Sympathetic Ganglionic Transmission and the Cardiovascular Changes of the Defense Reaction in the Cat

The effects of ganglionic blockade on the circulatory components of the defense reaction were studied in 25 anesthetized cats. Hexamethonium alone partially blocked the response; a combination of hexamethonium and atropine was necessary to block it completely. Vasodilation of skeletal muscle was reversed to vasoconstriction during hexamethonium infusion. Direct recording from pre- and postganglionic sympathetic nerves showed persisting ganglionic transmission during hexamethonium infusion that was subsequently blocked by atropine. Unit recordings showed that some ganglion cells were completely blocked by hexamethonium alone. Preganglionic discharge was unaffected. It is suggested that ganglion cells giving rise to cholinergic vasodilator fibers have fewer atropine-sensitive receptor sites than do cells from which adrenergic constrictor fibers arise.