P2X(3) IS EXPRESSED BY DRG NEURONS THAT TERMINATE IN INNER LAMINA-II

The P2X(3) receptor subunit, a member of the P2X family of ATP-gated i on channels, is almost exclusively localized in sensory neurons. In th e present study, we sought to gain insight into the role of P2X(3) and P2X(3)-containing neurons in sensory transmission, using immunohistoc hemical approaches. In rat dorsal root ganglia (DRG), P2X(3)-immunorea ctivity (-ir) was observed in small- and medium-sized neurons. Approxi mately 40% of DRG neuronal profiles in normal rats contained PeX(3)-ir . In rats that had received neonatal capsaicin treatment, the number o f P2X(3)-positive neurons was decreased by approximately 70%. Analysis of the colocalization of P2X(3)-ir with cytochemical markers of DRG n eurons indicated that approximately 94% of the P2X(3)-positive neurona l profiles were labelled by isolectin B-4 from Bandeiraea simplicifoli a, while only 3% contained substance P-ir, and 7% contained somatostat in-ir. In dorsal horn of rat spinal cord, P2X(3)-ir was observed in th e inner portion of lamina II and was reduced subsequent to dorsal rhiz otomy, as well as subsequent to neonatal capsaicin treatment. Finally, PeX(3)-ir accumulated proximal to the site of sciatic nerve ligation, and was seen in nerve fibres in skin and corneal epithelium. In summa ry, our results suggest that P2X(3) is expressed by a functionally het erogeneous population of BSI-B-4-binding sensory neurons, and is trans ported into both central and peripheral processes of these neurons.