Revisiting the human seminiferous epithelium cycle.

STUDY QUESTION: Can all types of testicular germ cells be accurately identified by microscopy techniques and unambiguously distributed in stages of the human seminiferous epithelium cycle (SEC)? SUMMARY ANSWER: By using a high-resolution light microscopy (HRLM) method, which enables an improved visualization of germ cell morphological features, we identified all testicular germ cells in the seminiferous epithelium and precisely grouped them in six well-delimitated SEC stages, thus providing a reliable reference source for staging in man. WHAT IS ALREADY KNOWN: Morphological characterization of germ cells in human has been done decades ago with the use of conventional histological methods (formaldehyde-based fixative -Zenker-formal- and paraffin embedding). These early studies proposed a classification of the SEC in six stages. However, the use of stages as baseline for morphofunctional evaluations of testicular parenchyma has been difficult because of incomplete morphological identification of germ cells and their random distribution in the human SEC. STUDY DESIGN, SIZE, DURATION: Testicular tissue from adult and elderly donors with normal spermatogenesis according to Levin's, Johnsen's and Bergmann's scores were used to evaluate germ cell morphology and validate their distribution and frequency in stages throughout human spermatogenesis. PARTICIPANTS/MATERIALS, SETTING, METHODS: Testicular tissue from patients diagnosed with congenital bilateral agenesis of vas deferens (n = 3 adults) or prostate cancer (n = 3 elderly) were fixed in glutaraldehyde and embedded in araldite epoxy resin. Morphological analyses were performed by both light and transmission electron microscopy. MAIN RESULTS AND THE ROLE OF CHANCE: HRLM method enabled a reliable morphological identification of all germ cells (spermatogonia, spermatocytes and spermatids) based on high-resolution aspects of euchromatin, heterochromatin and nucleolus. Moreover, acrosomal development of spermatids was clearly revealed. Altogether, our data redefined the limits of each stage leading to a more reliable determination of the SEC in man. LIMITATIONS, REASONS FOR CAUTION: Occasionally, germ cells can be absent in some tubular sections. In this situation, it has to be taken into account the germ cell association proposed in the present study to classify the stages. WIDER IMPLICATIONS OF THE FINDINGS: Our findings bring a new focus on the morphology and development of germ cells during the SEC in human. Application of HRLM may be a valuable tool for research studies and clinical andrology helping to understand some testicular diseases and infertility conditions which remain unsolved. STUDY FUNDING/COMPETING INTEREST: Experiments were partially supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Pesquisa de Minas Gerais (FAPEMIG) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). The authors declare that there are no conflicts of interest. TRIAL REGISTRATION NUMBER: Not applicable.

Vitamin B12-induced spermatogenesis recovery in cimetidine-treated rats: effect on the spermatogonia number and sperm concentration.

The H2-receptor antagonist cimetidine is an antiulcer drug also used for the treatment of cancer due to its antiangiogenic effect. However, this drug has caused structural changes in the seminiferous tubules. Vitamin B12 has been used as a therapeutic agent for the treatment of male infertility. The supplementation of rats with vitamin B12 during cimetidine treatment has recovered the damaged seminiferous tubules, but how this vitamin restores the seminiferous epithelium has not been clarified. In this study, we evaluated whether vitamin B12 improves the number of spermatogonia, spermatocytes, and sperm concentration in cimetidine-treated rats. Adult male rats were treated for 50 days as follows: cimetidine group received 100 mg kg-1 b.w. of cimetidine, cimetidine-B12 group received cimetidine and 3 µg of vitamin B12-hydroxocobalamin, B12 group received only 3 µg of vitamin, and control group received saline. Sperm concentration was calculated and historesin-embedded testes sections were used for the quantitative analyses of spermatogonia (A; In/B) and spermatocytes. TUNEL method and PCNA immunofluorescence were performed. Cimetidine caused a significant reduction in sperm concentration. TUNEL-positive spermatogonia and spermatocytes were correlated to a significant reduction in the number of these cells. In cimetidine-B12 group, sperm concentration was higher than cimetidine group and a significant increase in the number of spermatogonia (stages II-VI) was correlated to a high incidence of PCNA-immunolabeled spermatogonia and spermatocytes. The results show that the supplementation of rats with vitamin B12 during cimetidine treatment increases sperm concentration and exerts a potential effect in the recovery of spermatogonia and spermatocytes.

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 37.61×10(6) cells, and daily sperm production per gram of testis averaged 209.68×10(6) 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.

Spermatogenesis is seasonal in the large hairy armadillo, Chaetophractus villosus (Dasypodidae, Xenarthra, Mammalia).

Very little is known about the distinct reproductive biology of armadillos. Very few studies have investigated armadillo spermatogenesis, with data available only for Euphractus sexcinctus and Dasypus novemcinctus. In the present study, we analysed male germ cell differentiation in the large hairy armadillo Chaetophractus villosus throughout the year, describing a cycle of the seminiferous epithelium made of eight different stages. Evaluation of the testis/body mass ratio, analysis of the architecture of the seminiferous epithelium and the frequency of defective seminiferous tubules allowed identification of a temporal interruption of spermatogenesis during the period between mid-May to July (mid-end autumn) in correlation with very low testosterone levels. Overall, these results suggest that spermatogenesis is seasonal in C. villosus.

Mice spermatogonial stem cells transplantation induces macrophage migration into the seminiferous epithelium and lipid body formation: high-resolution light microscopy and ultrastructural studies.

Transplantation of spermatogonial stem cells (SSCs), the male germline stem cells, in experimental animal models has been successfully used to study mechanisms involved in SSC self-renewal and to restore fertility. However, there are still many challenges associated with understanding the recipient immune response for SSCs use in clinical therapies. Here, we have undertaken a detailed structural study of macrophages elicited by SSCs transplantation in mice using both high-resolution light microscopy (HRLM) and transmission electron microscopy (TEM). We demonstrate that SSCs transplantation elicits a rapid and potent recruitment of macrophages into the seminiferous epithelium (SE). Infiltrating macrophages were derived from differentiation of peritubular monocyte-like cells into typical activated macrophages, which actively migrate through the SE, accumulate in the tubule lumen, and direct phagocytosis of differentiating germ cells and spermatozoa. Quantitative TEM analyses revealed increased formation of lipid bodies (LBs), organelles recognized as intracellular platforms for synthesis of inflammatory mediators and key markers of macrophage activation, within both infiltrating macrophages and Sertoli cells. LBs significantly increased in number and size in parallel to the augmented macrophage migration during different times post-transplantation. Our findings suggest that LBs may be involved with immunomodulatory mechanisms regulating the seminiferous tubule niche after SSC transplantation.

Taenia crassiceps: A secretion-substance of low molecular weight leads to disruption and apoptosis of seminiferous epithelium cells in male mice.

The present research was performed to isolate and study the effects of a low molecular weight (<1300Da) parasite-associated substance, obtained from peritoneal fluids of female mice infected with Taenia crassiceps cysticerci, on seminiferous epithelium cells of male mice testis. The results showed an intense disruption of Sertoli cells and germ cells within the seminiferous tubules of experimental mice, along with the destruction of their gap junction (GJ). Significant generalized apoptosis of germ cells within seminiferous tubules was determined by TUNEL staining (P=0.0159). In addition, a significant number of infiltrating macrophages were found in the luminal space of these seminiferous tubules (P<0.0001). Finally, electron microscopy studies revealed structural and morphological abnormalities in the somatic cells (Sertoli and Leydig cells) and in the germ cells, primarily in the round and elongate spermatids.

The actin filament network associated to Sertoli cell ectoplasmic specializations.

Junctional devices in Sertoli cells conform the blood-testis barrier and play a key role in maturation and differentiation of germ cells. The spacial distribution of ectoplasmic specializations of Sertoli cells was studied by beta-actin immunolabelling, using laser confocal and transmission electron microscopy. For confocal microscopy, beta-actin immunolabelling of ectoplasmic specializations was studied over the background of either prosaposin or glutaredoxin immunolabelling of the Sertoli cytoplasm. Labelling was found near the basal lamina, surrounding early spermatocytes (presumably in leptotene-zygotene) or at one of two levels in the seminiferous epithelium: (1) around deep infoldings of the Sertoli cell cytoplasm, in tubular stages before spermiation, and (2) in the superficial part of the seminiferous epithelium, in tubular stages after or during spermiation. For transmission electron microscopy, beta-actin immunolabelling of ectoplasmic specializations was also used. Ectoplasmic specializations were found at two different levels of the seminiferous epithelium. We also used freeze fracture to analyze the characteristics of tubulo-bulbar complexes, a known component of apical ectoplasmic specializations. Also, these different approaches allowed us to study the complex arrangement of the actin cytoskeleton of Sertoli cells branches, which surround germ cells in different stages of the spermatogenic cycle. Our results show a consistent labelling for beta-actin before, during and after the release of spermatozoa in the tubular lumen (spermiation) suggesting a significant role of the actin network in spermatic cell differentiation. In conclusion, significant interrelations among the beta-actin network, the junctional complexes of the blood-testis barrier and the ectoplasmic specializations were detected at different stages of the seminiferous cycle.

Structure of the lining epithelium of the cauda epididymis of the golden hamster.

The ductus epididymis has roles in the maturation and storage of spermatozoa. The main function of the cauda epididymis is the storage of spermatozoa; however, this region exerts other morphophysiological roles. So, this study was aimed at investigating structural features of the cauda epididymis epithelium, which could indicate roles other than the storage. The relative percentages of the cell types in the epithelium were 74.9, 6.9, 12.5 and 5.6% of principal, clear, basal and halo cells respectively. Large intercellular spaces were seen among the lateral plasmatic membranes of adjacent principal cells or among these cells and others cell types. These spaces were found to be filled with multivesicular bodies, myelin figures, scrolls and debris of membranes or flocculent dense material. Clear cells had the cytoplasms filled with lysosomes ((3/4) of basal cytoplasm), and vacuoles and vesicles ((1/4) of apical cytoplasm). The observations allowed us to infer that clear cells could act in the process of endocytosis and also in water transfer from the lumen to the interstitium through the epithelium compartment. Moreover, transcytosis may occur at the cauda epididymis of Golden hamster.

Heteropterys aphrodisiaca infusion reduces the collateral effects of cyclosporine A on the testis.

Cyclosporine A (CsA) is known to have testicular toxicity, leading to male infertility. Stimulant and aphrodisiac properties have been attributed to the plant, Heteropterys aphrodisiaca. Thus, the present work was undertaken to evaluate the association of the drug and the medicinal herb in Wistar rats, applying testicular morphometry and ultrastructure. Twenty-four rats were used, divided into four groups: I, control; II, CsA; III, simultaneous use of CsA and H. aphrodisiaca; IV, H. aphrodisiaca. Daily administration by gavage was carried out, during 56 days, of water (sham), CsA in a dose of 15 mg/kg per day and/or H. aphrodisiaca in a dose of 0.5 ml of the infusion prepared with 25 g of roots/100 ml of boiling water. Increased body weight was observed for all groups, but the animals that received only CsA showed the smallest body weight gain. Morphometry showed increased connective tissue volumetric proportion and decreased Leydig cell volumetric proportion in CsA-treated rats. Using transmission electron microscopy, it was possible to ascertain that CsA caused seminiferous epithelium degeneration, resulting in Sertoli cell vacuolization, abnormal round and elongated spermatids and large accumulation of residual cytoplasm at the epithelium border next to the lumen. Expanded intercellular spaces between germ cells were still observed in H. aphrodisiaca-treated rat testes. The administration of H. aphrodisiaca infusion to CsA-treated rats diminished nearly all the CsA-induced damage to the testis ultrastructure, suggesting that H. aphrodisiaca infusion may be used combined with CsA to reduce CsA-induced injuries in the testis.

Ultrastructure of the seminiferous epithelium of ethyl methanesulphonate-treated mouse.

Ethyl methanesulphonate (EMS) is a mutagenic alkylating agent that induces marked elevations of sperm abnormalities in mice. In this paper, we report the ultrastructural findings on the morphology of the seminiferous epithelium of mice resulting from EMS administration. Eight- to twelve-weeks-old male mice were injected intraperitoneally with EMS at 200 mg kg(-1) body weight daily for five consecutive days. Analysis of smears of epididymis and semi-thin sections of testes revealed that the more suitable specimens for the ultrastructural analysis were tissues of mice killed at the third week, following EMS administration. At this time, the spermatid was the damaged cell type. Abnormalities were mainly observed in the morphology of the nucleus, the acrosome, chromatin distribution and in the arrangement of the cytoplasmic microtubules, and binucleated spermatids were also observed. EMS has the capacity to penetrate the blood-testis barrier, and thus it can damage post-meiotic spermatogenic cells. However, morphological abnormalities could be the consequence of damage exerted on the differentiated spermatogonia stage, the most sensitive spermatogenic cell to the action of chemical agents or drugs. Our findings contribute to elucidate the action mechanism of the damage exerted by EMS administration on the germinal male cells.

The seminiferous epithelium cycle and daily spermatic production in the adult maned wolf (Chrysocyon brachyurus, Illiger, 1811).

The duration of the seminiferous epithelium cycle was estimated in adult maned wolves (Chrysocyon brachyurus, Illiger, 1811), by applying intratesticular injections with tritiated thymidine. The total duration of the seminiferous epithelium cycle in this species was calculated in 8.99 days. So, taking into account that approximately 4.5 cycles of the seminiferous epithelium are necessary for the whole spermatogenesis process to complete, the production of spermatozoa from one spermatogonia will take about 40.45 days. The duration of the spermiogenesis was calculated to be 12.3 days. The eight stages of the seminiferous epithelium cycle were described by the tubular morphology method, which is based either on the form and position of the spermatid nuclei and the occurrence of meiotic divisions. The values of the relative frequency for the pre-meiotic, meiotic and post-meiotic phases in this species were 3.5, 0.78 and 4.8 days, respectively. The maned wolf produces about 29 million spermatozoa a day for each testis gram, therefore being classified among the species provided with a high spermatogenetic efficiency.

Analysis of the nucleolar cycle in the seminiferous epithelium of rodents

The nucleolus is a subcompartment of the nucleus and the site of ribosome biogenesis. During the mitotic and meiotic cell cycles, a disorganization and later reorganization of the nucleolar material occur, an event called nucleologenesis. In the spermatogenesis of mammals and other vertebrates, there is evidence of the disorganization of the nucleolus at the end of meiosis I, which supplies material for the cytoplasmic formation of an organelle called the “chromatoid body” (CB). The CB is a structure characteristic of spermatogenic cells and seems to be responsible for RNA metabolism in these cells and for some events of spermiogenesis, such as the formation of the acrosome, cellular communication between spermatids, and the formation of the spermatozoon middle piece and tail. The aim of this paper was to obtain information about the cytochemical and ultrastructural nature of the nucleolar cycle and the distribution of cytoplasmic RNAs in the seminiferous tubule cells of Rattus novergiucus, Mus musculus and Meriones unguiculatus. The testis was fixed in Bouin and Karnovsky solutions for conventional histological analysis and for cytochemical study that included: periodic acid-Schiff, hematoxylin-eosin, Feulgen reaction, silver-ion impregnation, Gomori’s reticulin stain, toluidine blue, modified method of critical electrolyte concentration, and basic and acid fast green. The blocks of testis fixed in glutaraldehyde were used for ultrastructural analysis by transmission electron microscopy. Ultrathin sections were double-stained with uranyl acetate and lead citrate. All the techniques used provided information on the origin and function of the CB in the spermatogenic cells. Therefore, considering the persistence of the RNA and nucleolar ribonucleoproteins during spermatogenesis of Rattus novergicus, Mus musculus and Meriones unguiculatus, our findings corroborate the statement that these molecular complexes are very important in the spermiogenesis phases...

Effects of chronic simulated hypobaric hypoxia on mouse spermatogenesis / Efectos de la Hipoxia Hipobárica Simulada Crónica sobre la Espermatogénesis en el Ratón

La disminución del aporte de O2 a los tejidos provoca daños de éstos, incluido el epitelio seminífero. Últimamente, se ha incrementado la población que trabaja a gran altura, interesando así el estudio de la hipoxia hipobárica sobre la espermatogénesis. Para este estudio se utilizaron dos grupos de ratones machos sexualmente maduros: Control (540 metros sobre el nivel del mar (msnm)) y grupo con hipoxia hipobárica simulada crónica (HHSC) (4.600 msnm) expuestos por 8, 16, 24 ó 33 días. Fueron evaluados hematocrito, reticulocitosis, peso de testículos, epidídimos y vesícula seminal; altura del epitelio seminífero, diámetro tubular, recuento y morfología espermática y lipoperoxidación de membranas de espermatozoides y parénquima testicular. El peso de testículos, epidídimos y vesícula seminal se redujo para empezar a recuperarse a los 33 días. El diámetro tubular y la altura del epitelio se redujeron y luego tendieron a aumentar sin normalizarse. El recuento y la morfología espermáticos fluctaron en el tiempo. Se puede concluir que la exposición a HHSC induce daño del epitelio seminífero, disminución de la lipoperoxidación en espermatozoides y tejido testicular, y altera la morfología testicular y espermática.

Reduction of O2 delivery to tissues damage them, including the seminiferous epithelium. Recently, population working in high altitude has increased, so that the study of hypobaric hypoxia on spermatogenesis becomes of interest. In this study we used two groups of male, sexually mature mice Control (C) (540 meters above sea level (masl)) and chronic simulated hypobaric hypoxia (CSHH) (4,600 masl) exposed during 8, 16, 24 or 33 days. Hematocrit; reticulocytosis; testicular, epididymal and seminal vesicle weight; seminiferous epithelium height, tubular diameter, sperm count and morphology and testicular parenchyme and spermatozoa membranes lipoperoxidation were measured. Weight of testis, epididymis and seminal vesicle were reduced but they recuperate at 33 days. Tubular diameter and epithelial height are reduced, subsequently they tend to increase without returning to normal values. The count and sperm morphology fluctuate along the exposure time. Lipoperoxidation levels of spermatozoa and testicular parenchyme are reduced. Therefore, we can conclude that exposure to CSHH induce damage in the seminiferous epithelium, decrease of lipoperoxidation in spermatozoa and testicular tissue, and damages the testicular and sperm morphology.

Cycle and duration of the seminiferous epithelium in puma (Puma concolor).

Puma or sussuarana (Puma concolor) is the second largest feline in the American continent and has an ample latitudinal distribution in very diverse habitats. In relation to its conservation status, the puma is considered an extinction-threatened species. The study of the testis morphology and the spermatogenic process in a species is fundamental for establishing the physiologic patterns that will make possible the selection of the protocols for assisted reproduction. A number of peculiarities associated with the reproductive biology of specific species such as the duration of spermatogenic process can be used to determine the frequency of sperm collection. Nine adult male pumas maintained in captivity were used to determine the relative frequency of stages in the seminiferous epithelium cycle. Three of them received intra-testicular injections of 0.1ml tritiated thymidine to determine the duration of the seminiferous epithelium cycle, and were subjected to biopsy 7 days later. The cycle of the seminiferous epithelium in puma was didactically described into eight stages by the tubular morphology method. The total duration of one seminiferous epithelium cycle in puma was calculated to be 9.89 days, and approximately 44.5 days are required for development of spermatozoon from spermatogonia. The duration of spermiogenesis, prophase and other events of meiosis were 14.08, 15.20 and 1.79 days, respectively. The relative frequency of the pre-meiotic, meiotic and post-meiotic phases were 3.98, 1.79 and 4.12 days, respectively.

Non-random distribution of spermatogonia in rats: evidence of niches in the seminiferous tubules.

The relationships and distribution of spermatogonia were studied as a function of the stage of the seminiferous epithelium cycle in rats. Primitive spermatogonia in the mouse are located along regions of the basal lamina that face the interstitium. Before studying the distribution of spermatogonia in rats, it was necessary to characterize the various types of spermatogonia, as recently performed for mice. The Strauss' linear index (Li) selectivity method was then used and spermatogonia of the A(single) (A(s)) to A(aligned) (A(al)) lineage were preferentially found to be located in regions opposing the interstitium at stages V, VII and IX of the spermatogenic cycle. Because relatively little tubule-to-tubule contact occurs in rats, the aim of this study was to determine whether tubule-to-tubule contact or tubule proximity (or alternatively, the amount of interstitium) was an important factor in spermatogonial position. In this regard, another method (tubule proximity) was devised to determine spermatogonial position that accounted for the presence of adjacent tubules. This method showed that the position of tubules, rather than tubule contact, was more accurate than the Li method in determining the location of spermatogonia in the rat. The results also showed a non-random distribution of spermatogonia resembling that of the mouse, and that tubule-to-tubule contact is not essential for the positioning of spermatogonia. In conclusion, the results of this study strongly indicate that the most primitive type A spermatogonia (A(s), A(paired) and A(al)) in rats are present in niches located in those areas of the seminiferous tubules that border the interstitial tissue.

Cytological steps during spermiogenesis in the house sparrow (Passer domesticus, Linnaeus).

Spermiogenesis of the domestic sparrow was investigated with the light and electron microscopes and a step by step classification is proposed. Three cell populations corresponding to early, mid and late spermatids were easily divided according to their positions in the seminiferous epithelium. In addition to this initial separation, six steps were recognized, based on nuclear morphology and the degree of chromatin condensation, in association to their acrosomal and flagellar development. Early spermiogenesis is the period previous to chromatin condensation. The first step can be recognized by the extending flagellum and the second by the pro-acrosome development in contact with the nucleus. During the third or intermediate step, chromatin condenses and the cell becomes polarized with the pro-acrosomic vesicle and the tail occupying opposite sides of the nucleus. Late spermiogenesis, including steps IV-VI, is marked by complete chromatin condensation. The final cellular modifications lead to the formation of a spiraled spermatozoon. This shape is due to the twisting of the acrosome and nucleus, as well as the helical arrangement of mitochondria around the axoneme along most of the flagellum, making an exceptionally long middle piece.

Passive immunization with anti-laminin immunoglobulin G modifies the integrity of the seminiferous epithelium and induces arrest of spermatogenesis in the guinea pig.

In the testis, the base of the Sertoli cells is in contact with the basement membrane matrix, in which the laminins constitute the major noncollagenous components. We have previously demonstrated that antibodies against a preparation enriched in basement membranes of seminiferous tubules (STBM) or a noncollagenous fraction of STBM passively transferred induced modifications to the basement membranes and focal sloughing of the seminiferous epithelium in the rat. In the present report, we tested the effect of passive immunization with anti-laminin IgG on the limiting membrane of the seminiferous tubules, spermatogenesis, and maintenance of the blood-testis barrier in the adult guinea pig. Rabbit antibodies to laminin 1 (IgG fraction) were injected in adult male guinea pigs (GP). Nonimmunized GP and GP immunized with normal rabbit serum IgG were used as controls. Measurements of variations in the diameter and lumen of the tubules and in the size of individual components of the tubular limiting membrane showed that the highest percentage of tubules with reduced lumen occurred 30 days after passive immunization with anti-laminin, when the limiting membrane was thickest and lesions to the seminiferous epithelium were most severe. The lesions included thickening of the limiting membrane, infolding in the basal lamina, deposits of immune complexes coincident with sloughing of pachytene spermatocytes and spermatids, and vacuolization of the Sertoli cells. Mononuclear cell infiltration of the tubules was rare. Permeability tracer studies revealed that Sertoli cell tight junctions remained impermeable. Fifty and 80 days after treatment, the basement membrane of the tubules and the progression of the spermatogenesis were normal. Passive immunization with anti-laminin IgG provided a valuable experimental model for the in vivo study of the influence of the basement membrane on the issue of spermatogenesis and the integrity of the seminiferous epithelium.

Morphologic study of the efferent ductules of the pigeon (Columba livia).

The efferent ductules of the pigeon are localized in the epididymal region and are topographically divided into proximal and distal, both portions being lined with stereociliated pseudostratified epithelium. Transmission electron microscopy shows five distinct cell types: light, dark, and angular non-ciliated cells with possible apocrine secretory role cells and halo cells, possibly intraepithelial leucocytes. The proximal efferent ductules have the widest diameter among all ductules in the epididymal region.

Stages of the cycle of the seminiferous epithelium of the viscacha (Lagostomus maximus maximus).

The adult male viscacha (Lagostomus maximus maximus) is a seasonal rodent. It exhibits a short period of testicular regression with partial arrest of spermatogenesis during winter (July-August). The present study provides the first description of the viscacha spermatogenic cycle during the period of maximum gonadal activity (summer-autumn). The testes were processed by using conventional techniques of light and electron microscopy. One-micrometer-thick sections stained with toluidine blue were used to clearly define the different cell associations. Spermatogenesis in this rodent is well organized and synchronized and has been divided into nine stages. The present classification is based on the morphogenesis of the acrosomal system (stages I-V) and the degree of elongation and condensation of the heads of the differentiating spermatids (stages VI-IX). Stage I is principally defined by round spermatids with a well-developed, juxtanuclear Golgi complex and without acrosomal components that are visible under the light microscope. Sperm release from the viscacha seminiferous epithelium occurs either in late stage III or in early stage IV. Stage IX is characterized by diplotene spermatocytes, figures of meiosis I or II, and secondary spermatocytes.