Males show stronger contextual fear conditioning than females after context pre-exposure

Estradiol affects the structure and function of the hippocampus. We have found that repeated estradiol affects neurogenesis and cell death in the hippocampus of adult female, but not male rats. In the present study we sought to determine whether using the same regimen of estradiol would influence hippocampus-dependent behaviour. Adult male and female rats were given estradiol or sesame oil for 15 days, and then tested using a contextual pre-exposure paradigm in which performance depends on the hippocampus. The time spent freezing displayed by rats was scored on subsequent days in (1) the training context, (2) a novel context in which rats had never been shocked, and (3) the training context a second time. Irrespective of treatment, males showed stronger memory for the context by exhibiting greater freezing in both the training context exposures and the novel context. Previous estradiol treatment, in either sex, did not affect the ability to learn and retain information about the training context. However, female rats treated with estradiol and exposed to a novel context after fear conditioning exhibited less freezing behaviour than controls. Taken together, our results demonstrate that gonadectomized male rats outperform females, regardless of previous treatment with estradiol, on a hippocampus-contextual fear conditioning test, and that previous estradiol treatment has a subtle effect on performance in female but not male rats. (C) 2009 Elsevier Inc. All rights reserved.