Structure of the paws in Didelphis virginiana

The paws of Didelphis virginiana show several unusual features. They possess dermatoglyphs on the foot pads, have opposable first digits and the pads show a peculiar vascular arrangement. The hallux lacks a claw. The degree of innervation and the number and size of Pacinian corpuscles indicates that the paws of the opossum are finely sensitive to pressure and vibration.     

Cellular mechanisms involved in cyclic stromal renewal of the uterus. I. The opossum, Didelphis virginiana.

At the close of a uterine cycle, the remodelling of the endometrial stroma of the North American opossum involves removal of extracellular material by macrophages. This study provides cytochemical and ultrastructural evidence which indicates that the laden macrophages are eliminated from the endometrium through emigration across the glandular and luminal epithelia. During diestrus or the early postpartum period, the abundant uterine glands relinguish their secretory function to acquire a transient function in the transportation of emigrating stromal cells. During the first three postpartum days endometrial regression in the stroma is marked by sudden appearance of monocytes, macrophages, lymphocytes, and plasma cells. Ultrastructural and cytochemical evidence indicates that the macrophages engulf the extracellular macromolecular material which, in the opossum, consists primarily of ground substance. Macrophages filled with ingested extracellular material aggregated beneath the glandular and luminal epithelia, where they acquire an extracellular coat that resembles the material of the basal lamina elsewhere. A fibroblast-like cell closely invests the macrophage at the time the extracellular material appears. Simultaneously, the secretory glandular epithelium is being converted to a highly ciliated one. Macrophages, often accompanied by lymphocytes, acquire intraepithelial positions in the glands. From here these stromal cells gain entrance to the glandular lumens. At this time the luminal contents are rich in acid phosphatase activity which most likely reflects the high lysosomal content of the emigrating macrophages. Evidence suggests that these intraluminal macrophages and lymphocytes are swept, by the recently differentiated ciliary lining, toward the glandular orifices and into the uterine cavity. It is hypothesized that this cyclic appearance and transepithelial elimination of macrophages is a cellular mechanism for removing large amounts of extracellular material without disruption of the endometrium.     

The cardiac, oxyntic and pyloric glands in the developing opossum (Didelphis virginiana)

In the opossum the fundic area of the gastric mucosa develops first, and oxyntic glands show early division into gastric pits and glandular components which then grow simultaneously. At 40 d postnatum the oxyntic glands are longer than the gastric pits but in the pyloric glands the pits still are longer than the glands and it is not until the 73rd postnatal day, that pyloric glands are longer than their pits. Development of the cardiac glands is delayed even more and the length of the gland does not surpass that of the pit until about 95 d postnatum. Argyrophil cells are concentrated in the cardia and fundus at birth and during early postnatal life, but the population of these cells shifts to the pylorus in the adult. Argyrophil cells of the cardiac, oxyntic and pyloric glands are concentrated in glandular regions with the highest mitotic activity.     

Immunohistochemical localization of relaxin in the reproductive system of the female opossum (Didelphis virginiana).

Relaxin-immunoreactivity was demonstrated in the cytoplasm in the luteal cells from pregnant and lactating opossums. Immunoreactivity for relaxin was not demonstrated elsewhere in the ovary, in the reproductive tract or in the placenta. The corpus luteum is thought to be the primary source of relaxin in Didelphis and in this regard is similar to several eutherian mammals including man.     

Ultrastructural observations on the shell membrane of the North American opossum (Didelphis virginiana)

Each developing opossum embryo is surrounded by a shell membrane which completely separates embryonic and maternal tissues. During the eighth and ninth prenatal days, the embryos together with their limiting shell membranes float freely within the uterine lumen, surrounded only by the secretions of the uterus. The shell membrane is transparent, nonelastic, tough, and capable of extreme deformation. It consists of a mat of interwoven fibers which vary in external diameter, are electron dense, and show no apparent substructure. The morphology and arrangement of component fibers are similar throughout the width of the shell membrane.     

Physiological interactions between enkephalin and excitatory amino acids in the cerebellar cortex of the opossum Didelphis marsupialis virginiana.

The opiate peptide enkephalin has been immunohistochemically localized within specific populations of climbing fibers and mossy fibers in the opossum's cerebellum. The intention of the present study was to determine the physiological effects of this peptide on Purkinje cell activity as well as to examine interactions between this peptide and the excitatory amino acids glutamate and aspartate. Iontophoretic application of enkephalin onto Purkinje cells in the posterior lobe vermis and adjacent hemisphere suppressed activity in nine of 16 (56%) spontaneously active units. Enkephalin increased the spontaneous activity of one unit and had no effect on six (38%) of the units. In addition, this peptide blocked the excitatory effects elicited by iontophoretic application of glutamate in 34 of 35 (97%) units tested and of aspartate in all cases. Enkephalin had no effect on one cell activated by glutamate. Simultaneous application of naloxone, a nonspecific opiate receptor antagonist, did not block the suppressive effects of enkephalin. Rather, there was a potentiation of suppressive responses as compared to that seen when each is applied alone. The results suggest that classically defined excitatory afferent projections to the cerebellum may be capable of both exciting and suppressing the activity of their target neurons. The excitatory action is likely mediated by an amino acid, whereas the release of the peptide enkephalin results in a decrease in unit activity. Further, it appears that enkephalin mediates its suppressive effect through mechanisms that are not mediated by opioid receptors.     

Spontaneous squamous cell carcinoma of the tongue and multiple bronchioloalveolar carcinomas in a Virginia opossum (Didelphis virginiana)

Two primary tumours, squamous cell carcinoma of the tongue and multiple bronchioloalveolar carcinomas, were diagnosed in a Virginia opossum (Didelphis virginiana). Two oral masses were located in the right ventrolateral surface of the tongue, near the frenulum, and the lungs contained multiple, widely distributed, nodular masses. Microscopically, the oral masses were composed of invasive cords of pleomorphic, polyhedral cells, typical of squamous cells. The multiple pulmonary masses consisted of non-ciliated, cuboidal, columnar, or occasionally polyhedral cells arranged in an alveolar pattern with multifocal areas of necrosis. This is the first report of spontaneous oropharyngeal squamous cell carcinoma in the Virginia opossum. However, multiple pulmonary adenomas have been reported previously in this species, the lesions being similar to those in sheep pulmonary adenomatosis (jaagsiekte). In the present study, immunohistochemical examination of the pulmonary tumours with a rabbit polyclonal antiserum to jaagsiekte retroviral capsid protein proved negative.     

Receptive field properties and latencies of cells in the lateral geniculate nucleus of the North American opossum (Didelphis virginiana)

Relay cells in the lateral geniculate nucleus (LGN) of the North American opossum were classified as types 1, 2, and 3 on the basis of their receptive field properties and afferent latencies to optic nerve (ON) and optic chiasm (OX) stimulation and antidromic latencies to stimulation of cortex. Type 1 and type 3 cells gave transient responses and type 2 cells gave sustained responses to appropriate standing contrast in the receptive field center. The differences in response pattern were quantified with a phasic-tonic index (PTI); the PTI values for type 2 cells (PTI less than 63) did not overlap those for type 1 cells (PTI greater than 68) or type 3 cells (PTI greater than 80). With a homogeneous field (1.3 cd/m2), the maintained discharge rates (spikes/s) of type 3 cells (less than 1-11) were significantly lower than those of type 1 cells (3-23) and of type 2 cells (1-22). For all type 2 cells tested with a counterphased sine-wave grating, a null position of the grating was found and the cells were classified as linear. The type 1 and type 3 cells tested were nonlinear (i.e., exhibited excitatory doubling and did not have a null grating position). The maximum velocity of movement that reliably elicited responses (cut-off velocity) was low for type 3 cells (mean = 29.1 degrees/s) and relatively high for type 1 cells (mean = 70.3 degrees/s). Cut-off velocities for type 2 cells (mean = 61.2 degrees/s) were slightly lower than for type 1 cells. Type 1 cells had relatively short afferent (ON and OX) latencies, fast afferent conduction velocities, and short antidromic (cortex) latencies; type 2 cells had intermediate afferent and antidromic latencies and intermediate afferent conduction velocities; and type 3 cells had relatively long afferent and antidromic latencies and slow afferent conduction velocities. The receptive field center diameters were similar for type 1 (4.2-25.5 degrees; mean = 11.4 degrees) and type 3 cells (2.8-23.7 degrees; mean = 11.0 degrees), whereas the receptive field centers for type 2 cells (2.9-15.1 degrees; mean = 6.9 degrees) were significantly smaller. The majority of type 1 (66.7%) and type 3 cells (63.3%) had on-center receptive fields, whereas the proportion of on-center fields was even greater for type 2 cells (83.0%). Only a few of the cells encountered in the opossum LGN (6%) had on-off receptive fields, and a portion of these could not be shown to be relay cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

The immune response of adult opossums (Didelphis virginiana) to the bacteriophage f2

Humoral immunity to the bacteriophage f2 was studied in adult opossums (Didelphis virginiana) and their responses were compared to those in New Zealand White rabbits. Antibodies were found in the serum of opossums 7 days after the subcutaneous injection of the antigen and peak antibody responses were observed between 10 and 21 days after immunization. A second injection of antigen resulted in increased antibody activity. In either case the level of serum antibody reached in opossums was less than that in rabbits. More striking, however, was the relatively slow conversion from γM to γG antibodies in opossums. The course of the immune response in adult opossums was more nearly like that of cold-blooded vertebrates than that of eutherian mammals.     

Aerobic bacteria cultured from the mouth of the American opossum (Didelphis virginiana) with reference to bacteria associated with bite infections.

The American opossum inflicts bite injuries both when hunted for food and when accidentally provoked when handled in captivity. This study involved aerobically culturing organisms from the mouths of seven wild opossums (Didelphis virginiana). Isolates included streptococci, coagulase-positive and -negative staphylococci, Aeromonas spp., Citrobacter freundii, Eikenella corrodens, and Escherichia coli.     

Cytoarchitecture of the substantia nigra pars lateralis in the opossum (Didelphis virginiana): A correlated light and electron microscopic study

Background: The substantia nigra has been divided into three subdivisions. However, the cytoarchitecture of one of these subdivisions, the pars lateralis (SNI), has not been previously examined in detail at the light and electron microscopic levels in any species. In the adult opossum, the three nigral subdivisions can be easily distinguished as distinct, rostrocaudally oriented cell groups separated by neuron-free zones. Thus it was possible to determine the boundaries of the SNI unambiguously. This report covers the results of an examination of the morphology and organization of the SNI in the opossum. Methods: Material from 13 opossums was used for this study. Eight of the animals had been previously stained for Nissl substance (n=4) or impregnated by the Golgi technique (n=4). The remaining five animals were prepared for electron microscopic studies using standard procedures. Results: Two cell types were identified on the basis of morphological differences, small and medium-large neurons. Small neurons (10–18 μm long axis) have large nuclei with moderate amounts of heterochromatin and a thin rim of cytoplasm. They have long (up to 500 μm), spine-free dendrites. Medium-large neurons (18–54 μm long axis) have rounded nuclei with electron-lucent nucleoplasm. Few indentations of the nuclear envelope were observed. The surrounding cytoplasm has dense arrays of organelles. Nissl bodies are particularly prominent in the form of pyramids with their bases at juxtanuclear positions and their apices directed toward emerging dendrites. Dendrites of medium-large neurons are long (some>1 mm in length), are primarily oriented in the frontal plane, and extend along the dorsal surface of or into the cerebral peduncle. Some cells have dendrites that are moderately spinous, whereas other neurons possess sparsely spinous dendrites. Relatively few synaptic profiles are observed to contact somata and proximal dendrites. Conclusion: This report provides added morphological support for the idea that the SNI is a distinct subdivision of the substantia nigra, a distinction previously made on the basis of the physiologically characterized relationship between the lateral substantia nigra and orienting behaviors and seizure-related function. © 1995 Wiley-Liss, Inc.     

The allantois of the North American opossum (Didelphis virginiana) with preliminary observations on the yolk sac endoderm and trophectoderm

During the middle of prenatal day 10, the opossum allantois forms as a ventral outgrowth of the hindgut. By day 11 it appears as a large, fluid filled sac and by the middle of day 12 (just prior to birth) it reaches its maximal development. The simple squamous epithelium lining the allantois consists of only one cell type that often contains numerous filaments in the apical cytoplasm. At the luminal surface, the apices of the cells are united by junctional complexes and desmosomes are present between adjacent cells. The luminal surface is irregular, whereas laterally and basally the cell membranes show few if any infoldings. Mitotic figures and presumptive degenerating cells occasionally occur in the allantoic epithelium which rests on a delicate basal lamina. The allantois is covered by a simple squamous mesothelium that lacks a distinct basal lamina. Between the two epithelial sheets lie mesenchymal cells, collagen fibers, and blood vessels. No specializations of cell membranes were noted in either of the epithelial layers. The yolk sac endoderm consists of a single layer of squamous cells whose cytoplasm contains scattered profiles of rough endoplasmic reticulum and mitochondria. Extensive lateral and basal infoldings of the plasmalemma were not observed in these endodermal cells. The morphology of the trophectodermal (trophoblastic) cells indicates a cell type that is active in the transport of materials. Since the endodermal cells that line the allantois lack morphological features that would suggest the presence of mechanisms for transport or exchange, and because they remain relatively unchanged throughout pregnancy, it is thought that the allantois functions primarily in the storage of urinary wastes during prenatal life.(ABSTRACT TRUNCATED AT 250 WORDS)