Localization of substance P-like immunoreactivity in nerves in the tooth pulp

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Abstract
The occurrence of substance P (SP)-like immunoreactivity was studied in cat dental pulp. In untreated animals SP-positive fibers were found in all areas of the pulp. Most fibers were seen in central parts of the pulp, but they were also observed in relation to the odontoblasts. Single, possibly unmyelinated, or fine caliber fibers or small bundles of them were seen running close to large, non-fluorescent myelinated nerves, to blood vessels or without any obvious association with either of these structures. Fourteen days after transection of the inferior alveolar nerve no SP-positive fibers were observed in pulps on the denervated side. Transection of the cervical sympathetic ganglion did not change the occurrence of SP-positive fibers. Apparently there are at least 2 types of afferent fibers in the dental pulp of the cat. Since the tooth pulp gives rise only to pain sensation when stimulated, the results give morphological support for a role of SP neurons in pain transmission.