Morphological studies of the distribution of neuroactive peptides in the trigeminal and oral mucosa regions of the rat.

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Peptidergic innervation of two types of oral tissues, oral mucosa and tooth pulp, was investigated by experimental immunohistochemistry.In oral mucosa, calcitonin gene-related peptide (CGRP)-like immunoreactive (IR) fibers and substance P (SP) IR fibers were observed in the submucosal layer. Some of these fibers were observed to enter the epithelium.The double labeling imunofluorescence method revealed that most of these fibers contain both CGRP and SP at the same time.On the other hand, CGRP-IR fibers were observed in the tooth pulp. SP-IR fibers were only occasionally detected. Fast blue (FB) was injected into the oral mucosa and into tooth pulp. Cell sizes of FB labeled CGRP-IR neurons in the trigeninal ganglia were measured and compared in these two cases.Most of the FB labeled CGRP-IR neurons were small in the buccal mucosa and medium to large in the tooth pulp. In rats treated at birth with capsaicin, CGRP and SP containing fibers in the oral mucosa totally disappeared, but CGRP- … More IR fibers were not affected in the tooth pulp. These findings suggest that these two types of oral tissues are innervated by different-sized CGRP-IR neurons in the trigeminal ganglia.The distribution of SP, CGRP, leucine enkephalin (LE), somatostatin (SOM), cholesystokinin-8 (CCK-8), neurotensin (NT). neuropeptide-Y (NPY) and tyrosin hydroxylase (TH) was investigated in the nucleus tractus spinalis nervi trigemini (nVsp) of the rat by means of immunohistochemistry. The highest density of the neuropeptides in the nVsp were observed in the superficial layer of the caudal subnucleus. This suggests that the peptides examined play roles in the conduction on modification of thermal and nociceptive information. On the other hand, TH reactive fibers were more diffusely distributed in the nVsp, which was quite different from those of neuropeptides.Distribution patterns of peptide containing cells and fibers, especially of SP and LE, in the superficial layer of the caudal subnucleus of nVsp were similar, suggesting the possibility of co-localization of these neuropeptides.CGRP-like immunoreactive cells were not observed in the nVsp but immunoreactive fibers were densely packed in the superficial layer. These fibers were considered to be primary afferents. Less