Acute administration of estrogen and progesterone impairs the acquisition of the spatial Morris water maze in ovariectomized rats

Although several markers of synaptic efficacy are enhanced during proestrus , spatial water maze performance is impaired. Because levels of both estrog en and progesterone are elevated in proestrus, the nature of their individu al and combined effects on spatial learning was examined. Long-Evans hooded rats were ovariectomized postpubertally and pretrained on a water maze wit h a visible platform (nonspatial). Following pretraining, rats were adminis tered estrogen (5 mug sc) or oil 48 and 24 h prior to testing and progester one (500 mug sc) or oil 4 h prior to testing. Rats were tested on a water m aze in a different room with a submerged platform (spatial) for 16 trials w ith random start location in a single testing day. Latency and path length to the target platform were significantly greater in estrogen plus progeste rone-treated animals than in controls. Neither estrogen nor progesterone al one significantly impaired performance relative to controls on either measu re. Swim speed was not significantly affected by any of the hormone treatme nts. Performance on a nonspatial cue task was not significantly altered by ovarian steroids. Thus, the combination of estrogen and progesterone produc es deficits in the acquisition of the Morris water maze that may be specifi c to spatial reference memory. These deficits could be due to hormonal infl uences on extrahippocampal structures or to detrimental effects on behavior resulting from the increased synaptic activity intrinsic to the hippocampu s proper. (C) 2000 Academic Press.