Alleviation of the negative effects of restraint stress on cognitive learning and memory retention in female rats by estrogen and tamoxifen

Abstract

Selective estrogen receptor modulators (SERMs) either mimic or block the effects of estrogen (Goldstein, 1998). Tamoxifen, a SERM, blocks the effects of estrogen in breast tissue (Walling, 2005), but its effects in other tissues, specifically in the brain, are poorly understood. Tamoxifen may reproduce the effect of estradiol in the brain (Le Saux et al., 2005) or it may inhibit memory (Jenkins et al., 2004). This study used ovariectomized rats injected with pharmacological doses of estrogen or tamoxifen. Cognitive learning and retention were evaluated based on performance in the Morris water maze. The hypothesis tested was that tamoxifen would simulate the effects of estrogen in the brain, resulting in cognitive learning and retention similar to estrogen-injected rats but different from the non-stressed control group. While no statistically significant results were noted in the retention protocol, a statistically significant difference between the tamoxifen and the control groups on days four and five in the learning protocol was observed. However, when comparing average learning times, the results suggested that tamoxifen does not mimic the effects of estrogen in the brain.