Abstract

Onset of puberty in male Djungarian hamsters is characterized by increased pituitary gonadotropin secretion and testes maturation, and is controlled by neurons within the brain which secrete gonadotropin-releasing hormone (GnRH). Puberty is associated with increased numbers of morphologically unipolar, but not bipolar, GnRH neurons in the medial preoptic area (MPOA) and diagonal band of Broca (DBB). To test the hypothesis that delayed sexual maturation arrests this increase, males were exposed to short days or administered melatonin. Males with delayed puberty had significantly fewer unipolar GnRH neuron numbers in the MPOA and DBB comparable to pubertal controls in long days. Unipolar GnRH cells are thus implicated in the process regulating gonadotropin secretion at puberty. All GnRH neurons do not project to the median eminence of the medial basal hypothalamus (MBH) to directly regulate pituitary gonadotropin secretion. To determine the projection of unipolar GnRH neurons, DiI, a neural tract tracer, was implanted postmortem into the median eminence of pubertal males. Both unipolar and bipolar GnRH cells contained DiI, i.e., projected to the MBH to regulate gonadotropin secretion. The majority of DiI-labelled GnRH cells were found in the MPOA and rostral forebrain. With sexual maturation, fewer GnRH neurons in all areas contained DiI suggesting that the onset of puberty is associated with a restructuring of GnRH input to the medial basal hypothalamus. Castration of prepubertal males had no effect on peripubertal GnRH cell numbers, subtype ratio, neuroanatomical distribution, or innervation of the MBH. The findings suggest that an increase in number of unipolar GnRH cells is a critical component associated with the onset of puberty in the male Djungarian hamster. However, both bipolar and unipolar GnRH neurons primarily in the MPOA and rostral forebrain are directly regulating gonadotropin secretion. A testes-independent restructuring of the direct GnRH input to the MBH appears to occur with sexual maturation. The increase in GnRH neuron number and decline in GnRH projections at puberty are suggested to produce a more effective secretion of GnRH to stimulate pituitary gonadotropin release and reproductive development of puberty.

LLU Discipline

Anatomy

Department

Anatomy

School

Graduate School

First Advisor

Steven M. Yellon

Second Advisor

Michael A. Kirby

Third Advisor

John W. Patrickson

Fourth Advisor

Dennis D. Rasmussen

Fifth Advisor

Robert L. Schultz

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

1992

Date (Title Page)

6-1992

Language

English

Library of Congress/MESH Subject Headings

Hamsters -- growth and development; Puberty, Delayed -- chemically induced; Gonadorelin -- antagonists and inhibitors; Preoptic Area -- physiology; Frontal Lobe -- physiology

Type

Dissertation

Page Count

x; 206

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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