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Biomedical subjects

T G Burrage

Publications and source records attributed to T G Burrage.

32 records · Page 2Linked to original sources
PubMed1986

Hormonal induction of secretory granules in a pituitary tumor cell line.

GH4C1 cells are a rat pituitary tumor cell strain that secretes PRL and GH but contains almost no secretory granules. Treatment of GH4C1 cells with a combination of estradiol (1 nM), insulin (300 nM), and epidermal growth factor (10 nM) increased the cellular content of PRL by more than 30-fold above control levels but only increased PRL accumulation in the medium 6-fold. To determine whether the increase in intracellular PRL was accompanied by an increase in secretory granules, we compared the numbers of granules in ultrathin sections from untreated GH4C1 cells and from cells treated with the combined hormone regimen and found a nearly 50-fold increase in granule number. Only 75% of the granules stained for PRL by the protein-A gold technique; the other 25% stained for neither PRL nor GH. The occasional granules found in untreated GH4C1 cells stained for PRL. The data demonstrate that the number of granules in GH4C1 cells can be regulated by hormone treatment and that the increase in intracellular PRL is found in storage granules.

Animals↗
PubMed1985

Rabies virus binding at neuromuscular junctions.

Morphological, immunocytochemical, biochemical, and immunological techniques have been used to describe rabies virus binding to a sub-cellular unit and molecular complex at the neuromuscular junction (NMJ). Early after infection in vivo, virus antigen and virus particles were found by immunofluorescence, electron microscopy and immunoelectron microscopy in regions of high density acetylcholine receptors (AChR) at NMJs. One monoclonal antibody (alpha-Mab) to the alpha subunit of the AChR blocked attachment of radio-labeled rabies virus to cultured muscle cells bearing high density patches of AChR. A sub-cellular structure, resembling an array of AChR monomers, bound both rabies virus antigens and alpha-Mab. By immunoblotting with electrophoretically transferred motor endplate proteins, rabies virus proteins and alpha-Mab bound to two proteins of 43 000 and 110 000 daltons. A rabies virus glycoprotein antibody detected virus antigen bound to the 110 000 dalton protein. An auto-immune (anti-idiotypic) response followed immunization of mice with rabies virus glycoprotein antigen; the antibody was directed to the 110 000 dalton protein. This auto-antibody altered the kinetics of neutralization by rabies virus antibody and induced the formation of rabies virus antibody after inoculation of mice. These results define, at the neuromuscular junction, a rabies virus receptor which may be part of the acetylcholine receptor complex.

Animals↗
PubMed1985

Cysteamine causes reduction of prolactin monomers followed by aggregation in the rat pituitary gland.

Storage forms of PRL were studied in control and cysteamine-treated cultures of estradiol-induced tumors in Fischer 344 rats and in secretory granules isolated from these tumors to further investigate the mechanism of action of cysteamine on PRL. The two major bands visible when protein is stained after electrophoresis of isolated granules migrate to the position of PRL and GH monomers. Electrophoresis under reducing conditions changes the position, but does not noticeably increase the amount of each band. [3H]PRL in cells labeled for 8 h with [3H]leucine also exists predominantly as monomer. Immunoreactivity of PRL in cell lysates or isolated granules is not affected by incubation with reducing agents beta-mercaptoethanol or glutathione at concentrations up to 5 mM, but cysteamine decreases PRL immunoreactivity in isolated granules at concentrations of 3 mM and higher. Electrophoresis of isolated granules after incubation with 25 mM cysteamine for 1 h demonstrates that cysteamine converts PRL to the reduced form. After 4 h, or after dilution of the granules before solubilization, the amount of reduced monomer is decreased, and larger molecular weight species appear. The reduced monomer can be recovered by electrophoresis under reducing conditions. The fully immunoreactive form can be recovered by incubation for 1 h with dithiothreitol at concentrations of 0.3 mM-3 mM. These data indicate that: PRL exists predominantly in monomeric form in the rat pituitary gland, and cysteamine reduces PRL, and formation of disulfide-linked aggregates of PRL occurs subsequently under some conditions.

Animals↗
PubMed1984

Rapid infection of salivary glands in Culiseta melanura with eastern equine encephalitis virus: an electron microscopic study.

Transmission electron microscopy was used to determine if eastern equine encephalitis (EEE) virus infects and replicates in the salivary glands of Culiseta melanura after 3 days of extrinsic incubation (EI). The Cs. melanura studied were from a colony strain, were orally infected, and had EI periods of 55-69 hours. Both naked nucleocapsids and enveloped virions were present in aggregates, suggestive of viral replication, within salivary gland acinar cells. Nucleocapsids were present in the cytoplasm below the plasma membrane that lined apical cavities. Enveloped virions occurred in the salivary matrix within apical cavities. Some nucleocapsids appeared to be budding through the plasma membrane around apical cavities and maturing into infectious virions. These results suggest that Cs. melanura is capable of biological transmission of EEE virus after less than or equal to 3 days of EI.

Alphavirus↗
PubMed1983

Immunoelectron microscopic localization of rabies virus antigen in central nervous system and peripheral tissue using low-temperature embedding and protein A-gold.

A protein A-gold technique was used in conjunction with low temperature embedding to visualize ultrastructurally mature virions and sites of viral replication in the brains of rabies virus-infected mice after peripheral inoculation of virus. The association of viral profiles and gold particles with synaptic membranes, microtubules and rough endoplasmic reticulum suggested a mechanism of rabies virus transport within the central nervous system. Early interactions of inflammatory cells with the virus inoculum were characterized by phagocytosis by non-degranulating neutrophils and mononuclear cells.

Animals↗
PubMed1982

Is the acetylcholine receptor a rabies virus receptor?

Rabies virus was found on mouse diaphragms and on cultured chick myotubes in a distribution coinciding with that of the acetylcholine receptor. Treatment of the myotubes with alpha-bungarotoxin and d-tubocurarine before the addition of the virus reduced the number of myotubes that became infected with rabies virus. These findings together suggest that acetylcholine receptors may serve as receptors for rabies virus. The binding of virus to acetylcholine receptors, which are present in high density at the neuromuscular junction, would provide a mechanism whereby the virus could be locally concentrated at sites in proximity to peripheral nerves facilitating subsequent uptake and transfer to the central nervous system.

Acetylcholine↗
PubMed1982

Distribution of cell surface saccharides and fibronectin on cultured chick myotubes: relationship to acetylcholine receptor clusters.

This study examines the distribution of glycoconjugates on the surface of cultured chick myotubes with a battery of lectins labeled with ferritin or horseradish peroxidase. In addition, the distribution of a specific glycoprotein, fibronectin, is investigated by immunocytochemistry. Particular attention is paid to the localization of these substances in specialized patches on the cell surface previously shown to contain a high density of acetylcholine receptors as demonstrated with horseradish peroxidase labeled alpha-bungarotoxin. The specialized patches are found to bind a greater amount of concanavalin A, ricin agglutinin I, and soy bean agglutinin and a lesser amount of wheat germ agglutinin than the general myotube surface. Limulus lectin is distributed over the entire cell surface while other lectins do not bind to any sites. The surface patches contain a high density of acetylcholine receptors as shown by double labeling with ferritin-labeled lectins and peroxidase labeled alpha-bungarotoxin. Fibronectin occurs in high concentration at the surface patches and is present over other regions of the cell surface as well. These results reveal differential patterns of distribution of glycoconjugates and fibronectin over the myotube surface. These regional differences may be related to the distribution of acetylcholine receptors or to recognition and attachment by the innervating nerve.

Animals↗
PubMed1979

Formation of sarcomeres in the embryonic heart of the lobster.

Cardiomyoblasts in the myocardium of embryonic lobsters at 3-4 weeks and 6 months of development were examined with the transmission electron microscope in order to describe the events in the formation of sarcomeres in a neurogenic cardiac system. Thick and thin myofilaments appear first in the cell periphery near the sarcolemma. They align in parallel in a sequential fashion to form consecutive sarcomeric units. Well-defined A and I bands appear before any semblance of a Z line is present. The initial sarcomere is anchored to the sarcolemma by the insertion of thin myofilaments into a region of electron dense material associated intimately with the sarcolemma. Myofibrils grow outward in several planes away from the electron-dense regions of membrane that serve as focal points for myofibril formation.

Animals↗
PubMedDate not supplied

African horsesickness: pathogenesis and immunity.

African horsesickness (AHS) is a serious, non-contagious disease of horses and other solipeds caused by an arthropod-borne orbivirus of the family Reoviridae. In horses, AHS causes three distinct clinicopathologic syndromes, the pulmonary, cardiac and fever forms of the disease. Recent work has shown that the primary determinant of the form of disease expressed by naive horses is the virulence of the virus inoculum. Horses which recover from AHS exhibit solid humoral immunity against homologous challenge. Protective antibodies appear to be directed towards neutralizing epitopes on AHS virus VP2. The relationship of neutralization to protection and vaccination is discussed.

African Horse Sickness↗
PubMedDate not supplied

The acetylcholine receptor as a cellular receptor for rabies virus.

Characterization of specific host cell receptors for enveloped viruses is a difficult problem because many enveloped viruses bind to a variety of substrates which are not obviously related to tissue tropisms in the intact host. Viruses with a limited cellular tropism in infected animals present useful models for studying the mechanisms by which virus attachment regulates the disease process. Rabies virus is a rhabdovirus which exhibits a marked neuronotropism in infected animals. Limited data suggest that spread occurs by transsynaptic transfer of virus. The results of recent experiments at Yale suggest that viral antigen is localized very soon after injection at neuromuscular junctions, the motor nerve endings on muscle tissue. On cultured muscle cells, similar co-localization with the acetylcholine receptor is seen both before and after virus multiplication. Pretreatment of these cells with some ligands of the acetylcholine receptor results in reduced viral infection. These findings suggest that a neurotransmitter receptor or a closely associated molecule may serve as a specific host cell receptor for rabies virus and thus may be responsible for the tissue tropism exhibited by this virus. In addition to clarifying aspects of rabies virus pathogenesis, these studies have broad implications regarding the mechanism by which other viruses or viral immunizations might mediate autoimmune diseases such as myasthenia gravis.

Adhesiveness↗