Neurogenic inflammation in nasal allergy: histochemical and pharmacological studies in guinea pigs. A review.

The role of neuropeptides in nasal allergy was examined in guinea pigs by histochemical and pharmacological study. Intranasal application of toluene diisocyanate (TDI) induced nasal allergy-like behaviors: sneezing and watery rhinorrhea, and decreased histamine content in the nasal mucosa in guinea pigs sensitized with TDI. The immunoreactivity of substance P (SP) and calcitonin gene-related peptide (CGRP) in the nerve terminals in the nasal mucosa was increased after intranasal application of TDI. We also observed a decrease in the immunoreactivity of SP and CGRP, and an increase in their mRNA expression in the trigeminal ganglion neurons. These findings indicate that exposure to TDI enhanced the biosynthesis of both SP and CGRP in the trigeminal ganglion neurons and their axonal transportation to the terminals in the nasal mucosa. In animals pretreated with capsaicin before sensitization, TDI did not induce nasal allergy-like behaviors and histamine release in the nasal mucosa. Since capsaicin depletes SP and CGRP in the sensory nerves, this finding indicates neuropeptide-mediated histamine release in the nasal mucosa. All these findings suggest that, on exposure to TDI, the antidromic release of SP and CGRP in the nasal mucosa triggers the release of histamine, resulting in the development of symptoms of nasal allergy.