Chronically stressed rats tested at 16 h recovery exhibit transient augmentation of plasma ACTH, whereas chronically stress rats challenged at 7 d recovery exhibit an attenuated plasma ACTH response to novel environment exposure. Plasma ACTH levels at 20, 40, and 60 min after the end of a 5-min exposure to a novel environment at 16 h (A), 4 d (B), 7 d (C), or 30 d (D) recovery from CVS. Values represent mean ± sem; n = 6 per group. *, P < 0.05 vs. control group.