Activation of unmyelinated afferents in chronically lesioned nerves by adrenaline and excitation of sympathetic efferents in the cat.

Neuroma-in-continuity was experimentally produced in cats by suturing the proximal stump of a transected hindlimb cutaneous nerve to the distal stump of the transected tibial nerve. Eleven to 20 months afterwards single non-myelinated fibres were identified by electrical recording from filaments of the nerves proximally from the neuroma. When tested with repetitive electrical stimulation of the lumbar sympathetic trunk (LST) or i.v. injections of adrenaline, C-fibres in 14 out of 30 filaments were excited by at least one of these stimuli (12 by adrenaline, 7 by stimulation of LST). The fibres responding to LST stimulation were already substantially excited by low frequency stimulation (1-2 Hz). During systemic hypoxia known to result in reflex increases of efferent sympathetic activity responses were elicited in 4 out of 6 C-fibres. Thus, stimuli simulating physiological conditions of sympathetic activity can excite afferent C-fibres in a chronically lesioned nerve.