Age-related decrease of the perineuronal satellite cell number in the rabbit spinal ganglia

This study was undertaken to establish whether a change in the perineuronal satellite cell number contributes to the age-related reduction of the volume ratio between the perineuronal glial sheaths and their associated nerve cell bodies, observed to occur in rabbit spinal ganglia. The volumes of the nerve cell bodies and the numbers of the related satellite cell nuclei were estimated on serial semithin sections from young adult and old rabbits. As satellite cells are mononucleate, the number of the nuclei corresponds to that of these cells. The satellite cell sheaths in both age groups were also examined under the electron microscope. The mean number of satellite cells was significantly smaller in the aged animals than in the young adults although the mean volume of the nerve cell bodies was significantly larger in the former. Cytoplasmic vacuoles, invaginations of the connective tissue and autophagic vacuoles were more frequent in the old rabbits. Satellite cells with pyknotic nuclei and remnants of degenerated satellite cells were only found in aged animals, although rather rarely. The decrease in the satellite cell number is one of the mechanisms by which the age-related reduction of the volume ratio between the perineuronal glial sheaths and their associated nerve cell bodies takes place. The decrease in the satellite cell number seems to occur, at least in part, through cell degeneration. However, other mechanisms (e.g., detachment of satellite cells from the perineuronal sheaths) cannot be excluded. Since satellite cells play a role in neuronal support, the significant decrease in their number probably has negative consequences for neuronal activity.