The effects of acoustic signals and sex steroids on dopaminergic function in male anurans

This dissertation investigates the effects of sex steroids and auditory stimulation on the dopaminergic systems in the male frog brain. Part 1 provides a review of the background literature and consists of two chapters. Chapter 1 reviews our current knowledge of neural substrates underlying anuran reproductive behavior and a description of anuran dopaminergic systems. Chapter 2 reviews what is currently known about the effects of sex steroids on dopaminergic systems and the interactions among sex steroids, dopaminergic systems and reproductive behavior. Part 2 contains the experimental section of the dissertation and consists of five chapters. In Chapter 3, I demonstrate that the dopamine receptors in the fore- and midbrain of the frog Rana pipiens possess pharmacological characteristics that are similar, but not identical, to known mammalian dopamine receptors. In Chapter 4, I describe the localization of the tyrosine hydroxylase immunoreactive (THir) cells in the fore- and midbrain of male Rana pipiens using a whole-mount immunohistochemical technique. In Chapter 5, I demonstrate that hormone treatment has an effect on numbers of THir cells in male R. pipiens CNS. Gonadectomized males possess far fewer THir cells compared to males that have received testosterone replacement. In Chapter 6, I describe the behavioral effects of the dopaminergic agonist, apomorphine, on locomotor control in frogs. Apomorphine causes locomotor impairments which are similar to that in mammals, and also decreases numbers of THir cells in R. pipiens CNS. In Chapter 7, I describe the effects of conspecific calls on the reproductive endocrinology and dopaminergic system in the male frog, R. sphenocephala. I demonstrate that frogs exposed to conspecific call undergo changes in reproductive physiology and possibly circulating androgen levels. I could not demonstrate that auditory stimulation influenced numbers of THir cells in the frog CNS. Part 3 consists of Chapter 8, and contains a summary of the results and concluding statements. Throughout this dissertation, I have shown that frogs possess dopaminergic systems that are functionally similar to mammals. In addition, I have shown that these dopaminergic systems can be influenced by changes in hormonal milieu, and therefore may play a role in modulating reproductive endocrinology. Although the dopaminergic systems in frogs are not completely identical to those found in mammals, similarities exist such that pharmacological agents developed in mammals can be used to assess the functional significance of neurochemical systems in non-mammalian taxa.