Mechanistic differences in neuropathic pain modalities revealed by correlating behavior with global expression profiling [microarray]

Chronic neuropathic pain is a major morbidity of neural injury, yet its mechanisms are incompletely understood. Hypersensitivity to previously non-noxious stimuli (allodynia) is a common symptom. Here, we demonstrate that the onset of cold hypersensitivity precedes tactile allodynia and this temporal divergence was associated with major differences in global gene expression in dorsal root ganglia (DRG). Transcripts whose expression correlate with the onset of cold allodynia were nociceptor-related, whereas those correlating with tactile hypersensitivity were enriched for immune cell activity. Selective ablation of TrpV1 lineage nociceptors resulted in mice that did not acquire cold allodynia but developed normal tactile hypersensitivity. Whereas, depletion of macrophages or T cells reduced neuropathic tactile allodynia but not cold hypersensitivity. We conclude that neuropathic pain is contributed to by reactive processes of sensory neurons and immune cells, each leading to distinct forms of pain hypersensitivity, potentially allowing effective drug development targeted to each pain modality. High temporal analysis of global gene expression in the DRG following spared nerve injury (SNI) correlated with behavior taken at the same time points. Expression and behavioral sensitivity taken at least daily over the first 10 days post SNI.