Histopathologic observations on the senescence-accelerated mice (SAM) reared under specific pathogen free conditions

Five to 12 months old senescence-accelerated mice reared under specific pathogen free conditions (SPF SAM) were subjected to histopathologic examination. Senescence-prone SAM-P/1/Ta, P/3/Ta, and P/8/Ta exhibited marked depletion in thymic cortical lymphocytes which were associated with lymph follicle formation in the medulla, and marked infiltration of lymphocytes in the submaxillary gland, kidney, and other peripheral tissues. Morphometrical analysis of the adrenal gland revealed cortical atrophy and medullary hyperplasia in male SAM-P/8/Ta at 5 months of age. Other characteristic changes were marked vacuolation of the renal proximal tubules in male P/3/Ta and P/8/Ta mice, and degeneration of vascular wall in the testis of P/3/Ta mice. The pathogenesis of these changes appeared to be related to the adrenal lesions. Systemic amyloid deposition, one of the characteristic features of SAM housed in conventional facilities was not observed under the SPF condition. Acceleration of senescence in SPF SAM may arise from disorders of the thymus and adrenal.