INTERACTION BETWEEN CENTRAL PATTERN GENERATORS FOR BREATHING AND SWALLOWING IN THE CAT

1. We examined the interaction between central pattern generators for respiration and deglutition in decerebrate, vagotomized, paralysed and ventilated cats (n = 10), by recording activity from the following ne rves: hypoglossal, phrenic, thyroarytenoid and triangularis sterni. Fi ctive breathing was spontaneous with carbon dioxide above the apnoeic threshold (end-tidal P(CO2), 32 +/- 4 mmHg) and fictive swallowing was induced by stimulating the internal branch of the left superior laryn geal nerve (SLN) continuously (0.2 ms pulse duration, 10 Hz). 2. In al l ten animals, SLN stimulation evoked short bursts of thyroarytenoid a nd hypoglossal nerve activity indicative of fictive swallowing. In two of ten animals, respiration was inhibited completely during deglutiti on. In the other eight animals, fictive breathing and swallowing occur red simultaneously. 3. With SLN stimulation below threshold for elicit ing swallowing, the respiratory rhythm decreased, the duration of insp iration did not change but the duration of expiration, especially stag e II, increased. Integrated nerve activities indicated that the rate o f rise and peak of phrenic nerve activity decreased, stage I expirator y activity of the thyroarytenoid and especially that of the hypoglossa l nerve increased and stage II expiratory activity of the triangularis sterni nerve was suppressed completely. However, if inspired carbon d ioxide was increased, i.e. hypercapnic ventilation, stage II expirator y activity remained partially during continuous SLN stimulation. 4. Fi ctive-swallowing bursts occurred only at respiratory phase transitions . At the minimal stimulus intensity that evoked repetitive swallowing bursts, the pattern of interaction between breathing and swallowing ce ntral pattern generators was consistent for each animal (n = 7) but wa s different across animals. In four animals, fictive swallows occurred at the phase transition between stage II expiration and inspiration, at the transition between inspiration and stage I expiration in one an imal; and in two other animals, at the transition between stage I and II of expiration.