The effects of neonatal capsaicin administration on trigeminal nerve chemoreceptors in the rat nasal cavity.

Trigeminal nerve fibers in the nasal cavity respond to a variety of volatile chemical stimuli. Some of these trigeminal nerve fibers have been suggested to be capsaicin-sensitive and thus belong to a class of pain receptor rather than constituting a separate class of chemoreceptor. Our current results confirm this suggestion. Trigeminal nerve responses to volatile chemical stimuli were eliminated in rats which were injected with capsaicin on the second day of life. Animals whose nerves were unresponsive to chemical stimuli also exhibited a loss of intraepithelial peptide-immunoreactive fibers in their nasal cavities. The results of this study suggest that trigeminal nerve fibers in the nasal cavity which respond to chemical stimuli may be polymodal nociceptors which contain substance P, calcitonin gene-related peptide, or perhaps other neuropeptides.