Seasonal Differences in Equine Spermatocytogenesis1

Spermatocytogenesis plays a pivotal role in regulation of spermatogenesis; however, its details remain relatively obscure in nonrodent species. The equine testis contains approximately 100% more spermatogonia in summer than in winter and appears to be a good model to identify the flexible components of spermatocytogenesis that cause seasonal changes in daily sperm production. Testes were taken from horses in the winter (n = 47) and in summer (n = 43). Tissues were fixed by glutaraldehydeperfusion and submission in osmium, embedded in Epon or methacrylate, sectioned at 0.5 jam or 5 jam, stained with toluidine blue, and observed using bright-field microscopy. The combined total number of A1, A2, A,, and B, (A plus B,) spermatogonia/ testis and the numbers of B2 spermatogonia or early primary spermatocytes were determined by stereology of Epon sections involving testicular volume density and volume of spermatogonial nuclei. In a subset of horses, different spermatogonial subtypes (A,, A2, A,, and B1) were counted per 100 Sertoli cells in each of the 8 spermatogenic stages and expressed as percentage of all A plus B, spermatogonia. The number of each spermatogonial subtype/testis for the large series of horses was calculated by multiplying the number of A plus B, spermatogonia/testis (determined for each horse) by the percentage of that given spermatogonial subtype. Season did not significantly affect the number of any given subtype per 100 Sertoli cells in any stage or percentages of different subtypes of spermatogonia. Numbers of A, (p < 0.05), A2, A,, B,, or B2 spermatogonia ( < 0.01) were greater in the breeding season. Season did not (p > 0.05) influence the yield of B2 spermatogonia per A, or B2 per B, spermatogonia; however, the yields of BS/A, and 82/A2 were greater (p < 0.01) in the breeding season. Seasonal differences in spermatogonial number are due to a combination of a small but significant increase in number of A, spermatogonia and a significant ( < 0.01) increase in yield of spermatogonial divisions early in spermatocytogenesis in the breeding season.

[1]  C. Cross,et al.  Bloom and Fawcett: A Textbook of Histology , 1995 .

[2]  L. Johnson,et al.  Isolation and staging of horse seminiferous tubules by transillumination. , 1990, Journal of reproduction and fertility.

[3]  L. Johnson,et al.  Staging equine seminiferous tubules by Nomarski optics in unstained histologic sections and in tubules mounted in toto to reveal the spermatogenic wave , 1990, The Anatomical record.

[4]  L. Johnson,et al.  Temporal appearance of seasonal changes in numbers of Sertoli cells, Leydig cells, and germ cells in stallions. , 1989, Biology of reproduction.

[5]  D. Thompson,et al.  Effect of seasonal changes in Leydig cell number on the volume of smooth endoplasmic reticulum in Leydig cells and intratesticular testosterone content in stallions. , 1987, Journal of reproduction and fertility.

[6]  D. Thompson,et al.  Seasonal variation in the total volume of Leydig cells in stallions is explained by variation in cell number rather than cell size. , 1986, Biology of reproduction.

[7]  W. Berndtson,et al.  A quantitative study of Sertoli cell and germ cell populations as related to sexual development and aging in the stallion. , 1986, Biology of reproduction.

[8]  L. Johnson.  A new approach to quantification of sertoli cells that avoids problems associated with the irregular nuclear surface , 1986, The Anatomical record.

[9]  L. Johnson,et al.  Annual cycle of the Sertoli cell population in adult stallions. , 1986, Journal of reproduction and fertility.

[10]  L. Johnson.  Increased daily sperm production in the breeding season of stallions is explained by an elevated population of spermatogonia. , 1985, Biology of reproduction.

[11]  D. Thompson,et al.  Age-related and seasonal variation in the Sertoli cell population, daily sperm production and serum concentrations of follicle-stimulating hormone, luteinizing hormone and testosterone in stallions. , 1983, Biology of reproduction.

[12]  R. P. Amann.  Spermatogenesis in the stallion: A review , 1981 .

[13]  L. Johnson,et al.  Age-related changes in the Leydig cell population, seminiferous tubules, and sperm production in stallions. , 1981, Biology of reproduction.

[14]  E. Weibel,et al.  Integrated stereological and biochemical studies on hepatocytic membranes. II. Correction of section thickness effect on volume and surface density estimates , 1978, The Journal of cell biology.

[15]  C. Huckins.  The morphology and kinetics of spermatogonial degeneration in normal adult rats: An analysis using a simplified classification of the germinal epithelium , 1978, The Anatomical record.

[16]  E. Swierstra,et al.  Reproductive physiology of the stallion. I. Spermatogenesis and testis composition. , 1974, Journal of reproduction and fertility.

[17]  B. W. Pickett,et al.  REPRODUCTIVE PHYSIOLOGY OF THE STALLION , 1974 .

[18]  N. Vandemark,et al.  The Male Reproductive System , 2004, The Quick and the Dead.

[19]  C. Huckins.  The spermatogonial stem cell population in adult rats. I. Their morphology, proliferation and maturation , 1971, The Anatomical record.

[20]  E. Bustos-obregon,et al.  Re-examination of spermatogonial renewal in the rat by means of seminiferous tubules mounted "in toto". , 1968, The American journal of anatomy.

[21]  Y. Clermont.  Quantitative analysis of spermatogenesis of the rat: a revised model for the renewal of spermatogonia. , 1962, The American journal of anatomy.

[22]  E. Oakberg.  A description of spermiogenesis in the mouse and its use in analysis of the cycle of the seminiferous epithelium and germ cell renewal. , 1956, The American journal of anatomy.

[23]  H. W. Chalkley.  Method for the Quantitative Morphologic Analysis of Tissues , 1943 .