ALTERATIONS IN MYELINATED FIBERS IN THE SCIATIC-NERVE OF RATS AFTER CONSTRICTION - POSSIBLE RELATIONSHIPS BETWEEN THE PRESENCE OF ABNORMAL SMALL MYELINATED FIBERS AND PAIN-RELATED BEHAVIOR

Morphology or peripheral myelinated fibres was analyzed in rats exhibiting hyperalgesia and allodynia with mechanical and thermal stimuli, consecutive to a mononeuropathy induced by 4 loose ligatures around a sciatic nerve. This preliminary study was based on weeks 2-3 after surgery, the time of the maximum alterations of the pain-related behaviour. At this time, contrasting with a marked decrease of the large afferent fibres a consistent number of ≪ 5 μm fibres was pointed out. In addition to their extremely short internodal length, the majority of these fibres had an abnormal g-ratio, thus an abnormal myelin sheath. It is suggested that this group of abnormal fibres might be related to the Aδ fibres described in neuromas and involved in pain-related behaviours seen in the mononeuropathic rats. © 1990.