RESUMO

The development of caenolestid marsupials (order Paucituberculata) is virtually unknown. We provide here the first description of Caenolestes fuliginosus embryos collected in the Colombian Central Andes. Our sample of four embryos comes from a single female caught during a fieldtrip at Río Blanco (Manizales, Caldas), in 2014. The sample was processed for macroscopic description using a Standard Event System and for histological descriptions (sectioning and staining). The grade of development of the lumbar flexure and coelomic closure differed between embryos, two of them being more advanced than the others (similar to McCrady's stages 30 and 29, respectively). The pericardial and peritoneal cavities were present, the hepatic anlage was organized in hepatic cords, the heart was in its final position, and the mesonephros was functional. Compared to other Neotropical marsupials, an early appearance of the frontonasal-maxillary fusion and the cervical growth (thickness) was observed; however, absorption of the pharyngeal arches into the body and lung development was delayed. Besides these differences, embryos were similar to equivalent stages in Didelphis virginiana and Monodelphis domestica. Previous proposals of litter size of four for C. fuliginosus are supported.

Assuntos

RESUMO

In eutherian mammals, sex differentiation is initiated by expression of the testis-determining gene on the Y chromosome. Subsequent phenotypic development of the reproductive tract and genitalia depends on the production of hormones by the differentiated testis. In marsupials the mechanisms of phenotypic development may vary from this pattern, as differentiation of the scrotal primordia has been shown to occur before that of the gonad. Thus, the development of the scrotum in the marsupial has been regarded as an androgen-independent process. We have sought to clarify the ontogeny of scrotal development and the appearance of androgen receptor immunoreactivity by examining Monodelphis domesticaembryos/pups from 1 day prior to birth until 2 days after birth. We have also used immunocytochemistry to determine the expression of the key steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase as an indicator of when the developing gonad may be capable of synthesizing androgens. Expression of this enzyme was first detected in the gonads and adrenals of both sexes 1 day prior to birth and before the appearance of scrotal bulges. Androgen receptor immunoreactivity was detected in the scrotal anlagen of male opossum pups as early as 1 day following birth. This finding is significantly earlier than previous reports and coincides with the appearance 1 day after birth of distinct scrotal bulges. Androgen receptor immunoreactivity was also observed in the genital tubercles of male pups, but not female pups, 2 days after birth. These results suggest that androgens may play an important role in the development of the male genitalia at a much earlier stage than that indicated by previously published work and that scrotal development in this species may not be androgen-independent.

Assuntos

RESUMO

The neuropeptide arginine vasopressin is involved in many centrally mediated functions and brain development. In this study, we have examined the ontogeny of arginine vasopressin-like immunoreactivity (AVP-IR) in the Brazilian opossum (Monodelphis domestica) brain to further understand the involvement of AVP in the forming central nervous system. Monodelphis is a small pouchless marsupial and its pups are born in an extremely immature state before neurogenesis is completed. In the adult brain, cell bodies containing AVP-IR were found in several nuclear groups and areas, and immunoreactive fibers were found to be widely distributed throughout the brain. The distribution of AVP-IR in the adult opossum brain generally resembled that reported for other species including the rat, however, some differences in localization of immunoreactive cells were observed. In the developing opossum brain, AVP-IR was first seen in the mesencephalon and diencephalon between embryonic days 12 and 13. Subsequently, a distinct group of AVP immunoreactive cells was present in the forming supraoptic nucleus on day 1 of postnatal life (1 PN) and at 3 PN in the paraventricular nucleus. Between 1 and 3 PN, a few cells transiently expressed AVP-IR in the forming thalamus and tegmental area. At these ages a few immunoreactive fibers were also detected in the forming cerebellum. These fibers were not seen at later ages in these areas. By 5 PN, an increased expression of AVP-IR was seen in the forming supraoptic and paraventricular hypothalamic nuclei, median eminence, and posterior pituitary. At 7 PN, immunoreactive cells and fibers were seen in several forebrain areas. The distribution pattern of AVP-IR became adult-like by 60 PN. A sex difference in the amount of AVP-IR in the lateral septum was also observed in the opossum brain at 60 PN. This difference persisted in the adult brain. Due to the early presence of AVP-IR in the Monodelphis brain before neurogenesis and morphogenesis is completed, we suggest that AVP may be involved in morphogenesis of the central nervous system. In addition, AVP may have a significant physiological function in regard to homeostasis before the forebrain contributes to these control mechanisms. Further studies, including physiological and developmental manipulations, will define the significance of the early presence of AVP during the differentiation and maturation of the central nervous system in Monodelphis.

Assuntos

RESUMO

Intestinal closure is the blocking of biopolymers transferred across the small intestine epithelium that coincides with gut maturation. Sixty-one fetuses of D. albiventris, 45 to 55 mm in Crown-Rump length, were studied. Forty-one fetuses were injected subcutaneously with hydrocortisone hemisuccinate (0.4 mg/15.0 g of body weight) daily for 7 days in order to produce intestinal closure (TA). The control group (CA), consisted of twenty fetuses. Seven days after injection several fragments from the duodenum and ileum were prepared for transmission electron microscopic examination. Microvillus lengths and widths were determined from micrographs (final magnification: 100,000 x). The volume of the microvillus was calculated as the volume of the cylinder. Quantitative differences of the microvilli between the treated and control groups taken from duodenum and ileum material were noted. The distribution of the microvilli in the apical part of the enterocytes was more irregular in controls than in the TA group. Quantitatively, microvillus length in the duodenum was more than 50 per cent greater in TA than in CA and more than 30 per cent greater in TA than in CA in the ileum. Consequently, microvilli volume in the duodenum in TA was about 65 per cent greater than in CA and about 33 per cent greater than in CA in the ileum. Microvilli width presented little change and no statistically significant differences were found between TA and CA in either the duodenum or the ileum. These changes in the microvilli of the treated animals most probably indicate improvement in the absorptive function of the epithelium.

Assuntos

RESUMO

The presence of insulin the brush border and apical pole of the cells lining the pouch opossum mesonephric and metanephric proximal tubules was demonstrated by immunofluorescence and immunoperoxidase techniques. Positive result for insulin was also observed in the tufts of capillaries of some metanephric corpuscles.

Assuntos

Assuntos