The effects of hormone replacement and tamoxifen on spatial learning and active avoidance learning in ovariectimized rats

M. C. Terek, A. Keser, Y. H. Dogan, T. Dagcı, B. Zeybek, L. Kanit, S. Ozsener, S. Pogun

Abstract: The aim of the present study is to investigate the effects of an estrogen receptor modulating agent tamoxifen, and different protocols of hormone replacement therapy that mimic clinical applications, on spatial learning and active avoidance learning in rats. We used 2 groups of normal rats for tamoxifen experiments (control group and drug group) and 4 groups for hormone replacement experiments: (1) ovariectomized rats with sesame oil injection, (2) ovariectomized rats with continuous estrogen injection, (3) ovariectomized rats with continuous combined estrogen and progesterone injection and (4) ovariectomized with continuous estrogen and intermittent (sequential) progesterone injection. Properly assigned control groups were used and cognitive processes were studied on animal models of surgical menopause using the Morris water maze and active avoidance learning paradigms. In the Morris water maze no significant differences in spatial learning were observed between the hormone replacement and tamoxifen groups. Active avoidance learning was impaired by ovariectomy. In female ovariectomized rats, spatial learning is not influenced by circulating ovarian hormones and tamoxifen. On the other hand, active avoidance learning is impaired by the absence of gonadal hormones.
Keywords: xifen, hormone replacement, Morris water maze, spatial learning