Characterization of specific pancreatic polypeptide receptors on basolateral membranes of the canine small intestine

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

The dorsal motor nucleus of the vagus and regulation of pancreatic secretory function

Recent investigation of the factors and pathways that are involved in regulation of pancreatic secretory function (PSF) has led to development of a pancreatic vagovagal reflex model. This model consists of three elements, including pancreatic vagal afferents, the dorsal motor nucleus of the vagus (DMV) and pancreatic vagal efferents. The DMV has been recognized as a major component of this model and so this review focuses on the role of this nucleus in regulation of PSF. Classically, the control of the PSF has been viewed as being dependent on gastrointestinal hormones and vagovagal reflex pathways. However, recent studies have suggested that these two mechanisms act synergistically to mediate pancreatic secretion. The DMV is the major source of vagal motor output to the pancreas, and this output is modulated by various neurotransmitters and synaptic inputs from other central autonomic regulatory circuits, including the nucleus of the solitary tract. Endogenously occurring excitatory (glutamate) and inhibitory amino acids (GABA) have a marked influence on DMV vagal output to the pancreas. In addition, a variety of neurotransmitters and receptors for gastrointestinal peptides and hormones have been localized in the DMV, emphasizing the direct and indirect involvement of this nucleus in control of PSF.

The influence of estradiol and diet on small intestinal glucose transport in ovariectomized rats

Although gender differences exist for intestinal absorption of nutrients and drugs, the possible role estradiol may play in modulating nutrient transport has not been established. Therefore, small intestine glucose transport was measured 1 week after administering estradiol to ovariectomized rats fed diets high in carbohydrate (C) or protein (P). Rats treated with estradiol ate 21% less (P<0.05) and lost body mass (7%; P<0.05) but did not have smaller intestines. Administration of estradiol increased rates of glucose transport, but only when the rats were fed the C diet. These findings indicate that estradiol causes a disconnect between food intake and the dimensions and nutrient transport capacities of the small intestine. Furthermore, the responses to estradiol are influenced by diet composition, are not of the same magnitude for rats and dogs, and can be predicted to affect systemic availability of nutrients and drugs.

Multiple Y receptors mediate pancreatic polypeptide responses in mouse colon mucosa

A functional study has been performed to characterise the Y receptors responsible for NPY, PYY and PP-stimulated responses in mouse colonic mucosal preparations. Electrogenic ion secretion was stimulated with VIP following which NPY, PYY and PP analogues were, to varying degrees, inhibitory. PYY(3-36), hPP, Gln(23)hPP and rPP were effective but less potent than full length PYY, NPY or their Pro(34)-substituted analogues, while the Y(5) agonist Ala(31), Aib(32)hNPY was the least active peptide tested. The Y(1) antagonists, BIBP3226 and BIBO3304 virtually abolished Pro(34)PYY and PYY responses while PYY(3-36) responses were selectively inhibited by the Y(2) antagonist, BIIE0246. A combination of BIBO3304 and BIIE0246 also partially attenuated hPP responses, leaving residual effects that were most probably Y(4)-mediated. Thus we conclude that Y(1), Y(2) and Y(4) receptors attenuate ion secretion in mouse colon.

Constitutive neuropeptide Y Y(4) receptor expression in human colonic adenocarcinoma cell lines

1. Three human adenocarcinoma cell lines, Colony-24 (Col-24), Col-6 and Col-1 have been studied as confluent epithelial layers able to transport ions vectorially in response to basolateral vasoactive intestinal polypeptide (VIP) and pancreatic polypeptides (PP). 2. Different species PP stimulated responses in Col-24 with Y(4)-like pharmacology. Bovine (b)PP, human (h)PP and porcine (p)PP were equipotent (EC(50) values 3.0--5.0 nM) while rat (r)PP, avian (a)PP and [Leu(31), Pro(34)]PYY (Pro(34)PYY) were significantly less potent. PYY was inactive. The PP pharmacology in Col-1 was comparable with Col-24. However, Col-6 cells were different; pPP had an EC(50) intermediate (22.0 nM) between that of bPP (3.0 nM) and hPP (173.2 nM), with aPP and rPP being at least a further fold less potent. 3. Deamidation of Tyr(36) in bPP (by O-methylation or hydroxylation) or removal of the residue resulted in significant loss of activity in Col-24. 4. GR231118 (1 microM) had no PP-like effects. In Col-24 and Col-1, GR231118 significantly attenuated bPP (30 nM) or hPP (100 nM) responses, but it did not alter bPP responses in Col-6. BIBP3226 and GR231118 both inhibited Y(1)-mediated responses which were only present in Col-6. 5. RT--PCR analysis confirmed the presence of hY(4) receptor mRNA in Col-24 and Col-1 epithelia but a barely visible hY(4) product was observed in Col-6 and we suggest that an atypical Y(4) receptor is expressed in this cell line.

PYY preference is a common characteristic of neuropeptide Y receptors expressed in human, rat, and mouse gastrointestinal epithelia

This investigation describes the relative potencies of four peptide agonists, namely, peptide YY (PYY), [Leu31,Pro34]PYY (Pro34PYY), neuropeptide Y (NPY), and [Leu31,Pro34]NPY (Pro34NPY), as antisecretory agents in human, rat, and mouse gastrointestinal preparations. The inhibition of agonist responses by the Y1-receptor antagonist BIBP 3226 was also tested in each preparation. An unexpectedly pronounced preference for PYY and Pro34PYY was observed in functional studies of two human epithelial lines stably transfected with the rat Y1 receptor (Y1-7 and C1Y1-6). NPY and Pro34NPY were at least an order of magnitude less effective than PYY in these functional studies but were only marginally less potent in displacement binding studies using membrane preparations of the same clonal lines. The orders of agonist potency obtained in Y1-7 and C1Y1-6 epithelia were compared with those obtained from a single human colonic adenocarcinoma cell line (Colony-6, which constitutively expresses Y1 receptors) and also from mucosal preparations of rat and mouse descending colon. Similar peptide orders of potency were obtained in rat and mouse colonic mucosae and Colony-6 epithelia, all of which exhibited PYY preference (although less pronounced than with Y1-7 and C1Y1-6 epithelia) and significant sensitivity to the Y1 receptor antagonist, BIBP 3226. We have compared the pharmacology of these five mammalian epithelial preparations and provide cautionary evidence against the reliance upon agonist concentration-response relationships alone, in the characterization of NPY receptor types.Key words: Y receptors, neuropeptide Y, gastrointestinal epithelia, ion transport.

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.

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.

Overexpression of hepatic pancreatic polypeptide receptors in chronic pancreatitis

Pancreatic polypeptide (PP) receptors have recently been demonstrated on liver microsomal membranes although the mechanisms of PP action on hepatocytes remain uncertain. The binding characteristics of these high affinity receptors under pathophysiologic conditions were studied in rats with oleic acid-induced chronic pancreatitis (CP), a state associated with diminished pancreatic PP content. Sixteen pancreatitic and 11 sham-operated control animals either were 16-h fasted or were given free access to food prior to organ removal. Competitive binding studies were performed by incubating hepatocyte microsomal preparation with 125I-labeled PP (20-40 pM) and increasing concentrations of nonlabeled PP (1 x 10(-10) to 1 x 10(-6) M). After total and nonspecific binding was quantified by gamma counting, coefficients of dissociation (Kd) and maximal binding sites (Bmax) were determined by Scatchard analysis of specifically bound radioactivity. Binding data were normalized to membrane protein content and expressed as means +/- standard error. Bmax was significantly greater in tissue from fed control animals than from fasted controls (4.46 +/- 0.36 versus 2.83 +/- 0.25, P < 0.05). Bmax was significantly greater under fasted conditions in tissue from CP animals than from controls (5.25 +/- 0.94 versus 2.83 +/- 0.25, P < 0.01). Under fed conditions, this differences was abolished by the increase in maximal binding in the control group. The fasting-associated decrease in maximal binding sites observed in controls did not occur in CP specimens. Increased Bmax in fed versus fasted control, as well as fasted CP versus fasted control, were associated with slight reciprocal decreases in receptor affinity. These data indicate that hepatic PP receptor concentration is upregulated in this model of chronic pancreatitis, most likely due to diminished exposure to ligand. Furthermore, normal PP receptor responses to the fed/fasted state are blunted in this condition. Regulatable PP receptor changes may play a role in altered hepatic metabolism previously observed in chronic pancreatitis.

Distribution of the NPY receptor subtype Y1 within human colon: evidence for NPY targeting a subpopulation of nitrergic neurons

Neuropeptide Y is a neurotransmitter in both the central nervous system and the enteric nervous system. Neuropeptide Y receptors have been demonstrated by in situ hybridization and ligand binding techniques to be present in both of these systems. In this study we report on the distribution of the Y1 isoform of the neuropeptide Y receptor (YY1) in human colon using an antibody raised against the Y1 receptor. This method permits greater resolution in determining the distribution of the receptor and provides the opportunity to study neurotransmitter markers in relationship to the Y1 receptor. Y1 receptor immunoreactivity was localized within ganglionic neurons and axons of the myenteric and submucosal nerve networks, axons within the muscularis mucosae, longitudinal and circular smooth muscle layers, sympathetic nerve fibers around blood vessels and within scattered cells in the mucosa and basal cells of the crypts. Neuropeptide Y/Y1 double staining showed that the peptide and its Y1 receptor subtype were often colocalized within ganglion cells of Henle's plexus in the submucosa. Thus, Y1 may act as an autoreceptor within the colonic gut wall. Nitric oxide synthase was found within most neurons of the myenteric plexus which displayed Y1-receptor immunoreactivity but this correlation was not seen in the submucosa. Instead, the colocalization of nitric oxide synthase and Y1-immunoreactivity was extremely low. These results indicate a striking difference in the Y1 Neuropeptide Y activation of nitrergic mechanisms within the myenteric and submucosal nerve networks.

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.

Effect of pancreatic polypeptide on rat dorsal vagal complex neurons

1. Pancreatic polypeptide (PP) microinjected into the dorsal vagal complex (DVC) elevates gastric activity through a vagal mechanism. Thus, it was hypothesized that PP alters the activity of nuclei comprising the DVC, i.e. the nucleus tractus solitarii (NTS) and the dorsal motor nucleus (DMN). 2. In vivo and in vitro approaches were used. For in vivo studies, micropipettes were used for recording and injecting vehicle or PP. Neurons were identified as NTS or DMN using orthodromic and antidromic activation, respectively, following vagal stimulation. Gastric-related DVC neurons were located using antral inflation. For in vitro studies, DMN neurons were recorded from medullary slices. 3. Of the twenty-eight NTS and DMN neurons identified, fifteen were activated, six inhibited and seven unaffected after PP microinjection. Forty-two gastric-related neurons were located in the DVC, of which twenty-five were stimulated by PP and seventeen exhibited no change. No gastric-related cells were inhibited. 4. For in vitro studies, 66% of DMN neurons were activated by PP (n = 27/47) while the remaining 33% were inhibited (n = 14/47). Similar results were obtained in normal or synaptic blockade media. 5. These results support the hypothesis that PP alters DVC neuronal activity, which may thereby lead to the previously observed alterations in gastric activity.

Neuropeptide Y family of hormones: receptor subtypes and antagonists

Neuropeptide Y (NPY) is the most abundant peptide present in the mammalian central and peripheral nervous system. NPY exhibits a variety of potent central and peripheral effects including those on feeding, memory, blood pressure, cardiac contractility and intestinal secretions. Classical pharmacological studies have shown that NPY effects are mediated by four different receptor subtypes, Y-1, Y-1-like, Y-2, and Y-3. However, the existence of numerous atypical activities provide strong evidence for the occurrence of additional NPY receptor subtypes. Pharmacological studies have further been facilitated by the recent cloning and expression of Y-1, Y-2, Y-4 (PP-1) and Y-5 receptors. Moreover, the cloned Y-5 receptor has been suggested to be the long awaited Y-1-like receptor involved in feeding. Structure-activity studies have laid a good foundation towards the development of receptor selective compounds, and to date potent Y-1 selective peptide and nonpeptide antagonists have been developed. The need to clone numerous receptor subtypes and to develop receptor selective compounds for physiological and perhaps clinical use is expected to keep NPY research active for many years to come.

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.

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.

Cloning and functional expression of a human Y4 subtype receptor for pancreatic polypeptide, neuropeptide Y, and peptide YY

The pancreatic polypeptide family includes pancreatic polypeptide (PP), neuropeptide Y (NPY), and peptide YY (PYY). Members of the PP family regulate numerous physiological processes, including appetite, gastrointestinal transit, anxiety, and blood pressure. Of the multiple Y-type receptors proposed for PP family members, only the Y1 subtype has been cloned previously. We now report the cloning of an additional Y-type receptor, designated Y4, by homology screening of a human placental genomic library with transmembrane (TM) probes derived from the rat Y1 gene. The Y4 genomic clone encodes a predicted protein of 375 amino acids that is most homologous to Y1 receptors from human, rat, and mouse (42% overall; 55% in TM). 125I-PYY binding to transiently expressed Y4 receptors was saturable (pKd = 9.89) and displaceable by human PP family derivatives: PP (pKi = 10.25) approximately PP2-36 (pKi = 10.06) > PYY (pKi = 9.06) approximately [Leu31,Pro34]NPY (pKi = 8.95) > NPY (pKi = 8.68) > PP13-36 (pKi = 7.13) > PP31-36 (pKi = 6.46) > PP31-36 free acid (pKi < 5). Human PP decreased [cAMP] and increased intracellular [Ca2+] in Y4-transfected LMTK- cells. Y4 mRNA was detected by reverse transcriptase-polymerase chain reaction in human brain, coronary artery, and ileum, suggesting potential roles for Y4 receptors in central nervous system, cardiovascular, and gastrointestinal function.

Functional characterization of receptors with affinity for PYY, NPY, [Leu31,Pro34]NPY and PP in a human colonic epithelial cell line

1. Confluent epithelial layers of a human adenocarcinoma cell line called Colony-6 have been shown to respond to nanomolar concentrations of vasoactive intestinal polypeptide (VIP), peptide YY (PYY), neuropeptide Y (NPY) and somatostatin (Som). 2. The VIP-induced increase in basal short-circuit current (SCC) was attenuated by basolateral application of Som, PYY or NPY, and also by the Y1-receptor agonist [Leu31,Pro34]NPY, as well as pancreatic polypeptide (PP). High concentrations (0.1-3.0 microM) of NPY(2-36) were effective but the C-terminal fragment NPY(13-36) (0.1-1.0 microM) and desamidoNPY (0.6 microM) were not active. A rank order of agonist EC50 values was: PYY > NPY > [Leu31,Pro34]NPY > PP > NPY(2-36) >> NPY (13-36). 3. Receptors for all these peptides were preferentially located within the basolateral domain. Apical addition of PP (1 microM) and Som (100 nM) had no effect upon basal SCC while apical VIP (10 nM) responses were 18%, and apical PYY (100 nM) were 27% the size of respective basolateral controls (100%). 4. Cross-desensitization was observed between [Leu31,Pro34]NPY (1 microM) and both PYY (100 nM) and PP (1 microM) and between PYY and NPY(2-36) (1 microM), but was not significant between PYY (100 nM) and PP (1 microM). We suggest that either these cells express a single new Y-receptor with an unusual phenotype or that two Y-receptor populations exist in Colony-6 cells.

Strong evolutionary conservation of neuropeptide Y: sequences of chicken, goldfish, and Torpedo marmorata DNA clones

Neuropeptide Y (NPY) is an abundant and widespread neuropeptide in the nervous system of mammals. NPY belongs to a family of 36-amino acid peptides that also includes pancreatic polypeptide and the endocrine gut peptide YY as well as the fish pancreatic peptide Y. To study the evolution of this peptide family, we have isolated clones encoding NPY from central nervous system cDNA libraries of chicken, goldfish, and the ray Torpedo marmorata, as well as from a chicken genomic library. The predicted chicken NPY amino acid sequence differs from that of rat at only one position. The goldfish sequence differs at five positions and shows that bony fishes have a true NPY peptide in addition to their pancreatic peptide Y. The Torpedo sequence differs from that of rat at three positions. As Torpedo NPY has no unique positions when compared with the other sequences, it seems to be identical to the NPY of the common ancestor of cartilaginous fishes, bony fishes, and tetrapods after 420 million years of evolution. The 30-amino acid carboxyl-terminal extension of the NPY precursor also displays considerable sequence conservation. These results show that NPY is one of the most highly conserved neuroendocrine peptides.

Structural requirements of pancreatic polypeptide receptor binding

Pancreatic polypeptide (PP) receptors have been identified and characterized on the basolateral membranes (BLM) of canine intestinal mucosa. The present study was designed to ascertain the structural requirements of the PP molecule for binding to its receptor. A radioreceptor assay using purified BLM was employed to elucidate receptors specific to PPs of various mammalian species and to modified bovine PP (bPP) fragments. Receptor cross-reactivities (CR) to various PPs and bPP fragments were established. Results show that percent receptor CR by PPs of various species was as follows: bPP (100%) greater than human PP (68%) greater than porcine PP (50%) greater than canine PP (45%) greater than ovine PP (36%) greater than rat PP (3%). The fragments bPP-(1-15), bPP-(1-17), bPP-(1-26), bPP-(16-23), bPP-(18-30), bPP-(24-36), bPP-(27-35), and bPP-(31-36) at 500 nM did not significantly displace tracer from receptor (less than 0.1% CR). Des-COOH-terminal tyrosinamide [bPP-(1-35)] produced less than 0.1% CR. Oxidation of bPP methionine-30 residue to methionine sulfoxide decreased displacement to 67%. Modification of native amidated tyrosinamide to the free acid abolished receptor binding, whereas esterification to the methyl ester of COOH-terminal tyrosine restored binding to 60%. Additionally, percent CR decreased progressively as amino acid residues were deleted from the NH2-terminal region. We conclude that the molecular homologue of PP primary structure is necessary for full receptor binding. Both the NH2- and COOH-terminal residues are required for recognition, and the COOH-terminal tyrosinamide must be intact for PP binding to its receptor.

Specific neuropeptide Y binding sites in chicken brain

In the present study, 125I-labeled neuropeptide Y (NPY) binding to chicken brain regions was evaluated. Cerebellum and cerebral cortex membranes bound significantly more 125I-NPY specifically than did membranes from other brain regions. Scatchard plots of NPY binding to cerebellar membranes were curvilinear; the high-affinity component had an affinity (Kd) of 1.1 nM, with a receptor concentration (Ro) of 182 fmol/mg membrane protein. Scatchard plots of NPY binding to chicken cerebral cortex membranes were linear, with a Kd of 0.63 nM and Ro of 90 fmol/mg. Unlabeled avian pancreatic polypeptide (APP) inhibited 125I-NPY binding to cerebellar membranes with a constant at which 50% inhibition occurs of 0.5 nM but showed essentially no affinity for cerebral cortex NPY binding sites. As previously reported, 125I-APP bound to cerebellar membranes with a Kd of 0.365 nM and an Ro of 323 fmol/mg, and unlabeled NPY showed about one order of magnitude lower affinity than did unlabeled APP for 125I-APP binding sites. Pseudo-Hill coefficients for APP binding to cerebellar APP receptors and NPY binding to cerebellar NPY receptors were 0.9. In contrast, pseudo-Hill plots for APP competition for 125I-NPY binding were curvilinear. It is concluded that the chicken cerebellum contains distinct APP and NPY receptors, whereas cerebral cortex contains only NPY receptors. APP is capable of binding with high affinity to the cerebellar, but not the cortical, NPY receptor.