PURPOSE. Neuropeptide Y (NPY) is one of the most abundant peptides in the central nervous system (CNS), including the retina. This peptide activates various different G-coupled receptors (NPY Y 1 , Y 2 , Y 4 , and Y 5 ) that are also present in the retina. However, the localization of NPY receptors in the several types of retinal cells is not completely known. In this study, we have looked at the distribution of NPY Y 1 and Y 2 receptors in rat retinal cells to reveal new perspectives on the role of NPY receptors in retina physiology.
METHODS.Rat retinal neural cell cultures were prepared from newborn Wistar rats (P3-P5) and pure rat Müller cell culture was obtained after treatment of these cells with ascorbic acid. 1 This 36-amino acid peptide was first isolated from the pig brain in 1982 by Tatemoto.2 NPY is one of the most abundant peptides in the central nervous system (CNS), including the retina, and is involved in numerous physiologic functions, such as feeding, memory processing, and cognition.3,4 NPY actions are mediated by G protein-coupled receptors, which have been named NPY Y 1 , Y 2 , Y 4 , Y 5 , and y 6 . 3,5 NPY is expressed in the retina of mammals and nonmammals. [6][7][8][9][10][11][12] In rodent retinas, NPY-immunoreactivity (NPY-ir) is present in the inner retina, it is localized in cell bodies at both inner nuclear layer (INL) and ganglion cell layer (GCL), and is also present in processes located in the inner plexiform layer (IPL).11,13 NPY shows one of the highest degrees of phylogenetic preservation, compared with other neuropeptides, and does not show marked differences between species.14,16 From a consideration of the phylogenetic preservation, it is expected that the NPY and NPY receptor distribution in the retina does not vary significantly between species. NPY-ir is present in amacrine cells in the majority of species studied (fish, frogs, lizards, rodents, baboons, pigs, cats, chickens, and pigeons). Cats, dogs, dolphins, and humans also show NPY in their ganglion cells, 9,17-20 while some turtles, lizards, and frogs present NPY-ir in bipolar cells. 8,21,22 Few studies have analyzed the distribution of NPY receptors either in the retina or in specific retinal cell types. The presence of both Y 1 and Y 2 receptors in the mouse retina has been confirmed by mRNA analysis 13,23 ; however, it is unclear which cell types express these receptors. Moreover, in primary cultures of Müller cells isolated from the retina of guinea pig, a functional assay of cell proliferation suggested the presence of NPY Y 1 receptor in these glial cells. 24 In human retinal pigment epithelium (RPE), mRNA encoding for NPY Y 1 , Y 2 , and Y 5 receptors has been detected, while in bovine RPE only mRNAs encoding for NPY Y 1 and Y 2 receptors have been found. 25 Although the presence of NPY receptors in the rat retina has been described, in particular in NPY Y 1 , Y 2 , Y 4 , and Y 5 mRNA expression, 26,27 little is known about their localization. The NPY Y 1 receptor-ir is localized in horizontal and amacrine ce...