Respiratory responses to electrical stimulation of the cervical sympathetic nerves in decerebrate, unanaesthetized cats

1. The effects of respiration of electrical stimulation of the peripheral cut end of the cervical sympathetic nerve were studied in seventeen decerebrate, unanaesthetized cats. 2. The tidal volume increased and the end‐tidal CO₂ fell within 2‐3 breaths after the onset of stimulation in fourteen cats. 3. In three experiments tidal volume and respiratory rate fell during stimulation and increased above the control when the stimulus was interrupted. 4. All respiratory responses to sympathetic stimulation were abolished after cutting the carotid sinus nerves and are attributed to activation of chemo‐ and baroreceptor afferents. 5. With the carotid sinus nerves intact, respiratory responses could be eliminated completely only by cutting the post‐ganglionic sympathetics that pass directly to the carotid body and the post‐ganglionic sympathetics that join the glossopharyngeal nerves to course with the sinus nerves to the carotid bifurcation. 6. Pentobarbitone (10 mg/kg) or chloralose (40 mg/kg) given intravenously depressed spontaneous ventilation and responses to sympathetic nerve stimulation. 7. Stimulation changed blood pressure slightly in fourteen experiments; in ten it fell and in four it increased 10 mm Hg or less. After pentobarbitone or chloralose, stimulation elicited a pronounced pressor response. 8. The results of the study indicate that activation of sympathetic pathways to the carotid body constitutes an effective stimulus to ventilation.