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

Peptide YY signaling in the lateral parabrachial nucleus increases food intake through the Y1 receptor

Although central PYY delivery potently increases food intake, the sites of action and mechanisms mediating these hyperphagic effects are not fully understood. The present studies investigate the contribution of lateral parabrachial nucleus (lPBN) PYY-Y receptor signaling to food intake control, as lPBN neurons express Y receptors and receive PYY fibers and are known to integrate circulating and visceral sensory signals to regulate energy balance. Immunohistochemical results identified a subpopulation of gigantocellular reticular nucleus PYY-producing neurons that project monosynaptically to the lPBN, providing an endogenous source of PYY to the lPBN. lPBN microinjection of PYY-(1-36) or PYY-(3-36) markedly increased food intake by increasing meal size. To determine which receptors mediate these behavioral results, we first performed quantitative real-time PCR to examine the relative levels of Y receptor expression in lPBN tissue. Gene expression analyses revealed that, while Y1, Y2, and Y5 receptors are each expressed in lPBN tissue, Y1 receptor mRNA is expressed at fivefold higher levels than the others. Furthermore, behavioral/pharmacological results demonstrated that the hyperphagic effects of PYY-(3-36) were eliminated by lPBN pretreatment with a selective Y1 receptor antagonist. Together, these results highlight the lPBN as a novel site of action for the intake-stimulatory effects of central PYY-Y1 receptor signaling.

Functional autoradiography of neuropeptide Y Y1 and Y2 receptor subtypes in rat brain using agonist stimulated [35S]GTPgammaS binding

Neuropeptide Y, one of the most abundant brain peptides, has been found to modulate several important biological functions via a family of G-protein coupled receptors. To investigate the localization of functional NPY receptor subtypes in the rat brain, we performed agonist-induced [35S]GTPgammaS autoradiography. The Y1/Y4/Y5 agonist Leu(31), Pro(34)-NPY increased [35S]GTPgammaS binding in several brain areas with a regional distribution consistent with that produced when labeling adjacent sections with [125I]-Leu(31), Pro(34)-PYY. The Y1 selective antagonist BIBP3226 antagonized the Leu(31), Pro(34)-NPY stimulated increase in [35S]GTPgammaS binding in all areas examined. The Y2 agonist C2-NPY stimulated [35S]GTPgamma binding in numerous brain areas with a regional distribution similar to the binding observed with [125I]-PYY 3-36. No increase in [35S]GTPgammaS binding above basal was observed in any brain area evaluated using Y4 and Y5 selective agonists. This study demonstrates abundant Y1 and Y2 receptor activation in the rat brain, while evidence for functional Y4 and Y5 receptors was not observed.

Peripheral signals in the control of satiety and hunger

PURPOSE OF REVIEW

Food intake is critical for survival and is a complex behavior with multiple levels of control. Short-term, meal-related signals arise from many sources including the gastrointestinal tract, the environment, and higher centers in the brain. As described in this review, inputs from the gastrointestinal tract can exert potent effects on meal initiation, meal termination, and meal frequency. The complex array of signals generated from the gastrointestinal system and from adipose tissue, which participate in the regulation of food intake, and specifically how these signals relate to satiety and hunger, is the focus of this review.

RECENT FINDINGS

Literature on the role of the well-studied gastrointestinal peptide, cholecystokinin, in satiety, in addition to its interaction with long-term adiposity signals in mediating food intake will be reviewed. In addition, literature on the gastrointestinal hormones glucagon-like-peptide 1, apolipoprotein A-IV and peptide YY, and how they may act to regulate satiety, is described. Finally, the newly discovered hormone, ghrelin, and how it relates to meal initiation and hunger is discussed.

SUMMARY

A better understanding of these systems and how they relate to body adiposity will prove to have important clinical applications. The available data suggest that interventions directed at multiple targets in the energy homeostasis system may be necessary to achieve and maintain weight loss.

Blockade of pancreatic polypeptide-sensitive neuropeptide Y (NPY) receptors by agonist peptides is prevented by modulators of sodium transport. Implications for receptor signaling and regulation

Ligand binding to rodent pancreatic polypeptide-responding neuropeptide Y (NPY) receptors (here termed PP/NPY receptors), or to cloned Y4 or Y5 receptors, is selectively inhibited by amiloride, peptide or alkylating modulators of sodium transport. The PP/NPY and Y4 receptors are also selectively blocked by human or rat pancreatic polypeptide (PP) and the blocking peptides are not dissociated by high concentrations of alkali chlorides (which restore most of the binding of subtype-selective agonists to Y1 and Y2 sites). The PP/NPY receptors could also be blocked by NPY and related full-length peptides, including Y1-selective agonists (IC50 300-400 pM). The cloned Y(4) receptors from three species are much less sensitive to NPY or PYY. The sensitivity of both the PP/NPY sites and the Y(4) sites to Y2-selective peptides is quite low. The ligand attachment to PP/NPY sites is also very sensitive to peptidic Y1 antagonist ((Cys31,NVal34NPY27-36))2, which however blocks these sites at much higher molarities. Blockade of PP/NPY and Y4 sites by agonist peptides can be largely prevented by N5-substituted amiloride modulators of Na+ transport, and by RFamide NRNFLRF.NH2, but not by Ca2+ channel blockers, or by inhibitors of K+ transport. Protection of both PP/NPY and Y4 sites against blockade by human or rat pancreatic polypeptide is also afforded by short N-terminally truncated NPY-related peptides. The above results are consistent with a stringent and selective activity regulation for rabbit PP/NPY receptor(s) that may serve to differentiate agonists and constrain signaling, and could involve transporter-like interactants.

Immunohistochemical localization of the neuropeptide Y Y1 receptor in rat central nervous system

The diverse effects of neuropeptide Y (NPY) are mediated through interaction with G-protein coupled receptors. Pharmacological analysis suggests the Y1 receptor mediates several of NPY's central and peripheral actions. We sought to determine the distribution of Y1 protein throughout the rat central nervous system by means of indirect immunofluorescence using the tyramide signal amplification method and a novel, amino terminally-directed Y1 antisera. This antisera was verified as specific for Y1 by solution-phase competition ELISA, Western blot and in situ blocking experiments. High concentrations of Y1 immunoreactivity were found in the claustrum, piriform cortex (superficial layer), arcuate hypothalamic nucleus, interpeduncular nucleus, paratrigeminal nucleus, and lamina II of the spinal trigeminal nucleus and entire spinal cord. Moderate levels of Y1 immunoreactivity were found the in the main olfactory bulb, dorsomedial part of suprachiasmatic nucleus, paraventricular hypothalamic nucleus, ventral nucleus of lateral lemniscus, pontine nuclei, mesencephalic trigeminal nucleus, external cuneate nucleus, area postrema, and nucleus tractus solitarius. Low levels of Y1 immunostaining were distributed widely throughout layers II-III of the cerebral cortex (i.e., orbital, cingulate, frontal, parietal, insular, and temporal regions), nucleus accumbens core, amygdalohippocampal and amygdalopiriform areas, dentate gyrus, CA1 and CA2 fields of hippocampus, principal and oral divisions of the spinal trigeminal nucleus, islands of Calleja and presubiculum. These findings are discussed with reference to previously reported receptor autoradiography, immunohistochemistry and mRNA analyses to further support the role of Y1 in NPY-mediated biology.

Expression of a novel neuropeptide Y receptor subtype involved in food intake: an in situ hybridization study of Y5 mRNA distribution in rat brain

Our group has reported on the cloning of a novel rat neuropeptide Y (NPY) receptor involved in NPY-induced food intake, the Y5 receptor. The distribution in rat brain of the mRNA encoding this receptor has been determined by in situ hybridization histochemistry, using radiolabeled oligonucleotide probes. Control experiments were carried out in cell lines transfected with either rat Y1 or rat Y5 cDNAs. With the exception of the cerebellum, only the antisense probes yielded hybridization signal in rat brain tissue sections. A number of brain regions contained hybridization signals indicative of Y5 mRNA localization. Chief among these were various hypothalamic nuclei, including the medial preoptic nucleus, the supraoptic nucleus, the paraventricular nucleus, and the lateral hypothalamus. Other regions with substantial hybridization signals included the midline thalamus, parts of the amygdala and hippocampus, and some midbrain and brain-stem nuclei. In general a low density of Y5 mRNA was observed in most cortical structures, with the exception of the cingulate and retrosplenial cortices, each of which contained a moderate abundance of Y5 hybridization signal. The distribution of this receptor mRNA is consistent with a role for the Y5 receptor in food intake and also suggests involvement in other processes mediated by NPY.

Multiple receptors for neuropeptide Y in the hippocampus: putative roles in seizures and cognition

Neuropeptide Y (NPY) is widely distributed throughout the central nervous system (CNS) and is one of the most conserved peptides in evolution, suggesting an important role in the regulation of basic physiological functions, including learning and memory. In addition, experimental studies have suggested that NPY, together with its receptors, may have a direct implication in several pathological disorders, including epilepsy/seizure. NPY-like immunoreactivity and NPY receptors have been shown to be present throughout the brain, but is concentrated in the hippocampus. The hippocampal formation has been repeatedly implicated in the modulation of cognition, as well as the pathogenesis of seizure. This review will concentrate on the hippocampal distribution of NPY, its receptors and the putative role played by this peptide in seizure, together with the regulation of cognitive function associated with learning and memory.