Figure 1.

Timeline and procedures for Experiments 1–4. In Experiment 1, all rats were acclimated to the HR/BP apparatus prior to the experimental manipulations. Subsequently, rats were exposed to two acute stress sessions, comprised of immobilization during cat exposure (psychosocial stress; cat icon; n = 8) or home cage exposure (no psychosocial stress; rat cage icon; n = 10), that were separated by 10 days. We obtained blood samples and cardiovascular measurements from all rats following each of the two acute stress sessions. Psychosocially stressed rats were also given unstable housing conditions from Day 1 until the beginning of behavioral testing, which occurred three weeks after the second cat exposure. In Experiment 2, we repeated the explicit stress procedures from Experiment 1 (n = 10 per group) without performing blood sampling and cardiovascular measurements after each of the acute stress sessions. On Day 32, we assessed the effects of this paradigm on growth rate, as well as adrenal gland and thymus weight. In Experiment 3, groups of rats were given: (1) two inescapable cat exposures, in conjunction with daily social stress (psychosocial stress; n = 8), (2) two inescapable cat exposures, alone (cat only; n = 10), (3) two exposures to home cage, in conjunction with daily social stress (social stress only; n = 10) or (4) two exposures to home cage, alone (no psychosocial stress; n = 8) to determine whether both stress manipulations (i.e., inescapable cat exposure and daily social stress) were necessary to produce the observed effects on rat physiology and behavior. In Experiment 4, two groups of rats (psychosocial stress, n = 19 and no psychosocial stress, n = 20) were exposed to the same manipulations employed in Experiment 2. On Days 32 and 33, a subsection of each group of rats was injected with yohimbine (YOH: 10 and 12, respectively) or vehicle (VEH: 9 and 8, respectively) prior to behavioral testing.