Fig. 2.

Impacts of stress chronicity and sex on subsequent fear learning. Depicted: Schematic illustration of the timeline of the experiment and the figure panels in which data from various components of the experiment are displayed (panel A). Percent freezing during stress pretreatment (panels B & C, days 1–15), generalization testing (panel D, day 16), context preexposure (panel E, days 17–19), single-shock baseline (panel F, day 20), and context test (panel G, day 21). Male (M) and female (F) rats received either acute stress exposure (15 footshocks) on day 1 or 15 (AS1 or AS15), chronic stress (CS) exposure (15 footshocks), or identical context exposure with no shock (No Stress; AN & CN). Following stress pretreatment, all rats were exposed to a novel context that shared some similar dimensions to the stress pretreatment context. All groups were then preexposed to a completely novel environment for 8 min/day for 3 consecutive days. Twenty-four hours after the termination of preexposure, all groups received a single footshock in the preexposed context. Then, all groups were tested for contextual fear learning 24 h later. All groups that received footshock during stress pretreatment readily reached asymptotic contextual fear conditioning (panels B & C). Groups that received chronic stress or that received acute stress on day 1 of the chronic stress procedure showed greater generalized fear compared to all other groups in the similar (panel D) or totally novel contexts (panel E). Increased baseline levels of generalized fear prior to the SEFL single-shock exposure were non-significant (panel F). AS and CS groups showed greater freezing behavior during the context test compared to unshocked controls, and CS showed higher freezing as compared to AS (panel G). Error bars denote mean ± SEM. *, ***, **** denotes significance (p ≤ .05, p ≤ .001, and p ≤ .0001, respectively) compared between indicated groups (horizontal square brackets), compared between each Stress group and its respective No Stress control (horizontal line), or compared between a specific Stress group and its respective No Stress control (free-standing).