Sympathetic neural outflow in spinal man. A preliminary report

Microelectrode recordings were made from peroneal skin or muscle fascicles in 11 patients with traumatic spinal cord transection. Spontaneous neural activity was sparse. Both in skin and muscle nerve recordings pressure on the abdomen over the bladder, electrical skin stimulation and skin pinching below the level of the lesion gave rise to single bursts of multiunit impulse activity occurring after latencies of 0.5-1 s. Bursts were never evoked by sound stimuli or by skin stimuli applied above the level of the lesion. Bursts were unaffected by local anesthetic blocks of the nerve distal to the recording site but were abolished by proximal blocks. Conduction velocity of the bursts was approximately 0.7 m/s. After a latency of 2-5 s peroneal neural bursts were followed by cutaneous vasoconstriction and/or skin resistance reduction. Durations of vasoconstrictor responses were often much longer than in intact subjects. It is concluded that the activity was sympathetic and comprised of vasoconstrictor and sudomotor impulses of spinal origin. The parallel activation of bursts in skin and muscle fascicles suggests that sympathetic outflow from the isolated spinal cord is less differentiated than when supraspinal connections are intact. This, together with the long duration vasoconstrictor responses may contribute to the increased blood pressure during attacks of 'autonomic hyperreflexia'.