Autotomy in rats following peripheral nerve transection is attenuated by preceding formalin injections into the same...

The influence of an evolving painful inflammatory lesion on the development of autotomy, a behavioural model of denervation pain, was studied in rats suffering sciatic and saphenous nerves transection 30 or 60 min, and 1, 3, 7 or 14 days after being injected with formalin (50 microl, 5%, s.c). Hindpaws pressure and heat nociceptive thresholds and volume of the injected paw were assessed, in non-operated rats, at the above time-points. The main effects on autotomy were: (1) a significant attenuation when formalin injection preceded the neurectomies by 1 day or more, a period characterized by hypalgesia of the injected paw to both mechanical (during the first week) and thermal (spanning up to the third day after formalin) stimuli and inflammation (lasting for 14 days); (2) a significantly earlier onset when formalin was injected 30 min before neurectomies. Possible mechanisms linking nociceptive responsiveness and inflammation to the development of autotomy are discussed.