Total neuronal numbers of rat lumbosacral primary afferent neurons do not change with age.

Total cell numbers and neuronal diameters of L6 and S1 dorsal root ganglia, which provide a sensory innervation to pelvic viscera were determined in young adult (3-months-old) and compared to those in old (24-months-old) male rats. Two methods of cell counting, serial (section) reconstructions and total profile counting, were used in this study. Our data showed that the total number of L6 and S1 dorsal root ganglia (DRG) cells and their diameters remain essentially constant from 3 to 24 months of age. These results have shown that rat DRG cell numbers do not change during adult life and that neurogenesis of DRG cells in adult rats or neuronal cell death in aged rats cannot be supported. These findings are also consistent with other data supporting the maintenance of pelvic sensory innervation in old age.