A DESCENDING SYMPATHOINHIBITORY TRACT IN VENTROLATERAL COLUMN OF CAT

The spinal cord at the level of C1 to C2 was explored in chloraloseurethane anaesthetized cats. Lesions and stimulations were performed to localize a sympathoinhibitory tract transmitting the baroreceptor reflex. A. Lesions The baroreceptor reflex was abolished only when bilateral lesions included extensive parts of the dorsolateral column destroying sympathotonic efferents. The blood-pressure was thereby reduced to a level of 50-60 mm Hg. B. Stimulations In curarized and atropinized animals the ventral part of the spinal cord was explored by unipolar stimulations with square wave pulses of 1 msec duration and up to 5 V intensity. The ventral part of the spinal cord cranially to the stimulated point was then destroyed by high frequency coagulation. The effects of the stimulation were measured by recording either the blood-pressure or the activity of the renal sympathetic nerve. Stimulation in a region ventrolateral to the ventral horn caused distinct reduction in blood-pressure and inhibition of the sympathetic activity. The effects are believed as indicating an excitation of descending sympathoinhibitory fibers. Their association with different functional systems is discussed. © 1969 Springer-Verlag.