The menthol and cold sensation receptor TRPM8 in normal human nasal mucosa and rhinitis.

Background: Menthol and cold sensation trigger symptoms and reflex responses in the upper airway, but the underlying molecular mechanisms are unknown. We have therefore studied nerve fibres expressing the menthol and cold receptor TRPM8 in normal human mucosa, and in rhinitis. TRPM8 nerve fibres were compared with those expressing other TRP receptors including TRPV1 (capsaicin and heat receptor), and TRPA1 (mechano-cold receptor).
Methods: Immunohistology and image-analysis were used to study TRP receptors in biopsies of nasal turbinate from control subjects, patients with allergic rhinitis, and non-allergic rhinitis.
Results: TRPM8-immunoreactive nerve fibres were observed in the sub-epithelium, and were profuse around blood vessels in deeper regions, where they were markedly greater in number than TRPV1+ fibers. Image analysis of TRPM8 in sub-epithelial and vascular regions showed no significant differences between control and the rhinitis patient groups. TRPA1-immunoreactivity was weak and seen rarely in nerve fibres.
Conclusion: We show that TRPM8 nerve fibres are abundant in nasal mucosa particularly around blood vessels, and may mediate neurovascular reflexes. TRPM8 antagonists deserve consideration for therapeutic trial in rhinitis.