Selective up-regulation of the vasodilator peptide apelin after dorsal root but not after spinal nerve injury

Regeneration of sensory neurons is limited in response to lesion of their central axons when compared to lesion of their peripheral axons. To identify transcriptional changes underlying this differential regenerative response between dorsal root and spinal nerve axons, the L5 dorsal root ganglion (DRG) of adult rats was investigated three days after crushing the respective nerve branches by performing high density genome oligonucleotide microarrays. RT-PCR, in situ hybridization and immunohistochemistry confirmed the up-regulation of the vasodilator peptide apelin in non-neuronal cells of the DRG after dorsal root but not after spinal nerve lesion. Induction of apelin mRNA and peptide is accompanied by increased vascular permeability around neuronal cell bodies as demonstrated by Evans-blue albumin (EBA) leakage. Enhanced vasodilation and increased vascular permeability cause intraganglionic edema, which may play a key role in the reduced axonal regeneration rate after dorsal root injury.