Distribution of sensory properties among axotomized cutaneous C-fibres in adult rats

A few hours after peripheral axons of cutaneous afferent neurons have been transected, some of their novel endings become excitable by physical or che mical stimuli.(1,78,12-14) It has been assumed that these axon endings pref erentially respond to those stimuli which have excited their previous recep tive endings. We studied the prevalence of sensory properties among 784 unm yelinated sural nerve fibres which had been axotomized 2-24h before, by app lying mechanical and thermal forces to the nerve lesion site. Among 126 res ponding C-fibres, the majority was unimodal, responding exclusively to mech anical (31%), cold (23%) or heat (18%) stimuli. The remainder were either m echano-heat sensitive (10%), mechano-cold sensitive (6%) or heat and cold s ensitive (12%), The distribution of sensory properties among acutely axotom ized sural nerve C-fibres is therefore largely similar to the recently publ ished distribution of receptor types among intact sural nerve C-fibre affer ents.(11) Thus, the hypothesis that responses of axotomized afferent fibres reflect their original receptive properties is corroborated. Knowledge of underlying transduction mechanisms may lead to specific pharmacological too ls for suppression of ectopic discharges in unmyelinated axotomized afferen ts, which probably contribute to neuropathic pain states. (C) 1999 IBRO, Pu blished by Elsevier Science Ltd.