HYPOGLOSSAL AND PHRENIC-NERVE RESPONSES TO CAROTID BARORECEPTOR STIMULATION

We examined the relationship between hypoglossal and phrenic nerve act ivities and carotid sinus pressure. In 12 adult cats that were decereb rate, vagotomized, paralyzed, and mechanically ventilated, we isolated the left carotid sinus for perfusion and denervated the right carotid sinus. Mean arterial blood pressure was maintained at 90-100 mmHg usi ng a low resistance-reservoir containing saline and connected to the a bdominal aorta. Constant pressure was applied to the carotid sinus reg ion. We found that increased carotid sinus pressure immediately inhibi ted inspiratory-synchronous (phasic) hypoglossal nerve activity and th at there was a direct inverse relationship between phasic hypoglossal activity and carotid sinus pressure up to a carotid pressure of 285 mm Hg. Increased carotid sinus pressure had no effect on tonic hypoglossa l nerve activity and only slightly inhibited phrenic nerve activity. C utting the left carotid sinus nerve abolished this response. We also a pplied pressure pulses to the carotid sinus at discrete times during t he phrenic cycle. We found that baroreceptor inhibition of phasic hypo glossal nerve activity was gated during the phrenic cycle: maximum inh ibition occurred when the pulse was applied in late expiration. We con clude that carotid baroreceptor stimulation preferentially inhibits in spiratory synchronous hypoglossal nerve activity and that this afferen t information traveling in the carotid sinus nerve is gated by the res piratory control center.