Of Gansu Zokor Male Gonad Seasonal Variation

Seasonal breeding is one of the survival strategies in animals, and it is the result of adapting natural selection in evolutionary process. The research on mechanism of its reproduction has also been the important issues of the reproductive biology, developmental biology and reproductive endocrinology. The occurrence and the formation of sperm have two interrelated factors, one is related to the development of spermatogenic cells, the other is closely related to the regulation of reproductive hormones.The morphological changes of spermatogenic cells in the annual cycle, sex steroid hormone changes in the season patterns and sex hormone receptor expression in the adult male Gansu zokor's (Myospalax cansus) testis were observed and analyzed relatively systemically using histology, radioimmunoassay and immunohistochemistry during the different months. The purposes of these studies are to further explain the seasonal reproduction pattern and its control mechanism of Myospalax cansus, and accumulate data for enriching and developing the reproductive biology. The results are as follows:1 Seasonal changes in mass and volume of testes were very pronounced in Myospalax cansus. The largest weigh and volume of testes were observed in April, and the smallest were February. The testis index, testis volumes were same as the annual changes of testis mass. The curves of annual variation were all unimodality.2 The spermatogenetic cycle of Myospalax cansus comprises seven stages with significant features: Stage I , from February to April, the testis were at the stage of spermatogonia proliferation. In this period, testis index and the number of spermatogonia began to rise. Other spermatogenic cells had not yet formed; Stage II to III, from March to April, primary spermatocyte meiosis period. The testis index was highest in this stage, and spermatogenic cells were in spermatocyte stage, the primary spermatocyte meiosis generated to secondary spermatocyte; Stage IV, from April to May, spermatocytes continued to split, germ cells appeared in seminiferous tubules; Stage V, in May, sperm formation, spermatids of seminiferous tubules were transformed to spermatozoa, a large number of sperms existed in the lumen; Stage VI, spermatozoa emission period, from May to June, testis index were a significant drop and mature spermatozoa excluded gradually; VII, the testicular activity ceased basically from July to September, November to January of the following year, the spermatogenic activity ceased completely. Therefore, Myospalax cansus are animals of seasonal reproduction, spermatogenesis cycle is discontinuous type. 3 Changes of sex steroid hormone levels in serum were correlated significantly with testicular activity in adult male Myospalax cansus during the breeding season. In annual cycle, the curve of variation in serum testosterone concentration was unimodal type. Testosterone (T) concentration in mid-April increased rapidly, reached its peak in mid-May, then dropped significantly. Serum estradiol (E₂) concentrations fell in mid-May, but the slow decline was no significant differences between the months. Changes of serum progesterone (P) concentration were slightly different from T and E2. P levels fluctuated near the basic value between mid-February to mid-March. There were a significant increase in mid-March, and the peak appeared in mid-April, followed by a significant downward trend. Thus, serum T concentration of male Myospalax cansus is closely correlated with the maintenance of spermatogenesis activities, male and male combat, courtship and mating. Physiological functions of E₂ may be to maintain spermatocytes proliferation, and promote the formation of spermatozoa. P levels may be an important factor for the start of mating behavior.4 The results of Androgen receptor (AR) , estrogen receptor (ER) , progesterone receptor (PR) in spermatogenic cells shows that sex steroids can act directly on spermatogenic cells, andregulate spermatogenesis. AR expressed stronger in spermatocytes and spermatogenic cells, ER in germ cells and sperm expressed strong in the second spermatocyte, PR in Leydig cells also expressed stronger. Thus, it is speculated that the androgen receptor and estrogen receptor may be related to the proliferation of spermatogonia, division of spermatocytes, and also closely related to the formation of spermatozoa. PR may regulate Leyding cells their own synthesis and secretion of testosterone to control spermatogenesis.In short, this reseach indicates that Myospalax cansus is seasonal breeding animals. It breeds offspring once a year, and the reproductive period is from April to June. The peak is May. So, we can make full use of the breeding season to prevent and control rodents in practice.