Behavioural pain-related disorders and contribution of the saphenous nerve in crush and chronic constriction injury of the rat sciatic nerve.

This study evaluated the pain-related behaviours induced by 2 models of peripheral sciatic nerve injuries in the rat: transient nerve crush and chronic constriction injury (CCI). Various lesions of the saphenous nerve were performed in order to investigate the role of saphenous innervation in behavioural disorders induced by these nerve injuries. Behavioural testing included assessment of responses to phasic stimulation (mechanical and thermal) and observation of 'spontaneous' pain-related behaviour. Results confirmed that the model of CCI induces marked and prolonged phasic and spontaneous pain-related disorders (up to week 7). Rats with crush injury exhibited moderate and transient hyperalgesia and allodynia to mechanical and thermal stimulation on the lesioned side (with a maximum at day 3 and a recovery by week 1). Section plus ligation of the ipsilateral saphenous nerve on the day of surgery prevented nociceptive behaviours and induced persistent mechanical and thermal anaesthesia or hypoesthesia of the lesioned paw in both models (lasting up to 3-4 weeks). Section without ligation of the saphenous nerve induced comparable results in rats with sciatic crush, but did not significantly modify nociceptive behaviours in rats with CCI. These data emphasise the role of adjacent saphenous nerve in the mechanisms of pain-related disorders induced by these peripheral nerve lesions. On the contralateral paw, pain-related modifications were also observed in both models, suggesting that unilateral nerve lesions induce remote modifications extending beyond the site of the injured nerve.