Sexually dimorphic cognitive style, female sex hormones, and cortical nitric oxide

Recent studies using the water maze (WM) found marked sex differences in be havioral strategy employed in place learning tasks in adult rats. When a ch ange in the platform position is introduced following learning the place of a platform (visible or hidden) in a different position, female rats escape to the newly positioned visible platform faster than males. Nitric oxide ( NO) is implicated in place learning, and there are regional sex differences in its stable metabolites, NO2- +NO3- in rat brain. Furthermore, NO2- + NO 3- levels are sensitive to ovariectomy in female rats. The effect of sex ho rmones on brain development and function is well documented. The present st udy was undertaken to study the effects of ovariectomy and hormonal manipul ations on cognitive performance in a WM task designed to test differences i n behavioral strategy in Sprague-Dawley rats (n = 48) of both sexes. Some o f the females rats were ovariectomised and received either hormone replacem ent (estrogen or progesterone alone or in combination) or the vehicle. Cort ical and hippocampal NO2- + NO3- levels were determined after behavioral te sting. There were no group differences in cognitive ability or non-cognitiv e factors such as motivation or swim speed. Males and intact females differ ed in their cognitive style, but hormonal manipulations in female rats did not affect this relative use of behavioral strategy. There was a correlatio n between performance on the trial where sex differences were most prominen t and NO2- + NO3- levels in the cortex. Our results suggest that the activa tional effects of circulating gonadal hormones do not play a major role in sexually dimorphic cognitive styles. (C) 2000 Elsevier Science Inc. All rig hts reserved.