Vanilloid receptor expression and capsaicin excitation of rat dental primary afferent neurons

Little is known about the molecular mechanisms that cause excitation of neurons which innervate the teeth. We investigated whether rat dental sensory neurons express the vanilloid (capsaicin) receptor (VRI). Dental sensory neurons were identified by retrograde transport of the fluorescent dye DiIC(18) placed in maxillary molars. Patch-clamp recordings in culture showed that 65% of DiIC(18)-labeled rat trigeminal ganglion neurons are excited by capsaicin. Responders covered the entire range of cell sizes examined (soma diameter, 24 to 48 mum). All non-responders had a soma diameter > 33 mum. Capsazepine (1 muM) reduced the capsaicin-evoked membrane current (6/6) and depolarization (7/7 responders). RT-PCR amplified a 375-bp product from DiIC(18)-labeled neurons which was identical to that expected for VRI. Thus, many rat dental primary afferent neurons are excited by capsaicin, and the response appears to be mediated by VRI. These results suggest that pharmacological blockers of VRI may provide significant relief of dental pain.