GLIAL OVEREXPRESSION OF NGF ENHANCES NEUROPATHIC PAIN AND ADRENERGIC SPROUTING INTO DRG FOLLOWING CHRONIC SCIATIC CONSTRICTION IN MICE

Adrenergic sprouts within axotomized dorsal root ganglia (DRG) may con tribute to neuropathic pain, and may arise under the influence of nerv e growth factor (NGF). We investigated effects of chronic constriction injury (CCl) on behavior and sprouting in mice in which NGF overexpre ssion is driven by a glial protein (GFAP) promotor. GFAP-NGF mice were naturally hyperresponsive to radiant heat, and had enhanced ipsilater al responses to thermal and mechanical stimulation following CCl compa red to wild-type mice. Sympathetic axons were already present in intac t DRG of GFAP-NGF mice. Following CCl, sprouting in ipsilateral and to a lesser extent contralateral DRG occurred in both genotypes, but the sprout density 2 weeks post-lesion was much greater in GFAP-NGF mice. These results demonstrate a connection between the endogenous ectopic overexpression of NGF and (1) neuropathic pain behaviour and (2) symp athetic sprouting in the DRG. (C) 1998 Elsevier Science Ireland Ltd. A ll rights reserved.