Trigeminal nerve-mediated nasal chemesthesis: Chemosensory mechanisms of the Vth cranial nerve.

摘要

Classically, the peripheral receptors of the trigeminal chemosensory system in the nasal cavity are described as free nerve endings arising from the ethmoid and nasopalatine branches of the trigeminal nerve. Chemical activation of the trigeminal system through these fibers leads to a variety of protective behavioral and physiological reflexes in addition to the sensory perceptions of irritation and pain. Despite this important protective function, the current understanding of the mechanisms underlying trigeminal chemosensitivity is vague at best. Specifically, it remains unclear how simple intraepithelial free nerve endings are able to interact with the wide variety of structurally diverse chemicals that have been demonstrated to activate the trigeminal nerve.; In the present series of experiments, ethmoid nerve recordings and respiratory responses to a variety of chemical stimuli were obtained from rats under varying pharmacological treatments. In conjunction with behavioral experiments conducted in capsaicin-desensitized animals, and with immunohistochemical analysis of the nasal epithelium, these results indicate a hitherto unreported complexity in the receptor mechanisms of the nasal trigeminal chemosensory system. Evidence is presented for multiple transduction mechanisms, including indirect neural activation via a peripheral enzymatic step, direct activation via a receptor-based mechanism, and the involvement of a previously unreported cellular component of the nasal trigeminal system.