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Biomedical subjects

M Tavassoli

Publications and source records attributed to M Tavassoli.

At least 235 records · Page 13Linked to original sources
PubMed1980

A novel stromal cell type in the rat marrow recognizable by its preferential uptake of lanthanum.

A novel stromal cell type is described in the rat bone marrow. It is distinguishable from other stromal cells (macrophages, reticular cells, etc.) by its preferential uptake of the electron dense tracer lanthanum nitrate, which can then serve as a marker for this cell type. In low concentration of lanthanum, this cell type is the only marrow cell that takes up the tracer. Other stromal cells do not take ip up even in high concentration. This novel stromal type is associated with both erythropoietic and granulopoietic areas of the marrow tissue. Its branching cytoplasm is very light in density and contains no characteristic cytoplasmic organelles. Its function is not yet known.

Animals↗
PubMed1979

Fusion-fission reorganization of membrane: a developing membrane model for thrombocytogenesis in megakaryocytes.

Freeze-fracture and thin-section electron microscopy indicate that a sequence of fusion-fission leads to reorganization of membranes and the demarcation of platelets within the cytoplasm of megakaryocyte. Invagination of the megakaryocyte plasma membrane leads to the formation of tubular structures within the cytoplasm of megakaryocytes. Fusion of these tubular membranes in the plane of their long axes is followed by fission in the perpendicular plane. This results in the formation of two flat membranes, forming plasma membranes of two adjacent platelets. A similar fusion-fission reorganization of membranes could mediate a wide variety of other biologic phenomena. These observations also indicate that megakaryocytes are located in the subendothelial compartment of the marrow with their projections penetrating the endothelium and reaching the lumen. This direct contact with the circulation may serve as a means of receiving information as to the requirements of the body for platelet production.

Animals↗
PubMed1979

Lymphoreticular fragments, the cellular debris of acute lymphosarcoma cell leukemia.

Lymphosarcoma cell leukemia cells have a propensity to fragment. In the following case, these fragments were initially interpreted by an electronic cell counter as platelets, thereby obscuring a true thrombocytopenic situation. These fragments may also resemble polychromatophilic red cells thus giving rise to the erroneous impression that a hemolytic process is accompanying this B cell leukemia.

Adult↗
PubMed1979

Retention of hemopoiesis in tail vertebrae of newborn rats.

In newborn rats, the marrow cavity of tail vertebrae is hemopoietic and contains no adipose tissue. The latter develops soon after birth to replace the hemopoietic tissue within the nonexpansile volume of the marrow cavity. By transposing the tail into the warmer environment of the abdomen, hemopoiesis was retained, and the development of adipose tissue was prevented in the transposed segment, when the operation was done in preweanling but not in adult animals. Systemic stimuli of erythropoiesis (phlebotomy, induced hemolysis) acted synergistically with the temperature increment to retain hemopoiesis. The findings support the concept that adipose cells in the yellow marrow are relatively stable and once developed, they are not readily mobilized. The findings may also explain the discrepancies in the results obtained by rat tail transposition.

Adipose Tissue↗
PubMed1979

Cytochemical diagnosis of acute myelomonocytic leukemia.

Blood and bone-marrow smears from adult patients with acute leukemias were stained for esterase reaction, consecutively with naphthol AS D-chloracetate (chloracetate esterase) followed by alpha naphthyl butyrate (nonspecific esterase). The two substrates were, respectively, granulocyte- and monocyte-specific. By this method three subgroups of acute nonlymphocytic leukemias could be distinguished. Leukemic cells may be positive for either chloracetate esterase or nonspecific esterases, and the authors believe these two subgroups represent "true" granulocytic and "pure" monocytic leukemias. In a third group, leukemic cells contained both esterases in the same cell, and it is believed this group may represent "true" myelomonocytic leukemias. In the majority of patients in this group, leukemia evolved from a preleukemic phase. When only Romanowsky-stained smears are used, the monocytoid feature and absolute elevated monocyte counts in acute granulocytic leukemia may lead to an erroneous diagnosis of the leukemia as acute myelomonocytic leukemia. This happened in five of the 13 cases in the study. The presence of granulocyte- and monocyte-specific esterases in a single cell supports the concept of a common origin of granulocytes and monocytes. The authors conclude that the combined esterase reaction can distinguish among acute granulocytic leukemia, acute monocytic leukemia, and acute myelomonocytic leukemia.

Bone Marrow Examination↗
PubMed1979

Junctional structures in haemopoiesis: a study of bone marrow using freeze-fracture and lanthanum impregnation techniques.

Intercellular regions of contact in the haemopoietic compartment of normal rat bone marrow were studied using freeze-fracture and lanthanum tracer techniques. Small adhering junctions (like desmosomes and their variants) were found between haemopoietic and stromal cells but tight, gap or septate junctions could not be identified. These findings are in agreement with the concept that extensive junctional structures may be inconsistent with orderly development of this transient cell system, preventing the delivery of mature cells into the circulation and resulting in ineffective haemopoiesis. Occasionally 'pinching off' of a portion of the cytoplasm of erythroid cells by stromal cells was seen, providing a means for intercellular communication. Structures similar to intercellular bridges responsible for direct intercellular communication were also seen.

Animals↗
PubMed1979

Absence of tight junctions in endothelium of marrow sinuses: possible significance for marrow cell egress.

The nature of contact between endothelial cells in rat marrow sinuses was studied. Colloidal lanthanum permeated freely into the interendothelial space. Moreover, using freeze-fracture technique, we failed to show junctional structures where these endothelial cells came into contact. With thin sectioning electron microscopy, we observed occasional submembranous densities but the interendothelial distance measured 20 nm and no membrane fusion was seen. Absence of tight junctions between endothelial cells of marrow sinuses may serve a function in marrow cell egress by permitting these cells to slide over each other, thereby changing the luminal size. Within the fixed volume of marrow, an increase in luminal size results in displacement of haemopoietic cells into the lumen.

Animals↗
PubMed1978

Studies on bone marrow histogenesis: morphometric and autoradiographic studies of regeneration marrow stroma in extramedullary autoimplants and after evacuation of marrow cavity.

The marrow cavity of the rat tibia was mechanically evacuated and autoimplanted to the subcutaneous tissue. The regenerative process which restored the integrity of marrow stroma and hemopoiesis, was morphometrically evaluated in whole mount of tibia. Following evacuation, the clot filled the cavity. The granulation tissue then appeared and expanded, penetrating and replacing the clot. The fibroblasts of the granulation tissue differentiated into osteoblasts forming osteoid bone. Within its interstices, the primordial marrow consisting of loose connective tissue and vascular sinuses appeared and hemopoiesis resumed. Expansion of hemopoiesis resulted in the resorption of bone and within three weeks the tibial cavity was restored to the pre-evacuation state. Autoradiography indicated that the labeling index was initially high in fibroblasts and osteoblasts but was subsequently reduced while it increased in osteocytes, cells of Haversian canals, stromal and hemopoietic cells of marrow. The finding is in disagreement with the view that the regenerative process originates from the Haversian canal. When the label was introduced on day 4 post-operatively, it subsequently appeared in osteocytes, cells of Haversian canal, stromal elements of the marrow, but not in the hemopoietic cells. This indicates complete dissociation of marrow stroma and hemopoietic stem cell.

Animals↗
PubMed1978

Methods for establishing a working immunoradiometric assay for serum ferritin.

The two-site immunoradiometric assay for measurement of serum ferritin requires purified human ferritin and an avid high-titer antihuman ferritin antibody. Some of the antibody is radioiodinated following purification by immunoadsorption. All methods for preparation of these materials for the assay are described in minute detail. Performance of the assay itself and calculation of results are also described, and attention is drawn to several potential pitfalls. Adherence to these detailed descriptions will help to eliminate difficulties experienced by centers wishing to establish their own working serum ferritin assay.

Adolescent↗
PubMed1978

Ultrastructural analysis of haemopoiesis in W/Wv anaemic mice.

This study is an ultrastructural analysis of haemopoiesis in W/Wv anaemic mice in whom the anaemia is caused by a defect in the haemopoietic stem cell. Cellularity of marrow is normal but there is an increase in the proportion of less mature cells suggesting a delay in maturation. In addition, heterochromatin constitutes a higher proportion than normal of the nucleus in most stages of maturation suggesting a defect in DNA activation. The findings suggest that in this strain not only the differentiation of the haemopoietic stem cell but also the maturation of the committed cell is defective.

Anemia, Macrocytic↗
PubMed1978

Cytochemistry of marrow and extramedullary adipocytes in monolayer cultures.

The behavior of isolated, disaggregated white adipose cells obtained from marrow and extramedullar sites in the rabbit was compared in monolayer cultures. Both cell types transform within 2 weeks into fibroblast-like cells which can be maintained in subcultures. Both in freshly isolated state and in fibroblast-like state the marrow adipocyte contains esterase activities reacting with naphthol AS acetate and D-chloracetate. These activites are not present in extramedullary cells. In addition, alpha-naphthyl butyrate-reacting esterase, present in both cell types, is fluoride-resistant in marrow adipocytes but labile in extramedullar cells. These differences are consistent with heterogeneity of white adipose tissue and suggest different potentials for marrow and extramedullary adipocytes.

Adipose Tissue↗
PubMed1978

Red cell delivery and the function of the marrow-blood barrier: a review.

The last step in mammalian erythropoiesis consists of nuclear elimination and delivery of the non-nucleated red cell (reticulocyte) into the circulation. This is accomplished by migration of reticulocytes through the wall of the vascular sinuses which forms an anatomical barrier between the hemopoietic compartment and the circulation. This barrier is instrumental in a complicated mechanism to ensure orderly traffic of new cells in response to the requirement of the organism. Thus, it exerts a control over which cells will migrate into the vascular lumen and when they will do so. Defective red cells and nucleated red cells are prevented from migration; even normal reticulocytes may be temporarily held back if their presence in the circulation would exceed the requirement of the body. Little is known about how this barrier operates to control the red cell delivery. Literature relevant to this subject has been reviewed and an attempt is made to formulate some basic questions in this area.

Animals↗