Fig. 4

Sex-specific social behavior patterns over adolescence require C3–C3R interactions. a Experimental design: separate cohorts of experimental animals (n = 8/sex/age) were single-housed for 24 h prior to test, after which time a novel age-matched and sex-matched conspecific was introduced into their home cage. Ten minutes of interactions were recorded, and later an experimenter blinded to the conditions coded the interactions for either total play or social exploration (i.e., non-play social behavior). Only behaviors initiated by the experimental animal were considered. Males: b Male social play behavior transiently increased at P30 (Table 4A), c with no changes in social exploration over development (Table 4B). Females: d Female social play behavior did not change over development (Table 4C), e while social exploration peaked from P30 to 38 (Table 4D). f To determine if C3–C3R interactions regulating D1r levels between P30 and 38 in males is required for the decline in social play behavior observed at this time, NIF or vehicle was injected bilaterally in P30 males or P22 females (n = 10/sex/treatment). Animals were then single housed for 24 h at P37 or P29, and assessed for social behavior as described at P38 and P30, respectively. Males: g Interrupting C3–C3R interactions at P30 increased social play behavior at P38 (Table 4E), h without affecting social exploration (Table 4F). Females: i Female social play behavior, while at a low basal level, also modestly increased at P30 after P22 NIF injection (Table 4G), j with no changes in social exploration (Table 4H). Data were analyzed either with one-way ANOVAs and Holm-Sidak’s post-hoc comparisons or with two-tailed unpaired t-tests. Histograms portray the mean ± SEM with individual data points overlaid. Significant post-hoc Holm-Sidak t-tests (b–e) and unpaired t-tests (g–j) (p < 0.05) comparisons are delineated with an asterisk. All statistics are in Table 4