Ectopic neural activity from myelinated afferent fibres in the lingual nerve of the ferret following three types of injury

Sensory disturbances following nerve injury may result from abnormal neural activity initiated at the injury site. We have studied the activity genera ted in the lingual nerve after three types of injury which may have variabl e potentials for the initiation of sensory disturbances. We have also compa red the results with those found after damage to the inferior alveolar nerv e, another branch of the trigeminal nerve, to determine whether differences in nerve fibre type or location affect the level of abnormal activity. In anaesthetised adult male ferrets the left lingual nerve was either ligated and cut distally, chronically constricted, or sectioned and allowed to rege nerate. Following recovery periods of 3 days-6 months, single unit electrop hysiological recordings were made from central to the injury site. After al l three types of injury, some of the damaged axons at the injury site devel oped spontaneous activity (up to 36% of units) and mechanical sensitivity ( up to 35% of units). There were significantly fewer spontaneously active un its after ligation than after the other two types of injury but the level o f mechanical sensitivity was not significantly different between the three types of injury. There was a significant increase in the spontaneous activi ty between 3 weeks and later recovery periods following both ligation and s ection injuries, and this late increase was not seen in our previous studie s on the inferior alveolar nerve. Differences in the time-course of ectopic activity in adjacent branches of the trigeminal nerve suggest that the fib re types or anatomical relationships affect the outcome of injury. (C) 2000 Elsevier Science B.V. All rights reserved.