Neuronal and behavioral differences between Mus musculus domesticus (C57BL/6JBy) and Mus musculus castaneus (CAST/Ei)

Melatonin in Neurodevelopmental Disorders: A Critical Literature Review

The article presents a review of the relationships between melatonin and neurodevelopmental disorders. First, the antioxidant properties of melatonin and its physiological effects are considered to understand better the role of melatonin in typical and atypical neurodevelopment. Then, several neurodevelopmental disorders occurring during infancy, such as autism spectrum disorder or neurogenetic disorders associated with autism (including Smith-Magenis syndrome, Angelman syndrome, Rett's syndrome, Tuberous sclerosis, or Williams-Beuren syndrome) and neurodevelopmental disorders occurring later in adulthood like bipolar disorder and schizophrenia, are discussed with regard to impaired melatonin production and circadian rhythms, in particular, sleep-wake rhythms. This article addresses the issue of overlapping symptoms that are commonly observed within these different mental conditions and debates the role of abnormal melatonin production and altered circadian rhythms in the pathophysiology and behavioral expression of these neurodevelopmental disorders.

Detection of Morphological Abnormalities in Schizophrenia: An Important Step to Identify Associated Genetic Disorders or Etiologic Subtypes

Current research suggests that alterations in neurodevelopmental processes, involving gene X environment interactions during key stages of brain development (prenatal period and adolescence), are a major risk for schizophrenia. First, epidemiological studies supporting a genetic contribution to schizophrenia are presented in this article, including family, twin, and adoption studies. Then, an extensive literature review on genetic disorders associated with schizophrenia is reviewed. These epidemiological findings and clinical observations led researchers to conduct studies on genetic associations in schizophrenia, and more specifically on genomics (CNV: copy-number variant, and SNP: single nucleotide polymorphism). The main structural (CNV) and sequence (SNP) variants found in individuals with schizophrenia are reported here. Evidence of genetic contributions to schizophrenia and current knowledge on genetic syndromes associated with this psychiatric disorder highlight the importance of a clinical genetic examination to detect minor physical anomalies in individuals with ultra-high risk of schizophrenia. Several dysmorphic features have been described in schizophrenia, especially in early onset schizophrenia, and can be viewed as neurodevelopmental markers of vulnerability. Early detection of individuals with neurodevelopmental abnormalities is a fundamental issue to develop prevention and diagnostic strategies, therapeutic intervention and follow-up, and to ascertain better the underlying mechanisms involved in the pathophysiology of schizophrenia.

Melatonin: From Pharmacokinetics to Clinical Use in Autism Spectrum Disorder

The role of melatonin has been extensively investigated in pathophysiological conditions, including autism spectrum disorder (ASD). Reduced melatonin secretion has been reported in ASD and led to many clinical trials using immediate-release and prolonged-release oral formulations of melatonin. However, melatonin’s effects in ASD and the choice of formulation type require further study. Therapeutic benefits of melatonin on sleep disorders in ASD were observed, notably on sleep latency and sleep quality. Importantly, melatonin may also have a role in improving autistic behavioral impairments. The objective of this article is to review factors influencing treatment response and possible side effects following melatonin administration. It appears that the effects of exposure to exogenous melatonin are dependent on age, sex, route and time of administration, formulation type, dose, and association with several substances (such as tobacco or contraceptive pills). In addition, no major melatonin-related adverse effect was described in typical development and ASD. In conclusion, melatonin represents currently a well-validated and tolerated treatment for sleep disorders in children and adolescents with ASD. A more thorough consideration of factors influencing melatonin pharmacokinetics could illuminate the best use of melatonin in this population. Future studies are required in ASD to explore further dose-effect relationships of melatonin on sleep problems and autistic behavioral impairments.

Genomic variation in the vomeronasal receptor gene repertoires of inbred mice

BACKGROUND

Vomeronasal receptors (VRs), expressed in sensory neurons of the vomeronasal organ, are thought to bind pheromones and mediate innate behaviours. The mouse reference genome has over 360 functional VRs arranged in highly homologous clusters, but the vast majority are of unknown function. Differences in these receptors within and between closely related species of mice are likely to underpin a range of behavioural responses. To investigate these differences, we interrogated the VR gene repertoire from 17 inbred strains of mice using massively parallel sequencing.

RESULTS

Approximately half of the 6222 VR genes that we investigated could be successfully resolved, and those that were unambiguously mapped resulted in an extremely accurate dataset. Collectively VRs have over twice the coding sequence variation of the genome average; but we identify striking non-random distribution of these variants within and between genes, clusters, clades and functional classes of VRs. We show that functional VR gene repertoires differ considerably between different Mus subspecies and species, suggesting these receptors may play a role in mediating behavioural adaptations. Finally, we provide evidence that widely-used, highly inbred laboratory-derived strains have a greatly reduced, but not entirely redundant capacity for differential pheromone-mediated behaviours.

CONCLUSIONS

Together our results suggest that the unusually variable VR repertoires of mice have a significant role in encoding differences in olfactory-mediated responses and behaviours. Our dataset has expanded over nine fold the known number of mouse VR alleles, and will enable mechanistic analyses into the genetics of innate behavioural differences in mice.

Systematic detection of polygenic cis-regulatory evolution

The idea that most morphological adaptations can be attributed to changes in the cis-regulation of gene expression levels has been gaining increasing acceptance, despite the fact that only a handful of such cases have so far been demonstrated. Moreover, because each of these cases involves only one gene, we lack any understanding of how natural selection may act on cis-regulation across entire pathways or networks. Here we apply a genome-wide test for selection on cis-regulation to two subspecies of the mouse Mus musculus. We find evidence for lineage-specific selection at over 100 genes involved in diverse processes such as growth, locomotion, and memory. These gene sets implicate candidate genes that are supported by both quantitative trait loci and a validated causality-testing framework, and they predict a number of phenotypic differences, which we confirm in all four cases tested. Our results suggest that gene expression adaptation is widespread and that these adaptations can be highly polygenic, involving cis-regulatory changes at numerous functionally related genes. These coordinated adaptations may contribute to divergence in a wide range of morphological, physiological, and behavioral phenotypes.

Persistence of reduced aggression in vasopressin 1b receptor knockout mice on a more "wild" background

It has been previously reported that vasopressin 1b receptor knockout (Avpr1b(-/-)) mice have reduced levels of aggressive behavior compared to wildtype littermates. However, as the background of the mice was always a mixture of 129/SvJ and C57BL/6, we wanted to determine if the phenotype persisted when our laboratory line was crossed with a wild-derived sub-species of house mice. To this end, we crossed our Avpr1b(-/-) mice with Mus musculus castaneus, one of the few sub-species that will breed with laboratory strains. Subsequent F(2) offspring were tested in a resident-intruder behavioral test to assess aggressive behavior. We found that even on this more "wild" background, Avpr1b(-/-) mice continued to demonstrate longer attack latencies and fewer attacks in a resident-intruder test than wildtype littermates. These findings are consistent with previous reports of reduced aggressive behavior in Avpr1b(-/-) mice and show that the deficit does persist on a different background strain. Further, these findings confirm the importance of the Avpr1b to normal displays of social forms of aggressive behavior.

Abnormal motor phenotype in the SMNDelta7 mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a recessive motor neuron disease that affects motor neurons in the anterior horn of the spinal cord. SMA results from the reduction of SMN (survival motor neuron) protein. Even though SMN is ubiquitously expressed, motor neurons are more sensitive to the reduction in SMN than other cell types. We have previously generated mouse models of SMA with varying degrees of clinical severity. So as to more clearly understand the pathogenesis of motor neuron degeneration in SMA, we have characterized the phenotype of the SMNDelta7 SMA mouse which normally lives for 13.6+/-0.7 days. These mice are smaller than their non-SMA littermates and begin to lose body mass at 10.4+/-0.4 days. SMNDelta7 SMA mice exhibit impaired responses to surface righting, negative geotaxis and cliff aversion but not to tactile stimulation. Spontaneous motor activity and grip strength are also significantly impaired in SMNDelta7 SMA mice. In summary, we have demonstrated an impairment of neonatal motor responses in SMNDelta7 SMA mice. This phenotype characterization could be used to assess the effectiveness of potential therapies for SMA.

Effects of selective dopamine D1-like and D2-like agonists on prepulse inhibition of startle in inbred C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice

RATIONALE

Prepulse inhibition (PPI) and locomotor activity have been used to investigate the effects of antipsychotic and stimulant drugs and their underlying dopaminergic mechanisms. Whereas D2-like agonists consistently decreased PPI and increased locomotion in rats in previous studies, we recently reported that these hallmark behavioral effects were not observed in several mouse strains. Nevertheless, we recently identified three mouse strains (C3H/HeJ, SPRET/EiJ, and CAST/EiJ) that exhibited locomotor hyperactivity after administration of a selective D2-like agonist.

OBJECTIVES

We hypothesized that, similar to rats, C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice would exhibit decreased PPI after administration of a D2-like agonist.

RESULTS

Administration of the D2-like agonist quinelorane dose-dependently decreased PPI in C3H/HeJ and SPRET/EiJ mice. In agreement with previous reports in rats and other strains of mice, the D1-like agonist R-6-Br-APB also decreased PPI in C3H/HeJ and SPRET/EiJ mice. In contrast, CAST/EiJ mice had low levels of baseline PPI in our standard test session and quinelorane and R-6-Br-APB had no effect on PPI under those conditions. Through the optimization of session parameters, we obtained higher baseline PPI in CAST/EiJ mice and found that quinelorane but not R-6-Br-APB decreased PPI. In summary, similar to rats and unlike previous published reports on several strains of mice, we have now identified three strains of mice in which a D2-like agonist decreased PPI.

CONCLUSIONS

The C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice may more closely mirror the Sprague Dawley rat than most other mouse strains and may confer advantages in cross-species behavioral pharmacology studies related to D2 receptor function.

Early motor development is abnormal in complexin 1 knockout mice

Complexin I expression is dysregulated in a number of neurological diseases including schizophrenia and depression. Adult complexin 1 knockout (Cplx1(-/-)) mice are severely ataxic and show deficits in exploration and emotional reactivity. Here, we evaluated early behavioural development of Cplx1(-/-) mice. Cplx1(-/-) mice showed marked abnormalities. They develop ataxia by post-natal day 7 (P7), and by P21 show marked deficits in tasks requiring postural skills and complex movement. These deficits are consistent with abnormalities in sensory and motor development found in infants that develop schizophrenia in later life. A role for complexin I depletion should be considered in diseases where deficits in early sensory and motor development exist, such as autism and schizophrenia.

Visual detection, pattern discrimination and visual acuity in 14 strains of mice

Based on the procedure of Prusky et al. (2000, Vision Research, 40, 2201-2209), we used a computer-based, two-alternative swim task to evaluate visual detection, pattern discrimination and visual acuity in 14 strains of mice from priority groups A and B of the JAX phenome project (129S1/SvImJ, A/J, AKR/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/Ei, DBA/2J, FVB/NJ, MOLF/Ei, SJL/J, SM/J and SPRET/Ei). Each mouse was tested for eight trials/day for 8 days on each of the three tests. There was a significant strain difference in visual ability in all three tests. Mice with reported normal vision (129S1/SvImJ, C57BL/6J and DBA/2J) and one albino strain (AKR/J) performed very well in these tasks. The other albino strains (A/J, BALB/cByJ and BALB/cJ) took longer to learn the tasks than mice with normal vision and did not reach the criterion of 70% correct. Mice with retinal degeneration (C3H/HeJ, FVB/NJ, MOLF/Ei and SJL/J) performed only at chance levels as did the three strains with unknown visual abilities (CAST/Ei, SM/J and SPRET/Ei). Because many behavioral tasks for rodents rely on visual cues, we suggest that the visual abilities of mice should be evaluated before they are tested in commonly used visuo-spatial learning and memory tasks.

Quantitative trait loci for carbohydrate and total energy intake on mouse chromosome 17: congenic strain confirmation and candidate gene analyses (Glo1, Glp1r)

Quantitative trait loci (QTL) for carbohydrate (Mnic1) and total energy (Kcal2) intake on proximal mouse chromosome 17 were identified previously from a C57BL/6J (B6) X CAST/Ei (CAST) intercross. Here we report that a new congenic strain developed in our laboratory has confirmed this complex locus by recapitulating the original linked phenotypes: B6.CAST-17 homozygous congenic mice consumed more carbohydrate (27%) and total energy (17%) compared with littermate wild-type mice. Positional gene candidates with relevance to carbohydrate metabolism, glyoxalase I (Glo1) and glucagon-like peptide-1 receptor (Glp1r), were evaluated. Glo1 expression was upregulated in liver and hypothalamus of congenic mice when compared with B6 mice. Analyses of Glp1r mRNA and protein expression revealed tissue-specific strain differences in pancreas (congenic>B6) and stomach (B6>congenic). These results suggest the possibility of separate mechanisms for enhanced insulin synthesis and gastric accommodation in the presence of high carbohydrate intake and larger food volume, respectively. Sequence analysis of Glp1r found a G insert at nt position 1349, which results in earlier termination of the open reading frame, thus revealing an error in the public sequence. Consequently, the predicted length of GLP-1R is 463 aa compared with 489 aa, as previously reported. Also, we found a polymorphism in Glp1r between parental strains that alters the amino acid sequence. Variation in Glp1r could influence nutrient intake in this model through changes in the regulatory or protein coding regions of the gene. These congenic mice offer a powerful tool for investigating gene interactions in the control of food intake.

SNPdetector: a software tool for sensitive and accurate SNP detection

Identification of single nucleotide polymorphisms (SNPs) and mutations is important for the discovery of genetic predisposition to complex diseases. PCR resequencing is the method of choice for de novo SNP discovery. However, manual curation of putative SNPs has been a major bottleneck in the application of this method to high-throughput screening. Therefore it is critical to develop a more sensitive and accurate computational method for automated SNP detection. We developed a software tool, SNPdetector, for automated identification of SNPs and mutations in fluorescence-based resequencing reads. SNPdetector was designed to model the process of human visual inspection and has a very low false positive and false negative rate. We demonstrate the superior performance of SNPdetector in SNP and mutation analysis by comparing its results with those derived by human inspection, PolyPhred (a popular SNP detection tool), and independent genotype assays in three large-scale investigations. The first study identified and validated inter- and intra-subspecies variations in 4,650 traces of 25 inbred mouse strains that belong to either the Mus musculus species or the M. spretus species. Unexpected heterozygosity in CAST/Ei strain was observed in two out of 1,167 mouse SNPs. The second study identified 11,241 candidate SNPs in five ENCODE regions of the human genome covering 2.5 Mb of genomic sequence. Approximately 50% of the candidate SNPs were selected for experimental genotyping; the validation rate exceeded 95%. The third study detected ENU-induced mutations (at 0.04% allele frequency) in 64,896 traces of 1,236 zebra fish. Our analysis of three large and diverse test datasets demonstrated that SNPdetector is an effective tool for genome-scale research and for large-sample clinical studies. SNPdetector runs on Unix/Linux platform and is available publicly (http://lpg.nci.nih.gov).

Functional analysis of genes implicated in Down syndrome: 1. Cognitive abilities in mice transpolygenic for Down Syndrome Chromosomal Region-1 (DCR-1)

Down syndrome occurs every 1/1000 births and is the most frequent genetic cause of mental retardation. The genetic substrate of Down syndrome, an extra chromosome 21, was discovered by Lejeune, half-a-century ago, and the chromosome has been fully sequenced, although the gene(s) implicated in the mental retardation observed with the syndrome are still unknown. Observations of patients with partial trisomy of the 21q22.2 fragment suggest that most of the signs of the syndrome, including mental retardation, could be influenced by the region referred to as the Down Minimal Chromosomal Region-1 (DCR-1) for that reason. Using the extensive syntenies between human chromosome 21 and murine chromosome 16, Smith et al. (1995, 1997) developed transpolygenic mice with human chromosome 21 fragments covering the DCR-1. Here, we explored cognitive performances in mice over-expressing the genes carried by these fragments with the Morris water-maze and fear-conditioning procedures. The 152F7 transpolygenic mice had lower performance levels, compared to non-transgenic and other transgenic mice on most measurements in the water-maze. In fear-conditioning, all transgenic mice recorded lower performance levels compared to controls in the altered context stage. The 230E8, 141G6 and 285E6 mice failed to learn or react when the sound used as the conditional stimulus was added. These results showed that the 152F7 region played a crucial role in cognitive impairment, supporting the hypothesis of DYRK-1A gene involvement. However, the data presented here also suggest that other chromosomal regions within the DCR-1 may be involved in specific cognitive functions.

The relationship between dominance rank and spatial ability among male meadow voles (Microtus pennsylvanicus)

Males of many mammalian species exhibit contest competition and scramble competition for mates, but the relationship between these 2 forms of competition remains poorly understood. The authors measured dominance rank and spatial ability as traits likely to be selected by contest and scramble competition, respectively, among male meadow voles (Microtus pennsylvanicus). The spatial ability of males was assessed using water maze tests, and dominance rank was determined using paired trials in a neutral arena. Dominant males had better spatial-learning ability and tended to have quicker learning speed but did not have better spatial memory than less aggressive subordinates. Therefore, the authors found no evidence that contest and scramble competition have favored alternative reproductive phenotypes among male meadow voles.

Behavioral Characterization of Wild Derived Male Mice (Mus musculus musculus) of the PWD/Ph Inbred Strain: High Exploration Compared to C57BL/6J

PWD/Ph is an inbred mouse strain derived from wild mice trapped in central Czech Republic. These mice are of the Mus musculus musculus subspecies, whose ancestors separated from those of Mus musculus domesticus about one million years ago. There is a high degree of variation in the genomic sequence and a wide range of phenotypes between PWD/Ph and standard laboratory inbred mouse strains, the genomes of which are principally Mus musculus domesticus in origin, making PWD/Ph mice an useful resource for complex trait research. As a first step in taking advantage of this resource, a preliminary characterization of the behavior of PWD/Ph mice was performed. Groups of 10 PWD/Ph and C57BL/6J male mice were tested in the open field, novel object exploration task and Morris water maze. PWD/Ph were marginally more anxious than C57BL/6J mice in the open field but subsequently displayed much higher levels of exploration and lower anxiety than C57BL/6J mice following introduction of a novel object. As C57BL/6J itself is rated as highly explorative among classical inbred strains, PWD/Ph probably represents an extreme among mouse strains for this specific behavior. PWD/Ph and C57BL/6J mice differed in their water escape training profiles in the Morris water maze, perhaps reflecting different motivational factors. However, there were no differences in overall cognitive ability (spatial learning) as both groups learned to find the hidden platform and performed equally well when the location of the platform was changed. This is the first quantification of the behavior of PWD/Ph mice and the results are promising for the potential of the consomic panel currently being generated with PWD/Ph and C57BL/6J as a tool for the molecular dissection of behavior.

Mouse susceptibility to anthrax lethal toxin is influenced by genetic factors in addition to those controlling macrophage sensitivity

Bacillus anthracis lethal toxin (LT) produces symptoms of anthrax in mice and induces rapid lysis of macrophages (M phi) derived from certain inbred strains. We used nine inbred strains and two inducible nitric oxide synthase (iNOS) knockout C57BL/6J strains polymorphic for the LT M phi sensitivity Kif1C locus to analyze the role of M phi sensitivity (to lysis) in LT-mediated cytokine responses and lethality. LT-mediated induction of cytokines KC, MCP-1/JE, MIP-2, eotaxin, and interleukin-1 beta occurred only in mice having LT-sensitive M phi. However, while iNOS knockout C57BL/6J mice having LT-sensitive M phi were much more susceptible to LT than the knockout mice with LT-resistant M phi, a comparison of susceptibilities to LT in the larger set of inbred mouse strains showed a lack of correlation between M phi sensitivity and animal susceptibility to toxin. For example, C3H/HeJ mice, harboring LT-sensitive M phi and having the associated LT-mediated cytokine response, were more resistant than mice with LT-resistant M phi and no cytokine burst. Toll-like receptor 4 (Tlr4)-deficient, lipopolysaccharide-nonresponsive mice were not more resistant to LT. We also found that CAST/Ei mice are uniquely sensitive to LT and may provide an economical bioassay for toxin-directed therapeutics. The data indicate that while the cytokine response to LT in mice requires M phi lysis and while M phi sensitivity in the C57BL/6J background is sufficient for BALB/cJ-like mortality of that strain, the contribution of M phi sensitivity and cytokine response to animal susceptibility to LT differs among other inbred strains. Thus, LT-mediated lethality in mice is influenced by genetic factors in addition to those controlling M phi lysis and cytokine response and is independent of Tlr4 function.

Genetic correlates of gene expression in recombinant inbred strains: a relational model system to explore neurobehavioral phenotypes

Full genome sequencing, high-density genotyping, expanding sets of microarray assays, and systematic phenotyping of neuroanatomical and behavioral traits are producing a wealth of data on the mouse central nervous system (CNS). These disparate resources are still poorly integrated. One solution is to acquire these data using a common reference population of isogenic lines of mice, providing a point of integration between the data types. Recombinant inbred (RI) mice, derived through inbreeding of progeny from an inbred cross, are a powerful tool for complex trait mapping and analysis of the challenging phenotypes of neuroscientific interest. These isogenic RI lines are a retrievable genetic resource that can be repeatedly studied using a wide variety of assays. Diverse data sets can be related through fixed and known genomes, using tools such as the interactive web-based system for complex trait analysis, www.WebQTL.org. In this report, we demonstrate the use of WebQTL to explore complex interactions among a wide variety of traits--from mRNA transcripts to the impressive behavioral and pharmacological variation among RI strains. The relational approach exploiting a common set of strains facilitates study of multiple effects of single genes (pleiotropy) without a priori hypotheses required. Here we demonstrate the power of this technique through genetic correlation of gene expression with a database of neurobehavioral phenotypes collected in these strains of mice through more than 20 years of experimentation. By repeatedly studying the same panel of mice, early data can be re-examined in light of technological advances unforeseen at the time of their initial collection.

Mitochondrial DNA modifies cognition in interaction with the nuclear genome and age in mice

Several lines of evidence indicate an association between mitochondrial DNA (mtDNA) and the functioning of the nervous system. As neuronal development and structure as well as axonal and synaptic activity involve mitochondrial genes, it is not surprising that most mtDNA diseases are associated with brain disorders. Only one study has suggested an association between mtDNA and cognition, however. Here we provide direct evidence of mtDNA involvement in cognitive functioning. Total substitution of mtDNA was achieved by 20 repeated backcrosses in NZB/BlNJ (N) and CBA/H (H) mice with different mtDNA origins. All 13 mitochondrial genes were expressed in the brains of the congenic quartet. In interaction with nuclear DNA (nDNA), mtDNA modified learning, exploration, sensory development and the anatomy of the brain. The effects of mtDNA substitution persisted with age, increasing in magnitude as the mice got older. We observed different effects with input of mtDNA from N versus H mice, varying according to the phenotypes. Exchanges of mtDNA may produce phenotypes outside the range of scores observed in the original mitochondrial and nuclear combinations. These findings show that mitochondrial polymorphisms are not as neutral as was previously believed.

A rating scale for wildness and ease of handling laboratory mice: results for 21 inbred strains tested in two laboratories

Rating scales for difficulty in capturing and holding mice were devised that proved to be easy to use and highly sensitive to differences among mouse strains on the A and B priority lists of the Mouse Phenome Project. The simplicity of the scales makes it feasible to rate wildness during behavioral test sessions without adding much to testing time or distracting the technician from the principal task at hand. Overall wildness and placidity ratings obtained by combining capture and hold ratings provide a good impression of the difficulties encountered while working with lab mice in the course of complex experiments. Ratings of 21 inbred strains during the course of 15 behavioral tests in two laboratories demonstrated that the SPRET/Ei, PERA/Ei, CAST/Ei and SWR/J strains were particularly difficult to handle. The NOD/LtJ strain posed no special challenge in the Edmonton laboratory but was very difficult to handle in the Portland lab. The rating scales should be useful for judging the difficulties in working with novel targeted or induced mutations in mice as well as effects of a variety of environmental treatments or drugs.

QTL analysis of self-selected macronutrient diet intake: fat, carbohydrate, and total kilocalories

The present study investigated the inheritance of dietary fat, carbohydrate, and kilocalorie intake traits in an F(2) population derived from an intercross between C57BL/6J (fat-preferring) and CAST/EiJ (carbohydrate-preferring) mice. Mice were phenotyped for self-selected food intake in a paradigm which provided for 10 days a choice between two macronutrient diets containing 78/22% of energy as a composite of either fat/protein or carbohydrate/protein. Quantitative trait locus (QTL) analysis identified six significant loci for macronutrient intake: three for fat intake on chromosomes (Chrs) 8 (Mnif1), 18 (Mnif2), and X (Mnif3), and three for carbohydrate intake on Chrs 17 (Mnic1), 6 (Mnic2), and X (Mnic3). An absence of interactions among these QTL suggests the existence of separate mechanisms controlling the intake of fat and carbohydrate. Two significant QTL for cumulative kilocalorie intake, adjusted for baseline body weight, were found on Chrs 17 (Kcal1) and 18 (Kcal2). Without body weight adjustment, another significant kcal locus appeared on distal Chr 2 (Kcal3). These macronutrient and kilocalorie QTL, with the exception of loci on Chrs 8 and X, encompassed chromosomal regions influencing body weight gain and adiposity in this F2 population. These results provide new insight into the genetic basis of naturally occurring variation in nutrient intake phenotypes.

Sensory and motor development in mice: genes, environment and their interactions

Sensory and motor developmental tests were designed to characterize spontaneous mutations in rodents. These tests are currently used to investigate developmental abnormalities associated with gene overexpression or gene targeting in mice. Here, we present an overview of our studies focused on 15 tests designed to measure sensory and motor development from birth to weaning in mice. Psychometric characteristics and factorial structure of these measures are considered first. The genetic correlates of these measures obtained with neurological mutants and gene mapping are compared. As a general rule, the contribution of genotype to the phenotypic variance of sensory and motor measures of development is low, inviting exploration of other sources of variation. Results from ovary transplantation, embryo transfer and fostering methods indicate that different components of maternal environment (cytoplasmic, uterine or postnatal) contribute to the behavioral phenotype. Although more difficult to detect, interactions between genotype and environment are involved.

Genome-tagged mice (GTM): two sets of genome-wide congenic strains

An important approach for understanding complex disease risk using the mouse is to map and ultimately identify the genes conferring risk. Genes contributing to complex traits can be mapped to chromosomal regions using genome scans of large mouse crosses. Congenic strains can then be developed to fine-map a trait and to ascertain the magnitude of the genotype effect in a chromosomal region. Congenic strains are constructed by repeated backcrossing to the background strain with selection at each generation for the presence of a donor chromosomal region, a time-consuming process. One approach to accelerate this process is to construct a library of congenic strains encompassing the entire genome of one strain on the background of the other. We have employed marker-assisted breeding to construct two sets of overlapping congenic strains, called genome-tagged mice (GTMs), that span the entire mouse genome. Both congenic GTM sets contain more than 60 mouse strains, each with on average a 23-cM introgressed segment (range 8 to 58 cM). C57BL/6J was utilized as a background strain for both GTM sets with either DBA/2J or CAST/Ei as the donor strain. The background and donor strains are genetically and phenotypically divergent. The genetic basis for the phenotypic strain differences can be rapidly mapped by simply screening the GTM strains. Furthermore, the phenotype differences can be fine-mapped by crossing appropriate congenic mice to the background strain, and complex gene interactions can be investigated using combinations of these congenics.

Applications of the Morris water maze in the study of learning and memory

The Morris water maze (MWM) was described 20 years ago as a device to investigate spatial learning and memory in laboratory rats. In the meanwhile, it has become one of the most frequently used laboratory tools in behavioral neuroscience. Many methodological variations of the MWM task have been and are being used by research groups in many different applications. However, researchers have become increasingly aware that MWM performance is influenced by factors such as apparatus or training procedure as well as by the characteristics of the experimental animals (sex, species/strain, age, nutritional state, exposure to stress or infection). Lesions in distinct brain regions like hippocampus, striatum, basal forebrain, cerebellum and cerebral cortex were shown to impair MWM performance, but disconnecting rather than destroying brain regions relevant for spatial learning may impair MWM performance as well. Spatial learning in general and MWM performance in particular appear to depend upon the coordinated action of different brain regions and neurotransmitter systems constituting a functionally integrated neural network. Finally, the MWM task has often been used in the validation of rodent models for neurocognitive disorders and the evaluation of possible neurocognitive treatments. Through its many applications, MWM testing gained a position at the very core of contemporary neuroscience research.

Standardizing tests of mouse behavior: reasons, recommendations, and reality

As more investigators with widely varying backgrounds enter the field of mouse behavioral genetics, there is a growing need to standardize some of the more popular tests because differences between laboratories in the details of behavioral testing and the pretesting environment can contribute to failures to replicate results of genetic experiments. It is argued here that we have sufficient knowledge to warrant a wise choice of a short list of standard strains and even details of apparatus and protocols for several kinds of behavioral tests. Equating the laboratory environment does not appear to be feasible. Instead, we need to learn what kinds of behavioral tests yield the most stable results in different labs and what kinds are most sensitive to the ubiquitous variations among test sites. Methods for making an informed choice of sample size for evaluating interactions between the laboratory environment and genotype are available and should be utilized in standardization trials. New resources for convenient sharing of data will greatly aid in collaborative and comparative studies involving several sites. Like the sequencing of an entire genome, test standardization is something that needs to be done only once if it is done properly, and the work will then benefit the field of behavioral and neural genetics for many years.

Genetic architecture of testis and seminal vesicle weights in mice

Comparisons across 13 inbred strains of laboratory mice for reproductive organ (paired seminal vesicles and paired testes) weights indicated a very marked contrast between the C57BL/6By and NZB/BINJ mice. Subsequently these strains were selected to perform a quantitative genetic analysis and full genome scan for seminal vesicle and testis weights. An F(2) population was generated. The quantitative genetic analyses indicated that each was linked to several genes. Sixty-six short sequences for length polymorphism were used as markers in the wide genome scan strategy. For weight of paired testes, heritability was 82.3% of the total variance and five QTL contributed to 72.8% of the total variance. Three reached a highly significant threshold (>4.5) and were mapped on chromosome X (LOD score 9.11), chromosome 4 (LOD score 5.96), chromosome 10 (LOD score 5.81); two QTL were suggested: chromosome 13 (LOD score 3.10) and chromosome 18 (LOD score 2.80). Heritability for weight of seminal vesicles was 50.7%. One QTL was mapped on chromosome 4 (LOD score 9.21) and contributed to 24.2% of the total variance. The distance of this QTL to the centromere encompassed the distance of the QTL linked with testicular weight on chromosome 4, suggesting common genetic mechanisms as expected from correlations in the F(2). Both testis and seminal vesicle weights were associated with a reduction in the NZB/BINJ when this strain carried the Y(NPAR) from CBA/H whereas the Y(NPAR) from NZB/BINJ in the CBA/H strain did not modify reproductive organ weights, indicating that the Y(NPAR) interacts with the non-Y(NPAR) genes. The effects generated by this chromosomal region were significant but small in size.

Sex differences in the parental behavior of rodents

The reproductive strategy of many mammalian species that give birth to altricial young involves intense and prolonged care of their offspring. In most cases, the mother provides all nurturance, but in some cases fathers, older siblings, or unrelated conspecifics participate in parental care. The display of these behaviors by animals other than mothers is affected by numerous factors, including their sex. We herein review the literature on similarities and/or differences between male and female laboratory rodents (rats, mice, voles, gerbils, and hamsters) in their parental responsiveness and discuss how the parental behavior of males and females is influenced by hormones, developmental processes, and prior social experiences. Understanding the mechanisms that generate sex differences in the parental responsiveness of rodents may indicate how similar sex differences in parental care are generated in other mammals.