Placental glycotype of the caviomorph rodent Lagostomus maximus and its evolution within Eutheria.

The main evolutionary milestone in the oviparity-viviparity transition is placentation. The placenta is an organ with great morphological diversity among eutherians. The expression of different glycosidic residues (Gr) in the near-term placenta constitutes its glycotype. In this study, the expression of different Gr was determined by lectin histochemistry in early, midterm, and near-term placentas of the plains viscacha (Lagostomus maximus), a caviomorph rodent with the highest poliovulatory rate and embryonic resorption rate among eutherians. Besides, a matrix with the expression of each Gr in the exchange trophoblast of viscacha and other eutherians was constructed to map and infer phylogenetic and evolutionary relationships. Between early, midterm, and near-term placentas, variations in the pattern expression of Gr were observed. The glycotype of the near-term placenta is composed of a high diversity of Gr. Reconstruction of the ancestral state for each Gr present in the near-term placenta showed a diverse scenario: some sugars were common to the species of Placentalia included in this study. In the analyzed species with synepitheliochorial and epitheliochorial placentas, no differential glycosylation patterns between them were observed. In species with invasive placentas, such as the endotheliochorial placentas of Carnivora, some common Gr were detected among them, while others were species-specific. In species with hemochorial placenta, the same Gr are shared. Particularly, in the viscacha greater differences with species of the Hominidae and even Muridae families were observed. Nevertheless, greater similarities with other caviomorph rodents were detected. Placental glycotype of each species constitutes an excellent tool to achieve phylogenetic and evolutionary inferences among eutherians.

Prenatal development in Lagostomus maximus (Rodentia, Chinchillidae): A unique case among eutherian mammals of physiological embryonic death.

Embryonic death followed by resorption is a conserved process in mammals. Among the polyovular species, Lagostomus maximus (plains viscacha) constitutes a model of early and physiological embryonic death, since out of a total of 10-12 implants, 8-10 are resorbed during early/intermediate gestation, surviving are only the most caudal implantations of each uterine horn. This regular reproductive event is unique to this species, but many characteristics of the implantations during the early gestation of L. maximus, when embryonic death processes begin are unknown. The aim of the present work was to analyze the implantation sites of this species using morphological, morphometric, histochemical, lectinhistochemical, and immunohistochemical techniques to infer the possible causes of this event. Macroscopically, the length and width of the implantation sites significantly increased in a craniocaudal direction. Histochemically, the implantation sites did not differ in the expression of glycoconjugates and glycosidic residues. Furthermore, no variations were observed in cell renewal, hormone receptor expression, and decidualization. Both the glandular and vascular areas of the implantation sites significantly increased in the craniocaudal axis. Some necrotic cells and an inflammatory response with a predominance of lymphocytes and fibrin were observed in the cranial and middle but not in the caudal implantation sites. We conclude that signs of embryonic death and resorption are already observed in the early gestation of L. maximus. Our results reaffirm the hypothesis that postulates the key potential role of uterine glands and blood vessels in the gestation of the species, with emphasis on embryonic death. This pattern of embryonic death in L. maximus makes this species an unconventional mammalian model, which adds to the peculiarities of polyovulation (200-800 oocytes/estrus) and hemochorial placentation.

Comparison of the structural and ultrastructural characteristics of the female prostate between pregnant and non-pregnant plains viscacha (Lagostomus maximus).

Some years ago, our group reported the presence of the female prostate in all the studied females of the plains viscacha (Lagostomus maximus). The goal of the present study was to characterize and compare the female prostate gland between adult pregnant and non-pregnant plains viscacha using histochemical, lectin-histochemical and immunohistochemical techniques, as well as optic and electron microscopy. Structurally, alveoli are lined by a simple epithelium formed by different cell types: basal cells, secretory cells in different stages of the secretory cycle and cells of clear cytoplasm. Secretory cells are the most abundant cell type, differing between them depending on the quantity and electron-density of their granules. The basal cells are less abundant and are responsible for the renewal of the alveolar epithelium. Likewise, other cells with secretory morphology were found in all the studied females; these have a clear cytoplasm, few granules and mitochondria. It could be considered that they are degranulated secretory cells or that they have partially released their granules. The stroma of the organ is formed by connective tissue and smooth muscle fibers, which are immunohistochemically evidenced against desmin. Histochemical and lectin-histochemical analysis revealed the presence of different glucidic residues in the different cell types. No structural, histochemical, lectin-histochemical, and ultrastructural differences were observed between pregnant and non-pregnant females of plain viscachas, except for the expression of some lectins. The paraurethral gland of Lagostomus maximus can be used as a model for studying the gland in other species since its structural and ultrastructural characteristics do not depend on the hormonal status of the female.

Early and natural embryonic death in Lagostomus maximus: Association with the uterine glands, vasculature, and musculature.

The uterus is an organ with great plasticity due to the morphological and physiological changes it experiences during the estrous cycle and pregnancy. In mammals, pregnancy requires diverse sex hormones, growth factors and cytokines, among others, for promoting uterine remodeling to favor implantation, placentation, and embryo/fetus survival and growth. The hystricognathi rodent Lagostomus maximus (plains viscacha) has a high rate of embryonic resorption. The cranial and middle implants are reabsorbed 25-35 days after intercourse while the caudal embryos continue with their development until two precocial offspring are born. So far, no uterine studies of non-pregnant L. maximus females were performed to determine the possible existence of variations in the organ that could be related to the differential survival of the implants. We used ultrasonography, as well as morphological, morphometric, histochemical, lectinhistochemical, and immunohistochemical methods to study differences in the uterine glands (area), vasculature (area), and musculature (thickness) along the uterine horns in non-pregnant females. Along the uterus, all these structures were in more advanced developmental condition in the caudal region as compared to more anterior positions. These regional variations could be decisive in explaining the reason why only caudal implantations come to term. In contrast, no differences in the in the luminal and glandular epithelial cells, nor in the degree of cell proliferation and apoptosis, and hormonal receptor staining were found. These parameters could be related to implantation along the uterine horns, but not to the differential survival of the implants.

Histochemistry of the zona pellucida of the ovary of a species with natural polyovulation: Lagostomus maximus (Rodentia, Hystricomorpha, Chinchillidae).

This study reports the histochemistry and the distribution of glycoconjugates (GCs) in the zona pellucida (ZP) of preantral, secondary, tertiary, polyovulatory and atretic follicles of ovaries from non-pregnant (NPr) and pregnant (Pr) females of Lagostomus maximus. GCs were studied using histochemical and lectin histochemical methods. The viscacha ZP was positive to all the histochemical techniques. In addition, it was observed that the intensity of staining of the ZP was constant in the different follicular stages between both female groups. The lectin histochemical study revealed that ZP was positive for certain lectins (WGA, RCA-I and CON-A) and that the labelling did not vary between the different follicular stages, but between the two groups of females. By using both histochemical techniques, it was established that the GCs present in the ZP label the complexity of the area. These results allow us to increase our knowledge on the biology of the viscacha's ovary, particularly contributing to the study of polyovulation.

Hypothalamic IGF-I gene therapy prolongs estrous cyclicity and protects ovarian structure in middle-aged female rats.

There is substantial evidence that age-related ovarian failure in rats is preceded by abnormal responsiveness of the neuroendocrine axis to estrogen positive feedback. Because IGF-I seems to act as a permissive factor for proper GnRH neuronal response to estrogen positive feedback and considering that the hypothalamic content of IGF-I declines in middle-aged (M-A) rats, we assessed the effectiveness of long-term IGF-I gene therapy in the mediobasal hypothalamus (MBH) of M-A female rats to extend regular cyclicity and preserve ovarian structure. We used 3 groups of M-A rats: 1 group of intact animals and 2 groups injected, at 36.2 weeks of age, in the MBH with either a bicistronic recombinant adeno-associated virus (rAAV) harboring the genes for IGF-I and the red fluorescent protein DsRed2, or a control rAAV expressing only DsRed2. Daily vaginal smears were taken throughout the study, which ended at 49.5 weeks of age. We measured serum levels of reproductive hormones and assessed ovarian histology at the end of the study. Although most of the rats injected with the IGF-I rAAV had, on the average, well-preserved estrous cyclicity as well as a generally normal ovarian histology, the intact and control rAAV groups showed a high percentage of acyclic rats at the end of the study and ovaries with numerous enlarged cysts and scarce corpora lutea. Serum LH was higher and hyperprolactinemia lower in the treated animals. These results suggest that overexpression of IGF-I in the MBH prolongs normal ovarian function in M-A female rats.

Morphological characterization of the female prostate (Skene's gland or paraurethral gland) of Lagostomus maximus maximus.

The Skene's (paraurethral) gland is the histologic homologue to the male prostate. Much experimental work has been done on women and on various rodents. In this study we describe for the first time the anatomical and histological characteristics of the paraurethral gland in the plain viscacha (Lagostomus maximus maximus). This gland is formed by tubuloalveolar adenomers surrounded by connective tissue and smooth muscle fibers. The adenomers are lined by cuboidal or columnar epithelium. In the lumen of the adenomers, PAS positive secretions could be detected. The conduits are lined by bi-stratified epithelium. In some aspects this gland is similar to that of other mammals.

Mitotic activity of the duodenal crypt enterocytes in mice transplanted with EA21a mammary carcinoma.

The presence of a tumor generally changes the mitotic activity of the normal cell population in mice. In the present work, the mitotic activity of the duodenal crypt enterocytes in EA21a mammary carcinoma-bearing mice was determined. The results show that there is a patent circadian variation in normal mice and, in the presence of the EA21a mammary tumor, cell proliferation is stimulated. Stimulation was evident in enterocytes from the intermediate as well as the superficial regions of the crypt. Some humoral factors produced by the transplanted tumor could interfere with the regulatory mechanism of the mitotic activity of duodenal crypt enterocytes.