Date of Award

5-2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Developmental and Brain Sciences

First Advisor

Jin Ho Park

Second Advisor

Susan L. Zup

Third Advisor

Vivian Ciaramitaro

Abstract

In multiple rodent species, gonadal steroids during puberty refine the organization of brain and behavior and activate behaviors in adulthood. Approximately one third of B6D2F1 hybrid mice retain the full repertoire of male sexual behavior long term after castration (“maters”), thus exhibiting steroid-independent activation in adulthood. However, the development of steroid-independent behaviors is poorly understood. In this dissertation, we probe the effects of gonadal steroids during puberty on steroid-independent sociosexual behaviors, c-Fos immunoreactivity in response to an estrous female, sexually dimorphic brain regions, and markers of central and peripheral metabolic function. We also characterize the timing of puberty in the B6D2F1 male mouse and evaluate methods of exogenous estradiol administration during puberty. Previous work from our lab showed that exposure to pubertal testosterone is necessary for this phenotype. In the first set of studies, we replicated this finding, as zero prepubertally castrated animals demonstrated the ejaculatory reflex in adulthood. Additionally, neither pubertal steroids nor mater status was sufficient for sexual partner preference. All experimental animals were naïve before castration, suggesting that sexual experience may also be necessary for maters to display this behavior, likely in conjunction with pubertal steroids. We also show that prepubertally gonadectomized males had greater c-Fos immunoreactivity than either testosterone-replaced males in one experiment and sham-operated males in a second experiment. In the second set of studies, we characterized puberty in the B6D2F1 male mouse. Preputial separation began on postnatal day 25, and anogenital distance and body weight change began to plateau on postnatal day 37. Pubertal hormone exposure altered the area of the medial preoptic area and medial amygdala, such that these regions were significantly smaller in prepubertally castrated males. We also determined that peroral methods of exogenous estradiol administration yield levels of circulating estradiol closest to physiology. Finally, in the third set of experiments, we report that exogenous testosterone exposure during puberty changes the trajectory of body growth, food consumption, and alters Kiss1 expression in the arcuate nucleus. These findings warrant future research into the effects of exogenous hormone administration during sensitive periods on metabolism. These data have important implications for the health of adolescents.

Comments

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Available for download on Saturday, June 04, 2022

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