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Biomedical subjects

R Silberberg

Publications and source records attributed to R Silberberg.

At least 37 records · Page 2Linked to original sources
PubMed1984

LET-distributions and doses of HZE radiation components at near-Earth orbits.

Among cosmic rays, the heavy nuclei ranging from carbon to iron provide the principal contribution to the dose equivalent. The LET-distributions and absorbed dose aid dose equivalent have been calculated and are presented as a function of shielding and tissue self-shielding. At solar minimum, outside the magnetosphere, the unshielded dose equivalent of nuclei with atomic number Z > or = 6 is about 47 rem/year. The contribution of the target nuclei adds 7 rem/year. With 4 g/cm2 aluminum shielding, and at a depth of 5 cm in a biological phantom of 30 cm diameter, the respective values are 11 and 10 rem/year. Corresponding dose rates for orbits with various inclinations are presented, as well as the LET distributions of various components of cosmic rays.

Cosmic Radiation↗
PubMed1984

Radiation doses and LET distributions of cosmic rays.

Among cosmic rays, the heavy nuclei ( HZE particles) like iron provide the dominant contribution to the dose equivalent during exposures in space. The LET distributions and radiation doses of cosmic-ray components have been calculated--with and without the quality factors--for a set of shielding and tissue self-shielding penetration depths. The relative contributions of heavy ions among solar flare particles to the dose equivalent are also explored. The transport calculations of the nuclei in air, shielding materials, and biological tissue-like material were carried out using the partial and total nuclear cross-section equations and nuclear propagation codes of Silberberg and Tsao . Outside the magnetosphere , at solar minimum, the product of the unshielded dose and the quality factors of cosmic-ray protons and heavy nuclei with atomic number Z greater than or equal to 6 are about 5 and 47 rem/year, respectively. With 4 g/cm2 aluminum shielding and at a depth of 5 cm in a biological phantom of 30 cm diameter, the respective values of the dose equivalents are about 4 and 11 rem/year. Due to the hard spectrum of cosmic rays, the attenuation of protons thus is relatively modest, while that of heavy nuclei is larger due to the larger interaction cross section. The dose equivalent of neutrons in the shielded case mentioned above is similar to that of protons. The biological risks are tentatively assessed in terms of the BEIR 1980 report. Uncertainties in risks due to possible large RBE values at low doses of high-LET radiation and due to the microbeam nature of damage by heavy ions are pointed out. Certain experiments and studies by radiobiologists are suggested for reducing the uncertainties in the estimates of the risks.

Cosmic Radiation↗
PubMed1983

Early onset of disk degeneration and spondylosis in sand rats (Psammomys obesus).

The sand rat is a desert animal which feeds mainly on salt bush, a shrub with a high salt content in its leaves. Sand rats have been used for the study of renal function, and since they may develop diabetes if kept on a laboratory diet without a supplement of salt bush, they have been used for investigation of diabetes-related disorders as well. Older diabetic and non-diabetic sand rats are prone to develop severe degeneration of the intervertebral disks, disk herniation, and subsequent hyperostotic spondylosis. This report is concerned with the relation of these processes to aging. The vertebral columns of 25 sand rats which were fed a standard laboratory diet and a supplement of salt bush ad libitum were examined. The sand rats ranged from 12 to 18 months of age. The vertebral columns were dissected, prepared for microscopic examination, and the findings were compared with those obtained previously in sand rats from 1 1/2 to 2 1/2 years of age. Both disk degeneration and spondylosis were comparable in course and frequency to the changes found in the older sand rats. It was concluded that factors other than age are involved in the pathogenesis of disk degeneration in the sand rat.

Animals↗
PubMed1983

Comparison of truncal and caudal lesions in the vertebral column of the sand rat (Psammomys obesus).

Caudal vertebrae of sand rats (Psammomys obesus) of two age-groups were examined histologically, and the findings were compared with those obtained previously in the truncal spines of these animals. Degenerative processes were basically similar in both locations, although they were somewhat attenuated in the tail. By contrast, the incidences of disk herniation and of spondylosis were much more common in the trunk than in the tail. We concluded that in the sand rat there is a common, probably systemic, denominator for disk degeneration at all sites, and suggest that this factor is related to the peculiar water and/or electrolyte metabolism of these desert animals. Factors causing herniation of the degenerated disk and spondylosis seem to be related to local stresses which, in the presence of marked disk degeneration, may not exceed physiological limits.

Age Factors↗
PubMed1981

Effect of diabetes on the vertebral column of rats and its modification by estradiol.

In vertebrae of genetically selected sucrose-fed diabetic rats a statistically significant bone deficit was found after diabetes had been present for about 8 months. No osteopenia was observed in diabetic rats following treatment with estrogenic hormone for 5--7 months. The development of osseous centers in the end plates of the vertebrae was retarded in diabetic rats, but was about normal in diabetic rats given estrogen. No differences were noted in the growth zones or in the tendency to develop articular lesions in rats of the various groups. Possible differences in the amount of GAG in intervertebral discs of diabetic and non-diabetic rats respectively await further confirmation.

Animals↗
PubMed1981

Biochemical studies of bone from diabetic rats and rats bearing transplanted pancreatic islets.

A comparison of lysozymal enzymes involved in glycosaminoglycan metabolism in cortical bone found significantly increased activity in the presence of streptozotocin-induced diabetes. The presence of transplanted pancreatic islets and restitution of the normal systemic insulin and glucose values did not alter these changes. The enzyme activity of cancellous bone appeared to be even less responsive to diabetic pathology with changes developing only with advancing age.

Aging↗
PubMed1980

Quantitative histochemical changes in intervertebral discs in diabetes.

A comparison of the nuclei pulposi of 4 diabetic and 2 nondiabetic subjects disclosed a statistically significant decrease in hexosamine, a statistically significant increase of hydroxyproline, and significantly increased activities of four enzymes involved in the metabolism of carbohydrates. The results are considered preliminary in view of the small size of the sample.

Adult↗
PubMed1979

Diastropic dwarfism: a histochemical and ultrastructural study of the endochondral growth plate.

Chondro-osseous tissue from five patients with diastropic dwarfism was studied by histologic, histochemical, and electron microscopic methods. The major abnormalities observed were: 1) irregular distribution of chondrocytes undergoing degeneration in the resting cartilage; 2) abnormal distribution of collagens in the resting cartilage; 3) a spectrum of fibrous matrix lesions in the resting cartilage which ranged from focal areas of aggregated collagen fibrils to large cystic lesions in which intracartilagenous ossification occurred; and 4) shortened, irregular cellular columns within the growth plate which were occasionally disrupted by matrix lesions extending from the resting cartilage. These alterations in chondro-osseous morphology have not been observed in any of the other skeletal dysplasias examined to date and appear to be pathognomonic for this disorder.

Adolescent↗
PubMed1979

Degeneration of the intervertebral disks and spondylosis in aging sand rats.

Aging sand rats (Psammomys obesus) kept on a standard laboratory diet supplemented by salt bush--their natural source of food--were examined for changes of the vertebral column. From about 6 months of age on, degeneration of the intervertebral disks was noted. The changes increased in severity with increasing age, and from 1 1/2 years of age on, massive multiple disk herniations were seen. Associated with these lesions were spondylosis of "intervertebral" as well as hyperostotic type, and osteoarthrosis of the apophyseal joint. The sand rat seems to be an excellent model for the study of the pathogenesis of spinal diseases associated with the aging process.

Aging↗
PubMed1977

Epiphyseal growth and osteoarthrosis in blotchy mice.

Blotchy mice which carry a gene causing inadequate cross-linking of collagen were investigated for the progress of epiphyseal growth and for the appearance of changes in the knee joints following cessation of growth. In male mice of the strain, which are hemizygous for the gene, early growth proceeded in a histologically normal fashion, although the metaphyseal bone was less abundant than usual. From the age of 3 1/2 months on, the animals developed osteoarthrosis of the knee joints and at the time of death at 5-6 1/2 months of age, 88% of the animals had osteoarthrosis. The findings are discussed with special reference to a possible role of the collagen of the articular cartilage in the pathogenesis of some forms of osteoarthrosis.

Animals↗
PubMed1977

Enzyme studies in the articular cartilage of diabetic rats and of rats bearing transplanted pancreatic islets.

The articular cartilage of normal rats, of rats made diabetic with streptozotocin, and of rats made diabetic with streptozotocin and subsequently transplanted with isologous pancreatic islets was examined for the activities of enzymes engaged in the synthesis and degradation of glycosaminoglycans (mucopolysaccharides). The activities assayed were those of the degrading enzymes B-glucuronidase, B-acetyglucosaminidase, B-acetylgalactosaminidase, B-galactosidase, and those active in synthesis: uridine diphosphate dehydrogenase, glucose-6-phosphate dehyrogenase, and phosphofructokinase. In the diabetic animals all enzyme activities were increased, thos of the degrading enzymes more than those of the others. Implantation of pancreatic islets reversed the changes produced by diabetes, enzyme activities returning to near-normal levels.

Acetamides↗
PubMed1976

Ultrastructure of articular cartilage of achondroplastic mice.

Articular chondrocytes of achondroplastic mice (cn/cn) resemble ultrastructurally those of their non-achondroplastic siblings (Cn/Cn or Cn/cn), except for premature deposition of glycogen and a tendency to undergo regression. The latter may be slight or extreme. The ultimate cause of the vulnerability of the chondrocytes and the cause of the heterogeneity of the reaction could not be determined with the method employed. Nevertheless, increased vulnerability accounts for cell death under conditions which are usually not injurious, and which may be either physiologic or altered by endogenous or exogenous factors.

Achondroplasia↗
PubMed1976

Obesity and joint disease.

In male mice of strain C57Bl, obesity caused by intraperitoneal administration of aurothioglucose failed to alter the course of spontaneous osteoarthrosis. The distribution of osteoarthrosis of the knee joint and of spondylosis of the thoracic and lumbar spine was haphazard in regard to body weight, and levels of plasma and hepatic lipids. It is concluded that the arthrosis-promoting effects of fat-enriched diets are not mediated by the simultaneously occurring obesity.

Aging↗
PubMed1976

Aging changes in intervertebral discs and spondylosis in Chinese hamsters.

Vertebrae and intervertebral discs of Chinese hamsters, a species of rodents that develop spontaneous diabetes, were investigated for age-linked changes and for the occurrence of spondylosis. Aging changes in the intervertebral discs were similar in diabetic and nondiabetic animals. The incidence of spondylosis was significantly increased and its onset was accelerated in the diabetic animals. The mechanisms operative in the pathogenesis of the lesions and their relation to the human disease are discussed.

Aging↗
PubMed1976

Articular cartilage of diabetic Chinese hamsters.

Investigations were carried out in order to determine whether animals with spontaneous diabetes are prone to develop skeletal lesions comparable to those found in diabetic human subjects. The present report deals with the ultrastructure of the cartilage of the hip joint of diabetic Chinese hamsters and nondiabetic control animals. In the diabetic animals, chondrocytes of the femoral head showed atrophy of the endoplasmic reticulum, bizarre mitodhoncria, and huge lipid inclusions, which are changes suggestive of disturbed function.

Animals↗