The generation of blood cells has been observed in the spleen and in the bone marrow of the platypus. Hemopoiesis was found to be far more active in the spleen than in the bone marrow judging by the number of proliferating hemopoietic elements within a unit area of tissue from each organ. Granulocytes, erythroblasts, and megakaryocytes, with the related immature forms for each cell line, were noted in the spleen. In contrast, there were very few examples of immature forms of these cell lines and a complete absence of mature megakaryocytes in the bone marrow. These findings suggest that the spleen is the primary hemopoietic organ in the platypus. Since the platypus is one of two species representing the most primitive existing mammals, it seems likely that the spleen may be the primary hemopoietic organ in mammalian evolution.

Splenic hemopoiesis of the platypus (Ornithorhynchus anatinus): evidence of primary hemopoiesis in the spleen of a primitive mammal.

The intermediate zone (IZ) of nonperfused and perfused spleens in three species of primitive mammals (shrew, mole, platypus) was studied morphologically. The IZ is a tissue zone consisting of plexiform vessels, probably venous capillaries, and is located transitionally between the white and red pulp. The IZ is separated from the white pulp by the arterial net (AN), in which the white pulp arteries terminate. Development of the IZ differs between the three species examined being distinctive in the platypus and shrew. The IZ is thin in the mole spleen. A closed type of arteriovenous (A-V) anastomosis was demonstrated in or around the IZ in the two Insectivora species examined. In the shrew spleen, peripheral arterial branches running within the IZ anastomose with the AN around the follicle. The AN anastomoses eventually with venous plexiform vessels of the IZ around the nonfollicular area of the white pulp to form a closed system. In the mole spleen, A-V anastomoses were noted between white pulp arteries (follicular and AN) and veins of the red pulp, either by direct communication or through fenestrated IZ vessels compatible with the plexiform vessels of the shrew spleen. A-V anastomosis in the IZ is probable, but not confirmed, in the platypus spleen, as analysis was limited to a nonperfused specimen. Well-developed ellipsoids were noted around arterial terminals of the IZ in the shrew spleen. Ellipsoids were also noted around all arterial terminals of the mole spleen directed to the red pulp. Most ellipsoids of the mole spleen appeared located within the IZ. No ellipsoids were present around arterial terminals of the IZ in the platypus spleen. Closed circulation was noted in terminals of the pulp artery in spleens of all three species. All pulp arteries of the mole spleen are postellipsoid segments of white pulp (AN and follicle) arteries. No ellipsoids were found around terminals of the pulp artery (penicillar artery) in shrew and platypus spleens. The IZ is probably homologous to the perilymphatic sinusoid (vein) of the lungfish spleen and may be regarded as part of the red pulp. The IZ may be representative of primitive mammalian spleens that have closed circulation. The marginal zone (MZ) of common mammalian spleens is probably a modified IZ by differentiation (remodelling) of the intrasplenic vein. In this process, withdrawal of venous vessels from the IZ occurred, leaving a lymphoreticular zone with open circulation (MZ). The marginal sinus reported in some mammalian spleens is probably a modified AN formed during this process. Possible morphological alterations of the spleen in vertebrate phylogeny are discussed.

"Intermediate zone" of mammalian spleens: light and electron microscopic study of three primitive mammalian species (platypus, shrew, and mole) with special reference to intrasplenic arteriovenous communication.

There is a general scarcity of data on the histological structure of major organs in the Eurasian beaver (Castor fiber). This study presents the histological characteristics of beaver organs such as the liver, spleen, cardiac muscle, lungs and kidneys. Tissue samples were collected from 21 beavers and analysed. Selected samples of tail tissue were additionally examined. Tissue samples were placed in neutral buffered formalin and embedded in paraffin. 4-μm-thick sections were stained with haematoxylin and eosin, and other staining techniques were also used. Scant amounts of inter-lobular connective tissue were found in the liver. Ion or copper deposition was not observed, but scattered cytoplasmic glycogen deposits were present in hepatocytes. Our results suggest that beavers have defensive rather than storage spleens. Interestingly, the presence of melanin in splenic red pulp was noted. The histological structure of the examined organs closely resembled that of other rodent species. According to our knowledge, this is the first study evaluating the histological structure of beaver organs. Nevertheless, precise characterization of the evaluated organs requires further work with the involvement of accurate and reliable techniques, such as molecular biology or electron microscopy methods.

Histological Evaluation of Selected Organs of the Eurasian Beavers (Castor fiber) Inhabiting Poland.

A 16-mo-old female house musk shrew (Suncus murinus) with a 1-wk history of a rapidly growing subcutaneous mass in the interscapsular region was euthanized and submitted for necropsy. Macroscopic examination identified an irregular, well-demarcated, solid, tan-white subcutaneous mass. A small cavity containing a microchip device was present at the center of the mass. In addition, massive splenomegaly was evident grossly. Histologically, the subcutaneous mass comprised spindle cells arranged in a storiform pattern of interweaving bundles, consistent with a high-grade soft tissue sarcoma with multifocal necrosis. Immunohistochemical investigation suggested that the neoplastic cells were positive for neuron-specific enolase and (rarely) α-smooth muscle actin and negative for cytokeratin, desmin, S100, and vimentin. In light of the mesenchymal histopathologic phenotype and the lack of specific immunoreactivity pattern, the mass was considered to be most consistent with a poorly differentiated sarcoma. To our knowledge, this is the first report of a microchip-associated soft tissue sarcoma in a shrew.

Microchip-associated sarcoma in a shrew (Suncus murinus).

The overall survival time response of Suncus murinus, one of the insectivora, under wholebody x-irradiation in the dose range of 500 to 50, 000 rad was investigated. Three segments of bone marrow, gastrointestinal (GI), and central nervous system (CNS) deaths in the dosesurvival time response curve were similar to those of other species such as mice, rats, and mongolian gerbils. The mean survival time with the bone marrow syndrome was about 9 days after 700 and 800 rads. The LD/50 was 736 ± 30 rad in comparison with 547 ± 15 rad in C3H/He mice. Typical severe GI death manifested within 5.5-4.6 days following doses between 1, 200 and 10, 000 rad, where the survival time was almost constant. In spite of the absence of large intestinal type mucosa in this species, the relationship between transit time of the epithelial cells along villus wall (about 50 hrs) and the survival time with the typical GI syndrome was similar to those of data obtained with various rodents possessing a large intestine. CNS death was evident above 20, 000 rad, and the survival time rapidly decreased with dose increase. A pattern of dose-weight loss response was found to correspond directly with the dose required to initiate the syndrome involved, as the curve can be mostly superimposed on the dose-survival time response curve if the weight loss is inversed.

/pdf/dose-survival-time-response-of-suncus-murinus-from-whole-3e4h6vmm3u.pdf

Dose-Survival Time Response of Suncus murinus from Whole-body Irradiation

In the spleen of the musk shrew, a marginal zone was clearly demonstrable between the white pulp and the red pulp. The white pulp was separated from the marginal zone by a septum, a circumferential layer of reticular cells and fibres, and between the marginal zone and red pulp there was a population difference of blood cells. The white pulp consisted of periarterial lymphatic sheaths and lymphoid follicles including germinal centres. The marginal zone was filled by numerous erythrocytes, some lymphocytes, granulocytes and a few macrophages, while the red pulp had a large number of neutrophils, eosinophils, megakaryocytes and their precursors. In the red pulp erythroblasts tended to form islets, and there were a few basophils, plasma cells, plasmablasts and macrophages. Haematopoiesis was also active in the bone marrow.

Light and electron microscopic observations of the spleen in the musk shrew, Suncus murinus.

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Light and electron microscopic observations of the spleen in the musk shrew, Suncus murinus.