Colony formation of C57BL/6J mice in visible burrow system: identification of eusocial behaviors in a background strain for genetic animal models of autism

Abstract

Deficits in social interaction are primary characteristics of autism, which has strong genetic components. Genetically manipulated mouse models may provide a useful research tool to advance the investigation of genes associated with autism. To identify these genes using mouse models, behavioral assays for social relationships in the background strains must be developed. The present study examined colony formation in groups of one male and three female mice (Experiment 1) and, groups of three male mice (Experiment 2) of the C57BL/6J strain in a semi-natural visible burrow system. For adult mixed-sex colonies, 4-h observations during both the dark and light cycles for 15 days demonstrated day-dependent increases in huddling together in the chamber accompanied by decreased frequencies of active social behaviors. Sequential analyses of social interactions indicated that approaches to the back of the approached animal typically elicited flight, while approaches to the front of the approached animal failed to do so. This was seen for female to female, and for female to male approaches, as well as male to female approaches, strongly counterindicating a view that rear approach/flight specifically reflects female responsivirity to unwanted male sexual approach. For adult male colonies, similar protocols found that these social behaviors were similar to those of adult mixed-sex colonies. These findings suggest two potentially useful measures of eusocial behavior in mice, of possible value for genetic mouse models of autism; that is, huddling together and approaches to the front but not the back, of conspecifics.

Fig. 1

A schematic diagram of the visible burrow system using in the present experiments. C: chamber, mesh pattern: a layer of sawdust bedding

Fig. 2

The percentage of observations in each location of chambers (upper graphs) and spent for each huddle or being alone (lower graphs) for males (M; N= 4) and females (F; N= 12) during both the dark and light periods in Experiment 1. Data are expressed as mean percentage (±S.E.M.). P: preferred chamber, C: connected chamber, and U: unconnected chamber. For females, * indicates significant differences between day of testing compared to day 1; p<.05. # indicates significant differences between chambers compared to preferred chamber; p<.05, in upper graphs, and between dark and light periods; p<.05, in lower graphs.

Fig. 3

The mean numbers of counts that males (N= 4) and females (N= 12) displayed each behavior (frontal approach, back approach, or flight) during both the dark and light periods in Experiment 1. Data are expressed as mean counts (±S.E.M.). For females, * indicates significant differences between day of testing compared to day 1; p<.05. # indicates significant differences between dark and light periods; p<.05.

Fig. 4

The mean percentage of observations in each location of chambers (upper graphs) and spent for each huddle or being alone (lower graphs) for male C57BL/6J mice (N= 21) in Experiment 2. Data are expressed as the mean percentage (±S.E.M.). * indicates significant differences between days compared to day 1; p<.05. # indicates significant differences between chamber compared to preferred chamber, p<.05, in upper graphs, while between dark and light periods, p<.05, in lower graphs.

Fig. 5

The mean numbers of counts that male mice (N= 21) displayed each behavior (frontal approach, back approach, or flight) during both the dark and light periods in Experiment 2. Data are expressed as mean counts (±S.E.M.). * indicates significant differences between day of testing compared to day 1; p<.05. # indicates significant differences between dark and light periods; p<.05.