Decreased cued fear discrimination learning in female rats as a function of estrous phase

Abstract

Relative to males, female rats can show enhanced contextual fear generalization (demonstrating a fear response in a safe or neutral context) dependent on estrogen receptor activation. The current experiment aimed to extend this finding to cued fear conditioning. Females in low-estrogen phases of the estrous cycle showed good discrimination, similar to males, between a conditional stimulus that predicted shock (CS+) and an equally familiar one that did not (CS-), while females in the proestrus (high estrogen) phase demonstrated similar levels of fear between the CS+ and CS-. These results demonstrate that cued fear generalization is similarly influenced by endogenous estrogens.

Figure 1.

Means and SEM during the pre-CS, CS−, CS+, ITI, and post-CS periods during the retrieval session for males (A), low-estrogen females (B), and high-estrogen females (C). Asterisks indicate P < 0.05 between CS− and CS+. Groups were constructed based on the estrous phase at the time of retrieval.

Figure 2.

Means and SEM during the pre-CS, CS−, CS+, ITI, and post-CS periods during the retrieval session for males (A), low-estrogen females (B), and high-estrogen females (C). Asterisks indicate P < 0.05 between CS− and CS+. Groups were constructed based on the estrous phase at the time of acquisition.

Figure 3.

Means and SEM during the CS− and CS+ periods during the retrieval session separated into males, and High E and Low E females (A) as well as examining each individual phase of the estrous cycle (B). Asterisks indicate P < 0.05 between CS− and CS+.