Ultrastructure of spermatogenesis in the white-lined broad-nosed bat, Platyrrhinus lineatus (Chiroptera: Phyllostomidae)

Seasonal evaluation of spermatogenesis of the hematophagous bat Desmodus rotundus in the Caatinga biome

This study was aimed to characterize the spermatogenic process and its seasonal variation in Desmodus rotundus, in the Caatinga biome, a water-limited ecosystem, with marked water restriction during most of the year. Collections of adult animals were performed during the dry and rainy seasons, and after euthanasia, their testes were processed histologically to perform morphological, morphometric, ultrastructural and immunohistochemical analyzes. The percentage of seminiferous epithelium, number of Leydig cells per gram of testis, and population of Sertoli cells and A-type spermatogonia presented by D. rotundus were significantly higher in the rainy season, while the percentage of lumen, mitotic index, support capacity performed by Sertoli cells, and overall yield of spermatogenesis were higher in the dry season. The ultrastructure of spermatogenesis was similar to that described in other mammals, and the immunohistochemical analysis revealed activity of the aromatase enzyme in Sertoli cells, Leydig cells, spermatocytes and spermatids, as well as the presence of androgen receptors in Sertoli cells and Leydig cells. FGF2 activity was detected in primary spermatocytes in zygotene and pachytene, as well as secondary spermatocytes and rounded and elongated spermatids, while the BCL-2 protein was expressed in primary spermatocytes in zygotene and pachytene, secondary spermatocytes, and rounded spermatids. The activity of these molecules was similar in both seasons, and associated with the morphometric findings, indicates maintenance in the integrity of the seminiferous epithelium throughout the year. The seasonal study of D. rotundus spermatogenesis indicates a continuous spermatogenesis pattern and suggests a greater production of spermatozoa in the rainy season in the Caatinga biome.

Evaluation of reproductive parameters in male Neotropical bats during dry and rainy months in a specific area of the Cerrado biome

The aim of this study was to analyse the reproductive aspects of male bats of three common species of the Phyllostomidae family: Artibeus lituratus, Platyrrhinus lineatus and Sturnira lilium, during dry and rainy months in a specific area of the Cerrado biome. Body weight was significantly higher during the dry months for S. lilium. The gonadosomatic index (GSI) and testicular weight were not significantly different between dry and rainy periods. The tubular parameters were significantly bigger in A. lituratus than in the other two species during both periods. No difference in the tubular/interstitial ratio was observed in any of the species during both periods. In both periods, all sperm cells and germ cell developmental stages were visible on seminiferous tubules whereas sperm cells were observed in epididymides of all sampled animals. The percentage of morphologically normal sperm was low (35%-60%), with no difference between periods. Spermatozoa from A. lituratus presented a leaf-shaped head, while the head was round-shaped in the other two species. In conclusion, our data suggest that males from the three studied species did not present reproductive latency during the most critical weather periods (dry and rainy months) in the metropolitan region of Brasilia, Brazil.

The spermatogenic process of the common vampire bat Desmodus rotundus under a histomorphometric view

Among all bat species, Desmodus rotundus stands out as one of the most intriguing due to its exclusively haematophagous feeding habits. However, little is known about their spermatogenic cycle. This study aimed at describing the spermatogenic process of common vampire bats through testicular histomorphometric characterization of adult specimens, spermatogenic production indexes, description of stages of the seminiferous epithelium cycle and estimative of the spermatogenic process duration. Morphometrical and immunohistochemical analyzes for bromodeoxiuridine were conducted under light microscopy and ultrastructural analyzes were performed under transmission electron microscopy. Vampire bats showed higher investment in gonadal tissue (gonadosomatic index of 0.54%) and in seminiferous tubules (tubulesomatic index of 0.49%) when compared to larger mammals. They also showed a high tubular length per gram of testis (34.70 m). Approximately half of the intertubular compartment was found to be comprised by Leydig cells (51.20%), and an average of 23.77x10⁶ of these cells was found per gram of testis. The germline cells showed 16.93% of mitotic index and 2.51% of meiotic index. The overall yield of spermatogenesis was 60% and the testicular spermatic reserve was 71.44x10⁷ spermatozoa per gram of testis. With a total spermatogenesis duration estimated at 37.02 days, vampire bats showed a daily sperm production of 86.80x10⁶ gametes per gram of testis. These findings demonstrate a high sperm production, which is commonly observed in species with promiscuous mating system.

Structure, histochemistry and seasonal variations of the male reproductive accessory glands in the Pallas’s mastiff bat, Molossus molossus (Chiroptera: Molossidae)

Due to their wide geographical distribution, bats suffer considerable influence from abiotic factors on their reproductive strategies, detected through behavioural or functional assessment of the gonads and accessory glands. The present study aimed to characterise anatomically and morphologically the reproductive accessory glands (RAGs) of Molossus molossus (Molossidae) and evaluate their seasonal variations. The RAGs were removed, fixed, sectioned after histological processing and submitted to the following stains: haematoxylin–eosin, periodic acid­–Schiff (PAS) and Gömöri’s reticulin. Our data demonstrated that the RAGs of M. molossus are composed of a semi-lobed prostatic complex associated with the urethra and a pair of inguinal bulbourethral glands. Histology and three-dimensional reconstruction of the prostatic complex demonstrated the existence of two regions: ventral and dorsal (named according to the position around the urethra). The two regions had distinctive morphological and histological differences, with the ventral region being the most prominent and the dorsal formed by four lobes. Considering the seasonal evaluation, we can infer that the prostatic complex of M. molossus is active throughout the seasons in São Paulo State (Brazil) and, although each of the prostatic regions has inherent characteristics, they synchronise to establish the main reproductive peak in spring (early rainy season).

Ultrastructure of the epididymis and vas deferens of agoutis at different stages of sexual development

The agouti (Dasyprocta spp.) is a rodent found predominantly in the Brazilian Caatinga and has importance as an alternative source of protein. In this study, the objective was to describe the ultrastructure of components of sperm pathways, especially the epididymis and vas deferens, during sexual development of agoutis kept in captivity. Segments of the vas deferens and epididymis of 8 agouti males at different stages of sexual development (prepubescent, prepubertal, pubescent, and adult) were fixed in glutaraldehyde. The following laboratory procedures were performed: histology following the standard protocol for semithin cut (toluidine blue), and transmission electron microscopy. This was a pioneer study in which it was observed that the epididymis of agoutis is composed of principal, basal, halogen, apical, and clean cells. During prepubescent and prepubertal stages, clean cells were observed in addition to principal, basal, and halogen cells. Once puberty was reached, apical cells were also present, and clean cells were no longer visible. This epithelial change during sexual development is possibly due to physiological functions. The interaction between these cells supports this, and age probably influenced the change. With regard to the vas deferens, this study was also a pioneer to note that before pubescence there were two muscle layers, differing from older animals, which had three muscle layers. This may be due to lack of sperm transit in younger animals. We concluded that the pseudostratified stereociliated epithelium of the epididymis and vas deferens of agoutis kept in captivity undergo morphological and functional changes during sexual development.

Evaluation of the cell population of the seminiferous epithelium and spermatic indexes of the bat Sturnira lilium (Chiroptera: Phyllostomidae)

Due to the scarcity of information about patterns of spermatogenesis in bats, this study aimed to provide information on the testicular activity of the bat Sturnira lilium along the annual seasons. Thus, a series of morphometrical and stereological analyses were made using the testes of adult S. lilium in order to achieve a better understanding of the sperm production dynamics. Light and transmission electron microscopy analyses were performed in testicular fragments of animals captured during dry and rainy seasons. The testes followed the pattern of organization described for other mammals, and there were no morphological differences between organs collected either in dry or in rainy seasons. Each tubular cross-section in stage 1 was made of 0.5 type-A spermatogonia, 4.4 primary spermatocytes in preleptotene/leptotene, 3.7 in zygotene, 11.9 in pachytene, 35.6 round spermatids and 8.5 Sertoli cells. The mitotic and meiotic indexes were 15.4 and 2.9 cells, respectively, while the spermatogenesis yield was 68.7 cells. The testicular sperm reserves was 37.61×10⁶ cells, and daily sperm production per gram of testis averaged 209.68×10⁶ cells, both highest averages occurring in the rainy season. S. lilium male bats have a continuous reproductive pattern, high spermatogenesis yield and low support capacity by the Sertoli cells.

Ultrastructure of spermatogenesis in the short-tailed fruit bat, Carollia perspicillata (Chiroptera: Phyllostomidae: Carollinae)

Among species of the Chiroptera, spermatogenesis and the fully differentiated spermatozoa differ in morphological and ultrastructural detail. This study therefore aimed to ultrastructurally characterize the spermatogenesis and the spermatozoa of Carollia perspicillata (Phyllostomidae) and compare the process with other species of bats and mammals. The differentiation of spermatogonia is similar to other bats and to Primates, with three main spermatogonia types: Ad, Ap, and B. Meiotic divisions proceed similarly to those of most mammals and spermiogenesis is clearly divided into 12 steps, in the middle of the range of developmental steps for bats (9-16 steps). The process of acrosome formation is similar to that found in Platyrrhinus lineatus, with the acrosome formed by two different types of proacrosomal vesicles. The ultrastructure of the spermatozoon is similar to other bats already described and resembles the typical mammalian sperm model; however, its morphology differs from other mammals such as marsupials and rodents, on account of a simpler spermatozoon head morphology, which indicates a pattern that is more closely related to the sperm cells of humans and other primates. Our data demonstrated that spermatogenesis in C. perspicillata presents great ultrastructural similarities to P. lineatus. This pattern is not surprising, because both species belong to the same family (Phyllostomidae); however, it is observed that C. perspicillata presents some characteristics that are more closely related to phylogenetically distant species, such as Myotis nigricans (Vespertilionidae), which is a fact that deserves attention.

Ultrastructure of germ cells, Sertoli cells and mitochondria during spermatogenesis in mature testis of the Chinese Taihang black goats (Capra hircus)

The objective of this study was to describe the ultrastructure of germ cells, Sertoli cells and mitochondria in mature testis of the Chinese Taihang black goat. The characteristics of germ cell nucleus and mitochondria changing during spermatogenesis were investigated by transmission electron microscopy (TEM). The results showed that the spermatogonium was elliptical, and its nucleus was about 4-5 μm. The round mitochondria can be observed throughout the cytoplasm around the nucleus. Small patches of heterochromatin were distributed throughout the nucleus. Spermatocyte was oval-shaped with a nucleus of about 4-4.5 μm in diameter. The heterochromatin began to attach to the inner surface of the nuclear membrane. Spermatid was about 4 μm and oval in shape. Its nucleus was oval or round and approximately 2-3 μm in diameter. The borderline between nucleus membrane and karyoplasm was distinct. During spermiogenesis, spermatid nucleus was condensed and elongated, and chromatin reached the highest condensation in the mature spermatozoon. The mid-piece was surrounded by mitochondria at the neck region. The sperm tail showed the typical "9+2″ structure, contained axoneme and central singlet microtubules. The nuclei of the Sertoli cells were irregular shaped and showed indentations in the membrane. In the mature testes of goat bucks, abundant mitochondria were around the germ cells and Sertoli cells. The scattered mitochondria were aggregated around the base of the flagellum (axoneme) during the spermatid differentiation stage. In conclusion, the present study showed that the spermatogenic process of Taihang black goat followed the pattern of mammals with some specific.

Stages and duration of the seminiferous epithelium cycle in the bat Sturnira lilium

Knowledge of the stages that compose the seminiferous epithelium cycle (SEC) and determination of the duration of spermatogenic processes are fundamental for the accurate quantification of the dynamics of spermatogenesis. The aim of this study was to characterize the stages that compose the SEC of the bat Sturnira lilium, including evaluation of the average frequency of each of these stages throughout the year and calculation of the duration of the spermatogenic process. An ultrastructural characterization of the formation of the acrosomal cap was also performed. Testicular fragments were processed for morphological and immunohistochemical analysis as well as ultrastructural analysis using transmission electron microscopy. According to the tubular morphology method, the SEC in S. lilium is divided into eight stages, following the pattern found in other mammals. Primary spermatocytes were found at zygotene in stage 1 of the cycle. There was no variation in frequency of each of the stages over the seasons, with stage 1 being the most frequent, and stage 7 the least frequent. The duration of one seminiferous epithelium cycle was 3.45 days, and approximately 15.52 days were required for the development of sperm from spermatogonia. Ultrastructural characterization allowed the formation of the acrosomal cap in round spermatids to be monitored. In conclusion, the stages that compose the SEC in S. lilium are generally similar to those described for other mammals, but the duration of the spermatogenic process is shorter than previously recorded for mammals. The presence of primary spermatocytes at zygotene in stage 1 of the cycle is probably due to the longer duration of this stage.