Spermatogenesis in mature and regressed testes of the vole (Microtus agrestis). (17/710)

Eight stages of spermatogenesis, each with a characteristic frequency and germ cell association could be recognized in the vole. There was no difference between laboratory bred and field animals in the frequency of the stages. Counts of the different types of germ cell showed that there was considerable cell loss during spermatogonial mitotic and spermatocytic meiotic divisions. Only 60% of germ cells became spermatozoa in sexually mature animals, and 19% in the regressing testes of voles exposed to short photoperiods. Animals with regressed testes probably have lowered circulating levels of gonadotrophins and testicular hormones, so that the greater germ loss suggests the importance of these hormones in the regulation of germ cell wastage. From the cell counts in mature animals, a scheme of cell divisions has been suggested by which spermatogonia produce progressively more highly differentiated germ cells while continuing to perpetuate stem cells.  (+info)

Comparative morphology and histochemistry of glands associated with the vomeronasal organ in humans, mouse lemurs, and voles. (18/710)

The vomeronasal organ (VNO) is a chemosensory structure of the vertebrate nasal septum that has been recently shown to exist in nearly all adult humans. Although its link to reproductive behaviors has been shown in some primates, its functionality in humans is still debated. Some authors have suggested that the human VNO has the capacity to detect pheromones, while others described it as little more than a glandular pit. However, no studies have utilized histochemical techniques that would reveal whether the human VNO functions as a generalized gland duct or a specialized chemosensory organ. Nasal septal tissue from 13 humans (2-86 years old) were compared to that of two adult lemurs (Microcebus murinus) and eight adult voles (four Microtus pennsylvanicus and four Microtus ochrogaster). Sections at selected intervals of the VNO were stained with periodic acid-Schiff (PAS), alcian blue (AB), AB-PAS, and PAS-hematoxylin procedures. Results revealed typical well-developed VNOs with tubuloacinar glands in Microtus and Microcebus. VNO glands were AB-negative and PAS-positive in voles and mouse lemurs. Homo differed from Microtus and Microcebus in having more branched, AB and PAS-positive glands that emptied into the VNO lumen. Furthermore, the human VNO epithelium had unicellular mucous glands (AB and PAS-positive) and cilia, similar to respiratory epithelia. These results demonstrate unique characteristics of the human VNO which at once differs from glandular ducts (e.g., cilia) and also from the VNOs of mammals possessing demonstrably functional VNO.  (+info)

A longitudinal study of an endemic disease in its wildlife reservoir: cowpox and wild rodents. (19/710)

Cowpox is an orthopoxvirus infection endemic in European wild rodents, but with a wide host range including human beings. In this longitudinal study we examined cowpox in two wild rodent species, bank voles Clethrionomys glareolus and wood mice Apodemus sylvaticus, to investigate the dynamics of a virus in its wild reservoir host. Trapping was carried out at 4-weekly intervals over 3 years and each animal caught was uniquely identified, blood sampled and tested for antibodies to cowpox. Antibody prevalence was higher in bank voles than in wood mice and seroconversion varied seasonally, with peaks in autumn. Infection was most common in males of both species but no clear association with age was demonstrated. This study provides a model for studying other zoonotic infections that derive from wild mammals since other approaches, such as one-off samples, will fail to detect the variation in infection and thus, risk to human health, demonstrated here.  (+info)

Development of mouse-bank vole interspecific chimaeric embryos. (20/710)

One bank vole (Clethrionomys glareolus) embryo and two mouse embryos were combined at the 8- to 16-blastomere stage and cultured in vitro for 33-47 h. In 66% of cases single regular blastocysts were formed. The chimaeric composition of blastocysts was confirmed karyologically. Out of the 222 blastocysts transplanted to 49 pseudopregnant mouse recipients, a total of 52 implantations were found in 20 recipients. Among the 52 implantations, 14 contained embryos and the remaining were resorptions. The majority of embryos were abnormal and fell into two categories: (1) groups of cells surrounded by Reichert's membrane and lying freely in a cavity filled with giant trophoblastic cells, (2) small and retarded egg-cylinders usually composed of endoderm and ectoderm only, and containing a proamniotic cavity. The ectoplacental cone of these embryos was poorly developed or lacking altogether. Two normal-looking embryos were recovered on the 9th and 10th day (4-somite and ca. 12-somite stage). Chimaerism of the younger embryo was confirmed karyologically. No evidence of chimaerism was available in the case of older embryo which was examined histologically. Thirteen implantations examined between 11th and 17th day contained only resorptions. It is suggested that the main cause of the heavy mortality of chimaeric embryos is the profound difference in the course of embryogenesis of these two species immediately following implantation.  (+info)

The ultrastructure of the anterior pituitary gland of the vole, Microtus agrestis, in normal and experimentally manipulated animals. (21/710)

The ultrastructural appearance of the various types of cell present in the anterior pituitary of the vole has been described. There was a great measure of similarity between the cytological picture in this species and in the rat. Prolactotrophs contained the largest secretory granules, which were of variable shape; the granules of somatotrophs, whilst only slightly smaller than those of prolactotrophs, were invariably round, and of more uniform size; corticotrophs were represented by cells which were extremely angular, and whose secretory granules, besides being smaller than those of somatotrophs, were arrayed around the periphery of the cell below the plasma membrane; gonadotrophs contained granules of a similar size to those found in cortiocotrophs, but were found throughout the cytoplasm of the cells, whic were round to ovoid in shape; thyrotrophs contained the smallest granules of all, the shape of the cell itself bein angular...  (+info)

Puumala (PUU) hantavirus strain differences and insertion positions in the hepatitis B virus core antigen influence B-cell immunogenicity and protective potential of core-derived particles. (22/710)

Hepatitis B virus (HBV) core-derived chimeric particles carrying a Puumala (PUU) hantavirus (strain Vranica/Hallnas) nucleocapsid (N) protein sequence (aa 1-45), alternatively inserted at three distinct positions (N-, C-terminus, or the internal region), and mosaic particles consisting of HBV core as well as core/PUU (Vranica/Hallnas) N (aa 1-45) readthrough protein were generated. Chimeric particles carrying the insert at the N-terminus or the internal region of core induced some protective immune response in bank voles (Clethrionomys glareolus) against a subsequent PUU virus (strain Kazan) challenge; 40-50% of the animals showed markers of protection. In contrast, internal insertion of PUU strain CG18-20 N (aa 1-45) into the HBV core caused a highly protective immune response in the bank vole model. Immunizations with particles carrying aa 75-119 of PUU (CG18-20) N at the C-terminus of core verified the presence of a second, minor protective region in the N protein. A strong PUU N-specific antibody response was detected not only in bank voles immunized with chimeric particles containing internal and N-terminal fusions of PUU N protein but also in animals immunized with the corresponding mosaic particles. Except for the exclusive occurrence of antibodies directed against aa 231-240 of N in non-protected animals post virus challenge, there was no additional obvious difference in the epitope-specificity of N-specific antibodies from immunized animals prior and post virus challenge.  (+info)

Molecular evolution of puumala hantavirus in Fennoscandia: phylogenetic analysis of strains from two recolonization routes, Karelia and Denmark. (23/710)

Like other members of the genus HANTAVIRUS: in the family BUNYAVIRIDAE:, Puumala virus (PUUV) is thought to be co-evolving with its natural host, the bank vole Clethrionomys glareolus. To gain insight into the evolutionary history of PUUV in northern Europe during the last post-glacial period, we have studied wild-type PUUV strains originating from areas along two postulated immigration routes of bank voles to Fennoscandia. Full-length sequences of the S RNA segment and partial sequences (nt 2168-2569) of the M segment were recovered by RT-PCR directly from bank vole tissues collected at three locations in Russian Karelia and one location in Denmark. Phylogenetic analysis showed that strains from Karelia and Finland belong to the same genetic lineage, supporting the hypothesis that PUUV spread to present Finland via a Karelian land-bridge. The Danish PUUV strains showed no particularly close relatedness to any of the known PUUV strains and formed a distinct phylogenetic lineage on trees calculated for both S and M segment sequences. Although no direct link between the Danish PUUV strains and those of the southern Scandinavian lineage was found, within the S segment of Danish PUUV strains, two regions with higher similarity to either northern Scandinavian or - to a less extent - southern Scandinavian genetic lineages were revealed, suggesting evolutionary connections of their precursors.  (+info)

Evolutionary modification of development in mammalian teeth: quantifying gene expression patterns and topography. (24/710)

The study of mammalian evolution often relies on detailed analysis of dental morphology. For molecular patterning to play a role in dental evolution, gene expression differences should be linkable to corresponding morphological differences. Because teeth, like many other structures, are complex and evolution of new shapes usually involves subtle changes, we have developed topographic methods by using Geographic Information Systems. We investigated how genetic markers for epithelial signaling centers known as enamel knots are associated with evolutionary divergence of molar teeth in two rodent species, mouse and vole. Our analysis of expression patterns of Fgf4, Lef1, p21, and Shh genes in relation to digital elevation models of developing tooth shapes shows that molecular prepatterns predict the lateral cusp topography more than a day in advance. A heterotopic shift in the molecular prepatterns can be implicated in the evolution of mouse molar, changing locations from which historically homologous cusps form. The subtle but measurable heterotopic shifts may play a large role in the evolution of tooth cusp topographies. However, evolutionary increase in the number of longitudinal cusps in vole molar has involved accelerated longitudinal growth and iterative addition of new cusps without changes in lateral cusp topography. The iterative addition of cusps after the establishment of lateral cusp topography may limit the independence of individual morphological features used in evolutionary studies. The diversity of mammalian molar patterns may largely result from the heterotopic and iterative processes.  (+info)