 in the cerebellum redirects trafficking away from the normally preferred antigenic site the spinal cord and acts as a leukocyte "sink" that markedly enhances the inflammatory cell accumulation and disease. The mechanisms underlying this process likely include the induction of specific chemokines, activation of microglia, and activation and loss of integrity of the blood-brain barrier present in the cerebellum of the GFAP-IL6 mice before the induction of EAE.

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.

Early signs of neurolipidosis-related behavioural alterations in a murine model of metachromatic leukodystrophy

Arylsulfatase A (ASA)-deficient mice represent an animal model for the lysosomal storage disorder metachromatic leukodystrophy (MLD). Although the model has been applied in pathophysiological and therapeutic studies, the behavioural phenotype of ASA(-/-) mice is only partially characterized, and the most decisive outcome measures for therapy evaluation only emerge beyond 1 year of age. Presently, ASA(-/-) mice and ASA(+/-) control mice were studied at 6 and 12 months of age on an extensive battery including tests of neuromotor ability, exploratory behaviour, and learning and memory. Overt signs of ataxia were not observed in 6-month-old ASA(-/-) mice, but quantitative gait analysis during open-field exploration revealed that ASA(-/-) mice displayed increased hind base width and increased stride lengths for all paws. Their covert motor incoordination was evident in a correlation analysis which unveiled decreased harmonisation of concurrent gait parameters. For example, while ASA(+/-) controls demonstrated substantial convergence of front and hind base width (r=0.54), these variables actually diverged in ASA(-/-) mice (r=-0.37). Furthermore, various behavioural observations indicated emotional alterations in ASA(-/-) mice. Six-month-old ASA(-/-) mice also showed decreased response rates in scheduled operant responding. The present findings could provide relevant behavioural outcome measures for further use of this murine MLD model in preclinical studies.

The parallel rod floor test: a measure of ataxia in mice

The parallel rod floor test is a new model of ataxia in mice. It allows the simultaneous measurement of ataxia and locomotor activity. This protocol is designed for researchers examining ethanol-induced motor incoordination in mice, but it should be applicable to other sedative/hypnotic drugs and to testing cerebellar mutant mice or mice with engineered genetic defects. This protocol takes 3 d, with the time per day depending on how many animals are tested. The test allows researchers to quantify differences in motor coordination among genotypes of mice that may differ in locomotor activity. Unlike many other methods for assessing incoordination, the parallel rod floor test yields similar patterns of genetic sensitivity across a range of variant forms of the apparatus.

Age-dependent variation in behavior following acute ethanol administration in male and female adolescent rhesus macaques (Macaca mulatta)

BACKGROUND

There has been considerable focus on the adolescent stage of development in the study of alcohol use and the etiology of alcohol-related problems. Because adolescence is a process of dynamic change rather than a discrete or static stage of development, it is important to consider ontogenetic changes in the response to ethanol within the adolescent time period. In rodents, levels of ethanol-induced motor impairment have been shown to increase from early to late adolescence. This study investigated associations between behavior following acute ethanol administration and age, rearing condition (mother-reared vs nursery-reared), and serotonin transporter (rh5-HTTLPR) genotype in a sample of alcohol-naïve adolescent rhesus macaques.

METHODS

Rhesus macaques (n=97; 41 males, 56 females), ranging in age from 28 to 48 months, were administered intravenous (IV) doses of ethanol (2.2 g/kg for males, 2.0 g/kg for females) twice in 2 separate testing sessions. A saline/ethanol group (n=16; 8 males, 6 females) was administered saline in 1 testing session and ethanol in the second session. Following each IV injection, subjects underwent a 30-minute general motor behavioral assessment. Behavior in the saline/ethanol group was compared between the saline and ethanol-testing sessions using analysis of variance. Behavioral data for the larger study sample were averaged between the 2 testing sessions and summarized using factor analysis. Rotated factor scores were used as dependent variables in multiple regression analyses to test for relationships between behavior and age, rearing condition, and rh5-HTTLPR genotype.

RESULTS

During the ethanol-testing session, behaviors indicative of motor impairment (stumbles, falls, sways, bumping the wall, and unsuccessful jumps) were frequently observed in the saline/ethanol group, while they did not occur under the saline-testing session. Factor analysis of behavior following ethanol administration in the larger study sample yielded 3 factors: Ataxia, Impaired Jumping Ability, and Stimulation. Significant negative correlations between age and Ataxia were found for both males and females. Females also exhibited positive correlations between age and Impaired Jumping Ability and age and Stimulation. No significant correlations were found with either rearing condition or rh5-HTTLPR genotype.

CONCLUSIONS

These findings suggest that ontogenetic changes during adolescence in the behavioral response to ethanol differ between rodents and primates. Furthermore, sex differences in the behavioral response to ethanol appear to develop during adolescence.

Hybrid C57BL/6J x FVB/NJ mice drink more alcohol than do C57BL/6J mice

BACKGROUND

From several recent strain surveys (28 strains: Bachmanov et al., personal communication; 22 strains: Finn et al., unpublished), and from data in >100 other published studies of 24-hr two-bottle ethanol preference, it is known that male C57BL/6 (B6) mice self-administer about 10-14 g/kg/day and that female B6 mice self-administer about 12-18 g/kg/day. No strain has been found to consume more ethanol than B6. In one of our laboratories (Texas), we noted a markedly greater intake of ethanol in an F1 hybrid of B6 and FVB/NJ (FVB) mice.

METHODS

To confirm and extend this finding, we repeated the study at another site (Portland) using concentrations up to 30% ethanol and also tested B6xFVB F1 mice in restricted access drinking procedures that produce high levels of alcohol intake.

RESULTS

At both sites, we found that B6xFVB F1 mice self-administered high levels of ethanol during two-bottle preference tests (females averaging from 20 to 35 g/kg/day, males 7-25 g/kg/day, depending on concentration). F1 hybrids of both sexes drank significantly more 20% ethanol than both the B6 and FVB strains. Female F1 hybrids also drank more 30% ethanol. In the restricted access tests, ethanol consumption in the F1 hybrids was equivalent to that in B6 mice.

CONCLUSIONS

These data show that this new genetic model has some significant advantages when compared to existing inbred strains, and could be used to explore the genetic basis of high ethanol drinking in mice.

Effects of genetic and procedural variation on measurement of alcohol sensitivity in mouse inbred strains

Mice from eight inbred strains were studied for their acute sensitivity to ethanol as indexed by the degree of hypothermia (HT), indexed as the reduction from pre-injection baseline of their body temperature. Two weeks later, mice were tested for their loss of righting reflex (LRR) after a higher dose of ethanol. The LRR was tested using the "classical" method of watching for recovery in animals placed on their backs in a V-shaped trough and recording duration of LRR. In a separate test, naive animals of the same strains were tested for HT repeatedly to assess the development of rapid (RTOL) and chronic tolerance (CTOL). We have recently developed a new method for testing LRR that leads to a substantial increase in the sensitivity of the test. Strains also have been found to differ in the new LRR test, as well as in the development of acute functional tolerance (AFT) to this response. In addition, our laboratory has periodically published strain difference data on the older versions of the HT and LRR responses. The earlier tests used some of the exact substrains tested currently, while for some strains, different substrains (usually, Nih versus Jax) were tested. We examined correlations of strain means to see whether patterns of strain differences were stable across time and across different test variants assessing the same behavioral construct. HT strain sensitivity scores were generally highly correlated across a 10-23 years period and test variants. The CTOL to HT was well-correlated across studies, and was also genetically similar to RTOL. The AFT, however, was related to neither RTOL nor CTOL, although this may be because different phenotypic end points were compared. The LRR data, which included a variant of the classical test, were not as stable. Measures of LRR onset were reasonably well correlated, as were those taken at recovery (e.g., duration). However, the two types of measures of LRR sensitivity to ethanol appear to be tapping traits that differ genetically. Also, the pattern of genetic correlation between HT and LRR initially reported in 1983 was not seen in current and contemporaneous studies. In certain instances, substrain seems to matter little, while in others, substrains differed a great deal. These data are generally encouraging about the stability of genetic differences.

Calcium-stimulated adenylyl cyclases are critical modulators of neuronal ethanol sensitivity

The importance of the cAMP signaling pathway in the modulation of ethanol sensitivity has been suggested by studies in organisms from Drosophila melanogaster to man. However, the involvement of specific isoforms of adenylyl cyclase (AC), the molecule that converts ATP to cAMP, has not been systemically determined in vivo. Because AC1 and AC8 are the only AC isoforms stimulated by calcium, and ethanol modulates calcium flux by the NMDA receptor, we hypothesized that these ACs would be important in the neural response to ethanol. AC1 knock-out (KO) mice and double knock-out (DKO) mice with genetic deletion of both AC1 and AC8 display substantially increased sensitivity to ethanol-induced sedation compared with wild-type (WT) mice, whereas AC8 KO mice are only minimally more sensitive. In contrast, AC8 KO and DKO mice, but not AC1 KO mice, demonstrate decreased voluntary ethanol consumption compared with WT mice. DKO mice do not display increased sleep time compared with WT mice after administration of ketamine or pentobarbital, indicating that the mechanism of enhanced ethanol sensitivity in these mice is likely distinct from the antagonism of ethanol of the NMDA receptor and potentiation of the GABA(A) receptor. Ethanol does not enhance calcium-stimulated AC activity, but the ethanol-induced phosphorylation of a discrete subset of protein kinase A (PKA) substrates is compromised in the brains of DKO mice. These results indicate that the unique activation of PKA signaling mediated by the calcium-stimulated ACs is an important component of the neuronal response to ethanol.

Alcohol withdrawal severity in inbred mouse (Mus musculus) strains

Male mice (Mus musculus) from 15 standard inbred strains were exposed to a nearly constant concentration of ethanol (EtOH) vapor for 72 hr, averaging 1.59 +/- 0.03 mg EtOH/mL blood at withdrawal. EtOH- and air-exposed groups were tested hourly for handling-induced convulsions for 10 hr and at Hours 24 and 25. Strains differed markedly in the severity of withdrawal (after subtraction of control values), and by design these differences were independent of strain differences in EtOH metabolism. Correlation of strain mean withdrawal severity with other responses to EtOH supported previously reported genetic relationships of high EtOH withdrawal with low drinking, high conditioned taste aversion, low tolerance to EtOH-induced hypothermia, and high stimulated activity after low-dose EtOH. Also supported were the positive genetic correlations among EtOH, barbiturate, and benzodiazepine withdrawal. Sensitivity of naive mice to several chemical convulsant-induced seizures was also correlated with EtOH withdrawal.

Characterization of the parallel rod floor apparatus to test motor incoordination in mice

Impairment of motor coordination, or ataxia, is a prominent effect of alcohol ingestion in humans. To date, many models have been created to examine this phenomenon in animals. Evidence suggests that the tasks thought to measure this behavior in mice actually measure different components of this complex trait. We have characterized the parallel rod floor apparatus to quantify ethanol-induced motor incoordination. Using genetically heterogeneous mice, we evaluated the influence of rod diameter and inter-rod distance on dose-related ethanol-induced motor incoordination to select parameters that optimized testing procedures. We then used the DBA/2J and C57BL/6J inbred strains of mice to examine the effect of 2 g/kg of ethanol, by serially testing mice on two floor types, separated by 1 week. Finally, we tested eight inbred strains of mice on four floor types to examine patterns of strain sensitivity to 2 g/kg of intraperitoneal ethanol and determined the test parameters that maximized strain effect size. Motor incoordination varied depending on the floor type and strain. When data from strain 129S1/SvlmJ were removed from the analyses because of their extreme behavior, the greatest strain effect size was observed on one floor type during the first 10 min of testing after 2 g/kg of intraperitoneal ethanol. These findings suggest that the parallel rod floor apparatus provides a useful means for examining ethanol-induced motor incoordination in mice but that specific testing procedures are important for optimizing detection of motor incoordination and genetic influences.

Ethanol's effects on gait dynamics in mice investigated by ventral plane videography

BACKGROUND

Performance of mice in motor function tests for ethanol sensitivity is often task dependent, not reflective of coordinated movement, and reported qualitatively. Therefore, we applied a new imaging technique to record and quantify coordinated gait dynamics in mice in response to ethanol.

METHODS

We applied ventral plane videography to record and report gait indices in mice walking on a transparent treadmill belt. We examined the effects of ethanol on gait in C57BL/6J (B6) and DBA/2J (D2) mice walking at a speed of 25 cm/sec. B6 and D2 are two inbred strains that are widely used to study the genetic influences of ethanol on motor function.

RESULTS

Gait posture in D2 mice was less stable than in B6 mice. B6 mice always showed an alternate step sequence, whereas D2 mice sometimes showed cruciate and rotary step sequences. Ethanol in increasing doses increased stride frequency, decreased stride length, and increased stride length variability in D2 mice but not in B6 mice. The forelimb braking duration was significantly shortened and the hind limb propulsion duration was significantly prolonged with a high dose of ethanol in D2 mice but not in B6 mice. Differences in gait indices between the two strains of mice were more pronounced of the forelimbs with the highest dose of ethanol (2.75 g/kg).

CONCLUSION

Our data suggest that the higher susceptibility of D2 compared with B6 mice to the effects of ethanol on motor function may be attributed to less stable basal gait characteristics that are perturbed by ethanol. The ability of this method to quantify step sequence patterns and gait indices of forelimb and hind limbs could provide new data regarding ethanol-induced motor incoordination.

An analysis of the genetics of alcohol intoxication in inbred mice

We compared the behaviors of eight inbred mouse strains across 18 variables, using 11 behavioral assays, and gave ethanol (EtOH) as an intoxicant. Genetic influences on behavior and sensitivity to EtOH were pronounced, but strain sensitivities were generally only modestly correlated across tasks. Certain well-correlated clusters of responses suggested that some genes affect similar neurobiological substrates. No strains of mice were generally sensitive or resistant to intoxication across tasks. Anthropomorphically appealing concepts like 'muscle strength' had little explanatory power across tasks. A battery of selected tests was proposed for future studies. Overall, the results show that each mouse behavioral assay captures only a portion of ataxia, a genetically complex behavioral domain. Conversely, multiple behavioral capacities are apparently required for performance in each specific assay. Thus, if only one or two tests are used to evaluate motor function in genetically engineered mutant mice, only a small portion of the domain will be assessed and results may be misleading. This caveat likely extends to many behavioral domains (e.g. learning and memory, anxiety).