Destruction by anti-NGF of autonomic, sudomotor neurones and subsequent hyperinnervation of the foot pad by sensory fibres.

Treatment of newborn rats with antiserum to nerve growth factor (NGF) for the first 6 postnatal days produced a loss of the sympathetic neurones that normally project to the sweat glands of the hind paws of the rat, indicating that cholinergic sympathetic neurones require NGF postnatally for their survival. Following this immunosympathectomy, there was an increase in the proportion of glands containing sensory fibres having substance-P-like immunoreactivity (SP-LI). This sensory sprouting was not as extensive as that after sympathectomy using 6-hydroxydopamine (6-OHDA). During normal development, fibres showing SP-LI are associated with the glands, particularly during the first and second postnatal weeks. Prolongation of the antibody treatment until the third postnatal week reduced the sensory fibre ingrowth from the region of the glands, suggesting that the basis of this growth is the increased availability of NGF following sympathetic denervation. Retrograde cell labelling using the fluorescent dye, fast blue, indicated that the anti-NGF treatment did not significantly decrease the number of sensory neurones projecting to an individual foot pad. These results support the hypothesis that sympathetic and sensory neurones compete for NGF produced by target tissues.