Aging-related morphological changes in the main olfactory bulb of the fischer 344 rat

—Aging-related changes in several structural characteristics of the main olfactory bulb (MOB) were evaluated using Fischer 344 rats 3, 18, 30 or 36 months of age. Histological examination of the nasal mucosa revealed no evidence of concurrent rhinitis in any of the animals studied. The internal granular layer of the MOB exhibited continual growth, increasing in volume by a factor of 63% over the range of ages studied. The sizes of MOB mitral cell perikarya and nuclei, expressed either as observed cross-sectional areas or as estimated mean volumes, did not change significantly as a function of age. The numbers of mitral cells exhibiting 2 nucleoli in the plane of section decreased from about 22% in the youngest animals to about 4% in the 18- and 30-month old animals and to nil in the oldest animals. These results are discussed in relation to findings of other investigators using Sprague-Dawley or Wistar rats. It is concluded that major structural age changes in the rat MOB are strain dependent.