Inhibition of renal nerve sympathetic activity by spinal stimulation in rat

We determined the physiological and anatomical properties of systems mediating renal nerve inhibition elicited by electrical and chemical stimulation of the cervical dorsolateral funiculus of the anesthetized spinally transected rat. Stimulus-response characteristics suggested that this system was well suited for a role in tonic inhibition of sympathetic activity. Inhibition was elicited from a region of the cervical spinal cord extending from a lateral position near the accessory nerve to the dorsal columns. Inhibition could not be elicited by spinal stimulation before lesions had been placed rostral to stimulation sites in the lateral funiculi. Inhibition was blocked by similarly placed lesions caudal to stimulation sites. Therefore, this system may course in the lateral funiculus, and it may be tonically active in intact rats. Renal sympathetic activity could be inhibited by electrical stimulation caudal to large, chronic, spinal lesions. Therefore, some component of the inhibitory system was either antidromically activated or propriospinal. Glutamate applied to the dorsolateral surface of the cervical spinal cord elicited inhibition indistinguishable from that elicited by electrical stimulation, which suggested that neurons with somas located superficially at cervical levels may be responsible for some component of the spinally elicited inhibition.