Sciatic nerve section induces mechanical hyperalgesia in skin adjacent to the deafferented region in rats: lack of correlation with autotomy behavior.

We have studied the development of cutaneous hypersensitivity in the innervation area of the saphenous nerve and autotomy behavior in rats after unilateral sciatic nerve section. Hypersensitivity was assessed by stimulating the saphenous area with mechanical (von Frey hairs and analgesimeter), cold (immersion) or heat (immersion or radiant heat) stimuli 10 days after sciatic nerve section. We did not observe any hypersensitivity to thermal stimulation or weak mechanical stimulation produced by von Frey hairs. A significant decrease in withdrawal threshold to intense mechanical pressure produced by analgesimeter was observed, indicating the possible presence of mechanical hyperalgesia. Eleven of 17 rats had started autotomy at this time, but there was no correlation between the presence of autotomy and mechanical hyperalgesia. It is concluded that in our experimental setting, only mechanical hyperalgesia was present 10 days after axotomy. Moreover, autotomy behavior and adjacent hyperalgesia may be triggered by different mechanisms.