Nerve growth factor treatment increases stimulus-evoked release of sensory neuropeptides in the rat spinal cord

In the adult rat, nerve growth factor (NGF) upregulates the nociceptive peptide substance P (SP) and calcitonin gene-related peptide (CGRP) in neuronal cell bodies of C fibres but the effects of NGF on release of these neuropeptides from the central afferent terminals have not been reported. Thus, this study compared rats treated with six doses of NGF over 2 weeks with controls and measured the release of the neuropeptides, SP and CGRP from the dorsum of the lumbar spinal cord in vitro. NGF (1.0 mg/kg s.c.) greatly increased basal and stimulus-evoked SP and CGRP release; at 0.1 mg/kg, NGF did not affect SP release but significantly increased CGRP basal outflow and evoked release. In a different set of experiments, topical application of NGF (100 ng/ml) to cords from naive rats did not increase stimulus-evoked release of SP or CGRP. These findings show marked stimulation by NGF treatment in vivo of release of sensory neuropeptides during stimulation of dorsal roots, albeit at relatively large doses of the neurotrophin.