P2X₄ receptors induced in spinal microglia gate tactile allodynia after nerve injury

Pain after nerve damage is an expression of pathological operation of the nervous system, one hallmark of which is tactile allodynia - pain hypersensitivity evoked by innocuous stimuli. Effective therapy for this pain is lacking, and the underlying mechanisms are poorly understood. Here we report that pharmacological blockade of spinal P2X₄ receptors (P2X ₄Rs), a subtype of ionotropic ATP receptors, reversed tactile allodynia caused by peripheral nerve injury without affecting acute pain behaviours in naive animals. After nerve injury, P2X₄R expression increased strikingly in the ipsilateral spinal cord, and P2X₄Rs were induced in hyperactive microglia but not in neurons or astrocytes. Intraspinal administration of P2X₄R antisense oligodeoxynucleotide decreased the induction of P2X₄Rs and suppressed tactile allodynia after nerve injury. Conversely, intraspinal administration of microglia in which P2X ₄Rs had been induced and stimulated, produced tactile allodynia in naive rats. Taken together, our results demonstrate that activation of P2X ₄Rs in hyperactive microglia is necessary for tactile allodynia after nerve injury and is sufficient to produce tactile allodynia in normal animals. Thus, blocking P2X₄Rs in microglia might be a new therapeutic strategy for pain induced by nerve injury.