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Biomedical subjects

D J Allen

Publications and source records attributed to D J Allen.

At least 55 records · Page 3Linked to original sources
PubMed1986

Effects of chrysotile asbestos on coho salmon and green sunfish: evidence of behavioral and pathological stress.

The effects of chrysotile asbestos on larval coho salmon (Oncorhynchus kisutch) and juvenile green sunfish (Lepomis cyanellus) were investigated at levels approximating those reported in the Great Lakes basin (10(6) fibers/liter). Behavioral stress effects, such as loss of rheotaxic position and balance, were observed in salmon exposed at 3.0 X 10(6) fibers/liter and in sunfish exposed at 1.5 and 3.0 X 10(6) fibers/liter. Coho larvae at 1.5 X 10(6) fibers/liter were significantly more susceptible to an anesthetic stress test, becoming ataxic and losing equilibrium faster than control cohorts (P less than 0.001). Two of 106 larvae exposed at 3.0 X 10(6) fibers/liter developed tumorous swellings and three additional fish developed coelomic distentions. Cytological examination of ventral epidermal tissue revealed cellular histolysis, and evidence by transmission electron microscopy confirmed the presence of asbestos in the salmon larvae. Distortion of the lateral line region in asbestos-treated coho salmon was linked to behavioral and orientational aberrations. Differential mortality was not observed between control and treated groups of either test species.

Animals↗
PubMed1986

Scanning and transmission electron microscopic study of recovered porcine aortic valved conduits.

Four explanted porcine aortic valved conduits were examined using scanning and transmission electron microscopy. Sources of obstruction such as neointima or "peel" and calcification were observed. In one sample the neointima was found to possess an unusually large expanse of squamous cells partially lining the luminal surface. This lining much resembled a normal endothelium, which is not an expected feature of neointima. Cells, presumably of host origin, were noted upon the leaflet surfaces. They did not seem as well organized as those found on the neointima. Calcification did not seem greatly advanced but was clearly apparent. Certain treatments proposed by others to curtail calcification are discussed and amended herein. SEM examination of three of these conduits provided good evidence of lining cells on only the inflow surface of the leaflet. The fourth conduit, however, showed cells on both inflow and outflow surfaces. These cells possessed certain characteristics of cells from leaflets of the other three conduits, but questions remain as to the precise identification of all of these lining cells. TEM examination provided cytological evidence of macrophage-like cells lining the inflow surface of a leaflet.

Adolescent↗
PubMed1986

Comparative electron microscopic study of bovine, porcine and human parietal pericardium, as materials for cardiac valve bioprostheses.

Light, scanning and transmission electron microscopy were used in the comparison of bovine, porcine and human parietal pericardium. Bovine pericardium is widely used for heart valve bioprosthesis, is thicker than the other two, and has more coarse connective tissue fiber components, whereas porcine pericardium possesses relatively larger quantities of fat cells in regular layers. Human tissue is thinner than either the bovine or porcine parietal pericardium and its mesothelium seems less delicate. The human tissue, being thinner, may provide a source of materials for valves with significant hemodynamic characteristics. Such material might be used to produce small diameter valves directed towards younger patients. Though the literature does not mention its usage, porcine pericardium is of intermediate thickness and it too may serve in the future as a construction material for valve bioprostheses.

Adipose Tissue↗
PubMed1985

Permeability of external gill filaments in the embryonic shark. Electron microscopic observations using horseradish peroxidase as a macromolecular tracer.

External gill filaments of sharks are purely transient embryonic structures. They contain a single vascular sinusoidal loop that is continuous with the afferent and efferent branchial arteries. Each filament is comprised of a squamous epithelial bilayer that rests upon a prominent basal lamina. A collagenous stroma separates the epithelium from the underlying endothelium. The epithelium, from an embryo 4.5 cm in total length, is characterized by microvilli with smooth walled vesicles at their bases, a luminal glycocalyx, prominent tubular and vesicular elements, rough endoplasmic reticulum, a Golgi complex, a flattened nucleus, coated vesicles, lipid-like inclusion bodies and sparse cytoplasmic fibrils. Adjacent epithelial cells are joined by a zonula occludens, a zonula adherens and up to five maculae adherentes. The endothelium possesses mitochondria, rough endoplasmic reticulum, a Golgi complex, coated vesicles and many micropinocytotic vesicles on both the adluminal and abluminal surfaces. The endothelium has no basal lamina and is not associated with smooth muscle. After exposure to horseradish peroxidase (HRP) for 10 min, reaction product nearly occludes the cytoplasm of some surface epithelial cells. The deeper epithelial cells have reaction product in smooth walled vesicular and tubular elements. Reaction product is also present in smooth walled endothelial vesicles. Gill filaments from a 10 cm embryo show marked changes from earlier stages. In the epithelial cells, there is an increase in the number of cytoplasmic filaments and the formation of a dense terminal web. Fewer vesicles, tubules, rough endoplasmic reticulum and mitochondria, and a less elaborate Golgi complex characterize the epithelium. The endothelium remains unchanged. The amount of collagen increases and fibroblasts are observed in the stroma. These modifications contribute to the strength of the filaments and allow the gills to withstand increased abrasion by the developing skin denticles. These experiments establish the capability of external gill filaments to take up a macromolecular tracer in the form of horseradish peroxidase. Later in development, the yolk sac of R. terraenovae becomes modified as a yolk sac placenta which functions both in respiration and hematrophic nutrition. In viviparous sharks, the uterus elaborates nutrient-rich secretions. External gill filaments may thus serve as a nutrient absorptive membrane before the establishment of the yolk sac placenta as well as perform its respiratory function.

Animals↗
PubMed1984

Morphological and histochemical studies on the parotid gland of Praomys (Mastomys) natalensis.

The parotid gland of Praomys (Mastomys) natalensis follows the same anatomical pattern of Rodentia since no peculiar morphological and histochemical features were found in the present study that differentiate it from homologous glands in other rodents. It consists of serous secreting components and intralobular ducts that demonstrate no sexual dimorphism. Histochemical studies reveal that the glandular cells of the Praomys' parotid gland contain no acid mucosubstance, but that material of a neutral glycoprotein nature can be found in the secreting cells of acini, epithelium of the ducts, and the ductal lumina.

Animals↗
PubMed1984

Microscopic study of normal parietal pericardium and unimplanted Puig-Zerbini pericardial valvular heterografts.

This investigation used light microscopy and transmission and scanning electron microscopy to study native human and bovine parietal pericardium, glutaraldehyde-fixed bovine pericardial patch-grafts, and bovine pericardial cusps of unimplanted Incor or Puig - Zerbini heart valves. The primary objective was to obtain a data base for the future evaluation of postimplantation structural alteration in this valve and in other cardiac valvular bioprostheses constructed of pericardium. The mesothelial cell layer in normal pericardium was best preserved in the bovine tissue. In both bovine patch-grafts and Puig - Zerbini valvular cusps, the serosal surface usually was completely devoid of mesothelial cells and revealed an underlying, finely fibrillar basal lamina. The fibrosa varied in thickness and organization, both within and between the two species, but similar nervous, vascular, and connective tissue components were observed in each. The epipericardial surface was smoother, had fewer elastic fibers, and possessed more surface cells in the human tissue than in the bovine tissue. No evidence of significant tissue degeneration or remodeling was noted in either the stored patch-grafts or heart valves when compared with control bovine and human pericardial tissue layers.

Animals↗
PubMed1983

Antifertility effects of tetradecyl sodium sulphate in rabbits.

Acrosin and acrosomal hyaluronidase were inhibited by tetradecyl sodium sulphate (TDSS) in vitro at concentrations of less than 10(-4) M. TDSS prevented the removal in vitro of the cumulus oophorus by testicular hyaluronidase and the zona pellucida by acrosin. TDSS had a contraceptive effect in rabbits when administered intravaginally before coitus or released at levels of 1-3 micrograms/day from intrauterine silicone rubber devices.

Acrosin↗
PubMed1983

Morphological alterations in dura mater encephali used as ventricular wall grafts in the canine heart.

Structural changes within homologous dura mater patch-grafts surgically implanted in the right ventricular wall of the heart were studied in nine adult dogs utilizing light microscopy and transmission and scanning electron microscopy. Physical examination of the dogs after surgery presented no clinical signs of abnormalities caused by either the surgery or the nature of the graft. After one week of implantation, a fibrous organization extending from the wound margins over the entire graft greatly increased its thickness. In addition, it was observed that (1) an increase in cellularity, vascularity and connective tissue elements occurred on the external surface of the patch-graft, (2) these same changes occurred regardless of which surface (periosteal or arachnoidal) was used as the external or pericardial surface, (3) the graft core underwent a transition from a relatively acellular and avascular connective tissue structure into one that was heavily infiltrated by a variety of cellular elements and new blood vessels, and (4) these morphological changes were interpreted as an attempt to incorporate the graft into the host tissue, resulting in an increase in both viability and stability of the graft. These findings indicate that homologous dura mater is a suitable material for use in the surgical repair of the cardiac wall.

Animals↗
PubMed1983

Study of the periosteal and arachnoidal aspects of dura mater implanted surgically in the ventricular wall of the canine heart.

After surgical removal of a portion of the cardiac wall, homologous dura mater cardiac grafts were sutured to the margins of the incision in the sternocostal wall of the right ventricle of the canine heart and recovered after 1, 4, 6 and 8 weeks of implantation. Representative tissue specimens were processed for and studied by means of SEM and TEM. The primary objectives were to study morphological changes in the dura mater grafts used to repair the lesions or defects in the cardiac wall and to compare alterations in the periosteal and arachnoidal aspects of the dura mater grafts after being implanted for varying periods of time. After one week of implantation, an amorphous layer of fibrin was deposited on or near the luminal surface of the original dura mater grafts. At four weeks of grafts implantation, a 'remodeling' process was apparent below the luminal surface of the graft. Although a large accumulation of fibrin was still present at this time, there was also an increase in the number of cellular and fibrillar components within the implant. Large numbers of macrophages and active fibroblasts were visible at this time along with new collagen. At the sixth week of implantation, an abundance of active fibroblasts, the presence of normal collagen and a darkly staining material interpreted as recently synthesized connective tissue components, fibrin deposits and/or degenerating collagen were also observed. Phagocytosis of the remaining fibrin was noted during this period indicating a continuation of the remodeling process at the luminal surface. Finally, after eight weeks of implantation, it was revealed that the original densely woven and relatively acellular graft had become infiltrated with various blood cells and vascular channels.

Animals↗
PubMed1982

Evidence of remodeling in dura mater cardiac valves.

Subcellular changes in 12 dura mater cardiac valves (in the mitral or aortic position) surgically removed after 23 to 108 months of implantation owing to calcification, rupture, or endocarditis show signs of a remodeling process. Significant morphologic changes in the connective tissue fiber matrices and cell populations were noted in the recovered valvular leaflets. Macrophages were found within electronlucent (cleared-out) areas, and they seemed to play an essential role in the remodeling process by ingesting and digesting selected connective tissue components. Fibroblasts found within these "rebuilding" areas in the dura mater tissue possessed small cytoplasmic vesicles (65 nm in diameter) being extruded from the cell. Evidence of early collagen formation was also found in association with both peripheral filaments and peripheral condensations, as well as within the connective tissue matrices surrounding the cellular elements, where electron dense amorphous material was observed. In conclusion, the long-term durability of dura mater bioprosthetic cardiac valves may be directly related to (1) glycerin stabilization and preservation of the collagen fibers, (2) the viability of the fibroblasts and macrophages within the implanted valves, and (3) the unique morphology and fine structure of the double-layered dura mater encephali. We hypothesize that the fibroblasts or myofibroblast-like cells found within the implanted leaflets, no matter what their origin, are capable of giving form and organization to the early developing connective tissue.

Adolescent↗
PubMed1981

Reactivation of Epstein-Barr virus-specific cytotoxic T cells by in vitro stimulation with the autologous lymphoblastoid cell line.

Unfractionated mononuclear (UM) cells and T cells freshly prepared from the blood of adult donors were co-cultivated in microtest plate wells with progressively lower numbers of cells from the autologous EB-virus-transformed B-cell line. The fresh cells present in co-cultures from EB virus antibody-negative (seronegative) donors regularly facilitated autologous cell line outgrowth, monitored after 4 weeks, whereas outgrowth was markedly inhibited in the corresponding co-cultures from seropositive donors. Larger-scale co-cultures, set up at a ratio of 80-100 fresh UM cells to one autologous virus-transformed B cell, were harvested after 8 to 12 days and the T-cell subpopulation was examined for cytotoxicity both by growth inhibition and by chromium release assays. Cytotoxic T cells were generated exclusively in seropositive donor co-cultures and were strongly active against the autologous virus-transformed cell line without affecting either autologous uninfected B cells or any of a range of EB virus genome-negative target cell lines chosen as sensitive indicators of non-specific cytotoxicity. Recognition of allogeneic EB-virus-transformed cells was restricted to those whose HLA-A and/or B and/or B and/or C antigen expression matched that of the effector cells themselves;; moreover target cell lysis was specifically inhibited in the presence of monoclonal antibodies binding to these HLA antigens. The results indicate that EB-virus-specific HLA-restricted memory T cells, present in the blood of previously-infected individuals, can be reactivated in vitro using the established autologous virus-transformed cell line as a stimulus. THe reactivated cytotoxic cells appear to recognize a virus-induced lymphocyte-detected membrane antigen, LYD-MA, analogous to that first invoked to explain the cytotoxic response to primary EB virus infection observed during infectious monoucleosis.

Adult↗