Cardiovascular response, feeding behavior and locomotor activity in mice lacking the NPY Y1 receptor

Cardiac function in neuropeptide Y Y4 receptor-knockout mice

Autonomic control of cardiovascular function in neuropeptide Y (NPY) Y4 receptor-knockout mice was investigated using pancreatic polypeptide (PP), NPY and specific agonists and antagonists for other NPY receptors well characterised in cardiovascular function. Y4 receptor-knockout mice, anaesthetised with sodium pentobarbitone, displayed slower heart rate, indicated by a higher pulse interval and lower blood pressure compared to control mice. After vagus nerves were cut heart rate increased but was still significantly slower than in control mice. PP had no effect on blood pressure or cardiac vagal activity in either group of mice, which was consistent with earlier studies in other species. Injection of NPY evoked an increase in blood pressure but the response was significantly reduced in Y4 receptor-knockout mice compared to the controls. The reduction in pressor activity was not Y1 mediated as the selective Y1 antagonist, BIBP 3226, was effective in blocking NPY pressor activity in knockout mice. In addition, cardiac vagal inhibitory activity evoked by low doses of NPY was also reduced when compared to control responses. As N-acetyl [Leu(28, 31)] NPY 24-36 inhibited vagal activity dose dependently in both groups of mice with no difference in response at any dose, it is unlikely that this effect also is receptor mediated. We propose that the reduced vasoconstrictor and vagal inhibitory activity evoked by NPY in Y4 receptor-knockout mice is due to a lack of adrenergic tone bought about by a proposed reduction in sympathetic activity, possibly resulting from altered NPY activity secondarily affecting adrenergic transmission. We conclude that Y4 receptor deletion disrupts autonomic balance within the cardiovascular system.

Marked neuropeptide Y-induced contractions via NPY-Y1 receptor and its desensitization in rat veins

The aim of this study was to investigate neuropeptide Y (NPY)-induced vasoconstrictions in rat blood vessels and which NPY receptor subtype is involved in vasoconstrictions. NPY produced marked contractions in rat common jugular, brachial, portal, femoral and tail veins, and vena cava inferior, whereas it produced little or no contractions in rat common carotid, brachial, femoral and tail arteries, and thoracic and abdominal aortae. The maximal NPY-induced contractions were larger than maximal phenylephrine (PE)-induced contractions in the veins. These NPY-induced contractions were blocked by the Y1 antagonists, SRL-21, and BIBP3226 but not by the Y5 antagonist, L-152804. A Y2 agonist, NPY (13-36), did not produce contractions. RT-PCR showed that NPY-Y1 was the only receptor subtype in the veins indicating that NPY-induced contractions are mediated through the Y1 receptor. Pretreatment with NPY showed a rapid and long-lasting desensitization of these contractions. The marked NPY-induced contractions and its desensitization in the veins suggest the physiological relevance of NPY in the venous circulation.

Y2 receptor deletion attenuates the type 2 diabetic syndrome of ob/ob mice

Hypothalamic neuropeptide Y (NPY) is implicated in the regulation of a variety of physiological functions, notably energy homeostasis and reproduction. Chronically elevated NPY levels in the hypothalamus, as in genetically obese ob/ob mice, are associated with obesity, a syndrome of type 2 diabetes, and infertility. However, it is not known which of the five cloned Y receptors mediate these effects. Here, we show that crossing the Y2 receptor knockout mouse (Y2(-/-)) onto the ob/ob background attenuates the increased adiposity, hyperinsulinemia, hyperglycemia, and increased hypothalamo-pituitary-adrenal (HPA) axis activity of ob/ob mice. Compared with lean controls, ob/ob mice had elevated expression of NPY and agouti-related protein (AgRP) mRNA in the arcuate nucleus and decreased expression of proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) mRNA. Y2 deletion in ob/ob mice significantly increased the hypothalamic POMC mRNA expression, with no effect on NPY, AgRP, or CART expression. [Y2(-/-)ob/ob] mice were no different from ob/ob littermates with respect to food intake and body weight, and Y2 receptor deficiency had no beneficial effect on the infertility or the reduced hypothalamo-pituitary-gonadotropic function of ob/ob mice. These data demonstrate that Y2 receptors mediate the obese type 2 diabetes phenotype of ob/ob mice, possibly via alterations in melanocortin tonus in the arcuate nucleus and/or effects on the HPA axis.

Hypothalamic regulation of energy homeostasis

The co-ordinated regulation of food intake and energy expenditure takes place in the hypothalamic regions of the brain. Current understanding of the systems involved in this regulation suggests that, in the hypothalamus, there are two major groups of neuropeptides involved in orexigenic and anorexic processes. The orexigenic neuropeptides are neuropeptide Y (NPY) and agouti-related peptide (AgRP) and the anorexic neuropeptides are alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine and amphetamine-related transcript (CART). Theneurons expressing these neuropeptides interact with each other and with signals from the periphery (such as leptin, insulin, ghrelin and glucocorticoids) to regulate feeding behaviour, energy expenditure and various endocrine axes. Although direct evidence is limited, there are examples of genetic obesity in humans which suggest that the balance between orexigenic and anorexic pathways in the hypothalamus is also pivotally important in the maintenance of energy homeostasis in humans.

Neuropeptide Y and its receptors as potential therapeutic drug targets

Neuropeptide Y (NPY) is a 36-amino-acid peptide that exhibits a large number of physiological activities in the central and peripheral nervous systems. NPY mediates its effects through the activation of six G-protein-coupled receptor subtypes named Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Evidence suggests that NPY is involved in the pathophysiology of several disorders, such as the control of food intake, metabolic disorders, anxiety, seizures, memory, circadian rhythm, drug addiction, pain, cardiovascular diseases, rhinitis, and endothelial cell dysfunctions. The synthesis of agonists and antagonists for these receptors could be useful to treat several of these diseases.

The neuropeptide Y receptors, Y1 and Y2, are transiently and differentially expressed in the developing cerebellum

Neuropeptide Y (NPY), a peptide widely expressed in the brain, acts through the protein G-coupled receptors Y1, Y2 and Y5. In the adult rat, this peptide modulates many important functions such as the control of energy balance and anxiety. Its involvement in brain development has been less investigated. In the present study, we have analysed the expression of Y1 and Y2 in the developing rat cerebellum using RNase protection assay. Both receptors were detected in the embryo but at very low levels. Their expression then increased, reaching a peak at postnatal day 10. At later stages, we observed a down-regulation of both Y1 and Y2 mRNA levels. This pattern of expression was delayed in hypothyroid rats, suggesting that the regulation of NPY receptors was strictly related to cerebellar development stages. In situ hybridisation and immunohistochemistry analyses revealed specific localisations of the receptors. Y1 was exclusively expressed by Purkinje cells while Y2 was found mostly in granule cells of the internal granule cell layer. These observations argue in favour of specific roles for Y1 and Y2 in the developing cerebellum. In an initial attempt to characterise these roles, we have determined the number of apoptotic cells in the developing cerebellum of Y2(-/-) mice and analysed the effects of NPY on primary cultures of cerebellar granule neurones. Our data showed that the absence of Y2 did not increase cell death in the internal granule cell layer of the developing cerebellum, and that NPY by itself did not prevent the death of differentiated granule cells cultured in serum-free medium. However, we found that co-treatment of the cells by NPY and neuromediators such as NMDA or GABA strongly promoted the survival of granule neurones. Taken together, these observations suggest an involvement of the NPY receptors in cerebellar ontogenesis that remains to be demonstrated in vivo.

Metabolic lessons from genetically lean mice

Different types of lean mice have been produced by genetic manipulation. Leanness can result from deficiency of stored energy or a lack of adipocytes to store the lipid. Mice lacking functional adipocytes are usually insulin resistant and have fatty livers, and elevated circulating triglyceride levels. Insulin resistance may result from the lack of adipocyte hormones (such as leptin) and increased metabolite (such as triglyceride) levels in nonadipose tissue. Mice with depleted adipocyte triglyceride levels typically are insulin sensitive and have normal or low liver and circulating triglycerides. Mechanisms to produce depleted adipocytes include increased energy expenditure by peripheral tissues, peripheral mechanisms to decrease food intake, and altered central regulation of these processes.

Critical role for GALR1 galanin receptor in galanin regulation of neuroendocrine function and seizure activity

The GALR1 galanin receptor is expressed at high levels within the central nervous system. To determine which specific actions of galanin are mediated by GALR1, we have developed mice with an insertional inactivating mutation within the gene encoding GALR1 (Galr1). Homozygous Galr1-/- mice are viable and capable of breeding. They exhibit no significant difference in growth rate relative to Galr1+/+ controls but have reduced circulating levels of insulin-like growth factor-I (IGF-I) and exhibit spontaneous tonic-clonic seizures. The phenotype of these mice identifies a critical role for GALR1 in neuroendocrine regulation and in mediating the anti-seizure activity of galanin.

Neuropeptide Y (NPY) and depression: from animal studies to the human condition

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. In addition, both pre-clinical and clinical evidence have suggested that NPY, together with its receptors, may have a direct implication in several psychiatric disorders, including depression and related illnesses. NPY-like immunoreactivity and NPY receptors are expressed throughout the brain, with varying concentrations being found throughout the limbic system. Such brain structures have been repeatedly implicated in the modulation of emotional processing, as well as in the pathogenesis of depressive disorders. This review will concentrate on the distribution of NPY, its receptors, and the putative role played by this peptide in depressive illness based on both pre-clinical and clinical evidence.

Effects of a high-fat diet and strain on hypothalamic gene expression in rats

OBJECTIVE

This study was designed to investigate whether dietary fat and genetic background might differentially alter the expression of hypothalamic genes involved in food intake.

RESEARCH METHODS AND PROCEDURES

Three-month-old Osborne-Mendel (OM) and S5B/Pl rats were fed either a high-fat or a low-fat diet for 14 days. mRNA for neuropeptide Y (NPY), corticotrophin-releasing hormone, NPY Y-1 receptor and Y-5 receptor, and serotonin 2c (5-HT2c) receptors were measured using Northern blotting or ribonuclease protection assays.

RESULTS

OM rats showed an increased expression of NPY and corticotrophin-releasing hormone compared with S5B/Pl rats. The expression of NPY-Y1 and -Y5 receptor mRNA was significantly higher in the hypothalamus of OM rats compared with S5B/Pl rats. The expression of 5HT-2c receptor mRNA was significantly reduced in both strains of rats eating a high-fat diet when compared with the animals eating the low-fat diet.

DISCUSSION

These data suggest that over activity of the NPY system may contribute to the development of obesity in OM rats and that expression of the 5HT-2c receptor gene may be modulated by dietary fat.

New pharmacological tools for obesity

Obesity is a multi-factorial, chronic disorder that has reached epidemic proportions in most industrialized countries and is threatening to become a global epidemic. Obese patients are at a higher risk from coronary artery disease, hypertension, hyperlipidemia, diabetes mellitus, certain cancers, cerebrovascular accidents, osteoarthritis, restrictive pulmonary disease, and sleep apnea. Obesity is a particularly challenging clinical condition to treat, because of its complex pathophysiological basis. Indeed, body weight represents the integration of many biological and environmental components. Efforts to develop innovative anti-obesity drugs have been recently intensified. In broad terms, researchers use different distinct strategies: first, to reduce energy intake; second, to increase energy expenditure; third, to alter the partitioning of nutrients between fat and lean tissue. In the present review we concentrate on the first of these strategies, by underlining the new pharmacological tools which are presently studied.

Lessons in obesity from transgenic animals

Many genetic manipulations have created models of obesity, leanness or resistance to dietary obesity in mice, often providing insights into molecular mechanisms that affect energy balance, and new targets for anti-obesity drugs. Since many genes can affect energy balance in mice, polymorphisms in many genes may also contribute to obesity in humans, and there may be many causes of primary leptin resistance. Secondary leptin resistance (due to high leptin levels) can be investigated by combining the ob mutation with other obesity genes. Some transgenic mice have failed to display the expected phenotype, or have even been obese when leanness was expected. Compensatory changes in the expression of other genes during development, or opposing influences of the gene on energy balance, especially in global knockout mice, may offer explanations for such findings. Obesity has been separated from insulin resistance in some transgenic strains, providing new insights into the mechanisms that usually link these phenotypes. It has also been shown that in some transgenic mice, obesity develops without hyperphagia, or leanness without hypophagia, demonstrating that generalised physiological explanations for obesity in individual humans may be inappropriate. Possibly the most important transgenic model of obesity so far created is the Type 1 11beta-hydroxysteroid dehydrogenase over-expressing mouse, since this models the metabolic syndrome in humans. The perspectives into obesity offered by transgenic mouse models should assist clinical researchers in the design and interpretation of their studies in human obesity.

Effects of ACE inhibitor and beta-adrenergic blocker on plasma NPY and NPY receptors in aortic vascular smooth muscle cells from SHR and WKY rats

To investigate the effects of the angiotensin-converting enzyme (ACE) inhibitor, peridopril, and the beta-adrenergic blocker, metoprolol, on plasma neuropeptide Y (NPY), and NPY receptors in aortic vascular smooth muscle cells (VSMCs) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR), both strains of rats were fed with different doses of the drugs (peridopril or metoprolol) for 7 days to get the optimal dosages. After that, 18 male SHR and 18 male age-matched WKY rats were divided into three groups: control, peridopril (2mg/kg/day) and metoprolol (2mg/kg/day). After two months of treatment, VSMCs were isolated from the media layer of the aortic wall. Results showed that the SHRs had higher plasma concentrations and binding sites/affinity for NPY as compared to WKY rats. Peridopril dose-dependently decreased plasma NPY concentrations in WKY rats, and the absolute changes of plasma NPY were greater in SHRs than in WKY rats. Metoprolol showed none of these changes. Metoprolol decreased while peridopril increased NPY binding sites/affinity in SHRs. This indicated that lowered plasma NPY concentration and decreased NPY receptor in VSMCs, might play some roles in the anti-hypertensive mechanisms mediated by ACE inhibitor and beta-adrenergic blockers.

Expression of the neuropeptide Y Y1 receptor in the CNS of rat and of wild-type and Y1 receptor knock-out mice. Focus on immunohistochemical localization

The distribution of neuropeptide Y (NPY) Y1 receptor-like immunoreactivity (Y1R-LI) has been studied in detail in the CNS of rat using a rabbit polyclonal antibody against the C-terminal 13 amino acids of the rat receptor protein. The indirect immunofluorescence technique with tyramide signal amplification has been employed. For specificity and comparative reasons Y1 knock-out mice and wild-type controls were analyzed. The distribution of Y1R mRNA was also studied using in situ hybridization. A limited comparison between Y1R-LI and NPY-LI was carried out.A widespread and abundant distribution of Y1R-LI, predominantly in processes but also in cell bodies, was observed. In fact, Y1R-LI was found in most regions of the CNS with a similar distribution pattern between rat and wild-type mouse. This staining was specific in the sense that it was absent in adjacent sections following preadsorption of the antibody with 10(-5) M of the antigenic peptide, and that it could not be observed in sections of the Y1 KO mouse. In contrast, the staining obtained with an N-terminally directed Y1R antiserum did not disappear, strongly suggesting unspecificity. In brief, very high levels of Y1R-LI were seen in the islands of Calleja, the anterior olfactory nucleus, the molecular layer of the dentate gyrus, parts of the habenula, the interpeduncular nucleus, the mammillary body, the spinal nucleus of the trigeminal, caudal part, the paratrigeminal nucleus, and superficial layers of the dorsal horn. High levels were found in most cortical areas, many thalamic nuclei, some subnuclei of the amygdaloid complex, the hypothalamus and the nucleus of the stria terminalis, the nucleus of the solitary tract, the parabrachial nucleus, and the inferior olive. Moderate levels of Y1R-LI were detected in the cornu Ammonis and the subicular complex, many septal, some thalamic and many brainstem regions. Y1R staining of processes, often fiber and/or dot-like, and occasional cell bodies was also seen in tracts, such as the lateral lemniscus, the rubrospinal tract and the spinal tract of the trigeminal. There was in general a good overlap between Y1R-LI and NPY-LI, but some exceptions were found. Thus, some areas had NPY innervation but apparently lacked Y1Rs, whereas in other regions Y1R-LI, but no or only few NPY-positive nerve endings could be detected. Our results demonstrate that NPY signalling through the Y1R is common in the rat (and mouse) CNS. Mostly the Y1R is postsynaptic but there are also presynaptic Y1Rs. Mostly there is a good match between NPY-releasing nerve endings and Y1Rs, but 'volume transmission' may be 'needed' in some regions. Finally, the importance of using proper control experiments for immunohistochemical studies on seven-transmembrane receptors is stressed.

Distribution of neuropeptide Y Y1 receptors in rodent peripheral tissues

Using a sensitive immunohistochemical technique, the localization of neuropeptide Y (NPY) Y1-receptor (Y1R)-like immunoreactivity (LI) was studied in various peripheral tissues of rat. Wild-type (WT) and Y1R-knockout (KO) mice were also analyzed. Y1R-LI was found in small arteries and arterioles in many tissues, with particularly high levels in the thyroid and parathyroid glands. In the thyroid gland, Y1R-LI was seen in blood vessel walls lacking alpha-smooth muscle actin, i.e., perhaps in endothelial cells of capillaries. Larger arteries lacked detectable Y1R-LI. A distinct Y1R-immunoreactive (IR) reticulum was seen in the WT mouse spleen, but not in Y1R-KO mouse or rat. In the gastrointestinal tract, Y1R-positive neurons were observed in the myenteric plexus, and a few enteroendocrine cells were Y1R-IR. Some cells in islets of Langerhans in the pancreas were Y1R-positive, and double immunostaining showed coexistence with somatostatin in D-cells. In the urogenital tract, Y1R-LI was observed in the collecting tubule cells of the renal papillae and in some epithelial cells of the seminal vesicle. Some chromaffin cells of adrenal medulla were positive for Y1R. The problem of the specificity of the Y1R-LI is evaluated using adsorption tests as well as comparisons among rat, WT mouse, and mouse with deleted Y1R. Our findings support many earlier studies based on other methodologies, showing that Y1Rs on smooth muscle cells of blood vessels mediate NPY-induced vasoconstriction in various organs. In addition, Y1Rs in other cells in parenchymal tissues of several organs suggest nonvascular effects of NPY via the Y1R.

Bis(31/31')[[Cys(31), Nva(34)]NPY(27-36)-NH(2)]: a neuropeptide Y (NPY) Y(5) receptor selective agonist with a latent stimulatory effect on food intake in rats

The actions of neuropeptide Y (NPY) are mediated by at least six G-protein coupled receptors denoted as Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Investigations using receptor selective ligands and receptor knock-out mice suggest that NPY effects on feeding are mediated by both Y(1) and Y(5) receptors. We have previously shown that Cys-dimers of NPY C-terminal peptides exhibit Y(1) selectivity relative to Y(2) receptors. Re-investigation of their selectivity with respect to the newly cloned receptors, has identified bis(31/31') [[Cys(31), Nva(34)]NPY(27-36)-NH(2)] (BWX-46) as a Y(5) receptor selective agonist. BWX-46 selectively bound Y(5) receptors, and inhibited cAMP synthesis by Y(5) cells with potencies comparable to that of NPY. Moreover, BWX-46 (10 microM) exhibited no significant effect on the cAMP synthesis by Y(1), Y(2), and Y(4) cells. Thus, BWX-46 constitutes the lowest molecular weight Y(5) selective agonist reported to date. Intrahypothalamic (i.h.t)-injection of 30 and 40 microg of BWX-46 stimulated the food intake by rats in a gradual manner, reaching maximal level 8 h after injection. This response was similar to that exhibited by other Y(5) selective agonists, but differed from that of NPY, which exhibited a rapid orexigenic stimulus within 1 h. It is suggested that the differences in the orexigenic stimuli of NPY and Y(5) agonists may be due to their differences in the signal transduction mechanisms.

Important role of hypothalamic Y2 receptors in body weight regulation revealed in conditional knockout mice

Neuropeptide Y is implicated in energy homeostasis, and contributes to obesity when hypothalamic levels remain chronically elevated. To investigate the specific role of hypothalamic Y2 receptors in this process, we used a conditional Y2 knockout model, using the Cre-lox system and adenoviral delivery of Cre-recombinase. Hypothalamus-specific Y2-deleted mice showed a significant decrease in body weight and a significant increase in food intake that was associated with increased mRNA levels for the orexigenic NPY and AgRP, as well as the anorexic proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) in the arcuate nucleus. These hypothalamic changes persisted until at least 34 days after Y2 deletion, yet the effect on body weight and food intake subsided within this time. Plasma concentrations of pancreatic polypeptide and corticosterone were 3- to 5-fold increased in hypothalamus-specific Y2 knockout mice. Germ-line Y2 receptor knockout also produced a significant increase in plasma levels of pancreatic polypeptide. However, these mice differed from conditional knockout mice in that they showed a sustained reduction in body weight and adiposity associated with increased NPY and AgRP but decreased POMC and CART mRNA levels in the arcuate nucleus. The transience of the observed effects on food intake and body weight in the hypothalamus-specific Y2 knockout mice, and the difference of this model from germ-line Y2 knockout mice, underline the importance of conditional models of gene deletion, because developmental, secondary, or extrahypothalamic mechanisms may mask such effects in germ-line knockouts.

Attenuation of hypercholesterolemia and hyperglycemia in ob/ob mice by NPY Y2 receptor ablation

Neuropeptide Y (NPY) is a 36 amino acid peptide well known for its role in regulating food intake and energy homeostasis. It has previously been shown that the NPY Y2 receptor is required for a full biological response to leptin in the central nervous system. We have examined the impact of this receptor on plasma levels of lipid and cholesterol in wild type and obese (ob/ob) mice. The results show that an absence of Y2 in female mice has no effect on cholesterol level in normal lean mice but profoundly decreases serum cholesterol and glucose levels in ob/ob mice. We conclude that NPY, interacting with the Y2 receptor, participates in cholesterol and glucose homeostasis of obese mice.

The neuropeptide Y Y1 receptor regulates leptin-mediated control of energy homeostasis and reproductive functions

The orexigenic neurotransmitter neuropeptide Y (NPY) plays a central role in the hypothalamic control of food intake and energy balance. NPY also exerts an inhibition of the gonadotrope axis that could be important in the response to poor metabolic conditions. In contrast, leptin provides an anorexigenic signal to centrally control the body needs in energy. Moreover, leptin contributes to preserve adequate reproductive functions by stimulating the activity of the gonadotrope axis. It is of interest that hypothalamic NPY represents a primary target of leptin actions. To evaluate the importance of the NPY Y1 and Y5 receptors in the downstream pathways modulated by leptin and controlling energy metabolism as well as the activity of the gonadotrope axis, we studied the effects of leptin administration on food intake and reproductive functions in mice deficient for the expression of either the Y1 or the Y5 receptor. Furthermore, the role of the Y1 receptor in leptin resistance was determined in leptin-deficient ob/ob mice bearing a null mutation in the NPY Y1 locus. Results point to a crucial role for the NPY Y1 receptor in mediating the NPY pathways situated downstream of leptin actions and controlling food intake, the onset of puberty, and the maintenance of reproductive functions.

Pharmacological characterization of cloned chicken neuropeptide Y receptors Y1 and Y5

The neuropeptide Y (NPY) receptor subtypes Y1 and Y5 are involved in the regulation of feeding and several other physiological functions in mammals. To increase our understanding of the origin and mechanisms of the complex NPY system, we report here the cloning and pharmacological characterization of receptors Y1 and Y5 in the first non-mammal, chicken (Gallus gallus). The receptors display 80-83% and 64-72% amino acid sequence identity, respectively, with their mammalian orthologues. The three endogenous ligands NPY, peptide YY (PYY) and pancreatic polypeptide (PP) have similar affinities as in mammals, i.e. NPY and PYY have subnanomolar affinity for both receptors whereas chicken PP bound with nanomolar affinity to Y5 but not to Y1. A notable difference to mammalian receptor subtypes is that the Y1 antagonist SR120819A does not bind chicken Y1, whereas BIBP3226 does. The Y5 antagonist CGP71863A binds to the chicken Y5 receptor. Anatomically, both Y1 and Y5 have high mRNA expression levels in the infundibular nucleus which is the homologous structure of the hypothalamic arcuate nucleus in mammals. These results suggest that some of the selective Y1 and Y5 antagonists developed in mammals can be used to study appetite regulation in chicken.

Ups and downs for neuropeptides in body weight homeostasis: pharmacological potential of cocaine amphetamine regulated transcript and pre-proglucagon-derived peptides

Although most humans experience an underlying upwards drift of the body-weight set-point, body weight appears tightly regulated throughout life. The present review describes the structural basis of the adipostat and hypothesise, which components may constitute available targets for pharmacotherapy of excess body weight. Hypothalamic neurones constitute the major components of the body weight homeostasis maintaining device. Together with neurones of the nucleus of the solitary tract, neurones of the hypothalamic arcuate nucleus constitute the sensory components of the adipostat. The arcuate nucleus neurones respond to circulating levels of leptin and insulin, both of which reflect the levels of energy stored as triacylglycerol in adipocytes. The arcuate nucleus projects heavily to the hypothalamic paraventricular nucleus. Neurones of the hypothalamic paraventricular nucleus are hypothesised to constitute, at least partly, the adipostat motor pattern generator, which upon stimulation activates either net anabolic or catabolic physiological responses. The overall sensitivity of the adipostat is influenced by gain setting neurones hypothesised to be located in the dorsomedial hypothalamic nucleus and lateral hypothalamic area. Cocaine amphetamine regulated transcript (CART) peptides and pre-proglucagon derived peptides, glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) are catabolic neurotransmitters synthesised in neurones of the arcuate nucleus and the nucleus of the solitary tract, respectively. The present review summarises the available evidence that both families of peptides constitute endogenous transmitters mediating satiety and touch upon potential pharmacological exploitation of this knowledge.

Neuropeptide Y receptors as targets for anti-obesity drug development: perspective and current status

Neuropeptide Y is a widely distributed neuropeptide that elicits a plethora of physiological effects via interaction with six different receptors (Y(1)-y(6)). Recent attention has focused on the role of neuropeptide Y in the regulation of energy homeostasis. Neuropeptide Y stimulates food intake, inhibits energy expenditure, increases body weight and increases anabolic hormone levels by activating the neuropeptide Y Y(1) and Y(5) receptors in the hypothalamus. Based on these findings, several neuropeptide Y Y(1) and Y(5) receptor antagonists have been developed recently as potential anti-obesity agents. In addition, mice lacking neuropeptide Y, the neuropeptide Y Y(1) receptor or the neuropeptide Y Y(5) receptor have been generated. The data obtained to date with these newly developed tools suggests that neuropeptide Y receptor antagonists, particularly neuropeptide Y Y(1) receptor antagonists, may be useful anti-obesity agents. However, the redundancy of the neurochemical systems regulating energy homeostasis may limit the effect of ablating a single pathway. In addition, patients in whom the starvation response is activated, such as formerly obese patients who have lost weight or patients with complete or partial leptin deficiency, may be the best candidates for treatment with a neuropeptide Y receptor antagonist.

Clinical potentials of neuropeptide Y family of hormones

Neuropeptide Y (NPY) family of hormones exhibits a wide spectrum of central and peripheral activities mediated by six G-protein coupled receptor subtypes denoted as Y1, Y2, Y3, Y4, Y5, and y6. Investigations to date have implicated NPY in the pathophysiology of a number of diseases including feeding disorders, seizures, anxiety, diabetes, hypertension, congestive heart failure and intestinal disorders. These observations suggest that long-acting, potent NPY receptor selective agonists and antagonists developed could be used to treat a variety of diseases. These possibilities are discussed in this paper.

Receptor subtypes Y1 and Y5 mediate neuropeptide Y induced feeding in the guinea-pig

1. Neuropeptide Y (NPY) is one of the most potent stimulants of food intake. It has been debated which receptor subtype mediates this response. Initially Y(1) was proposed, but later Y(5) was announced as a 'feeding' receptor in rats and mice. Very little is known regarding other mammals. The present study attempts to characterize the role of NPY in feeding behaviour in the distantly related guinea-pig. When infused intracerebroventricularly, NPY dose-dependently increased food intake. 2. PYY, (Leu(31),Pro(34))NPY and NPY(2 - 36) stimulated feeding, whereas NPY(13 - 36) had no effect. These data suggest that either Y(1) or Y(5) receptors or both may mediate NPY induced food intake in guinea-pigs. 3. The Y(1) receptor antagonists, BIBO 3304 and H 409/22 displayed nanomolar affinity for the Y(1) receptor (K(i) values 1.1+/-0.2 nM and 5.6+/-0.9 nM, respectively), but low affinity for the Y(2) or Y(5) receptors. When guinea-pigs were pretreated with BIBO 3304 and H 409/22, the response to NPY was inhibited. 4. The Y(5) antagonist, CGP 71683A had high affinity for the Y(5) receptor (K(i) 1.3+/-0.05 nM) without having any significant activities at the Y(1) and Y(2) receptors. When CGP 71683A was infused into brain ventricles, the feeding response to NPY was attenuated. 5. The present study shows that NPY stimulates feeding in guinea-pigs through Y(1) and Y(5) receptors. As the guinea-pig is very distantly related to the rat and mouse, this suggests that both Y(1) and Y(5) receptors may mediate NPY-induced hyperphagia also in other orders of mammals.

Obesity therapy: altering the energy intake-and-expenditure balance sheet

Obesity is associated with numerous health complications, which range from non-fatal debilitating conditions such as osteoarthritis, to life-threatening chronic diseases such as coronary heart disease, diabetes and certain cancers. The psychological consequences of obesity can range from lowered self-esteem to clinical depression. Despite the high prevalence of obesity and the many advances in our understanding of how it develops, current therapies have persistently failed to achieve long-term success. This review focuses on how fat mass can be reduced by altering the balance between energy intake and expenditure.

Diverse functions of neuropeptide Y revealed using genetically modified animals

Neuropeptide Y (NPY), a peptide abundantly expressed in the mammalian nervous system, has been extensively studied using traditional pharmacological and behavioral models. Central administration of NPY or synthetic ligands for its receptors has indicated a role of NPY in anxiety-related behaviors, feeding, regulation of blood pressure, circadian rhythm and other functions. Some limitations inherent in pharmacological approaches, such as lack of selectivity of receptor antagonists, can be elegantly circumvented using genetically modified animals. For NPY, mice lacking NPY, the Y1, the Y2 or the Y5 receptors have been generated. In addition, both mice and rats overexpressing NPY in the central nervous system are available. Here, we review the research carried out so far in the NPY-field using genetically modified animals. Together, these models indicate that stress-related behaviors and regulation of voluntary alcohol intake perhaps are among the most important functions of central NPY, and may provide attractive targets for developing novel therapies in depression, anxiety disorders and alcohol dependence.

Appetite suppression based on selective inhibition of NPY receptors

AIM

The aim of this review is to critically assess available evidence that blockade of the actions of NPY at one of the five NPY receptor subtypes represents an attractive new drug discovery target for the development of an appetite suppressant drug.

RESULTS

Blockade of the central actions of NPY using anti-NPY antibodies, antisense oligodeoxynucleotides against NPY and NPY receptor antagonists results in a decrease in food intake in energy-deprived animals. These results appear to show that endogenous NPY plays a role in the control of appetite. The fact that NPY receptors exist as at least five different subtypes raises the possibility that the actions of endogenous NPY on food intake can be adequately dissociated from other effects of the peptide. Current drug discovery has produced a number of highly selective NPY receptor antagonists which have been used to establish the NPY Y(1) receptor subtype as the most critical in regulating short-term food intake. However, additional studies are now needed to more clearly define the relative contribution of NPY acting through the NPY Y2 and NPY Y5 receptors in the complex sequence of physiological and behavioral events that underlie the long-term control of appetite.

CONCLUSIONS

Blockade of the NPY receptor may produce appetite-suppressing drugs. However, it is too early to state with certainty whether a single subtype selective drug used alone or a combination of NPY receptor selective antagonists used in combination will be necessary to adequately influence appetite regulation.

Rapid internalization and recycling of the human neuropeptide Y Y(1) receptor

Desensitization of G protein-coupled receptors (GPCRs) involves receptor phosphorylation and reduction in the number of receptors at the cell surface. The neuropeptide Y (NPY) Y(1) receptor undergoes fast desensitization. We examined agonist-induced signaling and internalization using NPY Y(1) receptors fused to green fluorescent protein (EGFP). When expressed in HEK293 cells, EGFP-hNPY Y(1) receptors were localized at the plasma membrane, desensitized rapidly as assessed using calcium responses, and had similar properties compared to hNPY Y(1) receptors. Upon agonist challenge, the EGFP signal decreased rapidly (t(1/2) = 107 +/- 3 s) followed by a slow recovery. This decrease was blocked by BIBP3226, a Y(1) receptor antagonist, or by pertussis toxin, in agreement with Y(1) receptor activation. Internalization of EGFP-hNPY Y(1) receptors to acidic endosomal compartments likely accounts for the decrease in the EGFP signal, being absent after pretreatment with monensin. Concanavalin A and hypertonic sucrose, which inhibit clathrin-mediated endocytosis, blocked the decrease in fluorescence. After agonist, intracellular EGFP signals were punctate and co-localized with transferrin-Texas Red, a marker of clathrin-associated internalization and recycling, but not with LysoTracker Red, a lysosomal pathway marker, supporting receptor trafficking to recycling endosomes rather than the late endosomal/lysosomal pathway. Pulse-chase experiments revealed no receptor degradation after internalization. The slow recovery of fluorescence was unaffected by cycloheximide or actinomycin D, indicating that de novo synthesis of receptors was not limiting. Use of a multicompartment model to fit our fluorescence data allows simultaneous determination of internalization and recycling rate constants. We propose that rapid internalization of receptors via the clathrin-coated pits recycling pathway may largely account for the rapid desensitization of NPY Y(1) receptors.

Multiple NPY receptors Inhibit GABA(A) synaptic responses of rat medial parvocellular effector neurons in the hypothalamic paraventricular nucleus

We have recently shown that NPY and alpha-melanocyte-stimulating hormone, which potently induce or inhibit feeding, respectively, have opposing modulatory actions on GABAergic synapses in the medial parvocellular region of the paraventricular hypothalamic nucleus (mpPVN). Because this action might underlie the effects of NPY on feeding, we have examined the pharmacology of NPY responses using electrophysiological recordings. Focal electrical stimulation within the PVN elicited a GABA(A) synaptic response in some mpPVN neurons, which was reversibly inhibited by NPY in a concentration-dependent manner (EC(50) = 28 nM). NPY did not alter the response to the GABA(A) agonist, muscimol. Agonist responses to NPY analogs were not consistent with a single NPY receptor subtype; the most subtype selective agonists were less effective than the more broadly selective ones. Antagonist blockade of individual receptor subtypes partly inhibited NPY action, while fully blocking effects of selective agonists. Combining Y1 and Y5 antagonists blocked actions of NPY entirely, but the Y2 antagonist also completely blocked actions of NPY in some neurons. NPY inhibits GABA(A) synaptic transmission onto mpPVN neurons, but this can be mediated by three different NPY receptors. Controversy regarding the receptor or receptor subtypes involved in NPY-mediated feeding may arise from the multiple NPY receptors present.

Chronic administration of neuropeptide Y into the lateral ventricle of C57BL/6J male mice produces an obesity syndrome including hyperphagia, hyperleptinemia, insulin resistance, and hypogonadism

Neuropeptide Y (NPY) is involved in the central regulation of appetite, sexual behavior, and reproductive function. We have previously shown that chronic infusion of NPY into the lateral ventricle of normal rats produced an obesity syndrome characterized by hyperphagia, hyperinsulinism and collapse of reproductive function. We further demonstrated that acute inhibition of LH secretion in castrated rats was preferentially mediated by the NPY receptor subtype 5 (Y(5)). In the present study, the effects of chronic, central infusion of NPY, or the mixed Y2-Y5 agonist PYY(3-36), were evaluated both in normal male C57BL/6J mice and Sprague-Dawley rats. After a 7-day infusion to male mice, both NPY and PYY(3-36) at 5 nmol per day, induced marked hyperphagia leading to significant increases in body and fat pad weights. Furthermore, both compounds markedly reduced several markers of the reproductive axis. In the rat study, PYY(3-36) was more active than NPY to inhibit the pituitary-testicular axis, confirming the importance of the Y5 subtype for such effects. In the mouse, chronic NPY infusion induced a sustained increase in corticosterone and insulin secretion. Plasma leptin levels were also markedly increased possibly explaining the observed reduction in gene expression for hypothalamic NPY. Gene expression for hypothalamic POMC was reduced in the NPY- or PYY(3-36)-infused mice, suggesting that NPY exacerbated food intake by both acting through its own receptor(s), and reducing the satiety signal driven by the POMC-derived alpha-MSH. The present study in the mouse suggests in analogy with available rat data, that constant exposure to elevated NPY in the hypothalamic area unabatedly enhances food intake leading to an obesity syndrome including increased adiposity, insulin resistance, hypercorticism, and hypogonadism, reminiscent of the phenotype of the ob/ob mouse, that displays elevated hypothalamic NPY secondary to lack of leptin negative feedback action.

[Potential molecular targets for anti-obesity drugs--after the discovery of leptin]

The discovery of the adipose-derived hormone leptin has generated interest in the interaction between peripheral signals and brain targets involved in the regulation of feedings and energy balance. Potential anti-obesity drugs can be based on any intervention between the neuropeptide and its receptor that would alter the biological responses mediated by the neuronal network, in particular, food intake, metabolism and energy expenditure. Modulation of neurons in the arcuate nucleus by leptin results in reduced expression of neuropeptide Y and agouti-related protein, and increased expression of pro-opiomelanocortin (the precursor of a-melanocyte-stimulating hormone) and cocaine- and amphetamine- regulated transcript. Whether leptin finds its way into general usage as an anti-obesity drug, the use of modern methods to identify and target the components of leptin signaling pathway will form the basis for new pharmacological approaches to the treatment of obesity.

Mouse feeding behavior: ethology, regulatory mechanisms and utility for mutant phenotyping

Ingestive behaviors, feeding and drinking, constitute unconditioned, obligatory functions that are tightly regulated in the rodent according to demands of the external and internal milieu. Dependent measures of food intake have been used extensively in rats to infer the identity and function of neurochemical pathways, which mediate energy balance. A recent interest in application of appetitive measures in mice can be attributed jointly to the discovery of novel markers of energy balance in genetically obese mice as well as systematic targeting of known feeding regulatory pathways in bioengineered mutant mice. Accordingly, this review will attempt to provide the reader interested in behavioral phenotyping of knockout or transgenic mice with information regarding the ethology of mouse eating behavior, known mechanisms of appetitive regulation and examples of successes and pitfalls encountered when studying food intake in mutant mice.

Knockout models resulting in the development of obesity

Our understanding of body weight regulation has been greatly advanced by the characterization of previously existing mutations in mice that cause obesity. Subsequent analysis of a number of mouse knockout models has greatly expanded the number of genes known to influence adiposity by affecting metabolic rate, physical activity, and/or appetite.

Neurohumoral regulation of body weight gain

The regulation of body weight is a complex process which relies on a balance between supply of nutrients and demand on these nutrients in the form of energy expenditure. Various central and peripheral mechanisms play a crucial role in maintaining this balance. While various neuropeptides in the central nervous system (CNS), particularly in the hypothalamus, maintain the necessary harmony between hyperphagia and anorexia, peripheral signals arising from the gastrointestinal tract (cholecystokinin-8 [CCK-8], amylin), pancreas (insulin) and adipose tissue (leptin) provide the necessary stimuli or a feedback inhibition for the synthesis and secretion of these hypothalamic neuropeptides. Various metabolites of the carbohydrate and fat metabolism are also involved in regulating the neuronal activity in the hypothalamus which ultimately leads to a release of key neuropeptides. In addition to the central mechanisms, peripheral mechanisms that regulate energy expenditure, particularly in the brown adipose tissue and skeletal muscle, are critical in maintaining the overall balance. Insight into these mechanisms sets the stage for developing novel strategies in the treatment of emerging childhood diseases such as obesity, anorexia nervosa, and bulimia. Further, delineation of these processes in the fetus and newborn sets the stage for investigating their role in molding the adult phenotype due to intrauterine adaptations.

Distinct roles of the Y1 and Y2 receptors on neuropeptide Y-induced sensitization to sedation

Intracranial injection of neuropeptide Y (NPY) increases the sensitivity to sodium pentobarbital and ketamin sedation and has similar properties as GABA agonists on sleep. Mice sensitive to sedation have increased levels of NPY in many brain regions and Y1(-/-) mice show a marked resistance to barbiturates. Here we characterized the role of the NPY Y receptors in anesthetic-induced sedation. We show that Y1 and Y2, but not Y5, receptors participate in the modulation of sedation. Administration of a Y1 agonist increased the sodium pentobarbital-induced sedation and Y1(-/-) mice were less sensitive to this anesthetic. However, Y2(-/-) mice display increased sensitivity, showing that Y2 modulates GABAergic induced sedation both pharmacologically and physiologically and has a functionally opposing role to the Y1 receptor. Analysis of Y1(-/-)/Y2(-/-) double mutant mice show that increased sensitivity by Y1 occurs independent of the Y2 receptor, while the decreased sensitivity mediated by Y2 depend on an intact Y1 receptor. In contrast to sodium pentobarbital, both Y1 and Y2 receptors increase the sensitivity in a collaborative fashion to NMDA antagonist-induced sedation. These data demonstrate the physiological and pharmacological impact of the Y1 and Y2 receptors on sedation.

Fasting, leptin treatment, and glucose administration differentially regulate Y(1) receptor gene expression in the hypothalamus of transgenic mice

NPY is a potent orexigenic signal and represents a key component of targets through which leptin exerts a regulatory restraint on body adiposity. Part of the orexigenic effects of NPY are mediated by hypothalamic NPY-Y(1) receptors. Here we studied the effect of fasting, leptin, and glucose administration on Y(1) receptor gene expression using a transgenic mouse model carrying a mouse Y(1) receptor/LacZ fusion gene. Transgene expression was determined by quantitative analysis of beta-galactosidase histochemical staining in the paraventricular, arcuate, ventromedial, and dorsomedial hypothalamic nuclei and in the medial amygdala, as a control region. Food deprivation for 72 h decreased transgene expression in the paraventricular nucleus but not in the arcuate nucleus. Leptin treatment, that was per se ineffective, counteracted the decrease of transgene expression induced in the paraventricular nucleus by 72 h fasting. Supplementing the drinking water with 10% glucose increased beta-galactosidase expression both in the paraventricular nucleus and arcuate nucleus of control mice. Finally, none of the treatments altered transgene expression in the dorsomedial hyphothalamic, ventromedial, and amygdaloid nuclei. Results suggest that changes in energetic balance affect Y(1) receptor expression in the paraventricular and arcuate nuclei and that leptin regulates the NPY-Y(1) system in the paraventricular nucleus. Different regulatory signals might modulate the NPY-Y(1) transmission in the dorsomedial hyphothalamic and ventromedial hyphothalamic nuclei.

Hypothalamic circuitry of neuropeptide Y regulation of neuroendocrine function and food intake via the Y5 receptor subtype

Neuropeptide Y (NPY) displays diverse modes of action in the CNS including the modulation of feeding behavior, gonadotropin releasing hormone release, and stress responses. Many of the above physiological actions have been at least partially attributed to actions of NPY on the NPY Y5 receptor subtype. We utilized an antibody directed against the NPY Y5 receptor to characterize the distribution of this receptor in the rat brain. Using Western blot analysis, this antibody recognized a single major band at approximately 57 kD. To further verify the specificity of the antibody, animals were treated for 5 days with antisense oligonucleotides for the Y5 receptor. The antisense treatment significantly reduced food intake and body weight. Furthermore, the Y5 antibody detected a significant decrease in Y5 receptor protein. Y5-like immunoreactivity (-ir) was observed throughout the hypothalamus, thalamus, hippocampus and cortex. Double-label immunofluorescence demonstrated that Y5-ir was colocalized with the following neuronal phenotypes in the hypothalamus, gonadotropin-releasing hormone, neurophysins, corticotropin-releasing hormone, and gamma-amino butyric acid. In addition, functional interactions were demonstrated by the presence of close appositions of NPY fibers with Y5-ir expressing cells. The wide distribution of the Y5 receptor-ir, as well as the colocalization within specific neuronal populations, agrees with the distribution of the Y5 receptor mRNA and the known physiological roles of the NPY/Y5 system. The role of the NPY/Y5 receptor system as a mediator between signals of peripheral energy availability and reproductive neuroendocrine function is discussed.

Neuropeptide Y alters sedation through a hypothalamic Y1-mediated mechanism

Neuropeptide Y (NPY) has been reported to profoundly influence and regulate brain circuits involved in a number of behaviours, like anxiety, alcohol intake, pain and energy homeostasis. Here we show that NPY increases sedation induced by different types of anaesthetics through interactions with the Y1 receptor. Consistently, in Y1-/- (homozygote knockout) mice NPY does not potentiate the pentobarbital-induced sedation. Similar results were obtained for avertin but not for ketalar- (NMDA antagonist) induced sedation. Local microinjection of NPY exhibited the strongest potentiating effect on pentobarbital-induced sedation in the posterior hypothalamic area and Y1 expression was found in the dorsal-premammillary and medial part of medial mammillary nuclei. These results show that Y1 is essential for NPY-induced enhancement of sedation and place this activity of NPY in the posterior hypothalamic area, a region of the brain previously implicated in the regulation of the wake-sleep cycle.

Modest overexpression of neuropeptide Y in the brain leads to obesity after high-sucrose feeding

Neuropeptide Y (NPY), one of the most abundant peptide transmitters in the mammalian brain, is assumed to play an important role in feeding and body weight regulation. However, there is little genetic evidence that overexpression or knockout of the NPY gene leads to altered body weight regulation. Previously, we developed NPY-overexpressing mice by using the Thy-1 promoter, which restricts NPY expression strictly within neurons in the central nervous system, but we failed to observe the obese phenotype in the heterozygote. Here we report that in the homozygous mice, overexpression of NPY leads to an obese phenotype, but only after appropriate dietary exposure. NPY-overexpressing mice exhibited significantly increased body weight gain with transiently increased food intake after 50% sucrose--loaded diet, and later they developed hyperglycemia and hyperinsulinemia without altered glucose excursion during 1 year of our observation period.

Genetic models of obesity and energy balance in the mouse

Obesity is a health problem of epidemic proportions in the industrialized world. The cloning and characterization of the genes for the five naturally occurring monogenic obesity syndromes in the mouse have led to major breakthroughs in understanding the physiology of energy balance and the contribution of genetics to obesity in the human population. However, the regulation of energy balance is an extremely complex process, and it is quickly becoming clear that hundreds of genes are involved. In this article, we review the naturally occurring monogenic and polygenic obese mouse strains, as well as the large number of transgenic and knockout mouse models currently available for the study of obesity and energy balance.

Neuropeptide Y Y(5) receptor antagonist CGP71683A: the effects on food intake and anxiety-related behavior in the rat

The effects of neuropeptide Y Y(5) receptor antagonist (trans-naphtalene-1-sulphonic acid [4-[(4-amino-quinazolin-2-ylamino)-methyl]-cyclohexylmethyl]-amide hydrochloride; CGP71683A), on food intake, anxiety and locomotor activity were studied. CGP71683A (1-10 mg/kg, i.p.) dose-dependently decreased nocturnal and fasting-induced food intake. CGP71683A did not have an anxiogenic-like effect in the rat social interaction test. In the elevated plus-maze test, where novel neuropeptide Y Y(1) receptor antagonist (2R)-5-([amino(imino)methyl)amino)-2-[(2.2-diphenylacetyl)-amino]-N-[(1R)-1-(4-hydroxyphenyl)ethyl-pentanamide (H 409/22) had anxiogenic-like effect, CGP71683A was inactive. In the open-field test, carried out immediately after the elevated plus-maze test, CGP71683A inhibited horizontal and vertical activity. CGP71683A did modify the habituation of locomotor response in novel environment. These data show that the inhibition of food intake induced by CGP71683A could not be explained by increased fearfulness, a state that is induced by neuropeptide Y Y(1) receptor antagonists. Thus, our data, obtained with first neuropeptide Y Y(5) receptor antagonist CGP71683A, suggest that in contrast to the neuropeptide Y Y(1) receptor, Y(5) receptor is not involved in tonic neuropeptide Y-induced anxiolysis.

The mPVN mediates blockade of NPY-induced feeding by a Y5 receptor antagonist: a c-FOS analysis

To identify the site(s) of NPY Y5 receptor (Y5R) mediation of NPY-induced feeding, we employed c-Fos immunostaining and a selective Y5R antagonist (Y5R-A), CGP71683A, in adult male rats. Intracerebroventricular (icv) administration of NPY stimulated feeding and c-Fos-like immunoreactivity (FLI) in the dorsomedial hypothalamus, supraoptic nucleus and the two subdivision of the hypothalamic paraventricular nucleus (pPVN), the parvocellular (pPVN), and magnocellular (mPVN). Y5R-A on its own, injected either intraperitoneally or icv, neither affected feeding nor FLI in hypothalamic sites. However, Y5R-A pretreatment suppressed NPY-induced food intake and FLI selectively in the mPVN. Taken together with our previous similar finding of Y1R involvement, these results suggest that NPY receptor sites concerned with feeding behavior reside selectively in the mPVN and Y1 and Y5 receptors are either coexpressed or expressed separately in those target neurons that promote appetitive drive.

Origins of the many NPY-family receptors in mammals

The NPY system has a multitude of effects and is particularly well known for its role in appetite regulation. We have found that the five presently known receptors in mammals arose very early in vertebrate evolution before the appearance of jawed vertebrates 400 million years ago. The genes Y(1), Y(2) and Y(5) arose by local duplications and are still present on the same chromosome in human and pig. Duplications of this chromosome led to the Y(1)-like genes Y(4) and y(6). We find evidence for two occasions where receptor subtypes probably arose before peptide genes were duplicated. These observations pertain to the discussion whether ligands or receptors tend to appear first in evolution. The roles of Y(1) and Y(5) in feeding may differ between species demonstrating the importance of performing functional studies in additional mammals to mouse and rat.

KO's and organisation of peptidergic feeding behavior mechanisms

Feeding behavior results from complex interactions arising between numerous neuromediators, including classical neurotransmitters and neuropeptides present in hypothalamic networks. One way to unravel these complex mechanisms is to examine animal models with a deletion of genes coding for the different neuropeptides involved in the regulation of feeding. The aim of this review is to focus on feeding and body weight regulation in mice lacking neuropeptide Y (NPY), melanocortins (POMC), corticotropin-releasing hormone, melanin-concentrating hormone, or bombesin-like peptides respectively. The phenotypes, which relate to the deletion of gene coding for the peptides, rarely include changes in body weight and food intake, indicating therefore the existence of redundant mechanisms to compensate for the loss of the peptide. The phenotype is much more marked when the gene deletion is targeted towards the functioning of the peptidergic machinery, e.g. the receptors and especially the POMC and NPY receptors, as well as one subtype of bombesin receptor (BRS-3). These knockout models are also interesting when examining the role of environmental and social factors in the determination of feeding behavior. They have granted us better knowledge of all these integrated and complex mechanisms. Moreover, they are also valuable tools for pharmacological studies when specific antagonists are lacking. From the information obtained by the study of knockouts, it is possible to determine certain targets for selective drugs that could be efficient for the pharmacological treatment of obesity. However, at the present state of our knowledge, it seems necessary to target several peptides in order to get good results with weight loss. It will also be imperative to associate these multitherapies with changes in eating and behavioral habits, in order to obtain complete effectiveness and long-lasting results.

Increased insulin concentrations and glucose storage in neuropeptide Y Y1 receptor-deficient mice

Mice lacking NPY Y1 receptors develop obesity without hyperphagia indicating increased energy storage and/or decreased energy expenditure. Then, we investigated glucose utilization in these animals at the onset of obesity. Fasted NPY Y1 knockouts showed hyperinsulinemia associated with increased whole body and adipose tissue glucose utilization and glycogen synthesis but normal glycolysis. Since leptin modulates NPY actions, we studied whether the lack of NPY Y1 receptor affected leptin-mediated regulation of glucose metabolism. Leptin infusion normalized hyperinsulinemia and glucose turnover. These results suggest a possible mechanism for the development of obesity without hyperphagia via dysfunction in regulatory loops involving NPY, leptin and insulin.

Ghrelin, an endogenous growth hormone secretagogue, is a novel orexigenic peptide that antagonizes leptin action through the activation of hypothalamic neuropeptide Y/Y1 receptor pathway

Ghrelin, an endogenous ligand for growth hormone secretagogue (GHS) receptor originally isolated from the stomach, occurs in the hypothalamic arcuate nucleus and may play a role in energy homeostasis. Synthetic GHSs have activated the hypothalamic arcuate neurons containing neuropeptide Y (NPY), suggesting the involvement of NPY in some of ghrelin actions. This study was designed to elucidate the role of ghrelin in the regulation of food intake. A single intracerebroventricular (ICV) injection of ghrelin (5-5,000 ng/rat) caused a significant and dose-related increase in cumulative food intake in rats. Ghrelin (500 ng/rat) was also effective in growth hormone-deficient spontaneous dwarf rats. Hypothalamic NPY mRNA expression was increased in rats that received a single ICV injection of ghrelin (500 ng/rat) (approximately 160% of that in vehicle-treated groups, P < 0.05). The ghrelin's orexigenic effect was abolished dose-dependently by ICV co-injection of NPY Y1 receptor antagonist (10-30 microg/rat). The leptin-induced inhibition of food intake was reversed by ICV co-injection of ghrelin in a dose-dependent manner (5-500 ng/rat). Leptin reduced hypothalamic NPY mRNA expression by 35% (P < 0.05), which was abolished by ICV co-injection of ghrelin (500 ng/rat). This study provides evidence that ghrelin is an orexigenic peptide that antagonizes leptin action through the activation of hypothalamic NPY/Y1 receptor pathway.

Reduced antinociception and plasma extravasation in mice lacking a neuropeptide Y receptor

Neuropeptide Y (NPY) is believed to exert antinociceptive actions by inhibiting the release of substance P and other 'pain neurotransmitters' in the spinal cord dorsal horn. However, the physiological significance and potential therapeutic value of NPY remain obscure. It is also unclear which receptor subtype(s) are involved. To identify a possible physiological role for the NPY Y1 receptor in pain transmission, we generated NPY Y1 receptor null mutant (Y1-/-) mice by homologous recombination techniques. Here we show that Y1-/- mice develop hyperalgesia to acute thermal, cutaneous and visceral chemical pain, and exhibit mechanical hypersensitivity. Neuropathic pain is increased, and the mice show a complete absence of the pharmacological analgesic effects of NPY. In the periphery, Y1 receptor activation is sufficient and required for substance P release and the subsequent development of neurogenic inflammation and plasma leakage. We conclude that the Y1 receptor is required for central physiological and pharmacological NPY-induced analgesia and that its activation is both sufficient and required for the release of substance P and initiation of neurogenic inflammation.