Complementary and overlapping expression of Y1, Y2 and Y5 receptors in the developing and adult mouse nervous system

Neuropeptide Y protects against methamphetamine-induced neuronal apoptosis in the mouse striatum

Methamphetamine (METH) is an illicit drug that causes neuronal apoptosis in the mouse striatum, in a manner similar to the neuronal loss observed in neurodegenerative diseases. In the present study, injections of METH to mice were found to cause the death of enkephalin-positive projection neurons but not the death of neuropeptide Y (NPY)/nitric oxide synthase-positive striatal interneurons. In addition, these METH injections were associated with increased expression of neuropeptide Y mRNA and changes in the expression of the NPY receptors Y1 and Y2. Administration of NPY in the cerebral ventricles blocked METH-induced apoptosis, an effect that was mediated mainly by stimulation of NPY Y2 receptors and, to a lesser extent, of NPY Y1 receptors. Finally, we also found that neuropeptide Y knock-out mice were more sensitive than wild-type mice to METH-induced neuronal apoptosis of both enkephalin- and nitric oxide synthase-containing neurons, suggesting that NPY plays a general neuroprotective role within the striatum. Together, our results demonstrate that neuropeptide Y belongs to the class of factors that maintain neuronal integrity during cellular stresses. Given the similarity between the cell death patterns induced by METH and by disorders such as Huntington's disease, our results suggest that NPY analogs might be useful therapeutic agents against some neurodegenerative processes.

Characterization of neuropeptide Y2 receptor protein expression in the mouse brain. I. Distribution in cell bodies and nerve terminals

Neuropeptide Y (NPY), a 36-amino-acid peptide, mediates biological effects by activating Y1, Y2, Y5, and y6 receptors. NPY neurons innervate many brain regions, including the hypothalamus, where NPY is involved in regulation of a broad range of homeostatic functions. We examined, by immunohistochemistry with tyramide signal amplification, the expression of the NPY Y2 receptor (Y2R) in the mouse brain with a newly developed rabbit polyclonal antibody. Y2R immunoreactivity was specific with its absence in Y2R knockout (KO) mice and in adjacent sections following preadsorption with the immunogenic peptide (10(-5) M). Y2R-positive processes were located in many brain regions, including the olfactory bulb, some cortical areas, septum, basal forebrain, nucleus accumbens, amygdala, hippocampus, hypothalamus, substantia nigra compacta, locus coeruleus, and solitary tract nucleus. However, colchicine treatment was needed to detect Y2R-like immunoreactivity in cell bodies in many, but not all, areas. The densest distributions of cell bodies were located in the septum basal forebrain, including the bed nucleus, and amygdala, with lower density in the anterior olfactory nucleus, nucleus accumbens, caudal striatum, CA1, CA2, and CA3 hippocampal fields, preoptic nuclei lateral hypothalamus, and A13 DA cells. The widespread distribution of Y2R-positive cell bodies and fibers suggests that NPY signaling through the Y2R is common in the mouse brain. Localization of the Y2R suggests that it is mostly presynaptic, a view supported by its frequent absence in cell bodies in the normal mouse and its dramatic increase in cell bodies of colchicine-treated mice.

Selective increase of dark phase water intake in neuropeptide-Y Y2 and Y4 receptor knockout mice

Neuropeptide-Y (NPY) is involved in the regulation of ingestive behaviour and energy homeostasis. Since deletion of the NPY Y2 and Y4 receptor gene increases and decreases food intake, respectively, we examined whether water intake during the light and dark phases is altered in Y2 and Y4 receptor knockout mice. The water consumption of mice staying in their home cages was measured by weighing the water bottles at the beginning and end of the light phase during 4 consecutive days. Control, Y2 and Y4 receptor knockout mice did not differ in their water intake during the light phase. However, during the dark phase Y2 and Y4 receptor knockout mice drank significantly more (46-63%, P<0.05) water than the control mice. The total daily water intake over 24 h was also enhanced. The enhanced water intake during the dark phase was not altered by the beta-adrenoceptor antagonist propranolol or the angiotensin AT1 receptor antagonist telmisartan (each injected intraperitoneally at 10 mg/kg). These data indicate that NPY acting via Y2 and Y4 receptors plays a distinctive role in the regulation of nocturnal water consumption. While beta-adrenoceptors and angiotensin AT1 receptors do not seem to be involved, water intake in Y2 and Y4 receptor knockout mice may be enhanced because presynaptic autoinhibition of NPY release and inhibition of orexin neurons in the central nervous system are prevented.

cDNA cloning and mRNA expression of neuropeptide Y in orange spotted grouper, Epinephelus coioides

A full-length cDNA encoding the neuropeptide Y (NPY) was cloned from the hypothalamus of orange spotted grouper (Epinephelus coioides) by rapid amplification of cDNA ends approaches. The NPY cDNA sequence is 688 bp long and has an open reading frame of 300 bp encoding prepro-NPY with 99 amino acids. The deduced amino acid sequences contain a 28-amino-acids signal peptide followed by a 36-amino-acids mature NPY peptide. mRNA expression of NPY was determined using semi-quantitative RT-PCR followed by Southern blot analysis. NPY mRNA was expressed in olfactory bulb, telencephalon, pituitary, hypothalamus, optic tectum-thalamus, medulla oblongata, cerebellum and spinal cord. Low levels of NPY mRNA expression were found in retina, ovary and stomach, while much lower levels of expression were detected in liver, heart, gill, skin, anterior intestine, thymus and blood. No NPY mRNA expression was observed in unfertilized eggs, newly fertilized eggs, 16-cells stage and morula stage of the embryo and lower levels of expression were detected in the blastula, gastrula and neurula stages. It was highly expressed from lens formation stage to 52-day-old larval stage. NPY might be involved in the late embryonic and larval development of the orange spotted grouper.

Peptide YY(3-36) inhibits morning, but not evening, food intake and decreases body weight in rhesus macaques

Peptide YY(3-36) [PYY(3-36)] is a hormone that is released after meal ingestion that is currently being investigated for the treatment of obesity; however, there are conflicting reports of the effects of PYY(3-36) on energy balance in rodent models. To shed light on this controversy, we studied the effect of PYY(3-36) on food intake and body weight in a nonhuman primate. Intravenous PYY(3-36) infusions before a morning meal transiently suppressed the rate of food intake but did not suppress the evening meal or 24-h intake. Twice-daily or continuous intravenous PYY(3-36) infusions to supraphysiological levels (levels that exceeded normal physiological levels) again suppressed the rate of feeding for the morning but not the evening meal. Twice-daily intravenous PYY(3-36) infusions for 2 weeks significantly decreased body weight in all test animals (average weight loss 1.9%) without changing insulin response to glucose infusion. These results show that endogenous PYY(3-36) may alter morning but not evening meal intake, and supraphysiological doses are required for effective suppression of food intake.

Effect of peripheral axotomy on pain-related behavior and dorsal root ganglion neurons excitability in NPY transgenic rats

In order to clarify the physiologic role of NPY in sensory processing, we obtained intracellular recordings of DRG neurons from wild type (WT) and NPY overexpressing transgenic rats (NPY-TG) before and after injury. We investigated medium and large diameter DRG neurons since upregulation of NPY peptide following the nerve injury occurs primarily in those cells. Neurons were classified as Aalpha/beta and Adelta using conduction velocity and action potential duration. Prior to the injury, Aalpha/beta neurons of NPY-TG rats conducted more slowly and had a more brief AHP than similar cells from the WT group. Adelta neurons at baseline conducted faster in TG animals compared to WT. Ligation of the 5th lumbar spinal nerve (SNL) produced certain changes in Aalpha/beta cells that were evident only in the TG group. These include increased refractory period, increased input resistance, AHP prolongation and a depolarizing shift in threshold for AP initiation. The expected injury-induced CV slowing was not seen in NPY-TG Aalpha/beta cells. In the Adelta cell group, injury produced a depolarizing shift in the resting membrane potential, an increase in AP duration and decrease in AHP and refractory period duration only in WT rats, while NPY-TG cells lacked these injury-induced changes. Behavior tests showed diminished sensory response to nerve injury in NPY-TG rats, i.e., shorter duration of enhanced pain-related behavior and attenuation of contralateral effect. In conclusion, our observations suggest that NPY overexpression leads to reduced neuronal activity following nerve injury in a cell-specific manner.

Differential suppression of seizures via Y2 and Y5 neuropeptide Y receptors

Neuropeptide Y (NPY) prominently inhibits epileptic seizures in different animal models. The NPY receptors mediating this effect remain controversial partially due to lack of highly selective agonists and antagonists. To circumvent this problem, we used various NPY receptor knockout mice with the same genetic background and explored anti-epileptic action of NPY in vitro and in vivo. In Y2 (Y2-/-) and Y5 (Y5-/-) receptor knockouts, NPY partially inhibited 0 Mg2+-induced epileptiform activity in hippocampal slices. In contrast, in double knockouts (Y2Y5-/-), NPY had no effect, suggesting that in the hippocampus in vitro both receptors mediate anti-epileptiform action of NPY in an additive manner. Systemic kainate induced more severe seizures in Y5-/- and Y2Y5-/-, but not in Y2-/- mice, as compared to wild-type mice. Moreover, kainate seizures were aggravated by administration of the Y5 antagonist L-152,804 in wild-type mice. In Y5-/- mice, hippocampal kindling progressed faster, and afterdischarge durations were longer in amygdala, but not in hippocampus, as compared to wild-type controls. Taken together, these data suggest that, in mice, both Y2 and Y5 receptors regulate hippocampal seizures in vitro, while activation of Y5 receptors in extra-hippocampal regions reduces generalized seizures in vivo.

Neuropeptide Y Y1 receptor mRNA in rodent brain: distribution and colocalization with melanocortin-4 receptor

The central neuropeptide Y (NPY) Y1 receptor (Y1-R) system has been implicated in feeding, endocrine, and autonomic regulation. In the present study, we systematically examined the brain distribution of Y1-R mRNA in rodents by using radioisotopic in situ hybridization histochemistry (ISHH) with a novel sensitive cRNA probe. Within the rat hypothalamus, Y1-R-specific hybridization was observed in the anteroventral periventricular, ventromedial preoptic, suprachiasmatic, paraventricular (PVH), dorsomedial, ventromedial, arcuate, and mamillary nuclei. In the rat, Y1-R mRNA expression was also seen in the subfornical organ, anterior hypothalamic area, dorsal hypothalamic area, and in the lateral hypothalamic area. In addition, Y1-R hybridization was evident in several extrahypothalamic forebrain and hindbrain sites involved in feeding and/or autonomic regulation in the rat. A similar distribution pattern of Y1-R mRNA was observed in the mouse brain. Moreover, by using a transgenic mouse line expressing green fluorescent protein under the control of the melanocortin-4 receptor (MC4-R) promoter, we observed Y1-R mRNA expression in MC4-R-positive cells in several brain sites such as the PVH and central nucleus of the amygdala. Additionally, dual-label ISHH demonstrated that hypophysiotropic PVH cells coexpress Y1-R and pro-thyrotropin-releasing hormone mRNAs in the rat. These observations are consistent with the proposed roles of the central NPY/Y1-R system in energy homeostasis.

Interaction between neuropeptide Y and alpha-melanocyte stimulating hormone in amygdala regulates anxiety in rats

Neuropeptide Y (NPY) and alpha-melanocyte stimulating hormone (alpha-MSH) have been implicated in pathophysiology of feeding and certain mood disorders, including anxiety and depression. Both the peptides are abundantly present in CNS, especially in the hypothalamus and amygdala. Although they are known to exert opposite effects, particularly with reference to anxiety, the underlying mechanisms are not known. We were interested in studying the interaction between these two peptides in the regulation of anxiety, within the framework of amygdala. We administered agents like NPY, alpha-MSH, selective melanocortin-4 receptor (MC4-R) antagonist HS014 and NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY, alone and in combinations, unilaterally in right amygdala of rats and measured the response using elevated plus maze test. While NPY and [Leu(31), Pro(34)]-NPY increased the time spent and number of entries in the open arms suggesting anxiolytic-like effects, alpha-MSH resulted in opposite responses. Anxiolytic-like effect of NPY (10 nM) or [Leu(31), Pro(34)]-NPY (5 nM) was significantly reduced following prior alpha-MSH (250 ng) administration. Co-administration of HS014 (1 nM) and NPY (5 nM) or [Leu(31), Pro(34)]-NPY (1 nM) at subeffective doses evoked synergistic anxiolysis. Since the closed arm entries displayed by animals of all the groups were in a similar range, the effects might not be ascribed to the changes in general locomotor activity. These results suggest that endogenous alpha-MSH and NPY containing systems may interact in the amygdala and regulate exploratory behavior in an animal model of anxiety.

Body weight is regulated by the brain: a link between feeding and emotion

Regulated energy homeostasis is fundamental for maintaining life. Unfortunately, this critical process is affected in a high number of mentally ill patients. Eating disorders such as anorexia nervosa are prevalent in modern societies. Impaired appetite and weight loss are common in patients with depression. In addition, the use of neuroleptics frequently produces obesity and diabetes mellitus. However, the neural mechanisms underlying the pathophysiology of these behavioral and metabolic conditions are largely unknown. In this review, we first concentrate on the established brain machinery of food intake and body weight, especially on the melanocortin and neuropeptide Y (NPY) systems as illustration. These systems play a critical role in receiving and processing critical peripheral metabolic cues such as leptin and ghrelin. It is also notable that both systems modulate emotion and motivated behavior as well. Secondly, we discuss the significance and potential promise of multidisciplinary molecular and neuroanatomic techniques that will likely increase the understanding of brain circuitries coordinating energy homeostasis and emotion. Finally, we introduce several lines of evidence suggesting a link between the melanocortin/NPY systems and several neurotransmitter systems on which many of the psychotropic agents exert their influence.

Y1-receptors regulate the expression of Y2-receptors in distinct mouse forebrain areas

Y-receptor-knockout mice have become an important tool to elucidate specific physiological roles of individual Y-receptors. However, their phenotypes are not always confirmatory to results obtained by pharmacological investigations in vivo or in vitro. These discrepancies may, at least in part, be due to compensatory changes in the expression of remaining Y-receptor types. To determine whether deletion of individual Y-receptors results in altered mRNA expression and/or binding toward other Y-receptor types, we applied in-situ hybridization and radioligand-binding studies on brain slices of Npy1r-, Npy2r- or Npy5r-knockout mice. Significant changes were seen in Y1-receptor-deficient mice. Thus, Y2-receptor mRNA and (125)I-peptide YY(3-36) binding in the hippocampus proper were increased by up to 55% and 89%, respectively. Similar increases in (125)I-peptide YY(3-36) binding were observed in the caudo-dorsal extension of the lateral septum, an area heavily targeted by hippocampal projections and involved in Y1-receptor-regulated anxiety. Increased (125)I-peptide YY(3-36) binding and Y2-receptor mRNA levels were also observed in the medial amygdaloid nucleus. In contrast, (125)I-peptide YY(3-36) binding was reduced in the central amygdaloid nucleus. Y2-receptor mRNA in the intermediate part of the lateral septum was reduced by 42%. Only minimal changes were observed in Y2- or Y5-receptor-deficient mice. Our results demonstrate that compensatory changes in the expression of Y2-receptors occur in Y1-receptor-deficient mice. These adaptations are likely to contribute to changed physiological function. Thus, alterations in Y2-receptors have to be taken in account upon discussion of Y1-receptor function, especially in emotional aspects like anxiety and aggression, but also alcoholism.

Neuropeptide Y attenuates NMDA-induced phase shifts in the SCN of NPY Y1 receptor knockout mice in vitro

Neuropeptide Y (NPY) blocks the effect of light on the mammalian circadian clock during the subjective night. The present study explores the role of the NPY Y1 receptor in this interaction. The effect of NPY when co-applied with NMDA, a glutamate agonist that can mimic the effect of light, was examined in NPY Y1-/- mice (background strain 129SVXBalb/c) using electrophysiology. Cells in the suprachiasmatic nucleus (SCN), the master circadian pacemaker, show a circadian rhythm in spontaneous firing rate that can be recorded in vitro. The results demonstrated that NPY attenuated the phase shifts to NMDA in both the Y1-/- mice and control mice, indicating that the Y1 receptor does not mediate the NPY blockade of photic-like phase shifts. The peak in frequency in the untreated control brain slices from Y1-/- mice was advanced by approximately 1 h as compared to the Y1+/+ mice. The Y1 receptor may contribute to a functional model of circadian rhythms, but apparently is not essential for the effects of NPY on photic phase shifts.

Peripheral and central administration of a selective neuropeptide Y Y1 receptor antagonist suppresses ethanol intake by C57BL/6J mice

BACKGROUND

Neuropeptide Y (NPY) is a 36-amino acid neuromodulator that is expressed throughout the central nervous system. Recent genetic and pharmacological evidence suggests that the NPY Y1 receptor modulates ethanol intake. To further characterize the role of the Y1 receptor, we examined voluntary ethanol consumption by mice after administration of [(-)-2-[1-(3-chloro-5-isopropyloxycarbonylaminophenyl)ethylamino]-6-[2-(5-ethyl-4-methyl-1,3-tiazol-2-yl)ethyl]-4-morpholinopyridine] (compound A), a novel and selective Y1 receptor antagonist (Y1RA) that acts centrally on brain receptors when administered peripherally.

METHODS

C57BL/6J mice were habituated to drinking a 10% (v/v) ethanol solution by using a two-bottle-choice procedure and were then given an intraperitoneal (ip) injection (5 ml/kg) of the Y1RA (0, 25, 50, or 75 mg/kg). In a second study, mice were given intracerebroventricular infusion of the Y1RA (0, 30, or 100 microg). Finally, we determined whether the Y1RA alters open-field locomotor activity, ethanol-induced sedation (3.8 g/kg, ip), or blood ethanol levels.

RESULTS

Relative to control treatment, ip injection (50 and 75 mg/kg) and intracerebroventricular infusion (100 microg) of the Y1RA significantly reduced ethanol consumption and food intake without altering water drinking. However, the Y1RA did not alter open-field locomotor activity, ethanol-induced sedation, or blood ethanol levels.

CONCLUSIONS

These data indicate that acute blockade of the NPY Y1 receptor with a systemically bioavailable NPY Y1RA reduces voluntary ethanol consumption by C57BL/6J mice. These results are consistent with observations that hypothalamic infusion of NPY increases ethanol drinking by rats.

Identification of hypothalamic genes implicated in the development of obesity in Psammomys obesus using differential display PCR

The hypothalamus is a key central controller of energy homeostasis and is the source and/or site of action of many neuropeptides involved in this process. The aim of this study was to isolate hypothalamic genes differentially expressed between lean and obese Psammomys obesus, a polygenic animal model of obesity and type 2 diabetes. Differential display PCR was used to compare hypothalamic gene expression profiles of lean and healthy, obese and hyperinsulinemic, and obese, diabetic P. obesus in both the fed and fasted states. We conducted differential display with 180 separate primer combinations to amplify approximately 9,000 expressed transcripts. Sixty differentially expressed bands were excised. Taqman PCR was performed on 36 of these transcripts to confirm differential gene expression in a larger sample population. Of these 36 transcripts, 9 showed homology to known genes, and 27 were considered to be novel sequences. Gene expression profiles for two of these genes are presented here. In conclusion, differential display PCR was successfully used to isolate several transcripts that may be involved in the central regulation of energy balance. We are currently conducting numerous studies to further investigate the role of these genes in the development of obesity in P. obesus.

Localization of neuropeptide Y receptor Y5 mRNA in the guinea pig brain by in situ hybridization

Neuropeptide Y (NPY) has prominent stimulatory effects on food intake in virtually all animals that have been studied. In mammals, the effect is primarily mediated by receptors Y1 and Y5, which seem to contribute to different aspects of feeding behavior in guinea pigs and rats/mice. Interestingly, differences in receptor distribution among mammalian species have been reported. To get a broader perspective on the role of Y5, we describe here studies of guinea pig (Cavia porcellus), a species which due to its phylogenetic position in the mammalian radiation is an interesting complement to previous studies in rat and mouse. Guinea pig brain sections were hybridized with two 35S-labeled oligonucleotides complementary to Y5 mRNA. The highest expression levels of Y5 mRNA were observed in the hippocampus and several hypothalamic and brain stem nuclei implicated in the regulation of feeding, such as the paraventricular, arcuate and ventromedial hypothalamic nuclei. This contrasts with autoradiography studies that detected low Y5-like binding in these areas, a discrepancy observed also in rat and human. Y5 mRNA expression was also seen in the striatum, in great contrast to mouse and rat. Taken together, these data show that Y5 mRNA distribution displays some interesting species differences, but that its expression in feeding centers seems to be essentially conserved among mammals, adding further support for an important role in food intake.

NPY and Y receptors: lessons from transgenic and knockout models

Neuropeptide Y (NPY) in the central nervous system is a major regulator of food consumption and energy homeostasis. It also regulates blood pressure, induces anxiolysis, enhances memory retention, affects circadian rhythms and modulates hormone release. Five Y receptors (Y1, Y2, Y4, Y5 and Y6) are known to mediate the action of NPY and its two other family members, peptide YY (PYY) and pancreatic polypeptide (PP). Increased NPY signaling due to elevated NPY expression in the hypothalamus leads to the development of obesity and its related phenotypes, Type II diabetes and cardiovascular disease. Dysregulation in NPY signaling also causes alterations in bone formation, alcohol consumption and seizure susceptibility. The large number of Y receptors has made it difficult to delineate their individual contributions to these physiological processes. However, recent studies analysing NPY and Y receptor overexpressing and knockout models have started to unravel some of the different functions of these Y receptors. Particularly, the use of conditional knockout models has made it possible to pinpoint a specific function to an individual Y receptor in a particular location.

A role for neuropeptide Y in neurobiological responses to ethanol and drugs of abuse

In recent years, evidence has emerged suggesting that neuropeptide Y (NPY) is involved with neurobiological responses to ethanol and other drugs of abuse. Here, we provide an overview of physiological, pharmacological, and genetic research showing that: (A) administration of ethanol, as well as ethanol withdrawal, alter central NPY expression, (B) NPY modulates ethanol consumption under certain conditions, and (C) NPY signaling modulates the sedative effects of several drugs, including ethanol, sodium pentobarbital, and ketamine. Evidence suggesting possible mechanism(s) by which NPY signaling modulates ethanol consumption are considered. It is suggested that NPY may influence ethanol consumption by regulating basal levels of anxiety, by modulating the sedative effects of ethanol, and/or by modulating ethanol's rewarding properties.

Distribution of NPY receptors in the hypothalamus

Neuropeptide Y (NPY) neurons abundantly innervate the hypothalamus, where NPY is involved in the regulation and integration of a broad range of homeostatic functions. In order to understand NPY-mediated behavioral, autonomic and neuroendocrine effects, it is important to characterize in detail the distribution of the hypothalamic NPY receptors. In this review, we briefly summarize the origin of NPY and its two related peptides, peptide YY and pancreatic polypeptide in the hypothalamus. Moreover, based on the results obtained with histological techniques such as in situ hybridization, immunohistochemistry and ligand binding, we summarize data on the hypothalamic distribution of the known NPY receptors, the Y1 Y2, Y4 and Y5 receptors as best characterized to date. These NPY receptors are found with individual distribution patterns in many hypothalamic neurons including neuroendocrine motoneurons, magnocellular neurosecretory neurons and numerous neurons connecting the hypothalamus with the limbic and the autonomic nervous systems. The histochemical analyses allow characterization of coexisting molecules and in this way definition of the neurochemistry of NPY circuitries. By showing coexistence of various NPY receptors they provide a morphological basis for in vitro studies showing heterodimerization of NPY receptors. The NPY neurons and their circuitries underlie the integrative role of NPY as a pleiotropic neuropeptide in the regulation of homeostasis.

Neuropeptide Y and energy homeostasis: insights from Y receptor knockout models

A complex system has evolved to regulate food intake and to maintain energy homeostasis. A series of short-term hormonal and neural signals that derive from the gastrointestinal tract, such as cholecystokinin (CCK), pancreatic polypeptide (PP) and peptide YY-(3-36), recently discovered to regulate meal size. Others such as ghrelin initiate meals, and insulin and leptin, together with circulating nutrients, indicate long-term energy stores. All these signals act on central nervous system sites which converge on the hypothalamus, an area that contains a large number of peptide and other neurotransmitters that influence food intake with neuropeptide Y (NPY) being one of the most prominent ones. Five Y receptors are known which mediate the action of neuropeptide Y and its two other family members, peptide YY and pancreatic polypeptide. Elevated neuropeptide Y expression in the hypothalamus leads to the development of obesity and its related phenotypes, Type II diabetes and cardiovascular disease. The limited availability of specific pharmacological tools and the considerable number of Y receptors have made it difficult to delineate their individual contributions to the regulation of energy homeostasis. However, recent studies analysing transgenic and knockout neuropeptide Y and Y receptor mouse models have started to unravel some of the individual functions of these Y receptors potentially also helping to develop novel therapeutics for a variety of physiological disorders including obesity.

Assessment of ethanol consumption and water drinking by NPY Y(2) receptor knockout mice

In recent years, pharmacological and genetic evidence have emerged suggesting that neuropeptide Y (NPY) and the NPY Y(1) receptor are involved with neurobiological responses to ethanol. Pharmacological data implicate a role for the NPY Y(2) receptor in ethanol self-administration. The purpose of the present study was to determine if genetic mutation of the Y(2) receptor would modulate ethanol consumption and/or ethanol-induced sedation. Here, we report that mutant mice lacking the NPY Y(2) receptor (Y(2)(-/-)), when maintained on a mixed 50% 129/ SvJ x 50 % Balb/cJ background, drink significantly less of solutions containing 3 or 6% (v/v) ethanol relative to wild-type (Y(2)(+/+)) mice. These mice drink normal amounts of solutions containing sucrose or quinine, have normal blood ethanol clearance, and show normal sensitivity to ethanol-induced sedation. However, Y(2)(-/-) mice that are backcrossed to a Balb/cJ background show normal consumption of ethanol, indicating that the contributions of the NPY Y(2) receptor to ethanol consumption are genetic background dependent. Consistent with previous data suggesting that NPY modulates water drinking, Y(2)(-/-) mice of both genetic backgrounds consume significantly more water than Y(2)(+/+) mice. The present results suggest roles for the NPY Y(2) receptor in the modulation of ethanol and water consumption.

Characterization of neuropeptide Y Y2 and Y5 receptor expression in the mouse hypothalamus

Neuropeptide Y (NPY) neurons abundantly innervate the hypothalamus, where NPY is involved in the regulation of a broad range of homeostatic functions. In the present work we studied NPY Y2 and Y5 receptor (R) gene expression in the mouse hypothalamus by using immunohistochemical detection of beta-galactosidase (beta-gal), a gene reporter molecule for Y2R and Y5R in Y2R-knockout (KO) and Y5R-KO mice, respectively. With this approach, cells normally expressing Y2R or Y5R are immunopositive for beta-gal. In the hypothalamus of the Y2R-KO mouse, beta-gal immunoreactivity (-ir) was found in numerous neurons of the medial preoptic nucleus as well as in the lateral anterior, periventricular, dorsomedial, tuberal, perifornical, and arcuate nuclei. Most of the dopaminergic neurons in the A13 dorsal hypothalamic group were beta-gal positive, whereas other hypothalamic dopaminergic neurons rarely displayed beta-gal-ir. In the arcuate nucleus, most of the beta-gal-positive neurons expressed NPY, but colocalizations with beta-endorphin were also found; in the tuberal and perifornical nuclei, many beta-gal-positive neurons contained nitric oxide synthase. beta-Gal-ir was also found in other forebrain regions of the Y2R-KO mouse, including the amygdala, thalamic nuclei, hippocampal CA3 area, and cortex. In the hypothalamus of the Y5R-KO mouse, beta-gal-positive neurons were found mainly in the arcuate nucleus and contained beta-endorphin. The present data show that Y2R and Y5R are expressed in distinct groups of hypothalamic neurons. High levels of Y2R expression in the preoptic nuclei suggest an involvement of Y2R in the regulation of reproductive behavior, whereas Y2R expression in the arcuate, dorsomedial, and perifornical nuclei may be relevant to feeding and body weight control. The finding that A13 dopaminergic neurons express Y2R suggests a new mechanism putatively involved in the central control of feeding, in which NPY can modulate dopamine secretion. The distribution of Y5R expression supports earlier evidence for involvement of this receptor in control of feeding and body weight via NPY's action on proopiomelanocortin-expressing neurons. J. Comp. Neurol. 470:256-265, 2004.

Change in the expression of NPY receptor subtypes Y1 and Y2 in central and peripheral neurons related to the control of blood pressure in rats following experimental hypertension

Neuropeptide Y (NPY) is known to participate in central mechanisms of blood pressure control. However, variations on the expression of its receptors in response to a hypertensive challenge are not well defined, specially when considering that Y1 and Y2 often mediate opposite responses. In this study we have employed in situ hybridization to analyze changes in mRNA expression of NPY receptor subtypes Y1 and Y2 in the nucleus tractus solitarii (NTS), paraventricular nucleus of the hypothalamus (PVN) and petrosal and nodose ganglions 2 h, 3 and 7 days after aortic coarctation induced hypertension. Quantification by image analysis showed significant differences between sham-operated and aortic-coarcted hypertensive rats. Y1 receptor mRNA expression was increased (39%) in petrosal ganglion, 3 days after surgery. Y2 receptor mRNA expression was increased (143%) in the NTS of hypertensive compared with sham rats 2 h after surgery. Y2 receptor mRNA was decreased (62%) in the nodose ganglion of hypertensive compared with sham rats 2 h after surgery. No change was seen in Y1 and Y2 mRNA expression in the PVN in any analyzed period. The data suggest that NPY Y1 and Y2 receptors might participate in the mechanisms involved in the establishment/maintenance of hypertension induced by aortic coarctation. Acute changes seem to be involved with the adaptation to the new hypertensive state.

Neuropeptide Y selectively potentiates alpha1-adrenoceptor-mediated contraction through Y1 receptor subtype in rat femoral artery

The aim of this study was to investigate the synergism between neuropeptide Y and other vasoconstrictors (phenylephrine and serotonin) and which neuropeptide Y receptor subtype is responsible for the neuropeptide Y-induced potentiation. Exogenous neuropeptide Y (10 nM) potentiated alpha1-adrenoceptor-mediated (PE-induced) contraction in rat femoral artery permissively without its direct action, but not in the thoracic aorta. In contrast, neuropeptide Y produced no change in serotonin-induced contraction in both arteries. Increasing concentrations of neuropeptide Y caused dose-dependent potentiation of the phenylephrine-induced contraction in the femoral artery. This potentiation was blocked by a selective neuropeptide Y-Y1 receptor antagonist, BIBP3226 [(R)-N2-(diphenylacetyl)-N-[4-hydroxyphenyl)methyl]-argininamide] (1 microM). Semiquantitative reverse transcriptase polymerase chain reaction showed the selective expression of neuropeptide Y-Y1 receptor mRNA in the femoral artery. These findings indicated that the neuropeptide Y-induced selective potentiation of alpha1-adrenoceptor-mediated contraction is mediated through neuropeptide Y-Y1 receptor in rat femoral artery.

Novel neuropeptide Y Y2-like receptor subtype in zebrafish and frogs supports early vertebrate chromosome duplications

The Y receptors comprise a family of G-protein coupled receptors with neuropeptide Y-family peptides as endogenous ligands. The Y receptor family has five members in mammals and evolutionary data suggest that it diversified in the two genome duplications proposed to have occurred early in vertebrate evolution. If this theory holds true, it allows for additional family members to be present. We describe here the cloning, pharmacological characterization, tissue distribution, and chromosomal localization of a novel subtype of the Y-receptor family, named Y7, from the zebrafish. We also present Y7 sequences from rainbow trout and two amphibians. The new receptor is most similar to Y2, with 51-54% identity. As Y2 has also been cloned from some of these species, there clearly are two separate Y2-subfamily genes. Chromosomal mapping in zebrafish supports origin of Y7 as a duplicate of Y2 by chromosome duplication in an early vertebrate. Y7 has probably been lost in the lineage leading to mammals. The pharmacological profile of the zebrafish Y7 receptor is different from mammalian Y2, as it does not bind short fragments of NPY with a high affinity. The Y7 receptor supports the theory of early vertebrate genome duplications and suggests that the Y family of receptors is a result of these early genome duplications.

Chronic neuropeptide Y infusion into the lateral ventricle induces sustained feeding and obesity in mice lacking either Npy1r or Npy5r expression

Neuropeptide Y (NPY) is a powerful orexigenic neurotransmitter. The NPY Y1 and Y5 receptors have been implicated in mediating the appetite-stimulating activity of NPY. To further investigate the importance of these two receptors in NPY-induced hyperphagia after chronic central administration, we used mice lacking either Npy1r or Npy5r expression. NPY infusion into the lateral ventricle of wild-type mice stimulated food intake and induced obesity over a 7-d period. Fat pad weight as well as plasma insulin, leptin, and corticosterone levels were strongly increased in NPY-treated mice. In addition, NPY infusion resulted in a significant decrease in hypothalamic NPY and proopiomelanocortin expression. Interestingly, the lack of either Npy1r or Npy5r expression in knockout mice did not affect such feeding response to chronic NPY infusion. Moreover, the obesity syndrome that developed in these animals was similar to that in wild-type animals. Taken together, these data strongly suggest biological redundancies between Y1 and Y5 receptor signaling in the NPY-mediated control of food intake.

Alcoholism and obesity: overlapping neuropeptide pathways?

Ethanol is a caloric compound, and ethanol drinking and food intake are both appetitive and consummatory behaviors. Furthermore, both ethanol and food have rewarding properties. It is therefore possible that overlapping central pathways are involved with uncontrolled eating and excessive ethanol consumption. A growing list of peptides has been shown to regulate food intake and/or energy homeostasis. Peptides such as the melanocortins, corticotropin releasing factor, and cholecystokinin promote reductions of food intake while others such as galanin and neuropeptide Y stimulate feeding. The present review highlights research aimed at determining if ingestive peptides also regulate voluntary ethanol intake, with an emphasis on the melanocortins and neuropeptide Y. It is suggested that research directed at ingestive peptides may expand our understanding of the neurobiological mechanisms that drive ethanol self-administration, and may reveal new therapeutic candidates for treating alcohol abuse and alcoholism.

Comparative distribution of neuropeptide Y Y1 and Y5 receptors in the rat brain by using immunohistochemistry

Neuropeptide Y (NPY) Y1 and Y5 receptor subtypes mediate many of NPY's diverse actions in the central nervous system. The present studies use polyclonal antibodies directed against the Y1 and Y5 receptors to map and compare the relative distribution of these NPY receptor subtypes within the rat brain. Antibody specificity was assessed by using Western analysis, preadsorption of the antibody with peptide, and preimmune serum controls. Immunostaining for the Y1 and Y5 receptor subtypes was present throughout the rostral-caudal aspect of the brain with many regions expressing both subtypes: cerebral cortex, hippocampus, hypothalamus, thalamus, amygdala, and brainstem. Further studies using double-label immunocytochemistry indicate that Y1R immunoreactivity (-ir) and Y5R-ir are colocalized in the cerebral cortex and caudate putamen. Y1 receptor ir was evident in the central amygdala, whereas both Y1- and Y5-immunoreactive cells and fibers were present in the basolateral amygdala. Corresponding with the physiology of NPY in the hypothalamus, both Y1R- and Y5R-ir was present within the paraventricular (PVN), supraoptic, arcuate nuclei, and lateral hypothalamus. In the PVN, Y5R-ir and Y1R-ir were detected in cells and fibers of the parvo- and magnocellular divisions. Intense immunostaining for these receptors was observed within the locus coeruleus, A1-5 and C1-3 nuclei, subnuclei of the trigeminal nerve and nucleus tractus solitarius. These data provide a detailed and comparative mapping of Y1 and Y5 receptor subtypes within cell bodies and nerve fibers in the brain which, together with physiological and electrophysiological studies, provide a better understanding of NPY neural circuitries.

Induced down-regulation of neuropeptide Y-Y1 receptors delays initiation of kindling

Neuropeptide Y appears to modulate epileptic seizures differentially according to the receptor subtypes involved. In the hippocampus, neuropeptide Y expression and release are enhanced in different models of epileptogenesis. On the contrary, the expression of Y1 receptors is decreased and it has been shown that activation of these receptors has pro-convulsant effects. The aim of our study was to investigate the role of Y1 receptors during hippocampal kindling epileptogenesis using (i) knock-out mice lacking Y1 receptors and (ii) intrahippocampal infusion of Y1 antisense oligodeoxynucleotide in rats. Y1 knock-out mice showed similar susceptibility to seizure induction and presented no difference in kindling development as compared with their control littermates. Conversely, local hippocampal down-regulation of Y1 receptors during the first week of hippocampal kindling, induced by a local infusion of a Y1 antisense oligodeoxynucleotide, significantly increased seizure threshold intensity and decreased afterdischarge duration. A reverse effect was observed during the week following the infusion period, which was confirmed by a significant decrease in the number of hippocampal stimulations necessary to evoke generalized seizures. At the end of this second week, an up-regulation of Y1 receptors was observed in kindled rats infused with the antisense as compared with the mismatch-treated controls. Our results in the rat suggest that the down-regulation of Y1 receptors in the hippocampus participates in the control of the initiation of epileptogenesis. The lack of an effect of the deficiency of Y1 receptors in the control of kindling development in Y1 knock-out mice could be due to compensatory mechanisms.

A role for neuropeptide Y in alcohol intake control: evidence from human and animal research

This article is based on proceedings of a symposium presented at the 2002 meeting of the Society for the Study of Ingestive Behavior and provides a brief overview of recent research suggesting a role for neuropeptide Y (NPY) in the modulation of ethanol drinking. The discussion focuses mainly on recent studies with genetic animal models including mutant mice lacking specific NPY receptor and selectively bred rodents, namely the Indiana alcohol-preferring (P) and alcohol-nonpreferring (NP) rats and the Indiana high alcohol drinking (HAD) and low alcohol drinking (LAD) rats. It is concluded that abnormal or low central NPY activity can promote high alcohol drinking and that NPY modulates alcohol consumption via the NPY Y1 and Y2 receptors.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Recent developments in our understanding of the physiological role of PP-fold peptide receptor subtypes

The three peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure known as the PP-fold. There are four known human G-protein coupled receptors for the PP-fold peptides, namely Y1, Y2, Y4, and Y5, each of them being able to bind at least two of the three endogenous ligands. All three peptides are found in the circulation acting as hormones. Although NPY is only released from neurons, PYY and PP are primarily found in endocrine cells in the gut, where they exert such effects as inhibition of gall bladder secretion, gut motility, and pancreatic secretion. However, when PYY is administered in an experimental setting to animals, cloned receptors, or tissue preparations, it can mimic the effects of NPY in essentially all studies, making it difficult to study the effects of PP-fold peptides and to delineate what receptor and peptide accounts for a particular effect. Initial studies with transgenic animals confirmed the well-established action of NPY on metabolism, food-intake, vascular systems, memory, mood, neuronal excitability, and reproduction. More recently, using transgenic techniques and novel antagonists for the Y1, Y2, and Y5 receptors, NPY has been found to be a key player in the regulation of ethanol consumption and neuronal development.

Neuropeptide y and alcoholism: genetic, molecular, and pharmacological evidence

This article presents the proceedings of a symposium presented at the combined meeting of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism, held in San Francisco, CA, in June 2002. The organizers and chairpersons were Subhash C. Pandey and Todd E. Thiele. The presentations were (1) Altered ethanol-induced sedation and ethanol drinking in mutant mice lacking specific NPY receptor, by Todd E. Thiele; (2) NPY in P and NP rats: polymorphism and mRNA expression, by Lucinda G. Carr; (3) The cAMP-dependent PKA in the central amygdala regulates alcohol intake through NPY gene, by Subhash C. Pandey; (4) Involvement of NPY in alcohol dependence: from animal models to human genetics, by Markus Heilig; and (5) Association of neuropeptide Y polymorphism with the occurrence of type 1 and type 2 alcoholism, by Erkki Ilveskoski.

Mitogenic actions of neuropeptide Y in vascular smooth muscle cells: synergetic interactions with the beta-adrenergic system

Neuropeptide Y (NPY), a sympathetic cotransmitter and vasoconstrictor, also stimulates vascular smooth muscle cell (VSMC) growth, but which of its Y1-Y5 receptors are involved remains unclear. In quiescent rat VSMCs, NPY receptor mRNAs were undetectable (reverse transcription-polymerase chain reaction), but Y1, Y2, and Y5 expression were upregulated or induced following NPY treatment. Concomitantly, NPY increased up to twofold [3H]thymidine incorporation and cell number bimodally, with a high-affinity peak at pM and low affinity peak at nM concentrations. The Y1 or Y5 (not Y2) antagonist alone did not change the high-affinity peak but decreased the low affinity peak by 50% and fully blocked NPY's response when combined. In VSMCs lacking NPY receptors and responsiveness, transient Y1 cDNA transfection restored their mitogenic response (blocked by the Y1 antagonist). In VSMCs with low or no NPY responsiveness, pre-exposure to beta-adrenergic receptor agonist (isoproterenol), forskolin, or dibutyryl cAMP augmented NPY's mitogenic effect, while upregulating Y1, Y2, and Y5 receptor expression (isoproterenol only). Thus, NPY is a potent vascular mitogen acting via Y1 and Y5 receptors. However, since their expression is low in nonproliferating cells, amplification of NPY's mitogenic responses requires upregulation of at least the Y1 receptor by NPY itself or beta-adrenergic, cAMP-dependent activation.

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.

Neuropeptide Y inhibits axonal transport of particles in neurites of cultured adult mouse dorsal root ganglion cells

Neuropeptide Y (NPY) plays a modulatory role in processing nociceptive information. The present study investigated the effects of NPY on axonal transport of particles in neurites of cultured adult dorsal root ganglion (DRG) cells using video-enhanced microscopy. Application of NPY decreased the number of particles transported in both the anterograde and retrograde directions. This effect was persistently observed during NPY application and was reversed after washout. The inhibitory effect of NPY was concentration dependent between 10(-9) M and 10(-6) M. The instantaneous velocity of individual particles moving in anterograde and retrograde directions was also reduced by NPY. Both the NPY Y1 receptor agonist [Leu31,Pro34]-NPY and NPY Y2 receptor agonist NPY(13-36) mimicked the effect of NPY on the number of transported particles. An immunocytochemical study using an antiserum against the NPY Y1 receptor protein revealed that the Y1 receptor was expressed in the majority (85.9 %) of cultured adult mouse DRG cells. Pre-treatment of cells with pertussis toxin, a GTP-binding protein (G protein) inhibitor, completely blocked the inhibitory effect of NPY. Each application of SQ-22536, an adenylate cyclase inhibitor, and H-89, a protein kinase A inhibitor, mimicked and occluded the effect of NPY. In contrast, dibutyryl cAMP (dbcAMP), a membrane permeable cAMP analogue, and forskolin, an activator of adenylate cyclase, produced a transient increase in axonal transport. The application of dbcAMP and forskolin in combination with NPY negated the effect of NPY alone. These results suggest that NPY, acting at Y1 and Y2 receptors, inhibits axonal transport of particles in sensory neurones. The effect seems to be mediated by a pertussis toxin-sensitive G protein, adenylate cyclase, and protein kinase A pathway. Therefore, NPY may be a modulatory factor for axonal transport in sensory neurones.

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 neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Y4 receptor knockout rescues fertility in ob/ob mice

Hypothalamic neuropeptide Y (NPY) has been implicated in the regulation of energy balance and reproduction, and chronically elevated NPY levels in the hypothalamus are associated with obesity and reduced reproductive function. However, it is not known which one of the five cloned Y receptors mediates these effects. Here we show that crossing the Y4 receptor knockout mouse (Y4(-/-)) onto the ob/ob background restores the reduced plasma testosterone levels of ob/ob mice as well as the reduced testis and seminal vesicle size and morphology to control values. Fertility in the sterile ob/ob mice was greatly improved by Y4 receptor deletion, with 100% of male and 50% of female Y4(-/-),ob/ob double knockout mice producing live offspring. Development of the mammary ducts and lobuloalveoli was significantly enhanced in pregnant Y4(-/-) and Y4(-/-),ob/ob females. Consistent with the improved fertility and enhanced mammary gland development, gonadotropin releasing hormone (GnRH) expression was significantly increased in Y4(-/-) and Y4(-/-),ob/ob animals. Y4(-/-) mice displayed lower body weight and reduced white adipose tissue mass accompanied by increased plasma levels of pancreatic polypeptide (PP). However, Y4 deficiency had no beneficial effects to reduce body weight or excessive adiposity of ob/ob mice. These data suggest that central Y4 receptor signaling specifically inhibits reproductive function under conditions of elevated central NPY-ergic tonus.

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.

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.

Hypothalamic Y2 receptors regulate bone formation

Neuropeptide Y (NPY) is a downstream modulator of leptin action, possibly at the level of the arcuate nucleus where NPY neurons are known to express both leptin receptors and Y2 receptors. In addition to the well-described role of NPY and leptin in energy balance and obesity, intracerebroventricular administration of NPY or leptin also causes bone loss. Here we show that Y2 receptor-deficient mice have a twofold increase in trabecular bone volume as well as greater trabecular number and thickness compared with control mice. We also demonstrate that central Y2 receptors are crucial for this process, since selective deletion of hypothalamic Y2 receptors in mature conditional Y2 knockout mice results in an identical increase in trabecular bone volume within 5 weeks. This hypothalamus-specific Y2 receptor deletion stimulates osteoblast activity and increases the rate of bone mineralization and formation, with no effect on osteoblast or osteoclast surface measurements. The lack of any changes in plasma total calcium, leptinemia, or hypothalamo-pituitary-corticotropic, -thyrotropic, -somatotropic, or -gonadotropic output suggests that Y2 receptors do not modulate bone formation by humoral mechanisms, and that alteration of autonomic function through hypothalamic Y2 receptors may play a key role in a major central regulatory circuit of bone formation.

NPY Y1 receptors are present in axonal processes of DRG neurons

Using a sensitive immunohistochemical method, the localization of the neuropeptide Y (NPY) Y1 receptor (Y1R) was studied in contralateral and ipsilateral dorsal root ganglion (DRG) neurons of rats subjected to different unilateral manipulations with focus on their axonal processes and projection areas. Y1R-like immunoreactivity (LI) was observed in the contralateral sciatic nerve and dorsal roots of lesioned rats, and double staining revealed colocalization with calcitonin gene-related peptide (CGRP). Y1R-LI was also seen in fibers close to and even within the epidermis. A fairly small number of nerve endings double-labeled for Y1R and CGRP were present in the dorsal horn. After unilateral crush of the sciatic nerve Y1R- and CGRP-LI accumulated in the same axons proximal to the lesion. After dorsal rhizotomy CGRP-LI was strongly reduced in the ipsilateral dorsal horn. No certain change was observed for Y1R- or NPY-LI, but Y1R/CGRP double-labeled nerve endings disappeared after the lesion. These results strongly suggest centrifugal transport of Y1Rs in DRG neurons, mainly to the peripheral sensory branches. To what extent these Y1Rs are functional has not been analyzed here, but a recent study on Y1R null mice provides evidence for involvement of prejunctional Y1Rs in peripheral sensory functions

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.

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.

Neuropeptide Y functions as a neuroproliferative factor

Neuropeptide Y (NPY) has a number of functions in mammalian physiology. Here we identify a role for NPY in promoting proliferation of postnatal neuronal precursor cells. NPY is synthesized in the postnatal olfactory epithelium by sustentacular cells, previously proposed to function only in structural support. Mice with a targeted deletion of NPY contain half as many dividing olfactory neuronal precursor cells as do controls. Furthermore, NPY-deficient mice develop significantly fewer olfactory neurons by adulthood. NPY acts on multipotent neuronal precursor or basal cells to activate rapidly and transiently the extracellular signal-regulated kinase (ERK)1/2 subgroup of mitogen-activated protein kinases. The NPY Y1 receptor subtype appears to mediate this effect. The ability of NPY to induce neuronal precursor proliferation is mediated by protein kinase C (PKC), indicating an upstream PKC-dependent activation of ERK1/2. These results indicate that NPY may regulate neuronal precursor proliferation in the adult mammal.

Differential regulation of neuropeptide Y receptors in the brains of NPY knock-out mice

To study the effect of NPY deletion on the regulation of its receptors in the NPY knockout (NPY KO) mice, the expression and binding of NPY receptors were investigated by in situ hybridization and receptor autoradiography using (125)I-[Leu(31),Pro(34)]PYY and (125)I-PYY(3-36) as radioligands. A 6-fold increase in Y2 receptor mRNA was observed in the CA1 region of the hippocampus in NPY KO mice, but a significant change could not be detected for Y1, Y4, Y5 and y6 receptors. Receptor binding reveals a 60-400% increase of Y2 receptor binding in multiple brain areas. A similar increase in Y1 receptor binding was seen only in the hypothalamus. These results demonstrate the NPY receptor expression is altered in mice deficient for its natural ligand.

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.

Neuropeptide Y and epilepsy: varying effects according to seizure type and receptor activation

In vitro and in vivo experiments suggest antiepileptic properties for NPY. In this study, the pharmacology of these effects was examined and compared in different rat models of seizures. Agonists for Y(1), Y(2) and Y(5) receptors reduced seizure-like activity in hippocampal cultures. Intracerebral injection of NPY or Y(5) agonists reduced the expression of focal seizures produced by a single electrical stimulation of the hippocampus. Conversely, NPY agonists increased the duration of generalized convulsive seizures induced by pentylenetetrazol. These results suggest that NPY reduces seizures of hippocampal origin through activation of Y(5) receptors. They also point to probable modulatory effects of NPY in brain structures other than the hippocampus, involved in initiation, propagation or control of seizures.