Discharge pattern of afferent fibers from a neuroma

Abstract

Discharge properties of afferent units from experimentally produced stump neuromata in the superficial peroneal nerve of the cat hind limb were investigated electrophysiologically. The superficial peroneal nerves were cut and ligated 6-245 days before the experiments. Myelinated and chiefly unmyelinated axons were analyzed. The following results were obtained: (1) 3.9 +/- 3% (mean +/- S.D.) of axons from early neuromata (days 6-27) and 13.4 +/- 10.7% of axons from old neuromata (more than 50 days after nerve severance) showed ongoing activity. The rate of ongoing activity was usually below 1 imp/sec (73%) and rarely above 4 imp/sec and its pattern, in most cases, was irregular. Some myelinated afferents had regular or irregular bursting patterns. (2) Mechanical stimulation of the neuroma excited 19.4 +/- 9.6% of the axons from young neuromata and 32.8 +/- 14.9% of the axons from old neuromata. Part of these mechanosensitive units exhibited pronounced after-discharges. Some 20% of the units which could be excited, probably ephaptically, by stimulation of other afferent fibers in the common peroneal nerve were excited by pressure applied to the neuroma. (3) About 20-40% of the units with ongoing activity (3-5% of all axons) responded weakly to intravenous injections of adrenaline and noradrenaline and to repetitive stimulation of the lumbar sympathetic trunk. (4) Recording from distally cut fiber bundles showed that part of the axons could be activated by electrical stimulation of the nerve distal to the recording site and by mechanical stimulation of the neuroma. Most of these axons were unmyelinated. This result indicates that afferent axons either branch or interact ephaptically a long distance proximal to the neuroma in the neuroma nerve. (5) The results are discussed with respect to similar results obtained on afferent fibers from experimentally produced neuromata of the sciatic nerve of mice and rats.

Regeneration of Unmyelinated Axons After Injury of Mammalian Peripheral Nerve

“…Similar effects are also seen after activating postganglionic sympathetic fibres ending in the neuroma by electrical stimulation of the lumbar sympathetic trunk (Blumberg & Janig, 1981;Devor & Janig, 1981;Korenman & Devor, 1981;Blumberg & Janig, 1984;Habler, Janig & Koltzenburg, 1987). Although most of these observations were made on myelinated neuroma fibres, Habler et al (1987) have shown unmyelinated ones respond to such stimulation as well.…”

“…There are some differences in opinion as to how common are all these events. The incidence varies with time after nerve injury (Govrin-Lippmann & Devor, 1978;Blumberg & Janig, 1984), between different strains of rat -it being uncommonly high in the Wistar-derived Sabra strain - (Devor, Inbal & Govrin-Lippmann, 1982;Burchiel & Russell, 1987), and between species (Blumberg & Janig, 184;Meyer, Raja & Campbell, 1985). There is also the suggestion that some pharmacological agents used routinely in the conduct of experiments could be a source of variation (Burchiel & Russell, 1987).…”

“…The information on spontaneous discharge of unmyelinated axons ending in stump neuromata comes from several brief or preliminary reports (Scadding, 1981;Devor & Raber, 1983;Devor & Govrin-Lippmann, 1983, 1985Zimmermann, Koschorke & Sanders, 1987;Leah, Koschorke, Welk & Zimmermann, 1988) and from a few fuller accounts (Blumberg & Janig, 1984;Burchiel & Russell, 1987;Matzner & Devor, 1987). Burchiel & Russell (1987) found no evidence of C fibre spontaneous activity whereas all the others have.…”

“…Evidence for tight, one-to-one coupling between axons in normal nerves has only been found very infrequently (Matthews, 1976;Brenan & Matthews, 1983;Lisney & Pover, 1983;Blumberg & Janig, 1984;Kocsis, Preston & Tang, 1984;Pover & Lisney, 1988), but the phenomenon is more commonplace in nerves that have been injured at some stage in their history Blumberg & Janig, 1982b;Lisney & Pover, 1983;Blumberg & Janig, 1984;Pover & Lisney, 1988). The coupling can be between two myelinated axons, two unmyelinated ones, or between a myelinated and an unmyelinated axon; the experiments carried out so far give no indication of which type of pairing is most common.…”

Tail docking in horses: a review of the issues

“…Neuroma is not systematically associated with acute or chronic pain. Pain, caused by abnormal spontaneous neuroma's activity or to increased sensibility of it (Swanson, 1961;Scadding, 1981;Blumberg and Jä nig, 1984), is influenced by the healing process quality, itself relying on the type of operation, the age and the quantity of tissue removed (horse: Said and Khami, 1984;poultry: Gentle et al, 1995;Lunam et al, 1996). Skin adhesion subsequent to tail docking has also been observed in docked dogs (Carr, 1979).…”