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AA Hirano, NC Brecha; Expression of the Neurokinin-3 (nk3) Receptor in Off-Type Cone Bipolar Cells in Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):736.
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Purpose: The tachykinin peptides, substance P, neurokinin A and neurokinin B, act at distinct G-protein-coupled receptors: neurokinin-1, -2 and -3 receptors, respectively. The tachykinin peptides are localized to sparsely distributed amacrine cells in the rodent retina. To determine the sites of action of neurokinin B, we characterized the cellular localization of the neurokinin-3 receptor (NK3R) in mouse retina. Methods: Mouse retinas were fixed with 4% paraformaldehyde and processed for indirect immunofluorescence immunohistochemistry. Antibodies used included a well-characterized affinity-purified polyclonal antibody to the C-terminus of NK3 receptor (amino acids 410-417; Grady et al., 1996) and monoclonal antibodies to calbindin, which labels 3 characteristic strata in the inner plexiform layer (IPL), and PKC, which labels rod bipolar cells (Haverkamp & Wässle, 2000). Results: Specific NK3 receptor immunoreactivity (NK3R-IR) was present in the outer plexiform layer, inner nuclear layer and the IPL. The NK3R-IR was principally localized to bipolar cells with large somata in the middle portion of the INL, at the plasma membrane over the entirety of the cell. Strongly immunostained axon terminals ended in a bushy arbor in the outer third of the IPL. More faintly labeled processes extended proximally in the IPL, forming a second, thin sublamina. Double label experiments with antibodies to NK3R and calbindin, and separately, with those to PKC, indicated that these NK3R-IR processes lay between the innermost calbindin stratum and the terminals of rod bipolar cells. There was no overlap between the NK3R-IR bipolar cells and the rod bipolar cells. Conclusion:These findings suggest that the NK3 receptor is most prominently expressed by OFF-type cone bipolar cells in the mouse retina, consistent with earlier reports on NK3 receptor immunoreactivity in the rat retina. In addition, there appears to be another narrow layer of NK3R-labeled processes within the ON sublamina of the IPL in mouse. These observations support the hypothesis that neurokinin B exerts its influence primarily at the level of OFF-type cone bipolar cells.
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