Strain-dependent development of sociability in adolescent mice.

<p>(a) Following 24 h of social isolation, early-adolescent (age = ≈4 wks) B6 test mice expressed more social investigation (SI) towards a novel, opposite-sex F1 mouse compared to age-matched BALB mice. There was no difference in SI among late-adolescent mice (age = 7–8 wks) from the BALB and B6 strains (N = 14 mice/genotype/age). The numeric symbol represents a significant (P = 0.01), planned orthogonal contrast between BALB and B6 mice. (b) Following 8 days of conditioning during early adolescence or late adolescence, B6 mice expressed a social conditioned place preference (SCPP), whereas BALB mice expressed social indifference at both time points (N = 14 mice/genotype/age). SCPP scores were calculated by subtracting the time a mouse spent in an isolation-paired environment from the duration it spent in a socially paired environment (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004387#s4" target="_blank">Materials & Methods</a>). The asterisks represent significant (P<0.05), planned orthogonal contrasts between BALB and B6 mice. All data are presented as the mean±s.e.m.