Pituitary adenylate cyclase-activating polypeptide-immunoreactive nerve fibers in rat and human tooth pulps

The distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) was examined in the tooth pulp. In rat and human tooth pulps, PACAP-immunoreactive (IR) nerve fibers were observed around blood vessels and in the subodontoblastic and odontoblastic layers. The predentine and dentine were devoid of such nerve fibers. The double immunofluorescence method indicated the co-expression of PACAP with calcitonin gene-related peptide (CGRP) or vasoactive intestinal polypeptide (VIP). Virtually all PACAP-IR nerve fibers co-expressed CGRP-immunoreactivity (IR) in the rat tooth pulp suggesting their sensory function. In addition, a retrograde tracing method indicated that PACAP-IR nerve fibers in the rat tooth pulp originated from the trigeminal ganglion. On the other hand, almost all PACAP-IR nerve fibers in the human tooth pulp co-expressed VIP-IR and, thus, thought to be autonomic in nature.