Microneurography: how the technique developed and its role in the investigation of the sympathetic nervous system.

A historical review is given of the development of microneurography and its application for studies of sympathetic nerve activity in humans.

Microelectrode recordings from human peripheral nerves (microneurography).

The development of microneurography, which began in the laboratory of clinical neurophysiology in Uppsala, is described.

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.

Analgesic effect of vibration and cooling on pain induced by intraneural electrical stimulation.

Psychophysical experiments were carried out on 16 human subjects to determine how low intensity mechanical and thermal skin stimuli interfere with the sensation of pain. Moderate or intense pain was induced by low frequency (2 Hz) electrical stimulation within cutaneous fascicles of the median nerve at wrist level, and vibration, pressure, cooling or warming were applied for short periods (usually 20-60 sec) within or outside the skin area to which the pain was projected. Vibration within the area of projected pain reduced the sensation of pain more efficiently than vibration outside that area. Moderate pain was sometimes completely inhibited but intense pain was only moderately reduced. Pressure and cooling produced some pain relief whereas mild warming had an ambiguous effect. Since the painful input derived from stimulation of fibres in the nerve trunk, and not from peripheral nociceptors, the pain suppressing effects of vibration and cooling are not explicable in terms of lowered excitability of the nociceptive nerve endings in the skin. Instead, the results indicate that activity in low threshold mechanoreceptive and cold sensitive units suppresses pain at central (probably segmental) levels.