A new test paradigm for social recognition evidenced by urinary scent marking behavior in C57BL/6J mice

Abstract

Olfaction is a major sensory element in intraspecies recognition and communication in mice. The present study investigated scent marking behaviors of males of the highly inbred C57BL/6J (C57) strain in order to evaluate the ability of these behaviors to provide clear and consistent measures of social familiarity and response to social signals. C57 males engage in scent marking when placed in a chamber with a wire mesh partition separating them from a conspecific. Male mice (C57 or outbred CD-1 mice) showed rapid habituation of scent marking (decreased marking over trials) with repeated exposure at 24-h intervals, to a stimulus animal of the C57 or CD-1 strains, or to an empty chamber. Subsequent exposure to a genetically different novel mouse (CD-1 after CD-1 exposure, or CD-1 after C57 exposure) or to a novel context (different shaped chamber) produced recovery of marking, while responses to a novel but genetically identical mouse (C57 after C57 exposure) or to the empty chamber did not. This finding demonstrated that male mice differentiate familiar and novel conspecifics as expressed by habituation and recovery of scent marking, but neither C57 or CD-1 mice can differentiate new vs. familiar C57 males; likely due to similarities in their odor patterns. The data also indicate that scent marking can differentiate novel from familiar contexts.

Fig. 1

The total number of urine marked squares for (a) C57 males exposed to CD-1 males (experiment 1); (b) CD-1 males exposed to CD-1 or a C57 male (experiment 2); (c) CD-1 males exposed to CD-1 males (experiment 2); and (d) C57 males (experiment 3). For all experiments, the initial block of trials involved exposure to an initially novel stimulus male, in an initially novel situation. All tests with novel males, as marked on graphs, were done in the same, now familiar, situations as the first block of trials. The inter-trial-interval was 24 hour. Data are expressed mean ± S.E.M. Significant differences between trials compared to trial 1, *;p<.05, and to trial 4, #; p<.05 in graph (a), (b), and (d), and to trial 1, *;p<.05, and to trial 3, #; p<.05 in graph (c).

Fig. 2

The total number of squares with urine marks in male C57 mice. During first four trials, C57 were exposed to the same empty chamber. On the fifth trial, they were exposed to another (novel) empty chamber. Inter-trial-interval was 24 hour. Data are expressed as mean ± S.E.M. Significant differences between trials compared to trial 1, * p<.05, and to trial 4, # p<.05.

Fig. 3

The total number of squares with urine marks in male C57BL/6J mice. During first five trials, C57 were exposed to the empty chamber. For subsequent 4 trials, they were exposed to the same chamber but with a single CD-1 male. On trial 10, they were exposed to the test chamber alone again, and then on trial 11, they were exposed to a novel CD-1. Inter-trial-interval was 24 hour. Data are expressed as mean ± S.E.M. Significant differences between trials compared to trial 1, * p<.05, to trial 6, # p<.05, and to trial 11, $ p<.05.