Brief report: altered social behavior in isolation-reared Fmr1 knockout mice.
Single housing wipes out preference for new social partners in fragile-X model mice, so keep group housing constant in any social assay.
01Research in Context
What this study did
The team raised two groups of Fmr1 knockout mice. Half lived alone after weaning. Half lived with cage mates.
At ten weeks the mice met a stranger in a three-chamber box. Cameras scored nose-to-nose sniff time and time spent in each side.
What they found
Isolation did not change basic social approach. Both groups spent equal time near the first stranger.
Isolated knockouts skipped the second stranger. They kept sniffing the now-familiar mouse and ignored the new one.
How this fits with other research
Ryan et al. (2019) saw the same test give mixed results in BTBR mice. Their fix was to swap stranger strain; M et al. show rearing history matters just as much.
Ellegood et al. (2011) mapped brain changes in another autism model. Adding M et al. tells us behavior can shift even when brain scans look fine.
Smith et al. (1994) first linked FMR1 gene loss to human fragile-X. Two decades later M et al. warn that lonely cages can mask or mimic gene effects in mice.
Why it matters
If you run social assays for drug or gene studies, house mice together. One week of isolation can erase the social novelty window you hope to measure. Check cage cards before each trial; mixed rearing histories could drown real treatment effects in noise.
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02At a glance
03Original abstract
Social behavior abnormalities in Fragile X syndrome (FXS) are characterized by social withdrawal, anxiety, and deficits in social cognition. To assess these deficits, a model of FXS, the Fmr1 knockout mouse (Fmr1 KO), has been utilized. This mouse model has a null mutation in the fragile X mental retardation 1 gene (Fmr1) and displays physical and behavioral characteristics similar to humans with FXS. Several studies have investigated the social behavior of this model, but the results on the behavioral phenotype have not been consistent. In order to further characterize the social behavior in the knockout, isolation-reared Fmr1 KO were evaluated to determine if they differ in their social behavior compared to wild-type littermate controls. Differences by genotype were not observed in social approach behavior; however, the knockout mice showed a significantly reduced preference for social novelty and decreased sniff time in the sociability phase. These findings add to the growing body of knowledge on the subtle differences in social behavior shown by the Fmr1 knockout mice, and that differences occur when the subjects are isolation-reared. Validity of the model and possible changes to methodology are discussed.
Journal of autism and developmental disorders, 2013 · doi:10.1007/s10803-012-1670-1