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.

Ectopic sensory discharges and paresthesiae in patients with disorders of peripheral nerves, dorsal roots and dorsal columns.

Ectopically generated and antidromically conducted nerve impulses were recorded in 5 patients with tungsten microelectrodes inserted into skin nerve fascicles. All patients had mainly positive sensory symptoms and reported paresthesiae which could be provoked by different maneuvers which suggested increased mechanosensitivity of the primary sensory neurons at different anatomic levels. Ectopic multiunit nerve activity correlating in intensity and time course to the positive sensory symptoms was recorded: when Tinel's sign was elicited in a patient with entrapment of the ulnar nerve at the elbow, when paresthesiae were provoked by elevation of the arm in a patient with symptoms consistent with a thoracic outlet syndrome, when paresthesiae were evoked by straining during chin-chest maneuver in a patient with an S1 syndrome due to a herniated lumbar disc, when a painful Lasegue's sign occurred during the straight-leg raising test in a patient with an S1 syndrome due to root fibrosis, and when Lhermitte's sign was elicited by neck flexion in a patient with multiple sclerosis. The sites for the ectopic impulse generation in these cases are suggested to be peripheral nerve, brachial plexus, dorsal root or dorsal root ganglion and dorsal columns. The paresthesiae were non-painful except in the patient with Lasegue's sign and the ectopic impulses were probably recorded from large myelinated afferent fibers.

Leukocyte oxygen radical production determines disease severity in the recurrent Guillain-Barré syndrome.

BACKGROUND: The recurrent Guillain-Barré syndrome (RGBS) is characterized by at least two GBS episodes with intervening remission. In a previous study of monophasic GBS, we reported that the magnitude of oxygen radical production ("respiratory burst") in peripheral blood leukocytes was inversely correlated to disease severity. The present study sought to establish a similar correlation in patients with RGBS. METHODS: Oxygen radical production in leukocytes was induced by formyl-Met-Leu-Phe (fMLF), Trp-Lys-Tyr-Met-Val-Met-NH2 (WKYMVM), or phorbol myristate acetate (PMA) and assessed by quantifying superoxide anion formed by the leukocyte NADPH oxidase. RESULTS: Disease severity, assessed using the MRC score, was negatively correlated to superoxide anion production triggered by fMLF or WKYMVM (p = 0.001 and 0.002, respectively; n = 10). Superoxide anion production also was significantly lower in RGBS patients with incomplete recovery after stimulation with fMLF (p = 0.004) or WKYMVM (p = 0.003). CONCLUSION: We conclude that a lower respiratory burst in leukocytes is strongly associated with a severe course of RGBS.

Inhibition of human muscle sympathetic activity by sensory stimulation.

Surprising sensory stimuli causing arousal are known to evoke short-lasting activation of human sympathetic activity in skin but not in muscle nerves; anecdotal observations suggest that there may even be an inhibition of muscle sympathetic nerve activity (MSNA). To test this hypothesis we recorded multiunit MSNA in the peroneal nerve in 19 subjects aged 19-71 years, while sensory stimuli, consisting of either an electrical skin stimulus to a finger or a visual flash, were delivered repeatedly with intervals of approximately 20 s. The stimuli were given either 200 or 400 ms after the R wave of the electrocardiogram. Dummy stimuli, consisting of trigger pulses without sensory stimulation served as controls. Electrical skin resistance reductions were monitored from the palm of a hand as electrodermal signs of arousal-induced cutaneous sympathetic activity. On a group basis both types of sensory stimuli attenuated the amplitude of one or two bursts of MSNA, while no such effects occurred after dummy stimuli. Individually, the inhibition was evoked by at least one stimulus modality or delay in 16 subjects whereas in three subjects no significant inhibition occurred. Skin resistance responses were evoked in all subjects. Some subjects responded to one, others to both stimulus modalities, and electrical stimuli were more effective than visual stimuli in causing MSNA inhibition as well as skin resistance reduction. On the other hand, electrodermal signs of arousal were equally common in subjects with and without inhibitory responses. We suggest that the MSNA inhibition evoked by sensory stimuli is an arousal effect which varies markedly between individuals.