Aging rat vestibular ganglion: I. Quantitative light microscopic evaluation

This study was undertaken to quantify age-related changes in the rat vestibular ganglion. Cell number, diameter, and proximal-distal distribution based on size were evaluated. Serial 5-μm plastic sections of the vestibular ganglion from 15 female Wistar rats were examined. Rats were divided into three age groups: young (Y, 3 to 5 months, n = 5), old (0, 24 to 26 months, n = 3), and very old (VO, 28 to 31 months, n = 7). Quantitative analysis indicated no significant differences ( P < .05) in the estimated number of ganglion cells (mean: Y = 1,690, 0 = 2,257, VO = 1,678), ganglion cell profile diameters (mean: Y = 22.5 μm, n = 2,886; O = 23.7 μm, n = 2,313; VO = 22.8 μm, n = 4,061), or proximal-distal localization (proximal: 22.3 μm, 24.4 μm, 22.7 μm; middle: 22.6 μm, 23.1 μm, 22.4 μm; distal: 23.3 μm, 23.4 μm, 23.7 μm; Y, O, and VO, respectively). When pooled, the old animals tended to have slightly larger cell profiles than the other groups. We noted a dramatic age-related increase of aging pigment within the ganglion cell profiles, making the old and very old animals easily distinguishable from the young. In most of the cell profiles, the aging pigment was more or less uniformly distributed throughout the cytoplasm. However, in some, aging pigment was accumulated at one pole of the cell profile. While no typical degenerating cellular profiles were found in any of the sections, several of the ganglion cell profiles from the old animals revealed dense cytoplasm, possibly indicating an early stage of degeneration.