Alteration of dorsal root ganglion P2X3 receptor expression and function following spinal nerve ligation in the rat

One subtype of ATP-gated ion channel, the P2X(3) receptor, is expressed primarily on peripheral sensory neurons. While it is known that P2X(3) receptors can participate in certain forms of nociceptive signaling, their involvement in neuropathic pain transmission is not known. We have examined the expression and function of P2X(3) receptors in a rat spinal nerve ligation model of neuropathic pain. Fourteen days following L5/L6 spinal nerve ligation, the corresponding dorsal root ganglia (DRG) were removed from animals exhibiting mechanical allodynia, and these were studied using immunohistochemical and electrophysiological techniques. Using a polyclonal antibody to label the P2X(3) receptor, a significant reduction in neuronal P2X(3) immunoreactivity was observed in the ipsilateral (injured) L5 and L6 DRG following nerve ligation. In vitro electrophysiological analysis of acutely isolated DRG neurons revealed a similar decrease in functional P2X(3)-containing receptors. In small diameter (22-25 micro m) neurons, a significant reduction in the number of cells exhibiting a response to alpha,beta-meATP was observed. However, a subset of small diameter neurons retained P2X(3) responses of equal amplitude to those recorded from naive and sham control DRG neurons. Interestingly, P2X(3) immunoreactivity and P2X(3)-like responses were also detected in a subset of larger diameter (50 micro m) neurons and the number and amplitude of these responses were unchanged after spinal nerve ligation. These results suggest that, while there appears to be a decrease in fast desensitizing P2X(3) receptors following L5/L6 nerve ligation injury, certain subsets of small and large DRG neurons maintain normal P2X(3) receptor expression and function. These remaining receptors may provide a P2X(3) receptor-mediated component to neuropathic pain.