Seasonal changes in immunolocalization of inhibin/activin subunits and testicular activity in wild male raccoon dogs (Nyctereutes procyonoides)

Canid Reproductive Biology: Norm and Unique Aspects in Strategies and Mechanisms

The reproductive physiology of canids is unique compared to other mammalian species. Specifically, the reproductive cycle of female canids is characterized by extended periods of proestrus and estrus followed by obligatory diestrus and protracted ovarian inactivity (anestrus). Although canid reproduction follows this general pattern, studies have shown variations in reproductive biology among species and geographic regions. Understanding of these differences is critical to the development of assisted reproductive technologies including estrus induction, gamete rescue, and embryo production techniques for canid conservation efforts. This review summarizes current knowledge of canid reproduction, including estrus cyclicity, seasonality, and seminal traits, with the emphasis on species diversity. The application of reproductive technologies in wild canid conservation will also be discussed.

Ovulation, fertilization and preimplantation embryonic development in raccoon dogs (Nyctereutes procyonoides)

A study involving 32 sexual mature females was conducted to characterize ovulation, fertilization and early embryonic development in vivo in raccoon dogs. Oocytes and embryos were collected from the oviducts and uteri, evaluated by stereomicroscopy. Ovulation occurred 25-32h after a female first accepted mounting, regardless of copulation, when the females were paired with a male in the same cage. Ovulated oocytes were at the primary stage. The number of ovulated eggs in females with or without mating was 9.96±2.65 and 9.00±1.92, respectively. Embryos at 2-4 cell, 8-16 cell, morula, blastocyst, and hatched blastocyst stage were observed at 29-73, 48-100, 98-126, 169-198 and 217-268h after first mating, respectively. Embryos were located in the oviduct prior to 4-cell stage and moved into the uterus after 16-cell stage. Embryos at different stages were often obtained from the same female. During the zygote underwent a series of cleavage divisions, the diameter of the embryo cell mass continuously increased through the 2-cell and 4-cell stage, then started to decrease and was the minimum size at the morula stage. At the blastocyst stage, embryos increased in volume, and finally developed into a hatching blastocyst with a thinner zona pellucida. This is the first full report of preimplantation embryonic development in the raccoon dog, which will facilitate the application of advanced assisted reproductive technology in canine species.

Seasonal changes in immunoreactivity of inhibin/activin subunits in the epididymis of wild ground squirrels (Citellus dauricus Brandt)

The inhibin/activin subunits (α, βA and βB) have been found in epididymal tissue of many mammals, but there have been no data available for wild seasonal breeders so far. The aim of this study was to investigate the immunoreactivities of inhibin/activin α, βA and βB subunits in the epididymis of wild ground squirrels during the breeding and nonbreeding seasons. Immunohistochemistry and Western blotting were performed to detect the epididymal immunolocalizations and immunoreactivities of the three subunits. Strong immunostaining of α subunit was present in the interstitial part of the caput epididymis and epithelial parts of the corpus epididymis and cauda epididymis during the breeding season, whereas no α subunit was found in the nonbreeding season. βA and βB subunits were expressed in all cell types of the epithelium throughout the whole seasonal cycle, and immunostaining in the breeding season was likely stronger compared with that of the nonbreeding season. These results suggested that the epididymis might be a potential source of inhibin and activin in the wild male ground squirrel, and the secretion of epididymal inhibin and activin showed distinct seasonal changes. Furthermore, inhibin and activin might function as paracrine and/or autocrine factors that have an effect on the epididymis.

Activity pattern, reproductive behaviors and gonadal hormones in the raccoon dog (Nyctereutes procyonoides)

The objectives of this study were to (1) assess year-round behaviors and activity patterns of captive raccoon dogs (Nyctereutes procyonoides) and (2) characterize the species' reproductive endocrinology. Behaviors and activity patterns of 12 (5.7) animals were recorded over a 1-year period. During that time, fecal samples were collected 2-7 times/week from 16 (7.9) individuals (six of these were included in the behavioral study) for the analysis of testosterone, progesterone and estrogen metabolite concentrations. Activity pattern and excretion of gonadal steroids followed a seasonal pattern. Specifically, dogs were cathemeral in summer, and primarily nocturnal in winter. In the males, testosterone concentrations were at baseline from April through September, began to rise in October and reached peak concentrations in February (P<0.05). In the females, elevated estrogen (P<0.05) was observed in March followed by an increase in progestagen concentrations from March through May (P<0.05) in both pregnant and pseudopregnant animals. Gender significantly influenced monthly testosterone/estrogen ratio (P<0.01); values were higher in males than in females throughout the year with overall percentage of overlapping values between males and females being 28%. In summary, this study characterized cirannual fluctuations in behaviors and gonadal steroid metabolites in the raccoon dog maintained in captivity. Because there is no obvious sexual dimorphism, the differences in testosterone/estrogen ratio may be useful for gender differentiation (72% accuracy), especially among individuals living in the wild.

Morphological features of the seminiferous epithelium in cat (Felis catus, L. 1758) testes

The aim of the present study was to assess the changes in the germinal epithelium in cats of different ages. Routine histological staining was applied to perform morphological and stereological examinations. The animals were divided into five groups according to age: under 8 months (n=28), 8-12 months (n=30), 12-36 months (n=33), 3-6 years (n=14) and older than 6 years (n=13). The appearance of the gonads of the males in the first group varied the most. The seminiferous tubules of the youngest cats consisted of a monolayer of supporting cells and a few spermatogonia. No tubular lumina were present, and the diameters of the seminiferous tubules reached 132.5 microm. We noted the typical arrangement of gametogenic cells with a tubule diameter of 191.83 microm in the second group. We observed multilayer germinal epithelia with the most significant production of gametes and a seminiferous tubule diameter of 202.61 microm in the third group. The diameters of the seminiferous tubules of the forth and fifth groups were 193.38 microm and 191.84 microm, respectively. The obtained data revealed that the most intensive morphological diversification of the seminiferous epithelium in cats occurs at about 7-8 months of age. The diameters of seminiferous tubules were highest in the third group of cats, and the activity of spermatogenesis of this group, expressed as the number of sperm per 10 mm(2), was also the most distinctive. The spermatogenesis process was most evident in cats between 12 and 36 months of age, which was also when the sperm concentration was highest per estimated surface.

Cellular Localization of Inhibin alpha-subunit, PKB/Akt and FoxO3a proteins in the ovaries of minipigs

Experiments were conducted to examine the cellular localization of inhibin alpha-subunit, protein kinase B (PKB/Akt), and FoxO3a proteins in the ovaries of minipigs, Chinese Xiang pigs, by immunohistochemistry. The results indicated that inhibin alpha-subunits were localized in the granulosa cells of follicles at all stages but were not localized in corpora lutea. PKB was localized in the granulosa cells of primordial follicles and in the basal layers of the granulosa cells of preantral and antral follicles, but were not localized in atretic follicles and corpora lutea. FoxO3a was localized in the granulosa cells of follicles at all stages and was extensively localized in the cytoplasma of the luteinized granulosa cells of corpora lutea. Together, the stage- and cell-specific expression patterns of inhibin alpha-subunit, FoxO3a, and PKB suggest that these proteins might play potential roles in follicular development, atresia, and luteinization in the minipig.