Upregulation of FGF-2 in reactive spinal cord astrocytes following unilateral lumbar spinal nerve ligation

Spinal nerve ligation results in dramatic changes in spinal cord primary C-afferent fibers, which include atrophy with an accompanied decrease in calcitonin-generelated peptide (CGRP). These changes parallel the activation of astrocytes, which have been implicated in the ensuing neuropathic pain states. As part of an effort to elucidate the role of the downstream effectors of astrocyte reactivity in the context of allodynia, the expression of fibroblast growth factor-2 (FGF-2) was examined following tight ligation of L5 and L6 spinal nerves. FGF-2 is a pleiotropic cytokine that is synthesized and secreted by neurons and astrocytes. FGF-2 immunoreactivity was increased in ipsilateral dorsal horn reactive astrocytes at 1 and 3 weeks following nerve ligation. Serniquantitative reverse transcriptase polymerase chain reaction (RT-PCR) of laser-captured dorsal spinal cord sections revealed an increase in FGF-2 mRNA in the dorsal horn ipsilateral to nerve injury compared to contralateral and SHAM. Furthermore, an increase in FGF-2 mRNA in ispilateral dorsal root ganglia (DRG) was seen by in situ hybridization. These results demonstrate that, in response to ligation-induced injury of sensory neurons, FGF-2 is upregulated in both DRG neurons and in spinal cord astrocytes, suggesting neurotrophic functions of this growth factor following peripheral nerve lesion and possibly in astrocyte-related maintenance of pain states.