Localization of neuropeptide receptor NPY4R in rat retina

Neuropeptide Y (NPY) is a significant neuromodulator implicated in a multitude of physiological functions via activating NPY receptors which belong to seven transmembrane G-protein-coupled receptors (GPCRs). However, the detailed cellular expression of NPY receptors in retina has been scarcely investigated. In this study, the expression of the special NPY4R receptor in rat retina was assessed using Western blot analysis and immunofluorescent staining. The detailed cellular localization of NPY4R receptor was studied using double immunofluorescent staining and laser-scanning confocal microscopy. Our data demonstrated that NPY4R receptor was weakly expressed in the inner segment of outer photoreceptors and extensively expressed in the outer segment of S-opsin-positive blue cones, L/M-opsin-positive red/green cones and in the somata of CB-positive horizontal cells, GAD65-positive GABAnergic amacrine cells, ChAT-positive cholinergic amacrine cells, TH-positive dopaminergic CA1 amacrine cells and CA2 amacrine cells, PV-positive AII amacrine cells, Brn3a-positive conventional ganglion cells and melanopsin-containing ipRGCs. In addition, NPY4R receptor was diffusely distributed throughout the full thickness of the inner plexiform layer and outer plexiform layer. However, the outer segment of Rho4D2-positive rods, the somata of ChX10-positive bipolar cells and CRALBP-positive Müller glial cells seemed to lack immunoreactivity of NPY4R receptor. The new finding that multiple types of retinal cell express NPY4R receptor provides new neurobiological basis for the participation of NPY in the regulation of retinal functions through activating NPY4R receptor.