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Biomedical subjects

J R Fraser

Publications and source records attributed to J R Fraser.

At least 37 records · Page 2Linked to original sources
PubMed1998

Determination of the frequency and distribution of vascular and parenchymal amyloid with polyclonal and N-terminal-specific PrP antibodies in scrapie-affected sheep and mice.

Brains from 17 histopathologically confirmed cases of scrapie, five of which had congophilic vascular amyloid, were stained immunohistochemically for prion protein (PrP) using a polyclonal antibody. Two clinically suspect but pathologically unconfirmed cases of natural sheep scrapie and the brains of four mice infected with the 111A murine scrapie strain were also examined. Selected sections containing amyloid were stained with each of two peptide antibodies which recognise the N-terminal amino acid residues which are lost following protease digestion of the disease-specific isoform of PrP. The mice infected with the 111A murine scrapie strain had large numbers of hypermature plaques. All the amyloid plaques from both natural sheep scrapie brains and experimental murine brains were heavily immunostained by the polyclonal and both peptide antibodies. In addition, disease-specific accumulations of PrP were detected in endothelial cells or in the intima of blood vessels of the cerebral cortex of sheep scrapie brains. The affected blood vessels were located in areas which otherwise lacked typical scrapie pathology. Vascular accumulations of PrP were also found in leptomeningeal and choroid plexus blood vessels. Vascular amyloid was found mainly in the neocortex. Vascular amyloid and disease-specific parenchymal accumulations of PrP were found in two sheep which showed clinical signs of scrapie but lacked its typical vacuolar pathology. These results show that the mature amyloid of scrapie is composed of, or contains a substantial proportion of, whole length PrP protein. Thus truncation of PrP is not essential for the aggregation of PrP into amyloid. The vascular amyloid of natural sheep scrapie originates from the accumulation and release of PrP from endothelial cells presumably following systemic scrapie infection. The topography of vascular amyloid distribution in Great Britain differs from that reported in the Netherlands. As amyloid deposition in mice is largely controlled by the strain of the infecting agent it is possible that the strain of the agent may influence vascular amyloid deposition.

Amyloid↗
PubMed1998

Electrophysiological properties of dorsal lateral geniculate neurons in brain slices from ME7 scrapie-infected mice.

Electrophysiological recordings using conventional intracellular techniques were obtained from dorsal lateral geniculate nucleus (dLGN) neurons in brain slices from ME7 scrapie-infected mice at specific time points throughout the incubation period of the disease. Comparisons were made with age-matched control mice. A number of dLGN neurons from control and scrapie-infected mice were injected with biocytin in order to examine their cellular morphology. Mice were infected with ME7 scrapie by an intraocular route and the mean (+/- SEM) incubation period of the disease was 276 +/- 3.5 days. Our results indicate that there were no differences in the electrophysiological or morphological parameters of neurons recorded in ME7 scrapie-infected and age-matched control mice at any stage of the disease up to 240 days postinoculation. After this time, however, no detectable electrical activity was recorded in the dLGN. This study demonstrates that in the ME7 scrapie-infected dLGN, relay neurons with normal physiological and morphological properties are present even at an advanced stage of the disease at a time when the dLGN is known to be subject to marked pathological changes and a profound neuronal loss.

Action Potentials↗
PubMed1998

Alterations in potassium currents may trigger neurodegeneration in murine scrapie.

Conventional electrophysiological intracellular recording techniques were used to test the hypothesis that enhanced calcium entry via voltage-gated calcium channels or the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor-channel complex may be a primary pathological mechanism triggering neurodegeneration in scrapie and related diseases. This study was carried out at a time when cell loss is known to occur and when hippocampal pyramidal cells in area CA1 are rendered hyperexcitable following scrapie infection. There was no change to the NMDA receptor-mediated component of the Schäffer collateral evoked excitatory postsynaptic potential (EPSP) or the level of spontaneous firing activity of CA1 cells following addition of the specific NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid (APV, 20 microM), to the perfusate in scrapie-infected mice, indicating that the NMDA receptor-channel complex is not compromised by scrapie. There was also no change seen in the non-NMDA mediated component of the EPSP. The calcium spike of CA1 pyramidal cells was not significantly altered by scrapie infection, indicating that high threshold voltage-gated Ca2+ channel function is not compromised by scrapie. By contrast, cells from scrapie-infected mice fired calcium spikes repetitively and the long, slow AHP, which in control cells inhibited repetitive firing, was absent. Cells from scrapie-infected mice showed more depolarized membrane potentials than controls but this difference in potential was no longer observed after exposure to TEA. These data indicate a loss of TEA-insensitive and TEA-sensitive potassium conductances. We suggest that altered potassium currents rather than increased calcium entry via voltage-sensitive calcium channels or the NMDA receptor complex may be the primary pathological mechanism triggering neurodegeneration in scrapie and related diseases.

2-Amino-5-phosphonovalerate↗
PubMed1998

Synaptic plasticity in the CA1 area of the hippocampus of scrapie-infected mice.

Using conventional in vitro extracellular field potential recordings we have investigated both short- and long-term synaptic plasticity in the hippocampal CA1 area of mice infected with ME7 scrapie. In agreement with earlier studies, no changes were seen in the properties of the Schäffer collateralevoked field excitatory postsynaptic potential during the early stages of the disease (up to 160 days, post inoculation, d.p.i) after which time the recorded potentials were seen to attenuate. Also, up to this time no changes were seen in either paired-pulse facilitation or post-tetanic potentiation, which are short-term phenomena associated with brief elevations in presynaptic calcium levels. However, there was a significant shift from the ability of slices to maintain long-term potentiation (LTP) from 100 d.p.i. onwards. In all of these experiments short-term potentiation (STP) was preserved, suggesting that from the time that abnormal PrP becomes detectable, or perhaps even earlier, the mechanisms responsible for stabilizing the maintenance phase of LTP are impaired. This result is discussed in terms of the relationship between STP and LTP and how this might be compromised by the conversion of cellular prion protein (PrPC) to the scrapie, protease resistant form of PrP (PrPSc).

Animals↗
PubMed1997

Scrapie-induced neuron loss is reduced by treatment with basic fibroblast growth factor.

Neuron loss can be a prominent feature of the pathology of transmissible spongiform encephalopathies (TSEs); recent evidence indicates that this loss occurs through apoptosis. Growth factor treatment of other neurodegenerative diseases has been shown to protect neurons destined for apoptosis, and several types of experimental retinopathy have been successfully treated with basic fibroblast growth factor (bFGF). In a murine scrapie model which develops a severe loss of photoreceptors, we administered a single intravitreal injection of bFGF four-fifths of the way through the disease process; this doubled the number of photoreceptors surviving for up to 5 weeks, i.e. to the terminal stages of the disease. This is the first time that a potential late-stage therapy for the TSEs has been demonstrated.

Animals↗
PubMed1997

Hyaluronan: its nature, distribution, functions and turnover.

Hyaluronan is a polysaccharide found in all tissues and body fluids of vertebrates as well as in some bacteria. It is a linear polymer of exceptional molecular weight, especially abundant in loose connective tissue. Hyaluronan is synthesized in the cellular plasma membrane. It exists as a pool associated with the cell surface, another bound to other matrix components, and a largely mobile pool. A number of proteins, the hyaladherins, specifically recognize the hyaluronan structure. Interactions of this kind bind hyaluronan with proteoglycans to stabilize the structure of the matrix, and with cell surfaces to modify cell behaviour. Because of the striking physicochemical properties of hyaluronan solutions, various physiological functions have been assigned to it, including lubrication, water homeostasis, filtering effects and regulation of plasma protein distribution. In animals and man, the half-life of hyaluronan in tissues ranges from less than 1 to several days. It is catabolized by receptor-mediated endocytosis and lysosomal degradation either locally or after transport by lymph to lymph nodes which degrade much of it. The remainder enters the general circulation and is removed from blood, with a half-life of 2-5 min, mainly by the endothelial cells of the liver sinuoids.

Animals↗
PubMed1997

In vivo toxicity of prion protein in murine scrapie: ultrastructural and immunogold studies.

Prion protein (PrP) is a cell surface, host coded, sialoglycoprotein which accumulates in excess in scrapie, Creutzfeldt-Jakob disease, bovine spongiform encephalopathy and other transmissible spongiform encephalopathies. Infection of mice with the 87 V or ME7 scrapie strains results in distinctive and very different light microscopical patterns of vacuolation and disease specific PrP accumulation. In both of these scrapie strains immunogold electron microscopy was used to locate PrP to the plasmalemma of neurons from where it was released into the neuropil. Initial PrP accumulation around neurons and in early plaques lacking amyloid fibrils was generally not associated with morphological changes either of the neuron or dendrite releasing the PrP or in the adjacent neuropil in which excess PrP accumulated. However, accumulation of pre-amyloid PrP in some brain areas was associated with specific degeneration of dendritic spines and axon terminals. Initial PrP aggregation into fibrils was also associated with tissue damage with both ME7 and 87 V plaques and diffuse accumulations. Tissue damage associated with fibrillogenesis was localized and would not be expected to have clinical significance. We conclude that pre-amyloid PrP release and accumulation is not invariably toxic, either to the neuron releasing PrP or to the neuropil into which it is released. However, axon terminal degeneration and dendritic spine loss in some neuroanatomical areas may be indicative of specific PrP toxicity and may be the main cause of neurological dysfunction in murine scrapie.

Animals↗
PubMed1996

The structure and function of hyaluronan: An overview.

Hyaluronan is a major component of synovial tissue and fluid as well as other soft connective tissues. It is a high-Mr polysaccharide which forms entangled networks already at dilute concentrations (< 1 mg/mL) and endows its solutions with unique rheological properties. Physiological functions of hyaluronan (lubrication, water homeostasis, macromolecular filtering, exclusion, etc.) have been ascribed to the properties of these networks. Recently a number of specific interactions between hyaluronan and a group of proteins named hyaladherins have also pointed towards a role of hyaluronan in recognition and the regulation of cellular activities. Many more or less well documented hypotheses have been proposed for the function of hyaluronan in joints, for example, that it should lubricate, protect cartilage surfaces, scavenge free radicals and debris, keep the joint cavities open, form flow barriers in the synovium and prevent capillary growth.

Animals↗
PubMed1996

Effect of increased interstitial fluid flux on fractional catabolic rate of high molecular weight [3H]hyaluronan injected in rabbit skin.

The removal rate of high molecular weight (M(r) 3 x 10(6) [3H]hyaluronan has been measured in rabbit paw skin in control and during increased local venous pressure induced by ligation of the femoral vein. The increased venous pressure resulted in a 20% increase of interstitial volume at 4 h after ligation, a value which relates to at least a doubling of lymph flow, i.e. also to doubling of fluid flux through the tissues. The fractional catabolic rate of hyaluronan was 0.0918 +/- 0.0170 h-1 (n = 10) and 0.0775 +/- 0.0206 h-1 (n = 11) in control and following increased venous pressure respectively (P > 0.05). Since the fractional catabolic rate of hyaluronan is not affected by increased venous pressure, the removal of hyaluronan via lymphatic drainage in rabbit paw skin must be small compared to the local turnover of the polysaccharide.

Animals↗
PubMed1996

Infectivity in extraneural tissues following intraocular scrapie infection.

Intraocular (i.o.) infection of mice with scrapie produces strain-specific targeting of replication and subsequent pathology within the visual system projection areas in the CNS, but also initiates an extraneural infection. Following i.o. infection with ME7 scrapie, infectivity was detected 24 h later in the Harderian gland, the superficial cervical lymph nodes (SCLNs) and the spleen, but not until 20 days in Peyer's patches and inguinal lymph nodes (ILNs). Persistent low levels of infectivity were found in the Harderian gland (which lies within the orbit), but the presence of PrP could not be confirmed by immunolabelling or Western blotting. SCLNs contained maximal amounts of infectivity by 20 days post-infection and remained at this level throughout the incubation period. ILNs reached a similar plateau at 60 days, as did Peyer's patches at 80 days and spleen at 100 days. Further investigation of the role of the spleen in pathogenesis showed that in contrast to ME7 scrapie, mice infected with 79A scrapie had high levels of infectivity in the spleen by 20 days post-infection, irrespective of the route of infection. In addition, the disease developed more rapidly following direct intrasplenic infection with ME7 scrapie than with intraperitoneal infection. Splenectomy at 7 days either before or after i.o. infection had no effect on the incubation period. These results indicate that the rate of replication of infectivity is both tissue and scrapie-strain dependent, and that extraneural spread of infection can occur via the lymphatic system.

Animals↗
PubMed1996

Effect of prostaglandin E2 and hyaluronan on mesangial cell proliferation. A potential contribution to glomerular hypercellularity in diabetes.

Proliferation of mesangial cells is a feature of several forms of human and experimental glomerulopathy, including that seen in diabetes. The nonsulfated glycosaminoglycan hyaluronan participates in the regulation of pericellular matrix assembly and is a mitogen in some cell types. We have shown previously that hyaluronan production is increased in the glomerulus in a glucose- and prostaglandin-dependent manner. We have investigated the effect of diabetes and of addition of hyaluronan and prostaglandin E2 (PGE2) on the uptake of [3H]thymidine by glomerular core preparations enriched in mesangial cells. When compared with nondiabetic controls, it was shown that [3H]thymidine uptake was significantly increased in glomerular core preparations from streptozotocin-induced diabetic rats (to 169 +/- 5%, P < 0.001). In glomerular cores from both experimental groups, hyaluronan (50-250 ng/ml) or PGE2 (10(-12) to 10(-8) mol/l) increased the uptake of [3H]thymidine. Further, mesangial cells from nondiabetic control glomerular cores, when maintained in culture in early passage, responded with increased [3H]thymidine uptake to raised glucose (5.6-25 mmol/l) and to added hyaluronan and PGE2. We propose that prostaglandin and hyaluronan production in response to a raised glucose environment in diabetes can contribute to mesangial hypercellularity.

Animals↗
PubMed1996

Serum hyaluronan as a disease marker.

Hyaluronan is a connective tissue polysaccharide which has also been found in blood serum in concentrations < 100 micrograms/L (average 30-40 micrograms/L in middle-aged persons). The serum level is regulated by the influx of the polysaccharide from the tissues via lymph and its receptor-mediated clearance by liver endothelial cells. Markedly high serum levels are noted in certain liver diseases, especially in patients with cirrhosis, when the clearance is impaired. In these cases serum hyaluronan can be used to follow the development of the disease. Serum hyaluronan is also a sensitive marker for impending rejection of liver transplants. Patients with rheumatoid arthritis constitute another major group with increased serum hyaluronan, but in this case the level varies markedly during the day corresponding to physical activity. There are good indications that in these subjects the excess hyaluronan comes from the joints. Under stringent sampling conditions of serum it should be possible to extract interesting information on the inflammatory joint process. Increased hyaluronan levels are also seen in other inflammatory diseases and it is of special interest that high hyaluronan levels in patients with septic conditions is a sign of poor prognosis. Certain tumours, notably Wilms' tumour and mesothelioma, produce factors which activate synthesis of hyaluronan and increase its serum level. Rare hereditary diseases with disturbances of hyaluronan metabolism and elevated blood levels have also been discovered, e.g. Werner's syndrome and cutaneous hyaluronanosis. Information accumulated during the last decade regarding the metabolism of hyaluronan has made this polysaccharide an interesting clinical marker for a number of pathological conditions.

Biomarkers↗
PubMed1995

Increased hyaluronan production in the glomeruli from diabetic rats: a link between glucose-induced prostaglandin production and reduced sulphated proteoglycan.

Exposure in vivo or in vitro to elevated glucose increases production of vasoactive prostaglandins by glomeruli and mesangial cells. This study aimed to determine whether this increased prostaglandin production could provide a link with later structural changes in diabetic nephropathy. Glomerular cores were prepared from control rats and streptozotocin-diabetic rats (3 weeks' duration). Over 24 h in culture hyaluronan production from diabetic glomerular cores was higher than production from control glomerular cores whether maintained in 5.6 mmol/l glucose (105.6 +/- 15.5 vs 53.6 +/- 8.5 ng hyaluronan per 250 glomerular cores, p < 0.001); in 25 mmol/l glucose (149.3 +/- 34.8 vs 62.7 +/- 7.8 ng hyaluronan per 250 glomerular cores, p < 0.01); or in 45 mmol/l glucose (176.8 +/- 23.3 vs 102.0 +/- 17.9 ng hyaluronan per 250 glomerular cores, p < 0.01). At 5.6 mmol/l glucose, exposure in vitro to prostaglandin E2 caused an increase in hyaluronan production [maximal at 10(-9) mol/l prostaglandin E2, 237 +/- 19 vs 42 +/- 4, ng hyaluronan per 250 glomerular cores, p < 0.001 (control) and 195 +/- 7 vs 103 +/- 5, ng hyaluronan per 250 glomerular cores, p < 0.001 (diabetic)]. In both control and diabetic glomerular cores hyaluronan production was reduced significantly by the cyclooxygenase inhibitor indomethacin (10(-5) mol/l) [24.7 +/- 3.33 vs. 40.25 +/- 4.11 ng hyaluronan per 250 glomerular cores, p < 0.05 (control) and 36.5 +/- 6.25 vs 118.0 +/- 22.6, p < 0.01 (diabetic)]. A direct spectrophotometric microassay was used to determine the concentration of sulphated glycosaminoglycans derived from papain-digested glomerular core proteoglycans.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Early unsuspected neuron and axon terminal loss in scrapie-infected mice revealed by morphometry and immunocytochemistry.

Neuronal loss is often quoted as an element of the pathology of the transmissible spongiform encephalopathies, but few data are published. To determine whether neuronal loss is a salient feature of murine scrapie, and whether there is a relationship with the other hallmark lesions of scrapie we compared the numbers of neurons, severity of vacuolation, axonal bouton density and distribution of prion protein (PrP) in the dorsal lateral geniculate nucleus (dLGN) following intraocular infection of C57BL/FaBtDk mice with ME7 scrapie. This route of infection limits the initial spread of infection to the retinal efferents, thus directing infectivity and subsequent pathological changes to the dLGN which is a major projection of the optic nerve. Morphometric assessment of neuron number in the dLGN was made on semi-serial sections from five infected and five normal brain injected controls at four 50-day intervals during the incubation period, and on terminally affected mice. The number of neurons decreased from around 20,000 at 50 days to under 1000 in the terminal group. Significant loss was identified in individual mice at 150 days post-infection, coincident with the onset of vacuolation: neuron number was found to have an inverse relationship to the severity of vacuolation. Axonal boutons in the dLGN (demonstrated by synaptophysin immunolabelling) were reduced at 200 days, and virtually absent in terminal mice. The intensity of PrP immunostaining progressively increased from 150 days, and in a separate experiment PrP was detected from 175 days by polyacrylamide gel electrophoresis of brain extracts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Tobacco use and smoking policy perceptions onboard an aircraft carrier.

Prior to implementing a shipwide no-smoking policy, the crew of U.S.S. Theodore Roosevelt (CVN 71) participated in a voluntary survey on tobacco-related matters. The survey queried participants on their tobacco-use history, subjective exposure to environmental tobacco smoke (ETS), and attitudes related to smoking policy prior to the cessation of all smoking activities aboard ship. Of the 2,221 crewmembers who participated (74% response rate), 36% classified themselves as current cigarette smokers. Nonsmokers estimated their general exposure to ETS between "low" to "moderate." Of all participants, 57% were in favor of the current restricted smoking policy, including 18% of currently smoking personnel. Follow-up research is being conducted to assess the long-term impact of the no-smoking policy on changes in attitudes regarding policy, tobacco-use rates, and ETS exposure.

Adult↗