Familiarity mediates social avoidance of stressed conspecifics in female rats.

(A) Schematic of the SAP test procedure with naive (n) conspecifics presented during social habituation and a naive and stressed (s) conspecific presented during SAP testing. Experimental rats received a series of 5-min exposures to the interaction arena over 3 days. (B) Mean (with individual replicates) social exploration time the experimental rats in each group engaged with naive or stressed conspecifics on Day 3. A sex-specific effect of familiarity was observed (F1,36 = 8.479, p = 0.006): Rats in the Male-Unfamiliar (p = 0.018), Male-Cagemate (p = 0.006), and Female-Unfamiliar groups spent less time exploring the stressed conspecific compared to the naive (p = 0.052), whereas Female-Cagemate rats spent more time exploring the stressed conspecifics (p = 0.009). (C) Mean (individual replicates with ± s.e.m.) data from (B) expressed as the percent of social exploration time directed toward the stressed conspecific. Male-Unfamiliar (one-sample t9 = 2.579, p = 0.029), Male-Cagemate (one-sample t,9 = 3.550, p = 0.029), and Female-Unfamiliar (one-sample t9 = 2.519, p = 0.032) percent preference scores were significantly less than 50%, indicating avoidance of the stressed conspecific. The Female-Cagemate percent preference score was greater than 50% (one-sample t9 = 2.613, p = 0.028) indicating approach to the stressed conspecific; the Female-Cagemate preference score was significantly greater than the preference score of all other groups. *** p < 0.001.