Date of Award

Spring 1-1-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Integrative Physiology

First Advisor

Pei-San Tsai

Second Advisor

David O. Norris

Third Advisor

Pieter T. Johnson

Abstract

Recently, a dominant hypothesis has emerged to suggest gonadotropin-releasing hormone (GnRH), corazonin (CRZ), adipokinetic hormone (AKH), AKH/corazonin-related peptide (ACP), and red pigment-concentrating hormone (RPCH) all share common ancestry to form a GnRH superfamily. The aim of this thesis was threefold. Specifically, it aims first to examine the anatomical distribution of a novel AKH, termed Aplysia-AKH (ap-AKH), in the opisthobranch mollusk, Aplysia californica. Second, in vivo functions of ap-AKH were investigated. Lastly, ap-AKH was compared to a related Aplysia peptide, Aplysia-GnRH (ap-GnRH) in distribution and function. To achieve these aims, the first research chapter (Chapter 2) examines ap-AKH transcript and mature peptide localization in the central nervous system (CNS) and peripheral tissues of A. californica. Results show that ap-AKH mRNA and peptide are localized exclusively in the CNS, with abdominal, cerebral, and pleural ganglia being the primary sites of ap-AKH production. However, ap-AKH-positive fibers were found throughout the CNS, suggesting diverse neuromodulatory roles. The distribution of ap-AKH differs markedly from that of ap-GnRH. Chapter 3 examines in vivo physiological changes induced by ap-AKH injections. ap-AKH significantly inhibited feeding, reduced body mass, increased gut motility, and reduced gonadal mass. The in vivo effects of ap-AKH differed substantially from ap-GnRH, but both peptides suppressed feeding, raising the possibility of some functional overlap. Overall, the distinct distribution and physiological effects of ap-AKH suggest ap-AKH has diverged functionally from ap-GnRH over the course of evolution. Further, that both ap-AKH and ap-GnRH failed to activate reproduction suggest the critical role of GnRH as a reproductive activator may be a phenomenon unique to vertebrates.

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