The Role of Gonadal Sex Steroids in Neuroplasticity of Brains of Male Peromyscus leucopus Subjected to Different Photoperiods
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Date
2013-05
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The Ohio State University
Abstract
Individuals of mammalian species inhabiting non-tropical regions undergo seasonal brain and behavioral changes in response to the annual cycle of changing photoperiod (h of light/ day). In one such species, white-footed mice (Peromyscus leucopus), short-days are correlated with reduced hippocampal volume and function (e.g., spatial learning and memory), decreased reproductive function, and decreased gonadal steroid hormone concentrations. Reproduction and hippocampal functions are energetically expensive, so decreasing these processes may be adaptive to conserve energy for winter survival. Decreased androgen concentrations may drive the short-day regression of hippocampal size and function. If gonadal steroids drive the long-day increase in hippocampal function, then gonadal steroid replacement should improve learning and memory in short days. We subjected gonadectomized adult male Peromyscus leucopus to either short- or long-photoperiods, and treated them either with testosterone (T), dihydrotestosterone (DHT), estradiol (E), or cholesterol to test the effects of T, or the primary androgenic and estrogenic T metabolites (DHT and E, respectively) on photoperiodic changes in spatial learning and memory using the Barnes maze. The effects of E and T were opposite depending on photoperiod; E enhanced spatial ability in long days, whereas T enhanced spatial performance in short days. During the memory probe trial, the errors and latency were similarly dependent on both photoperiod and the treatment of E or T. T and DHT reduced latency and errors in short days, and E reduced latency and errors in long days. This suggests that gonadal steroid enhancement of hippocampal function in long days is mediated by estrogen receptors, whereas short-day enhancements are mediated by androgen receptors. Sex steroids have been implicated in affecting hippocampal function across mammalian species, including humans, and these findings demonstrate that an environmental factor, namely day length, can influence the way in which these sex steroids affect hippocampal function and behavior.
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Alkire Award
Arts and Sciences Scholarship
Arts and Sciences Scholarship
Keywords
Photoperiod, Sex Steroids, Estrogen, Testosterone, Seasons, Peromyscus leucopus