Studies of normal and expansive cutaneous innervation territories of intact and regenerating C-fibres in the hindlimb of the rat.

Two sets of experiments were carried out in order to evaluate the unmyelinated (C) fibre innervation of the hindlimb of rats. In the first experiment the normal innervation territory of the various nerves to the skin in the hindfoot was examined by plasma extravasation of Evans blue after antidromic nerve stimulation. Considerable overlap was found in the territories of nerves on the dorsum of the toes and just proximal to the toes. In the second experiment the capacity of C-fibres in the saphenous nerve for growth into deafferented skin was examined. In rats in which the sciatic nerve was previously sectioned, the innervation territory of the intact saphenous nerve expanded slightly into that of the sciatic in about 20% of the cases by "collateral sprouting". When the sciatic nerve section was combined with ipsilateral saphenous nerve crush, the regenerating C-fibres in the saphenous nerve innervated the sciatic territory in almost 100% of cases, a process we termed "expansive regenerative reinnervation". We conclude that the existence of overlapping C-fibre innervation territories need to be considered in studies of "collateral sprouting". However, regenerating C-fibres can innervate foreign deafferented skin.