Structure-function analysis of stimulation of food intake by neuropeptide Y: effects of receptor agonists

Mechanisms for AgRP neuron-mediated regulation of appetitive behaviors in rodents

The obesity epidemic is a major health and economic burden facing both developed and developing countries worldwide. Interrogation of the central and peripheral mechanisms regulating ingestive behaviors have primarily focused on food intake, and in the process uncovered a detailed neuroanatomical framework controlling this behavior. However, these studies have largely ignored the behaviors that bring animals, including humans, in contact with food. It is therefore useful to dichotomize ingestive behaviors as appetitive (motivation to find and store food) and consummatory (consumption of food once found), and utilize an animal model that naturally displays these behaviors. Recent advances in genetics have facilitated the identification of several neuronal populations critical for regulating ingestive behaviors in mice, and novel functions of these neurons and neuropeptides in regulating appetitive behaviors in Siberian hamsters, a natural model of food foraging and food hoarding, have been identified. To this end, hypothalamic agouti-related protein/neuropeptide Y expressing neurons (AgRP neurons) have emerged as a critical regulator of ingestive behaviors. Recent studies by Dr. Timothy Bartness and others have identified several discrete mechanisms through which peripheral endocrine signals regulate AgRP neurons to control food foraging, food hoarding, and food intake. We review here recent advances in our understanding of the neuroendocrine control of ingestive behaviors in Siberian hamsters and other laboratory rodents, and identify novel mechanisms through which AgRP neurons mediate appetitive and consummatory behaviors.

Neuroendocrine Regulation of Food Intake in Polycystic Ovary Syndrome

Several peripheral and central signals are involved in the sophisticated regulation of food intake. Women with polycystic ovary syndrome (PCOS) are prone to consume a diet higher in saturated fat and foods with high glycemic index and show impaired appetite regulation and measures of satiety. As a consequence, obesity, mostly of the central type, is prevalent in the syndrome and worsens the endocrine and metabolic profile of the affected patients. This review article briefly analyzes the current knowledge about the neuroendocrine mechanisms underlying the interplay between feeding behavior, obesity, and reproductive abnormalities in PCOS.

Can Bayliss and Starling gut hormones cure a worldwide pandemic?

Bayliss and Starling first coined the term 'hormone' with reference to secretin, a substance they found that was produced by the gut, but released into the blood stream to act at a distance. The intestine is now known as the largest endocrine organ in the body, and it produces numerous hormones with a wide range of functions. These include controlling appetite and energy homeostasis. Obesity is one of the greatest health threats facing the world today. At present, the only successful treatment is surgery. Bariatric procedures such as the Roux-en-Y bypass work by elevating gut hormones that induce satiety. Significant research has gone into producing versions of these hormones that can be delivered therapeutically to treat obesity. This review looks at the role of gut hormones in obesity, and the development of gut hormone-derived obesity treatments.

Novel orexigenic pathway prostaglandin D2-NPY system--involvement in orally active orexigenic δ opioid peptide

Prostaglandin (PG) D(2), the most abundant PG in the central nervous system (CNS), is a bioactive lipid having various central actions including sleep induction, hypothermia and modulation of the pain response. We found that centrally administered PGD(2) stimulates food intake via the DP(1) among the two receptor subtypes for PGD(2) in mice. Hypothalamic mRNA expression of lipocalin-type PGD synthase (L-PGDS), which catalyzes production of PGD(2) from arachidonic acid via PGH(2) in the CNS, was increased after fasting. Central administration of antagonist and antisense ODN for the DP(1) receptor remarkably decreased food intake, body weight and fat mass. The orexigenic activity of PGD(2) was also blocked by an antagonist of Y(1) receptor for NPY, the most potent orexigenic peptide in the hypothalamus. Thus, the central PGD(2)-NPY system may play a critical role in food intake regulation under normal physiological conditions. We also found that orally active orexigenic peptide derived from food protein activates the PGD(2)-NPY system, downstream of δ opioid receptor. We revealed that the δ agonist peptide, rubiscolin-6-induced orexigenic activity was mediated by L-PGDS in the leptomeninges but not parenchyma using conditional knockout mice. In this review, we discuss the PGD(2)-NPY system itself, and orexigenic signals to activate it.

Paraventricular hypothalamic nucleus: axonal projections to the brainstem

The paraventricular hypothalamic nucleus (PVH) contains many neurons that innervate the brainstem, but information regarding their target sites remains incomplete. Here we labeled neurons in the rat PVH with an anterograde axonal tracer, Phaseolus vulgaris leucoagglutinin (PHAL), and studied their descending projections in reference to specific neuronal subpopulations throughout the brainstem. While many of their target sites were identified previously, numerous new observations were made. Major findings include: 1) In the midbrain, the PVH projects lightly to the ventral tegmental area, Edinger-Westphal nucleus, ventrolateral periaqueductal gray matter, reticular formation, pedunculopontine tegmental nucleus, and dorsal raphe nucleus. 2) In the dorsal pons, the PVH projects heavily to the pre-locus coeruleus, yet very little to the catecholamine neurons in the locus coeruleus, and selectively targets the viscerosensory subregions of the parabrachial nucleus. 3) In the ventral medulla, the superior salivatory nucleus, retrotrapezoid nucleus, compact and external formations of the nucleus ambiguous, A1 and caudal C1 catecholamine neurons, and caudal pressor area receive dense axonal projections, generally exceeding the PVH projection to the rostral C1 region. 4) The medial nucleus of the solitary tract (including A2 noradrenergic and aldosterone-sensitive neurons) receives the most extensive projections of the PVH, substantially more than the dorsal vagal nucleus or area postrema. Our findings suggest that the PVH may modulate a range of homeostatic functions, including cerebral and ocular blood flow, corneal and nasal hydration, ingestive behavior, sodium intake, and glucose metabolism, as well as cardiovascular, gastrointestinal, and respiratory activities.

Neuropeptide Y suppresses anorexigenic output from the ventromedial nucleus of the hypothalamus

Output from the hypothalamic ventromedial nucleus (VMN) is anorexigenic and is supported by the excitatory actions of leptin. The VMN is also highly sensitive to the orexigenic actions of Neuropeptide Y (NPY). We report that NPY robustly inhibits VMN neurons by hyperpolarizing them and decreasing their ability to fire action potentials. This action was mediated by Y(1) receptors coupled to the activation of GIRKs (G-protein-coupled inwardly rectifying potassium channels). Approximately 80% of VMN neurons expressing leptin receptors were sensitive to the actions of NPY, whereas 75% of NPY-sensitive neurons in VMN also responded to glucose by being uniformly inhibited by elevations in glucose. Interestingly, only approximately 36% of NPY-sensitive, leptin receptor b-expressing neurons were also glucosensitive. We suggest that NPY inhibits VMN neurons that are excited by leptin, thereby arresting the anorexigenic tone exerted by VMN neurons. The results further suggest a dynamic interplay between anorexigenic and orexigenic neuromodulators within the VMN to directly affect energy balance.

Alteration of ghrelin-neuropeptide Y network in obese patients with polycystic ovary syndrome: role of hyperinsulinism

OBJECTIVE

Insulin, ghrelin, neuropeptide Y (NPY) and leptin interact in the regulation of energy homeostasis. Most of these signals are altered in polycystic ovary syndrome (PCOS), which is characterized by a high prevalence of obesity. The present study was conducted to evaluate ghrelin-NPY and ghrelin-leptin interplays in relation to insulin secretion in obese PCOS subjects.

DESIGN

Pilot prospective study.

PATIENTS

Seven obese PCOS women and seven age-weight matched controls.

MEASUREMENTS

Hormonal measurements, oral glucose tolerance test (OGTT) and a ghrelin test (1 microg/kg i.v. bolus). PCOS patients repeated the clinical work-up after 4 months of metformin treatment (1500 mg/day orally).

RESULTS

At baseline, PCOS women showed a significantly higher insulinaemic response to the OGTT compared to controls (P < 0.05). In basal conditions, PCOS women exhibited lower NPY levels than controls (P < 0.01). Ghrelin injection markedly increased NPY in controls (P < 0.01), whereas PCOS women showed a deeply blunted NPY response to the stimulus (area under the curve--AUC-NPY: P < 0.01 vs. controls.). Metformin treatment induced a significant decrease in insulin levels (P < 0.01) and the concomitant recovery of NPY secretory capacity in response to ghrelin (AUC-NPY: P < 0.05 vs. baseline) in PCOS women. Leptin levels, which were similar in the two groups, were not modified by ghrelin injection; metformin did not affect this pattern.

CONCLUSION

Hyperinsulinaemia seems to play a pivotal role in the alteration of NPY response to ghrelin in obese PCOS women. This derangement could be implicated in the physiopatology of obesity in these patients.

Central prostaglandin D(2) stimulates food intake via the neuropeptide Y system in mice

We found that prostaglandin (PG) D(2), the most abundant PG in the central nervous system, stimulates food intake after intracerebroventricular administration in mice. The orexigenic effect of PGD(2) was mimicked by a selective agonist for the DP(1) receptor among two receptor subtypes for PGD(2), and abolished by its antagonist. Central administration of an antagonist or antisense oligodeoxynucleotide for the DP(1) receptor remarkably decreased food intake, body weight and fat mass. Hypothalamic mRNA levels of lipocalin-type PGD synthase were up-regulated after fasting. The orexigenic activity of PGD(2) was also abolished by an antagonist for neuropeptide Y (NPY) Y(1) receptor. Taken together, PGD(2) may stimulate food intake through central DP(1) receptor coupled to the NPY system.

Co-expression of neuropeptide Y Y1 and Y5 receptors results in heterodimerization and altered functional properties

Centrally administered neuropeptide Y (NPY) produces anxiolytic and orexigenic effects by interacting with Y1 and Y5 receptors that are colocalized in many brain regions. Therefore, we tested the hypothesis that co-expression of Y1 and Y5 receptors results in heterodimerization, altered pharmacological properties and altered desensitization. To accomplish this, the carboxyl-termini of Y1 and Y5 receptors were fused with Renilla luciferase and green fluorescent protein and the proximity of the tagged receptors assessed using bioluminescent resonance energy transfer. Under basal conditions, cotransfection of tagged Y1 receptor and Y5 produced a substantial dimerization signal that was unaffected by the endogenous, nonselective agonists, NPY and peptide YY (PYY). Selective Y5 agonists produced an increase in the dimerization signal while Y5 antagonists also produced a slight but significant increase. In the absence of agonists, selective antagonists decreased dimerization. In functional studies, Y5 agonists produced a greater inhibition of adenylyl cyclase activity in Y1/Y5 cells than cells expressing Y5 alone while NPY and PYY exhibited no difference. With PYY stimulation, the Y1 antagonist became inactive and the Y5 antagonist exhibited uncompetitive kinetics in the Y1/Y5 cell line. In confocal microscopy studies, Y1/Y5 co-expression resulted in increased Y5 signaling following PYY stimulation. Addition of both Y1 and Y5 receptor antagonists was required to significantly decrease PYY-induced internalization. Therefore, Y1/Y5 co-expression results in heterodimerization, altered agonist and antagonist responses and reduced internalization rate. These results may account for the complex pharmacology observed when assessing the responses to NPY and analogs in vivo.

Mechanism of dopamine mediated inhibition of neuropeptide Y release from pheochromocytoma cells (PC12 cells)

In rat pheochromocytoma (PC12) cells the dopamine D(2) receptor agonists apomorphine (APO) and n-propylnorapomorphine (NPA) produced a concentration dependent inhibition of K(+)-evoked neuropeptide Y release (NPY-ir). The effect of APO was blocked by the dopamine D(2)-receptor antagonist, eticlopride, but not the D(1)/D(3) or the D(4)/D(2) antagonists, SCH23390 or clozapine, respectively. The D(1)/D(5) receptor agonist, SKF38393 or the D(3) agonists PD128907 and 7-OH DPAT had no effect. Selective N and L-type voltage gated Ca(2+) channel blockers, omega-conotoxin GVIa (Ctx-GVIa) and nifedipine, respectively, produced a concentration dependent inhibition of NPY-ir release but were not additive with APO. The Ca(2+)/calmodulin-dependent protein kinase (CaM kinase) II inhibitor KN-62 produced a concentration-dependent inhibition of NPY-ir release but the combination of KN-62 and APO produced no further inhibition. PMA-mediated protein kinase C stimulation significantly increased both basal and K(+)-evoked release of NPY-ir, and in the presence of PMA APO had no inhibitory effect. The PKC antagonist, chelerythrine, inhibited K(+)-evoked NPY-ir release but was not additive with APO. Neither forskolin-mediated adenylate cyclase activation and the active cAMP analog Sp-cAMPS, nor the adenylate cyclase inhibitor SQ 22536, and the competitive inhibitor of cAMP-dependent protein kinases Rp-cAMPS, had any significant effect on K(+)-evoked NPY-ir release. This suggests the inhibitory effect of APO on K(+)-evoked release of NPY-ir from PC12 cells is most likely mediated through activation of dopamine D(2) receptors leading to direct inhibition of N and L-type voltage gated Ca(2+) channels, or indirect inhibition of PKC, both of which would reduce [Ca(2+)](i) and inactivate CaM kinase.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Region specific galanin receptor/neuropeptide Y Y1 receptor interactions in the tel- and diencephalon of the rat. Relevance for food consumption

The aim of this work was to determine the interactions between NPY and GAL receptor (GALR) subtypes in the hypothalamus and the amygdala using quantitative receptor autoradiography to analyze the binding characteristics of NPY-Y1 and Y2 receptor subtypes in the presence and absence of GAL. Food intake in satiated animals was evaluated after intraventricular co-injections of GAL and NPY-Y1 or Y2 agonists. The expression of c-Fos IR in both regions was also investigated. GAL decreases NPY-Y1 agonist binding in the arcuate nucleus by about 15% (p<0.01), but increases NPY-Y1 agonist binding in amygdala (18%) (p<0.01). These effects were blocked with the GAL antagonist M35. Y2-agonist binding was not modified by GAL. GAL blocked the food intake induced by the Y1 agonist (p<0.01). Co-injections of Y1 agonist and GAL also reduced the c-Fos expression induced by the Y1 agonist in the arcuate nucleus and the dorsomedial hypothalamic nucleus but increased c-Fos expression in amygdala. These results indicate the existence of antagonistic interactions between GALR and NPY-Y1 receptors in the hypothalamus and their functional relevance for food intake. In contrast, a facilitatory interaction between GALR and Y1 receptors exists in the amygdala which may be of relevance for fear related behaviour.

Alteration of NPY and Y1 receptor in dorsomedial and ventromedial areas of hypothalamus in anorectic tumor-bearing rats

Although previous studies have implicated NPY in the etiology of experimental cancer anorexia, the results have been difficult to interpret. Studies have suggested that although NPY level and message were decreased in the dorsomedial hypothalamic area (DMA), they were elevated in the ventromedial hypothalamic area (VMA). To better assess specific intra-area alterations of NPY, Y(1) receptor (Y(1) R), and agouti-related peptide (AgRP) in TB rats, we used radioimmunoassay, quantitative real-time RT-PCR, and immunohistochemistry. We found that NPY and AgRP mRNA were elevated significantly in whole hypothalamus of anorectic TB rats, while Y(1) R mRNA was decreased. Based on two replicates of four pooled samples each, both NPY and AgRP mRNA appeared to be elevated in the VMA of anorectic TB rats, while only AgRP exhibited a similar increase in the DMA. Levels of NPY were elevated in the VMA of both TB and pair-fed (PF) rats, but in the DMA only PF rats exhibited a significant NPY increase. NPY and Y(1) R immunohistochemistry revealed reduced NPY staining in PVN and ARC nucleus of TB and PF rats. Y(1) R immunostaining was also reduced in the ARC and PVN of TB rats, while PF rats exhibited elevated immunostaining in the PVN. These results continue to implicate dysfunction of NPY feeding systems in experimental cancer anorexia and suggest down-regulation of Y(1) R receptors as well as possible problems in NPY translation.

Regulation of hypothalamic NPY by diet and smoking

Appetite is regulated by a number of hypothalamic neuropeptides including neuropeptide Y (NPY), a powerful feeding stimulator that responds to feeding status, and drugs such as nicotine and cannabis. There is debate regarding the extent of the influence of obesity on hypothalamic NPY. We measured hypothalamic NPY in male Sprague-Dawley rats after short or long term exposure to cafeteria-style high fat diet (32% energy as fat) or laboratory chow (12% fat). Caloric intake and body weight were increased in the high fat diet group, and brown fat and white fat masses were significantly increased after 2 weeks. Hypothalamic NPY concentration was only significantly decreased after long term consumption of the high fat diet. Nicotine decreases food intake and body weight, with conflicting effects on hypothalamic NPY reported. Body weight, plasma hormones and brain NPY were investigated in male Balb/c mice exposed to cigarette smoke for 4 days, 4 and 12 weeks. Food intake was significantly decreased by smoke exposure (2.32+/-0.03g/24h versus 2.71+/-0.04g/24h in control mice (non-smoke exposed) at 12 weeks). Relative to control mice, smoke exposure led to greater weight loss, while pair-feeding the equivalent amount of chow caused an intermediate weight loss. Chronic smoke exposure, but not pair-feeding, was associated with decreased hypothalamic NPY concentration, suggesting an inhibitory effect of cigarette smoking on brain NPY levels. Thus, consumption of a high fat diet and smoke exposure reprogram hypothalamic NPY. Reduced NPY may contribute to the anorexic effect of smoke exposure.

Peripheral ghrelin deepens torpor bouts in mice through the arcuate nucleus neuropeptide Y signaling pathway

Many small mammals have the ability to enter torpor, characterized by a controlled drop in body temperature (Tb). We hypothesized that ghrelin would modulate torpor bouts, because torpor is induced by fasting in mice coincident with elevated circulating ghrelin. Female National Institutes of Health (NIH) Swiss mice were implanted with a Tb telemeter and housed at an ambient temperature (Ta) of 18 degrees C. On fasting, all mice entered a bout of torpor (minimum Tb: 23.8+/-2.0 degrees C). Peripheral ghrelin administration (100 microg) during fasting significantly deepened the bout of torpor (Tb minimum: 19.4+/-0.5 degrees C). When the arcuate nucleus (ARC) of the hypothalamus, a ghrelin receptor-rich region of the brain, was chemically ablated with monosodium glutamate (MSG), fasted mice failed to enter torpor (minimum Tb=31.6+/-0.6 degrees C). Furthermore, ghrelin administration had no effect on the Tb minimum of ARC-ablated mice (31.8+/-0.8 degrees C). Two major pathways that regulate food intake reside in the ARC, the anorexigenic alpha-melanocyte stimulating hormone (alpha-MSH) pathway and the orexigenic neuropeptide Y (NPY) signaling pathway. Both Ay mice, which have the alpha-MSH pathway blocked, and Npy-/-mice exhibited shallow, aborted torpor bouts in response to fasting (Tb minimum: 29.1+/-0.6 degrees C and 29.9+/-1.2 degrees C, respectively). Ghrelin deepened torpor in Ay mice (Tb minimum: 22.8+/-1.3 degrees C), but had no effect in Npy-/-mice (Tb minimum: 29.5+/-0.8 degrees C). Collectively, these data suggest that ghrelin's actions on torpor are mediated via NPY neurons within the ARC.

[Trp3, Arg5]-ghrelin(1-5) stimulates growth hormone secretion and food intake via growth hormone secretagogue (GHS) receptor

Ghrelin, a 28 amino acid peptide identified as an endogenous ligand for growth hormone secretagogue (GHS) receptor, stimulates food intake and growth hormone (GH) secretion. We designed low molecular weight peptides with affinity for the GHS receptor based on the primary structure of ghrelin. We found that [Trp3, Arg5]-ghrelin(1-5) (GSWFR), a novel pentapeptide composed of all L-amino acids, had affinity for the GHS receptor (IC50 = 10 microM). GSWFR stimulated GH secretion after intravenous or oral administration. Centrally administered GSWFR increased food intake in non-fasted mice. The orexigenic action of GSWFR was inhibited by a GHS receptor antagonist, [D-Lys3]-GH-releasing peptide-6, suggesting that GSWFR stimulated food intake through the GHS receptor. The orexigenic action of GSWFR was also inhibited by a neuropeptide Y (NPY) Y1 receptor antagonist, BIBO3304. These results suggest that the GSWFR-induced feeding is mediated by the NPY Y1 receptor.

Effect of enterostatin on the feeding responses to galanin and NPY

We have investigated the possibility that enterostatin may inhibit the intake of dietary fat by inhibiting either galanin or NPY-induced feeding pathways. Rats, adapted to either high fat (HF) or low fat-high carbohydrate (HC) diets and fitted with third ventricular cannulas were used to study the effects of intracerebroventricular (i.c.v.) enterostatin on i.c.v. NPY and galanin induced feeding responses in satiated rats. An equimolar dose of enterostatin (0.1 nmoles) inhibited, while a tenfold excess of enterostatin abolished the feeding response to galanin in rats adapted to a HF diet. The galanin stimulation of food intake was reduced in rats adapted to the HC diet and this response was less sensitive to inhibition by enterostatin. Enterostatin had no inhibitory effects on NPY-induced feeding in rats adapted to the HC diet and only a small inhibitory effect, at tenfold molar excess, in rats adapted to the HF diet. The ability of enterostatin to bind to galanin or NPY Y-1 receptors was investigated in ligand binding studies. Enterostatin failed to displace 125I-galanin or 125I-PYY from specific binding sites in rat forebrain homogenates or SK-N-MC cells respectively. The data provide support for the hypothesis that enterostatin specifically inhibits a galanin-responsive fat intake system, but indicate that this effect is not modulated by direct interaction with either galanin or NPY-Y1 receptors.

Modulation of neuropeptide Y expression in adult mice does not affect feeding

Despite numerous experiments showing that administration of neuropeptide Y (NPY) to rodents stimulates feeding and obesity, whereas acute interference with NPY signaling disrupts feeding and promotes weight loss, NPY-null mice have essentially normal body weight regulation. These conflicting observations suggest that chronic lack of NPY during development may lead to compensatory changes that normalize regulation of food intake and energy expenditure in the absence of NPY. To test this idea, we used gene targeting to introduce a doxycycline (Dox)-regulated cassette into the Npy locus, such that NPY would be expressed until the mice were given Dox, which blocks transcription. Compared with wild-type mice, adult mice bearing this construct expressed approximately 4-fold more Npy mRNA, which fell to approximately 20% of control values within 3 days after treatment with Dox. NPY protein also fell approximately 20-fold, but the half-life of approximately 5 days was surprisingly long. The biological effectiveness of these manipulations was demonstrated by showing that overexpression of NPY protected against kainate-induced seizures. Mice chronically overexpressing NPY had normal body weight, and administration of Dox to these mice did not suppress feeding. Furthermore, the refeeding response of these mice after a fast was normal. We conclude that, if there is compensation for changes in NPY levels, then it occurs within the time it takes for Dox treatment to deplete NPY levels. These observations suggest that pharmacological inhibition of NPY signaling is unlikely to have long-lasting effects on body weight.

Feeding effects of melanocortin ligands--a historical perspective

The process of energy homeostasis is a highly regulated process involving interacting signals between a variety of anorexigenic and orexigenic peptides, proteins and signaling molecules. The melanocortin system is an important component of this complex regulatory network. Involvement of the melanocortin pathway in the control of food intake and body weight regulation has been studied extensively in the past two decades. Previous studies that involve central administration of melanocortin molecules and examination of molecules that effect food intake in melanocortin knockout (KO) mice (MC3R, MC4R, POMC, AGRP and NPY) have been examined. In this review, we have summarized feeding studies that have resulted in the recognition of the melanocortin system as a major contributor to the complex neuroendocrine system regulating energy homeostasis.

Central neuropeptide Y induces proximal stomach relaxation via Y1 receptors in the dorsal vagal complex of the rat

Effects of neuropeptide Y (NPY) on motility of the proximal stomach was examined in anesthetized rats. Intragastric pressure was measured using a balloon situated in the proximal part of the stomach. Administration of NPY into the fourth ventricle induced relaxation of the proximal stomach in a dose-dependent manner. Administration of an Y1 receptor (Y1R) agonist [Leu31, Pro34]NPY induced a larger relaxation than NPY. The administration of an Y2 receptor agonist (NPY 13-36) did not induce significant changes in motility. Microinjections of [Leu31, Pro34]NPY into the caudal part of the dorsal vagal complex (DVC) induced relaxation of the proximal stomach. In contrast, similar injections into the intermediate part of the DVC increased IGP of the proximal stomach. Administration of NPY into the fourth ventricle did not induce relaxation after bilateral injections of the Y1R antagonist (1229U91) into the caudal DVC. These results indicate that NPY induces relaxation in the proximal stomach via Y1Rs situated in the DVC. Because bilateral vagotomy below the diaphragm abolished the relaxation induced by the administration of NPY into the fourth ventricle, relaxation induced by NPY is probably mediated by vagal preganglionic neurons. Intravenous injection of atropine methyl nitrate reduced relaxation induced by administration of NPY. Therefore, relaxation induced by NPY is likely mediated by peripheral cholinergic neurons.

New targets in the treatment of anorexia nervosa

The pathophysiology of anorexia nervosa (AN) is complex and involves alterations of serotonin, dopamine and histamine neurotransmitters. In addition, receptor activity is disturbed, presumably in response to the neurotransmitter changes. These alterations are reviewed in relation to symptomatology and outcome of AN. Neuropeptide and peripheral orexigenic and satiety peptide research is in its infancy but holds much promise to shed light on the pathophysiological mechanisms involved in this illness. Current drug therapies have not demonstrated the efficacy desired in the treatment of AN. Current therapies are reviewed and new drug targets are explored. Compounds that interact with serotonin, histamine and dopamine receptors may offer unique treatment opportunities. In the future, the manipulation of peptides may add to the therapeutic potential of pharmacotherapy.

Neuropeptide Y receptor antagonists in obesity

Neuropeptide Y (NPY) is a 36 amino acid amidated peptide with high sequence homology to the endocrine peptides, peptide YY (PYY) and pancreatic polypeptide (PP). They appear to interact with a family of receptors that possess high affinity for one or more of these peptides. Five members of the receptor family have been cloned, with several additional members postulated through pharmacological evidence. All are members of the seven transmembrane domain-G-protein coupled receptor family. The Y1 receptor is the best characterised, with several nonpeptide antagonists available. This receptor appears to mediate a constriction of the peripheral vasculature and the 'anxiolytic' effects of centrally administered NPY. Less is known about the other receptors in the family. The Y2 receptor is believed to be presynaptic and mediates a reduction in neurotransmitter release. The Y4 receptor appears to be the receptor for pancreatic polypeptide, with high amounts of mRNA for this receptor found in the periphery, but lower levels in the brain. The Y5 receptor is expressed in the hypothalamus and has been postulated to be the receptor which mediates the increased food consumption seen following centrally administered NPY. Finally, the Y6 receptor has been cloned in the mouse and other species, but does not appear to encode a functional gene product in humans. Several types of nonpeptide Y1 and a series of Y5 antagonists have been described in the patent literature, though these compounds have limitations that will confine their use to preclinical studies. Nevertheless, considerable progress has been made in understanding the role of NPY and its receptors in experimental obesity. The next step will be the discovery of potent and selective nonpeptide antagonists, to add further credence to the therapeutic potential.

Role of NPY and its receptor subtypes in foraging, food hoarding, and food intake by Siberian hamsters

Fasting has widespread physiological and behavioral effects such as increases in arcuate nucleus neuropeptide Y (NPY) gene expression in rodents, including Siberian hamsters. Fasting also stimulates foraging and food hoarding (appetitive ingestive behaviors) by Siberian hamsters but does relatively little to change food intake (consummatory ingestive behavior). Therefore, we tested the effects of third ventricular NPY Y1 ([Pro(34)]NPY) or Y5 ([D-Trp(34)]NPY) receptor agonists on these ingestive behaviors using a wheel running-based food delivery system coupled with simulated burrow housing. Siberian hamsters had 1) no running wheel access and free food, 2) running wheel access and free food, or 3) foraging requirements (10 or 50 revolutions/pellet). NPY (1.76 nmol) stimulated food intake only during the first 4 h postinjection ( approximately 200-1,000%) and mostly in hamsters with a foraging requirement. The Y1 receptor agonist markedly increased food hoarding (250-1,000%), increased foraging as well as wheel running per se, and had relatively little effect on food intake (<250%). Unlike NPY, the Y5 agonist significantly increased food intake, especially in foraging animals ( approximately 225-800%), marginally increased food hoarding (250-500%), and stimulated foraging and wheel running 4-24 h postinjection, with the distribution of earned pellets favoring eating versus hoarding across time. Across treatments, food hoarding predominated early postinjection, whereas food intake tended to do so later. Collectively, NPY stimulated both appetitive and consummatory ingestive behaviors in Siberian hamsters involving Y1/Y5 receptors, with food hoarding and foraging/wheel running (appetitive) more involved with Y1 receptors and food intake (consummatory) with Y5 receptors.

Physiologic estradiol levels enhance hypothalamic expression of the long form of the leptin receptor in intact rats

Estradiol is a potent hypophagic agent that reduces food intake and body weight without a concomitant fall in plasma leptin levels. We investigated whether the hypophagic effect of estradiol is mediated by stimulating POMC and/or inhibiting NPY neuronal pathways in the hypothalamus, which respectively inhibit and stimulate feeding. We examined hypothalamic gene expression of Ob-Rb, NPY, POMC, MC4-R, and AgRP in intact Wistar rats treated with estradiol for 48 hours. Food intake and body weight were reduced in estradiol-treated rats but fat mass was unchanged; plasma leptin and insulin levels were not significantly different from untreated, freely fed controls. In untreated rats that were pair-fed to match the estradiol-treated group, body weight was also reduced without changes in fat mass, although leptin and insulin levels decreased significantly. Ob-Rb expression was increased in both hypophagic groups despite serum leptin were only decreased in pair-fed animals, suggesting an estradiol-stimulating effect on Ob-Rb expression. No significant differences were found in POMC, AgRP, or MC4-R expression among any of the experimental groups. A significant but small decrease in NPY expression was also found in both hypophagic groups; this was explained by the combined effect of both surgery and reduced food intake. These results indicate that estradiol mediated hypophagia in intact rats could be brought about by an enhanced hypothalamic leptin sensitivity but is unlikely to be driven by changes in NPY or melanocortin system.

NPY and cohorts in regulating appetite, obesity and metabolic syndrome: beneficial effects of gene therapy

Neuropeptide Y is the most potent physiological appetite transducer known. The NPY network is the conductor of the hypothalamic appetite regulating orchestra in the arcuate nucleus-paraventricular nucleus (ARC-PVN) of the hypothalamus. NPY and cohorts, AgrP, GABA and adrenergic transmitters, initiate appetitive drive directly through Y1, Y5, GABAA and alpha1 receptors, co-expressed in the magnocellular PVN (mPVN) and ARC neurons and by simultaneously repressing anorexigenic melanocortin signaling in the ARC-PVN axis. The circadian and ultradian rhythmicities in NPY secretion imprint the daily circadian and episodic feeding patterns. Although a number of afferent hormonal signals from the periphery can directly modulate NPYergic signaling, the reciprocal circadian and ultradian rhythmicities of anorexigenic leptin from adipocytes and orexigenic ghrelin from stomach, encode a corresponding pattern of NPY discharge for daily meal patterning. Subtle and progressive derangements produced by environmental and genetic factors in this exquisitely intricate temporal relationship between the two opposing humoral signals and the NPY network promote hyperphagia and abnormal rate of weight gain culminating in obesity and attendant metabolic disorders. Newer insights at cellular and molecular levels demonstrate that a breakdown of the integrated circuit due both to high and low abundance of NPY at target sites, underlies hyperphagia and increased adiposity. Consequently, interruption of NPYergic signaling at a single locus with NPY receptor antagonists may not be the most efficacious therapy to suppress hyperphagia and obesity. Central leptin gene therapy in rodents has been shown to subjugate, i.e. bring under homeostatic control, NPYergic signaling and suppress the age-related and dietary obesity for extended periods and thus shows promise as a newer treatment modality to curb the pandemic of obesity and metabolic syndrome.

Brain insulin and feeding: a bi-directional communication

Insulin and specific insulin receptors are found widely distributed in the central nervous system (CNS) networks related in particular to energy homeostasis. This review highlights the complex regulatory loop between dietary nutrients, brain insulin and feeding. It is well documented that brain insulin has a negative, anorexigenic effect on food intake. At present, a specific role for brain insulin on cognitive functions related to feeding is emerging. The balance between orexigenic and anorexigenic pathways in the hypothalamus is crucial for the maintenance of energy homeostasis in animals and humans. The ingestion of nutrients triggers neurochemical events that signal nutrient and energy availability in the CNS, down regulate stimulators, activate anorexigenic factors, including brain insulin, and result in reduced eating. The effects of insulin in the CNS are under a multilevel control of food-intake peripherally and in the CNS, via the metabolic, endocrine and neural modifications induced by nutrients. Single meals as well as glucose and serotonin are able to regulate insulin release directly in the hypothalamus and may be of importance for its biological effects. Central mechanisms operating in glucose-induced insulin release show some analogy with the mechanisms operating in the pancreas. Leptin and melanocortins, peptides that down regulate food intake and are largely affected by nutrients, are highly interactive with insulin in the CNS probably via the neurotransmitter serotonin. In the hypothalamus, insulin and leptin share a common signaling pathway involved in food intake, namely the insulin receptor substrate, phosphatidylinositol 3-kinase pathway. Over or under-feeding, unbalanced single meals or diets, in particular diets enriched in fat, modify the amount of insulin actively transported into the brain, the release of brain insulin, the expression of insulin messenger RNA and potentially disrupt insulin signaling in the CNS. This impairment may result in disorders related to feeding behavior and energy homeostasis leading to profound dysregulations, obesity or diabetes.

Synthesis of new thiophene and benzo[b]thiophene hydrazide derivatives as human NPY Y5 antagonists

Neuropeptide Y is one of the most potent appetite stimulating hormones known. Novel thiophene and benzo[b]thiophene hydrazide derivatives were synthetized and evaluated biologically as NPY Y(1) and Y(5) receptor subtype antagonists. They were found to have nanomolar binding affinities for human NPY Y(5) receptor, obtaining the lead compound, trans-N-4-[N'-(thiophene-2-carbonyl)hydrazinocarbonyl]cyclohexylmethyl-4-bromobenzenesulfonamide, which binds with a 7.70 nM IC(50) to the hY(5) receptor.

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.

Neuropeptide Y: a physiological orexigen modulated by the feedback action of ghrelin and leptin

Neuropeptide Y (NPY), a 36-amino-acid neuropeptide is the most potent physiological appetite transducer known. Episodic NPY neurosecretion in hypothalamic target sites is temporally linked with onset of the daily feeding pattern. Upregulation of NPY signaling in the arcuate nucleus-paraventricular nucleus (ARC-PVN) neural axis is responsible for the hyperphagia evoked by dieting, fasting, hormonal and genetic factors, and disruption in intrahypothalamic signaling. Clusters of NPY-producing neurons in the ARC that coexpress gamma- amino butyric acid and agouti-related peptide, and those in the brain stem (BS) that coexpress catecholamines and galanin, participate in disparate manners to regulate appetitive behavior. NPY receptors, Y1, Y2, and Y5, expressed by various components of the NPY network, mediate NPY-induced feeding. Imbalance in NPY signaling due either to high or low abundance of NPY at target sites elicits hyperphagia leading to increased fat accretion and obesity. Recent studies show that intermittent, feedback action of opposing afferent hormonal signals-leptin from adipose tissue and ghrelin from stomach-regulate the episodic secretion of orexigenic NPY in the PVN-ARC. Apparently, the hypothalamic NPY network is the primary common pathway intimately involved in genesis of appetite- stimulating impulses.

Agonists for neuropeptide Y receptors Y1 and Y5 stimulate different phases of feeding in guinea pigs

1. The stimulatory effect of neuropeptide Y (NPY) on food intake is well established but the roles of the receptor subtypes Y(1) and Y(5) have been difficult to define. We have studied the effects of two novel Y(1)-preferring and two Y(5)-preferring agonists on feeding in guinea pigs. 2. The Y(1)-preferring receptor agonists [Arg(6),Pro(34)]pNPY and [Phe(7),Pro(34)]pNPY had high affinity for the Y(1) receptor (K(i) values 0.07 and 0.04 nM, respectively) and nanomolar affinity for the Y(5) receptor. Administration of either compound into the third brain ventricle increased food intake equally to NPY. 3. The Y(5) agonist [Ala(31),Aib(32)]pNPY displayed a moderate affinity for the Y(5) receptor (K(i) 7.42 nM) and a low affinity for Y(1) (K(i) 1.7 micro M). This compound had only a modest effect on feeding. 4. The other Y(5)-preferring peptide [cPP(1-7),NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP had a higher affinity at the Y(5) receptor (K(i) 1.32 nM) and also at the Y(1) receptor (K(i) 85 nM). It potently stimulated feeding: the food consumption after administration of this peptide was two-fold compared to NPY. 5. Our results support the view that both the receptor subtypes Y(1) and Y(5) are involved in the stimulation of feeding. As the action profiles of the Y(1) and Y(5) agonists on feeding parameters were different, it seems that they influence different phases of eating.

Pregnancy-induced hyperphagia is associated with increased gene expression of hypothalamic agouti-related peptide in rats

Pregnancy is characterized by an increase in food intake that, in turn, produce a positive energy balance in order to face the considerable metabolic demands associated with the challenge of reproduction. Since hypothalamus is a key brain region involved in many peripheral signals and neuronal pathways that control energy homeostasis and food intake, we investigated if during pregnancy the increase in food intake is mediated by stimulating orexigenic and/or inhibiting anorexigenic neural pathways. We examined hypothalamic gene expressions of Ob-Rb, NPY, AgRP, POMC, MC4-R, and preproorexins in pregnant Wistar rats at day 19 of gestation. Food intake and body weight were increased progressively during the pregnancy. Visceral fat mass depots and serum leptin levels were also increased when compared with virgin animals. No differences were found in mRNA expression of Ob-Rb, POMC, MC4-R, NPY or preproorexin between virgin and pregnant animals. However, pregnancy produced a selective increase in AgRP mRNA levels. These results indicate that the positive energy balance that occurred during pregnancy can hardly be explained by changes in Ob-Rb despite hyperleptinemia associated with pregnancy. The enhanced expression of AgRP suggests the involvement of this neuropeptide in mediating pregnancy-associated hyperphagia.

Effect of intracerebroventricular administration of the octadecaneuropeptide on the expression of pro-opiomelanocortin, neuropeptide Y and corticotropin-releasing hormone mRNAs in rat hypothalamus

Intracerebroventricular (i.c.v.) administration of the octadecaneuropeptide (diazepam-binding inhibitor [33-50]; ODN) exerts a potent anorexigenic effect in the rat. We studied the effect of ODN on three neuropeptides involved in feeding behaviour: the orexigenic peptide neuropeptide Y (NPY) and two anorexigenic peptides, corticotropin-releasing hormone (CRH) and the pro-opiomelanocortin (POMC)-derived peptide alpha-melanocyte-stimulating hormone. The effect of i.c.v. administration of ODN (0.1 microg/kg and 1 microg/kg) on mRNA expression of the peptides in male rat hypothalamus was evaluated by semiquantitative in situ hybridization. In the arcuate nucleus, NPY-expressing neurones were mostly found in the inner zone in close proximity of the third ventricle. ODN at the dose of 0.1 microg/kg induced a significant decrease of 17.4% in NPY mRNA expression, while the depressing effect was more marked (31.4%) with the highest dose of ODN (1 microg/kg). POMC-expressing neurones were more laterally located in the arcuate nucleus. Administration of ODN at 0.1 microg/kg and 1 microg/kg doses induced increases of 33.5% and 27.4% in POMC mRNA expression, respectively. Labelling obtained with the CRH cRNA probe was essentially distributed throughout the medial parvocellular area of the hypothalamic paraventricular nucleus. ODN, at doses of 0.1 and 1 microg/kg, resulted in 17.8% and 32.8% decreases in CRH mRNA expression, respectively. The present data suggest that ODN might exert its anorexigenic effect by increasing mRNA expression of POMC and decreasing mRNA expression of NPY in the arcuate nucleus.

Brain insulin: regulation, mechanisms of action and functions

1. While many questions remained unanswered, it is now well documented that, contrary to earlier views, insulin is an important neuromodulator, contributing to neurobiological processes, in particular energy homeostasis and cognition. A specific role on cognitive functions related to feeding is proposed, and it is suggested that brain insulin from different sources might be involved in the above vital functions in health and disease. 2. A molecule identical to pancreatic insulin, and specific insulin receptors, are found widely distributed in the central nervous system networks related to feeding, reproduction, or cognition. 3. The actions of insulin in the central nervous system may be under both multilevel and multifactorial controls. The amount of blood insulin reaching the brain, brain insulin stores and secretion, potential local biosynthesis and degradation of the peptide, and insulin receptors and signal transduction can be affected by metabolic factors induced by nutrients, hormones, neurotransmitters, and regulatory peptides, peripherally or in the central nervous system. 4. Glucose and serotonin regulate insulin directly in the hypothalamus and may be of importance for its biological effects. Central mechanisms regulating glucose-induced insulin secretion show some analogy with the mechanisms operating in the pancreas. 5. A cross-talk between insulin and leptin receptors has been observed in the brain, and a regulation of central insulin actions, potentially via serotonin modulation, by leptin, galanin, melancortins, and neuropeptide Y (NPY) is suggested. 6. A more complete knowledge of the biological role of insulin in brain function and dysfunction, and of the regulatory mechanisms involved in these processes, constitutes a real advancement in the understanding of the pathophysiology of metabolic and mental diseases and could lead to important medical benefits.

Decreased NPY innervation of the hypothalamic nuclei in rats with cancer anorexia

Whether the decrease in food intake that occurs at the onset of anorexia in tumor bearing (TB) rats is related to a change in the hypothalamic neuropeptide Y (NPY) system was tested by comparing NPY expression in sham operated Fischer Control and anorectic TB rats. Coronal cryocut sections of their fixed brain were processed by the peroxidase-antiperoxidase method with NPY polyclonal antibodies. NPY-immunoreactive fibers were widely distributed throughout the forebrain, but were most prominent in the hypothalamic paraventricular, suprachiasmatic, arcuate and periventricular nuclei. NPY-immunoreactive neurons were visualized in Control and anorectic TB rats in the preoptic region, the arcuate nucleus, and occasionally in the lateral hypothalamus. Semiquantitative image analysis showed a significant decrease in the NPY immunostaining in some hypothalamic nuclei of the anorectic TB rats, most prominently in the supraoptic nucleus, the parvocellular portion of the paraventricular nucleus, and, to a lesser extent, the suprachiasmatic and arcuate nuclei. No changes in NPY innervation were seen in the ventromedial nucleus and the lateral hypothalamus. The data support the hypothesis of an altered hypothalamic NPY system at the onset of anorexia in TB rats and also reveal the hypothalamic nuclei through which NPY influences food intake.

Immunolesion of norepinephrine and epinephrine afferents to medial hypothalamus alters basal and 2-deoxy-D-glucose-induced neuropeptide Y and agouti gene-related protein messenger ribonucleic acid expression in the arcuate nucleus

Neuropeptide Y (NPY) and agouti gene-related protein (AGRP) are orexigenic peptides of special importance for control of food intake. In situ hybridization studies have shown that NPY and AGRP mRNAs are increased in the arcuate nucleus of the hypothalamus (ARC) by glucoprivation. Other work has shown that glucoprivation stimulates food intake by activation of hindbrain glucoreceptor cells and requires the participation of rostrally projecting norepinephrine (NE) or epinephrine (E) neurons. Here we determine the role of hindbrain catecholamine afferents in glucoprivation-induced increase in ARC NPY and AGRP gene expression. The selective NE/E immunotoxin saporin-conjugated antidopamine-beta-hydroxylase (anti-dbetah) was microinjected into the medial hypothalamus and expression of AGRP and NPY mRNA was analyzed subsequently in the ARC under basal and glucoprivic conditions using (33)P-labeled in situ hybridization. Saporin-conjugated anti-dbetah virtually eliminated dbetah-immunoreactive terminals in the ARC without causing nonspecific damage. These lesions significantly increased basal but eliminated 2-deoxy-D-glucose-induced increases in AGRP and NPY mRNA expression. Results indicate that hindbrain catecholaminergic neurons contribute to basal NPY and AGRP gene expression and mediate the responsiveness of NPY and AGRP neurons to glucose deficit. Our results also suggest that catecholamine neurons couple potent orexigenic neural circuitry within the hypothalamus with hindbrain glucose sensors that monitor brain glucose supply.

Neuroendocrine regulation of eating behavior

The dual center hypothesis in the central control of energy balance originates from the first observations performed more than 5 decades ago with brain lesioning and stimulation experiments. On the basis of these studies the "satiety center" was located in the ventromedial hypothalamic nucleus, since lesions of this region caused overfeeding and excessive weight gain, while its electrical stimulation suppressed eating. On the contrary, lesioning or stimulation of the lateral hypothalamus elicited the opposite set of responses, thus leading to the conclusion that this area represented the "feeding center". The subsequent expansion of our knowledge of specific neuronal subpopulations involved in energy homeostasis has replaced the notion of specific "centers" controlling energy balance with that of discrete neuronal pathways fully integrated in a more complex neuronal network. The advancement of our knowledge on the anatomical structure and the function of the hypothalamic regions reveals the great complexity of this system. Given the aim of this review, we will focus on the major structures involved in the control of energy balance.

Regulation of neuropeptide Y in the rat amygdala following unilateral olfactory bulbectomy

While the mechanisms are not fully understood, olfactory bulbectomy (OBX) is a well-known rat model of depression and depression-related disorders such as anxiety and aggression. Alterations in neuropeptide Y (NPY) levels in the brain have been linked to depression and have been shown to be involved in the response to stress. This study explored the possible regulation of NPY immunoreactivity in specific regions of the amygdala 14 days after OBX in adult male Sprague-Dawley rats (n=6). Unilateral OBX and immunohistochemistry permitted comparisons of NPY in the ipsilateral amygdala with NPY in the contralateral (sham) amygdala. OBX resulted in significant increases (P<0.05) in NPY immunoreactivity in the anterior medial amygdala (threefold) and the posterior medial amygdala (2.5-fold). These regions receive projections from the accessory olfactory bulb (AOB). In contrast, the anterior and posterolateral cortical nuclei of the amygdala receive projections from the main olfactory bulb (MOB). NPY was not increased in these nuclei. These data show that not only does OBX increase NPY immunoreactivity in the amygdala, but also suggest that the AOB plays a prominent role in this regulation.

Novel potent antagonists of human neuropeptide Y Y5 receptor. Part 1: 2-oxobenzothiazolin-3-acetic acid derivatives

Novel NPY-Y5 antagonist FR73966 was discovered by screening of our in-house chemical library. The analogues were prepared by application of parallel synthesis techniques. Some of the resulting 2-oxobenzothiazolin-3-acetic acid derivatives exhibited nanomolar binding affinity for human NPY-Y5 receptors.

Novel potent antagonists of human neuropeptide Y-Y5 receptor. Part 4: tetrahydrodiazabenzazulene derivatives

Novel tetrahydrodiazabenzazulene derivatives, designed from the lead compound 1 discovered by screening of our in-house chemical library, were prepared and found to be potent neuropeptide Y-Y5 (NPY-Y5) receptor antagonists. The structure-activity relationships are described. Compounds 7 (FR240662) and 16 (FR252384) were especially attractive owing to their high affinities for the NPY-Y5 receptors, oral absorption and permeability to brain.

Novel potent antagonists of human neuropeptide Y Y5 receptors. Part 2: substituted benzo[a]cycloheptene derivatives

Novel benzo[a]cycloheptene derivatives were prepared for the purpose of searching new neuropeptide Y-Y5 (NPY-Y5) receptor antagonists. The structure-activity relationships are described and compound 2o (FR226928) showed the most potent affinity for Y5 receptor of all we prepared and was found to have higher potency and better selectivity for Y5 over Y1 receptor affinities when compared with the known lead compound 1.

Novel potent antagonists of human neuropeptide Y Y5 receptors. Part 3: 7-methoxy-1-hydroxy-1-substituted tetraline derivatives

As a part of our continuing research on NPY-Y5 receptor antagonists in the series of novel 6-methoxybenzo[a]cycloheptene derivatives, we discovered a novel skeleton, 7-methoxy-1-hydroxytetraline 7 which had been used as an intermediate, to be more suitable for increasing potencies leading to compound 3 (FR230481). Additionally, we discovered that the naphthalenesulfonamide moiety which was thought to be an essential pharmacophore could be replaced by the 5-chlorobenzothiazolin-3-acetic acid moiety to lead to potent compound 4 (FR233118). The structure-activity relationships on compounds 3,4 and their related derivatives are described. Unfortunately, although compounds 3 and 4 had very high affinities for Y5 receptors, their poor permeabilities to brain were shown by exo-vivo binding assays when orally administered.

Predominant role by CaM kinase in NPY Y(1) receptor signaling: involvement of CREB [corrected]

The role of Ca(2+)/cAMP-dependent signal transduction and transcription factor CREB in mediating NPY- Y(1) receptor function was investigated in SK-N-MC cells. The Y(1) receptor agonist, [Leu(31),Pro(34)]-NPY, inhibited forskolin-stimulated cAMP production which was insensitive to thapsigargin or the CaM kinase II inhibitor, KN-93. Although activation of the Y(1) receptor leads to an increase in CREB phosphorylation, [Leu(31),Pro(34)]-NPY inhibited CREB phosphorylation in KN-93-treated cells. SK-N-MC cells were also transfected with PathDetect cis-CRE and trans-CREB/trans-cFos reporter genes to monitor the role of Ca(2+)/cAMP signals, triggered by Y(1) receptor, on reporter gene activity. Treatment of the cis-CRE-luciferase expression vector-transfected cells with [Leu(31),Pro(34)]-NPY increased reporter gene activity by 2 fold through a KN-93 sensitive pathway. In contrast, the peptide inhibited forskolin-stimulated luciferase activity. Consistently, [Leu(31),Pro(34)]-NPY induced trans-CREB mediated luciferase activity through a CaM kinase dependent pathway, and inhibited forskolin-stimulated luciferase gene expression. However, no effect of the peptide was observed on trans-cFos- mediated luciferase activity. These findings suggest that the NPY Y(1) receptor induces the expression of CRE containing target genes through the CaM kinase-CREB pathway, and inhibits CRE containing genes when cellular cAMP levels are elevated.

The hypothalamus and the control of energy homeostasis: different circuits, different purposes

The hypothalamus regulates many aspects of energy homeostasis, adjusting both the drive to eat and the expenditure of energy in response to a wide range of nutritional and other signals. It is becoming clear that various neural circuits operate to different degrees and probably serve specific functions under particular conditions of altered feeding behaviour. This review will discuss this functional diversity by illustrating hypothalamic neurones that express neuropeptide Y (NPY), the melanocortin-4 receptor (MC4-R) and the orexins. NPY neurones in the arcuate nucleus (ARC) release NPY, a powerful inducer of feeding and obesity, in the paraventricular nucleus (PVN) and the lateral hypothalamic area (LHA). ARC-NPY neurones are inhibited by leptin and insulin and become overactive when levels of these hormones fall during undernutrition. They may function physiologically to protect against starvation. With disruption of the inhibitory leptin signals due to gene mutations, the NPY neurones are overactive, which contributes to hyperphagia and obesity in the ob/ob and db/db mice and fa/fa Zucker rat. The MC4-R is activated by alpha-melanocyte-stimulating hormone [alpha-MSH; a cleavage product of pro-opiomelanocortin (POMC), which is expressed in the other ARC neurones] and inhibits feeding. This effect is antagonised by agouti gene-related peptide (AGRP), which is coexpressed by the ARC-NPY neurones only. Activation of MC4-R, possibly mediated by blockade of AGRP release, appears to restrain overeating of a palatable diet. This response may be programmed by a transient rise in leptin soon after presentation of palatable food, and rats that fail to do this will overeat and become obese. Orexin-A and -B (corresponding to hypocretins 1 and 2) are expressed in specific LHA neurones. These have extensive reciprocal connections with many areas involved in appetite control, including the nucleus of the solitary tracts (NTS), which relays vagal afferent satiety signals from the viscera. Orexin neurones also have close anatomical connections with LHA glucose-sensitive neurones. Orexin-A induces acute feeding but does not cause obesity. Orexin neurones are stimulated by hypoglycaemia partly via the NTS and inhibited by food ingestion. These neurones may therefore be involved in the severe hyperphagia of hypoglycaemia and short-term control of feeding.

Oxyntomodulin inhibits food intake in the rat

Oxyntomodulin is derived from proglucagon processing in the intestine and the central nervous system. To date, no role in the central nervous system has been demonstrated. We report here that oxyntomodulin inhibits refeeding when injected intracerebroventricularly and into the hypothalamic paraventricular nucleus of 24-h fasted rats [intracerebroventricularly and into the paraventricular nucleus, 1 h, oxyntomodulin (1 nmol), 3.1 +/- 0.5 g; saline, 6.2 +/- 0.4 g; P < 0.005]. In addition, oxyntomodulin inhibits food intake in nonfasted rats injected at the onset of the dark phase (intracerebroventricularly, 1 h: oxyntomodulin, 3 nmol, 1.1 +/- 0.19 g vs. saline, 2.3 +/- 0.2 g; P < 0.05). This effect of oxyntomodulin on feeding is of a similar time course and magnitude as that of an equimolar dose of glucagon-like peptide-1. Other proglucagon-derived products investigated [glucagon, glicentin (intracerebroventricularly, 3 nmol; into the paraventricular nucleus, 1 nmol), and spacer peptide-1 (intracerebroventricularly and into the paraventricular nucleus, 3 nmol)] had no effect on feeding at any time point examined. The anorectic effect of oxyntomodulin (intracerebroventricularly, 3 nmol; into the paraventricular nucleus, 1 nmol) was blocked when it was coadministered with the glucagon-like peptide-1 receptor antagonist, exendin-(9-39) (intracerebroventricularly, 100 nmol; into the paraventricular nucleus, 10 nmol). However, oxyntomodulin has a lower affinity for the glucagon-like peptide-1 receptor compared with glucagon-like peptide-1 (IC(50): oxyntomodulin, 8.2 nM; glucagon-like peptide-1, 0.16 nM). One explanation for this is that there might be an oxyntomodulin receptor to which exendin-(9-39) can also bind and act as an antagonist.

Regulation of the Y1 neuropeptide Y receptor gene expression in PC12 cells

The Y1 receptor for neuropeptide Y (NPY-Y1) is constitutively expressed in PC12 cells. In this study, we examined the role of nerve growth factor (NGF), pituitary adenylyl cyclase activating polypeptide (PACAP) and dexamethasone on the expression of the gene encoding the rat NPY-Y1 receptor in PC12 cells. A fusion gene (pY1-Luc) was constructed where the reporter enzyme firefly luciferase was placed under the control of 700 bp of the promoter region of the rat NPY-Y1 receptor gene. This promoter region contains recognition consensus sequences for various transcription factors, including one activation protein-1 (AP-1) site, two cyclic AMP responsive element sites, one estrogen receptor element site and four glucocorticoid receptor element sites. NGF increased luciferase activity in a concentration dependent manner. This increase was inhibited by K-252a, a trk A receptor inhibitor, and calphostin C, a PKC inhibitor. PACAP-38 increased luciferase activity in a concentration dependent manner. This activation was inhibited by H-89. Dexamethasone increased transcription of NPY-Y1 gene in PC12 cells. These results indicate that differentiation of PC12 cells into endocrine-like phenotype by dexamethasone and into a neuronal-like phenotype by either NGF or PACAP-38 increases the transcriptional activity of the NPY-Y1 receptor gene in PC12 cells.

Feeding after fourth ventricular administration of neuropeptide Y receptor agonists in rats

Neuropeptide Y (NPY) and peptide YY (PYY) stimulate food intake after injection into the fourth cerebral ventricle, suggesting that NPY receptors in the hindbrain are targets for the stimulatory effect of these peptides on food intake. However, the NPY/PYY receptor subtype mediating the feeding response in the hindbrain is not known. To approach to this question we compared dose-effect of several NPY receptor agonists to stimulate food intake in freely-feeding rats 60- and 120-min after injection into the fourth cerebral ventricle. At the 120-min time point, PYY was 2- to 10-times as potent as NPY over the dose-response range and stimulated twice the total intake at the maximally effective dose (2-fold greater efficacy). NPY was 2-times as potent as the Y1, Y5 receptor agonist, [Leu(31)Pro(34)]NPY but acted with comparable efficacy. The Y5-, Y2-differentiating receptor agonist, NPY 2-36, was comparable in potency to PYY at low doses but equal in efficacy NPY and [Leu(31)Pro(34)]NPY. The Y2 receptor agonist, NPY 13-36, produced only a marginal effect on total food intake. The profile of agonist potency after fourth cerebral ventricle administration is similar to the profile obtained when these or related agonists are injected in the region of the hypothalamus. Agonists at both Y1 and Y5 receptors stimulated food intake with a rank order of potency that does not conclusively favor the exclusive involvement of a single known NPY receptor subtype. Thus it is possible that the ingestive effects of NPY and PYY are mediated by multiple or novel receptor subtypes in the hindbrain. And the relatively greater potency and efficacy of PYY raises the possibility that a novel PYY-preferring receptor in the hindbrain is involved in the stimulation of food intake.

Food intake inhibition and reduction in body weight gain in rats treated with GI264879A, a non-selective NPY-Y1 receptor antagonist

Neuropeptide Y has been proposed to play a major role in the hypothalamic regulation of feeding behavior through the activation of specific, central NPY receptor(s). In an effort to design small molecule antagonists of NPY receptors, we have synthesized a series of substituted dipeptides based on defined pharmacophores, previously identified by us and others as essential for the interaction with the peptide receptors. GI264879A behaves as a functional antagonist of Y1 receptors while displaying no binding selectivity for the different NPY receptor subtypes. We demonstrate here that administration of GI264879A to rats causes a significant decrease in food intake and body weight partly through a mechanism dependent on the integrity of the vagus nerve.