title: Estrogen enhances the retention of spatial reference memory in the open field tower task, but disrupts the expression of spatial memory following a novel start position.
abstract: Estrogen's (E) involvement in cognition has been difficult to characterize; numerous studies show that E can both enhance and impair learning and memory. One difficulty may be that experimental paradigms often examine only a single aspect of E's involvement in cognition, for example, the role E plays in the expression of memory after learning has taken place. In addition, the effect of aversive and/or stressful features inherent to many cognitive tests may contribute to the contradictory findings. The present experiment aims to examine the effect of estradiol (E2) on several elements of cognition in a specific experimental setting. We investigated the within-subject effects of long-term E2 replacement in ovariectomized (OVX) female rats on the acquisition and retention of a hippocampal-mediated spatial reference memory task in a familiar non-threatening environment. Results show that E2-replaced rats and OVX sham-replaced rats acquired the ability to navigate an open-field tower maze in order to obtain a food reward at the same rate. Subsequent to acquisition, both E2-replaced and OVX rats performed the task at comparable levels. However, following a 21-day retention interval, non-replaced rats exhibited a significant impairment in spatial memory when returned to the maze environment, while E2-replaced rats exhibited no change in maze performance. When the OVX group was performing once again at asymptote, test trials were administered during which the rats were placed in a non-experienced start location within the maze. This novel condition significantly reduced correct responses in E2-replaced females whereas OVX controls remained unaffected. These results suggest that while the presence of E2 is not important for acquisition of spatial memory in a safe familiar environment, it improves retention of spatial memory. Data further suggests that E2 disrupts the expression of spatial reference memory following an alteration of the test conditions sustaining a habitual response, possibly by the induced emotionally-arousing state of stress.
authors.affiliation: University of Vermont, Department of Psychology, Burlington, VT 05405, United States. olga.lipatova@uvm.edu
authors.forename: Olga
authors.initials: O
authors.lastname: Lipatova
authors.forename: Donna J
authors.initials: DJ
authors.lastname: Toufexis
mesh_terms: D000818:Animals; D004958:Estradiol / Q000494:pharmacology* / Q000502:physiology; D015914:Estrogen Replacement Therapy / Q000523:psychology*; D004967:Estrogens / Q000494:pharmacology* / Q000502:physiology; D005260:Female; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D018782:Maze Learning / Q000187:drug effects* / Q000502:physiology; D010052:Ovariectomy / Q000523:psychology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012153:Retention, Psychology / Q000187:drug effects* / Q000502:physiology
chemical_list: D004967:Estrogens; D004958:Estradiol