P2X sub(3) is expressed by DRG neurons that terminate in inner lamina II

The P2X sub(3) receptor subunit, a member of the P2X family of ATP-gated ion channels, is almost exclusively localized in sensory neurons. In the present study, we sought to gain insight into the role of P2X sub(3) and P2X sub(3)-containing neurons in sensory transmission, using immunohistochemical approaches. In rat dorsal root ganglia (DRG), P2X sub(3)-immunoreactivity (-ir) was observed in small- and medium-sized neurons. Approximately 40% of DRG neuronal profiles in normal rats contained P2X sub(3)-ir. In rats that had received neonatal capsaicin treatment, the number of P2X sub(3)-positive neurons was decreased by approximately 70%. Analysis of the colocalization of P2X sub(3)-ir with cytochemical markers of DRG neurons indicated that approximately 94% of the P2X sub(3)-positive neuronal profiles were labelled by isolectin B sub(4) from Bandeiraea simplicifolia, while only 3% contained substance P-ir, and 7% contained somatostatin-ir. In dorsal horn of rat spinal cord, P2X sub(3)-ir was observed in the inner portion of lamina II and was reduced subsequent to dorsal rhizotomy, as well as subsequent to neonatal capsaicin treatment. Finally, P2X sub(3)-ir accumulated proximal to the site of sciatic nerve ligation, and was seen in nerve fibres in skin and corneal epithelium. In summary, our results suggest that P2X sub(3) is expressed by a functionally heterogeneous population of BSI-B sub(4)-binding sensory neurons, and is transported into both central and peripheral processes of these neurons.