Sympathetic nerve activity to amputated lower leg in humans: Evidence of altered skin vasoconstrictor discharge

Transection of a peripheral nerve in the cat is known to cause a regional change in sympathetic impulse pattern. Our aim was to determine whether microneurography can be used to study sympathetic activity in the transected nerve of human amputees, and whether any such activity shows an abnormal pattern similar to that observed in the cat. Seven successful sympathetic recording sessions were performed in the peroneal nerve of four subjects with posttraumatic transtibial leg amputation; one of them was studied on four occasions. Muscle nerve sympathetic activity (MSA) was detected in all four subjects. Skin nerve sympathetic activity (SSA) was found in one patient only, but on three occasions. It was more difficult to obtain high quality sympathetic recordings than for intact nerves, particularly in patients amputated many years before our studies. MSA showed a qualitatively normal pattern at rest and during various manoeuvres. In three recordings from skin nerve fascicles without innervation zone, SSA displayed normal characteristics at room temperature and qualitatively normal responses to arousal stimuli and various manoeuvres. During body cooling there was an abnormal shift in SSA pattern with a reduction in burst duration instead of the increase occurring normally. Cardiac rhythmicity of SSA was more pronounced during body cooling than during body heating. This is also a reversal of the normal pattern. The abnormal SSA pattern during body cooling suggests increased baroreflex regulation of cutaneous vasoconstrictor neurones, similar to the change after nerve transection in the cat. This is the first time that human nerve recordings support the hypothesis of a regional alteration in sympathetic impulse pattern following a nerve lesion. The implications of this phenomenon for pain conditions remains to be explored; our patients did not suffer from phantom or stump pain.