Selective hypoxic loading of the ventrolateral medulla inhibits cholinergic outflow to the airways.

In these studies we determined the effects of local hypoxia confined to the superficial structures of the ventral medulla on cholinergic outflow to the airways. Studies were performed in alpha-chloralose anesthetized, paralyzed and mechanically ventilated cats. Topical application or microinjection of sodium cyanide to the intermediate area of the ventrolateral medulla significantly decreased tracheal tone, measured by changes in pressure in a balloon placed in bypassed segment of the trachea (Ptseg). The changes were reversible. When parasympathetic activity was abolished by atropine methylnitrate and tracheal tone was restored with serotonin, cyanide acting centrally had no effect on tracheal pressure. These data indicate that local hypoxic loading confined to the ventrolateral medullary structures may significantly modulate parasympathetic outflow to the airways, and alter airway related protective reflex responses.