Primary sensory neuron survival following targeted administration of nervegrowth factor to an injured nerve

Nerve injuries induce neurochemical changes within primary sensory neurons, including expression of neuropeptides, and a loss of a substantial proport ion of the neurons may possibly be caused by a lack of neurotrophic support . In the present study the role of nerve growth factor (NGF) in preventing these changes was investigated in monkeys by giving NGF peripherally throug h a fibronectin (Fn) conduit. A sensory nerve (superficial radial) was tran sected and a gap of 5 mm was bridged with either autologous sural nerve gra ft (SNG), Fn, or Fn impregnated with NGF (Fn-NGF). After four months the do rsal root ganglia, that received the cutaneous afferents of the nerve, were removed and analysed by quantitative immunohistochemistry using antibodies to calcitonin gene related polypeptide (CGRP) and substance P. The percent age of immunostained cells was taken as an indication of neuronal survival. The results showed that SNG and Fn-NGF reduced the loss of CGRP positive s ensory neurons compared with Fn alone. For substance P-positive neurons the differences were small with only a tendency towards reduction of neuronal death after NGF had been given, suggesting that NGF might act preferentiall y on a subpopulation of CGRP immunoreactive sensory neurons that do nor coe xist with substance P.