Expansion of innervation territory by afferents involved in plasma extravasation after nerve regeneration in adult and neonatal rats.

The capacity of the saphenous nerve for collateral sprouting was examined by electrophysiological recordings of the activity of low threshold mechanoreceptors and plasma extravasation after C-fiber stimulation in rats. When the sciatic nerve was sectioned neonatally or in adults little evidence was obtained for collateral sprouting of either mechanoreceptors or fibers involved in plasma extravasation in the intact saphenous nerve. In rats where the sciatic nerve was sectioned and the saphenous nerve was crushed either neonatally or in adults, expansive regenerative reinnervation by thin fibers, but not mechanoreceptors, was observed particularly in glabrous skin. Saphenous crush alone did not cause expansive regenerative reinnervation. The results indicate that much of the collateral sprouting or regenerative reinnervation of the skin observed in morphological studies may represent the presence of fibers not responding to the stimuli used in the present study. It is also suggested that some observations of collateral sprouting may represent changes in responsiveness to stimulation of skin areas with overlapping innervation territories.