REFLEX ACTIVATION OF THE SYMPATHETIC SYSTEM IN THE SPINAL CAT

Abstract

In a series of chronic spinal preparations (C6 transections) rises in blood sugar, increments in arterial pressure and heart rate, diminished clotting time, and contraction of the de-nervated nictitating membrane were reflexly induced by stimulating the cut sciatic nerve centrally. The sympathetic discharge thus elicited was not so intense as that which the same stimuli produce when the medulla and higher centres retain their normal connections with the spinal sympathetic outflow. Inactivation of the adrenals and denervation of the liver greatly reduced but did not completely abolish the rises in blood sugar, heart rate and arterial pressure. The observed activity implies the presence of a spinal mechanism whereby the pre-ganglionic neurons of the sympathetic system can be activated directly by nociceptive impulses traveling up the cord.