Sympathetic activity in man after spinal cord injury. Outflow to skin below the lesion

Microelectrode recordings were made in peroneal skin nerve fasicles in 8 patients with functionally complete spinal cord lesions mainly at cervical levels. Spontaneous neural activity was sparse but deep breaths, abdominal pressure over the bladder and mechanical and electrical skin stimuli applied caudal to the spinal transection induced bursts of neural impulses after a latency of 0.5 to 1 s. The efferent discharges were conducted with a velocity of 0.75 m/s and were followed by cutaneous vasoconstruction and/or reduction of skin resistance. It is concluded that the neural bursts contained sympathetic impulses of spinal origin. No systematic changes of nerve activity were induced by changes of ambient temperature, suggesting that sympathetic thermoregulatory reflexes do not occur at spinal level in man. The vasoconstriction following a single sympathetic burst had a longer duration in the spinal patients than in normal subjects. The low level of spontaneous activity does not suggest permanent spinal sympathetic hyperactivity, but the prolonged episodes of vasoconstriction may contribute to attacks of high blood pressure in patients with spinal cord lesions.