Acute progesterone treatment impairs spatial working memory in intact male and female rats.

INTRODUCTION: The aim of this study was to determine if progesterone affects spatial and non-spatial working memory in intact male and female rats. METHODS: Rats received subcutaneous injections of progesterone (500 microg) or vehicle (sesame oil). Four hours after hormone treatments, spatial and non-spatial memories were tested using novel object recognition and spatial object recognition tasks. RESULTS: Vehicle-treated female rats had higher progesterone serum levels than males, but progesterone treatment produced equivalent progesterone serum levels in both sexes. In the object recognition task--a non-spatial memory task-females showed better performance than males, and progesterone had no effect on either sex. However, in the object replacement task--a spatial memory task-progesterone significantly impaired the retention in both male and female rats as compared with vehicle-treated groups. CONCLUSION: These results suggest that acute progesterone treatment interferes with spatial working memory consolidation, but not recognition (non-spatial) working memory. As such, the observed sexual incongruities in progesterone's effects on working memory suggest that progesterone-based hormone therapies have a negative impact on cognition.