Superior laryngeal nerve section abolishes capsaicin evoked chemoreflex in anaesthetized rats.

Respiratory effects of an intravenous injection of capsaicin were investigated in nine vagotomized and subsequently laryngeally deafferentated, urethane- and chloralose-anaesthetized and spontaneously breathing rats. Bolus injection of capsaicin (5 micrograms/kg) into the right femoral vein induced an expiratory apnoea of 4.23 +/- 0.63 s duration (mean +/- SEM). In post-apnoeic breathing, tidal volume increased by 14% from the control level (P < 0.05) in all nine rats treated by vagotomy. Section of the superior laryngeal nerves (SLNs) precluded the occurrence of apnoea. Results of this study indicate that in vagotomized rats sensory input from the larynx constitutes an important pathway to the nodose ganglia endowed with capsaicin receptors.