The influence of context pre-exposure and shock number on contextual fear conditioning in male and female rats.

Contextual fear conditioning is a form of Pavlovian conditioning in which organisms learn to associate an aversive stimulus with the environment in which it occurs. Understanding contextual fear is relevant to anxiety disorders such as posttraumatic stress disorder (PTSD) and it is useful in answering basic questions regarding the neural and molecular systems underlying learning. Even though women comprise approximately half of the population and show higher rates of PTSD than men, there is a poor understanding of how sex affects contextual fear conditioning in rodents. Previous studies have produced discrepant results, with some studies reporting sex differences in contextual fear while others have observed no difference between males and females. One possibility is that parametric differences across studies might explain some of these discrepancies. Here, we tested whether the number of shocks during conditioning or pre-exposure to the conditioning context, factors known to influence the strength of contextual fear, would dictate whether sex differences in contextual fear are observed. Our results show that males exhibited higher levels of contextual fear as measured by freezing behavior, irrespective of the number of shocks or whether the rats were pre-exposed to the conditioning chamber prior to conditioning. These results indicate that sex difference in contextual fear can persist even when the experimental conditions are favorable for robust learning.