Effects of vagal and laryngeal afferents on apnoeic response to serotonin in cats.
Intravenous serotonin (5-HT) elicits apnoea followed by subsequent, shallow tachypnoea. The present study was designed to ascertain whether laryngeal afferents play a role in the respiratory reflex response. Administration of 5-HT into the femoral vein (i.v.) or to the laryngeal artery (lar. art.) in anaesthetized, spontaneously breathing cats caused an expiratory apnoea that was significantly reduced (i.v.) or abolished (lar. art.) by bilateral midcervical vagotomy. Subsequent bilateral division of the superior laryngeal nerves (SLNs) did not affect the magnitude of apnoea on i.v. administration. Supranodose vagotomy abolished the occurrence of post-serotonin apnoea following i.v. injection, which is consistent with earlier results. During the phase of rapid, shallow breathing the peak respiratory airflows were significantly increased on i.v. 5-HT injection in all neural states of cats, whereas laryngeal artery administration failed to produce a significant change in respiration airflows from baseline. Serotonin significantly increased breathing frequency in the intact and denervated (vagus and SLN cut bilaterally) cats independent of the route of injection. The results show that serotonin effects the respiratory pattern with large contribution of pulmonary vagal but not laryngeal afferents. However, the occurrence of the expiratory apnoea was related to large extent to the integrity of the infranodose vagi.
Szereda-Przestaszewska
M
M
Department of Neurophysiology, PAS Medical Research Centre, Warsaw, Poland.
Wypych
B
B
D000818:Animals; D001049:Apnea / Q000139:chemically induced / Q000503:physiopathology; D002415:Cats; D005260:Female; D007275:Injections, Intravenous; D007823:Laryngeal Nerves / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010366:Peak Expiratory Flow Rate; D011652:Pulmonary Circulation / Q000187:drug effects; D012119:Respiration / Q000187:drug effects*; D012701:Serotonin / Q000008:administration & dosage / Q000494:pharmacology*; D014628:Vagotomy; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology*
D012701:Serotonin