Local oedema and general excitation of cutaneous sensory receptors produced by electrical stimulation of the saphenous nerve in the rat

Abstract

Recordings were made from multifibre strands of the saphenous nerve of rats anaesthetized with urethane and given Evan's blue intravenously. Stimulation of A plus C fibres of the saphenous nerve, but not A fibres alone, at 10 Hz for 5 min produced dye leakage in the skin of the hind limb. Stimulation of the nerve at A plus C fibre voltages with the stimulating electrodes placed distal to the recording electrodes produced reversible block of nerve impulses at the stimulating electrodes. However, when the stimulating electrodes were placed proximal to the recording electrodes, stimulation of the nerve at A plus C fibre voltages, but not at A fibre voltages, produced an increase in activity in nerve strands. An increase in activity was also observed in experiments where the contralateral saphenous nerve was stimulated. These effects were not abolished by pretreatment of rats with reserpine. The early phase of the local oedema response appeared to be reduced by local pretreatment with compound 48/80 but the excitatory action on nerve terminals was not. The effects of nerve stimulation were not mimicked by intravenous injection of 5HT, ATP or adenosine into the contralateral saphenous vein. It is suggested that several substances might be released on antidromic stimulation of C fibres and that the resulting general excitation of sensory nerve terminals might play a role in modifying the central nervous system response to nociceptive information.