Effects of Ovariectomy on Learning in Rats in Health and after Early Proinflammatory Stress

We report here studies on the effects of ovariectomy (OE) in females performed at age 35 days on the development and extinction of a conditioned fear reaction and on learning in the Morris water maze in adult rats. The behavior of OE females was compared with the behavior of males and sham-operated females. We compared the effects of OE in animals after early proinflammatory stress (administration of bacterial lipopolysaccharide on postnatal days 3 and 5, LPS group) and in a control group (administration of physiological saline, PS group). OE hindered the development of a conditioned fear response to sound in the LPS group and also slowed the extinction of fear in both the PS and LPS groups as compared with sham-operated females. On training in the Morris water maze, OE in the PS group improved learning in females as compared with sham-operated females, making them as successful in solving the spatial task as males. Early proinflammatory stress had similar effects on males and OE females, degrading many measures of learning in the Morris maze. OE did not affect working memory in the daily platform change test. OE eliminated sex differences in the behavior of females as compared with males in many respects and made them more prone to proinflammatory stress.