Effects of serotonin on laryngeal resistance and respiratory timing in lung denervated rabbits.

The effects of intravenous injection of serotonin on laryngeal resistance and respiratory timing were assessed in urethane-chloralose anaesthetised, spontaneously breathing, lung-denervated rabbits. Serotonin injection consistently produced significant increases in the inspiratory laryngeal resistance in baseline recordings but not following section of the carotid sinus nerves (CSNs), whereas expiratory laryngeal resistance increased under both experimental conditions. The respiratory rate was increased, mainly due to shortening of the expiratory time. Injection of serotonin after motor denervation of the larynx due to mid-cervical vagotomy induced a small, significant decrease in expiratory laryngeal resistance and shortened the respiratory times significantly less than after CSN neurotomy. The respiratory effects of serotonin seem to some extent independent of its main afferent pathways and might possibly occur via stimulation of C-fibre afferents in the extrathoracic trachea and larynx.