Neuropeptide Y stimulates inositol phospholipid hydrolysis in rat brain miniprisms

Neuropeptide Y receptor-mediated sensitization of ATP-stimulated inositol phosphate formation

Activation of bovine chromaffin cell neuropeptide Y (NPY) receptors coupled to Gi (Y1) results in the enhancement of ATP-stimulated inositol phosphate formation. NPY alone does not alter inositol phosphate (InsP) formation in these cells, suggesting that some form of receptor cross talk is involved in this process. In some cell types, serial stimulation of Gi-linked and Gs- or Gq-linked receptors results in an increase in intracellular messenger production (cyclic AMP or InsP), a process referred to as heterologous sensitization. NPY preincubation with bovine chromaffin cells followed by the addition of ATP results in a dose-dependent increase in ATP-stimulated InsP formation (EC50 = 2.0 x 10-8 M), which is maximal within 1 min. InsP formation resulting from NPY preincubation persists for more than an hour after NPY removal, declining with time in a linear fashion. [Leu31Pro34]NPY and NPY are equally effective at producing sensitization, whereas NPY13-36 is ineffective, suggesting that NPY acts through the Y1 receptor. Confirmation of the receptor subtype identity was made by including the Y1-selective antagonist HU-404 during the preincubation, which prevented the sensitizing effect of NPY. NPY sensitization was blocked by pertussis toxin pretreatment, demonstrating Gi/Go involvement. ATP-stimulated InsP formation, with and without NPY preincubation, was sensitive to the phospholipase C inhibitor, U73122 [1-(6-([17beta-3-methoxyestra-1,3,5(10)-trien-17-yl]-amino)hexyl)-1H-pyrrole-2,5-dione]. In conclusion, short-term exposure of bovine chromaffin cells to NPY results in a long-lasting increase in the subsequent stimulation of InsP formation by ATP.

Limited signal transduction repertoire of human Y(5) neuropeptide Y receptors expressed in HEC-1B cells

In HEC-1B cells transfected with human Y(5) neuropeptide Y (NPY) receptors (but not in non-transfected cells) NPY inhibited forskolin-stimulated cAMP accumulation in a pertussis toxin-sensitive manner (-log EC(50) 8.88 +/- 0.25). Elevations of intracellular Ca(2+) were largely restricted to very high NPY concentrations and similar in transfected and nontransfected cells. NPY did not increase inositol phosphate accumulation and did not activate a variety of isoforms of protein kinase C or mitogen-activated protein kinases. We conclude that at least upon expression in HEC-1B cells the signal transduction of Y(5) NPY receptors is limited to inhibition of cAMP accumulation.

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.

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.

Neuropeptide Y and somatostatin-like immunoreactivity in neurons of the monkey amygdala

Neurons in the monkey amygdala exhibiting neuropeptide Y-like immunoreactivity and somatostatin-like immunoreactivity were identified using an avidin-biotin immunohistochemical technique. Differential co-existence of the two peptides was demonstrated using two-color immunoperoxidase and adjacent section methods. Numerous neuropeptide Y-positive neurons were observed in the basolateral and superficial amygdaloid nuclei. A moderate number of neuropeptide Y-positive neurons was seen in the medial subdivision of the central nucleus, but only a few neurons were observed in the lateral subdivision. Numerous somatostatin-positive neurons were stained in all major amygdaloid nuclei and always outnumbered neuropeptide Y-positive cells. All amygdaloid nuclei contained numerous peptide-positive fibers whose density varied depending on the nucleus. Approximately 90% of neuropeptide Y-positive neurons also exhibited somatostatin-like immunoreactivity. The percentage of somatostatin-positive neurons that exhibited neuropeptide-Y immunoreactivity varied in different nuclei. In the superficial amygdaloid nuclei, medial subdivision of the central nucleus and most portions of the basolateral nuclei the predominant cell type stained with both the neuropeptide Y and somatostatin antibodies was a spine-sparse non-pyramidal neuron. In the dorsal portion of the lateral nucleus, however, most peptide-positive neurons had spiny dendrites. Only the cell bodies and proximal dendrites of somatostatin-positive neurons in the lateral subdivision of the central nucleus were immunostained. This study demonstrates that specific cell populations in the primate amygdala contain neuropeptide Y, somatostatin or both peptides. Most peptide-positive neurons in the basolateral and superficial amygdaloid nuclei appear to be local circuit neurons that contribute to the dense plexus of peptide-positive axons in these regions. The finding of neurons with spiny dendrites in the dorsal part of the lateral nucleus suggests that these cells may be functionally different from peptide-positive neurons in other portions of the basolateral amygdala. The lateral subdivision of the central nucleus is distinguished from other amygdaloid nuclei by containing a large population of somatostatin-positive neurons that do not exhibit neuropeptide Y immunoreactivity.

Structure-activity relationships of neuropeptide Y analogues with respect to Y1 and Y2 receptors

Secondary structure investigations, affinities, and activities of neuropeptide Y analogues with respect to the Y1 and the Y2 receptor are reviewed. The results are discussed with respect to the different prerequisites for affinities to both receptor subtypes. The results from a systematic scanning of the hormone using L-alanine and from a large variety of discontinuous and cyclic analogs suggest that two different conformations of neuropeptide Y are adopted at the Y1 and Y2 receptors. Whereas a C-terminal turn structure is suggested for Y1 receptor affinity, an alpha-helical conformation of the C-terminus is afforded for good binding to the Y2 receptor.

Lack of NPY-induced feeding in cobalt protoporphyrin-treated rats is a postreceptor defect

The administration of cobalt protoporphyrin results in transient decreases in food intake and prolonged weight loss in rats. After IVC injection of cobalt protoporphyrin, the food intake of treated rats falls to 10% of vehicle-treated control rats within 48 h. At the same time, the concentrations of mRNA for neuropeptide Y increase approximately twofold in the hypothalamus. The failure of these animals to display a feedings response to elevation of endogenous NPY concentration is mimicked by their failure to respond to exogenous. ICV injections of neuropeptide Y. Because NPY binding studies are confounded by high nonspecific binding, radiolabeled PYY was used to measure binding to hypothalamic membranes and for autoradiography with hypothalamic sections. No abnormalities in the number of receptors or the affinity of the binding interaction were noted. In addition, hypothalamic concentrations of cyclic AMP were unchanged following treatment with either cobalt protoporphyrin or NPY. These results indicate that the locus of the failure of CoPP-treated animals to feed after administration of NPY must be either distal to, or unrelated to, the NPY receptor in the hypothalamus.

Roles of second-messenger systems and neuronal activity in the regulation of lordosis by neurotransmitters, neuropeptides, and estrogen: a review

Many neurotransmitters and neuropeptides can affect the rodent feminine sexual behavior, lordosis, when administered in the ventromedial hypothalamus (VMH), midbrain central gray (MCG), or other brain regions. A survey of the electrophysiological and biochemical actions of these neural agents revealed that there is a very consistent association between lordosis facilitation with both the activation of the phosphoinositide (PI) pathway and the excitation of VMH and MCG neurons. In contrast, lordosis inhibition is associated, less consistently, with alterations of the adenylate cyclase (AC) system and the inhibition of neuronal activity. The findings that lordosis could be facilitated by going beyond membrane receptors and directly activating the PI pathway, suggest that this second-messenger pathway is a common mediator for the lordosis-facilitating agents. Furthermore, as in the case of stimulating membrane receptors, direct activation of this common mediator also requires estrogen priming for lordosis facilitation. Therefore, it is likely that the PI pathway is modulated by estrogen in the permissive action of estrogen priming. Indeed, a literature review shows that estrogen can affect selective isozymes of key enzyme families of the PI pathway at various levels. Such selective modulations, at several levels, could easily alter the course of a PI cascade; thence, the eventual functional outcome. These findings prompt us to propose that estrogen enables lordosis to be facilitated by a selective modulation of the PI pathway.

Inhibitory effects of neuropeptide Y on splanchnic glycogenolysis and renin release in humans

Neuropeptide Y (NPY) is stored in sympathetic nerves and NPY levels increase several times during exercise. NPY administration during prolonged exercise causes reduced splanchnic glucose production. To elucidate the effects of NPY on adrenaline (Adr)-stimulated splanchnic glycogenolysis these substances were infused to seven healthy subjects in the post-absorptive state. Blood samples were drawn from an arterial and a central hepatic vein catheter for determination of splanchnic blood flow, exchanges of metabolites and arterial levels of NPY, catecholamines, insulin, glucagon and renin in the basal state and during 20 min Adr infusion (0.1-0.3 nmol kg-1 min-1). After basal values were reached a 60 min NPY infusion was initiated. At 40 min of NPY infusion the Adr infusion was repeated. Adr alone increased splanchnic blood flow (41%, P < 0.01), arterial glucose concentration (29%, P < 0.001) and splanchnic glucose production (102%, P < 0.01). During the NPY infusion both splanchnic blood flow and arterial glucose fell (P < 0.05). Although the combined NPY and Adr infusion caused the same proportional increases in splanchnic blood flow, arterial glucose and splanchnic glucose production as with Adr alone the absolute values were lower (all P < 0.05). Arterial insulin as well as Adr and noradrenaline increased with the combined NPY-and Adr infusion as with Adr alone. Arterial plasma renin activity was 12% lower with the combined NPY and Adr-infusion compared to Adr infusion alone. These results indicate further an inhibitory effect of NPY on splanchnic glycogenolysis and suggest that NPY inhibits Adr-stimulated renin release.

Subtypes of receptors for neuropeptide Y: implications for the targeting of therapeutics

Neuropeptide Y is a 36 amino acid peptide that was originally discovered in extracts of porcine brain. The peptide has a broad distribution in the central or peripheral nervous system. Receptors for this peptide were originally subdivided into postsynaptic Y-1 receptors and presynaptic Y-2 receptors. The Y-1 receptor has recently been cloned and appears to mediate several effects of NPY including vasoconstriction and an anxiolytic effect in animal models of anxiety. The Y-2 receptor inhibits the release of neurotransmitters in the CNS by the inhibition of the mobilization of intracellular calcium. Additional receptors have been proposed including a Y-3 receptor that recognizes NPY but not the related endocrine peptide, PYY. The functional importance of these newer receptors remains to be established. The absence of useful antagonists has made the study of NPY a challenge for investigators in the field. The potential utility of such molecules is discussed.

Effect of peripheral axotomy on expression of neuropeptide Y receptor mRNA in rat lumbar dorsal root ganglia

Using in situ hybridization, the expression of the mRNA for a neuropeptide Y (NPY) receptor, was studied in lumbar (L) 4 and 5 dorsal root ganglia (DRGs) of normal rats and at various intervals after unilateral sciatic nerve transection. Twenty percent of all normal DRG neurons were NPY receptor mRNA-positive, and the majority of these neurons were of the small type, with only a few labelled medium-sized and large neurons. In L5 normal ganglia NPY receptor mRNA colocalized with substance P, calcitonin gene-related peptide and galanin mRNAs in small neurons, but not in medium-sized or large neurons containing these peptides. NPY receptor mRNA was not observed in somatostatin or nitric oxide synthase mRNA-positive neurons. Sciatic nerve transection induced a marked decrease in NPY receptor mRNA levels. However, in parallel there was a transient increase in the number of NPY receptor mRNA-positive small neuron profiles, but the intensity of labelling was mostly very low, although a few strongly labelled, small neuron profiles were also encountered. In addition, axotomy caused a marked increase in the number of NPY receptor mRNA-positive large neuron profiles in the ipsilateral DRGs, and they constituted 15-20% of counted DRG neuron profiles and 45-65% of counted large neuron profiles, 7-28 days after axotomy. In L5 DRGs, ipsilateral to the axotomy, NPY receptor mRNA colocalized with NPY mRNA in many large and some medium-sized neuron profiles, with galanin mRNA in some small, medium-sized and large neuron profiles and with vasoactive intestinal polypeptide mRNA in some small and medium-sized neuron profiles and a few large profiles. Occasionally, NPY receptor mRNA was observed in nitric oxide synthase mRNA-positive small neurons. In the dorsal horn, NPY receptor mRNA-positive small neurons were concentrated in lamina II at L4 and L5 levels, and were scattered in deeper laminae. No marked changes were observed ipsilateral to the axotomy. No NPY receptor mRNA-positive cells were found in the normal rat gracile nucleus, or in this nucleus after axotomy. These results show that a NPY receptor may be a prejunctional receptor in primary afferent neurons and play a role in the modulation of somatosensory information, both in normal and lesioned primary afferent DRG cells. However, axotomy induced a distinct shift in NPY receptor mRNA expression from small to large neurons, indicating that sensitivity to NPY is switched from one modality to another.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of neuropeptide Y receptors in cultured astrocytes from neonatal rat brain

Specific binding sites for neuropeptide Y could be demonstrated in primary cultures of astrocytes from neonatal rat brain. Neuropeptide Y binding was saturable, reversible, and temperature dependent as revealed by saturation studies and kinetic experiments. Scatchard analysis of equilibrium binding data indicated a single population of high-affinity binding sites with respective KD and Bmax values of 0.43 nM and 6.9 fmol/2.7 x 10(5) cells. Physiological responses induced by neuropeptide Y could be detected in a distinct subpopulation of cultured astrocytes on the basis of two criteria: 1) electrophysiological responses and 2) single cell measurements of changes in [Ca2+]i. In that fraction of cells responding (20-70%, varying among cultures from different preparations), brief application of neuropeptide Y led to a membrane potential depolarization, lasting several minutes. When the membrane was clamped close to the resting membrane potential using the whole-cell patch-clamp technique, neuropeptide Y induced an inward current with a similar time course as the neuropeptide Y-induced membrane depolarization. As detected by single cell microfluorimetric (fura-2) measurements neuropeptide Y induced an increase of [Ca2+]i which was caused by the entry of extracellular Ca2+. Both the [Ca2+]i increase and the electrophysiological responses were unaffected by pretreatment of the astrocytes with pertussis toxin.

Neuropeptide Y suppresses the neurogenic inflammatory response in the rabbit eye; mode of action

Ocular injury in the rabbit causes miosis and breakdown of the blood aqueous barrier (aqueous flare response, AFR), reflecting a sensory nerve-mediated inflammatory response, elicited by the release of tachykinins and calcitonin gene-related peptide (CGRP) from C-fibers. Neuropeptide Y (NPY) occurs in sympathetic fibers in the eye. The study was designed to examine whether NPY and related peptides interfere with the inflammatory response to ocular injury in the rabbit in vivo. The isolated rabbit iris was studied with respect to NPY binding sites and second messenger coupling. The AFR and the miotic response to a standardized injury (infrared irradiation (IR) of the iris) were suppressed dose-dependently by NPY (0.01-1.0 nmol) injected intravitreally 30 min prior the trauma. The treated eye was compared with the contralateral eye, which received 0.9% saline and IR. The Y1 receptor agonist [Pro34]NPY, the Y2 receptor agonist NPY 13-36 and the structurally related peptide YY (1 nmol each) suppressed the AFR in response to IR. Injection of either NPY or the Y1 and Y2 receptor agonists (0.3 nmol each) suppressed the AFR evoked by exogenously applied CGRP (0.15 nmol). Saturation studies with 125I-NPY revealed both high and 'moderate' affinity binding sites in the iris. The Bmax values were 26 and 321 fmol/mg protein, respectively. NPY suppressed the forskolin-stimulated adenylate cyclase activity (IC50 value 19 nM). NPY did not affect basal or noradrenaline-induced accumulation of inositol phosphates in the iris. In conclusion, the rabbit iris seems to be rich in NPY receptors linked to inhibition of adenylate cyclase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y-induced inositol phospholipid hydrolysis in blood vessels from normotensive and spontaneously hypertensive rats

1. Neuropeptide Y (NPY) increased inositol phosphate (IP) formation in the femoral artery and vein of adult Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. 2. Noradrenaline (NA, 10(-6) M) induced IP accumulation in both strains of rats. 3. Subthreshold concentrations of NPY (3 x 10(-9) M for femoral vein and 10(-8) M for femoral artery) failed to modify NA (10(-6) M)-induced IP formation in both vessels. 4. These results suggest that the direct contractile effects but not the potentiation of NA-induced contractions may be directly linked to phosphatidylinositol turnover in adult SHR and WKY rats.

Cloned human neuropeptide Y receptor couples to two different second messenger systems

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian nervous system and exhibits a diverse range of important physiological activities, including effects on psychomotor activity, food intake, regulation of central endocrine secretion, and potent vasoactive effects on the cardiovascular system. Two major subtypes of NPY receptor (Y1 and Y2) have been defined by pharmacological criteria. We report here the molecular cloning of a cDNA sequence encoding a human NPY receptor and the corrected sequence for a rat homologue. Analysis of this sequence confirms that the receptor is a member of the G protein-coupled receptor superfamily. When expressed in Chinese hamster ovary (CHO) or human embryonic kidney (293) cells, the receptor exhibits the characteristic ligand specificity of a Y1 type of NPY receptor. In the 293 cell line, the receptor is coupled to a pertussis toxin-sensitive G protein that mediates the inhibition of cyclic AMP accumulation. In the CHO cell line, the receptor is coupled not to the inhibition of adenylate cyclase but rather to the elevation of intracellular calcium. These results demonstrate that second messenger coupling of the NPY-Y1 receptor is cell type specific, depending on the specific repertoire of G proteins and effector systems present in any cell type.

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

Subtypes of the neuropeptide Y (NPY) receptor in the rat brain were identified by the use of the selective Y-1 analog, [Leu34-Pro34] NPY. In rat brain homogenate binding studies, [Leu31-Pro34] NPY was found to produce a partial inhibition of 100 pM 125I-labeled peptide YY (PYY) binding with a plateau at 50-1000 nM [Leu31-Pro34] NPY resulting in a 70% inhibition of binding. The C-terminal fragment NPY 13-36, a putative Y-2 agonist, exhibited very little selectivity in rat brain homogenates. Scatchard analysis of 125I-labeled PYY binding to rat brain homogenate yielded biphasic plots with Kd values of 40 and 610 pM. Inclusion of 100 nM [Leu31-Pro34] NPY was found to eliminate the low affinity component of 125I-labeled PYY binding leaving a single, high affinity binding site with a Kd of 68 pM. In autoradiographic studies, displacement curves indicated that [Leu31-Pro34] NPY completely inhibited binding in the cerebral cortex with little effect on the binding in the hypothalamus. On the other hand NPY 13-36 inhibited binding in the hypothalamus at low concentrations but required higher concentrations to inhibit binding in the cerebral cortex. Other brain regions such as the hippocampus, appeared to contain both subtypes. Subsequent to these studies, a quantitative autoradiographic map was conducted using 50-100 pM 125I-labeled PYY in the presence and absence of [Leu31-Pro34] NPY which produced a selective displacement of binding in certain distinct brain regions. These areas included the cerebral cortex, certain thalamic nuclei and brainstem while ligand binding was retained in other brain regions including the zona lateralis of the substantia nigra, lateral septum, nucleus of the solitary tract and the hippocampus. Numerous brain regions appeared to contain both receptor subtypes. Therefore, the Y-1 and Y-2 receptor subtypes exhibited a somewhat distinct distribution in the brain. In addition, 125I-labeled PYY appears to label the Y-2 receptor with relatively higher affinity when compared to the Y-1 receptor.

NPY-stimulated Ca2+ mobilization in SK-N-MC cells is enhanced after isoproterenol treatment

Neuropeptide Y (NPY) receptors in the SK-N-MC human neuroblastoma cell line couple to mobilization of intracellular Ca2+ and inhibition of adenylylcyclase. Pretreatment of SK-N-MC cells with isoproterenol enhanced the NPY-stimulated Ca2+ mobilization, mainly by increasing the maximal response to NPY. The enhancement was time-(maximal after 24 h) and concentration-dependent (maximal at 10 microM isoproterenol), blocked by the beta-adrenergic antagonist propranolol, and mimicked by forskolin. Concomitant treatment with cycloheximide prevented the enhancing effect of isoproterenol, suggesting the involvement of protein synthesis. Isoproterenol treatment did not alter the number or affinity of 125I-labeled NPY binding sites, the amount of pertussis toxin substrates, or NPY-mediated inhibition of cAMP accumulation. Similarly, isoproterenol treatment had no effect on basal intracellular Ca2+ and on Ca2+ increases elicited by carbachol, caffeine, or ionomycin. We conclude that isoproterenol treatment can sensitize NPY receptor responsiveness in a way that is specific for Ca2+ mobilization mechanisms used by this hormone.

Effects of intracerebroventricular D-myo-inositol-1,2,6-trisphosphate (PP56), a proposed neuropeptide Y (NPY) antagonist, on locomotor activity, food intake, central effects of NPY and NPY-receptor binding

D-myo-Inositol-1,2,6-trisphosphate (PP56) is a novel experimental drug which is structurally related to the intracellular second messenger IP3. Among other pharmacological effects, PP56 has been shown to antagonize neuropeptide Y (NPY) induced vasoconstriction with a high degree of specificity. We examined the effects of i.c.v. PP56 on locomotor activity and food intake in rats, and on the hypoactivity and hyperphagia induced by NPY. In the open field, PP56 given alone increased locomotor activity by up to 85%. It did not prevent NPY induced hypoactivity to any extent. PP56 given alone did not affect food intake except for a small increase after the highest dose tested (200 nmol). When NPY was given after pretreatment with PP56, NPY induced hyperphagia was significantly reduced. A similar effect, however, was seen with regard to the hyperphagia produced by another orexigenic peptide, galanin. PP56 did not affect the binding of 125I-NPY to brain membranes in vitro, or to cells of two different neuroblastoma cell lines which selectively express NPY Y1 or Y2 receptors. In summary, PP56 acted as a locomotor stimulant per se. Only one of the two tested central effects of NPY could be antagonized by PP56, and then only partially and in a non-specific manner. The central effects of PP56 do not seem to be produced at the level of NPY receptors.

Pertussis toxin attenuates postsynaptic actions of neuropeptide Y on the guinea-pig uterine artery

The mechanisms by which neuropeptide Y (NPY) mediates its postsynaptic actions on the guinea-pig uterine artery, were investigated by incubating arterial segments in culture medium containing pertussis toxin (PTX). Arteries were incubated with 0, 0.25 or 1 microgram.ml-1 PTX for 24 or 48 h. Arterial segments incubated in culture medium without PTX showed the three postsynaptic responses to NPY which were reported previously in uncultured arteries: NPY further contracted segments which were precontracted with prostaglandin F2 alpha; NPY reduced the maximum relaxations produced by vasoactive intestinal peptide (VIP); and NPY produced a rightward shift in the VIP concentration-response curves. PTX attenuated the three actions of NPY on the uterine artery to different degrees. PTX also reduced the magnitude of contractions produced by prostaglandin F2 alpha, but did not affect contractions produced by 0.126 M KCl, or relaxations produced by VIP in the absence of NPY. These data indicate that all postsynaptic actions of NPY on the uterine artery, and contractions produced by prostaglandin F2 alpha, are at least partly mediated by pertussis toxin-sensitive GTP-binding proteins. It is not clear whether these multiple actions of NPY are mediated by one, or more than one, GTP-binding protein.

Chronic desipramine treatment reduces regional neuropeptide Y binding to Y2-type receptors in rat brain

Chronic treatment of rats with desipramine and imipramine (5 mg/kg/twice daily/i.p.) for 14 days caused a significant reduction in the binding of [3H]propionyl NPY to membranes prepared from frontal cortex, nucleus accumbens, hypothalamus and hippocampus. There was no change in binding of [3H]propionyl NPY in the parieto-occipital cortex, striatum or amygdala. Scatchard analysis of binding data from frontal cortical and hippocampal membranes showed that [3H]propionyl NPY bound to a single site with a Kd of approximately 0.3 nM. The loss of [3H]propionyl NPY binding in hippocampal and frontal cortical membranes revealed that chronic tricyclic antidepressant treatment produced a reduction in the number of binding sites with no change in the affinity for the ligand. Chronic desipramine treatment did not alter the ability of NPY (0.01-25 microM) to stimulate inositol phosphate accumulation in rat frontal cortical slices as compared to saline-treated animals. The lack of change of NPY-induced inositol phosphate accumulation following chronic desipramine treatment showed that there was no change to Y1 NPY-type receptors which are linked to the hydrolysis of inositol phospholipids. However, the ability of NPY (0.05-0.5 microM) to inhibit forskolin (1 microM) stimulated adenylate cyclase via Y2 NPY-type receptors in rat frontal cortical slices was significantly reduced following chronic desipramine treatment. This finding suggests that the reduction of [3H]proprionyl NPY binding in selective brain regions may be the result of an antidepressant-induced loss of Y2-type NPY receptors which are negatively linked to adenylate cyclase.

Presynaptic inhibition by neuropeptide Y in rat hippocampal slice in vitro is mediated by a Y2 receptor

1. The action of analogues and C-terminal fragments of neuropeptide Y (NPY) was examined on excitatory synaptic transmission in area CA1 of the rat hippocampal slice in vitro, by use of intracellular and extracellular recordings, to determine by agonist profile the NPY receptor subtype mediating presynaptic inhibition. 2. Neither NPY, analogues nor fragments of NPY affected the passive or active properties of the post-synaptic CA1 pyramidal neurones, indicating their action is at a presynaptic site. 3. The full-sequence analogues, peptide YY (PYY) and human NPY (hNPY), were equipotent with NPY at the presynaptic receptor, while desamido hNPY was without activity. 4. NPY2-36 was equipotent with NPY. Fragments as short as NPY 13-36 were active, but gradually lost activity with decreasing length. NPY 16-36 had no effect on extracellular field potentials, but still significantly inhibited excitatory postsynaptic potential amplitudes. Fragments shorter than NPY 16-36 had no measurable effect on synaptic transmission. 5. The presynaptic NPY receptor in hippocampal CA1 therefore shares an identical agonist profile with the presynaptic Y2 receptor at the peripheral sympathetic neuroeffector junction.

Neuropeptide Y receptor subtypes, Y1 and Y2

Heterogeneity among NPY (and PYY) receptors was first proposed on the basis of studies on sympathetic neuroeffector junctions, where NPY (and PYY) can exert three types of action: 1) a direct (e.g., vasoconstrictor) response; 2) a postjunctional potentiating effect on NE-evoked vasoconstriction; and 3) a prejunctional suppression of stimulated NE release; the two latter phenomena are probably reciprocal, since NE affect NPY mechanisms similarly. It was found that amidated C-terminal NPY (or PYY) fragments, e.g., NPY 13-36, could stimulate selectively prejunctional NPY/PYY receptors, which were termed Y2-receptors. Consequently, the postjunctional receptors which were activated poorly by NPY/PYY fragments, were termed Y1-receptors. Later work has indicated that the Y2-receptor may occur postjunctionally in selected sympathetic effector systems. The central nervous system appears to contain a mixture of Y1- and Y2-receptors as indicated by functional as well as binding studies. For instance, NPY and NPY 13-36 produced diametrically opposite effects on behavioral activity, indicating the action of the parent peptide on two distinct receptors. Cell lines, most importantly neuroblastomas, with exclusive populations of Y1- or Y2-receptors, have been characterized by binding and second messenger studies. In this work, selective agonists for the two receptor subtypes were used. Work of many investigators has formed the basis for subclassifying NPY/PYY effects being mediated by either Y1- or Y2-receptors. A preliminary subclassification based on effects of NPY, PYY, fragments and/or analogs is provided in Table 6. It is, however, to be expected that further receptor heterogeneity will be revealed in the future. It is argued that mast cells possess atypical NPY/PYY receptors. The histamine release associated with stimulation of the latter receptors may, at least in part, underlie the capacity of NPY as well as of short C-terminal fragments to reduce blood pressure. Fragments, such as NPY 22-36, appear to be relatively selective vasodepressor agents because of their weak vasopressor properties.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of the binding of [3H]proprionyl-neuropeptide Y to rat and human frontal cortical membranes

The binding characteristics of [3H]proprionyl-neuropeptide Y ([3H]proprionyl-NPY) were studied in frontal cortical membranes prepared from rat and human postmortem tissue. The specific binding of NPY decreased as the magnesium concentration increased from 1.05 to 10 mM. The binding was also influenced by the concentration of GTP in the buffer medium, with a resulting 45% decrease in NPY binding in the presence of 10(-6) M GTP. Using equilibrium binding studies, [3H]proprionyl-NPY was found to bind in both tissues with high affinity to a single class of receptors with a similar KD (0.035 nM). However, kinetic experiments in both tissues provided evidence for two components of [3H]proprionyl-NPY binding which may be related to receptor states. Competition binding experiments showed that peptide YY (PYY) was equal to NPY in its ability to displace [3H]proprionyl-NPY, whereas rat and human pancreatic polypeptide were without effect up to a concentration of 10(-6) M. This suggests that, whereas PYY and NPY may compete for the same receptor(s), the pancreatic polypeptides probably act on a separate population of receptors.

Neuropeptide Y: an overview of central distribution, functional aspects, and possible involvement in neuropsychiatric illnesses

Neuropeptide Y (NPY) was first discovered and characterized as a 36-amino-acid peptide neurotransmitter in 1982. It is widely distributed in the central nervous system, with particularly high concentrations within several limbic and cortical regions. A number of co-localizations with other neuromessengers such as noradrenaline, somatostatin, and gamma-aminobutyric acid have been demonstrated. A large number of physiological and pharmacological actions of NPY have been suggested. Recent clinical data also suggest the involvement of NPY in several neuropsychiatric illnesses, particularly in depressive and anxiety states. This article gives a comprehensive review of central distribution of NPY and its receptors, co-localizations and interactions with other neuromessengers, genetic aspects, pharmacological and physiological actions, influence on neuroendocrine functions, and possible involvement in various neuropsychiatric illnesses.

Neuropeptide Y (NPY) in human nasal mucosa

Neuropeptide Y (NPY), a potent vasoconstrictor peptide found in sympathetic neurons, was analyzed in human inferior turbinate nasal mucosal tissue. NPY content determined by radioimmunoassay was 3.13 +/- 0.79 pmol/g tissue (n = 6) in mucosa extracted with ethanol-acetic acid. NPY-immunoreactive nerves were found around small muscular arteries, arterioles, arteriovenous anastomoses, and as free fibers near arteriolar and venous vessels. They formed a plexus around the arterial vessels, and were also present between vascular smooth muscle cells. Few NPY fibers were present near glands or the epithelium. [125I]NPY binding sites were localized by autoradiography to small muscular arteries, arterioles, and a few venous sinusoids. In explant culture experiments, 4 microM NPY did not stimulate release of [3H]glucosamine-labeled glycoconjugates or lactoferrin (a product of serous cells) from nasal mucosal fragments. Degradation of NPY by a tissue homogenate was rapid (t1/2 = 13.5 +/- 2.3 min). The degradation was inhibited by thiorphan and phosphoramidon, inhibitors of neutral endopeptidase activity. NPY released from sympathetic neurons may play a role as a constrictor of arterial vessels and regulate vasomotor tone in the human nasal mucosa.

Effects of neuropeptide Y on alpha 1-and beta-adrenoceptor-stimulated second messenger systems in rat frontal cortex

Neuropeptide Y (NPY) (1 microM) significantly reduced the basal cAMP concentration in slices of rat frontal cortex. However, NPY (10(-9)-10(-6)M) did not alter the isoproterenol-stimulated (10(-9)-10(-5) M) accumulation of cAMP in the frontal cortical slices, showing that Y2 NPY receptors do not modulate the beta-adrenoceptor-stimulated adenylase cyclase activity. NPY (10(-8)-2.5 x 10(-5) M) was also demonstrated to stimulate inositol phosphate accumulation in rat frontal cortex slices in a dose-dependent manner. However, NPY (1 microM) did not potentiate the ability of phenylephrine (5 X 10(-8)-10(-4) M), an alpha 1-adrenoceptor agonist, to stimulate inositol phosphate hydrolysis. The combined effects of phenylephrine and NPY (1 microM) on inositol phosphate hydrolysis were additive, suggesting that the alpha 1-adrenoceptor and NPY Y1 receptor sites are located on different postsynaptic sites in rat frontal cortex. This study demonstrates the existence of both Y2 and Y1 NPY receptors in the rat frontal cortex based on second messenger systems, but there does not appear to be an interaction of NPY with either alpha 1- or beta-adrenoceptors.

Characterization of neuropeptide Y binding sites in rat cardiac ventricular membranes

Neuropeptide Y (NPY) binding sites in rat cardiac ventricular membranes have been characterized in detail. 125I-NPY bound to the membranes with high affinity. Binding was saturable, reversible and specific, and depended on time, pH and temperature. Analysis of the binding data obtained under optimal conditions, 2 hr, 18 degrees C and at pH 7.5, revealed the presence of low and high affinity binding sites. The high affinity binding sites had an apparent dissociation constant (Kd) of 0.38 nM and a binding capacity (Bmax) of 7.13 fmol/mg protein. The apparent Kd and Bmax for low affinity binding sites were 22.34 nM and 261.25 fmol/mg protein, respectively. Peptides unrelated to NPY did not compete with 125I-NPY for the binding sites even at 1 microM concentrations, whereas homologous peptides, peptide YY (PYY) and pancreatic polypeptide (PP), and NPY(13-36) inhibited 125I-NPY binding but with lower potency compared to NPY. 125I-NPY binding was sensitive to the nonhydrolyzable GTP analog, Gpp(NH)p, suggesting that the NPY receptor is coupled to the adenylate cyclase system. The ventricular membrane receptor characterized in this study may play an important role in mediating the physiological effects of NPY in the heart.

Neuropeptide Y binding and inhibition of cAMP accumulation in human neuroepithelioma cells

The specific binding of 125I-labeled neuropeptide Y (NPY) and the biological response to NPY receptor activation were measured in cultured human neuroepithelioma (SK-N-MC) cells. A single class of high-affinity binding sites [dissociation constant (KD) = 0.2 nM] was characterized both by equilibrium binding of 125I-NPY concentrations less than 1 nM and kinetically by the initial rates of 125I-NPY association and dissociation. Specific 125I-NPY binding was decreased in a concentration-dependent manner by inclusion of guanine nucleotides in the incubation medium. The existence of multiple affinity states or NPY receptor subtypes was suggested by 1) a Hill coefficient of less than 1.0 obtained when analyzing equilibrium binding with 125I-NPY concentrations greater than 1 nM, 2) biphasic dissociation of 125I-NPY, 3) an increase in the component of rapid dissociation and decrease in the component of slow dissociation when guanine nucleotides were present during dissociation of 125I-NPY, and 4) displacement of 125I-NPY by unlabeled peptide with a slope factor of 0.6. Exposure of intact cells to NPY caused a concentration-dependent pertussis toxin-sensitive inhibition of forskolin-stimulated cellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation [50% effective concentration (EC50) = 0.4 nM]. In contrast, NPY had no effect on cellular inositol phosphate content or protein kinase C activation. These results demonstrate that NPY binds specifically to a G protein-linked receptor that inhibits adenylate cyclase in SK-N-MC cells.

Interaction of 125I-neuropeptide Y with rat cardiac membranes

125I-Neuropeptide Y (NPY) bound specifically with high affinity to rat atrial and ventricular membranes. Scatchard analysis revealed the presence of single class of binding sites in both atrial and ventricular membranes. The apparent Kd and Bmax for atrial membranes were 0.63 nM and 70 fmol/mg protein, respectively; ventricular membranes had an apparent kd of 0.39 nM and a Bmax of 283 fmol/mg protein. NPY structural homologues peptide YY (PYY) and pancreatic polypeptide (PP) bound to the ventricular membranes NPY receptor, but with several fold lower potency compared to NPY. Binding of 125I-NPY to ventricular membranes was sensitive to guanosine triphosphate (GTP) suggesting that the NPY receptor is linked to adenylate cyclase system. The receptor characterized in this system may play a crucial role in mediating the cardiac effects of NPY.

Enhancement by neuropeptide Y (NPY) of the dihydropyridine-sensitive component of the response to alpha 1-adrenoceptor stimulation in rat isolated mesenteric arterioles

1. The mechanism by which neuropeptide Y (NPY) potentiates the vasoconstriction induced by alpha 1-adrenoceptor agonists was investigated in 3rd generation mesenteric arterioles of the rat. 2. At a maximally active concentration, nitrendipine (10(-6) M) displaced to the right the concentration-response curves to noradrenaline (pD2 decreased from 6.2 +/- 0.06 to 5.7 +/- 0.03) and phenylephrine (pD2 decreased from 5.6 +/- 0.03 to 5.3 +/- 0.03). Diltiazem (10(-5) M) also shifted to the right the concentration-response curve to phenylephrine (pD2 decreased from 6.0 +/- 0.06 to 5.5 +/- 0.04). In addition, the maximal response to phenylephrine was significantly decreased in the presence of either nitrendipine or diltiazem. 3. In the absence of a calcium channel blocking agent, NPY (100 nM) produced a leftward shift of the concentration-response curves to noradrenaline (pD2 increased from 6.2 +/- 0.06 to 6.5 +/- 0.05) and phenylephrine (pD2 increased from 5.6 +/- 0.03 to 6.0 +/- 0.06 and from 6.0 +/- 0.06 to 6.3 +/- 0.11). In the presence of either nitrendipine (10(-6) M) or diltiazem (10(-5) M), NPY (100 nM) did not alter the concentration-response curves to either noradrenaline or phenylephrine. 4. NPY was added to arterioles brought to the same level of tension (40% of the maximal contraction) either by phenylephrine alone (1.5 x 10(-6) M) or by a higher concentration of phenylephrine (3 x 10(-6) M) followed by the addition of prazosin (1.3 x 10(-9) M; a concentration at which it partially blocks alpha 1-adrenoceptors). In these conditions, the response to phenylephrine was completely abolished by nitrendipine (10-6 M) or by diltiazem (10-5M). Furthermore, NPY (10-1" to 10-7M) increased the arteriolar tension up to the maximal contractile capacity of the vessels with pD2 values of 8.6 + 0.02 and 8.7 + 0.01, in the absence and presence of prazosin, respectively. 5. Prazosin was replaced in the above protocol by other vasodilator agents acting through different mechanisms. Whether in the presence of 2 x 10-7M forskolin, 6 x 10-7M sodium nitroprusside (which stimulate adenylate cyclase or guanylate cyclase, respectively) or 2 x 10- 7M diltiazem (a concentration at which calcium entry is partially blocked), NPY enhanced phenylephrine-induced contraction to the maximum level with an identical potency (pD2 values of the peptide ranged from 8.3 to 8.7). 6. The results show that, in rat mesenteric arterioles, NPY potentiates only the calcium entry blockersensitive component of contraction induced by stimulation of alpha,-adrenoceptors. In addition, they provide evidence that the peptide counteracts with an equal potency the inhibitory effect of partial block of alpha,-adrenoceptors and of relaxing agents acting through different mechanisms. It is suggested that NPY enhances calcium entry induced by stimulation of alpha l-adrenoceptors in this tissue.

Neuropeptides in hypertension: role of neuropeptide Y and calcitonin gene related peptide

1. The effect of neuropeptide Y (NPY) on cardiovascular function at three levels of the noradrenergic axis where the peptide is known to co-exist with noradrenaline (NA) and or adrenaline (A) was studied in normotensive Sprague-Dawley (SD), Wistar-Kyoto (WKY) or spontaneously hypertensive rats (SHR). 2. In the perfused mesenteric arterial bed, NPY and the structurally similar peptide intestinal polypeptide (PYY) decreased the periarterial nerve stimulation induced release of NA and potentiated the increase in perfusion pressure to nerve stimulation or exogenously applied agonists (e.g. angiotensin, vasopressin, phenylephrine). In contrast to NPY and PYY, C-terminal NPY fragments inhibited NA release and produced a parallel decrease in perfusion pressure thus supporting the concept of Y1 (post) and Y2 (pre) NPY receptors. 3. In the mesenteric artery of SHR the prejunctional inhibitory effect of NPY was attenuated while the postjunctional response was enhanced. 4. Following intrathecal (Int) injection of NPY, there was a decrease in blood pressure, total peripheral resistance (predominantly by a decrease in mesenteric vascular resistance) and renal nerve activity. The depressor effect of Int NPY was attenuated in the SHR. 5. Unilateral injections of NPY into the posterior hypothalamic nucleus increased blood pressure, hindquarter and renal vascular resistance and renal nerve activity. The pressor effect was enhanced in the SHR. 6. Periarterial nerve stimulation of the perfused mesenteric artery produced a frequency dependent vasodilation in beds pretreated with guanethidine and precontracted with methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites in rat brain. Comparison with [125I]peptide YY receptor sites

The autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites was quantified in rat brain. The highest level of [125I]Bolton-Hunter neuropeptide Y binding sites was seen in the hippocampus (ventral stratum radiatum, CA3 subfield: 6029 +/- 250 fmol/g tissue). The distribution of these sites was clearly laminated, being particularly concentrated in the oriens layer (dorsal CA3 subfield: 2562 +/- 147 fmol/g tissue) and stratum radiatum (dorsal CA3 subfield: 2577 +/- 95 fmol/g tissue). Lower levels of sites were seen in the pyramidal cell layer (1708 +/- 105 fmol/g tissue) and the molecular layer (1155 +/- 116 fmol/g tissue). The cortical distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites was also laminated, being particularly enriched in superficial laminae (occipital cortex, layers I-II, 4038 +/- 148 fmol/g tissue; layers III-IV, 1392 +/- 97 fmol/g tissue and layers V-VI, 1522 +/- 138 fmol/g tissue). Other areas containing high amounts of sites included the anterior olfactory nuclei (ventral part, 4935 +/- 119 fmol/g tissue; lateral part, 4530 +/- 149 fmol/g tissue; dorsal part, 3378 +/- 140 fmol/g tissue and medial part, 2601 +/- 150 fmol/g tissue); anteromedial (5168 +/- 211 fmol/g tissue), medial (4611 +/- 107 fmol/g tissue) and lateral posterior thalamic nuclei (4465 +/- 189 fmol/g tissue); medial mammillary nucleus (5555 +/- 241 fmol/g tissue); medial geniculate nucleus (4747 +/- 56 fmol/g tissue); claustrum (4123 +/- 235 fmol/g tissue); posteromedial cortical amygdaloid nucleus (3524 +/- 138 fmol/g tissue), tenia tecta (2540 +/- 195 fmol/g tissue); lateral septum (1785 +/- 90 fmol/g tissue); suprachiasmatic hypothalamic nucleus (1604 +/- 115 fmol/g tissue), and substantia nigra, pars compacta (1846 +/- 142 fmol/g tissue) and pars lateralis (1750 +/- 165 fmol/g tissue). Areas moderately enriched with [125I]Bolton-Hunter neuropeptide Y binding sites included the zonal layer of the superior colliculus (1347 +/- 71 fmol/g tissue); anterior pretectal nucleus (1172 +/- 113 fmol/g tissue); ventral tegmental area (1090 +/- 97 fmol/g tissue); periventricular fibre system (1026 +/- 48 fmol/g tissue); core of nucleus accumbens (948 +/- 29 fmol/g tissue) and area postrema (799 +/- 87 fmol/g tissue). These results are discussed with regard to some of the suggested biological effects of neuropeptide Y in the central nervous system such as effects on learning, locomotion and circadian rhythms. Moreover, we also compared the distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites with that of [125I]peptide YY sites in rat brain. The resolution of the autoradiographic image is better with [125I]peptide YY most likely because of higher affinity and percentage of specific labelling.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y inhibits thyrotropin-releasing hormone-induced stimulation of melanotropin release from the intermediate lobe of the frog pituitary

Previous studies have shown that the release of melanotropin from frog neurointermediate lobes is under the control of two neuropeptides: thyrotropin-releasing hormone (TRH) stimulates, while neuropeptide Y (NPY) inhibits alpha-melanocyte-stimulating hormone (alpha-MSH) secretion from intact neurointermediate lobes in vitro. The aim of the present study was to investigate possible interactions between the two regulatory peptides at the pituitary level. Whole neurointermediate lobes or acutely dispersed pars intermedia cells from Rana ridibunda were perifused in vitro for 2 to 7.5 hr and the concentrations of alpha-MSH released into the effluent perifusate were monitored by radioimmunoassay. Administration of TRH (10(-7) M) or NPY (10(-7) M) to dispersed cells induced, respectively, marked stimulation or inhibition of alpha-MSH release. The effects of the two neuropeptides were similar to those observed using intact neurointermediate lobes, suggesting that TRH and NPY act directly on melanotropic cells. Perifused whole neurointermediate lobes were exposed to NPY (10(-8) to 3 x 10(-7) M) for 120 min and a single dose of TRH (10(-8) M) was administered during the prolonged infusion of NPY. Using this procedure, we observed a dose-dependent inhibition of TRH-evoked alpha-MSH release. These data support the concept that TRH and NPY act through a common intracellular pathway to regulate alpha-MSH release.

Pertussis toxin inhibits neuropeptide Y-induced feeding in rats

Neuropeptide Y (NPY) is the most powerful peptide drug stimulating feeding in rats. Rats with paraventricular hypothalamic (PVH) cannulae were used to investigate the mechanisms involved in NPY-induced feeding. Consistent with previous reports, injection of 2 micrograms of NPY into the PVH significantly increased the cumulative food intake over 1-, 2- and 4-hr periods. Ad lib feeding decreased significantly two days after pertussis toxin (PT) administration, but recovered to nearly normal levels on the fourth day. PT had no immediate effect on NPY-induced feeding; however, four days after PT was injected NPY (2 micrograms) did not increase the food intake compared to control. In vitro investigations showed that isoproterenol-stimulated adenylate cyclase activity in the hypothalamus of control rats was inhibited by NPY. In PT-treated rats, however, no inhibition of cAMP production was observed. These results suggest that cAMP may mediate NPY-induced feeding and that a PT-sensitive G protein may be involved in this signal transduction.