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Biomedical subjects

H K Narang

Publications and source records attributed to H K Narang.

At least 19 recordsLinked to original sources
PubMed1995

Efficacy of herpes vaccine and acyclovir (ACV) in a rabbit model following intraocular inoculation of herpes simplex virus.

It has been shown that injection of herpes simplex virus (HSV) type I into the vitreous body of the eye in 18-day-old albino rabbits consistently induced encephalitis. In the untreated group the lesions followed a defined anatomical pathway in the central nervous system and produced a chronic progressive disease with 95% survival. Detailed observations in the spread of HSV along the optic pathway determined the extent of damage at any given day. Some of the old rabbits developed typical herpetic lesions on nose and lips. HSV was demonstrated from these lesions by electron microscopy and also by tissue culture isolation. The combined efficacy of heat-killed herpes vaccine prepared from the same isolate and acyclovir (ACV) in this animal model was studied by starting treatment four days before or four days after the challenge. Ten animals immunised before the challenge were protected. However, immunisation after the challenge not only did not confer protection, but surprisingly, appeared to enhance the primary disease. All 10 rabbits immunised after the challenge developed weakness of the hind legs and progressed very rapidly to paralysis. ACV treatment alone did not completely abrogate the HSV infection, there appears to be reactivation of HSV which produced fresh small lesions. However, a combination of immunisation and treatment with ACV after the challenge of the 10 rabbits in the group prevented the development of weakness of the hind legs or paralysis. Detailed observations on the spread of HSV along the optic pathway revealed that pathological lesions and damage were limited in the ACV and combined treatment with ACV and vaccine group.

Acyclovir↗
PubMed1994

Evidence that homologous ssDNA is present in scrapie, Creutzfeldt-Jakob disease, and bovine spongiform encephalopathy.

Homogenized brain tissue from scrapie-infected hamsters and uninfected hamsters was subjected to sub-cellular fractionation to isolate nemavirus. Nucleic acid was extracted from these fractions, which also contained mitochondria. Agarose-gel electrophoresis revealed a band corresponding to the size of circular hamster mtDNA in both infected and uninfected samples, but slower migrating bands were observed only in samples from scrapie-infected brain. A single band of ssDNA corresponding to about 1.2 kb was purified by alkaline gel electrophoresis from the nucleic acid content of the enriched preparations of nemavirus. The ssDNA was synthesized into double-stranded DNA, cloned and sequenced. An unusual palindromic six base TACGTA repeat sequence was observed suggesting that 1.2 kb molecules consist of multiple copies of (TACGTA)n spaced along the length of the ssDNA with a preceding sequence TATATA. The comparison of the nucleotide sequence of the inserted DNA to the GenBank nucleotide database revealed no significant homology to other sequences. A probe prepared from the Nar 50 clone was hybridized against DNA prepared from scrapie, CJD, BSE and normal brains under various salt and temperature conditions. The probe reacted with a band of about 1.2 kb in scrapie, CJD and BSE but not with control normal DNA specimens, thereby confirming the presence of ssDNA in these SEs. The results suggest an intimate association between the presence of nemavirus particles and scrapie, CJD and BSE.

Animals↗
PubMed1994

Progression of cytomegalovirus in the rabbit following the intraocular injection of the virus.

There is growing recognition that cytomegalovirus (CMV) is one of the opportunistic infections in patients afflicted with AIDS. The purpose of the present study was to establish a chronic CMV infection of the central nervous system (CNS) in rabbits after intraocular inoculation, to evaluate the therapeutic value of the model for investigation of the effect of antiviral drugs. It was possible to establish a chronic human cytomegalovirus (HCMV) encephalitis after 14-day old rabbits were injected into the vitreous body of the eye with the HCMV. One control and two experimental rabbits were killed at 16 days and 1, 3, 6 and 9 months post-inoculation. HCMV was demonstrated from the retina, optic nerve and brain by electron microscopy. HCMV infection did not cause apparent clinical symptoms or signs in the injected animals. At the morphological level the virus-induced lesion revealed the following features: that the HCMV travels slowly along the optic nerve and crosses at the optic chiasma showing a few thickly myelinated and many demyelinated axons with astroglial scar tissue. There was no evidence of inflammatory response in the lesions as no lymphocytes, plasma cells or phagocytic cells with dead myelin or lipid contents were observed. Long term observations of HCMV inoculated rabbits showed that the intraocular lesions followed a defined anatomical pathway in the optic nerve, chiasma and brain, leading to progressive chronic disease. The rabbit model would be very suitable for the evaluation of the therapeutic value of the effect of antiviral drugs.

Animals↗
PubMed1993

Evidence that scrapie-associated tubulofilamentous particles contain a single-stranded DNA.

Unique virus-like tubulofilamentous particles, termed nemavirus, have been consistently observed in spongiform encephalopathic brains by electron microscopy in thin sections. Sodium dodecyl sulphate treatment of unfixed infected brain tissue on grids revealed a twisted fibril core of tubulofilamentous particles. The unmasked fibrils were identified as scrapie-associated fibrils by immunogold labelling. Both tubulofilamentous particles and scrapie-associated fibrils are not artefacts of protease treatment of protein formed in vitro during purification. Treatment with protease and nucleases revealed that each tubule consists of three layers: (i) an outer coat of protease-sensitive material; (ii) an intermediate layer that is digested by DNase and mung bean nuclease, and (iii) inner protease-resistant protein scrapie-associated fibril.

Animals↗
PubMed1992

Scrapie-associated tubulofilamentous particles in scrapie hamsters.

Examination of thin sections from the cerebral cortex of scrapie-infected hamster brains revealed characteristic circular 26-30 nm diameter tubulofilamentous particles, identical to those previously described in both experimentally induced scrapie in mice, hamsters and natural scrapie of sheep, bovine spongiform encephalopathy and human Creutzfeldt-Jakob disease and mice and chimpanzees infected with Creutzfeldt-Jakob disease. Longitudinal forms of tubulofilamentous particles were also observed in dendrites and myelinated axons. Both transverse and longitudinally cut particles were readily distinguished from microtubules and synaptic vesicles, thus there appears to be no relationship between tubulofilamentous particles, and microtubules or synaptic vesicles.

Animals↗
PubMed1991

Evidence of ssDNA in tubulofilamentous particles: their relationship to scrapie-associated fibrils.

Abnormal tubulofilamentous particles were identified by electron microscopy using a simple touch negative staining technique from brains of mice infected with four strains of the scrapie agent. Treatment by three proteolytic enzymes and subsequent treatment with DNase and mung bean nuclease of grids prepared from the infected animals confirmed previous observations that the tubulofilamentous particles observed in scrapie-effected brains are complex structures. The core of the tubulofilamentous particle scrapie-associated fibrils was revealed by treatment with SDS. Treatment with proteolytic enzymes and subsequent treatment with DNase or mung bean nuclease or S1 nuclease also revealed typical and transitional stages of scrapie-associated fibrils. However, treatment with RNase A had no effect. The data suggest that nucleic acid is a single-stranded DNA protected by a protein coat.

Animals↗
PubMed1991

Increased multimeric mitochondrial DNA in the brain of scrapie-infected hamsters.

We observed a marked increase in multimeric mitochondrial DNA (mtDNA) in brains of scrapie-infected hamsters compared with those of uninfected hamsters. Homogenized brain tissue was subjected to subcellular fractionation to isolate scrapie-associated fibrils and tubulofilamentous structures. Nucleic acids were extracted from the scrapie-associated fibril/tubulofilament fraction which also contained mitochondria. Agarose gel electrophoresis revealed a band corresponding to the size of circular hamster mtDNA in both infected and uninfected samples, but slower migrating bands were observed only in samples from scrapie-infected brain. We showed by molecular cloning, nucleotide sequencing, and Southern blotting that the slower migrating bands are mtDNA. These findings confirm the recent demonstration by differential hybridization that multimeric mtDNA occurs in hamster scrapie brain. Elevated levels of multimeric circular mtDNA have been reported previously in various tumors and cultured cell lines.

Animals↗
PubMed1990

Detection of single-stranded DNA in scrapie-infected brain by electron microscopy.

The nucleic acid content of enriched preparations of mitochondria/tubulofilamentous particles from normal and scrapie-infected hamster brains were examined by electron microscopy. After spreading on collodion-coated grids circular molecules of approximately 15.7 kb corresponding in size to mitochondrial DNA (mtDNA) were observed both in normal and scrapie-infected brains. In nucleic acid preparations from scrapie-infected brains multimeric mtDNA and single-stranded DNA strands of about 0.49 X 10(6) daltons were also visualized. These findings demonstrate the presence of a single-stranded DNA in scrapie-infected brains and are consistent with previous data based on enzyme digestion of nucleic acids isolated from scrapie-infected brains.

Animals↗
PubMed1988

A chronological study of experimental scrapie in mice.

The development of scrapie-associated particles and lesions in four regions of the brain was studied in mice over a period of 30 weeks. Characteristic tubulovesicular particles, identical to those previously described, were first found about half way through the incubation period in mice inoculated by four different routes. The particles are found in brains with scrapie and other spongiform encephalopathies; they have never been seen in other conditions, and potentially represent the infectious agent.

Animals↗
PubMed1988

Evidence that DNA is present in abnormal tubulofilamentous structures found in scrapie.

Abnormal tubulofilamentous structures have been identified in electron micrographs of thin sections and negatively stained impression grids prepared from brains of animals with scrapie and other spongiform encephalopathies, and we showed that such tubules contain a core of filamentous structures resembling scrapie-associated fibrils (SAF). We treated impression grids from brains of scrapie-infected hamsters with several substances that bind to or cleave proteins and nucleic acids to see if they had any effect on the abnormal tubulofilamentous structures. Treatment with three proteolytic enzymes reduced the caliber of the tubules from about 50 nm to 30 nm; subsequent treatment of the 30-nm tubules with DNase I left many typical SAF as well as transitional forms in which twisted SAF emerged from tubules. DNase treatment of the original thicker tubules had no effect, and no SAF were seen on grids. Treatment of the 30-nm tubules with any of three other nucleases (micrococcal, mung bean, and BAL-31) also produced SAF. However, treatment with RNase A had no effect either on the original 50-nm tubules or on the 30-nm tubules produced by proteolysis. Detergent treatment of any of the preparations produced SAF. Treatment with ethidium bromide resulted in staining of the tubules that was inhibited by magnesium ions. The data suggest that the abnormal tubulofilamentous particles found in spongiform encephalopathies may consist of an outer cylinder of protein, an inner cylinder of DNA, and an innermost core of SAF.

Animals↗
PubMed1988

Competitive enzyme-linked immunosorbent assay for Treponema pallidum antibodies.

A competitive enzyme-linked Treponema pallidum immunosorbent assay (CETPIA) was compared with the standard serological tests for syphilis. Of 3081 serum samples submitted, 2883 gave negative results in the CETPIA and the routine screening tests. Positive results were obtained in the CETPIA and in one or more of the specific treponemal tests with 115 samples. Discrepancies in the results of the CETPIA and standard serological tests were found with 83 serum samples, most of these were attributed to biological false positive reactions in the Venereal Disease Research Laboratory (VDRL) test. CETPIA may have a role in the serological diagnosis of syphilis.

Antibodies, Bacterial↗
PubMed1987

Tubulofilaments in negatively stained scrapie-infected brains: relationship to scrapie-associated fibrils.

A simple method was devised for negative-stain transmission electron microscopy of brain infected with the agent of scrapie. Brains of infected hamsters contained large masses of tubulofilamentous structures with irregular fuzzy surfaces. Brains of mice infected with Creutzfeldt-Jakob disease agent contained similar tubulofilaments in smaller numbers. The abnormal tubulofilaments resembled but were distinguished from normal microtubules. On grids soaked in sodium dodecyl sulfate the abnormal tubulofilaments were found in stages of fragmentation, an outer coat appearing t0 strip from the surface to reveal thinner fibrillary structures resembling scrapie-associated fibrils (SAF). The unmasked fibrils were identified as SAF by immunogold labeling, while the larger tubulofilaments were not labeled. The findings indicate that in infected brain tissue SAF may occur as an internal part of a larger structure that is disrupted by detergent and are not likely to be an artifact formed during extraction procedures.

Actin Cytoskeleton↗
PubMed1987

Abnormal tubulovesicular particles in brains of hamsters with scrapie.

Abnormal tubulovesicular particles of an average diameter of 23 nm have been observed in brains of mice with scrapie as well as in other animals with spongiform encephalopathies, but they were thought to be absent from the brains of hamsters with scrapie in which the highest known concentrations of the infectious agent occur. We observed in neuronal processes of hamsters as well as mice clusters of those tubulovesicular structures, most often in postsynaptic terminals. Such particles have now been seen regularly in both experimental and natural scrapie in all species examined as well as in other spongiform encephalopathies.

Animals↗
PubMed1986

An ion-exchange capture technique for routine identification of faecal viruses by electron microscopy.

Faecal specimens from 520 patients with non-bacterial, gastroenteritis were examined by electron microscopy using four methods. These were (1) a direct dip method, (2) low-speed centrifugation, (3) ultracentrifugation and (4) a calcium phosphate method. The calcium phosphate method combined with low-speed centrifugation (750 X g, 2,100 X g) was considered overall best. The calcium phosphate method makes it possible to handle a large number of faecal specimens by saving considerable time and labour.

Adenoviruses, Human↗
PubMed1986

Observations on the distribution of the Zwa (P1A1) antigen on fixed and unfixed platelets.

We have investigated the distribution of the Zwa antigen on unfixed platelets and platelets fixed in paraformaldehyde by examining thin sections of platelets by electron microscopy. Fixation of the platelets produces an even distribution of antigen around the surface membrane of the platelets. Unfixed platelets show clustering in some areas with other areas apparently free of antigen. In addition to this clustered antigen distribution, the unfixed platelets also show invaginations and vesicles containing antigen. The significance of these findings is discussed.

Antigens, Human Platelet↗
PubMed1985

Zwa antigen distribution on the human platelet: an electron microscope study using a colloidal gold labelled marker.

We present the application of a new technique for visualizing surface antigen distribution patterns on intact platelets, treated with anti Zwa antibody, using colloidal gold labelled anti-human immunoglobulin as a marker. Platelets from Zwa negative and from both heterozygous and homozygous Zwa positive individuals were examined for surface Zwa antigen distribution. Platelets fixed with paraformaldehyde show an even distribution of gold particles with a well-developed reticular pattern over their surfaces. Platelets heterozygous for Zwa shows considerable antigen variation, some platelets having similar quantities of antigen to, others much less than, homozygotes. The importance of platelet fixation prior to antigen demonstration by anti Zwa antibody and immunogold visualization is seen by the redistribution of antigen on unfixed platelets. It is suggested that this technique could be exploited to investigate the relationship between platelet surface antigens or structures and their functions.

Antibodies, Anti-Idiotypic↗