Axotomy-induced vacuolation of primary sensory neurons and effect of administered neurotrophic factors: a morphometric, immunocytochemical and ultrastructural study

Abstract

L 4 and L 5 dorsal root ganglia from adult Sprague-Dawley rats were examined 2 weeks, and 1, 2, 3, and 6 months after unilateral transection of the sciatic nerve at mid-thigh level. The incidence of neuronal vacuolation was assessed at each time point, using the contralateral ganglia as controls. In addition, immunohistochemistry, neuronal tracing and electron microscopy were performed on the ganglia of rats 1-2 months after sciatic transection, a time at which we observed the greatest incidence of vacuolation. The effect of allowing regeneration (after nerve crush) and of administration of the neurotrophic factors nerve growth factor, brain-derived neurotrophic factor, NT3 and ciliary neurotrophic factor upon the incidence of these neurons was examined. In this paper we report that following permanent axotomy of the sciatic nerve, large grossly distorting intracytoplasmic vacuoles can be seen in the ipsilateral L 4 and L 5 dorsal root ganglia. We show that the maximum incidence is at 1-2 months after axotomy and at this time these neurons exhibit many of the characteristics of large myelinated sensory neurons, such as RT97 and SSEA4 immunoreactivity. We found no evidence of DNA damage using the in situ end-labeling technique and that all these neurons expressed the growth-associated protein GAP43 in tissue immunostained for it. In addition we found that NT3 administration could significantly reduce their incidence, whereas other neurotrophins could not. We conclude that these vacuolated neurons are viable, persist for long periods following permanent axotomy and represent a distinct pathological response to trauma by certain neurons belonging to the large myelinated sensory neuron population.