It has been claimed that glutamate excitotoxicity might have a role in the pathogenesis of several retinal degenerative diseases, including glaucoma and diabetic retinopathy. Neuropeptide Y (NPY) has neuroprotective properties against excitotoxicity in the hippocampus, through the activation of Y1, Y2 and/or Y5 receptors. The principal objective of this study is to investigate the potential protective role of NPY against glutamate-induced toxicity in rat retinal cells (in vitro and in an animal model), unraveling the NPY receptors and intracellular mechanisms involved. Rat retinal neural cell cultures were prepared from newborn Wistar rats (P3-P5) and exposed to glutamate (500 μM) for 24 h. Necrotic cell death was evaluated by propidium iodide (PI) assay and apoptotic cell death using TUNEL and caspase-3 assays. The cell types present in culture were identified by immunocytochemistry. The involvement of NPY receptors was assessed using selective agonists and antagonists. Pre-treatment of cells with NPY (100 nM) inhibited both necrotic cell death (PI-positive cells) and apoptotic cell death (TUNEL-positive cells and caspase 3-positive cells) triggered by glutamate, with the neurons being the cells most strongly affected. The activation of NPY Y2, Y4 and Y5 receptors inhibited necrotic cell death, while apoptotic cell death was only prevented by the activation of NPY Y5 receptor. Moreover, NPY neuroprotective effect was mediated by the activation of PKA and p38K. In the animal model, NPY (2.35 nmol) was intravitreally injected 2 h before glutamate (500 nmol) injection into the vitreous. The protective role of NPY was assessed 24 h after glutamate (or saline) injection by TUNEL assay and Brn3a (marker of ganglion cells) immunohistochemistry. NPY inhibited the increase in the number of TUNEL-positive cells and the decrease in the number of Brn3a-positive cells induced by glutamate. In conclusion, NPY and NPY receptors can be considered potential targets to treat retinal degenerative diseases, such as glaucoma and diabetic retinopathy.

Neuropeptide Y (NPY) produced by arcuate nucleus (ARC) neurons has a strong orexigenic effect on target neurons. Hypothalamic NPY levels undergo wide-ranging oscillations during the circadian cycle and in response to fasting and peripheral hormones (from 0.25 to 10-fold change). The aim of the present study was to evaluate the impact of a moderate long-term modulation of NPY within the ARC neurons on food consumption, body weight gain and hypothalamic neuropeptides. We achieved a physiological overexpression (3.6-fold increase) and down-regulation (0.5-fold decrease) of NPY in the rat ARC by injection of AAV vectors expressing NPY and synthetic microRNA that target the NPY, respectively. Our work shows that a moderate overexpression of NPY was sufficient to induce diurnal over-feeding, sustained body weight gain and severe obesity in adult rats. Additionally, the circulating levels of leptin were elevated but the immunoreactivity (ir) of ARC neuropeptides was not in accordance (POMC-ir was unchanged and AGRP-ir increased), suggesting a disruption in the ability of ARC neurons to response to peripheral metabolic alterations. Furthermore, a dysfunction in adipocytes phenotype was observed in these obese rats. In addition, moderate down-regulation of NPY did not affect basal feeding or normal body weight gain but the response to food deprivation was compromised since fasting-induced hyperphagia was inhibited and fasting-induced decrease in locomotor activity was absent.These results highlight the importance of the physiological ARC NPY levels oscillations on feeding regulation, fasting response and body weight preservation, and are important for the design of therapeutic interventions for obesity that include the NPY.

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...

Neuropeptide Y (NPY) and NPY receptors are widely expressed in the central nervous system, including the retina. Retinal cells, in particular neurons, astrocytes, and Müller, microglial and endothelial cells express this peptide and its receptors (Y1, Y2, Y4 and/or Y5). Several studies have shown that NPY is expressed in the retina of various mammalian and non-mammalian species. However, studies analyzing the distribution of NPY receptors in the retina are still scarce. Although the physiological roles of NPY in the retina have not been completely elucidated, its early expression strongly suggests that NPY may be involved in the development of retinal circuitry. NPY inhibits the increase in [Ca(2+)]i triggered by elevated KCl in retinal neurons, protects retinal neural cells against toxic insults and induces the proliferation of retinal progenitor cells. In this review, we will focus on the roles of NPY in the retina, specifically proliferation, neuromodulation and neuroprotection. Alterations in the NPY system in the retina might contribute to the pathogenesis of retinal degenerative diseases, such as diabetic retinopathy and glaucoma, and NPY and its receptors might be viewed as potentially novel therapeutic targets.