Automated apparatus for quantitation of social approach behaviors in mice

Mouse models of social dysfunction, designed to investigate the complex genetics of social behaviors, require an objective methodology for scoring social interactions relevant to human disease symptoms. Here we describe an automated, three chambered apparatus designed to monitor social interaction in the mouse. Time spent in each chamber and the number of entries are scored automatically by a system detecting photocell beam breaks. When tested with the automated equipment, juvenile male C57BL/6J mice spent more time in a chamber containing a stranger mouse than in an empty chamber (sociability), similar to results obtained by the observer scored method. In addition, automated scoring detected a preference to spend more time with an unfamiliar stranger than a more familiar conspecific (preference for social novelty), similar to results obtained by the observer scored method. Sniffing directed at the wire cage containing the stranger mouse correlated significantly with time spent in that chamber, indicating that duration in a chamber represents true social approach behavior. Number of entries between chambers did not correlate with duration of time spent in the chambers; entries instead proved a useful control measure of general activity. The most significant social approach behavior took place in the first five minutes of both the sociability and preference for social novelty tests. Application of these methods to C57BL/6J, DBA/2J and FVB/NJ adult males revealed that all three strains displayed tendencies for sociability and preference for social novelty. To evaluate the importance of the strain of the stranger mouse on sociability and preference for social novelty, C57BL/6J subject mice were tested either with A/J strangers or with C57BL/6J strangers. Sociability and preference for social novelty were similar with both stranger strains. The automated equipment provides an accurate and objective approach to measuring social tendencies in mice. Its use may allow higher-throughput scoring of mouse social behaviors in mouse models of social dysfunction.     

雄性Fmr1基因敲除小鼠血液生理生化指标及性激素水平的比较研究

目的比较雄性Fmr1基因敲除小鼠和FVB小鼠血液生理生化值和血清性激素水平,探讨Fmr1基因对动物生长发育和生殖生理等方面的影响。方法分别测定血液生理指标、血清生化指标、血清电解质和血清E2、LH、FSH、T和PRL的含量,并进行统计学处理和分析。结果雄性Fmr1基因敲除小鼠与FVB小鼠比较,血液生理指标中MCV和PCT有显著差异（P〈0．05）,而RBC、HCT、HGB、MCH和WBC等无显著差异（P〉0．05）;血清生化指标中除TBIL、[IP^3＋]、[Mg^2＋]（P〈0．05）和AIP、BUN（P〈0．01）外,TPROT、GLB、A／G、BUN、CREAT、[K^＋]、[Na^＋]等项均无显著差异（P〉0．05）。性激素水平E2、LH值差异无显著性（P〉0．05）,FSH、T、PRL差异极显著（P〈0．01）。结论Fmr1基因可影响动物的某些生理生化及激素水平。     

Variation in Galr1 expression determines susceptibility to exocitotoxin-induced cell death in mice

Inbred strains of mice differ in their susceptibility to excitotoxin-induced cell death, but the genetic basis of individual variation in differential susceptibility is unknown. Previously, we identified a highly significant quantitative trait locus (QTL) on chromosome 18 that influenced susceptibility to kainic acid-induced cell death ( Sicd1 ). Comparison of susceptibility to seizure-induced cell death between reciprocal congenic lines for Sicd1 and parental background mice indicates that genes influencing this trait were captured in both strains. Two positional gene candidates, Galr1 and Mbp , map to 55 cM, where the Sicd1 QTL had been previously mapped. Thus, this study was undertaken to determine if Galr1 and/or Mbp could be considered as candidate genes. Genomic sequence comparison of these two functional candidate genes from the C57BL/6J (resistant at Sicd1 ) and the FVB/NJ (susceptible at Sicd1 ) strains showed no single-nucleotide polymorphisms. However, expression studies confirmed that Galr1 shows significant differential expression in the congenic and parental inbred strains. Galr1 expression was downregulated in the hippocampus of C57BL/6J mice and FVB.B6- Sicd1 congenic mice when compared with FVB/NJ or B6.FVB- Sicd1 congenic mice. A survey of Galr1 expression among other inbred strains showed a significant effect such that 'susceptible' strains showed a reduction in Galr1 expression as compared with 'resistant' strains. In contrast, no differences in Mbp expression were observed. In summary, these results suggest that differential expression of Galr1 may contribute to the differences in susceptibility to seizure-induced cell death between cell death-resistant and cell death-susceptible strains.     

FVB.129P2-Pde6b(+) Tyr(c-ch)/Ant, a sighted variant of the FVB/N mouse strain suitable for behavioral analysis

Mice of the FVB/N strain are severely visual impaired as a result of tyrosinase gene defects, leading to a deficiency of the key enzyme for melanin synthesis in skin and eye and of cyclic guanosine monophosphate phosphodiesterase gene defects, which results in albinism (Tyr(c/c)) and retinal degeneration (Pde6b(rd1/rd1)), respectively. Nevertheless, FVB/N mice are commonly used for the generation of transgenic animals because of their large, strong pronuclei and high breeding performance. However, due to visual impairment of the FVB/N animals, the resulting transgenic animals cannot be used in tests that depend on vision, including tests of cognitive behavior. Therefore, we have bred a sighted version of the FVB/N strain by an outcross between FVB/N and 129P2/OlaHsd, followed by repeated backcrosses to FVB/N mice while selecting against albinism and homozygosity of the retinal degeneration mutation. After 11 generations of backcrossing, sighted animals were intercrossed to generate the congenic FVB.129P2-Pde6b(+) Tyr(c-ch)/Ant strain, which is pigmented (Tyr(c-ch)/(c-ch)) and devoid of the genetic predisposition to retinal degeneration. The accurate visual abilities of the FVB.129P2-Pde6b(+) Tyr(c-ch)/Ant mice, for which we propose the name FVBS/Ant, demonstrated a clear visual evoked potential in the presence of normal eye histology and improved performance in the Morris water maze test.     

Ubiquitous expression of mRFP1 in transgenic mice

Fluorescent proteins provide a powerful means to track gene expression and cellular behaviors in the study of model organisms such as mice. Among the new generation of fluorescent protein markers, the monomeric red fluorescent protein mRFP1 is particularly attractive because of its rapid maturation and minimal interference with GFP and GFP-derived markers. Here we evaluate the utility of mRFP1 as a marker in transgenic mice. We show that high level and ubiquitous expression of mRFP1 does not affect mouse development, general physiology, or reproduction. mRFP1 expression can be readily detected with unaided eyes under daylight in transgenic mice on the albino background. The intensity of mRFP1 signals can be used to distinguish homozygous and heterozygous transgenic mice. Together, these features make mRFP1 an attractive marker for broad applications in transgenic research.     

Rapid fluorescencein situ hybridization on interphasic nuclei to discriminate between homozygous and heterozygous transgenic mice

Homozygous and heterozygous transgenic mice of the Tg152 line overexpressing the human copper/zinc superoxide dismutase (hSOD-1) were rapidly differentiated by fluorescencein situ hybridization (FISH) using intérphase lymphocyte nuclei. We have devised a simple and fast method for preparing interphase nuclei with very small quantities of whole mouse blood, avoiding several steps of the classical FISH technique. Lymphocyte separation and cell culture were not required. This technique provides an excellent tool for the unambiguous detection of homozygous and heterozygous transgenic mice in a litter. It can be used to check young animals since 2 l of whole blood is sufficient. We also show that in this transgenic line numerous copies of the hSOD-1 transgene are. integrated at a single autosomal locus, in tandem head-to-tail organization     

Congenic strains provide evidence that a mapped locus on chromosome 15 influences excitotoxic cell death

Inbred strains of mice differ in their susceptibility to excitotoxin‐induced cell death, but the genetic basis of individual variation is unknown. Prior studies with crosses of the FVB/NJ (seizure‐induced cell death susceptible) mouse and the seizure‐induced cell death resistant mouse, C57BL/6J, showed the presence of three quantitative trait loci (QTLs), named seizure‐induced cell death 1 (Sicd1) to Sicd3. To better localize and characterize the Sicd2 locus, two reciprocal congenic mouse strains were created. While the B6.FVB‐Sicd2 congenic mouse was without effect on modifying susceptibility to seizure‐induced excitotoxic cell death, the FVB.B6‐Sicd2 congenic mouse, in which the chromosome (Chr) 15 region of C57BL/6J was introgressed into FVB/NJ, showed reduced seizure‐induced excitotoxic cell death following kainate administration. Phenotypic comparison between FVB and the congenic FVB.B6‐Sicd2 strain confirmed that the Sicd2 interval harbors gene(s) conferring strong protection against seizure‐induced excitotoxic cell death. Interval‐specific congenic lines (ISCLs) that encompass Sicd2 on Chr 15 were generated and were used to fine‐map this QTL. Resultant progeny were treated with kainate and examined for the extent of seizure‐induced cell death in order to deduce the Sicd2 genotypes of the recombinants through linkage analysis. All of the ISCLs exhibited reduced cell death associated with the C57BL/6J phenotype; however, ISCL‐2 showed the most dramatic reduction in seizure‐induced cell death in both area CA3 and in the dentate hilus. These findings confirm the existence of polymorphic loci within the reduced critical region of Sicd2 that regulate the severity of seizure‐induced cell death.     

Effects of FVB/NJ and C57Bl/6J strain backgrounds on mammary tumor phenotype in inducible nitric oxide synthase deficient mice

The ability to genetically manipulate mice has led to rapid progress in our understanding of the roles of different gene products in human disease. Transgenic mice have often been created in the FVB/NJ (FVB) strain due to its high fecundity, while gene-targeted mice have been developed in the 129/SvJ-C57Bl/6J strains due to the capacity of 129/SvJ embryonic stem cells to facilitate germline transmission. Gene-targeted mice are commonly backcrossed into the C57Bl/6J (B6) background for comparison with existing data. Genetic modifiers have been shown to modulate mammary tumor latency in mouse models of breast cancer and it is commonly known that the FVB strain is susceptible to mammary tumors while the B6 strain is more resistant. Since gene-targeted mice in the B6 background are frequently bred into the polyomavirus middle T (PyMT) mouse model of breast cancer in the FVB strain, we have sought to understand the impact of the different genetic backgrounds on the resulting phenotype. We bred mice deficient in the inducible nitric oxide synthase (iNOS) until they were congenic in the PyMT model in the FVB and B6 strains. Our results reveal that the large difference in mean tumor latencies in the two backgrounds of 53 and 92 days respectively affect the ability to discern smaller differences in latency due to the Nos2 genetic mutation. Furthermore, the longer latency in the B6 strain enables a more detailed analysis of tumor formation indicating that individual tumor development is not stoichastic, but is initiated in the #1 glands and proceeds in early and late phases. NO production affects tumors that develop early suggesting an association of iNOS-induced NO with a more aggressive tumor phenotype, consistent with human clinical data positively correlating iNOS expression with breast cancer progression. An examination of lung metastases, which are significantly reduced in PyMT/iNOS^−/− mice compared with PyMT/iNOS^+/+ mice only in the B6 background, is concordant with these findings. Our data suggest that PyMT in the B6 background provides a useful model for the study of inflammation-induced breast cancer.     

FVB/N (H2 q ) mouse is resistant to arthritis induction and exhibits a genomic deletion of T-cell receptor V beta gene segments

 Animal models of autoimmune diseases have been instrumental in advancing our understanding of autoimmunity in humans. Collagen-induced arthritis (CIA) in mice is an autoimmune disease model of rheumatoid arthritis. Susceptibility to CIA in mice is linked to genes of the major histocompatibility complex (MHC). CD4⁺ T cells that express the T-cell receptor (TCR) Tcra-V11.1 and/or Tcrb-V8.2 play a key role in the pathogenesis of arthritis in the DBA/1 mouse (H2 ^q ). We identified an inbred mouse strain, FVB/NJ (H2 ^q ), that is resistant to arthritis induction and exhibits a genomic deletion of certain Tcrb-V gene segments. We report a novel polymerase chain reaction-based method for the rapid identification of new mouse strains that exhibit germline Tcrb-V gene deletions. We mapped for the first time both the 5′ and 3′ breakpoints of the Tcrb-V deletion in the FVB/NJ, SWR, SJL, C57L, and C57BR strains to within 1.1 kilobases. Since there is an association between a particular Tcra-V allele (Tcra-V11.1 ^d ) and arthritis susceptibility in H2 ^q mouse strains, we examined the allelic polymorphisms of the Tcra-V11 gene subfamily members between the arthritis-susceptible DBA/1 mouse and the arthritis-resistant FVB/NJ mouse strain. The amino acid sequences of the Tcra-V11.1 alleles differ at two positions (codons 18 and 68). Therefore, the resistance of FVB/NJ mouse to arthritis induction may be due in part to Tcra-V11.1 coding sequence polymorphism and Tcrb-V8.2 gene segment deletion, as we have recently demonstrated in the case of SWR mouse strain. Received: 12 January 1999 / Revised: 17 March 1999     

Acute locomotor responses to cocaine in adolescents vs. adults from four divergent inbred mouse strains

Growing evidence suggests that adolescent mice display differential sensitivity to the acute locomotor activating effects of cocaine as compared to adults, but the direction of the difference varies across studies and the reasons are not clear. Few studies have directly examined genetic contributions to age differences in locomotor stimulation from cocaine. The goal of this study was to determine the extent to which reduced stimulation in C57BL/6J adolescents as compared to adults generalizes to other strains. Therefore, we examined male and female mice from four genetically divergent inbred stains (BALB/cByJ, C57BL/6J, DBA/2J and FVB/NJ) at two ages, postnatal day 30 and postnatal day 65. Mice received either saline or cocaine (15 or 30 mg/kg), and then immediately were placed back into their home cages. Locomotor activity was recorded continuously in the home cage by video tracking. Adolescents displayed reduced stimulation as compared to adults for C57BL/6J, BALB/cByJ and female FVB/NJ mice. No age differences were observed for DBA/2J or male FVB/NJ. No main effects of sex were observed. Strain differences in pharmacokinetics, neural development or physiology could contribute to the observed differences between ages across strains. Future comparative studies could discover biological differences between strains that explain age differences in cocaine sensitivity.