The Effects of Perinatal Pcb Exposure and Hypothyroidism on Motor Development in the Sprague-dawley Rat

Polychlorinated biphenyls (PCB) are environmental endocrine disruptors, altering thyroid hormone concentrations in mammals. Normal thyroid hormone concentrations, particularly thyroxine (T 4), are necessary for normal growth and development in the fetus, and throughout infancy and into adulthood. The importance of thyroid hormone to development has been demonstrated clinically by the effects of maternal dysthyroidism on the offspring, as well as congenital dysthyroidism in the child. Untreated congenital hypothyroidism, for example, often results in poor bone growth, learning disabilities, and varying stages of mental retardation. To better characterize the effects of perinatal PCB exposure on motor function and behavior, the present study aimed to determine whether the developmental toxicity of PCB is a result of altered neuroendocrine function in the developing rat caused by maternal hypothyroidism. In this study, Sprague-Dawley rat pups were exposed pre-and post-natally to PCB or thiouracil, and a psychomotor battery of tests was used to evaluate motor activity and behavior at infant, adolescent, and adult ages. Tyrosine hydroxylase concentrations in the striatum and ventral tegmental area (VTA) were also evaluated in PCB-treated and control animals to provide insight into the dopaminergic system. The results of the study indicated both PCB and thiouracil affected motor function, activity, and behavior in infant, adolescent, and adult rats, with some negative neuroendocrine effects continuing into adulthood. Whereas hypothyroidism may be directly responsible for some of the behavioral and physiological alterations, PCB-exposure may independently induce irreversible long term effects on motor and neuroendocrine function. iii This work is dedicated to my husband, Dan, in gratitude for his love, patience, and mentorship, and to my parents, Rodney and Paula, and grandmother, Marjorie, for their love and support. iv ACKNOWLEDGMENTS