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Biomedical subjects

R H Kimberlin

Publications and source records attributed to R H Kimberlin.

At least 37 records · Page 2Linked to original sources
PubMed1988

Incubation periods in six models of intraperitoneally injected scrapie depend mainly on the dynamics of agent replication within the nervous system and not the lymphoreticular system.

The pathogenesis of intraperitoneally injected ME7 scrapie has been studied in two Sinc genotypes of mice which gave predictable but widely different incubation periods. Comparisons were made with three other mouse scrapie models and one model in hamsters (involving different strains of agent and an untyped isolate from sheep). Average incubation periods ranged from 114 days in the fastest model (263K/hamsters) to 482 days in the slowest (ME7/Sincp7 mice). There were only small differences between models in the times of onset of replication in spleen and cervical lymph nodes. We suggest that the lymphoreticular stage of pathogenesis initiates neuroinvasion in the peripheral nervous system within a few days to a few weeks of infection. Thereafter, pathogenesis appears to be dominated by neural events and replication in brain becomes detectable after approximately 54% of the remaining incubation period has elapsed, irrespective of its length. It is concluded that the differences between incubation periods of the six scrapie models depend mainly on the rate of a continuous process of replication and spread of infection in the peripheral and central nervous system, which is predetermined by scrapie strain and host genotype. The unpredictability of some other scrapie models (and the natural disease) could be explained by additional factors which restrict neuroinvasion from the lymphoreticular system.

Animals↗
PubMed1987

Scrapie associated fibrils in the diagnosis of scrapie in sheep.

Previous research has consistently demonstrated by electron microscopy the presence of scrapie associated fibrils in brain extracts prepared from mice and hamsters with clinical signs of experimental scrapie. In the present study similar fibrils were seen in all the brain extracts prepared from 11 Cheviot or Suffolk sheep with natural or experimental scrapie that had been diagnosed clinically and confirmed neuropathologically. They were not found in the brain extracts of nine sheep that did not have scrapie and which included four that had been injected with infected material but did not develop the disease. The presence of such fibrils can therefore be used as an additional diagnostic criterion for natural scrapie in sheep.

Animals↗
PubMed1987

Pathogenesis of scrapie is faster when infection is intraspinal instead of intracerebral.

Previous studies of mice infected peripherally with 139A scrapie showed that scrapie agent initially replicates outside the CNS and that invasion of the CNS occurs several weeks later by neural spread of infection along visceral autonomic fibres to the mid-thoracic cord, and thence to brain. Direct intracerebral infection of brain bypasses the need for extraneural replication and gives shorter incubation periods than peripheral routes. However, it was also found that the duration of the scrapie replication phase in brain, before clinical disease develops, is actually shorter with peripheral routes than with the intracerebral route. We have now investigated this surprising observation using the intraspinal route to reproduce just the neural phase of scrapie pathogenesis seen after peripheral infection. In studies of three strains of scrapie (263K, 139A and ME7) in either hamsters or mice, we have fulfilled the prediction that incubation periods should be shorter after intraspinal infection than after intracerebral infection. Detailed studies of 139A scrapie showed that the shorter incubation period by the intraspinal route could be accounted for by the shorter duration of the scrapie replication phase in brain before clinical disease developed. As a consequence, the severity of the vacuolar lesions in brain at the clinical stage of all three scrapie models was less after intraspinal infection than after intracerebral infection but the severities of vacuolation after intraspinal and intraperitoneal infection were remarkably similar. We speculate that (a) the site of injection (or of invasion) of the central nervous system determines which neural pathways become accessible for the spread of scrapie infection, and that (b) the duration of the neural phase of scrapie pathogenesis is related to the complexity of the pathways between the site of invasion and the clinical target areas in which, it is suggested, scrapie must replicate for disease to develop.

Animals↗
PubMed1987

Temporary and permanent modifications to a single strain of mouse scrapie on transmission to rats and hamsters.

The interspecies transmission of scrapie is frequently associated with exceptionally long incubation periods at first passage in the new host compared to later passages (the species barrier effect). The basis of this was investigated using the 139A strain of scrapie which had been cloned by three serial passages in mice at limiting infectious doses. Cloned scrapie was passaged through hamsters (twice) or rats (thrice) and then reisolated in mice. Large species barrier effects were encountered on mouse-to-hamster and hamster-to-mouse passage resulting in the isolation of a mutant strain, 139-H/M, with properties very different from 139A. In contrast, the strain reisolated from rats was indistinguishable from 139A. However, a large species barrier was encountered at the mouse-to-rat passage but not at the rat-to-mouse passage. It is suggested that the transmission of scrapie between species may be associated with no change in properties or a permanent change in the scrapie genome due to the selection of mutants. A third possibility, the donor species effect, is a temporary change occurring only at first passage in the new host species which is largely or entirely caused by the introduction of material from the previous host. We speculate that the donor species effect could be explained if some host protein forms a functional part of the infectious agent.

Animals↗
PubMed1986

The major polypeptide of scrapie-associated fibrils (SAF) has the same size, charge distribution and N-terminal protein sequence as predicted for the normal brain protein (PrP).

Scrapie-associated fibrils (SAF) are unique structures characteristic of the group of unconventional slow infections which includes scrapie and Creutzfeldt-Jakob disease. A major component of hamster fibrils has been described as a protease-resistant glycoprotein with an apparent mol. wt of 27,000-30,000 (PrP27-30). However, we report here that if fibrils are prepared by procedures designed to minimise proteolysis the PrP proteins co-purifying with hamster SAF have mol. wts of 33,000-35,000 (PrP33-35) and 26,000-29,000 (PrP26-29). We find a Lys-Lys-Arg-Pro-Lys sequence at the amino terminus of these SAF proteins, that is absent from PrP27-30, and which has recently been predicted to be the N-terminal sequence of the native PrP protein of uninfected brain. The major SAF protein (PrP33-35) and its normal brain homologue are shown to have the same apparent mol. wt and ionic charge distribution by two-dimensional gel analysis, silver staining and immunoblotting. These results support our view that PrP33-35 and the normal brain PrP protein may have the same covalent structure, and that the PrP protein is recruited into these amyloid-like SAF or into association with a non-protein component of SAF by an irreversible event initiated directly or indirectly by scrapie infection.

Amino Acid Sequence↗
PubMed1986

Learning ability of mice infected with different strains of scrapie.

CD-1 mice were infected intraperitoneally with one of 4 different strains of scrapie and tested simultaneously at or near the end of incubation. There were no differences between any of the scrapie injected groups and controls in spontaneous motor activity, or in the shock thresholds and entry latencies measured during training in a one-trial passive avoidance test. On testing, the avoidance responses were normal for the mice infected with 22C or ME7, but these mice did not show overt clinical signs (e.g., ataxia) at the time. The 139A and 79A infected mice were showing clinical signs when tested and impaired responses were found in the mice trained at a low shock threshold. However the impairment was completely overcome at a higher shock level. These results suggest that only limited reductions in learning ability are associated with some of the shorter incubation models of scrapie. Specific suggestions are made of how a learning deficit might be produced in certain scrapie models which could be useful in studies of some aspects of dementia.

Animals↗
PubMed1986

Pathogenesis of scrapie (strain 263K) in hamsters infected intracerebrally, intraperitoneally or intraocularly.

After intracerebral (i.c.) infection of hamsters, the 263K strain of scrapie replicated at a nearly constant exponential rate until clinical disease developed when titres in brain averaged 9.8 log10 LD50 i.c. units/g. After intraperitoneal infection, scrapie replication was first detected in spleen, then in thoracic spinal cord and finally in lumbar cord and brain. This pattern suggests that invasion of the central nervous system occurs by spread of infection along certain visceral autonomic nerves. Infectivity was detected in the thoracic cord only 3 to 4 weeks after infection (incubation period 16 weeks) indicating the exceptional neuroinvasiveness of this scrapie model. This observation and the failure of splenectomy to lengthen incubation period raises the possibility of direct infection of nerve tissue in the peritoneum and transport to the thoracic cord with minimal prior replication of scrapie agent extraneurally. After intraocular infection of the right eye, replication (or accumulation) of scrapie was detected in the right optic nerve and left superior colliculus, then in the right superior colliculus and finally in the left optic nerve and medulla. This pattern shows that scrapie infection can spread along nerves, possibly by intra-axonal transport. The duration of agent replication in brain (between detectable onset of replication and clinical disease) was shortest after intraperitoneal infection (51 to 58 days), longer after intracerebral infection (81 to 88 days) and longest after intraocular infection (greater than 121 days). These differences may reflect the relative efficiency of the neural pathways by which infectivity spreads from different sites of entry in the brain to the postulated 'clinical target areas'.

Animals↗
PubMed1986

Suppression of scrapie infection in mice by heteropolyanion 23, dextran sulfate, and some other polyanions.

Studies of polyanions that suppress scrapie have been done to pinpoint the cell types in the lymphoreticular system which are important in pathogenesis and to suggest possible prophylactic or therapeutic strategies for the unconventional slow viruses. A regime of three daily injections of the inorganic heteropolyanion HPA-23 reduced the effective scrapie dose by more than 99%; i.e., some mice survived peripherally injected doses of 100 50% lethal dose units. The effect was greatest when the first dose of HPA-23 was given 4 h after injecting scrapie, but it declined rapidly as this interval was increased, and there was virtually no effect 2 days after infection. A single dose of high-molecular-weight organic polyanions such as carrageenan or dextran sulfate (DS-500) greatly reduced (i.e., greater than 99%) the efficiency of scrapie infection. In contrast to HPA-23, DS-500 was equally effective whether given 4 days before or 8 h after the time of infection. The antiscrapie effect of DS-500 appeared to be independent of its activity as a B-cell mitogen and of its ability to produce a cytotoxic blockade of phagocytic cells. DS-500 probably caused the aggregation and loss from blood of scrapie inoculum which was present immediately after injection, but it had additional effects on scrapie at later times.

Animals↗
PubMed1985

Selection of Swaledale sheep of reduced susceptibility to experimental scrapie.

A flock of 294 Swaledale sheep was injected with brain tissue from different sources so as to include strains of natural scrapie currently affecting the Swaledale breed. Discounting intercurrent deaths, 85 per cent of the flock developed clinical scrapie within an observation period of 2557 days (seven years). Scrapie cases fell into distinct early and late groups, occurring at (mean +/- sem) 287 +/- 7 days and 1207 +/- 38 days after injection, respectively. Breeding groups were formed from the survivors after the early cases had occurred and successive lamb crops were produced. Two groups of progeny and two groups of controls were injected with scrapie. The incidence of scrapie in the progeny (27 per cent) was much lower than in the controls (64 per cent). The incidence in the progeny was also assessed in relation to the response of their parents: it was high (about 40 per cent) when one or both parents developed late scrapie but otherwise very low (about 5 per cent). Hence the progeny of surviving parents had a greatly reduced susceptibility to the strains of scrapie used. Seventy-two of these selected progeny formed a nucleus flock which is being bred at Redesdale. The next stage of the experiment is to assess the effect of selected rams in recorded flocks with a high incidence of natural scrapie.

Animals↗
PubMed1985

Neurotransmitter metabolites, enzymes and receptors in experimental scrapie.

A comprehensive study has been made of metabolites, enzymes and receptors for a variety of neurotransmitter systems in different parts of the CNS from mice affected with 139A scrapie. Studies were made at the early clinical stage so as to minimise secondary alterations in terminally sick mice. Even though histological lesions (vacuolation) are widespread in the CNS in this model of scrapie, no consistent neurochemical changes were found in mid- or anterior brain. In the cerebellum, the activity of glutamic acid decarboxylase was reduced and the binding of [3H]muscimol to gamma-aminobutyric acid receptors was increased. In the brain stem, the concentration of 5-hydroxyindoleacetic acid (5-HIAA) was increased and there was a reduced binding of appropriate ligands to serotonin and to muscarinic cholinergic receptors. In the spinal cord, the activity of choline acetyl transferase was reduced and the concentration of 5-HIAA was increased. The extent of these alterations was about 20-40% of control values. The specificity of these changes for a few neurotransmitter systems in hind brain and spinal cord raised the possibility of their being a primary cause of clinical disease and led us to study a different scrapie model. Present and published findings show that an increased concentration of 5-HIAA, some alterations in the binding properties of serotonin receptors and a decreased number of muscarinic receptor sites are common to both 139A scrapie in CW mice and 263K scrapie in hamsters.

Animals↗
PubMed1985

Competition between strains of scrapie depends on the blocking agent being infectious.

Compton White mice (Sincs7) were injected twice intraperitoneally, first with the 22A strain of scrapie agent (in brain homogenates) and then, after 105 days, with the 22C strain. Incubation periods were calculated from the time of the first injection. The experiment was designed so that, with no interaction between strains, the second strain (22C) should have produced cases about 300-350 days after the first injection, depending on the dose of 22C. This was well before the limit of 470 days set by the mean incubation period minus 3 SD of 22A alone: a limit which was used to distinguish 22C from 22A clinical cases. In fact, 22A blocked 22C as shown by (i) the lengthening of 22C incubation periods, (ii) the reduced proportion of cases due to 22C, and (iii) the reduced effective titer of 22C. The blocking efficiency of 22A was not greatly reduced by physicochemical treatments that had little or no effect on its infectivity by the intraperitoneal route. However, treatment of 22A homogenates with 6 M urea virtually eliminated infectivity and also abolished blocking ability. It is concluded that competition depends on the infectivity of the scrapie strain used for blocking.

Animals↗
PubMed1984

Sheep lymphocyte antigens and scrapie.

The frequencies of 15 lymphocyte antigens were determined in 2 experimental flocks of Herdwick sheep derived from the same foundation stock. The Blue Flock had been bred for resistance, and the Red flock for susceptibility, to a standard dose of the SSBP/1 source of scrapie injected subcutaneously. Although there were marked frequently differences between the 158 Red flock and 51 Blue flock sheep tested these differences could be attributed to genetic drift. Within the Red flock no significant frequency differences were observed between 16 sheep which developed natural scrapie and their healthy flockmates. All Red flock lambs born in 1980 were injected subcutaneously with SSBP/1 scrapie; there was no difference in antigen frequency between the group which subsequently developed experimental scrapie (30) and the group which did not (21). The segregation of antigen haplotypes in the Red flock pedigrees showed no evidence of MHC linkage with either natural or experimental scrapie.

Alleles↗
PubMed1984

Pathogenesis of mouse scrapie: distribution of agent in the pulp and stroma of infected spleens.

Fourteen spleens were collected from mice infected with the 139A strain of scrapie, at a time when the concentration of agent in spleen was at a plateau. Scrapie infectivity was present in both the pulp and stromal fractions, but the concentration in stroma was about 10 times greater than that in pulp. On average, 1000 pulp cells were required to give 1 LD50 unit of scrapie infectivity. Linear regression analysis of data from 64 mouse spleens showed that the total infectivity correlated with tissue weight (P less than 0.001). The titres of the 14 stromal fractions were significantly correlated with whole spleen weight (P less than 0.02) and with the weight of stroma (P less than 0.02), but not with pulp weight. Hence, the titres in the isolated stroma probably reflect those of the stroma in vivo. In contrast, there was no correlation between total pulp titre and spleen weight, pulp weight or pulp cell number. Moreover, gentle washing of pulp cells removed about 80% of the total infectivity. This suggests that much of the pulp titre is adventitiously associated with cells and is in fact agent released from damaged stroma.

Animals↗
PubMed1983

The antiviral compound HPA-23 can prevent scrapie when administered at the time of infection.

The effects of up to 12 daily doses of HPA-23 (ammonium 5-tungsto-2-antimoniate) on scrapie were studied using five experimental models of the disease, some with widely different incubation times. Treatment of animals with HPA-23, starting just before injecting scrapie, produced survivors. In some experiments, animals were fully protected against several hundred infectious units of scrapie. Treatment of animals after infection was far less effective. Prolonging the treatment for several weeks was no more effective than treating for a few days. In a very long incubation model of scrapie, the course of 12 daily doses of HPA-23 represented less than 3 per cent of the total incubation period. HPA-23 may interact with certain cells of the lymphoreticular system, preventing infection and, perhaps, the early replication of agent.

Animals↗
PubMed1983

Further studies on changes in immunoglobulin G in the sera and CSF of Herdwick sheep with natural and experimental scrapie.

Previous studies showed that the concentration of IgG in serum was increased in a high proportion of Herdwick sheep in the clinical stage of natural scrapie. The present paper reports similar findings in Herdwicks with experimental scrapie in which the clinical signs were different. Further studies of the natural disease showed increased concentrations of IgG in CSF due to passive filtration from serum and not to local antibody production in the CNS. Qualitative differences in serum IgG have also been found in natural scrapie, involving a shift in the major IgG isotype from IgG1 to IgG2. The significance of these changes is not known but the limited evidence available may indicate a progressive dysfunction in certain sub-populations of lymphocytes in sheep scrapie.

Animals↗
PubMed1983

Disinfection studies with two strains of mouse-passaged scrapie agent. Guidelines for Creutzfeldt-Jakob and related agents.

A variety of disinfection procedures were tested on two strains of scrapie agent, treated either as brain macerates (autoclaving) or as 10% homogenates (chemical treatments). It is suggested that a given treatment should produce a titre loss, of both strains of scrapie, of at least 10(4) units before it be regarded as useful for the disinfection of the agents of scrapie and Creutzfeldt-Jakob disease (CJD). By this criterion, treatment at room temperature with about 4% Hycolin (0.6% chlorinated phenols), 0.2% permanganate, 5% Tego (dodecyl-di(aminoethyl)-glycine) or 5% sodium dodecyl sulphate (SDS) are unsuitable. However, data indicate that SDS might be used to reduce the heat stability of scrapie agent. Hypochlorite (Sterilex) was the only satisfactory chemical reagent tested. At least 10(4)-10(5) units of infectivity were lost by treatment with hypochlorite containing 1,000 ppm available chlorine after a 4-16 h exposure, or containing 10,000 ppm available chlorine after a half-hour exposure. The latter result points to the use of concentrated hypochlorite (about 2% available chlorine; approximately 20% Sterilex) to decontaminate surfaces. We suggest that the cleaning action of SDS, or other strong detergents, might also help to decontaminate surfaces, but studies on this are needed. Autoclaving at 126 degrees C for 1-2 h reduced titres by 10(3)-10(7) units, depending on the strain of agent. However, total disinfection of brain containing high titres of infectivity was approached only at 136 degrees C when titre losses of about 10(6) units were obtained by autoclaving for 4-32 min. Further studies are needed before we can make simple, general recommendations for the disinfection of CJD agents in hospital practice.

Animals↗
PubMed1983

Pathogenesis of mouse scrapie: evidence for spread of infection from central to peripheral nervous system.

The onset of replication has been studied in spinal cord, dorsal root ganglia and spinal nerves of CW mice infected intraperitoneally with the 139A strain of scrapie. The patterns obtained suggest a centrifugal spread of infection from central to peripheral nervous systems. Infectivity titres in the peripheral nervous system reached a plateau long before the end of the incubation period, and the maximum titres were much lower than in the central nervous system. This suggests that there is a restriction of replication in the peripheral nervous system similar to that already known in extraneural tissues.

Animals↗