Molecular characterization of a second mouse pancreatic polypeptide receptor and its inactivated human homologue

Characterization of the cloned atlantic cod neuropeptide Y-Yb receptor: peptide-binding requirements distinct from known mammalian Y receptors

Five members of the neuropeptide Y (NPY) receptor family have been cloned in mammals. The recently cloned NPY receptor in the Atlantic cod seems to be distinct from the mammalian subtypes as it has only 50% identity to Y1, Y4, and y6 and only 30% to Y2 and Y5. In most of the other families of G-protein-coupled receptors, species homologues have 65-90% identity between fishes and mammals. The functional expression and detailed pharmacological characterization of this cod NPY receptor, designated Yb, is reported. Membranes of cells transiently transfected with cod Yb showed saturable [(125)I]PYY binding with a K(d) of 45 pM. The pharmacological profile is similar to those of both the zebrafish Yb and Yc receptors and distinct from those of the mammalian NPY receptors. In competition experiments the cod Yb receptor had the following rank order of potencies: porcine PYY = porcine NPY = p[Leu(31), Pro(34)]NPY > zebrafish PYY > zebrafish NPY >> NPY2-36 = NPY3-36 > NPY18-36 > bovine PP = [D-Trp(32)]NPY > BIBP3226. This is in sharp contrast to the high selectivity of BIBP3226 for the Y1 receptor from all mammalian species. Together with the low amino acid identity of cod Yb with the mammalian Y1, Y4, and y6 receptors, this is further support for the notion that fish Yb constitutes a distinct NPY receptor subtype.

Neuropeptide Y receptor subtype with unique properties cloned in the zebrafish: the zYa receptor

Neuropeptide Y (NPY) belongs to a family of structurally related neuroendocrine peptides for which five different G-protein-coupled receptor subtypes have been cloned in mammals. To identify additional subtypes we have performed PCR with degenerate primers in different species. We describe here the cloning and pharmacological profile of a unique NPY receptor subtype in the zebrafish that has tentatively been called the zYa receptor. It has 46-50% amino acid identity to the mammalian Y1, Y4 and y6 receptors and the previously cloned zebrafish receptors zYb and zYc, and only about 27% to Y2 and Y5. The zYa receptor binds NPY and PYY from mammals as well as zebrafish with high affinities and has a K(d) of 28 pM for porcine (125)I-PYY. It has a unique binding profile displaying some features in common with each of the mammalian Y1, Y2 and Y5 receptors. In a microphysiometer assay the receptor responds with extracellular acidification. Chromosomal mapping in the zebrafish genome of zYa, zYb and zYc receptor genes indicates a possible orthologous relationship between zYc and mammalian y6, but identifies no obvious mammalian ortholog for zYa (zYb is a recent copy of zYc in the fish lineage). These results imply that previous studies of NPY in fishes, which have striven to interpret the effects within the framework of mammalian Y1, Y2, and Y5 receptors, need to be reevaluated. Thus, the sequence comparisons, pharmacological properties, and chromosomal localization suggest that the zYa receptor is a novel NPY receptor subtype which is likely to be present also in mammals.

Characterization of rabbit kidney and brain pancreatic polypeptide-binding neuropeptide Y receptors: differences with Y1 and Y2 sites in sensitivity to amiloride derivatives affecting sodium transport

Sites sensitive to human and rat pancreatic polypeptides (hPP and rPP) accounted for more than 30% of the specific binding of [125I](Leu31,Pro34) human peptide YY (LP-PYY) in particulates from rabbit kidney cortex, and about 10% of the specific binding in membranes from rabbit hypothalamus. The binding of [125I]hPP or [125I]rPP showed a high-affinity displacement with either hPP, rPP, LP-PYY, neuropeptide Y or peptide YY (Ki below 50 pM for all), while being quite insensitive to Y2-selective ligands. The PP binding had a high sensitivity to alkali cations and inhibitors of phospholipase C, very similar to that of LP-PYY binding 'masked' by excess cold hPP. However, as different from the Y1-like LP-PYY binding, but similar to the binding of the Y2-selective ligand [125I]human peptide YY(3-36) (hPYY(3-36)), the PP binding showed a low sensitivity to guanosine polyphosphates. The PP binding was much more sensitive to N5-substituted amiloride inhibitors of Na+ transport than the binding of LP-PYY, or that of hPYY(3-36). The inhibition of PP binding by N5-substituted amilorides was not enhanced by guanine nucleotides or by phospholipase C blockers. However, pairing of N5-substituted amilorides disproportionately increased the inhibition of hPP binding. Thus, in rabbit kidney or hypothalamus, the high-affinity PP-responding sites share some of the basic properties of the Y1 and Y2 sites, but are distinguished from both by a high sensitivity to compounds affecting sodium transport. These PP/NPY receptors could associate with membrane structures involved in the control of ion balance and osmotic responses.

NPY receptor subtype in the rabbit isolated ileum

1. The purpose of this work was to verify the hypothesis that the rabbit ileum is a selective preparation for the NPY Y5 receptor by using new selective antagonists recently synthesized. Spontaneous contractions of the rabbit isolated ileum were recorded and binding experiments were performed in cells expressing the human NPY Y1, Y2, Y4 or Y5 receptor subtype. 2. NPY analogues produced a concentration-dependent transient inhibition of the spontaneous contractions of the rabbit ileum with the following order of potency hPP > rPP > PYY > or = [Leu31,-Pro34]-NPY > NPY >> NPY13-36. Pre-exposure to rPP, PYY, [Leu31,Pro34]-NPY or NPY (but not NPY13-36) inhibited the effect of subsequent administration of hPP suggesting cross-desensitization of the preparation. The apparent affinity of the various agonists studied was correlated to the affinity reported for the human Y4 receptor subtype (and to a lesser extent for the rat Y4 subtype) but not to the affinity for the Y5 receptor subtype. 3. BIBO 3304, a selective NPY Y1 receptor antagonist, and CGP 71683A, a selective NPY Y5 receptor antagonist, did not affect the response to hPP. JCF 109, another NPY Y5 receptor antagonist, produced an inhibition of the response to hPP but only at the highest dose tested (10 microM) which also, by itself, produced intrinsic inhibitory effects. 4. 1229U91, a non-selective ligand for Y1, Y2, Y4 and Y5 receptors with high affinity toward the Y1 and Y4 receptor subtypes, produced a concentration-dependent transient inhibition of the spontaneous contractions of the rabbit ileum and a dose-dependent inhibition of the response to hPP (apparent pKB: 7.2). 5. These results suggest that in the rabbit ileum, the NPY receptor involved in the inhibition of the spontaneous contractile activity is a NPY Y4 receptor subtype.

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.

Autoradiographic reevaluation of the binding properties of 125I-[Leu31,Pro34]peptide YY and 125I-peptide YY3-36 to neuropeptide Y receptor subtypes in rat forebrain

125I-[Leu31,Pro34]peptide YY (PYY) and 125I-PYY3-36, initially described as selective neuropeptide Y Y1 and Y2 receptor ligands, respectively, were recently shown to label also Y4 and Y5 receptors. We used receptor autoradiography to assess whether these ligands can be reliably used to investigate the various neuropeptide Y receptors in rat forebrain. In most of the brain regions examined (in coronal sections at the level of dorsal hippocampus), specific 125I-[Leu31,Pro34]PYY binding was completely inhibited by 1 microM BIBP-3226, a selective Y1 receptor ligand, but unaffected by 10 nM rat pancreatic polypeptide, selectively inhibiting Y4 receptors, suggesting that Y4 receptors are present in negligible numbers compared with Y1 receptors in the areas examined. Significant numbers of BIBP-3226-insensitive 125I-[Leu31,Pro34]PYY binding sites were measured in the CA3 subfield of the hippocampus only, possibly representing Y5 receptors. 125I-PYY3-36 binding was unchanged by 1 microM BIBP-3226, whereas a population of 125I-PYY3-36 binding sites was sensitive to 100 nM [Leu31,Pro34]neuropeptide Y, likely representing Y5 receptors. The possibility of distinguishing between Y2 and Y5 receptors using 125I-PYY3-36 as radioligand was validated by their different regional distribution and their distinct changes 24 h after kainate seizures, i.e., binding to Y5 receptors was selectively decreased in the outer cortex, whereas binding to Y2 receptors was enhanced in the hippocampus. Thus, the use of selective unlabeled compounds is required for distinguishing the various receptor subtypes labeled by 125I-[Leu31,Pro34]PYY and 125I-PYY3-36 in rat brain tissue.

Evidence of a specific pancreatic polypeptide receptor in rat arterial smooth muscle

Pancreatic polypeptide (PP) is a member of the PP fold family of regulatory peptides. Studies have shown that neuropeptide Y, peptide YY, and PP increased gastrointestinal motility. The GI effects of neuropeptide Y and peptide YY were accompanied by an increase in mean arterial blood pressure; however, PP decreased mean arterial blood pressure. Cloning of a receptor of the neuropeptide Y family with high affinity for PP has been reported. This Y4 receptor is present in intestine, pancreas, and prostate, and its mRNA has been detected in brain and coronary artery. We found in vitro evidence of PP-mediated inhibition of arterial neurogenic vasoconstriction. We have also detected Y4 mRNA in rat peripheral arteries. These findings suggest a potential role for the Y4 receptor in regulating vascular tone.

Molecular cloning and characterization of an invertebrate homologue of a neuropeptide Y receptor

Neuropeptide Y is an abundant and physiologically important peptide in vertebrates having effects on food intake, sexual behaviour, blood pressure and circadian rhythms. Neuropeptide Y homologues have been found in invertebrates, where they are very likely to play similar, important roles. Although five neuropeptide Y-receptor subtypes have been identified in mammals, none has been reported from invertebrates. Here we describe the cloning of a neuropeptide Y-receptor from the brain of the snail Lymnaea stagnalis. The identity of the receptor was deduced by expressing the neuropeptide Y-receptor-encoding cDNA in Chinese Hamster Ovary cells, which were subsequently challenged with size-fractionated Lymnaea brain extracts. An active peptide, selected on the basis of its ability to induce changes in cAMP levels, was purified to homogeneity, analysed by mass spectrometry and amino acid sequence determination, and turned out to be a Lymnaea homologue of neuropeptide Y.

Suppression of sensory C fiber-mediated contractions by neuropeptide Y Y1 receptors in the guinea pig bronchi

The aim of the study was to examine which neuropeptide Y (NPY) receptor types that are coupled to inhibition of sensory C fiber-mediated contractions of the guinea pig bronchi. NPY and PYY evoked a concentration-dependent inhibition of the electrically stimulated contractions. The Y1 receptor-selective antagonist BIBP3226 (1 microM) evoked a rightward shift of the NPY-induced response. Also the Y1 (and Y4-Y6) receptor agonist [Leu31,Pro34]NPY suppressed the stimulated contractions with a potency similar to the parent molecule. BIBP3226 (1 microM) also attenuated the response induced by [Leu31,Pro34]NPY. The Y2 receptor agonist [Cys2, Aoc524, D-Cys27]NPY suppressed the stimulated contractions at 1 microM only. NPY 2-36 was much less potent than NPY itself and pretreatment with BIBP3226 did not affect the inhibitory response. Human pancreatic polypeptide (Y4-Y6 receptor agonist) was inactive (< or = 1 microM). In conclusion, NPY is capable of suppressing sensory nerve-mediated contractions in the guinea pig bronchi mainly via Y1 receptors.

NPY-induced feeding involves the action of a Y1-like receptor in rodents

We have reported that the potent peptidic Y1 antagonist, 1229U91, significantly suppressed NPY-induced and spontaneous feeding [32,33]. However, information on the precise selectivity of 1229U91 for NPY receptors is lacking. The Y5 receptor has been considered a key receptor for feeding regulation. In the present study we showed that 1229U91 has high affinities for the human and rat Y1 receptors (Ki = 0.041 nM and 0.16 nM, respectively) and also a high affinity for the human Y4 receptor (Ki = 0.33 nM), whereas it shows moderate affinities for the human Y2, Y5 and rat Y5 receptors (K values of 20-170 nM). Moreover, 1229U91 potently inhibits NPY-induced [Ca2+]i increases in cells expressing human Y1 receptors. In contrast, 1229U91 is an agonist at other NPY receptors like the Y2, Y4 and Y5 receptors. Intracerebroventricular (i.c.v.)-injected 1229U91 (30 microg/head) significantly suppressed human NPY-induced feeding in SD rats, while 1229U91 only moderately inhibited bovine pancreatic polypeptide (bPP; an in vivo Y5 agonist)-induced feeding. These results indicate that the food intake evoked by NPY might be mediated by the Y1 receptor, rather than the Y5 receptor. Thus, the Y1 receptor or possibly a novel Y1-like receptor sensitive to 1229U91 may play a key role in the regulation of NPY-induced feeding.

The cloned guinea pig pancreatic polypeptide receptor Y4 resembles more the human Y4 than does the rat Y4

Pancreatic polypeptide (PP) is involved in gastrointestinal functions and forms, together with neuropeptide Y (NPY) and peptide YY (PYY), the PP-fold family of peptides. The PP-binding receptor subtype Y4 has so far been cloned in human, rat, and mouse, and displays extensive species differences regarding sequence, pharmacology, and distribution. To explore this variability further, we have cloned the Y4 receptor in the guinea pig, which is evolutionarily equally distantly related to both humans and rodents. The guinea pig Y4 receptor is 84% identical to the human Y4 receptor, but only 74-75% identical to the rat and mouse receptors. The two latter are 75-76% identical to human Y4. The guinea pig Y4 receptor bound 125I-hPP with a dissociation constant (Kd) of 29+/-3 pM. The pharmacological profile of guinea pig Y4 has the following rank order of potencies: PP > NPY approximately = PYY approximately = LP-NPY approximately = LP-PYY > NPY2-36 >> [D-Trp32]NPY. Thus, the guinea pig receptor is more similar to the human Y4 than to the rat Y4 both in sequence and pharmacology. This agrees with the greater identity between guinea pig and human PP compared to rat PP. These comparisons suggest that the rodent PPs and Y4 receptors have an accelerated replacement rate.

Molecular biology and pharmacology of multiple NPY Y5 receptor species homologs

NPY is a 36-amino acid peptide which exerts its physiological effects through the activation of a family of G-protein coupled receptors. In vivo and in vitro characterization of the recently cloned rat Y5 receptor suggests that it is a primary mediator of NPY-induced feeding (Gerald et al., Nature 1996;382:168-171). We now report the molecular cloning and pharmacological characterization of the human, dog and mouse homologs of the Y5 receptor. With the exception of a 21 amino acid repeat in the amino terminus of the mouse Y5 receptor, the sequence of the four species homologs appear to be highly conserved, with 88% to 97% amino acid identities between any two species. Similarly, the pharmacological profiles of the four species homologs as determined in porcine 125I-PYY binding assays show a great deal of conservation, with the following rank order of affinity: human or porcine NPY, PYY, [Leu31,Pro34]NPY, NPY(2-36), human PP > human [D-Trp32]NPY > rat PP, C2-NPY. Northern blot analysis reveals that the Y5 receptor is widely distributed in the human brain, with the strongest signals detected in the cortex, putamen and caudate nucleus. The chromosomal localization of the human Y5 receptor, previously shown to be overlapping and in the opposite orientation to the Y1 receptor, is determined to be 4q31, the same locus as previously demonstrated for the human Y1 receptor (Herzog et al., J Biol Chem 1993;268:6703-6707), suggesting that these receptors may be coregulated. These Y5 species homologs along with corresponding animal models may be useful in the search for novel therapeutics in the treatment of obesity and related feeding disorders.

Neuropeptide Y and Y1-receptor agonists increase blood flow through arteriovenous anastomoses in rat tail

The purpose of this study was to characterize neuropeptide Y (NPY)-induced vasodilation in the rat tail. Sterile surgical technique was used (with pentobarbital sodium anesthesia) to equip rats with a jugular catheter and a blind-ended thermocouple reentrant tube next to the carotid artery. Tail skin and core temperature were measured with thermocouples during experiments. Tail skin blood flow was monitored with a laser Doppler flowmeter, and tail total blood flow and volume were measured with plethysmography. After baseline data were collected, saline, NPY (16, 32, 64, and 128 microg/kg), [Leu31 Pro34]NPY (63.25 microg/kg), or NPY[13-36] (44.7 microg/kg) was administered intravenously. Tail total blood flow, volume, and tail skin temperature increased, whereas tail skin blood flow and core temperature decreased in response to both NPY- and the Y1-receptor agonist [Leu31 Pro34]NPY but not in response to saline or NPY[13-36]. Studies conducted with the use of color microspheres demonstrated that arteriovenous anastomoses are involved in this NPY-induced vasodilation.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

A comparison of actions of neuropeptide Y (NPY) agonists and antagonists at NPY Y1 and Y2 receptors in anaesthetized rats

The pancreatic polypeptide family includes three members, neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP), with sequence homology between members and species varying from approximately 50 to 80%. Some of these peptides were compared in the mammalian cardiovascular system for activity mediated by actions on pre- (Y2) and post-junctional (Y1) NPY receptors. NPY and PYY, with sequence homology of 67% have similar actions on Y1 and Y2 receptors. Rat pancreatic polypeptide (rPP) with sequence homology of approximately 50% is inactive at both. This study reports that the chimeric peptide, hPP1-11/NPY12-36 and the truncated peptide NPY2-36 show similar activity to NPY mediated through both receptor types in vivo, while salmon PYY (sPYY), with 81% homology to NPY, has improved potency at both receptor subtypes. NPY3-36 has equal activity with NPY on actions mediated through Y2 receptors, but significantly reduced activity mediated through Y1 receptors. Two NPY antagonists were also examined: PYX2 was inactive in vivo and 1229U91 showed potent, long-lasting activity on Y1 receptor-mediated effects.

PYY-preferring receptor in the dorsal vagal complex and its involvement in PYY stimulation of gastric acid secretion in rats

1. Microinjection of peptide YY (PYY, 7-46 pmol) into the dorsal vagal complex (DVC) stimulated gastric acid secretion in urethane-anaesthetized rats. Using a variety of neuropeptide Y (NPY) and PYY derivatives, we characterized the pharmacological profile of the receptor mediating the acid secretory response to PYY. 2. [Pro34]rat(r)/porcine(p)PYY and [Pro34]human(h)PYY (23-117 pmol), microinjected unilaterally into the DVC resulted in a similar maximal increase in net acid secretion reaching 68+/-11 and 89+/-31 micromol 90 min(-1) respectively. 3. Rat/hNPY and pNPY (47 pmol) microinjected into the DVC induced a similar net gastric acid secretion (27+/-8 and 23+/-8 micromol 90 min(-1) respectively) and a higher dose (116 pmol) tended to reduce the response. 4. Pancreatic polypeptide (PP, 4-46 pmol), [Leu31,Pro34]r/hNPY (47 and 117 pmol) and the Y2 selective agonists, hPYY3-36, pNPY5-36 and PNPY13-36 (25-168 pmol) microinjected into the DVC failed to influence basal gastric acid secretion. 5. The rank order of potency of PYY > or = [Pro34]r/pPYY = [Pro34]hPYY> r/hNPY = pNPY to stimulate gastric acid secretion upon injection into the DVC and the ineffectiveness of PP, [Leu31,Pro34]NPY and C-terminal NPY/PYY fragments suggest that a PYY-preferring receptor subtype may be involved in mediating the stimulating effect.

Responses to neuropeptide Y in adult hamster suprachiasmatic nucleus neurones in vitro

We investigated the effects of neuropeptide Y and related analogues on the extracellularly recorded spontaneous firing rate activity of adult Syrian hamster suprachiasmatic nucleus neurones in vitro. Sixty-seven neurones were tested with neuropeptide Y: 45% were suppressed, 4% were activated, and the remaining 51% were unresponsive. These responses were not blocked by the GABA receptor antagonist bicuculline, indicating that neuropeptide Y-evoked responses did not appear to be dependent on GABA(A) receptor activation. We tested the effects of the neuropeptide Y Y1 receptor agonist [Leu31, Pro34]neuropeptide Y and the neuropeptide Y Y2 receptor agonist neuropeptide Y-(13-36) on nine cells suppressed by neuropeptide Y in order to determine the receptor subtype(s) mediating the effects of neuropeptide Y. Four of nine cells were suppressed by [Leu31, Pro34]neuropeptide Y only, one of nine was suppressed by neuropeptide Y-(13-36) only, two of nine were suppressed by both compounds, while the remaining two cells did not respond to either compound. These data suggest that neuropeptide Y can modulate suprachiasmatic nucleus function directly, without recruitment of GABA(A) interneurones. Further, our results indicate that neuropeptide Y may act on more than one receptor subtype within the adult hamster suprachiasmatic nucleus.

Distribution of a novel hypothalamic neuropeptide Y receptor gene and it's absence in rat

A recently reported Y receptor that has been confusingly referred to as both Y5 and Y2b has now been designated as Y6 by the IUPHAR organization. Using random primed Y6 coding sequence as a hybridization probe we examined the mRNA expression pattern and gene distribution of the Y6 receptor in a variety of species. We detail the relative abundance of Y6 message in mouse and human tissues and report the apparent absence of message for this receptor in any rat tissues tested. We also document the presence of the Y6 gene in chicken, rabbit, cow, dog, mouse, monkey and human, but the complete absence of the Y6 gene in rat.

Pancreatic polypeptide: identification of target tissues using an in vivo radioreceptor assay

The definitive function of pancreatic polypeptide in mammalian physiology remains unknown. The identification of specific PP target tissues should be helpful to further investigations into the possible regulatory actions of this peptide. An in vivo radioreceptor assay was used in the rat to locate potential binding sites of I(125) bovine PP. In vitro, high concentrations of unlabeled hormone competitively inhibit binding to receptors by low concentrations of labeled hormone. In vivo studies showed that, in the presence of concentrated unlabeled pancreatic polypeptide, labeled PP distributes between the plasma and interstitial fluid. When excess unlabeled PP is replaced with saline in the companion animals, the labeled peptide appears to distribute in a volume that exceeds the combined plasma volume and interstitial fluid volume of the tissue. Using this in vivo receptor assay, the distribution volume that exceeds the anatomic extracellular volume has been identified as the receptor compartment. With this assay we demonstrated in the rat specific and displaceable PP binding to the ductus choledochus, duodenum, ileum, and adrenal gland. The NVV determined in the adrenal gland of experimental animals was 3.9 times greater than that found in the control group. Binding was rapid and was displaced only by excess unlabeled pancreatic polypeptide. Neither excess insulin nor excess neuropeptide Y significantly reduced this binding.

Multiplicity of neuropeptide Y receptors: cloning of a third distinct subtype in the zebrafish

Five different receptor subtypes for neuropeptide Y (NPY) have recently been cloned in mammals. We have discovered three distinct subtypes by PCR in the zebrafish, Danio rerio, and describe here one of these called zYc. The protein sequence identity is 46-51% to mammalian subtypes Y1, Y4 and Y6 and to zebrafish Ya, i.e., the same degree of identity as these subtypes display to one another. The identity to zYb is higher, 75%, indicating that zYb and zYc share a more recent ancestor. The zYc receptor binds NPY and PYY (peptide YY) from mammals as well as zebrafish with high affinities and has a Kd of 16 pM for 125I-pPYY. The pharmacological profile is similar to, but distinct-from, mammalian Y1. zYc inhibits cAMP synthesis. This work suggests that NPY has more receptor subtypes than any other peptide that binds to G protein-coupled receptors. Work is in progress to see if the zebrafish receptors are present in mammals.

Distribution of [Leu31,Pro34]NPY-sensitive, BIBP3226-insensitive [125I]PYY(3-36) binding sites in rat brain: possible relationship to Y5 NPY receptors

Recently, using molecular cloning approaches, three new neuropeptide Y (NPY)/peptide YY (PYY) receptors have been described in rodent brain, with pharmacological profiles that differ from the three previously described Y1, Y2 and Y3 NPY receptors and the Y4 pancreatic polypeptide- (PP-) preferring receptor. Two of these new receptors are spice variants and are called Y5 receptors, whilst a third receptor has been called Y6 and has been suggested to be expressed only in the mouse. In the absence of a totally selective Y5 and/or Y6 radioligands, we have examined [125I]PYY(3-36) binding, which binds Y2 and Y5/Y6 receptors, using homogenate assays and quantitative receptor autoradiography to study the distribution of the three newly discovered Y5/Y6 receptors by masking binding to Y1 receptors with high concentrations of the non-peptidergic selective Y1 antagonist, BIBP3226, and using either [Leu31,Pro34]NPY or human PP to mask binding to Y5 and Y6 receptors, leaving binding to Y2 receptors. Using this approach, [125I]PYY(3-36) labels a small population of Y1 receptors and a larger population of binding sites that are insensitive to BIBP3226, human PP and [Leu31,Pro34]NPY, presumed to be Y2 receptors. There was also [125I]PYY(3-36) binding to sites sensitive to NPY, human PP and [Leu31,Pro34]NPY, but insensitive to BIBP3226, located in the hypothalamus, amygdala, hippocampus and thalamus. As one of the recently cloned Y5 receptors is synthesized in these regions, as shown by in-situ hybridization techniques, we suggest that the small population of [125I]PYY(3-36) binding sites which are sensitive to human PP and [Leu31,Pro34]NPY, but insensitive to BIBP3226, may represent binding to Y5 receptors. We have been unable, however, to visualize a smaller population of Y6 receptors which are labelled by [125I]PYY3-36 and sensitive to [Leu31,Pro34]NPY, but not to BIBP3226 and human PP, confirming that the murine Y6 receptor does not appear to be expressed in rat brain.

Immunocytochemical localization of the NPY/PYY Y1 receptor in enteric neurons, endothelial cells, and endocrine-like cells of the rat intestinal tract

Neuropeptide Y (NPY) and peptide YY (PYY) are structurally related peptides that are considered to mediate inhibitory actions on gastrointestinal motility, secretion, and blood flow. Several receptor subtypes for these peptides have been identified and the Y1, Y2, Y4/PP1, Y5, and Y5/PP2/Y2b receptors have been cloned. In this article we report the immunocytochemical localization of the Y1 receptor to myenteric and submucosal nerve cell bodies, endothelial cells, and scattered endocrine-like cells of rat intestinal tract. Moreover, double immunofluorescence demonstrates that subpopulations of the Y1 receptor-positive nerve cell bodies are immunopositive for NPY, vasoactive intestinal polypeptide, and nitric oxide synthase. In part, such co-localizations were made possible by use of peroxidase-mediated deposition of tyramide, which permitted use of antisera derived from the same species. Our observations suggest the existence of multiple neuronal, endothelial, and endocrine target sites for NPY and PYY and that some of the actions of these regulatory peptides can be mediated by vasoactive intestinal peptide and nitric oxide synthase.

Neuropeptide Y receptor genes mapped in human and mouse: receptors with high affinity for pancreatic polypeptide are not clustered with receptors specific for neuropeptide Y and peptide YY

Ppyr1, Npy5r, and Npy6r, the genes encoding mouse type 4, type 5, and type 6 members of the neuropeptide Y receptor family, have been mapped by interspecific backcross analysis to conserved linkage groups on mouse Chr 14, Chr 8, and Chr 18, respectively. The human genes, PPYR1 and NPY5R, have been localized to chromosomes 10q and 4q, respectively, by analysis of a panel of rodent-human somatic cell hybrids and yeast artificial chromosomes. These studies complete the mapping of the cloned NPY receptor subtypes in human and mouse and, together with previous studies, establish that the genes encoding receptors with high affinity for pancreatic polypeptide are not clustered with the genes encoding receptors specific for neuropeptide Y and peptide YY. The physical association of these receptor genes correlates with ligand-binding properties, rather than sequence identity, and suggests a complex evolutionary relationship.

Neuropeptide Y (NPY) and peptide YY (PYY) effects in the epididymis of the guinea-pig: evidence of a pre-junctional PYY-selective receptor

1. The effects of peptide YY (PYY), neuropeptide Y (NPY) and structurally related peptides upon field stimulation-induced and phenylephrine-mediated contractile responses in the cauda epididymis of the guinea-pig were investigated. 2. Preparations of cauda epididymis responded to field stimulation with contractions which were completely attenuated by both the neurotoxin, tetrodotoxin (500 nM), and also by the alpha-adrenoceptor antagonist, phentolamine (3 microM). PYY (n=7) and the truncated peptide analogue PYY(3-36) (n=5) inhibited field stimulation-induced contractions (pIC50+s.e.mean: 8.9+/-0.2 and 9.4+/-0.2, respectively). Pancreatic polypeptide (PP, up to 1 microM, n=6), NPY (up to 100 nM, n=6) and the NPY analogues [Leu31,Pro34]NPY (n=6) and NPY(13-36) (both up to 1 microM, n=5) had no significant effect. 3. The NPY Y1 receptor antagonist BIBP3226 ((R)-N2-(diphenylacetyl)-N[(4-hydroxyphenyl)-methyl]-argininami de) at 750 nM (n=6) and 7.5 microM (n=6) did not affect the PYY-mediated inhibition of field stimulation-induced contractions (pIC50 8.9+/-0.3 and 9.0+/-0.3, respectively). In the presence of BIBP3226 (7.5 microM), NPY (n=6) inhibited field stimulation-induced contractions (pIC50 8.0+/-0.2). 4. NPY, PYY and PYY(3-36) inhibited [3H]-noradrenaline release from preparations of epididymis (pIC50 values 7.9+/-0.7, 9.6+/-0.8 and 10.0+/-0.9, respectively, all n=6). The agonists PP and [Leu31,Pro34]PYY (both up to 100 nM) were without significant effect (both n=6). 5. In preparations of cauda epididymis, stimulated with threshold concentrations of the alpha1-adrenoceptor agonist, phenylephrine (1 microM), both NPY (n=6) and PYY (n=7) elicited concentration-dependent increases in contractile force (with pEC50 values of 8.9+/-0.2 and 8.6+/-0.1, respectively). The effects of both NPY (n=6) and PYY (n=6) were antagonized by preincubation with BIBP3226 (75 nM; apparent pK(B)+/-s.e. values 8.3+/-1.0 and 8.2+/-0.6, respectively). The peptide analogues NPY(13-36) (n=5), PYY(3-36) (n=7) and [Leu31,Pro34]NPY (n=5) did not significantly augment responses to threshold concentrations of phenylephrine. 6. These results are consistent with the proposal that distinct NPY receptors mediate the (prejunctional) inhibition of field stimulation-induced contractions and the (postjunctional) potentiation of responses to phenylephrine in the cauda epididymis of the guinea-pig. The rank order of agonist potency (NPY > or = PYY >> NPY(13-36), [Leu31,Pro34]NPY and PYY(3-36) and the high potency of BIBP3226 indicate that the postjunctional receptor may be Y1-like. The rank orders of agonist potency in inhibiting field stimulation-induced contractile responses and [3H]-noradrenaline release (PYY(3-36) > or = PYY > NPY >> PP, NPY(13-36), [Leu31,Pro34]NPY and PYY(3-36) > or = PYY > NPY >> PP, [Leu31,Pro34]PYY, respectively) are consistent with the action of these peptides at a PYY-preferring receptor subtype, which may be distinct from the presently characterized NPY receptor subtypes.

Cloning and characterization of a novel neuropeptide Y receptor subtype in the zebrafish

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) form a family of structurally related peptides. As we have previously isolated clones for NPY and PYY from the zebrafish (Danio rerio), we wished to clone the receptors for these peptides to allow correlation of ligand and receptor distribution. We describe here the cloning and functional expression of a receptor with equally high identity to the NPY-Y1 receptor as to the recently cloned Y4/PP1 and Y6 receptors with an overall amino acid sequence identity of approximately 50%. Furthermore, the zebrafish receptor gene lacks the intron present in the coding region in vertebrate Y1 genes. These features strongly suggest that the zebrafish receptor represents a separate subtype. Hence, we have named it zYb for zebrafish Y-receptor b. (We have also discovered a unique receptor called zYa.) The zYb receptor has a binding profile that is reminiscent of Y1 with affinities for NPY and PYY in the low picomolar range, whereas affinities for Y2-selective ligands are considerably lower. It couples to adenylyl cyclase by inhibiting cAMP synthesis. Receptor mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR) in brain, eye, and intestine. The binding profile and amino acid identity show that the zebrafish zYb receptor is related to Y1 but represents a distinct subtype that is likely to be present also in mammals.

Autoreceptor-induced inhibition of neuropeptide Y release from PC-12 cells is mediated by Y2 receptors

Pheochromocytoma (PC)-12 cells express Y1, Y2, and Y3 neuropeptide Y (NPY) receptors when differentiated with nerve growth factor (NGF). The present work evaluated NGF-differentiated PC-12 cells as a model system to study modulation of NPY release by NPY autoreceptors. We demonstrated that both K+ and nicotine stimulated concomitant release of NPY and dopamine from differentiated PC-12 cells. We also showed in this study that NPY release from PC-12 cells was attenuated in a concentration-dependent manner by peptide YY (PYY)-(13-36), a selective agonist for the Y2 type of NPY receptors. This result demonstrated that NPY release could be modulated by NPY autoreceptors of the Y2 subtype. The inhibitory action of PYY-(13-36) may be mediated at least in part by inhibition of N-type Ca2+ channels, because PYY-(13-36) could not produce further inhibitory effects in the presence of a maximum effective concentration of omega-conotoxin, an N-type Ca2+-channel blocker. The inhibition by PYY-(13-36) could be blocked by pretreatment of cells with pertussis toxin, suggesting that an inhibitory GTP-binding protein was involved. Furthermore, the function of NPY autoreceptors could be modulated by other receptors such as beta-adrenergic and ATP receptors. The evoked release of NPY was also attenuated by ATP and adenosine, which have been shown to be colocalized and coreleased with NPY from sympathetic nerve terminals. These results suggest that PC-12 cells differentiated with NGF may be an ideal model to study regulatory mechanisms of NPY release and that autoreceptor-mediated regulation of NPY release appears to act through the Y2 subtype of the NPY receptor.

Nonpeptide antagonists of neuropeptide receptors: tools for research and therapy

The recent development of selective and highly potent nonpeptide antagonists for peptide receptors has constituted a major breakthrough in the field of neuropeptide research. Following the discovery of the first nonpeptide antagonists for peptide receptors ten years ago, numerous other antagonists have been developed for most neuropeptide families. These new, metabolically stable compounds, orally active and capable of crossing the blood-brain barrier, offer clear advantages over the previously available peptide antagonists. Nonpeptide antagonists have provided valuable tools to investigate peptide receptors at the molecular, pharmacological and anatomical levels, and have considerably advanced our understanding of the pathophysiological roles of peptides in the CNS and periphery. Evidence from animal and clinical studies suggests that nonpeptide antagonists binding to peptide receptors could be useful for the treatment of disease states associated with high levels of neuropeptides. In this article Catalina Batancur, Mounia Azzi and William Rostène will address the recent developments in nonpeptide antagonists for neuropeptide receptors, with a particular focus on their CNS actions.

Characterization of the receptor response for the neuropeptide Y-evoked suppression of parasympathetically-mediated contractions in the guinea pig trachea

Neuropeptide Y (NPY) acts via several distinct receptor types. The aim of the present study was to examine which NPY receptors are coupled to inhibition of parasympathetically-mediated contractions of the isolated guinea pig trachea. Electrical field stimulation of tracheal rings evoked a rapid twitch, which was abolished by atropine (1 microM). NPY, the structurally related hormone peptide YY (PYY), the Y2 receptor agonist [Cys2, Aoc5-24, D-Cys27]NPY, as well as NPY 5-36 and NPY 13-36 evoked a concentration-dependent inhibition of the electrically-stimulated twitches. Pretreatment with the Y1 receptor-selective antagonist BIBP3226 (1 microM) failed to prevent the NPY-induced inhibition. Although less potent than NPY, the Y1 (and Y4-Y6) receptor agonist [Leu31, Pro34]NPY also inhibited the electrically-stimulated twitches. Another NPY-related peptide, pancreatic polypeptide, which recognizes Y4-Y6 receptors did not affect the stimulated twitches at concentrations up to 1 microM. However, pretreatment with the Y1 receptor-selective antagonist BIBP3226 (1 microM) virtually abolished the inhibition evoked by [Leu31, Pro34]NPY. None of the peptides affected the baseline tension and BIBP3226 (1 microM) per se did not affect the amplitude of the electrically-stimulated twitches. In conclusion, it seems that NPY and PYY are capable of suppressing parasympathetically mediated contractions in the guinea pig trachea mainly via Y2 receptors, but there is also a small contribution from Y1 receptors.

Genomic organization and functional characterization of the mouse GalR1 galanin receptor

Galanin mediates diverse physiological functions in digestive, endocrine, and central nervous systems through G-protein-coupled receptors. Two galanin receptors have been cloned but the gene structures are unknown. We report genomic and cDNA cloning of the mouse GalR1 galanin receptor and demonstrate that the coding sequence is uniquely divided into three exons encoding the N-terminal portion through the fifth transmebrane domain, the third intracellular loop, and the sixth transmembrane domain through the C-terminus. Functional analysis of the encoded cDNA revealed active ligand binding and intracellular signaling. The expression is detected in brain, spinal cord, heart and skeletal muscle.

Y-receptor subtypes--how many more?

The Y-receptors belong to the G protein-coupled receptor superfamily and mediate a wide variety of physiological effects, such as regulation of blood pressure, anxiety, memory retention, hormone release and food intake. Since the first human Y-receptor was cloned in 1992, the search for additional subtypes has been an area of intense study. Recently four new NPY-receptor subtypes have been isolated, revealing surprisingly limited sequence identity with values as low as 30%. Several reports indicate further heterogeneity of this receptor family, for example a peripheral Y2 receptor. However, since many studies have been carried out with different peptide analogs and radioligands in different species, there is substantial confusion regarding the pharmacological profile of the receptors. This may have led to an exaggeration of the potential number of discrete receptors.

Cloning of a novel member of the G protein-coupled receptor family related to peptide receptors

We have used PCR with degenerate oligonucleotide primers to clone novel members of the G protein-coupled receptor (GPCR) superfamily. We report here a novel gene, CEPR, which encodes a candidate receptor that is most similar to the peptide receptor family. The coding region of the human CEPR gene predicts a seven transmembrane domain (TM) receptor of 375 amino acids. CEPR has 28-30 percent amino acid identity to angiotensin II and interleukin 8 receptors, and slightly lower percent identity to many other GPCRs. Northern blot analysis reveals a 3.3 kb CEPR transcript in different regions of human brain and in various peripheral tissues. The ubiquitous tissue distribution of CEPR, its expression in early development, and its conservation in evolution indicate a potentially important biological function for this receptor and its putative peptide ligand.

Inhibition of stimulated cyclic AMP production by multiple neuropeptide Y receptors in the rat brainstem

Neuropeptide Y (NPY) has been shown to modulate blood pressure, heart rate and to inhibit the baroreceptor reflex at the level of nucleus tractus solitarius (NTS). The aim of this study was to examine effects of NPY and its related peptides on forskolin (1 microM)-stimulated cyclic AMP production in slices of the rat NTS. Each peptide was present at 0.3 microM. Pretreatment with NPY inhibited the stimulated increase in cyclic AMP levels in slices of rat NTS. Also [Pro34]NPY, an analog, which activates Y1, Y3 (and Y5) receptors inhibited the stimulated increase in cyclic AMP levels. However, pretreatment with the Y1 receptor-selective antagonist BIBP3226 (3 microM) did not affect the [Pro34]NPY-evoked inhibition of cyclic AMP levels. In addition, [Leu31,Pro34]NPY, an Y1 (and PP1/Y4 and Y5) receptor agonist did not inhibit the stimulated increase in cyclic AMP production. Also the Y2 receptor-selective agonist C2-NPY inhibited the stimulated elevation of cyclic AMP levels, while peptide YY, which does not recognize Y3 receptors did not significantly affect the stimulated cyclic AMP production. In conclusion, it seems that Y2 and Y3 receptors are coupled to inhibition of adenylate cyclase activity in the rat NTS.

A structure-activity analysis of the cloned rat and human Y4 receptors for pancreatic polypeptide

We cloned and expressed the rat Y4 receptor for pancreatic polypeptide (PP). Structure-activity profiles derived from 125I-PP binding assays and [cAMP] radioimmunoassays reveal a selective receptor interaction with rat PP vs. neuropeptide Y (NPY) or peptide YY (PYY). Rat and human Y4 receptor clones share 75% amino acid identity. Based on [cAMP] radioimmunoassay, the human Y4 receptor exhibits a less selective interaction with rat PP vs. NPY or PYY and a greater dependence on N-terminal PP residues, relative to rat Y4. Differences in sequence and structure-activity profiles suggest the rat be used with caution to model human Y4 receptor function.