THE CONSEQUENCES OF MICRONEUROGRAPHY ELECTRODE-INDUCED INJURY OF PERIPHERAL-NERVES OBSERVED IN THE RAT AND MAN

The consequences of microneurography were assessed, using tungsten and coaxial electrodes in rat and man. Firstly, the sequelae of microneur ography were examined for up to 1 month in a rat sciatic nerve model, using 3 techniques. Expression of the injury-associated protein GAP-43 was measured by immunofluorescence in sciatic nerve and dorsal root g anglia 3 and 28 days following sciatic nerve injury by microneurograph y electrodes. No increase in GAP-43 was observed in sciatic nerve 3 da ys following injury, but 28 days after injury the coaxial electrode wa s associated with an increase in GAP-43 expression, All electrodes wer e associated with an increase in GAP-43 in dorsal root ganglia 28 days after injury. The capacity of unmyelinated afferent fibres to induce neurogenic oedema was examined up to the 28th post-experimental day, a s measured by Evan's Blue extravasation. The tungsten electrode induce d a decrease in extravasation, which persisted for 28 days. In contras t, the decrease in plasma extravasation associated with lesions induce d by the coaxial electrode returned to baseline within 7 days. The hin d-limb withdrawal time from a noxious stimulus was also measured up to 28 days following injury. Both types of electrode induced a significa nt change in the immediate post-experimental period, but this returned to normal within 1 week. The direction of change differed between the tungsten and coaxial electrodes. In humans, symptomatology questionna ires were collected after microneurography experiments with the coaxia l electrode. Thirty-two volunteers were studied. Two subjects reported mild paraesthesiae, which fully resolved within 24 h. This compares f avourably with similar studies of the tungsten electrode.