Neurochemical Properties of Dental Primary Aff erent Neurons

Abstract

The long belief that dental primary afferent (DPA) neurons are entirely composed of nociceptive neurons has been challenged by several anatomical and functional investigations. In order to characterize non-nociceptivepopulation among DPA neurons,retrograde transport fluorescent dye was placed in upper molars of rats and immunohistochemical detection of peripherin and neurofilament 200 in the labeled trigeminal ganglia was performed. As the results, majority ofDPA neurons were peripherinexpressing small-sized neurons, showing characteristic ofnociceptive C-fi bers. However, 25.7% of DPA were stained with antibody against neurofi lament 200, indicating signifi cant portion of DPA neurons are related to large myelinated Aβ fi bers. Th ere were a small number of neurons thatexpressed both peripherin and neurofilament 200, suggestive of Aδ fibers. The possible transition of neurochemical properties by neuronal injury induced by retrograde labeling technique was ruled out by detection of minimal expression of neuronal injury marker, ATF-3. These results suggest that in addition to the large population of C-fiber-related nociceptive neurons, a subset of DPA neurons is myelinated large neurons,which is related to low-threshold mechanosensitive Aβfi bers. We suggest that these Aβ fi ber-related neurons might play a role as mechanotransducers of fl uid movement within dentinal tubules.