P2X3-IR in lumbosacral spinal cord from young postnatal (P0-P14) rats. Low power images of P2X3-IR in lumbosacral spinal cord from P0 (A), P7 (C) and P14 (E). To demonstrate the location of the sacral parasympathetic nucleus (SPN) in these young rat pups, tissues were stained for neuronal nitric oxide synthase (nNOS, green; A-F). In animals from P0-P7, P2X3-IR was diffusely distributed in the dorsal horn being present in lamina II but in deeper laminae as well (A, C). In addition, dense P2X3-immunoreactive fiber bundles were present in the dorsal commissure (DCM; A, C). Higher power images (B, D, F) of the boxed regions in A, C, E that demonstrate P2X3-IR (red) in close association with nNOS-IR cells (green). Prominent P2X3-IR (red) was present in the lateral collateral pathway (LCP) of Lissauer extending from lamina I to the region of the SPN (B, D, F). Reduction in P2X3-IR in the DCM and LCP was apparent by P14 (E). By P14, P2X3-IR was more restricted to lamina II in the DH (E). Calibration bar represents 80 μm in A, C, E and 50 μm in B, D, F.