Transcriptional profiling of dorsal root ganglia in a neuropathic pain model using microarray and laser capture microdissection

Chronic neuropathic pain arises following nerve injury and persists long after the initial damage has recovered. To enhance understanding of the molecular mechanisms that underlie this pain state, the gene expression profiles of the dorsal root ganglia (DRG) from spinal nerve ligation (SNL; L5/L6 region) were examined using microarray techniques 14 days post-insult and compared with gene expression patterns in DRG of sham-operated animals. There were 350 dysregulated gene products with a majority of those transcripts changing >= 2-fold. Genes that had an altered expression pattern were classified into the following groups: cellular homeostasis and remodeling, ion channels and receptors, enzymes, immune response, neuronal markers, synaptic plasticity, and a transcription factors category. Several genes involved in synaptic plasticity (e.g., Narp and synaptobrevin) were downregulated, whereas genes involved in the immune response (e.g., MHCll) and cell regeneration/proliferation (e.g., Reg-2 and GADD45) were upregulated. To obtain a more in-depth profile of genes that exhibited altered expression in the SNL model, subpopulations of the small nociceptive (diameter < 25 mu m) and the large mechanosensitive (diameter > 40 mu m) neurons from the L5/L6 DRG were isolated by laser capture microdissection (LCM). Microarray analysis revealed a greater number of dysregulated genes in the large diameter neurons than in the small neurons. While some genes (e.g., 5HT(3A), synaptotagmin 4, GFR alpha 1) showed similar changes in expression in both small and large neurons in the SNL model, several genes were dysregulated in only one neuronal subtype. Altered expression of NPYR5, P2X(3), and Nell I occurred only in small neurons whereas altered expression of P2X(5), PKC epsilon, and Na(v)1.1 occurred only in large neurons. For the first time, expression changes that occur in specific subpopulations of neurons isolated by LCM are given and provide a detailed view of the molecular landscape of neuropathic pain in the DRG. The utilization of LCM may help to pinpoint the underlying components that play a role in this complex pathophysiology.