Comparative distribution of neuropeptide Y Y1 and Y5 receptors in the rat brain by using immunohistochemistry

Differential roles for neuropeptide Y Y1 and Y5 receptors in anxiety and sedation

Central administration of neuropeptide Y (NPY) causes both anxiolysis and sedation. Previous studies suggest that both effects are mediated via NPY Y1 receptors. However, most of these studies were carried out before the advent of specific NPY receptor ligands. Therefore, a potential role for other NPY receptors in anxiety and sedation remains a possibility. In the present study, we addressed this issue by testing the effects of intracerebroventricular (i.c.v.) injection of NPY as well as specific receptor agonists for the Y1 receptor ([D-His(26)]NPY), Y2 receptor (C2-NPY), and Y5 receptor ([cPP(1-7),NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP) in the elevated plus maze and open field tests. As with NPY, the Y1 agonist had a dose-dependent anxiolytic-like effect in both behavioral tests. In contrast to NPY, which caused significant sedation in the open field test, the Y1 agonist was without sedative effect. The Y2 agonist showed neither anxiolytic-like nor sedative effects. The Y5 agonist showed anxiolytic-like activity in both behavioral tests and caused sedation in the same dose range as NPY in the open field test. These results indicate that anxiolytic-like effects of i.c.v.-administered NPY in rats are mediated via both Y1 and Y5 receptors, whereas sedation is mediated via Y5 receptors.

Neuropeptide Y attenuates NMDA-induced phase shifts in the SCN of NPY Y1 receptor knockout mice in vitro

Neuropeptide Y (NPY) blocks the effect of light on the mammalian circadian clock during the subjective night. The present study explores the role of the NPY Y1 receptor in this interaction. The effect of NPY when co-applied with NMDA, a glutamate agonist that can mimic the effect of light, was examined in NPY Y1-/- mice (background strain 129SVXBalb/c) using electrophysiology. Cells in the suprachiasmatic nucleus (SCN), the master circadian pacemaker, show a circadian rhythm in spontaneous firing rate that can be recorded in vitro. The results demonstrated that NPY attenuated the phase shifts to NMDA in both the Y1-/- mice and control mice, indicating that the Y1 receptor does not mediate the NPY blockade of photic-like phase shifts. The peak in frequency in the untreated control brain slices from Y1-/- mice was advanced by approximately 1 h as compared to the Y1+/+ mice. The Y1 receptor may contribute to a functional model of circadian rhythms, but apparently is not essential for the effects of NPY on photic phase shifts.

Characterization of a new neuropeptide Y Y5 agonist radioligand: [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP

In order to optimally characterize a class of neuropeptide Y (NPY) receptors expressed in a tissue enriched with multiple subtypes (Y1, Y2, Y4 and Y5) and to establish its detailed distribution, it is critical to use highly selective and specific probes that possess very low non-specific binding. In that context, we recently reported on the development of [125I][hPP(1-17), Ala31, Aib32]NPY as Y5 receptor radioligand. However, the non-specific binding obtained with this radioligand was too high to allow for detailed receptor autoradiography studies [Br. J. Pharmacol. 139 (2003) 1360]. Iodinated [cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP may represent a better Y5 radioligand in that regard. Accordingly, [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP binding was investigated in rat brain membrane homogenates and its specificity and selectivity established in rat Y1, Y2, Y4 and Y5 transfected HEK293 cells. No specific binding was detected in HEK293 cells transfected with the rat Y1, Y2 or Y4 receptors, while saturable binding was observed in cells transfected with the rat Y5 receptor cDNA and in rat brain membrane homogenates (KD of 0.5-0.7 nM). Competition binding experiments performed in rat brain membrane homogenates demonstrated that specific [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP binding was competed with nanomolar affinities by Y5 agonists and antagonists such as [Leu31,Pro34]PYY, PYY(3-36), [cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP, [Ala31, Aib32]NPY, [hPP(1-17), Ala31, Aib32]NPY, CGP71683A and JCF109, but not by Y1 (BIBP3226 and BIBO3304), Y2 (BIIE0246) and Y4 (GR231118) ligands. Non-specific binding was also lower than that reported for [125I][hPP(1-17), Ala31, Aib32]NPY. Interestingly, detailed analysis of competition binding curves obtained with [Leu31, Pro34]PYY, hPP, PYY(3-36) and [cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP against specific [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP sites were best fitted to a two-site model. Additionally, receptor autoradiography studies revealed the presence of specific [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP binding sites in the lateral septum and area postrema while other brain regions contained much lower levels of specific binding. Taken together, these data suggest that [125I][cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP represents a useful tool to study the unique feature of the Y5 receptor subtype.

Distribution of NPY receptors in the hypothalamus

Neuropeptide Y (NPY) neurons abundantly innervate the hypothalamus, where NPY is involved in the regulation and integration of a broad range of homeostatic functions. In order to understand NPY-mediated behavioral, autonomic and neuroendocrine effects, it is important to characterize in detail the distribution of the hypothalamic NPY receptors. In this review, we briefly summarize the origin of NPY and its two related peptides, peptide YY and pancreatic polypeptide in the hypothalamus. Moreover, based on the results obtained with histological techniques such as in situ hybridization, immunohistochemistry and ligand binding, we summarize data on the hypothalamic distribution of the known NPY receptors, the Y1 Y2, Y4 and Y5 receptors as best characterized to date. These NPY receptors are found with individual distribution patterns in many hypothalamic neurons including neuroendocrine motoneurons, magnocellular neurosecretory neurons and numerous neurons connecting the hypothalamus with the limbic and the autonomic nervous systems. The histochemical analyses allow characterization of coexisting molecules and in this way definition of the neurochemistry of NPY circuitries. By showing coexistence of various NPY receptors they provide a morphological basis for in vitro studies showing heterodimerization of NPY receptors. The NPY neurons and their circuitries underlie the integrative role of NPY as a pleiotropic neuropeptide in the regulation of homeostasis.

NPY and cohorts in regulating appetite, obesity and metabolic syndrome: beneficial effects of gene therapy

Neuropeptide Y is the most potent physiological appetite transducer known. The NPY network is the conductor of the hypothalamic appetite regulating orchestra in the arcuate nucleus-paraventricular nucleus (ARC-PVN) of the hypothalamus. NPY and cohorts, AgrP, GABA and adrenergic transmitters, initiate appetitive drive directly through Y1, Y5, GABAA and alpha1 receptors, co-expressed in the magnocellular PVN (mPVN) and ARC neurons and by simultaneously repressing anorexigenic melanocortin signaling in the ARC-PVN axis. The circadian and ultradian rhythmicities in NPY secretion imprint the daily circadian and episodic feeding patterns. Although a number of afferent hormonal signals from the periphery can directly modulate NPYergic signaling, the reciprocal circadian and ultradian rhythmicities of anorexigenic leptin from adipocytes and orexigenic ghrelin from stomach, encode a corresponding pattern of NPY discharge for daily meal patterning. Subtle and progressive derangements produced by environmental and genetic factors in this exquisitely intricate temporal relationship between the two opposing humoral signals and the NPY network promote hyperphagia and abnormal rate of weight gain culminating in obesity and attendant metabolic disorders. Newer insights at cellular and molecular levels demonstrate that a breakdown of the integrated circuit due both to high and low abundance of NPY at target sites, underlies hyperphagia and increased adiposity. Consequently, interruption of NPYergic signaling at a single locus with NPY receptor antagonists may not be the most efficacious therapy to suppress hyperphagia and obesity. Central leptin gene therapy in rodents has been shown to subjugate, i.e. bring under homeostatic control, NPYergic signaling and suppress the age-related and dietary obesity for extended periods and thus shows promise as a newer treatment modality to curb the pandemic of obesity and metabolic syndrome.

Characterization of neuropeptide Y Y2 and Y5 receptor expression in the mouse hypothalamus

Neuropeptide Y (NPY) neurons abundantly innervate the hypothalamus, where NPY is involved in the regulation of a broad range of homeostatic functions. In the present work we studied NPY Y2 and Y5 receptor (R) gene expression in the mouse hypothalamus by using immunohistochemical detection of beta-galactosidase (beta-gal), a gene reporter molecule for Y2R and Y5R in Y2R-knockout (KO) and Y5R-KO mice, respectively. With this approach, cells normally expressing Y2R or Y5R are immunopositive for beta-gal. In the hypothalamus of the Y2R-KO mouse, beta-gal immunoreactivity (-ir) was found in numerous neurons of the medial preoptic nucleus as well as in the lateral anterior, periventricular, dorsomedial, tuberal, perifornical, and arcuate nuclei. Most of the dopaminergic neurons in the A13 dorsal hypothalamic group were beta-gal positive, whereas other hypothalamic dopaminergic neurons rarely displayed beta-gal-ir. In the arcuate nucleus, most of the beta-gal-positive neurons expressed NPY, but colocalizations with beta-endorphin were also found; in the tuberal and perifornical nuclei, many beta-gal-positive neurons contained nitric oxide synthase. beta-Gal-ir was also found in other forebrain regions of the Y2R-KO mouse, including the amygdala, thalamic nuclei, hippocampal CA3 area, and cortex. In the hypothalamus of the Y5R-KO mouse, beta-gal-positive neurons were found mainly in the arcuate nucleus and contained beta-endorphin. The present data show that Y2R and Y5R are expressed in distinct groups of hypothalamic neurons. High levels of Y2R expression in the preoptic nuclei suggest an involvement of Y2R in the regulation of reproductive behavior, whereas Y2R expression in the arcuate, dorsomedial, and perifornical nuclei may be relevant to feeding and body weight control. The finding that A13 dopaminergic neurons express Y2R suggests a new mechanism putatively involved in the central control of feeding, in which NPY can modulate dopamine secretion. The distribution of Y5R expression supports earlier evidence for involvement of this receptor in control of feeding and body weight via NPY's action on proopiomelanocortin-expressing neurons. J. Comp. Neurol. 470:256-265, 2004.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.