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Biomedical subjects

M Noble

Publications and source records attributed to M Noble.

At least 109 records · Page 6Linked to original sources
PubMed1988

The quantification of synthetic corticosteroids using isotope dilution gas chromatography negative chemical ionization mass spectrometry.

Prednisolone, dexamethasone and betamethasone were labelled with deuterium via a simple synthetic procedure and used as internal standards in the gas chromatographic/mass spectrometric analysis of the corresponding undeuterated compounds. The mass spectrometer was used in the negative chemical ionization mode, which gave fragmentation of the methoxime trimethylsilyl ether derivatives favourable for their quantification. The method was applicable to the quantification of synthetic corticosteroids contained in human aqueous humour in the 0.1-10-ng range.

Absorption↗
PubMed1988

The differentiation of O-2A progenitor cells into oligodendrocytes is associated with a loss of inducibility of Ia antigens.

Current data suggest that some astrocytes, one of the 3 main types of macroglia in the central nervous system (CNS), can be induced by interferon-gamma (IFN-gamma) to express major histocompatibility complex class II antigens (immune-associated or Ia) and present antigen to T lymphocytes. In contrast, oligodendrocytes, another type of macroglia, cannot be induced to express Ia. The astrocytes which have been shown to express Ia are from a particular glial lineage and are called type-1 astrocytes. The oligodendrocyte-type-2 astrocyte (O-2A) lineage, which gives rise to oligodendrocytes, also gives rise to a second class of astrocytes called type-2 astrocytes and the ability of type-2 astrocytes or the common O-2A progenitor cell to express Ia is not known. We have now found that both type-2 astrocytes and O-2A progenitor cells can be induced to express Ia by IFN-gamma but Ia expression is not induced in oligodendrocytes in parallel cultures. Thus, it appears that differentiation of O-2A progenitor cells into oligodendrocytes is specifically associated with a loss of inducibility of Ia. This apparent loss of the capacity for Ia expression, and presumably antigen presentation, in oligodendrocytes (the cells which produce myelin in the CNS) is of particular interest in view of the ability of immunization of myelin components to produce autoimmune-mediated paralytic disease.

Age Factors↗
PubMed1988

Ras-mediated cell cycle arrest is altered by nuclear oncogenes to induce Schwann cell transformation.

The cellular responses to ras and nuclear oncogenes were investigated in purified populations of rat Schwann cells. v-Ha-ras and SV40 large T cooperate to transform Schwann cells, inducing growth in soft agar and allowing proliferation in the absence of added mitogens. Expression of large T alone reduces their growth factor requirements but is insufficient to induce full transformation. In contrast, expression of v-Ha-ras leads to proliferation arrest in Schwann cells expressing a temperature-sensitive mutant of large T at the restrictive temperature. Cells arrest in either the G1 or G2/M phases of the cell cycle, and can re-enter cell division at the permissive temperature even after prolonged periods at the restrictive conditions. Oncogenic ras proteins also inhibit DNA synthesis when microinjected into Schwann cells. Adenovirus E1a and c-myc oncogenes behave similarly to SV40 large T. They cooperate with Ha-ras oncogenes to transform Schwann cells, and prevent ras-induced growth arrest. Thus nuclear oncogenes fundamentally alter the response of Schwann cells to a ras oncogene from cell cycle arrest to transformation.

Animals↗
PubMed1988

Abetalipoproteinaemia in adults: role of vitamin therapy.

The retinal and neurological complications of abetalipoproteinaemia may be preventable by replacing vitamins A and E from an early age, but their role in adult presentations is less clear. Two adult females with abetalipoproteinaemia have received 8 and 10 years respectively of replacement therapy with vitamins A, E and linoleic acid. In Case 1, visual function improved objectively on commencing therapy but has subsequently deteriorated and her neuropathy has slowly progressed. The rate of progression of neurological impairment in Case 2 was slowed but not halted by therapy, and her severe visual disturbance was unaffected. Replacement by fat soluble vitamins has only a limited role in the management of abetalipoproteinaemia once irreversible neurological/retinal damage has occurred.

Abetalipoproteinemia↗
PubMed1985

In vitro studies on the comparative sensitivities of cells of the central nervous system to diphtheria toxin.

We have used tissue culture techniques and cell type-specific antibodies to compare the sensitivity of the various cell types of the white matter tracts of the rat central nervous system to in vitro exposure to diphtheria toxin (DTx). We have found that oligodendrocytes and Type 2 astrocytes (Raff et al. 1983a), which at least in the rat optic nerve, appear to be derived from a single bipotential progenitor cell (Raff et al. 1983b), are both more susceptible to DTx than are either Type 1 astrocytes or spinal neurones. The loss of oligodendrocytes and Type 2 astrocytes caused by exposure to DTx in vitro appeared to be irreversible. Even when cultures were maintained for a month following initial treatment with DTx, these glial populations were not reestablished, suggesting that precursors for these macroglial cell types were as sensitive to the effects of DTx as were the oligodendrocytes and Type 2 astrocytes themselves. Our results are discussed in the light of the failure of diphtheritic lesions to remyelinate in vivo.

Animals↗
PubMed1984

The growth of olfactory neurons in short-term cultures of rat olfactory epithelium.

We have found that purified astrocytes will support the growth of olfactory epithelial neurons ( OENs ) in vitro. Candidate OENs were visible by light microscopy within one day after plating of dissociated cells from neonatal rat ethmoturbinates . Electron microscopy showed that OENs expressed the unique ultrastructural features which characterize these cells in situ, showing that regulation of neuronal morphology and ultrastructure can function independently of contact with other cells of the appropriate tissue. Characteristics of the cultures are such that this in vitro system would be useful in electrophysiological investigations of the chemosensory olfactory neurons.

Animals↗
PubMed1984

Purified astrocytes promote the in vitro division of a bipotential glial progenitor cell.

Optic nerves of neonatal rats contain a bipotential glial progenitor cell which can be induced by tissue culture conditions to differentiate into either an oligodendrocyte (the myelin-forming cell of the CNS) or a type 2 astrocyte (an astrocyte population found only in the myelinated tracts of the CNS). In our previous studies most oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells differentiated within 3 days in vitro with relatively little division of the progenitors or their differentiated progeny. We have now found that the O-2A progenitors are stimulated to divide in culture by purified populations of type 1 astrocytes, another glial cell-type found in the rat optic nerve. This cell-cell interaction appears to be mediated by a soluble factor(s) and results in the production of large numbers of both progenitor cells and oligodendrocytes. As type 1 astrocytes are the major glial cell-type in the optic nerve when oligodendrocytes first begin to be produced in large numbers in vivo, our results suggest that this astrocyte subpopulation may play an important role in expanding the oligodendrocyte population during normal development.

Animals↗
PubMed1984

Long-term follow-up of intraocular lens implants: the first 127 compared with the latest 100 of the same style in a span of 9 years.

The long-term follow up of the first 127 patients (127 eyes) treated by one surgeon with cataract extraction and Federov I lens implantation is reported. The proportion of patients achieving visual acuity of 6/12 or better had decreased since the one year follow-up. Corneal oedema was the most serious long-term complication. This group of patients is compared with the latest 100 patients (100 eyes) operated on by the same surgeon using the same type of implant. There was a reduction of some operative complications, and improvement in surgical techniques had resulted in a lower sample endothelial cell loss at one month.

Aged↗
PubMed1984

Glia are a unique substrate for the in vitro growth of central nervous system neurons.

We have examined the consequences of surface interactions with glial and nonglial cells on the in vitro growth of CNS neurons. When cerebellar or spinal cord cells were plated onto monolayers highly enriched in cortical astrocytes or sciatic nerve Schwann cells, neurons generally grew as single cells and showed relatively little tendency to aggregate. Similarly, neurites showed little tendency to fasciculate. In contrast, when plated onto fibroblast, heart muscle-fibroblast, or astrocyte-free meningeal monolayers, neurons rapidly aggregated, and neurite outgrowth was primarily in large fascicles. There were no glia detectable in the majority of aggregates or fascicles, suggesting that aggregation and fasciculation were due to interactions between neurons. Neurite outgrowth over 24 hr was also greater on astrocytes than on nonglia. Whether or not aggregation and fasciculation occurred was due to surface properties of the glial and nonglial cells. When neurons were added to astrocyte and nonglial monolayers growing in medium conditioned by a large excess of co-cultured nonglia or astrocytes, respectively, the pattern of neuronal growth was determined by the type of monolayer with which the neurons were in contact. Moreover, the initial growth of neurons on heat-killed astrocytes was indistinguishable from growth on living astrocytes. The pattern of neuronal growth on these different monolayers suggests that neurons are more adherent to glia than to other neurons but are more adherent to other neurons than to nonglia. Such an adherence hierarchy could explain the consistent finding of an apposition of neurons to glial surfaces during neuronal migration and axon outgrowth. Our findings also suggest that the interaction of axons with the non-neuronal milieu through which they grow may play an important role in regulating fasciculation, a process which has generally been treated as due primarily to axon-axon interactions.

Animals↗
PubMed1983

Two types of astrocytes in cultures of developing rat white matter: differences in morphology, surface gangliosides, and growth characteristics.

Two types of glial fibrillary acidic protein-positive (GFAP+) astrocytes were found in cultures of developing rat optic nerve. Type 1 astrocytes had a fibroblast-like morphology, did not bind tetanus toxin or the monoclonal antibody A2B5 (both of which bind to specific polysialogangliosides), and were stimulated to divide by an extract of bovine pituitary and by epidermal growth factor (EGF). Type 2 astrocytes had a neuron-like morphology, bound tetanus toxin and A2B5 antibody, and were not stimulated to divide by bovine pituitary extract or by EGF. Although both types of astrocytes were present in cultures of white matter, only type 1 astrocytes were found in cultures of gray matter. Astrocytes did not convert from one type to the other in culture: while many type 1 astrocytes adopted a neuron-like morphology when exposed to dibutyryl cyclic adenosine 3':5'-monophosphate, or pituitary or brain extracts, especially in serum-free medium, such morphologically altered cells did not bind tetanus toxin or A2B5 antibody. Although small numbers of tetanus toxin-binding, A2B5+, GFAP+ cells were present in suspensions of freshly dissected, neonatal optic nerves, most of the type 2 astrocytes in cultures of such optic nerves developed from tetanus toxin-binding, A2B5+, GFAP- cells, which were induced to express GFAP by the culture conditions. Since type 2 astrocytes have a neuron-like morphology and bind tetanus toxin and A2B5 antibody, these ligands cannot be used on their own as neuron-specific markers in central nervous system cultures.

Animals↗
PubMed1983

Latex agglutination test to identify coagulase, clumping factor and protein A produced by staphylococci.

Since a rapid latex agglutination method for identifying Staphylococcus aureus has recently been described, we attempted to identify which factors in staphylococci produce a positive reaction so as to indicate the possible applications and limitations of the test. Latex particles prepared with human plasma (latex-plasma), immune serum globulin (ISG) (latex-ISG) or bovine fibrinogen (latex-fibrinogen) were evaluated. Purified protein A or staphylococcal colonies possessing protein A caused latex-ISG and latex-plasma to agglutinate. Colonies which had clumping factor (CF) caused latex-fibrinogen and latex-plasma to agglutinate. A factor, with molecular weight and physical properties identical to staphylococcal coagulase, present in the supernatant of overnight broth inoculated with S. aureus caused latex-fibrinogen and latex-plasma to agglutinate but not latex-ISG. Thus, when latex particles are prepared using plasma, the preparation appears to identify coagulase, CF and protein A.

Coagulase↗
PubMed1982

Development of oligodendrocytes and Schwann cells studied with a monoclonal antibody against galactocerebroside.

We have generated a hybridoma cell line secreting a monoclonal antibody that specifically binds to the surfaces of oligodendrocytes and Schwann cells, the cells involved in myelin formation in the central and peripheral nervous systems, respectively. Binding studies using purified sphingolipids showed that this antibody reacts strongly with galactocerebroside (GalC), the major galactosphingolipid of myelin. The antibody was used in conjunction with rabbit antisera against sulfatide, the sulfated form of GalC, to examine the developmental appearance of these lipids on the surfaces of oligodendrocytes and Schwann cells. In addition, the loss of GalC and sulfatide from freshly dissociated Schwann cells was compared. These studied showed that GalC is expressed on the cell surface prior to sulfatide on both of these cell types in vivo and in vitro. Conversely, dissociated Schwann cells lose their cell surface sulfatide more rapidly than they lose their surface GalC under nonmyelinating conditions.

Aging↗