Supranodose vagotomy eliminates respiratory depression evoked by dermorphin in anaesthetized rats

The respiratory effects of stimulation of mu-opioid receptors were studied in spontaneously breathing anaesthetized rats that were either neurally intact or subjected to bilateral supranodosal vagotomy. An intravenous dermorphin bolus of 0.5 mg/kg evoked the apnea followed by breathing of reduced rate and compensatory augmentation of tidal volume, which resulted in an invariable minute ventilation. Cardiovascular effects consisted of hypotension and temporary fall in heart rate. In rats initially treated by supranodosal vagotomy, dermorphin did not evoke any respiratory and cardiovascular effects. These results indicate that vagal pathway and the nodose ganglia are involved in dermorphin-induced respiratory depression.