Social Approach Behaviors are Similar on Conventional Versus Reverse Lighting Cycles, and in Replications Across Cohorts, in BTBR T+ tf/J, C57BL/6J, and Vasopressin Receptor 1B Mutant Mice

Strains of mice that show characteristic patterns of behavior are critical for research in neurobehavioral genetics. Possible confounding influences of the laboratory environment were studied in several inbred strains and one null mutant by simultaneous testing in three laboratories on a battery of six behaviors. Apparatus, test protocols, and many environmental variables were rigorously equated. Strains differed markedly in all behaviors, and despite standardization, there were systematic differences in behavior across labs. For some tests, the magnitude of genetic differences depended upon the specific testing lab. Thus, experiments characterizing mutants may yield results that are idiosyncratic to a particular laboratory.

Autism is a behaviorally defined neurodevelopmental disorder of unknown etiology. Mouse models with face validity to the core symptoms offer an experimental approach to test hypotheses about the causes of autism and translational tools to evaluate potential treatments. We discovered that the inbred mouse strain BTBR T+tf/J (BTBR) incorporates multiple behavioral phenotypes relevant to all three diagnostic symptoms of autism. BTBR displayed selectively reduced social approach, low reciprocal social interactions and impaired juvenile play, as compared with C57BL/6J (B6) controls. Impaired social transmission of food preference in BTBR suggests communication deficits. Repetitive behaviors appeared as high levels of self-grooming by juvenile and adult BTBR mice. Comprehensive analyses of procedural abilities confirmed that social recognition and olfactory abilities were normal in BTBR, with no evidence for high anxiety-like traits or motor impairments, supporting an interpretation of highly specific social deficits. Database comparisons between BTBR and B6 on 124 putative autism candidate genes showed several interesting single nucleotide polymorphisms (SNPs) in the BTBR genetic background, including a nonsynonymous coding region polymorphism in Kmo. The Kmo gene encodes kynurenine 3-hydroxylase, an enzyme-regulating metabolism of kynurenic acid, a glutamate antagonist with neuroprotective actions. Sequencing confirmed this coding SNP in Kmo, supporting further investigation into the contribution of this polymorphism to autism-like behavioral phenotypes. Robust and selective social deficits, repetitive self-grooming, genetic stability and commercial availability of the BTBR inbred strain encourage its use as a research tool to search for background genes relevant to the etiology of autism, and to explore therapeutics to treat the core symptoms.

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.