The kidneys of 441 full-lifespan rats of Wistar (WAG/Rij) and Brown Norway (BN/Bi) strains and a Sprague-Dawley stock were evaluated histologically for chronic progressive nephrosis. Age- and strain-related susceptibility to chronic progressive nephrosis, in terms of degree of lifetime pathological change, was characterized for male and female WAG/Rij and BN/Bi and female Sprague-Dawley rats. Criteria for minimal chronic progressive nephrosis included thickening of the basement membrane of a glomerular capsule, cast formation, and atrophy of a segment of a proximal convolution with thickened basement membrane. The focal and segmental changes in increasing numbers of nephrons were criteria for severity of the disease. Sprague-Dawley rats showed comparatively rapid development of chronic progressive nephrosis during their second year of life, in contrast to the BN/Bi rats that were affected only slightly prior to 28 and 31 months of age, after which the disease progressed slowly. WAG/Rij rats appeared to assume an intermediate position between the other strains, the latter probably representing the extremes in the expression of this disease.

In order to assess the risk of exposure to ionizing radiation in man, and to evaluate the results of therapeutic measures, the mortality of rhesus monkeys irradiated with X-rays and fission neutrons and the effect of autologous bone marrow transplantation have been investigated. The LD50/30d values for X- and neutron-irradiated monkeys amount to 525 and 260 rad respectively, resulting in an r.b.e. of approximately 2 for the occurrence of the bone marrow syndrome. Protection of the animals by autologous bone marrow transplantation was observed up to doses of 860 rad of X-rays and 440 rad of fission neutrons. After both fission-neutron irradiation and X-irradiation in the lowest range of lethal doses, the bone marrow syndrome was found to occur without the concurrent incidence of the intestinal syndrome. The studies indicate that, for humans accidentally exposed to what would otherwise be lethal doses of fast neutrons, bone marrow transplantation may be beneficial.

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Absrracr. Spontaneous paresis and paralysis associated with degenerative spinal cord and spinal nerve root lesions occurred in three strains of rats used in studies of aging. Focal or segmental spinal cord lesions had mild to severe dernyelination, loss of nerve axons, and lipid-filled gitter cells. The lesions were limited to the white matter and were most severe in the lateral and ventral funiculi. The nerve roots had cholesterol clefts, focal hemorrhage, and demyelination. Atrophy of the skeletal muscle probably was secondary to the cord lesions. Vertebral lesions that involved the spinal canal and vascular blood flow were found, which may explain pathogenesis.Spontaneous posterior paralysis with associated spinal cord and spinal nerve root lesions occurs in several rat strains [3, 5, 131. The syndrome is usually associated with aging since the paralysis has been seen only in rats more than 2 years old. Along with paralysis, severe atrophy of skeletal muscle in the posterior part of the body also has been seen. The condition is progressive and eventually results in death. The cause and pathogenesis are unknown. Some rats had tumors in the spinal cord or canal that could have caused paralysis whilst others had large pituitary tumors. However, in most rats, no specific cause could be found.Three different strains of rats were kept for aging studies at the Institute for Experimental Gerontology. Sporadic cases of paralysis occurred in two strains, but the incidence was very low. We have noticed that the third strain (F, hybrid of the other two strains) has a much higher incidence of posterior paresis and paralysis. Preliminary studies on these rats are presented and the pathologic features are compared to those in other reports [3, 5, 9, 131.