Animals received 3 injections of either vehicle or M. vaccae (0.1 mg, s.c.). Six d after the third injection, baseline juvenile social exploration (JSE) was measured in all animals. Twenty-four h after baseline testing, animals were exposed to stress (IS; inescapable tailshock) or served as home cage controls (HCCs). Twenty-four h post-IS, JSE was measured. Data are presented as a percent of baseline JSE. N = 10–12 animals per group. Data are presented as the mean + s.e.m. The IS/vehicle treatment group significantly differed from all other groups, * p < 0.05.