EFFECTS OF MEDULLARY MIDLINE LESIONS ON COUGH AND OTHER AIRWAY REFLEXES IN ANESTHETIZED CATS

The involvement of rapheal and medial parts of the medullary reticular formation in both generation of airway reflexes and changes in breath ing were studied in 18 chloralose or pentobarbitone anaesthetized, non -paralyzed cats. Chemical lesions to the medullary midline region (0-4 mm rostral to the obex) produced by localized injections of the neuro toxin kainic acid regularly abolished the cough reflexes evoked from t he tracheobronchial and laryngopharyngeal regions and ice most cases a lso the expiration reflex induced from the glottal area. The aspiratio n reflex elicited from the nasopharynx was spared, but was less intens e. However, the signs of cough and expiration reflexes were preserved hi the neurogram of the recurrent laryngeal nerve. The experiments hav e shown the importance of raphe nuclei and other medullary midline str uctures for the occurrence of cough and expiration reflexes. One possi ble explanation for the elimination of these expulsive processes is th e removal of an important source of facilitatory input to the spinal r espiratory motoneurons or to the brainstem circuitries that mediate co ugh and expiration reflexes. The role of the medullary midline in modu lation of eupnoeic breathing and blood pressure is also discussed.