Dissertation/Thesis Abstract

Effects of exposure to environmental pollutants on sexual behavior, reproduction, and brain gene expression
by Miranda, Robert Alan, Ph.D., Northern Arizona University, 2013, 160; 3562152
Abstract (Summary)

Environmental pollutants can act as endocrine disruptors to affect the biology of organisms including, development, reproduction, behavior, and overall health. Many endocrine disrupting chemicals (EDCs) can mimic or inhibit functions of sex steroids which are critical for the development and maintenance of vertebrate reproductive systems. Sex steroids also interact with arginine vasotocin (AVT)/arginine vasopressin (AVP; mammalian homologue) systems to mediate vertebrate social and sexual behaviors, including vocalizations in male anurans. I used the Western clawed frog, Xenopus tropicalis, as an amphibian model species to evaluate the effects of exposure to EDCs on AVT-regulated behaviors and on brain AVT and sex steroid signaling systems.

In order to understand the role of neurohormones and social stimuli in behavior of X. tropicalis, I studied the effect AVT and human chorionic gonadotropin (hCG) administration and the influence of different social contexts on sexual behaviors, including calling, in males. I found that AVT and hCG treatment alone and in combination induces male sexual behavior, and the presence of a female is necessary to stimulate this behavior. I also analyzed the expression of genes related to AVT and sex steroid signaling in the brain of male and female X. tropicalis to identify genes that are expressed sexually dimorphically and could be potentially altered by EDC exposure.

Then I utilized the behavior and gene expression assays I developed to study the effects of developmental exposure to the synthetic androgen 17β-trenbolone (17β-TB) on behavior, fecundity, morphology, and brain gene expression in adult X. tropicalis. Developmental 17β-TB exposure reduced sexual behavior and inhibited female egg release during breeding trials. Exposure to 17β-TB also blocked oviduct development and altered AVT-related brain gene expression in females.

In another study I evaluated the effects of adult exposure to the common EDCs bisphenol A (BPA), nonylphenol (NP), and triclosan (TCS) or a mixture of the three on sexual behavior, morphology, and brain gene expression in adult male Xenopus tropicalis. Behavior and brain gene expression were not significantly affected, but TCS-exposed animals had a lower normalized liver weight than animals exposed to BPA or the chemical mixture. Males exposed to BPA, NP, and the mixture also exhibited increased oviduct development compared to TCS-exposed males, and the source of the animals influenced oviduct development.

Results from my dissertation research demonstrate that exposure to endocrine disruptors can affect multiple levels of physiology. Gender, timing of exposure and nature of the chemical are also critical factors in determining these physiological effects. Importantly, because there is evolutionary conservation in vertebrates for the role of sex hormones in regulating the reproductive system as well as the AVT/AVP system and related social behaviors, my work has important broader implications for endocrine-disrupting effects from environmental chemical exposure for all wildlife and humans.

Indexing (document details)
Advisor: Propper, Catherine R.
Commitee: Allan, Gerard J., Deviche, Pierre, Nishikawa, Kiisa C.
School: Northern Arizona University
Department: Biological Sciences
School Location: United States -- Arizona
Source: DAI-B 74/09(E), Dissertation Abstracts International
Subjects: Toxicology, Surgery, Endocrinology
Keywords: Brain gene expression, Pollutants, Reproduction, Sexual behavior
Publication Number: 3562152
ISBN: 978-1-303-09662-4
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