Abstract
Aging in women is associated with low estrogen, but also with cognitive decline and affective disorders. Whether low estrogen is causally responsible for these behavioral symptoms is not clear. Thus, we aimed to examine the role of estradiol in anxiety-like behavior and memory in rats at middle age. Twelve-month old female rats underwent ovariectomy (OVX) or were treated with 1 mg/kg of letrozole—an aromatase inhibitor. In half of the OVX females, 10 μg/kg of 17β-estradiol was supplemented daily for 4 weeks. Vehicle-treated sham-operated and OVX females served as controls. For behavioral assessment open field, elevated plus maze and novel object recognition tests were performed. Interaction between ovarian condition and additional treatment had the main effect on anxiety-like behavior of rats in the open field test. In comparison to control females, OVX females entered less frequently into the center zone of the open field (p < 0.01) and showed lower novel object discrimination (p = 0.05). However, estradiol-supplemented OVX rats had higher number of center-zone entries (p < 0.01), spent more time in the center zone (p < 0.05), and showed lower thigmotaxis (p < 0.01) when compared to OVX group. None of the hormonal manipulations affected anxiety-like behavior in the elevated plus maze test significantly, but a mild effect of interaction between ovarian condition and treatment was shown (p = 0.05). In conclusion, ovariectomy had slight negative effect on open-field ambulation and short-term recognition memory in middle-aged rats. In addition, a test-specific anxiolytic effect of estradiol supplementation was found. In contrast, letrozole treatment neither affected anxiety-like behavior nor memory.
Highlights
Post-menopause is a life period in women accompanied by reproductive senescence, including decline in ovarian sex hormones [1]
To confirm the endocrine changes induced by ovariectomy, estradiol supplementation and letrozole treatment, uterus weight and plasma testosterone were measured
We found that ovariectomy, but not letrozole, may attenuate open-field ambulation and slightly impair recognition memory in middle-aged females
Summary
Post-menopause is a life period in women accompanied by reproductive senescence, including decline in ovarian sex hormones [1]. The underlying mechanism of age-related cognitive decline and anxiety is unclear, but the role of estrogen loss is considered [7,8,9,10]. Estrogen and Behavior in Aging may result from the aging process as well as from loss in ovarian endocrine function [11]. To analyze the causal effect of menopause-related decline in sex hormone production, further experimental studies are needed. Estradiol replacement in the surgical model of menopause may improve cognitive functions and decrease anxiety-like behavior in rodents [14, 21,22,23,24,25,26,27,28,29,30,31]
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