Changes in pulpal nerves with aging.

Aging of cat tooth pulp nerves involves ultrastructural changes, and changes in the expression of some neuropeptides and in the expression of the receptor for nerve growth factor. Electron microscopy of old pulps demonstrates loss and degeneration of unmyelinated and myelinated axons, as well as demyelination. Immunohistochemical findings show a marked age-related decrease in pulpal calcitonin-gene related peptide- and substance P-like immunoreactivity, and a reduction in nerve growth factor receptor-like immunoreactivity. Changes in neuropeptide expression are not entirely due to loss of nerve fibers, since most aging pulps contain nerve growth factor receptor-positive fibers which lack neuropeptide-like immunoreactivity. The changes reported here parallel the observation that there is an age-related reduction in sensitivity to pulpal stimulation, but may also contribute to the development of oral sensory phenomena such as neuropathic pain. Moreover, the senescent transformation of pulpal nerves probably affects hemoregulation of the pulp, and may thus have consequences for pulpal extraneuronal tissue.