In cats anaesthetized with sodium pentobarbitone (35 mg kg-1), an investigation was made of the mechanisms underlying the enhancement of aortic chemoreceptor activity through the excitatory effect mediated by the sympathetic outflow to them during hypoxia and hypotension. 2. Removal of the right stellate ganglion significantly (P < 0.01) reduced the responses of the chemoreceptors to hypoxia and hypotension. Injection of a bolus of sodium pentobarbitone reduced the responses before, but not after, stellectomy. This indicated that the excitatory sympathetic influence on the chemoreceptors (attributed to glomeral vasoconstriction leading to reduction in blood flow) is exerted entirely through the right stellate ganglion. This excitatory effect was abolished after cutting the vagi and both carotid sinus nerves. 3. It is concluded that, in addition to the direct excitatory effect of hypoxia on aortic chemoreceptors, a reflex chemoreceptor excitatory component is mediated through the vagi, carotid sinus nerves and right stellate ganglion.
