Nasal stimulation by water down-regulates cough in anesthetized rabbits

The 'cough center' can be tuned by various afferent inputs, suggesting possible interactions at a central level of neural pathways originating from distant anatomical sites. The present study was designed to determine whether brief mechanical stimulation of the trachea can trigger cough during apnea elicited by nasal instillation of water. Twelve anesthetized, tracheotomized rabbits were studied. Mechanical stimulation of the trachea was performed under 3 conditions: baseline control, after instillation of saline into the nose and during apnea following instillation of water. The baseline breathing pattern did not differ between the 3 conditions. In a series of 171 stimulations, expiration reflex occurred in 81% of stimulations during apnea with a significantly (p<0.0001) lower peak expiratory flow than at baseline or during saline instillation. The incidence of responses comprising a cough reflex was also lower during water instillation than at either baseline or with saline (p<0.0001). These results indicate that stimulation of nasal afferents with distilled water likely down-regulates cough.