Comparative distribution of neuropeptide Y immunoreactivity and receptor autoradiography in rat forebrain

Application of a peptide bank from porcine brain in isolation of regulatory peptides

Over the past years, the introduction of biological assay systems, random peptide sequencing and orphan receptor screening has led to the isolation and identification of new regulatory peptides with potential clinical impact. We have developed a method for separating peptides into about 300 fractions from large amounts of porcine brain tissue. The preparation of this peptide bank consists of three steps including ultrafiltration followed by cation-exchange separation and reversed-phase chromatography. These fractions represent the peptide bank with desalted and lyophilized peptides from brain tissue. Molecular masses of the peptides in the fractions are determined by matrix-assisted laser desorption ionization MS and a mass data bank is subsequently generated. For systematic analysis of the peptides, a subsequent two-step purification procedure is followed by Edman sequencing resulting in the identification of different peptides. A survival assay with a neuronal cell line revealing the stimulatory and inhibitory activities is applied as a model to test the 300 fractions. This primary screen indicates that the biological activities of the extracted peptides are easily characterized and, moreover, can be related to the biochemical entities. We conclude that the established peptide bank is an efficient and useful tool for the isolation of regulatory brain peptides applying different purification strategies.

Cardiorespiratory responses to intracerebroventricular injection of neuropeptide Y in anaesthetised dogs

Cardiovascular and respiratory effects of intracerebroventricular (icv) administration of neuropeptide Y (NPY) and separate, preferential agonists for NPY Y1 and Y2 receptors were observed in anaesthetised dogs. Central injections of NPY resulted in significant cardiac slowing and decreases in arterial pressure. These cardiovascular effects were blocked by central injection of the NPY Y1- preferring antagonist 1229U91. Central injection of NPY did not have a significant effect on ventilation, but the NPY Y1 antagonist 1229U91 administered alone caused a significant increase in ventilation. The NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreased ventilation while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24--36 significantly increased it. A similar inverse relationship was seen with respect to blood pressure, with the NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreasing blood pressure, while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24-36 significantly increased it. These findings suggest a role for NPY Y1 receptors in pathways mediating decreases in ventilation and blood pressure, and for NPY Y2 receptors in those mediating increased ventilation and blood pressure.

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

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

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

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

Autoradiographic localization of receptors for neuropeptide Y (NPY) in the brain of broiler and leghorn chickens (Gallus domesticus)

Broiler and leghorn chickens show an extreme difference in ingestive and reproductive behavior. As neuropeptide Y (NPY) influences both behaviors the goal of this study was to elucidate the distribution, expression and affinity of NPY binding sites in broiler and leghorn chicken brain. By means of in vitro autoradiography, sections of chicken brains were incubated with 3H-NPY as tracer and NPY as displacer. Scatchard analysis revealed a curvilinear plot suggesting two subtypes of the NPY binding site in the chicken brain, a high affinity one (KD = 2-4 nM) and one with a lower affinity (KD = 18-24 nM). Binding sites for NPY are localized with high density in the different subdivisions of the neostriatum and the hyperstriatum, the cerebellum, the nucleus septalis lateralis and medialis, the nucleus ruber and the nucleus tractus solitarii. A lower density of NPY binding sites was found in the different subdivisions of the striatum, the nucleus mesencephalicus lateralis pars dorsalis, the paleostriatum, the archistriatum intermedium pars ventralis, the nucleus geniculatus lateralis, the nucleus taeniae, the locus ceruleus, the nucleus rotondus, the nucleus habenularis medialis, the nucleus dorsomedialis anterior (rostralis) thalami, the pituitary and the area of the hypothalamus with its nuclei such as the nucleus paraventricularis magnocellularis and the nucleus preopticus medialis. Comparison of the localization of NPY binding sites in the brains of broilers and leghorns showed no differences but the density of both receptor types is two to three times higher in broilers than in leghorns.

Central nervous system pharmacology of neuropeptide Y

Neuropeptide Y (NPY) is a 36-amino acid peptide belonging to the pancreatic polypeptide family that has marked and diverse biological activity across species. NPY originally was isolated from mammalian brain tissue somewhat more than 10 years ago and, since that time, has been the subject of numerous scientific publications. NPY and its proposed three receptors (Y1, Y2 and Y3) are relatively abundant in and uniquely distributed throughout the brain and spinal cord. This review will highlight the results from a number of research-oriented studies that have examined how NPY is involved in CNS function and behavior, and how these studies may relate to the possible development of medicines, either NPY-like agonists or antagonists, directed towards the treatment of disorders such as anxiety, pain, hypertension, schizophrenia, memory dysfunction, abnormal eating behavior and depression.

Regulation of adenylate cyclase by galanin, neuropeptide Y, secretin and vasoactive intestinal polypeptide in rat frontal cortex, hippocampus and hypothalamus

This study characterizes regional regulation of adenylate cyclase by galanin, neuropeptide Y (NPY), secretin and vasoactive intestinal peptide (VIP) in rat brain frontal cortex, hypothalamus and hippocampus. In our experimental system, galanin caused small detectable activation (10-20%) of basal adenylate cyclase activity in frontal cortex and hippocampus but had no effect on basal adenylate cyclase activity in hypothalamus. Galanin inhibited forskolin-stimulated adenylate cyclase in all three brain regions-hypothalamus, hippocampus and frontal cortex by 54.5%, 44.3% and 25.7%, respectively. NPY reduced basal and forskolin-stimulated enzyme activities by 35% only in frontal cortex, but not in the other two brain areas. Secretin had no effect in frontal cortex but caused similar adenylate cyclase activation in hypothalamus and hippocampus. VIP had a stimulatory effect of 32.8% and 32.4% in frontal cortex and hippocampus, respectively. The results indicate regional differences in adenylate cyclase modulation by the four peptides and reveal interesting relations in comparison with peptide and receptor densities in the three investigated brain regions.

In vivo central actions of NPY(1-30), an N-terminal fragment of neuropeptide Y

The purpose of the present study was to examine the possible central actions of a N-terminal fragment of NPY, NPY(1-30), on five measures typically influenced by the native peptide: decreased spontaneous activity, enhancement of muscle tone (increased grasping response), catalepsy, hypothermia, and stimulation of food intake. The peptides were administered ICV in doses ranging from 2.5 to 160 micrograms (0.75-48 nmol) and their effects on the three motor variables as well as thermal and feeding responses were evaluated and compared. Globally, results indicate that, similarly to NPY, the N-terminal fragment NPY(1-30), decreased spontaneous activity and induced hypothermia. However, the fragment displayed approximately half of the potency of NPY for producing these effects. On the other hand, contrary to NPY, NPY(1-30) did not affect muscle tone or food consumption and did not induced catalepsy in animals. These results demonstrate for the first time central actions of a N-terminal fragment of NPY and lend further support to the hypothesis that the receptors mediating the central actions of NPY are pharmacologically different.

[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.

Neurobehavioral profile of neuropeptide Y

In order to better delineate the profile of central actions of neuropeptide Y (NPY), the effects of intracerebroventricular administration of several doses (2.5-20 micrograms) of the peptide on spontaneous activity, muscular tone, body temperature, food intake, nociception and cataleptic manifestations were examined in rats. Results indicate that, starting at 5 micrograms. NPY significantly decreased motor activity of animals in a dose-related fashion. NPY also significantly lowered body temperature of animals. The hypothermic effect was obtained following injections of 10.0 and 20.0 micrograms of the peptide. Administration of the same two doses of NPY resulted in significant increases in food intake, muscular tone and induced a significant catalepsy in animals. On the other hand, nociceptive response times of animals in the hot plate test were not affected by any of the NPY doses tested. Together, these results indicate that the profile of NPY's neurobehavioral actions is more complex than previously reported and suggest that the peptide might be implicated functionally in a variety of neurophysiological processes.

In vivo structure activity study supports the existence of heterogeneous neuropeptide Y receptors

The purpose of the present study was to examine relationships between structure and activity of the peptide for stimulating food intake and decreasing body temperature in rats. Various NPY fragments and structural analogs were administered intracerebroventricularly in several doses (2.5-160 micrograms) and their effects on feeding and body temperature evaluated and compared. Globally, results indicate that the C-terminal portion of the peptide is responsible for both central effects of NPY. However, the distributions of potencies of the various fragments and analogs for increasing food intake and decreasing body temperature were clearly different. The most salient difference was that deletion of the N-terminal residue Tyr1 of NPY resulted in a five-fold loss in the potency for decreasing rectal temperature, whereas NPY2-36 was relatively more potent than the native peptide to increase food intake in animals. These results suggest that the purported receptors mediating the effect of NPY on food intake are different than those responsible for the influence of the peptide on body temperature. The results of the present in vivo work are discussed in relation to those obtained in previous in vitro studies.

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)

Comparison of [125I]Bolton-Hunter neuropeptide Y binding sites in the forebrain of various mammalian species

The forebrain distribution of [125I]Bolton-Hunter (BH) neuropeptide Y (NPY) binding sites was compared in 4 mammalian species including rat, hamster, guinea pig and monkey. In all species studied, high densities of [125I]BH NPY binding sites were observed in the hippocampus. In this structure, [125I]BH NPY binding sites were distributed in a laminar fashion, with high densities seen in the oriens layer and stratum radiatum. However, species differences were seen in certain brain areas such as striatum, septum, thalamus and hypothalamus. These differences should be taken into account when studying central effects of neuropeptide Y.