Date of Award

Winter 1995

Project Type

Dissertation

Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

William E Berndtson

Abstract

Most quantitative investigations of spermatogenesis requites identification of stages of the cycle of the seminiferous epithelium. The current "tubular morphology" system of staging for the rabbit permits identification of only eight stages and is not applicable to all experimental conditions. A more advantageous staging system, based on changes in the acrosome and morphology of the developing spermatids, had not been developed for the rabbit. Knowledge of spermatogonial kinetics, including the identity of spermatogonial subtypes and the number and timing of spermatogonial divisions, is also important, but had not been fully elucidated in this species. This investigation was undertaken to develop an acrosomic system for identifying stages of spermatogenesis and to eiucidate the kinetics of spermatogenesis in the rabbit.

Acrosomal development was examined in testes from twelve 8.5-mo-old New Zealand White rabbits. Eleven stages of spermatogenesis were identified, the relative frequencies of which were 8.5, 5.9, 9.4, 6.3, 7.0, 9.6, 17.3, 9.7, 8.5, 5.7 and 12.0% for Stages I-XI, respectively. Also, the types of cells present at each stage were characterized and quantified within round seminiferous tubular cross sections using light microscopy. Based on direct enumeration of 525,566 cells, a model for the kinetics of spermatogenesis was proposed, which recognizes five successive spermatogonial divisions. These involved spermatogonia of types A$\sb1$, A$\sb2$, Intermediate 1, Intermediate 2 and B at stages VII-IX, X-I, I-II, III and V, respectively. The division of Intermediate 1 spermatogonia was bivalent, producing both Intermediate type 2 and A$\sb1$ spermatogonia. Such divisions, termed stem cell renewal, replenish the original supply of type A$\sb1$ spermatogonia necessary to sustain spermatogenesis. Primary spermatocytes arose from dividing type B spermatogonia during stage V and divided in turn late in stage X of the next cycle to form secondary spermatocytes. The latter divided at the end of stage XI to form young spermatids. Although most seminiferous tubular cross sections contained cells characteristic of one specific stage, some asynchronous germ cell development was observed. The proposed staging system and model for the spermatogonial kinetics should serve as useful tools for future investigations involving quantitative aspects of spermatogenesis in the rabbit.

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