Stereological analysis of liver parenchymal cells from young and old rats.

Hepatocyte morphology of the three zones of the liver lobule was evaluated by stereological analysis in 3-month-old and 35-month-old virgin female WAG/Rij rats. In the old rats, the volume of the nucleus and cytoplasm, and volume densities of smooth endoplasmic reticulum and lysosomes were increased in all areas of the liver lobule, while the volume density of glycogen was decreased. In addition, mitochondrial and vacuolar densities decreased in midzonal hepatocytes. These results are discussed in comparison with other (conflicting) literature data, and the relevance of a more uniform choice of ages, breeding conditions, sex, strain and other secondary criteria is emphasized. The importance of a subdivision of the liver lobule into zones is stressed, as it allows the consideration of environmental factors in the interpretation of morphological changes with age.

The epithelial cell component of the thymuses of aged female BN/Bi rats: a light microscopic, electron microscopic, and autoradiographic study.

Thymuses of virgin female BN/Bi rats of various ages were studied by light microscopy, electron microscopy, and autoradiography. The thymuses appeared to undergo a normal involution during the first 2 years of life. In rats 2 to 4 years of age, there was an apparent proliferation of epithelial cords and tubules suggestive of a true hyperplasia. The appearance of these epithelial cords and tubules in the otherwise atrophied thymuses of old animals (more than 30 months of age) is described. The predominant epithelial cell type, containing dark apical granules, showed morphologic evidence of secretion. 3H-leucine labeling confirmed active protein synthesis and secretion by these cells. Lymphocytes and macrophages were identified within the lumina and between the epithelial cells of the epithelial cords and tubules suggesting that they were able to migrate into and probably out of these structures.

A naturally occurring epizootic caused by Sendai virus in breeding and aging rodent colonies. I. Infection in the mouse.

An acute Sendai virus epizootic occurred simultaneously in a breeding colony, in experimental and stock animal rooms, and in a colony of aging mice. During the 2-month period that the infection was at its maximum, death rates were approximately doubled. In some strains, the preweanling death rate reached 100%. RFM and BALB/c mice were most susceptible and NZB mice least susceptible. The mortality during the period of Sendai virus infection was increased for most strains and age groups except for the oldest female RFM and NZB mice. Death rates during the epizootic were lowest in young adult mice (greater than 10 weeks of age) and highest in the very young mice (less than 10 weeks of age) and in the oldest male and the moderately aged female mice. Although a substantial number of older mice died during the epizootic, examination of the age-specific death rates indicated that the increase in deaths remained relatively constant for all ages over 10 weeks. This showed that the older mice were not more susceptible to Sendai virus infection. As a sequela of the epizootic, focal chronic pneumonia was found in 10-40% of the mice coming to necropsy even 1 year later.