A rodent model of social rejection

Abstract

Rats help conspecifics by releasing them from a restrainer only when they have previous social experience with the strain of the restrained rat. When rats have been cross-fostered with rats of a different strain than their own since birth and have never interacted with rats of their own strain, they do not help rats of their own strain when tested as adults. Here we interrogated whether a cross-fostered rat expressed his lack of motivation to help through any behaviors beyond not-helping. Accordingly, a cross-fostered rat was placed in an arena with a trapped rat and the door to the centrally located restrainer was taped shut. We found that cross-fostered rats moved more slowly and approached the trapped rat less than did control, regularly-raised rats tested under the same conditions. We then asked whether the behavior of the cross-fostered rats influenced the trapped rat. After being restrained with cross-fostered rats, trapped rats showed a decrease in exploratory behavior in an open field test compared to trapped rats who were raised normally. The same decrease in movement was observed after subject rats were allowed to freely interact with cross-fostered rats. These results suggest that rats that do not help demonstrate their disinterest to a trapped rat and that trapped rats exposed to apathetic rats show behavior suggestive of an increase in anxiety. In sum, the paradigm introduced here could serve as a rodent model for social rejection.