Quantitative trait loci for novelty/stress-induced locomotor activation in recombinant inbred (RI) and recombinant congenic (RC) strains of mice

Mapping of a chromosome 12 region associated with airway hyperresponsiveness in a recombinant congenic mouse strain and selection of potential candidate genes by expression and sequence variation analyses

In a previous study we determined that BcA86 mice, a strain belonging to a panel of AcB/BcA recombinant congenic strains, have an airway responsiveness phenotype resembling mice from the airway hyperresponsive A/J strain. The majority of the BcA86 genome is however from the hyporesponsive C57BL/6J strain. The aim of this study was to identify candidate regions and genes associated with airway hyperresponsiveness (AHR) by quantitative trait locus (QTL) analysis using the BcA86 strain. Airway responsiveness of 205 F2 mice generated from backcrossing BcA86 strain to C57BL/6J strain was measured and used for QTL analysis to identify genomic regions in linkage with AHR. Consomic mice for the QTL containing chromosomes were phenotyped to study the contribution of each chromosome to lung responsiveness. Candidate genes within the QTL were selected based on expression differences in mRNA from whole lungs, and the presence of coding non-synonymous mutations that were predicted to have a functional effect by amino acid substitution prediction tools. One QTL for AHR was identified on Chromosome 12 with its 95% confidence interval ranging from 54.6 to 82.6 Mbp and a maximum LOD score of 5.11 (p = 3.68×10⁻³). We confirmed that the genotype of mouse Chromosome 12 is an important determinant of lung responsiveness using a Chromosome 12 substitution strain. Mice with an A/J Chromosome 12 on a C57BL/6J background have an AHR phenotype similar to hyperresponsive strains A/J and BcA86. Within the QTL, genes with deleterious coding variants, such as Foxa1, and genes with expression differences, such as Mettl21d and Snapc1, were selected as possible candidates for the AHR phenotype. Overall, through QTL analysis of a recombinant congenic strain, microarray analysis and coding variant analysis we identified Chromosome 12 and three potential candidate genes to be in linkage with airway responsiveness.

A cautionary note on ignoring polygenic background when mapping quantitative trait loci via recombinant congenic strains

In gene mapping, it is common to test for association between the phenotype and the genotype at a large number of loci, i.e., the same response variable is used repeatedly to test a large number of non-independent and non-nested hypotheses. In many of these genetic problems, the underlying model is a mixed model consistent of one or very few major genes concurrently with a genetic background effect, usually thought as of polygenic nature and, consequently, modeled through a random effects term with a well-defined covariance structure dependent upon the kinship between individuals. Either because the interest lies only on the major genes or to simplify the analysis, it is habitual to drop the random effects term and use a simple linear regression model, sometimes complemented with testing via resampling as an attempt to minimize the consequences of this practice. Here, it is shown that dropping the random effects term has not only extreme negative effects on the control of the type I error rate, but it is also unlikely to be fixed by resampling because, whenever the mixed model is correct, this practice does not allow to meet some basic requirements of resampling in a gene mapping context. Furthermore, simulations show that the type I error rates when the random term is ignored can be unacceptably high. As an alternative, this paper introduces a new bootstrap procedure to handle the specific case of mapping by using recombinant congenic strains under a linear mixed model. A simulation study showed that the type I error rates of the proposed procedure are very close to the nominal ones, although they tend to be slightly inflated for larger values of the random effects variance. Overall, this paper illustrates the extent of the adverse consequences of ignoring random effects term due to polygenic factors while testing for genetic linkage and warns us of potential modeling issues whenever simple linear regression for a major gene yields multiple significant linkage peaks.

Analysis of quantitative trait loci in mice suggests a role of Enoph1 in stress reactivity

Significant progress in elucidating the genetic etiology of anxiety and depression has been made during the last decade through a combination of human and animal studies. In this study, we aimed to discover genetic loci linked with anxiety as well as depression in order to reveal new candidate genes. Therefore, we initially tested the behavioral sensitivity of 543 F2 animals derived from an intercross of C57BL/6J and C3H/HeJ mice in paradigms for anxiety and depression. Next, all animals were genotyped with 269 microsatellite markers with a mean distance of 5.56 cM. Finally, a Quantitative Trait Loci (QTL) analysis was carried out, followed by selection of candidate genes. The QTL analysis revealed several new QTL on chromosome 5 with a common core interval of 19 Mb. We further narrowed this interval by comparative genomics to a region of 15 Mb. A database search and gene prioritization revealed Enoph1 as the most significant candidate gene on the prioritization list for anxiety and also for depression fulfilling our selection criteria. The Enoph1 gene, which is involved in polyamine biosynthesis, is differently expressed in parental strains, which have different brain spermidine levels and show distinct anxiety and depression-related phenotype. Our result suggests a significant role in polyamines in anxiety and depression-related behaviors.

The clinical implications of mouse models of enhanced anxiety

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

Architecture of energy balance traits in emerging lines of the Collaborative Cross

The potential utility of the Collaborative Cross (CC) mouse resource was evaluated to better understand complex traits related to energy balance. A primary focus was to examine if genetic diversity in emerging CC lines (pre-CC) would translate into equivalent phenotypic diversity. Second, we mapped quantitative trait loci (QTL) for 15 metabolism- and exercise-related phenotypes in this population. We evaluated metabolic and voluntary exercise traits in 176 pre-CC lines, revealing phenotypic variation often exceeding that seen across the eight founder strains from which the pre-CC was derived. Many phenotypic correlations existing within the founder strains were no longer significant in the pre-CC population, potentially representing reduced linkage disequilibrium (LD) of regions harboring multiple genes with effects on energy balance or disruption of genetic structure of extant inbred strains with substantial shared ancestry. QTL mapping revealed five significant and eight suggestive QTL for body weight (Chr 4, 7.54 Mb; CI 3.32-10.34 Mb; Bwq14), body composition, wheel running (Chr 16, 33.2 Mb; CI 32.5-38.3 Mb), body weight change in response to exercise (1: Chr 6, 77.7Mb; CI 72.2-83.4 Mb and 2: Chr 6, 42.8 Mb; CI 39.4-48.1 Mb), and food intake during exercise (Chr 12, 85.1 Mb; CI 82.9-89.0 Mb). Some QTL overlapped with previously mapped QTL for similar traits, whereas other QTL appear to represent novel loci. These results suggest that the CC will be a powerful, high-precision tool for examining the genetic architecture of complex traits such as those involved in regulation of energy balance.

Fine mapping quantitative trait loci that influence alcohol preference behavior in the High and Low Alcohol Preferring (HAP and LAP) mice

The High Alcohol Preferring (HAP1) and Low Alcohol Preferring (LAP1) mouse lines were selectively bred for differences in alcohol intake. The HAP1 and LAP1 mice are essentially non-inbred lines that originated from an outbred colony of HS/Ibg mice, a heterogeneous stock developed from intercrossing 8 inbred strains of mice. In a former genomewide SNP association study, we identified quantitative trait loci (QTL) on chromosomes 1, 3, 5, and 9 (Bice et al. 2009). Provisional QTL were also identified on chromosomes 8 and X. In the present study, using the same F2 DNA samples, we placed a much denser set of SNPs within each of those QTL regions. Using the same analytical approach employed previously, which utilizes ancestral recombination to fine map the QLT interval, we obtained significant LOD scores on chromosomes 1, 3, and 9, only. Our results using a dense set of SNP markers suggest that there are multiple loci contributing to alcohol preference on those three chromosomes.

Behavioral characterization of A/J and C57BL/6J mice using a multidimensional test: association between blood plasma and brain magnesium-ion concentration with anxiety

Up to 29% of all adults will experience an anxiety-related disorder during their lives. Treatment of these disorders is still difficult and the exact mechanisms and pathways behind anxiety disorders remain to be elucidated. Although evidence exists for genetically based susceptibility of human psychiatric diseases, risk genes have rarely been identified up to now. Inbred mouse strains are, together with the crosses and genetic reference populations derived from them, important tools for the genetic dissection of complex behavioral traits in the mouse. Thus, inbred mouse models of human anxiety may be a potent starting tool to search for candidate genes in mice, which could then via comparative genomics be translated to the human situation. In this paper we investigate whether the A/J and C57BL/6J mouse inbred strains differ in a limited number of motivational systems (anxiety, exploration, memory, locomotion, and social affinity), but especially in anxiety-related behavior from each other. Young adult individuals from both genders of A/J and C57BL/6J strains were behaviorally phenotyped using a multidimensional test: the modified hole board. This paradigm basically is a combination of the traditional hole board and the open field test allowing to test for anxiety-related avoidance behavior, risk assessment, arousal, exploration, memory, locomotor activity, and social affinity, using just one single test. An acute, aversive stimulus (intra-peritoneal injection with saline) was applied to the animals to test for the robustness of their behavioral phenotype. In addition, presumed physiological indicators for anxiety (circulating glucose, cholesterol, and corticosterone, adrenal tyrosine hydroxylase, and blood plasma and brain magnesium) were investigated. It could be concluded that C57BL/6J and A/J mice differ with respect to almost all tested motivational systems. For some measures, including anxiety-related behavioral parameters, there were clear gender effects. The high-anxiety phenotype of A/J mice could be shown to represent a primary and robust characteristic. Further, blood plasma and brain magnesium levels were significantly correlated with several anxiety-related behavioral parameters. These results emphasize the hypothesized, and possibly causal, association between magnesium status and emotionality.

Behavioral and genetic investigations of low exploratory behavior in Il18r1(-/-) mice: we can't always blame it on the targeted gene

The development of gene-targeting technologies has enabled research with immune system-related knockout mouse strains to advance our understanding of how cytokines and their receptors interact and influence a number of body systems, including the central nervous system (CNS). A critical issue when we are interpreting phenotypic data from these knockout strains is the potential role of genes other than the targeted one. Although many of the knockout strains have been made congenic on a C57BL/6 (B6) genetic background, there remains a certain amount of genetic material from the129 substrain that was used in the development of these strains. This genetic material could result in phenotypes incorrectly attributed to the targeted gene. We recently reported low-activity behavior in Il10(-/-) mice that was linked to this genetic material rather than the targeted gene itself. In the current study we confirm the generalizability of those earlier findings, by assessing behavior in Il18(-/-) and Il18r1(-/-) knockout mice. We identified low activity and high anxiety-like behaviors in Il18r1(-/-) mice, whereas Il18(-/-) mice displayed little anxiety-like behavior. Although Il18r1(-/-) mice are considered a congenic strain, we have identified substantial regions of 129P2-derived genetic material not only flanking the ablated Il18r1 on Chromosome 1, but also on Chromosomes 4, 5, 8, 10, and 14. Our studies suggest that residual 129-derived gene(s), rather than the targeted Il18r1 gene, is/are responsible for the low level of activity seen in the Il18r1(-/-) mice. Mapping studies are necessary to identify the gene or genes contributing to the low-activity phenotype.

The role of the alpha 2A-adrenoceptor in mouse stress-coping behaviour

Acute stress is known to impair memory functions in both men and laboratory rodents. In human the alpha 2A-adrenoceptor system is known to play a critical role in regulating acute neuropsychological stress responses and, ultimately, stress-coping behaviour. In search for neurobiological and central nervous mechanisms behind these behaviours we investigated if the alpha 2A-adrenoceptor is involved in these mechanisms in mice. Phenotypical differences between the A/J and C57BL/6J (B6) mouse inbred strains were evaluated in previous studies. These data showed significant strain differences in various motivational systems (anxiety, exploration, locomotion, memory etc.). From the literature it is known that chromosome 19 contains the gene for the adrenergic alpha 2A receptor that is thought to be involved in emotional behaviours, among others anxiety-related avoidance behaviour and arousal. We investigated if this pathway could possibly be involved in avoidance/arousal susceptibility by applying an agonist (dexmedetomidine) and an antagonist (atipamezole) of the alpha 2A-adrenoceptor to male mice from a consomic strain (C57BL/6J-Chr 19(A)/NaJ, abbreviated to CSS19=anxious), and the corresponding donor (A/J=anxious) and host (B6=non-anxious) strains. The mice were tested in the modified hole board (mHB) test which allows for the assessment of a variety of behavioural patterns by use of only one test. In addition, a forced swimming test (FST) was conducted to test for stress-coping behaviour. Results of the behavioural testing in the mHB-test showed significant strains differences and strain-specific treatment effects for parameters describing anxiety-related endophenotypes. The FST revealed effects of dexmedetomidine and atipamezole on stress-coping behaviour. In conclusion, the involvement of the alpha 2A-adrenoceptor, located on mouse chromosome 19, on anxiety-related behaviour remains unclear and will possibly not play a main role in the development of anxiety-related behaviour in mice. However, we could show involvement of this receptor in stress-coping behaviour in mice.

Identification of novel chromosomal regions associated with airway hyperresponsiveness in recombinant congenic strains of mice

Airway responsiveness is the ability of the airways to respond to bronchoconstricting stimuli by reducing their diameter. Airway hyperresponsiveness has been associated with asthma susceptibility in both humans and murine models, and it has been shown to be a complex and heritable trait. In particular, the A/J mouse strain is known to have hyperresponsive airways, while the C57BL/6 strain is known to be relatively refractory to bronchoconstricting stimuli. We analyzed recombinant congenic strains (RCS) of mice generated from these hyper- and hyporesponsive parental strains to identify genetic loci underlying the trait of airway responsiveness in response to methacholine as assessed by whole-body plethysmography. Our screen identified 16 chromosomal regions significantly associated with airway hyperresponsiveness (genome-wide P <or= 0.05): 8 are supported by independent and previously published reports while 8 are entirely novel. Regions that overlap with previous reports include two regions on chromosome 2, three on chromosome 6, one on chromosome 15, and two on chromosome 17. The 8 novel regions are located on chromosome 1 (92-100 cM), chromosome 5 (>73 cM), chromosome 7 (>63 cM), chromosome 8 (52-67 cM), chromosome 10 (3-7 cM and >68 cM), and chromosome 12 (25-38 cM and >52 cM). Our data identify several likely candidate genes from the 16 regions, including Ddr2, Hc, Fbn1, Flt3, Utrn, Enpp2, and Tsc.

Genetic architecture for hole-board behaviors across substantial time intervals in young, middle-aged and old mice

A quantitative trait locus (QTL) analysis of behaviors across the life span was conducted in F(2) mice from a C57BL/6J x DBA/2J cross and 22 BXD recombinant inbred (RI) strains. Mice of three age groups were tested in a hole-board apparatus for 3 min on three occasions approximately 1 month apart (average age at test 150, 450 and 750 days, approximately 400 mice per group, divided equally by sex). Quantitative trait loci with small effect size were found on 11 chromosomes for hole-board activity (Hbact) and hole-board rearing (Hbrear). Analysis of 22 RI strains tested at 150 and 450 days of age found only suggestive linkage, with four QTL for Hbact overlapping with those from the F(2) analysis. There was a significant phenotypic correlation between Hbact and Hbrear (approximately 0.55-0.69) and substantial commonality among QTL for the two behaviors. QTL analyses of head-pokes (HP) and fecal boli (FB) only identified QTL at the suggestive level of significance. Age accounted for approximately 15% of the phenotypic variance (sex approximately 3%), and there were genotype by age interactions at approximately 25% of the Hbact and Hbrear QTL. Quantitative trait loci for Hbrear were relatively stable across the three measurement occasions (those for Hbact somewhat less so), although mean levels of each index declined markedly comparing the first to subsequent trials. Considered as a whole, the polygenic system influencing exploratory behaviors accounts for approximately the same amount of phenotypic variance as age (within the range studied), is stable across substantial periods of time, and acts, for the most part, independently of age and sex.

Identification of quantitative trait loci for locomotor activation and anxiety using closely related inbred strains

We carried out a quantitative trait loci (QTL) mapping experiment in two phenotypically similar inbred mouse strains, C57BL/6J and C58/J, using the open-field assay, a well-established model of anxiety-related behavior in rodents. This intercross was initially carried out as a control cross for an ethylnitrosurea mutagenesis mapping study. Surprisingly, although open-field behavior is similar in the two strains, we identified significant QTL in their F2 progeny. Marker regression identified a locus on Chr 8 having associations with multiple open-field measures and a significant interaction between loci on Chr 13 and 17. Together, the Chr 8 locus and the interaction effect form the core set of QTL controlling these behaviors with additional loci on Chr 1 and 6 present in a subset of the behaviors.

Evidence for epigenetic interactions for loci on mouse chromosome 1 regulating open field activity

The expression of motor activity levels in response to novel situations is under complex genetic and environmental control. Several genetic loci have been implicated in the regulation of this behavioral phenotype, but their relationship to epigenetic and epistatic interactions is relatively unknown. Here, we report on a quantitative trait locus (QTL) on mouse chromosome 1 for novelty-induced motor activity in the open field, using chromosome substitution strains derived from a high active host strain (C57BL/6J) and a low active donor strain (A/J). The QTL for open field (horizontal distance moved) peaked at the location of Kcnj9, however, QTL detection was initially masked by an interplay of both grandparent genetic origin and genetic co-factors influencing behavior on chromosome 1. Our findings indicate that epigenetic interactions can play an important role in the identification of behavioral QTLs and must be taken into consideration when applying behavioral genetic strategies.

Mouse chromosome 11 harbors genetic determinants of hippocampal strain-specific nicotinic receptor expression

Differences between isogenic mouse strains in cellular expression of the neuronal nicotinic acetylcholine (ACh) receptor subunit alpha 4 (nAChR alpha 4) by the dorsal hippocampus are well known. To investigate further the genetic basis of these variations, expression of the nAChR alpha 4 subunit was measured in congenic mouse lines derived from two strains exhibiting notable divergence in the expression of this subunit: C3H and C57BL/6. Congenic lines carrying reciprocally introgressed regions (quantitative trait loci; QTL) from chromosomes 4, 5, and 12 each retained the phenotype most closely associated with the parental strain. However, in congenic lines harboring the reciprocal transfer of a chromosome 11 QTL, a characteristic difference in the ratio of interneurons versus astrocytes expressing nAChR alpha 4 in the CA1 region is reversed relative to the parental strain. These finding suggest that this chromosomal segment harbors genes that regulate strain distinct hippocampal morphology that is revealed by nAChR alpha 4 expression.

High-resolution genetic mapping of mammalian motor activity levels in mice

The generation of motor activity levels is under tight neural control to execute essential behaviors, such as movement toward food or for social interaction. To identify novel neurobiological mechanisms underlying motor activity levels, we studied a panel of chromosome substitution (CS) strains derived from mice with high (C57BL/6J strain) or low motor activity levels (A/J strain) using automated home cage behavioral registration. In this study, we genetically mapped the expression of baseline motor activity levels (horizontal distance moved) to mouse chromosome 1. Further genetic mapping of this trait revealed an 8.3-Mb quantitative trait locus (QTL) interval. This locus is distinct from the QTL interval for open-field anxiety-related motor behavior on this chromosome. By data mining, an existing phenotypic and genotypic data set of 2445 genetically heterogeneous mice (http://gscan.well.ox.ac.uk/), we confirmed linkage to the peak marker at 79 970 253 bp and refined the QTL to a 312-kb interval containing a single gene (A830043J08Rik). Sequence analysis showed a nucleotide deletion in the 3' untranslated region of the Riken gene. Genome-wide microarray gene expression profiling in brains of discordant F(2) individuals from CS strain 1 showed a significant upregulation of Epha4 in low-active F(2) individuals. Inclusion of a genetic marker for Epha4 confirmed that this gene is located outside of the QTL interval. Both Epha4 and A830043J08Rik are expressed in brain motor circuits, and similar to Epha4 mutants, we found linkage between reduced motor neurons number and A/J chromosome 1. Our findings provide a novel QTL and a potential downstream target underlying motor circuitry development and the expression of physical activity levels.

Behavioural analysis of congenic mouse strains confirms stress-responsive Loci on chromosomes 1 and 12

The way in which animals respond to stressful environments correlates with anxiety-related behaviour. To begin identifying the genetic factors that influence anxiety, we have studied the stress-responsiveness of inbred mouse strains using a modified form of the open field activity test (OFA), termed the elevated (e) OFA. In particular, two strains show high (DBA/2J) or low (C57BL/6J) stress-responsiveness in the eOFA. Genetic studies of an F(2) intercross between these two strains previously identified two regions, on chromosomes (Chr) 1 and 12, linked to anxiety-related behaviour. To confirm that these regions contain loci for stress-responsiveness, we established separate congenic mouse strains for the linked Chr1 and Chr12 regions. Each congenic strain harbours a DBA/2J-derived interval encompassing the linked region on the C57BL/6J genetic background: the congenic intervals are between, but not including approximately 48.6 Mb and approximately 194.8 Mb on Chr1, and approximately 36.2 Mb and the distal end of Chr12. Cohorts of DBA/2J, C57BL/6J and congenic mice were analysed for a series of stress-responsive phenotypes using the eOFA test. Both congenic strains had significantly different stress-responsive phenotypes compared to the low-stress C57BL/6J parental strain, but the DBA/2J-derived Chr12 interval had a greater genetic effect than the DBA/2J-derived Chr1 interval for changing the behavioral phenotype of the parental C57BL/6J mouse strain. These results confirmed the presence of stress-responsive loci on Chr1 and Chr12. New stress-related phenotypes were also identified, which aided in comparing and differentiating DBA/2J, C57BL/6J and congenic mice.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

Role of GABA in anxiety and depression

This review assesses the parallel data on the role of gamma-aminobutyric acid (GABA) in depression and anxiety. We review historical and new data from both animal and human experimentation which have helped define the key role for this transmitter in both these mental pathologies. By exploring the overlap in these conditions in terms of GABAergic neurochemistry, neurogenetics, brain circuitry, and pharmacology, we develop a theory that the two conditions are intrinsically interrelated. The role of GABAergic agents in demonstrating this interrelationship and in pointing the way to future research is discussed.

Chromosomal assignment of quantitative trait loci influencing modified hole board behavior in laboratory mice using consomic strains, with special reference to anxiety-related behavior and mouse chromosome 19

Male mice from a panel of chromosome substitution strains (CSS, also called consomic strains or lines)--in which a single full-length chromosome from the A/J inbred strain has been transferred onto the genetic background of the C57BL/6J inbred strain--and the parental strains were examined in the modified hole board test. This behavioral test allows to assess for a variety of different motivational systems in parallel (i.e. anxiety, risk assessment, exploration, memory, locomotion, and arousal). Such an approach is essential for behavioral characterization since the motivational system of interest is strongly influenced by other behavioral systems. Both univariate and bivariate analyses, as well as a factor analysis, were performed. The C57BL/6J and A/J mouse parental inbred strains differed in all motivational systems. The chromosome substitution strain survey indicated that nearly all mouse chromosomes (with the exception of chromosome 2) each contain at least one quantitative trait locus (QTL) that is involved in modified hole board behavior. The results agreed well with previous reports of QTLs for anxiety-related behavior using the A/J and C57BL/6J as parental strains. The present study confirmed that mouse chromosomes 5, 8, 10, 15, 18 and 19 likely contain at least one anxiety QTL. There was also evidence for a novel anxiety QTL on the Y chromosome. With respect to anxiety-related avoidance behavior towards an unprotected area, we have special interest for mouse chromosome 19. CSS-19 (C57BL/6J-Chr19(A)/NaJ) differed in avoidance behavior from the C57BL/6J, but not in locomotion. Thus pleiotropic contribution of locomotion could be excluded.

Genetic determinants of emotionality and stress response in AcB/BcA recombinant congenic mice and in silico evidence of convergence with cardiovascular candidate genes

Genomic loci bearing stress-related phenotypes were dissected in recombinant congenic strains (RCS) of mice with C57BL/6J (B6) and A/J progenitors. Adult male mice from 14 A/J and 22 B6 background lines were evaluated for emotional reactivity in open-field (OF) and elevated plus-maze tests. Core temperature was monitored by radio telemetry during immobilization and on standard as well as salt-enriched diets. In addition, urinary electrolytes were measured. Genome-wide linkage analysis of the parameters revealed over 20 significant quantitative trait loci (QTL). The highest logarithm of odds (LOD) scores were within the previously-reported OF emotionality locus on Chr 1 (LOD = 4.6), in the dopa decarboxylase region on Chr 11 for the plus-maze (LOD = 4.7), and within a novel region of calmodulin 1 on Chr 12 for Ca++ excretion after a 24-h salt load (LOD = 4.6). RCS stress QTL overlapped with several candidate loci for cardiovascular (CV) disease. In silico evidence of functional polymorphisms by comparative sequence analysis of progenitor strains assisted to ascertain this convergence. The anxious BcA70 strain showed down regulation of Atp1a2 gene expression in the heart (P < 0.001) and brain (P < 0.05) compared with its parental B6 strain, compatible with the enhanced emotionality described in knock out animals for this gene, also involved in the salt-sensitive component of hypertension. Functional polymorphisms in regulatory elements of candidate genes of the CV/inflammatory/immune systems support the hypothesis of genetically-altered environmental susceptibility in CV disease development.

Loss of X-linked mental retardation gene oligophrenin1 in mice impairs spatial memory and leads to ventricular enlargement and dendritic spine immaturity

Loss of oligophrenin1 (OPHN1) function in human causes X-linked mental retardation associated with cerebellar hypoplasia and, in some cases, with lateral ventricle enlargement. In vitro studies showed that ophn1 regulates dendritic spine through the control of Rho GTPases, but its in vivo function remains unknown. We generated a mouse model of ophn1 deficiency and showed that it mimics the ventricles enlargement without affecting the cerebellum morphoanatomy. The ophn1 knock-out mice exhibit behavioral defects in spatial memory together with impairment in social behavior, lateralization, and hyperactivity. Long-term potentiation and mGluR-dependent long-term depression are normal in the CA1 hippocampal area of ophn1 mutant, whereas paired-pulse facilitation is reduced. This altered short-term plasticity that reflects changes in the release of neurotransmitters from the presynaptic processes is associated with normal synaptic density together with a reduction in mature dendritic spines. In culture, inactivation of ophn1 function increases the density and proportion of immature spines. Using a conditional model of loss of ophn1 function, we confirmed this immaturity defect and showed that ophn1 is required at all the stages of the development. These studies show that, depending of the context, ophn1 controls the maturation of dendritic spines either by maintaining the density of mature spines or by limiting the extension of new filopodia. Altogether, these observations indicate that cognitive impairment related to OPHN1 loss of function is associated with both presynaptic and postsynaptic alterations.

Animal models of behavioral dysfunctions: Basic concepts and classifications, and an evaluation strategy

In behavioral neurosciences, such as neurobiology and biopsychology, animal models make it possible to investigate brain-behavior relations, with the aim of gaining insight into normal and abnormal human behavior and its underlying neuronal and neuroendocrinological processes. Different types of animal models of behavioral dysfunctions are reviewed in this article. In order to determine the precise criteria that an animal model should fulfill, experts from different fields must define the desired characteristics of that model at the neuropathologic and behavioral level. The list of characteristics depends on the purpose of the model. The phenotype-abnormal behavior or behavioral dysfunctions-has to be translated into testable measures in animal experiments. It is essential to standardize rearing, housing, and testing conditions, and to evaluate the reliability, validity (primarily predictive and construct validity), and biological or clinical relevance of putative animal models of human behavioral dysfunctions. This evaluation, guided by a systematic strategy, is central to the development of a model. The necessity of animal models and the responsible use of animals in research are discussed briefly.

The genetic basis of emotional behaviour in mice

The last decade has witnessed a steady expansion in the number of quantitative trait loci (QTL) mapped for complex phenotypes. However, despite this proliferation, the number of successfully cloned QTL has remained surprisingly low, and to a great extent limited to large effect loci. In this review, we follow the progress of one complex trait locus; a low magnitude moderator of murine emotionality identified some 10 years ago in a simple two-strain intercross, and successively resolved using a variety of crosses and fear-related phenotypes. These experiments have revealed a complex underlying genetic architecture, whereby genetic effects fractionate into several separable QTL with some evidence of phenotype specificity. Ultimately, we describe a method of assessing gene candidacy, and show that given sufficient access to genetic diversity and recombination, progression from QTL to gene can be achieved even for low magnitude genetic effects.

Distinct functional characteristics of the lateral/basolateral amygdala GABAergic system in C57BL/6J and DBA/2J mice

It is generally understood that genetic mechanisms contribute to pathological anxiety and that C57BL/6 (B6) and DBA/2J (D2) mice, inbred strains differing markedly in their anxiety-like behaviors, may represent a model system to study these contributions. Because lateral/basolateral amygdala (BLA) GABA(A) receptors help regulate anxiety-like behaviors, we have tested the hypothesis that differences in receptor function/expression may be related to strain-specific differences in experimentally measured anxiety. First, we demonstrated that anxiety-like behaviors in two separate assays were more substantial in D2 mice. Then, using whole-cell electrophysiology of isolated neurons, we found that D2 BLA neurons expressed significantly greater GABA-gated responses than B6 BLA neurons. This was specific for GABA(A) receptors, because N-methyl-d-aspartate-gated responses were similar between strains. At the molecular level, this increased GABA(A) function was associated with higher levels of alpha 2 subunit mRNA expression in D2 BLA. Finally, to understand the ramifications of these functional and molecular biological differences, we examined both electrically evoked GABAergic responses and spontaneous synaptic currents using whole-cell recordings with in vitro slice preparations. Presynaptic GABAergic function was more robust in D2 compared with B6 slices. Together, our findings suggest that genetic mechanisms differentially represented in these two inbred mouse strains lead to robust differences in pre- and postsynaptic aspects of amygdala GABAergic function.

Maternal and Genetic Effects on Anxiety-Related Behavior of C3H/HeN, DBA/2J and NMRI Mice in a Motility-Box Following Blastocyst Transfer

Reciprocal embryo transfers were conducted to examine genetic and maternal effects on the behavior of inbred C3H/HeN and DBA/2J mice, and outbred NMRI mice using a motility-box. The behavioral variables measured were (i) horizontal locomotor activity assessed as the path and time spent during traveling; (ii) vertical activity assessed as the time spent with and numbers of rearings/leanings; (iii) and the time spent in the more anxiogenic central field. The transfer procedure per se resulted in a minor increase in vertical activity of inbred C3H/HeN mice, but had no effect in inbred DBA/2J mice. In contrast, outbred NMRI mice displayed a lower central field activity following embryo transfer indicating a higher anxiety level. Moreover, genetic differences between the mouse strains studied remained stable following embryo transfer for locomotor and vertical activity, but not central field activity depending on the recipient mother strain. Maternal effects were found for (i) vertical activity in the two inbred mouse strains, (ii) all behavioral variables studied in outbred NMRI mice, and (iii) an interaction with gender for the time spent in the anxiogenic central field. An additional fostering procedure revealed that the vertical activity of NMRI mice was modified towards the behavior of the recipient C3H/HeN strain by uterine factors, whereas the postnatal maternal effect of C3H/HeN mothers was the opposite. In summary, the effects of the embryo transfer procedure per se, stability of genetic characteristics following embryo transfer and maternal effects were related to the mouse strains used as donators and recipients, and the behavioral variables studied.