Fig. 1.

Experimental timelines and procedures. In Experiment 1, rats in the stress group were exposed to a 31-day chronic stress paradigm that consisted of two cat exposures and daily social instability. Stressed rats were immobilized and exposed to an adult, female cat for 1 h on Days 1 (during the light cycle) and 11 (during the dark cycle), and throughout the 31-day paradigm, the cage mates of stressed rats were randomly changed on a daily basis. Rats in the no stress group remained in their home cages on Days 1 and 11 and remained with the same cage mate throughout the paradigm. On Day 32, all rats were tested for anxiety-like behavior on the elevated plus maze (EPM); on Day 33, all rats were tested for their acoustic startle responses; and, on Day 34, all rats were tested for anxiety-like behavior in an open field. Vaginal smears were collected from all rats on Days 1, 11, 32, 33, and 34 to determine the stage of estrous. In Experiment 2, rats underwent ovariectomy or sham surgery at 4 weeks of age, after which they were randomly assigned to stress or no stress groups. Four weeks after surgery, all rats underwent the same procedures as outlined in Experiment 1, except no vaginal smears were collected. In Experiment 3, rats underwent ovariectomy or sham surgery at 4 weeks of age, after which they were randomly assigned to stress or no stress groups. Four weeks after surgery, all rats underwent the same stress procedures as outlined in Experiment 2. On Day 32, all rats were tested for anxiety-like behavior on the EPM. On Day 33, all rats were anesthetized, and their hearts were removed and exposed to ischemia / reperfusion, as outlined in the methods.