Abstract
BACKGROUND: Inflammation of the nasal mucosa leads to sneezing, nasal itch, rhinorrhea, and nasal blockage. Many of these symptoms are likely the result of nasal trigeminal sensory nerve stimulation by inflammatory mediators. Nasal challenge with the C-fiber stimulant capsaicin causes a different set of symptoms than those evoked by histamine, suggesting that these 2 stimuli may activate separate subpopulations of nasal sensory nerves. OBJECTIVE: To investigate the trigeminal sensory nerves innervating the guinea pig nasal mucosa and to address specifically the hypothesis that histamine and capsaicin activate distinct subgroups of these nerves. METHODS: Guinea pig trigeminal neurons (retrogradely labeled from the nasal mucosa) were assessed for their responses to histamine and capsaicin by studying changes in the intracellular free calcium concentration, and assessed for substance P immunoreactivity. RESULTS: Only 60% of the nasal-specific trigeminal sensory neurons were found to be capsaicin-sensitive. Histamine stimulated only a subset (