Spinal cord injury induces early and persistent lesional P2X4 receptor expression

Following spinal cord injury (SCI), neuropathic, chronic pain is a major cause of disability. Recently, glial P2X4 receptor (P2X4R) has been identified as a major contributor to the development of neuropathic pain after peripherial nerve injury. Here we report analysis of P2X4R expression following rat SCI. Significant lesional accumulation of P2X4R+ cells was detected as early as 24 h after SCI, reaching maximum cell numbers on Day 7. Thereafter cell numbers declined but persisted at significantly elevated, sub-maximal levels (> 70%) until 1 month post injury. Double-immunolabeling identified the majority of lesional P2X4R+ cells as activated microglia/macrophages and surviving neurons/neurites. Increase of P2X4R+, β-APP+ hypertrophic neurites correlated with proximity to the lesion. Further, P2X4R+ cells coexpressed the intracellular regulators of signalling cascades, COX-1 (> 20%), COX-2 (> 5%), RhoA (> 60%) and RhoB (> 10%).