[Leu31-Pro34] neuropeptide Y identifies a subtype of 125I-labeled peptide YY binding sites in the rat brain

NPY and Gene Therapy for Epilepsy: How, When,... and Y

Neuropeptide Y (NPY) is a neuropeptide abundantly expressed in the mammalian central and peripheral nervous system. NPY is a pleiotropic molecule, which influences cell proliferation, cardiovascular and metabolic function, pain and neuronal excitability. In the central nervous system, NPY acts as a neuromodulator, affecting pathways that range from cellular (excitability, neurogenesis) to circuit level (food intake, stress response, pain perception). NPY has a broad repertoire of receptor subtypes, each activating specific signaling pathways in different tissues and cellular sub-regions. In the context of epilepsy, NPY is thought to act as an endogenous anticonvulsant that performs its action through Y2 and Y5 receptors. In fact, its overexpression in the brain with the aid of viral vectors can suppress seizures in animal models of epilepsy. Therefore, NPY-based gene therapy may represent a novel approach for the treatment of epilepsy patients, particularly for pharmaco-resistant and genetic forms of the disease. Nonetheless, considering all the aforementioned aspects of NPY signaling, the study of possible NPY applications as a therapeutic molecule is not devoid of critical aspects. The present review will summarize data related to NPY biology, focusing on its anti-epileptic effects, with a critical appraisal of key elements that could be exploited to improve the already existing NPY-based gene therapy approaches for epilepsy.

What doesn't kill you makes you stranger: Dipeptidyl peptidase-4 (CD26) proteolysis differentially modulates the activity of many peptide hormones and cytokines generating novel cryptic bioactive ligands

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase found either on cell surfaces where it is highly regulated in terms of its expression and surface availability (CD26) or in a free/circulating soluble constitutively available and intrinsically active form. It is responsible for proteolytic cleavage of many peptide substrates. In this review we discuss the idea that DPP4-cleaved peptides are not necessarily inactivated, but rather can possess either a modified receptor selectivity, modified bioactivity, new antagonistic activity, or even a novel activity relative to the intact parent ligand. We examine in detail five different major DPP4 substrates: glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), peptide tyrosine-tyrosine (PYY), and neuropeptide Y (NPY), and stromal derived factor 1 (SDF-1 aka CXCL12). We note that discussion of the cleaved forms of these five peptides are underrepresented in the research literature, and are both poorly investigated and poorly understood, representing a serious research literature gap. We believe they are understudied and misinterpreted as inactive due to several factors. This includes lack of accurate and specific quantification methods, sample collection techniques that are inherently inaccurate and inappropriate, and a general perception that DPP4 cleavage inactivates its ligand substrates. Increasing evidence points towards many DPP4-cleaved ligands having their own bioactivity. For example, GLP-1 can work through a different receptor than GLP-1R, DPP4-cleaved GIP can function as a GIP receptor antagonist at high doses, and DPP4-cleaved PYY, NPY, and CXCL12 can have different receptor selectivity, or can bind novel, previously unrecognized receptors to their intact ligands, resulting in altered signaling and functionality. We believe that more rigorous research in this area could lead to a better understanding of DPP4's role and the biological importance of the generation of novel cryptic ligands. This will also significantly impact our understanding of the clinical effects and side effects of DPP4-inhibitors as a class of anti-diabetic drugs that potentially have an expanding clinical relevance. This will be specifically relevant in targeting DPP4 substrate ligands involved in a variety of other major clinical acute and chronic injury/disease areas including inflammation, immunology, cardiology, stroke, musculoskeletal disease and injury, as well as cancer biology and tissue maintenance in aging.

Co-expression of neuropeptide Y Y1 and Y5 receptors results in heterodimerization and altered functional properties

Centrally administered neuropeptide Y (NPY) produces anxiolytic and orexigenic effects by interacting with Y1 and Y5 receptors that are colocalized in many brain regions. Therefore, we tested the hypothesis that co-expression of Y1 and Y5 receptors results in heterodimerization, altered pharmacological properties and altered desensitization. To accomplish this, the carboxyl-termini of Y1 and Y5 receptors were fused with Renilla luciferase and green fluorescent protein and the proximity of the tagged receptors assessed using bioluminescent resonance energy transfer. Under basal conditions, cotransfection of tagged Y1 receptor and Y5 produced a substantial dimerization signal that was unaffected by the endogenous, nonselective agonists, NPY and peptide YY (PYY). Selective Y5 agonists produced an increase in the dimerization signal while Y5 antagonists also produced a slight but significant increase. In the absence of agonists, selective antagonists decreased dimerization. In functional studies, Y5 agonists produced a greater inhibition of adenylyl cyclase activity in Y1/Y5 cells than cells expressing Y5 alone while NPY and PYY exhibited no difference. With PYY stimulation, the Y1 antagonist became inactive and the Y5 antagonist exhibited uncompetitive kinetics in the Y1/Y5 cell line. In confocal microscopy studies, Y1/Y5 co-expression resulted in increased Y5 signaling following PYY stimulation. Addition of both Y1 and Y5 receptor antagonists was required to significantly decrease PYY-induced internalization. Therefore, Y1/Y5 co-expression results in heterodimerization, altered agonist and antagonist responses and reduced internalization rate. These results may account for the complex pharmacology observed when assessing the responses to NPY and analogs in vivo.

Effect of enterostatin on the feeding responses to galanin and NPY

We have investigated the possibility that enterostatin may inhibit the intake of dietary fat by inhibiting either galanin or NPY-induced feeding pathways. Rats, adapted to either high fat (HF) or low fat-high carbohydrate (HC) diets and fitted with third ventricular cannulas were used to study the effects of intracerebroventricular (i.c.v.) enterostatin on i.c.v. NPY and galanin induced feeding responses in satiated rats. An equimolar dose of enterostatin (0.1 nmoles) inhibited, while a tenfold excess of enterostatin abolished the feeding response to galanin in rats adapted to a HF diet. The galanin stimulation of food intake was reduced in rats adapted to the HC diet and this response was less sensitive to inhibition by enterostatin. Enterostatin had no inhibitory effects on NPY-induced feeding in rats adapted to the HC diet and only a small inhibitory effect, at tenfold molar excess, in rats adapted to the HF diet. The ability of enterostatin to bind to galanin or NPY Y-1 receptors was investigated in ligand binding studies. Enterostatin failed to displace 125I-galanin or 125I-PYY from specific binding sites in rat forebrain homogenates or SK-N-MC cells respectively. The data provide support for the hypothesis that enterostatin specifically inhibits a galanin-responsive fat intake system, but indicate that this effect is not modulated by direct interaction with either galanin or NPY-Y1 receptors.

Neuropeptide Y receptor antagonists in obesity

Neuropeptide Y (NPY) is a 36 amino acid amidated peptide with high sequence homology to the endocrine peptides, peptide YY (PYY) and pancreatic polypeptide (PP). They appear to interact with a family of receptors that possess high affinity for one or more of these peptides. Five members of the receptor family have been cloned, with several additional members postulated through pharmacological evidence. All are members of the seven transmembrane domain-G-protein coupled receptor family. The Y1 receptor is the best characterised, with several nonpeptide antagonists available. This receptor appears to mediate a constriction of the peripheral vasculature and the 'anxiolytic' effects of centrally administered NPY. Less is known about the other receptors in the family. The Y2 receptor is believed to be presynaptic and mediates a reduction in neurotransmitter release. The Y4 receptor appears to be the receptor for pancreatic polypeptide, with high amounts of mRNA for this receptor found in the periphery, but lower levels in the brain. The Y5 receptor is expressed in the hypothalamus and has been postulated to be the receptor which mediates the increased food consumption seen following centrally administered NPY. Finally, the Y6 receptor has been cloned in the mouse and other species, but does not appear to encode a functional gene product in humans. Several types of nonpeptide Y1 and a series of Y5 antagonists have been described in the patent literature, though these compounds have limitations that will confine their use to preclinical studies. Nevertheless, considerable progress has been made in understanding the role of NPY and its receptors in experimental obesity. The next step will be the discovery of potent and selective nonpeptide antagonists, to add further credence to the therapeutic potential.

Introduction to the reviews on neuropeptide Y

Neuropeptide Y (NPY) was first reported as an abundant peptide in brain tissue in 1982. Shortly thereafter, NPY was found to be a member of a peptide family consisting of the endocrine peptides pancreatic polypeptide (PP) and peptide YY (PYY). These peptides exert most of their biological effects through five G-protein coupled receptors termed Y1, Y2, Y4, Y5 and y6 that mediate either inhibition adenylate cyclase or increases in intracellular calcium. Since the discovery of NPY, a robust a body of literature has developed around the potential functions of this peptide. While initial findings identified NPY is an important contributor to the regulation of feeding, body weight and blood pressure, more recent work as revealed more subtle functions of this peptide and its potential role in affective disorders, bone formation and cravings. The accompanying twelve reviews detail important developments in our understanding of the functional role of NPY.

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.

Neuropeptide Y Y4 receptor homodimers dissociate upon agonist stimulation

The pancreatic polypeptide-fold family of peptides consists of three 36-amino acid peptides, namely neuropeptide Y (NPY), peptide YY, and pancreatic polypeptide (PP). These peptides regulate important functions, including food intake, circadian rhythms, mood, blood pressure, intestinal secretion, and gut motility, through four receptors: Y1, Y2, Y4, and Y5. Additional receptor subtypes have been proposed based on pharmacology observed in native tissues. Recent studies with other G-protein-coupled receptors have shown that homo- and heterodimerization may be important in determining receptor function and pharmacology. In the present study, the recently cloned rhesus (rh) Y4 receptor was evaluated using radioligand binding, and the pharmacological profile was found to be very similar to the human Y4 receptor. To study homo- and heterodimerization involving the Y4 receptor using bioluminescence resonance energy transfer 2 (BRET(2)), the carboxy termini of the rhesus Y1, Y2, Y4, and Y5 receptors were fused to Renilla luciferase, and rhY4 was also fused to green fluorescent protein. Dimerization was also studied using Western blot analysis. Using both BRET(2) and Western analysis, we found that the rhY4 receptor is present at the cell surface as a homodimer. Furthermore, agonist stimulation using the Y4-selective agonists PP and 1229U91 can dissociate these dimers in a concentration-dependent manner. In contrast, rhY4 did not heterodimerize with other members of the NPY receptor family or with human opioid delta and mu receptors. Therefore, homodimerization is an important component in the regulation of the Y4 receptor.

Development and characterization of a highly selective neuropeptide Y Y5 receptor agonist radioligand: [125I][hPP1-17, Ala31, Aib32]NPY

(1) The existence of multiple classes of neuropeptide Y (NPY) receptors (Y(1), Y(2), Y(4), Y(5) and y(6)) is now well established. However, one of the major difficulties in the study of these various receptor subtypes is the current lack of highly selective probes to investigate a single receptor class. Up to most recently, this was particularly true for the Y(4) and Y(5) subtypes. (2) [hPP(1-17), Ala(31), Aib(32)]NPY, the first highly selective Y(5) agonist, was iodinated using the chloramine T method and purified by high-pressure liquid chromatography. (3) Binding performed in rat brain homogenates revealed that equilibrium was reached after 120 min (t(1/2)=21 min) and 60 min (t(1/2)=12 min) at 25 and 100 pM [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY, respectively. (4) Isotherm saturation binding experiments demonstrated that [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY binds to an apparent single population with high-affinity (K(D) of 1.2 and 1.7 nM) and low-capacity (B(max) of 14+/-3 fmol/100,000 cells and 20+/-5 fmol/mg protein) sites in Y(5) receptor HEK293-transfected cells and rat brain membrane homogenates, respectively. No specific [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY binding sites could be detected in Y(1), Y(2) or Y(4) receptors transfected HEK293 cells, demonstrating the high selectivity of this ligand for the Y(5) subtype. (5) Competition binding experiments performed in rat brain membrane homogenates and Y(5)-receptor transfected HEK293 cells demonstrated that specific [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY binding was competed with high affinity by Y(5) agonists and antagonists such as [Ala(31), Aib(32)]NPY, [hPP(1-17), Ala(31), Aib(32)]NPY, hPP, CGP71683A and JCF109, but not by Y(1) (BIBP3226), Y(2) (BIIE0246) and Y(1)/Y(4) (GR231118) preferential ligands. (6) Taken together, these data demonstrate that [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY is the first highly selective Y(5) radioligand to be developed. This new probe should prove most useful for further detailed studies of the molecular and pharmacological properties of this receptor subtype in brain and peripheral tissues.

The use of bioluminescence resonance energy transfer 2 to study neuropeptide Y receptor agonist-induced beta-arrestin 2 interaction

The neuropeptide Y (NPY) family peptides NPY, peptide YY (PYY), and pancreatic polypeptide (PP) bind to four G protein-coupled receptors (GPCRs): Y1, Y2, Y4, and Y5. A key step in the desensitization and internalization of GPCRs is the association of the receptor with beta-arrestins. In the present study, these receptors were analyzed with respect to their ability to interact with GFP2-tagged beta-arrestin 2 using the new bioluminescence resonance energy transfer 2 method. Agonists induced a concentration-dependent association of beta-arrestin 2 with all four receptors. Whereas the Y1 receptor exhibited the highest maximum response and rapid association (t(1/2) = 3.4 min), the maximal signals for the association of Y2 and Y4 receptors were less than half of that of Y1, and the association rates were much slower. Interestingly, when evaluated at the Y4 receptor, the Y4 agonist 1229U91 [(Ile,Glu,Pro,Dpr,Tyr,Arg, Leu,Arg,Try-NH2)-2-cyclic(2,4'),(2',4)-diamide] was unable to provoke the same maximal response as human PP, suggesting that 1229U91 is a partial agonist. When stimulated by PYY, the Y5 receptor responded with a t(1/2) of 4.6 min and a maximal response approximately 60% of what was observed with Y1. Because beta-arrestins are key components in GPCR internalization, it is interesting to note that the receptor that is known to internalize rapidly (Y1) exhibits the most rapid association with beta-arrestin 2, whereas the receptor that is known to internalize slowly, or not at all (Y2) associates slowly with beta-arrestin 2.

Expression of the neuropeptide Y Y1 receptor in the CNS of rat and of wild-type and Y1 receptor knock-out mice. Focus on immunohistochemical localization

The distribution of neuropeptide Y (NPY) Y1 receptor-like immunoreactivity (Y1R-LI) has been studied in detail in the CNS of rat using a rabbit polyclonal antibody against the C-terminal 13 amino acids of the rat receptor protein. The indirect immunofluorescence technique with tyramide signal amplification has been employed. For specificity and comparative reasons Y1 knock-out mice and wild-type controls were analyzed. The distribution of Y1R mRNA was also studied using in situ hybridization. A limited comparison between Y1R-LI and NPY-LI was carried out.A widespread and abundant distribution of Y1R-LI, predominantly in processes but also in cell bodies, was observed. In fact, Y1R-LI was found in most regions of the CNS with a similar distribution pattern between rat and wild-type mouse. This staining was specific in the sense that it was absent in adjacent sections following preadsorption of the antibody with 10(-5) M of the antigenic peptide, and that it could not be observed in sections of the Y1 KO mouse. In contrast, the staining obtained with an N-terminally directed Y1R antiserum did not disappear, strongly suggesting unspecificity. In brief, very high levels of Y1R-LI were seen in the islands of Calleja, the anterior olfactory nucleus, the molecular layer of the dentate gyrus, parts of the habenula, the interpeduncular nucleus, the mammillary body, the spinal nucleus of the trigeminal, caudal part, the paratrigeminal nucleus, and superficial layers of the dorsal horn. High levels were found in most cortical areas, many thalamic nuclei, some subnuclei of the amygdaloid complex, the hypothalamus and the nucleus of the stria terminalis, the nucleus of the solitary tract, the parabrachial nucleus, and the inferior olive. Moderate levels of Y1R-LI were detected in the cornu Ammonis and the subicular complex, many septal, some thalamic and many brainstem regions. Y1R staining of processes, often fiber and/or dot-like, and occasional cell bodies was also seen in tracts, such as the lateral lemniscus, the rubrospinal tract and the spinal tract of the trigeminal. There was in general a good overlap between Y1R-LI and NPY-LI, but some exceptions were found. Thus, some areas had NPY innervation but apparently lacked Y1Rs, whereas in other regions Y1R-LI, but no or only few NPY-positive nerve endings could be detected. Our results demonstrate that NPY signalling through the Y1R is common in the rat (and mouse) CNS. Mostly the Y1R is postsynaptic but there are also presynaptic Y1Rs. Mostly there is a good match between NPY-releasing nerve endings and Y1Rs, but 'volume transmission' may be 'needed' in some regions. Finally, the importance of using proper control experiments for immunohistochemical studies on seven-transmembrane receptors is stressed.

Characterization of neuropeptide Y Y1-like and Y2-like receptor subtypes in the mouse brain

To characterize receptor subtypes in the mouse, we performed autoradiographic localization and pharmacological characterization studies using the selective radiolabeled agonists, [(125)I]-Leu(31), Pro(34)-PYY and [(125)I]-PYY 3-36. The pharmacology of [(125)I]-Leu(31), Pro(34)-PYY and [(125)I]-PYY 3-36 binding to mouse brain homogenates were consistent with Y1-like and Y2-like receptors, respectively. Using receptor autoradiography, high Y1-like binding was observed in the islands of Calleja and dentate gyrus. [(125)I]-PYY 3-36 binding was highest in the hippocampus, lateral septum, stria terminalis of the thalamus, and compacta and lateralis of the substantia nigra. In addition, there are differences in receptor distribution in mouse brain compared to other species that may translate into different functional roles for the NPY receptors within each species.

Neuropeptide Y receptors differentially modulate G-protein-activated inwardly rectifying K+ channels and high-voltage-activated Ca2+ channels in rat thalamic neurons

1. Using whole-cell patch-clamp recordings, infrared videomicroscopy and fast focal solution exchange methods, the actions of neuropeptide Y (NPY) were examined in thalamic slices of postnatal (10-16 days) rats. 2. NPY activated a K+-selective current in neurons of the thalamic reticular nucleus (RT; 20/29 neurons) and ventral basal complex (VB; 19/25 neurons). The currents in both nuclei had activation and deactivation kinetics that were very similar to those of GABAB receptor-induced currents, were totally blocked by 0.1 mM Ba2+ and showed voltage-dependent relaxation. These properties indicate that the NPY-sensitive K+ current is mediated by G-protein-activated, inwardly rectifying K+ (GIRK) channels. 3. In RT neurons, NPY application reversibly reduced high-voltage-activated (HVA) currents to 33 +/- 5 % (n = 40) of the control level but did not affect the T-type currents. Inhibition of Ca2+ currents was voltage independent and was largely mediated by effects on N- and P/Q-type channels. 4. NPY activation of GIRK channels was mediated via NPY1 receptors, whereas inhibition of N- and P/Q-type Ca2+ channels was mediated by NPY2 receptors. 5. These results show that neuropeptide Y activates K+ channels and simultaneously inhibits HVA Ca2+ channels via different receptor subtypes.

Differential regulation of GABA release and neuronal excitability mediated by neuropeptide Y1 and Y2 receptors in rat thalamic neurons

1. Neuropeptide Y (NPY) produced inhibitory effects on neurons of the thalamic reticular nucleus (RT; n = 18) and adjacent ventral basal complex (VB; n = 22), which included hyperpolarization (approximately 4 mV), a reduction in rebound and regular spikes and an increased membrane conductance. These effects were mediated predominantly via NPY1 receptor activation of G-protein-activated, inwardly rectifying K+ (GIRK) channels. 2. NPY reduced the frequency of spontaneous GABAA receptor-mediated inhibitory postsynaptic currents (sIPSCs) in RT (by 60 +/- 7 %, n = 14) and VB neurons (by 25 +/- 11 %, n = 16), but had no effect on the kinetic properties of sIPSCs. After removal of the RT nucleus, the inhibitory effects of NPY on sIPSCs in VB neurons remained (29 +/- 7 %, n = 5). The synaptic effects were mediated via NPY2 receptors. 3. NPY inhibited the frequency of miniature IPSCs (mIPSCs) in RT and VB neurons (by 63 +/- 7 %, n = 5, and 37 +/- 8 %, n = 10, respectively) in the presence of tetrodotoxin (TTX) (1 microM) but not TTX (1 microM) and Cd2+ (200 microM). 4. NPY inhibited evoked IPSCs in both RT (by 18 +/- 3 %, n = 6) and VB (by 5 +/- 4 %, n = 6) neurons without change in short-term synaptic plasticity. 5. We conclude that NPY1 and NPY2 receptors are functionally segregated in the thalamus: NPY1 receptors are predominantly expressed at the somata and dendrites and directly reduce the excitability of neurons in both the RT and VB nuclei by activating GIRK channels. NPY2 receptors are located at recurrent (RT) and feed-forward GABAergic terminals (VB) and downregulate GABA release via inhibition of Ca2+ influx from voltage-gated Ca2+ channels.

Sympathetic and parasympathetic interaction in vascular and secretory control of salivary glands in anaesthetised dogs

The present study was undertaken to examine sympathetic-parasympathetic interactions in the regulation of salivary gland function, with special reference to the possible role of the sympathetic cotransmitter neuropeptide Y (NPY). In dogs anaesthetised with pentobarbitone, electrical stimulation of the parasympathetic nerve to the submandibular gland evoked an increase in glandular blood flow and salivary secretion. Sympathetic nerve stimulation evoked a significant prolonged attenuation of vasodilator and secretory responses to subsequent parasympathetic stimulation. This attenuation was not significantly altered by alpha- and beta-adrenoceptor blockade. Systemic administration of the sympathetic cotransmitter, NPY, mimicked the effect of the sympathetic stimulation by significantly attenuating vasodilatation and salivary secretion. The NPY Y1 receptor agonist, [Leu31, Pro34]NPY and the specific NPY Y2 receptor agonist N-acetyl[Leu28, Leu31]NPY 24-36 both significantly attenuated the vasodilatation and salivary secretion evoked by stimulation of the parasympathetic nerve. The NPY Y1 receptor antagonist, GR231118 significantly antagonised the attenuation of vasodilatation caused by both sympathetic stimulation and the NPY Y1 receptor agonist. GR231118 also inhibited the pressor response of NPY. Intra-arterial injection of methacholine and stimulation of the parasympathetic nerve both caused local vasodilatation in the gland which was significantly attenuated by pretreatment with sympathetic stimulation or the NPY Y1 agonist. The NPY Y2-specific agonist did not attenuate methacholine-induced vasodilatation but did attenuate vasodilatation evoked by parasympathetic stimulation. The results indicate that NPY as a sympathetic cotransmitter may have a role in the regulation of vascular secretory function of salivary glands.

[(125)I]-GR231118: a high affinity radioligand to investigate neuropeptide Y Y(1) and Y(4) receptors

GR231118 (also known as 1229U91 and GW1229), a purported Y(1) antagonist and Y(4) agonist was radiolabelled using the chloramine T method. [(125)I]-GR231118 binding reached equilibrium within 10 min at room temperature and remained stable for at least 4 h. Saturation binding experiments showed that [(125)I]-GR231118 binds with very high affinity (K(d) of 0.09 - 0.24 nM) in transfected HEK293 cells with the rat Y(1) and Y(4) receptor cDNA and in rat brain membrane homogenates. No specific binding sites could be detected in HEK293 cells transfected with the rat Y(2) or Y(5) receptor cDNA demonstrating the absence of significant affinity of GR231118 for these two receptor classes. Competition binding experiments revealed that specific [(125)I]-GR231118 binding in rat brain homogenates is most similar to that observed in HEK293 cells transfected with the rat Y(1), but not rat Y(4), receptor cDNA. Autoradiographic studies demonstrated that [(125)I]-GR231118 binding sites were fully inhibited by the Y(1) antagonist BIBO3304 in most areas of the rat brain. Interestingly, high percentage of [(125)I]-GR231118/BIBO3304-insensitive binding sites were detected in few areas. These [(125)I]-GR231118/BIBO3304-insensitive binding sites likely represent labelling to the Y(4) receptor subtype. In summary, [(125)I]-GR231118 is a new radiolabelled probe to investigate the Y(1) and Y(4) receptors; its major advantage being its high affinity. Using highly selective Y(1) antagonists such as BIBO3304 or BIBP3226 it is possible to block the binding of [(125)I]-GR231118 to the Y(1) receptor allowing for the characterization and visualization of the purported Y(4) subtype. British Journal of Pharmacology (2000) 129, 37 - 46

Role of hypothalamic neuropeptide Y in feeding and obesity

The 36-amino-acid peptide, neuropeptide Y (NPY), is the most abundant peptide in the rat brain. When administered into the brain, NPY produces a variety of physiological actions including a pronounced stimulation of feeding in satiated rats. Elevations in hypothalamic NPY have been reported after food deprivation and in genetically obese rodents. NPY is believed to produce its actions through a portfolio of G-protein coupled receptors, Y1, Y2, Y4 and Y5. Studies using peptide analogs, receptor knockout animals and specific receptor antagonists suggest the Y1 and Y5 receptors are important in mediating the effects of NPY on food intake in rats. Development of specific receptor antagonists with improved pharmacokinetic properties will be required to determine the importance of NPY in human obesity and appetite disorders.

Regional distribution of Y-receptor subtype mRNAs in rat brain

Molecular cloning techniques have recently led to the identification of a growing number of neuropeptide Y-receptor subtypes, suggesting possible subtype-specific involvement in different physiological processes. Here we report the first study which determines and compares the mRNA expression of all four cloned functional Y-receptor subtypes (Y1, Y2, Y4 and Y5) in consecutive sections of the rat brain on a cellular level, using a uniform in situ hybridization technique. Our results demonstrate that Y-receptor subtype mRNA expression is widely distributed throughout the rat brain. Interestingly, coexpression of all four Y-receptors, at different levels, is particularly evident within the limbic system, including the hypothalamus, hippocampus, amygdala, piriform and cingulate cortices and tegmental areas, all of which are heavily involved in behaviour, emotion and homeostatic regulation. Particularly interesting is the demonstration that Y5-receptor mRNA expression always coincides with the presence of Y1-receptor mRNA (although not vice versa), possibly due to the overlapping organization and transcriptional control of their genes. However, it is also clear that several brain nuclei display preferential expression of one or a selective combination of Y-receptor subtype mRNAs. Furthermore, it is evident that there is regionalization of expression within certain loci which express all four receptor subtype mRNAs, particularly within the paraventricular and arcuate hypothalamic nuclei. Our results suggest that some of neuropeptide Y's (NPY) effects may be mediated through one particular subtype, whereas other physiological processes might require the coordinated action of different subtypes within the same or discrete areas.

Neuropeptide Y-related compounds and feeding

Neuropeptide Y (NPY) and related compounds increase short-term feeding. Previous studies have used different animal models, feeding schedules, sources of the compounds, and time and routes of administration. These differences in methodology are important in the variability reported on the potency of NPY-related compounds. To obtain reliable data on the relative efficacy, we tested NPY, NPY 3-36, and pancreatic polypeptide (PP) using an identical protocol and the same commercial source. These three NPY-related compounds were tested using the intracerebroventricular (i.c.v., into the third ventricle) administration, and the profile of the feeding enhancement including the dose response and potency was determined. Compounds were tested in parallel on at least 2 successive days. NPY, NPY 3-36, and PP exhibited different potencies in enhancing 2-h food intake. Comparison of their dose responses (using 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 microg/rat) demonstrated an overall potency of NPY 3-36 > NPY > PP for the high doses. To study ligand interactions, we examined the effects of various combinations of NPY-related compounds administered concomitantly. These combinations were justified based on the data obtained from the individual dose responses. The data show that the effects of NPY plus NPY 3-36 or NPY 3-36 plus PP were less than additive. When compared to the individual responses, the effects of NPY 3-36 were almost identical to those induced by the combinations using low doses of NPY plus NPY 3-36, or low and high doses of PP plus NPY 3-36. The results support the notion that NPY and its analogues induce a short-term feeding response by activating multiple receptor subtypes.

Characterization of the neuropeptide Y5 receptor in the human hypothalamus: a lack of correlation between Y5 mRNA levels and binding sites

Neuropeptide Y (NPY) is a 36-amino-acid peptide that appears to play a central role in the control of feeding behavior. Recently, a cDNA encoding a novel NPY receptor subtype (Y5) was cloned from the rat and human hypothalamus, and shown to have a pharmacology consistent with NPY-induced feeding. We have subsequently cloned this cDNA from human hypothalamus and stably expressed it in CHO cells. Consistent with earlier reports, hY5 has a high affinity for NPY, [Leu31, Pro34]NPY, and NPY(3-36), but low affinity for larger C-terminal deletions of NPY and BIBP3226. High levels of hY5 mRNA were found in the human testis, brain, spleen and pancreas, with lower levels in several other tissues. In the human brain, hY5 mRNA levels were typically higher than hY2, but lower in comparison to hY1 receptor mRNA. To quantify the relative amounts of hY1, hY2 and hY5 mRNA in the human hypothalamus, we employed competitive RT-PCR. Interestingly, the relative amount of hY5 mRNA was substantially higher than either hY1 or hY2. However, pharmacological characterization of NPY binding sites in human hypothalamus membranes revealed predominantly the hY2 subtype. These data establish that while hY5 mRNA levels are very high in the human hypothalamus, conventional radioligand binding techniques do not detect hY5-like binding site. Whether hY5-like binding sites exist in the other human tissues that express hY5 mRNA (and what function hY5 has in those tissues) awaits future investigation.

On the relationship of neuropeptide Y Y1 receptor-immunoreactive neuronal structures to the neuropeptide Y-immunoreactive nerve terminal networks. A double immunolabelling analysis in the rat brain

Neuropeptide Y is the most abundant peptide in the mammalian central nervous system and exhibits a variety of potent neurobiological functions. In the present study, double immunolabelling histochemistry was performed, using previously characterized antibodies against neuropeptide Y and the neuropeptide Y Y1 receptor subtype, to clarify the cellular distribution of Y1 receptors in the rat brain in relation to the neuropeptide Y-immunoreactive systems. Based on fluorescence and confocal laser microscopy analysis, morphological evidence is presented that the perikaryal and dendritic Y1 receptor-like immunoreactivity demonstrated in discrete regions of the tel-, diencephalon and of the lower brain stem, shown to be cytoplasmic and membrane associated, in many brain regions is not co-distributed with the neuropeptide Y-immunoreactive terminal network. These findings may partly be explained by the existence of volume transmission in Y1 receptor-mediated neuropeptide Y transmission involving short to long distance diffusion and/or convection of neuropeptide Y from its site of release to the neuronal target cells, containing the high-affinity Y1 receptors. Furthermore, neuropeptide Y and Y1 receptor-like immunoreactivities were in no case co-localized in the same nerve cell, suggesting that, in the rat brain, the Y1 receptor subtype may not be a neuropeptide Y autoreceptor.

Divalent cations influencing neuropeptide Y receptor subtype binding in rat hippocampus and cortex membranes as well as in recombinant cells

At least six types of neuropeptide Y (NPY) receptors (Y1-Y6) have been pharmacologically distinguished of which only the Y1, Y2, Y4 and Y5 subtypes have been thoroughly characterized. In order to further classify receptor subtypes in the brain, we performed receptor binding studies using rat cortical and hippocampal membranes and, in particular, studied the effects of different ion compositions of the buffer on the binding behaviour of several NPY agonists and the Y1 receptor antagonist BIBO3304. Ca2+ was necessary for reliable Y1 receptor subtype classification in rat cortical membranes (with Hill coefficients close to unity) for the peptide agonists. This was further substantiated by the Y1 selective antagonist BIBO3304 displaying an IC50 value of 0.9+/-0.5 nM for 80% of the total receptors, the remaining sites being BIBO3304 insensitive (IC50 > 10,000 nM). Replacing Ca2+ by Mn2+ resulted in a complete loss of BIBO3304 sensitive sites. On the other hand, using hippocampal membrane preparations, displacement curves with Hill coefficients close to unity were only obtained in the presence of Mn2+ ions, yielding a binding profile of receptors with low affinity for [Leu31,Pro34]NPY (IC50 = 50 nM) and for BIBO3304 (IC50 > 10,000 nM). Addition of Mn2+ ions to cortical or of Ca2+ ions to hippocampal membrane preparations resulted in binding profiles differing from typical receptor classification. Therefore, the influence of divalent cations on Y1 receptors expressed on recombinant cells was studied. In this monoreceptor system, Ca2+ was necessary to detect high amounts of specific binding and Mn2+ ions induced a change in the affinity state. These findings indicate that apparent NPY receptor heterogeneity does not only depend on the brain region examined and that divalent ions modulate ligand binding properties.

Neuropeptide Y and limbic seizures

Since its discovery in 1982, neuropeptide Y (NPY), a 36 amino-acid member of the pancreatic polypeptide family, has received considerable attention in the field of neuroscience. Originally isolated from porcine brain /86/, NPY is one of the most abundant and widely distributed peptides in the central nervous system. In the brain, NPY is present in the hypothalamus, limbic structures, cerebral cortex, brainstem and striatum /2,71/. Because of the widespread distribution of NPY, it has been implicated in the modulation of a variety of behaviors, including, but not limited to, circadian rhythms /1/, memory retention /33/, feeding /19,56/, sympathetic control of cardiovascular function /89/ and anxiety /42,43/. These functions have been reviewed elsewhere and will not be discussed in great detail here. The present review is intended to provide an overview of recent work implicating a role for NPY in limbic seizures.

Expression and characterization of the neuropeptide Y Y5 receptor subtype in the rat brain

The neuropeptide Y Y5 receptor subtype has generated great interest, especially regarding its possible involvement in feeding behaviors. However, its distribution and sites of expression in the mammalian brain are, in large part, unknown because of the lack of selective tools. We demonstrate in this study that specific [125I][Leu31, Pro34]PYY binding is competed in a biphasic manner by BIBP3226, a Y1 receptor antagonist, demonstrating the existence of sensitive and insensitive sites to BIBP3226. Assays performed by using [125I][Leu31,Pro34]PYY in the presence of 1 microM BIBP3226 to block the Y1 receptor subtype revealed a pharmacological profile highly similar to the cloned Y5 receptor. Moreover, results obtained with GW1229 suggest that the Y4 subtype represents only a very small proportion of the total population of NPY receptors in the rat brain. Quantitative receptor autoradiographic data revealed the discrete distribution of [125I][Leu31,Pro34]PYY/BIBP3226-insensitive Y5 sites in the rat brain, with the external plexiform layer of the olfactory bulb, the lateral septum, the anteroventral thalamic nucleus, the CA3 subfield of the ventral hippocampus, the nucleus tractus solitarius, and the area postrema being most enriched. Rather surprisingly, in the hypothalamus, a key structure modulating food intake, only low densities of Y5 binding sites were detected as well as in most other regions of the rat brain. These data suggest that the Y5 receptor protein is expressed and translated by a small percentage of hypothalamic neurons and that the effect of NPY on feeding behaviors likely is mediated by more than one class of NPY receptors. It also indicates that the Y5 receptor may be involved in other biological actions induced by NPY. Taken together, these data represent the first pharmacological demonstration of the expression and discrete localization of the Y5 receptor protein in the rat brain.

Preferential expression of the neuropeptide Y Y1 over the Y2 receptor subtype in cultured hippocampal neurons and cloning of the rat Y2 receptor

1 Neuropeptide Y (NPY) and NPY receptors are most abundant in the hippocampal formation where they modulate cognitive functions. Expression of NPY receptors in rat cultured primary hippocampal cells was investigated in the present study by use of combined molecular, pharmacological and immunohistochemical approaches, including the cloning of the rat Y2 receptor described here for the first time. 2 More than 70% of the hippocampal neurones were endowed with [125I]-[Leu31,Pro34]PYY Y1-like receptor silver grain accumulations and Y1 receptor immunostaining. These radio- and immuno-labelling signals were distributed over cell bodies and processes of bipolar, stellate and pyramidal-like neuronal cells, as confirmed by neurone-specific enolase and MAP-2 staining. 3 Competition binding profiles revealed that specific [125I]-[Leu31,Pro34]PYY binding was competitively displaced according to a ligand selectivity pattern prototypical of the Y1 receptor sub-type with [Leu31,Pro34]substituted NPY/PYY analogues >> C-terminal fragments = pancreatic polypeptides, with the non-peptide antagonist BIBP3226 being most potent. This profile excludes the possible labelling by [125I]-[Leu31,Pro34]PYY of the newly cloned Y4, Y5 and Y6 receptors. 4 The expression of the genuine Y1 receptor was confirmed by RT-PCR in hippocampal cultures. In contrast, negligible levels of Y2-like/[125I]-PYY3-36 binding were detected in these cultures in spite of the presence of its mRNA, as characterized by RT-PCR. The expression of both the Y1 and the Y2 receptor mRNAs was also noted in normal embryonic hippocampal tissues showing that signals expressed in cultured neurones were also present in utero. 5 Taken together, these results suggest that the Y1 receptor subtype may be of critical importance in the normal functioning of the rat hippocampus, especially during brain development and maturation.

The neuropeptide Y Y1 antagonist, 1229U91, a potent agonist for the human pancreatic polypeptide-preferring (NPY Y4) receptor

Recently, a novel high-affinity peptide antagonist, 1229U91, was published as a selective neuropeptide Y Y1 antagonist. The selectivity of 1229U91 was evaluated in the human NPY Y1 receptor containing cell line, SK-N-MC, and cells containing the cloned human NPY Y2, the pancreatic polypeptide-preferring (NPY Y4), and the NPY Y5 receptors. 1229U91 potently displaced [125I]-peptide YY (PYY) binding to human NPY Y1 receptors (IC50 = 0.245+/-0.004 nM, n = 4). but displayed little affinity for the human NPY Y2 and Y5 receptors (IC50 > 1000 nM). Interestingly, 1229U91 displaced [125I]-PYY with even greater affinity at the human NPY Y4 receptor (IC50 = 0.081+/-0.009 nM, n = 4). Using a cyclic AMP accumulation assay, 1229U91 blocked NPY inhibition of forskolin-induced adenylate cyclase activity in NPY Y1 receptor containing SK-N-MC cells. In the human NPY Y4 receptor expressing cell line, 1229U91 did not block pancreatic polypeptide (PP) inhibition of forskolin stimulated adenylate cyclase. However, in the absence of PP, 1229U91 was able to inhibit forskolin stimulated cyclic AMP accumulation (IC50 = 7.16+/-2.8 nM, n = 4). We conclude that 1229U91 binds non-selectively with high affinity to both human NPY Y1 and Y4 receptors. Furthermore, 1229U91 displays antagonist activity at the NPY Y1 receptor, while having agonist activity at the NPY Y4 receptor.

Marked decrease of neuropeptide Y Y2 receptor binding sites in the hippocampus in murine prion disease

Using autoradiographic binding methodology with monoiodinated peptide YY together with the agonists neuropeptide Y (NPY) and NPY (13-36), as well as in situ hybridization with oligonucleotide probes complementary to the NPY Y2 receptor (Y2-R) mRNA, we have studied whether or not intracerebral prion inoculation affects Y2-Rs in male CD-1 mice. Monoiodinated peptide YY binding, mainly representing Y2-Rs, was down-regulated by 85% in the CA1 strata oriens and radiatum and by 50-65% in the CA3 stratum oriens 110-140 days postinoculation. In the CA3 stratum radiatum, where the mossy fibers from the dentate granule cells project, there was a significant decrease in PYY binding at 110-120 days. Y2-R mRNA, moderately expressed both in the CA1 and CA3 pyramidal cell layers and the granule cell layer in the dentate gyrus, showed a slight, but not significant, decrease in CA3 neurons 130 days postinoculation. The results indicate that the accumulation of the scrapie prion protein in the CA1-3 region strongly inhibits NPY binding at the Y2-Rs, which, however, is only marginally due to reduced Y2-R mRNA expression. The loss of the ability of NPY to bind to inhibitory Y2-Rs may cause dysfunction of hippocampal circuits and may contribute to the clinical symptoms in mouse scrapie.

The ventral lateral geniculate nucleus and the intergeniculate leaflet: interrelated structures in the visual and circadian systems

The ventral lateral geniculate nucleus (vLGN) and the intergeniculate leaflet (IGL) are retinorecipient subcortical nuclei. This paper attempts a comprehensive summary of research on these thalamic areas, drawing on anatomical, electrophysiological, and behavioral studies. From the current perspective, the vLGN and IGL appear closely linked, in that they share many neurochemicals, projections, and physiological properties. Neurochemicals commonly reported in the vLGN and IGL are neuropeptide Y, GABA, enkephalin, and nitric oxide synthase (localized in cells) and serotonin, acetylcholine, histamine, dopamine and noradrenalin (localized in fibers). Afferent and efferent connections are also similar, with both areas commonly receiving input from the retina, locus coreuleus, and raphe, having reciprocal connections with superior colliculus, pretectum and hypothalamus, and also showing connections to zona incerta, accessory optic system, pons, the contralateral vLGN/IGL, and other thalamic nuclei. Physiological studies indicate species differences, with spectral-sensitive responses common in some species, and varying populations of motion-sensitive units or units linked to optokinetic stimulation. A high percentage of IGL neurons show light intensity-coding responses. Behavioral studies suggest that the vLGN and IGL play a major role in mediating non-photic phase shifts of circadian rhythms, largely via neuropeptide Y, but may also play a role in photic phase shifts and in photoperiodic responses. The vLGN and IGL may participate in two major functional systems, those controlling visuomotor responses and those controlling circadian rhythms. Future research should be directed toward further integration of these diverse findings.

Identification of multiple neuropeptide Y receptor subtypes in the human frontal cortex

Recently, we found abundant mRNA and binding sites for neuropeptide Y Y1-like receptors in the human cerebral cortex. However, an earlier study using indirect labeling methods failed to detect substantial neuropeptide Y1-like receptor binding in numerous areas of the human brain, including the cerebral cortex. To resolve the disparity in these findings, we characterized the neuropeptide Y receptor subtypes labeled with [125I]peptide YY in homogenates of human frontal cortex. Competition experiments using 100 pM [125I]peptide YY binding to human frontal cortex homogenates indicated predominantly neuropeptide Y Y2 receptors are labeled with this concentration of ligand. However, saturation analysis of [125I]peptide YY binding to frontal cortex membranes resulted in isotherms best characterized by a two-site fit. Binding of [125I]peptide YY to the high affinity (Kd = 40 pM) binding site was prevented using a 100 nM concentration of the neuropeptide Y Y2 receptor agonist peptide YY-(3-36). By masking the higher affinity site, we found a low affinity [125I]peptide YY binding site (Kd = 1.4 nM) exhibiting a pharmacology consistent with a neuropeptide Y Y1-like receptor. It appears that neuropeptide Y Y2 receptors are the predominant subtype labeled with low concentrations of[125I]peptide YY and that the neuropeptide Y Y1 receptor is a low affinity [125I]peptide YY binding site in the human frontal cortex.

Characterization of neuropeptide Y receptor subtypes in the normal human brain, including the hypothalamus

The aim of the present study was to investigate the existence and distribution of neuropeptide Y receptor subtypes in various regions of the normal human brain using the peptide YY derivative receptor probes, [125I][Leu31,Pro34]polypeptide YY/Y1 and [125I]polypeptide YY(3-36)/Y2, in addition to the non-selective ligand [125I]polypeptide YY. Membrane binding assays performed with post mortem frontal cortex homogenates revealed that [125I]polypeptide YY and [125I]polypeptide YY(3-36) bound in a time- and protein concentration-dependent manner. Very low amounts of specific [125I][Leu31,Pro34]polypeptide YY binding could be detected even in the presence of high amounts of protein, contrasting with results obtained with [125I]polypeptide YY and [125I]polypeptide YY(3-36), a preferential Y2 receptor probe. Analysis of saturation isotherms revealed that [125I]polypeptide YY(3-36) bound to a single class of high-affinity sites (0.5-2 nM). Significantly higher binding capacities were evident for [125I]polypeptide YY(3-36) as compared to [125I][Leu31,Pro34]polypeptide YY, suggesting that the human frontal cortex, in contrast to the rat, is mostly enriched with Y2 receptors. Ligand selectivity profile confirmed the hypothesis that polypeptide YY(3-36), neuropeptide Y and polypeptide YY but not the [Leu31,Pro34] derivatives are potent competitors of [125I]polypeptide YY and [125I]polypeptide YY(3-36) binding sites. Autoradiographic studies demonstrated further that cortical areas, as well as most other regions of the human brain, are particularly enriched with Y2/[125I]polypeptide YY(3-36) sites, while only low to very low amounts of Y1 binding were detected except in the dentate gyrus of the hippocampal formation. In the human hypothalamus, a preponderance of Y2 binding sites was also noted. Taken together, these results clearly establish that the distribution of the Y1 and Y2 receptor subtypes in human is different from the rodent brain, the Y2 subtype being most abundant in the human brain.

Increased potency of neuropeptide Y to antagonize alpha2-adrenoceptor function in the nucleus tractus solitarii of the spontaneously hypertensive rat

The regulation by neuropeptide Y of alpha2-adrenoceptors in the nucleus tractus solitarii was evaluated in the adult normotensive Wistar Kyoto rat and the adult spontaneously hypertensive rat. The microinjection of a submaximal dose of l-noradrenaline (800 pmol in 50 nl) alone into the nucleus tractus solitarii produced a significant reduction in the mean arterial blood pressure in either strain. The threshold dose (1 pmol in 50 nl) of neuropeptide Y(1-36) for the vasodepressor response in the Wistar Kyoto rat was five times higher than that (0.2 pmol in 50 nl) in the spontaneously hypertensive rat. Furthermore, neuropeptide Y(1-36) at 0.2 pmol in 50 nl could significantly counteract the vasodepressor response to l-noradrenaline (800 pmol in 50 nl) in the spontaneously hypertensive rat, but not in the Wistar Kyoto rat, in which 1 pmol in 50 nl of neuropeptide Y(1-36) must be employed to counteract the vasodepressor response to l-noradrenaline (800 pmol in 50 nl), although the vasodepressor responses are of a similar magnitude. The in situ hybridization and quantitative receptor autoradiographical experiments showed that the alpha2A-adrenoceptor messenger RNA levels and the B(max) value of the alpha2-adrenoceptor agonist [3H]p-aminoclonidine binding sites measured in the nucleus tractus solitarii of the spontaneously hypertensive rat were substantially lower than those in the Wistar Kyoto rat. The quantitative receptor autoradiographical results were consistent with the cardiovascular results and showed that in the spontaneously hypertensive rat, neuropeptide Y(1-36) at 1 nM led to a significant increase in the K(d) value of [3H]p-aminoclonidine binding sites. In the Wistar Kyoto rat, neuropeptide Y(1-36) produced this effect only at 10 nM. The present study provides evidence for an increase of the potency of neuropeptide Y(1-36) to antagonistically modulate alpha2-adrenoceptors in the nucleus tractus solitarii of the spontaneously hypertensive rat. This enhanced antagonistic action may partly be related to a reduction in the number of alpha2A-adrenoceptors in the nucleus tractus solitarii of the spontaneously hypertensive rat, since a decrease has been observed in the alpha2A-adrenoceptor messenger RNA levels and the alpha2-adrenoceptor binding sites in the spontaneously hypertensive rat. This increased potency of neuropeptide Y(1-36) to antagonize alpha2-adrenoceptor function in the nucleus tractus solitarii of the spontaneously hypertensive rat may contribute to the development of high blood pressure in this hypertensive strain.

Analysis of NPY receptor subtypes in the human frontal cortex reveals abundant Y1 mRNA and binding sites

Receptors for neuropeptide Y (NPY) are widely distributed throughout the mammalian brain. Using indirect labeling methods, the human brain was reported to contain predominantly the Y2 receptor subtype, whereas the rat brain contains a mixture of Y1 and Y2 receptor subtypes. To more accurately assess NPY receptors in the human brain, we used type Y1- and Y2-selective radioligands [125I] [Leu31,Pro34]PYY and [125I]PPY (3-36), respectively, to examine NPY receptors in the human frontal cortex. Contrary to an earlier report, abundant Y1 binding sites were found in homogenates of human frontal cortex. Moreover, saturation analysis showed similar densities of both Y1 (Kd = 433 +/- 36 pM, Bmax = 313 +/- 15 fmol/mg protein) and Y2 (Kd = 444 +/- 39 pM, Bmax = 458 +/- 22 fmol/mg protein) receptor subtypes in the human frontal cortex. Subsequently, Northern blot analysis revealed abundant expression of Y1 mRNA, with very low levels of Y2 mRNA, in cerebral cortex and in other areas of the human brain. These findings were confirmed by competitive RT-PCR in the human frontal cortex. Therefore, it appears that Y1 binding sites and mRNA are expressed abundantly in the human frontal cortex and, earlier findings, suggest that the human brain contains a mixture of Y1 and Y2 receptor subtypes.

[125I]Leu31, Pro34-PYY is a high affinity radioligand for rat PP1/Y4 and Y1 receptors: evidence for heterogeneity in pancreatic polypeptide receptors

Cloned receptors for the PP-fold peptides are subdivided into Y1, Y2, PP1/Y4, Y5 and Y6. NPY and PYY have similar affinity for Y1, Y2, Y5 and Y6 receptors while PP has highest affinity for PP1. Pro34-substituted analogs of NPY and PYY have selectivity for Y1 and Y1-like receptors over Y2 receptors. In the present study, we found the putative Y1-selective radioligand, [125I]Leu31, Pro34-PYY, also binds with high affinity to the rat PP1 receptor in cell lines expressing the receptor. However, in rat brain sections, [125I]Leu31, Pro34-PYY does not appear to bind to the interpeduncular nucleus, a brain region containing a high density of [125I]-bPP binding sites. Therefore, it appears there is additional heterogeneity in receptors recognizing PP.

Differential distribution of neuropeptide Y Y1 and Y2 receptors in rat and guinea-pig brains

The distribution of neuropeptide Y Y1 and Y2 receptors has been extensively studied in the rat using selective masking of [125I]peptide YY binding by Y1- and Y2-selective peptides. In the present study, we characterized the binding of the subtype-selective radioligands [125I](Leu31-Pro34)-peptide YY and [125I]peptide YY3-36 to rat and guinea-pig brains and identified differences in Y1 and Y2 distribution. [125I](Leu31Pro34)-peptide YY and [125I]peptide YY3-36 bound to single sites in rat and guinea-pig brains with pharmacologies consistent with the Y1 and Y2 receptors, respectively. Autoradiographic studies were conducted using adjacent sections from rat and guinea-pig brains. Compared to the rat, the distribution of both Y1 and Y2 receptors was markedly different in the guinea-pig. For example, a high level of Y1 binding was detected within the thalamus of the rat while, in the guinea-pig, very little Y1 binding was observed in this region. Y1 binding was very low in the rat hippocampus, while the guinea-pig hippocampus contained high levels of Y1 binding. High levels of both Y1 and Y2 binding were observed in the guinea-pig cerebellum while, in the rat, only low levels of Y2 binding were visible. Therefore, the guinea-pig brain exhibits dramatic differences in the pattern of Y1 and Y2 receptors when compared to the rat. It is likely that Y1 and Y2 receptors perform different roles in the central nervous system of guinea-pigs and rats.

Pharmacological characterization of neuropeptide Y-(2-36) binding to neuropeptide Y Y1 and Y2 receptors

Neuropeptide Y-(2-36) has been reported by several research groups to be a more potent orexigenic agent than intact neuropeptide Y. Therefore, it has been proposed that a novel 'Y1 variant' may modulate ingestive behavior. To define the receptor subtype involved in neuropeptide Y-stimulated feeding behavior, we evaluated the binding properties of neuropeptide Y-(2-36) and [125I]neuropeptide Y-(2-36) in established neuropeptide Y1 and Y2 containing cell lines and tissues. Neuropeptide Y-(2-36) displaced [125I]peptide YY binding to SK-N-MC cells (neuropeptide Y Y1 receptors) with a Ki of 3.69 nmol and SK-N-BE(2) cells (neuropeptide Y Y2 receptors) with a Ki of 3.08 nmol. Neuropeptide Y-(2-36) also displaced [125I]peptide YY binding to rat cerebral cortex, hippocampus and olfactory bulb with similar affinities. To examine the brain distribution of [125I]peptide YY, [125I]neuropeptide Y and [125I]neuropeptide Y-(2-36), adjacent sections were labeled and the binding sites detected by autoradiography. A similar distribution of binding was observed for each radioligand in all regions examined. Therefore, neuropeptide Y-(2-36) binds non-selectively to neuropeptide Y Y1 and neuropeptide Y Y2 receptors, but with lower affinity than neuropeptide Y and peptide YY. The increased potency and selectivity seen with neuropeptide Y-(2-36) in feeding studies cannot be explained on the basis of a unique in vitro pharmacology.

Localization of neuropeptide Y Y1 receptor-like immunoreactivity in catecholaminergic neurons of the rat medulla oblongata

Neuropeptide Y receptors in the medulla oblongata participate in central cardiovascular control. The neuropeptide Y1 receptor subtype gene and amino acid sequence have been identified by molecular cloning studies. In this study, a C-terminal peptide representing amino acids 355-382 of the neuropeptide Y1 receptor was synthesized and cross-linked to thyroglobulin to produce an antibody against a partial sequence of the neuropeptide Y1 receptor, used to localize neuropeptide Y1 receptor-like immunoreactivity in the catecholaminergic neurons of the medulla oblongata. The double colour immunofluorescence technique with a polyclonal antibody against the neuropeptide Y1 receptor and a monoclonal antibody against tyrosine hydroxylase revealed that in the rat medulla oblongata, a weak (the C3 cell group) to moderately intense (the A1, A2, C1 and C2 cell groups), diffuse cytoplasmic neuropeptide Y1 receptor-like immunoreactivity was distributed primarily in the noradrenergic and adrenergic cell bodies and occasionally seen in the noradrenergic and adrenergic cell processes. Almost all tyrosine hydroxylase-like immunoreactive cell bodies in the A1, A2, C1, C2 and C3 cell groups showed neuropeptide Y1 receptor-like immunoreactivity. The neuropeptide Y1 receptor-like immunoreactivity in the A2 cell group was somewhat stronger. The present findings show localization of specific neuropeptide Y1 receptor-like immunoreactivity in the vast majority of the noradrenergic and adrenergic cell bodies of the A1, A2, C1, C2 and C3 cell groups, which are putative cardiovascular regions. The results support the view that neuropeptide Y1 receptors in the medulla oblongata are involved in central cardiovascular control and may coexist with another important receptor, the alpha 2A-adrenoceptor, also involved in central, cardiovascular regulation, since the alpha 2A-adrenoceptor-like immunoreactivity has been shown to exist in almost all noradrenergic and adrenergic cell bodies in the brainstem. In conclusion, centrally administered neuropeptide Y may act in part via neuropeptide Y1 receptors located on the soma and dendrites of noradrenergic and adrenergic neurons, where it may interact with alpha 2-adrenoceptors at least in the noradrenergic A2 neurons. This noradrenaline system may be involved in at least part of the vasodepressor actions of neuropeptide Y, noradrenaline and adrenaline in the nucleus tractus solitarii in view of the present findings.

Antinociceptive effects of neuropeptide Y and related peptides in mice

This study compares the antinociceptive and orexigenic activities of NPY and analogs after intracerebroventricular administration in mice. NPY had an antinociceptive action in the mouse writhing test which was not affected by prior treatment with naltrexone, yohimbine, idazoxan or reserpine. A detailed examination revealed that NPY (0.023-0.7 nmol), PYY (0.007-0.07 nmol), NPY2-36 (0.023-0.23 nmol) and the Y1 agonist [Leu31, Pro34]-NPY (0.07-0.7 nmol) all produced a dose-dependent and complete suppression of acetic acid-induced writhing. In contrast, the Y2 agonist, NPY13-36, had little or no antinociceptive effect. As shown by their ED50 values, the relative potency of the peptides was PYY > NPY2-36 > or = NPY > [Leu31, Pro34]-NPY > > NPY13-36, suggesting that a Y1 rather than a Y2 or Y3 receptor subtype was implicated in the antinociceptive action. Thereafter, all peptides were assessed for their effects on food intake. With respect to dose and peptide specificity, the hyperphagic effects of NPY and related peptides paralleled those on nociception, suggesting a common receptor mechanism. However, a purported NPY antagonist, [D-Trp32]-NPY, attenuated NPY's effect on feeding yet this same peptide elicited a dose-dependent inhibition of acetic acid-induced writhing, suggesting some molecular distinction between antinociception and stimulation of food intake.

The cloned rat pancreatic polypeptide receptor exhibits profound differences to the orthologous receptor

Pancreatic polypeptide (PP) is produced in the islets of Langerhans and released in response to meals. It belongs to a family of peptides that also includes neuropeptide Y and peptide YY. In the present communication, we describe a rat receptor with high affinity for PP, therefore named PP1. Clones for the PP1 receptor were obtained by PCR using sequence information for the neuropeptide Y receptor Y1 from several species. The PP1 receptor has 46% overall amino acid sequence identity to the rat Y1 receptor and 56% identity in the transmembrane regions. The PP1 receptor displays a pharmacological profile that is distinct from previously described neuropeptide Y-family receptors. In competition with iodinated bovine PP, it binds rat PP with an affinity (K(i)) of 0.017 nM, while the affinities for peptide YY and neuropeptide Y are substantially lower with K(i) values of 162 and 192 nM, respectively. In stably transfected CHO cells, the PP1 receptor inhibits forskolin-stimulated cAMP synthesis. Northern blot hybridizations to a panel of mRNAs detected transcripts in testis and lung. A faint band was seen in colon and total brain. In contrast, the human receptor is expressed primarily in colon and small intestine. Whereas rat and human PP1 bind PP with the same affinity, the rat receptor has much lower affinity than its human ortholog for peptide YY and neuropeptide Y. Interestingly, the amino acid sequence identity between rat and human PP1 is only 75%. Thus, the sequence, the tissue distribution, and the binding profile of the PP1 receptor differ considerably between rat and human.

Conformational analysis of neuropeptide Y segments by CD, NMR spectroscopy and restrained molecular dynamics

Neuropeptide Y (NPY), a peptide amide comprising 36 residue has been shown to act as a potent vasoconstrictor. In order to shed light on the structural requirements for the biological activities with respect to the different prerequisites for affinity to the NPY receptor subtypes Y1 and Y2, in the present study the syntheses and conformational analyses of two C-terminal segments, NPY(18-36) and NPY(13-36), are described. The results obtained by CD measurements, two-dimensional NMR spectroscopy and a conformational refinement of the NMR-derived structure by molecular mechanics stimulations support the findings of previously published structure-activity relationship studies for biologically active and selective compounds. In particular, the alpha-helical conformation as well as an appropriate exposure of the side chains of the critical C-terminal dipeptide within NPY(18-36) are in agreement with the prerequisites proposed for Y2 receptor binding of that segment.

Autoradiographic distribution of [125I]Leu31,Pro34]PYY and [125I]PYY3-36 binding sites in the rat brain evaluated with two newly developed Y1 and Y2 receptor radioligands

The peptide YY derivatives [Leu31,Pro34]PYY and PYY3-36 are highly selective Y1 and Y2 agonists, devoid of activity on the Y3 receptor subtype [Dumont et al. (1994) Molec. Brain Res., 26:3220-3324]. These selective ligands were iodinated and used to evaluate the respective quantitative autoradiographic distribution of the Y1 and Y2 receptor subtypes in the rat brain, excluding a potential contamination from Y3 receptor. Specific [125I][Leu31,Pro34]PYY (Y1), and [125I]PYY3-36 (Y2) binding sites are detected in various brain regions, but each showed a differential distribution profile. Y1/[125I][Leu31,Pro34]PYY sites are especially concentrated in superficial layers of the cortex, the olfactory tubercle, islands of Calleja, tenia tecta, molecular layer of the dentate gyrus, several thalamic nuclei, and the posterior part of the medial mammaliary nucleus. These areas generally contained only low densities of Y2/[125I]PYY3-36 binding sites. In contrast, [125I]PYY3-36 binding is most abundant in multiple other regions including the lateral septum, piriform cortex, triangular septal nucleus, bed nucleus of the stria terminalis, oriens layer and stratum radiatum of the dorsal hippocampus, ventral tegmental area, substantia nigra, dorsal raphe nucleus, and the granular cell layer of the cerebellum. Few areas of the rat brain contained significant amounts of both [125I][Leu31,Pro34]PYY and [125I]PYY3-36 binding sites such as the anterior olfactory nuclei, oriens layer and stratum radiatum of the ventral hippocampus, nucleus tractus solitarius, area postrema, and inferior olive. Taken together, these results and the use of two selective radioligands demonstrate further the discrete, differential distribution of the Y1 and Y2 receptor subtypes in the rat brain.

Unexpected high density of neuropeptide Y Y1 receptors in the guinea pig spleen

Receptors for neuropeptide Y (NPY) and peptide YY (PYY) have been extensively characterized in the brain. Less is known about NPY receptor subtypes in the spleen, though it is well established that NPY produces vascular contraction in this tissue. In the present study, we found an unusually high density of Y1 receptors in the guinea pig spleen. These receptors are localized to the red pulp and exhibit a pharmacology that is consistent with the Y1 receptor. On the other hand, only very low densities for Y2 receptors were observed. Therefore, the guinea pig spleen may be a ideal tissue for further study of the role of Y1 receptors in cardiovascular and immune function.

Autoradiographic analysis of neuropeptide Y receptor binding sites in the rat hippocampus after kainic acid-induced limbic seizures

Changes in peptide YY receptor binding were investigated at various intervals after limbic seizures induced in rats by an intraperitoneal injection of kainic acid (10-12 mg/kg). Six to 24 h after kainic acid, specific peptide YY binding, representing Y1 and Y2 neuropeptide Y receptor subtypes, was markedly enhanced in the strata radiatum and oriens CA3 (increase by up to 185% and 178% of control values, respectively). Seven and 30 days after kainic acid, a reduction by up to 63% was found. The basal and kainic acid-induced changes in peptide YY binding were mainly represented by Y2 receptor sites. In the hilus of the dentate gyrus, an increase of global peptide YY binding by up to 400% was observed after 24 h which became attenuated to 125% after 30 days. In the molecular layer of the dentate gyrus global peptide YY binding increased by up to 87% between six and 24 h after kainic acid injection and was reduced by 37% after 30 days. Similar changes were observed in the cerebral cortex. Whereas in the hilus of the dentate gyrus peptide YY binding consisted mainly of Y2 sites, it represented predominantly Y1 receptors in the molecular layer and the cortex. The decline in global and Y2 specific peptide YY binding observed at 30 days in the hippocampus proper was prevented in animals protected from seizure-induced brain damage by an anticonvulsant dose of phenobarbital 3 h after injection of kainic acid. In the stratum moleculare of the dentate gyrus, Y2 specific binding was significantly enhanced while global peptide YY binding was slightly decreased compared to controls. These results show lasting changes in neuropeptide Y receptor binding sites after the acute seizures induced by kainic acid. Since neuropeptide Y modulates glutamatergic neurotransmission, these modifications may play an important role in the hippocampal excitability of chronically epileptic rats.

Neurochemical modulation of cardiovascular control in the nucleus tractus solitarius

The central control of cardiovascular function has been keenly studied for a number of decades. Of particular interest are the homeostatic control mechanisms, such as the baroreceptor heart-rate reflex, the chemoreceptor reflex, the Bezold-Jarisch reflex and the Breuer-Hering reflex. These neurally-mediated reflexes share a common termination point for their respective centrally-projecting sensory afferents, namely the nucleus tractus solitarius (NTS). Thus, the NTS clearly plays a critical role in the integration of peripherally initiated sensory information regarding the status of blood pressure, heart rate and respiratory function. Many endogenous neurochemicals, from simple amino acids through biogenic amines to complex peptides have the ability to modulate blood pressure and heart rate at the level of the NTS. This review will attempt to collate the current knowledge regarding the roles of neuromodulators in the NTS, the receptor types involved in mediating observed responses and the degree of importance of such neurochemicals in the tonic regulation of the cardiovascular system. The neural pathway that controls the baroreceptor heart-rate reflex will be the main focus of attention, including discussion of the identity of the neurotransmitter(s) thought to act at baroafferent terminals within the NTS. In addition, this review will provide a timely update on the use of recently developed molecular biological techniques that have been employed in the study of the NTS, complementing more classical research.

Neuropeptide Y gene expression and receptor autoradiography in hypertensive and normotensive rat brain

Neurones containing neuropeptide Y (NPY) may participate in central cardiovascular control by tonically influencing barosensitive neurones within the nucleus tractus solitarius. The present study has employed both in situ hybridisation histochemistry and receptor autoradiography, to visualise the expression of prepro-NPY mRNA in the forebrain and to determine the NPY receptor subtype(s) in the brainstem, respectively. Prepro-NPY gene expression was visualised in the hypothalamus, cortex, dentate gyrus and lateral reticular thalamus from age-matched spontaneously hypertensive rats (SHR) and normotensive Don Ryu rats (DRY) and Wistar Kyoto rats (WKY). Quantitative densitometry revealed an increase in the NPY transcript in the arcuate nucleus of SHR rats compared to their normotensive counterparts. Autoradiography using [125I]Bolton-Hunter-NPY (BH-NPY, 15 pM) demonstrated NPY binding sites in the area postrema, the commissural nucleus tractus solitarius (cNTS) and the inferior olivary complex. NPY (1 microM) and peptide YY (1 microM), but not [Leu31,Pro34]NPY (10-100 nM), fully inhibited the binding of [125I]BH-NPY. These results indicate that NPY receptors of the Y2 subtype predominate in the dorsal vagal complex. Unilateral nodose ganglionectomy resulted in a partial loss of NPY binding sites in the commissural NTS, but not the area postrema, suggesting that a proportion of binding sites (Y2 subtype) are present on central vagal terminals. While all three rat strains appear to have the same relative proportions of NPY receptor subtypes in the brainstem, the relevance of the differential NPY gene expression in the arcuate nucleus regarding central cardiovascular control mechanisms and/or the pathogenesis of hypertension remains to be elucidated.

Cloning of a human receptor of the NPY receptor family with high affinity for pancreatic polypeptide and peptide YY

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) are structurally related peptides found in all higher vertebrates. NPY is expressed exclusively in neurons, whereas PYY and PP are produced primarily in gut endocrine cells. Several receptor subtypes have been identified pharmacologically, but only the NPY/PYY receptor of subtype Y1 has been cloned. This is a heptahelix receptor that couples to G proteins. We utilized Y1 sequence information from several species to clone a novel human receptor with 43% amino acid sequence identity to human Y1 and 53% identity in the transmembrane regions. The novel receptor displays a pharmacological profile that distinguishes it from all previously described NPY family receptors. It binds PP with an affinity (Ki) of 13.8 pM, PYY with 1.44 nM, and NPY with 9.9 nM. Because these data may identify the receptor as primarily a PP receptor, we have named it PP1. In stably transfected Chinese hamster ovary cells the PP1 receptor inhibits forskolin-stimulated cAMP synthesis. Northern hybridization detected mRNA in colon, small intestine, pancreas, and prostate. As all three peptides are present in the gut through either endocrine release or innervation, all three peptides may be physiological ligands to the novel NPY family receptor PP1.