THE REFLEX ACTIVATION OF THE VASODILATOR FIBERS OF THE DORSAL ROOTS AND THEIR RÔLE IN VASODILATOR TONE

Abstract

Laminectomies were performed on cats, anesthetized with minimal doses of delvinal or nem-butal, so as to expose the whole spinal cord, which was kept warm and moist at all times. All the dorsal roots (C4-S3) were prepared so that simultaneous, immediate, and total rhizotomies could be performed. Similarly all the ventral roots from C8-L1 were prepared so that an immediate and total separation of the peripheral portion of the sympathetic system from the C. N. S. could be effected. In 5 such prepns., the blood pressure, recorded from the femoral artery, ranged from 100 mm.-150 mm. Hg. Depressor nerve stimulation (central end of the cut left vagus) evoked a decrease in blood pressure averaging 30 mm. Hg. Following total rhizotomies, the blood pressure rose to 180 mm. and stimulation of the depressor nerve failed to alter the blood pressure. Resection of the sympathetic outflow from the spinal cord caused a drop in blood pressure to around 100 mm. Hg. Stimulation of the depressor nerve again failed to cause any change in blood pressure. These results provide presumptive evidence that fibers of the dorsal spinal roots may provide an important vasodilator motor pathway in the reflex arc of which the depressor nerve is the afferent limb. The existence of vasodilator tone and the importance of these fibers in the maintenance of this tone are discussed. The dispensability of the sympathetic system in the cat and the possible existence of smooth muscle idiotonus in the vascular system are pointed out.