Embryonic-placental relationship in Lagostomus maximus as compared to other hystricognath rodents and eutherian mammals.

Reproductive specializations in caviomorphs (infraorder Hystricognathi), are very peculiar within the Order Rodentia. These include long gestations, the birth of offspring with an extreme degree of precociality, and short lactation periods. This study describes the embryo-placental relationship of viable implantation sites (IS) of the plains viscacha, Lagostomus maximus, after 46 post-coital days. The observations recorded in this study are comparatively discussed with those of other hystricognaths and eutherians. At this stage, the embryo resembles that of other eutherians. At this time of embryo development, the placenta exhibits a size, shape, and organization similar to that it will have in its mature state. Besides, the subplacenta is already highly folded. These characteristics are adequate to sustain the development of future precocial offspring. The mesoplacenta, a structure present in other hystricognaths and related to uterine regeneration is described for the first time in this species. This detailed description of the placental and embryonic structure contributes to the knowledge of the reproductive and developmental biology of the viscacha, as well as that of hystricognaths. These characteristics will allow testing other hypotheses related to the morphology and physiology of the placenta and subplacenta, and their relationship with the growth and development of precocial offspring in Hystricognathi.

Spontaneous embryonic death in plains viscacha (Lagostomus maximus - Rodentia), a species with unique reproductive characteristics.

Spontaneous embryonic death is a conserved reproductive event in Eutherians. The macro and microscopic characteristics of this type of death are similar between the different taxa. However, in the hystricomorphic rodent plains viscacha (Lagostomus maximus) is exceptional in terms of massiveness (80% embryonic resorption). In this species, of the 10-12 implantation sites (IS) (half in each uterine horn), only the caudal embryos will survive, resorbing the cranial and intermediate IS. We hypothesize that uterine structural variations in L. maximus restrict growth and promote embryo death, with the consequent loss of placental homeostasis in the cranial and middle IS. In this study, different studies (ultrasonography, macroscopy and microscopy) were carried out to analyze different aspects of the intermediate gestation of L. maximus (46 days postcoitus). Ultrasonographic studies revealed that the cranial and middle IS (IS-1, IS-2, and IS-3) had no recognizable embryonic and placental structures as compared to the caudal implantation sites (IS-4). Macroscopically, the areas corresponding to the embryos in the cranial and middle IS were occupied by a necrotic black semi-fluid mass. Moreover, the placenta in these IS was undifferentiated. However, in the caudal IS both the embryo and its placenta were distinguishable. Using histological and immunohistochemical techniques, it was observed that the placentas of IS-1, IS-2 and IS-3 were disorganized and showed hemorrhage, inflammatory infiltration containing neutrophils, macrophages, mast cells and foreign body giant cells, apoptotic trophoblast, and a layer of collagen fibers and fibroblasts that circumscribed each of these IS. In contrast, the placenta of the caudal IS showed an organized maternal-embryonic interface. The characteristics observed in IS in resorption of viscachas in intermediate gestation show that, regardless of gestation time, embryonic death has a similar macro and microscopic morphological pattern among eutherians with invasive placentation. However, the massiveness and sectorization of embryonic death in the plains viscacha make the species a unique model for the study of this reproductive event.

Placentation and embryo death in the plains viscacha (Lagostomus maximus).

Caviomorpha are an exceptional group among rodents due to their extended gestational period and the delivery of precocial offspring. Among them, Lagostomus maximus is characterized by its polyovulation, polyembryony, and the highest embryonic death known in mammals. Its chorioallantoic placenta is hemomonochorial, an ancestral character among rodents. It resembles more the human placenta than the murine models. As in all caviomophs, the chorioallantoic placenta is divided in a main placenta and a subplacenta. The former is organized in labyrinth lobes surrounded by trophospongium, as in most caviomorphs. The giant cells (more numerous than in other caviomorphs) near the decidua could be related to invasiveness. During placentation of L. maximus, uterine natural killer cells are found. These cells have been related to invasiveness and remodeling of blood vessels in Mus musculus and Homo sapiens, although in other caviomorphs are not frequently found. In L. maximus, the placenta develops in all conceptuses (5-6 per uterine horn). Necrosis was observed in each implantation site at day 70 post-coitum, except in that closest to the vagina in each horn. This process of embryo death followed by resorption begins at day 26-30 post-coitum. Recently, we found variations in the percentage of blood vessel and uterine gland areas that could explain the regional differences in embryo survival. The characteristics of the placenta and implantation of L. maximus are important to stablish a unique model for studying placentation as well as early embryonic death, of interest for human and veterinary medicine.

Key characteristics of the ovary and uterus for reproduction with particular reference to poly ovulation in the plains viscacha (Lagostomus maximus, chinchillidae).

One of the dogmas of mammalian reproduction states is that primordial germ cells in females are restricted to the intrauterine phase, and that only a small portion of oocytes is available for ovulation during the adult life. Among the rare exceptions to this rule is the plains viscacha. This specie polyovulates up to 800 oocytes per cycle, from which 10 to 12 are implanted, but only 1-2 conceptuses survive. To better understand the key mechanisms of this pattern of embryonic to uterine interactions, we analyzed 19 female genital systems by means of gross morphology, histology, stereology and immunohistochemistry. Data showed that a specialized, highly convoluted structure of the ovarian cortex developed during the intrauterine phase as a prerequisite for the massive super-ovulation, likely associated with the inhibition of apoptosis and continued proliferation of germ cells, as well as maintenance of several corpora lutea during the adult life. In addition, specializations of uterine vasculature and musculature were demonstrated. Altogether, these key morphological characteristics evolved in order to contribute as compensatory or controlling mechanism for polyovulation and polyimplantation that led these species into becoming an unique enigma in reproductive biology, and a potential animal model to provide explanations regarding to developmental specializations.

Analysis of glycoconjugates and morphological characterization of the descending colon and rectum of the plains viscacha, Lagostomus maximus.

Herbivores exhibit specializations at the intestinal level that facilitate the bacterial fermentation. The available information on the digestive physiology of Lagostomus maximus makes this rodent an interesting model to evaluate morpho-functional adaptations to herbivory. The general objective of this work was centered on the study of the morphology and histochemistry of the descending colon and rectum of L. maximus. To do so, a comparative analysis of the morphology, ultrastructure and glycosylation pattern of both anatomical regions was carried out. Histochemical results revealed that in both sectors of the large intestine, there are goblet cells with different glycosylation pattern within a morphologically homogeneous cell population. The main difference between both intestinal segments lay in the fact that the most distal region of the large intestine showed a greater proportion of sialomucins, characterized by being slightly O-acetylated. Further specific differences were revealed by lectin histochemistry. These data allowed to perform a functional interpretation of the cell types and secreted substances, thus contributing to a better understanding of the role of mucins in the intestinal tract functioning.

The colonic groove of the plains viscacha (Lagostomus maximus): Histochemical evidence of an abrupt change in the glycosylation pattern of goblet cells.

The ascending colon of most rodent species shows a longitudinal colonic groove that works as a retrograde transport pathway for a mixture of bacteria and mucus toward the cecum. We describe the morphology and glycosylation pattern of the colonic groove of Lagostomus maximus to analyze the role of mucins in this anatomical feature. We also studied the distribution pattern of the interstitial cells of Cajal (ICC) to evaluate their regulatory influence on gut motility. The groove originated near the cecocolic junction and extended along the mesenteric side of the ascending colon, limited at both ends by nonpapillated ridges. These ridges divided the lumen of the ascending colon into two compartments: a narrow channel and a large channel, called the groove lumen and the main lumen, respectively. The histochemical analysis showed differences in the glycosylation pattern of the goblet cells inside and outside the groove. Unlike the mucosa lining the main lumen of the colon, the groove was rich in goblet cells that secrete sulfomucins. The PA/Bh/KOH/PAS technique evidenced an abrupt change in the histochemical profile of goblet cells, which presented a negative reaction in the groove and a strongly positive one in the rest of the colonic mucosa. The anti-c-kit immunohistochemical analysis showed different ICC subpopulations in the ascending colon of L. maximus. Of all types identified, the ICC-SM were the only cells located solely within the colonic groove.

Comparative Analysis of the Morphology, Ultrastructure, and Glycosylation Pattern of the Jejunum and Ileum of the Wild Rodent Lagostomus maximus.

Morphological and histochemical analyses were performed to characterize the histology, ultrastructure, and glycosylation pattern of the jejunum and ileum of the wild rodent Lagostomus maximus. Enterocytes, goblet cells, Paneth cells, and enteroendocrine cells were identified in both intestinal epithelia. Two morphological types of enterocytes were identified only in the ileum based on their cytoplasm electron density. Although the histological and ultrastructural examination showed that the epithelia of both anatomical regions were morphologically similar, a certain specialization in their secretory products was evident. The glycosylation pattern of the jejunum and ileum was characterized in situ by histochemical and lectin histochemical methods. Histochemical results revealed the presence of carboxylated and sulfated gycoconjugates in both regions, although sulfomucins were clearly prevalent in the ileum. Sialic acid was highly O-acetylated and particularly abundant in the jejunum. The KOH/PA*/Bh/PAS technique evidenced a more intense histochemical reaction in the jejunal than in the ileum goblet cells, demonstrating a reduction of neutral mucin secretion in the distal small intestine. Further specific differences were revealed by lectin histochemistry. These data evidenced that the nature of mucus varies at different anatomical regions, probably adapted to physiological requirements.

Seasonal variations cause morphological changes and altered spermatogenesis in the testes of viscacha (Lagostomus maximus).

This study complements the previous investigations of the reproductive biology of male viscachas, a rodent of a seasonal Hystricognathi that exhibits photoperiod-induced morphological variations in the reproductive system. In the present study, a quantitative analysis of spermatogenesis was performed during the summer and the spring. Spermatogonial cells were analyzed to determine by immunolabelling for STRA8 and DAZL, which are essential for spermatogenesis. Six free-living male viscachas were captured, three animals in the summer during the period of reproductive activity and three animals in the spring during the period of testicular regression. The testes of the viscachas were collected and processed for light microscopy, macroscopic and immunochemical analyses. The germ and Sertoli cells present in the seminiferous tubules were quantitatively analyzed in each animal. The efficiency coefficient for spermatogonial mitosis, meiotic yield, overall spermatogenesis yield and Sertoli cell index, revealed that the Sertoli cells in male viscachas captured during the summer had a reduced capacity to structurally and nutritionally support the developing round spermatids compared with the male viscachas captured during the spring. The animals produced less sperm during the spring than the summer, suggesting a seasonal impact on spermatogenesis. Immunolabelling for STRA8 and DAZL was detected during summer and spring seasons. These results suggest that in seasonal rodents, such as the male viscachas, the photoperiod promotes significant changes in the testis and in the germ cell yield.

Presence of binucleate neurons in the spinal cord of young and senile rats.

The presence of binucleate cells constitutes a normal feature of some animal tissues but is rare in the normal brain and has not been documented in the spinal cord. We assessed different segments of the rat spinal cord in order to determine the frequency and distribution of binucleate neurons in this structure as well as the impact of aging on this neuronal population. Young (4-5 months) and senile (32 months) female Sprague-Dawley rats were used. Sections from cervical, thoracic and lumbar segments were histochemically and immunohistochemically (NeuN) stained and the frequency and distribution of binucleate neurons was determined by manual counting. The frequency of binucleate neurons in all of the analysed segments was comparable between young and senile animals. Binucleate neurons were particularly frequent in the C5 and C6 segments. The overall distribution of binucleate neurons in the different laminae assessed was, Lm-III = 19%; Lm-VI = 17%; Lm-VII = 39%; LmVIII = 8%; Lm-IX = 11%; Lm-X = 6%, and was comparable between young and senile rats. We conclude that binucleate neurons occur as a normal feature of the rat spinal cord and that their frequency and distribution does not change with aging.

Effects of tumors on the daily mitotic activity of mouse pars intermedia.

We have investigated the effects of EA21a and EA34 mammary carcinomas on daily PI cell proliferation in mice. Animals were divided into groups grafted with either EA34 or EA21a carcinomas (and a non-grafted control group). They were all injected intraperitoneally with 2 microg colchicine per g of body weight 4 h before sacrifice and the number of mitoses per 1000 nuclei was calculated. The mitotic index (MI) of pars-intermedia epithelial cells in control animals showed significant temporal variations. However, the MI from mice grafted with EA34 or EA21a carcinomas showed no such variation. There was no difference between the daily MIs of controls and tumor grafted groups. The absence of a 24 h mitotic activity curve in both EA21a and EA34 tumor-bearing animals demonstrates a lower level of synchronization of cells entering mitosis.