Neuropeptide Y-induced Feeding Research Articles

Neuropeptide Y-induced feeding is dependent on GABAA receptors in neonatal chicks

In mammals and birds, neuropeptide Y (NPY) and gamma-aminobutyric acid (GABA) are found in brain areas known to be involved in the control of ingestive behavior and act to increase voluntary food intake. In rats, significant evidence suggest a functional and behavioral interaction between NPY and GABA mediated transmission in various brain regions, including the arcuate and paraventricular nuclei of the hypothalamus which can be important in the regulation of feeding behavior. In the present study, the effect of intracerebroventricular (ICV) administration of NPY and GABA receptor antagonists on food intake was examined in neonatal chicks. The ICV injection of NPY strongly stimulated food intake while co-administration of NPY and picrotoxin, a GABA(A) antagonist, (but not CGP54626, a GABA(B) antagonist) weakened food intake induced by NPY. These results suggest that central NPY stimulates food intake in neonatal chicks by interaction with the GABAergic system via GABA(A) receptors.

Response of neuropeptide Y-induced feeding to μ-, δ- and κ-opioid receptor antagonists in the neonatal chick

It is known that opioid antagonists reduce the orexigenic effect of neropeptide Y (NPY) in mammals. We studied the effect of three opioid antagonists on NPY-induced feeding in male broiler chicks. β-Funaltrexamine (β-FNA), naloxonazine (NAL), ICI-174,864 (ICI) or nor-binaltorphimine (nor-BNI), antagonists of μ-, μ 1-, δ- or κ-receptors, and NPY were co-injected in chicks. Food intake was measured 30 min after treatment. Co-injection of β-FNA or NAL was effective in reducing NPY-induced feeding, whereas ICI and nor-BNI had little effect on NPY-induced feeding. These data suggest that the μ-opioid receptor, especially the μ 1-opioid has some relation to NPY-induced feeding, and implies that an endogenous ligand, such as β-endorphin, participates in the orexigenic effect of NPY in neonatal chicks.

Neuropeptide Y immunoreactivity and corticotropin-releasing hormone mRNA level are increased in the hypothalamus of mouse bearing a human oral squamous cell carcinoma

We examined gene expression of corticotropin-releasing hormone and neuropeptide Y level in the hypothalamic paraventricular nucleus of mouse bearing a human oral squamous cell carcinoma. A cell line derived from a human oral squamous cell carcinoma was inoculated into the lower dorsal area of nude mice. Body weight, tumor size and daily food intake were recorded every morning. Mice were sacrificed for corticotropin-releasing hormone mRNA in situ hybridization and neuropeptide Y immunohistochemistry, when the tumor ratio reached to 11-13% of real body weight. The results were compared with the age-matching non-tumor controls injected with saline instead of carcinoma cell. Body weight gain was significantly reduced in tumor bearing mice, however, no compensatory hyperphagia was found, i.e. daily food intake of the tumor mice did not differ from the non-tumor mice. Both neuropeptide Y immunoreactivity and corticotropin-releasing hormone mRNA level were significantly increased in the hypothalamic paraventricular nucleus of tumor mice. These results suggest that a human oral squamous cell carcinoma may induce anorexia, at least partly, via increasing the hypothalamic expression of corticotropin-releasing hormone in the tumor subjects. Additionally, neuropeptide Y-induced feeding appears to be inhibited in this tumor anorexia model, and this may correlate with increased expression of corticotropin-releasing hormone.

Discovery and optimization of a series of carbazole ureas as NPY5 antagonists for the treatment of obesity.

The hypothesis that antagonists of the neuropeptide Y5 receptor would provide safe and effective appetite suppressants for the treatment of obesity has prompted vigorous research to identify suitable compounds. We discovered a series of acylated aminocarbazole derivatives (e.g., 3a) that are potent and selective Y5 antagonists, representing interesting starting points but suffering from poor bioavailability and concerns about potential toxicity as a consequence of the embedded aminocarbazole fragment. It proved relatively easy to improve the drug metabolism and pharmacokinetic (DMPK) properties by variation of the side chain (as in 4a) but difficult to eliminate the aminocarbazole fragment. For compounds in this series to have the potential to be drugs, we believed that both the compound itself and the component aniline must be free of mutagenic activity. Parallel structure-activity relationship studies looking at the effects of ring substitution have proved that it is possible by incorporation of a 4-methyl substituent to produce carbazole ureas with potent Y5 activity, comprised of carbazole anilines that in themselves are devoid of mutagenic activity in the Ames test. Compound 4o (also known as NPY5RA-972) is highly selective with respect to Y1, Y2, and Y4 receptors (and also to a diverse range of unrelated receptors and enzymes), with an excellent DMPK profile including central nervous system penetration. NPY5RA-972 (4o) is a highly potent Y5 antagonist in vivo but does not block neuropeptide Y-induced feeding nor does it reduce feeding in rats, suggesting that the Y5 receptor alone has no significant role in feeding in these models.

The kappa-opioid antagonist GNTI reduces U50,488-, DAMGO-, and deprivation-induced feeding, but not butorphanol- and neuropeptide Y-induced feeding in rats

Antagonists selective for either kappa- [e.g. nor-binaltorphimine (nor-BNI)] and mu- (e.g. beta-funaltrexamine) opioid receptors have previously been shown to reduce both kappa- and mu-opioid-induced feeding. In the present studies, the anorectic effects of GNTI, a newly synthesized antagonist selective for kappa-opioid receptors, were studied in rats. GNTI (0.032–0.32 nmol; i.c.v.), administered 15 min prior to food access, reduced feeding induced by the kappa-opioid agonist U50,488 (producing a 70% maximal decrease), the mu-opioid agonist DAMGO (90% maximal decrease), and 24 h acute food deprivation (60% maximal decrease). GNTI did not reduce the orexigenic effects of butorphanol, an agonist that binds to both kappa- and mu-opioid receptors, and neuropeptide Y (NPY). Taken together, these results suggest that GNTI is a potent anorectic agent and opioid antagonist in rats. Like nor-BNI, GNTI reduced feeding induced by both kappa- and mu-opioid agonists. However, unlike nor-BNI, GNTI did not alter the orexigenic effects of butorphanol or NPY. Given the selectivity of GNTI and its effectiveness in several of the present experiments, its potency, and its short duration of action compared to nor-BNI, GNTI may serve to be a useful tool to study behavioral effects mediated by kappa-opioid receptors.

Central administration of α-melanocyte stimulating hormone inhibits fasting- and neuropeptide Y-induced feeding in neonatal chicks

In the present study, the effect of intracerebroventricular (i.c.v.) administration of α-melanocyte stimulating hormone (α-MSH) on food intake of neonatal chicks was examined. In experiment 1, i.c.v. injection of α-MSH (0.04, 0.2 and 1 μg) significantly inhibited food intake of 3-h fasted chicks in a dose-dependent manner. In experiment 2, α-MSH strongly inhibited neuropeptide Y-induced feeding when neuropeptide Y (2.5 μg) and several doses of α-MSH were given simultaneously i.c.v. These results suggest that α-MSH plays an important role in the regulation of food intake of neonatal chicks.

Hypocretin/Orexin- and melanin-concentrating hormone-expressing cells form distinct populations in the rodent lateral hypothalamus: Relationship to the neuropeptide Y and agouti gene-related protein systems

Cells in the lateral hypothalamus and in the arcuate nucleus play prominent roles in the central control of food intake; however, a neurochemical link connecting these potential components of a hypothalamic circuitry regulating energy metabolism remains to be established. In the present study, the topographical relationship between cells expressing mRNAs encoding melanin-concentrating hormone and the newly discovered neuropeptide family hypocretins/orexins was studied in the rat and mouse lateral hypothalamus by using double-labeling in situ hybridization. Cells expressing the two mRNAs formed completely distinct populations, with hypocretin/orexin cells located primarily perifornically and in the magnocellular lateral hypothalamic nucleus; melanin-concentrating hormone cells extended in a wider area both laterally and periventricularly and appeared to partly surround the hypocretin/orexin population. In the arcuate nucleus, cells expressing neuropeptide Y and agouti gene-related protein were studied by routine fluorescence and/or confocal microscopy immunohistochemistry. Double staining demonstrated that a large proportion of the neuropeptide Y-positive cell bodies in this nucleus also contained agouti gene-related protein-like immunoreactivity. Moreover, these two peptides also coexisted in nerve terminals surrounding and in close relationship to perikarya and processes of both hypocretin/orexin- and melanin-concentrating hormone-immunoreactive cells in the lateral hypothalamus, whereby the former appeared to receive a more dense innervation. These results thus provide evidence for an arcuate-lateral hypothalamic neuropeptide Y/agouti gene-related protein pathway. Furthermore, the results implicate hypocretin/orexin and melanin-concentrating hormone-expressing cells as downstream targets in neuropeptide Y-induced feeding.

Neuropeptide Y-Induced Feeding and Its Control

Publisher Summary This chapter critically reviews evidence of physiologically relevant appetite stimulation by neuropeptide Y (NPY) and to forecast how this knowledge might be applied in the context of eating disorders. Recently, a novel receptor for NPY, termed “Y5”, has been cloned from rat hypothalamus and appears to meet all the criteria necessary to be designated the “feeding” receptor distinct from previously cloned Y-type receptors. Striking appetite stimulation by NPY receptor agonists under pharmacological conditions can only elucidate the true physiological role of this neuropeptide if NPY receptor antagonists are found to be equally effective in blunting feeding produced under naturalistic conditions. Evidence for insulin actions on NPY gene expression was provided by studies that demonstrated that central infusion of insulin could depress elevated preproNPY mRNA levels induced by food deprivation of lean Zucker rats but was without effect on preproNPY mRNA content in fed or fasted obese Zucker rats. The extrapolation of the NPY-induced overeating and overweight syndrome in rodents to human obesity must await knowledge about the role of NPY in the human brain.

Interaction of the Hypothalamic Paraventricular Nucleus and Central Nucleus of the Amygdala in Naloxone Blockade of Neuropeptide Y-Induced Feeding Revealed byc-fosExpression

Neuropeptide Y (NPY) is a powerful inducer of food intake with a key site of action in the paraventricular nucleus (PVN) of the hypothalamus. An effective method for inhibiting the effects of NPY is pretreatment with the opioid antagonists naloxone or naltrexone. In the present study, we used immunohistochemistry for cFos as a marker of neuronal activity to map the effects of PVN-injected NPY and blockade of these effects by peripheral injection of naloxone. Injection of NPY into the PVN resulted in an increase in food intake that was blocked by peripheral administration of naloxone. PVN NPY also resulted in increased cFos immunoreactivity (cFos-IR) in the PVN independent of food intake, and although peripheral naloxone inhibited NPY-induced feeding, it did not alter cFos-IR in the PVN. cFos-IR in the central nucleus of the amygdala (CNA) increased in response to both NPY and naloxone. Furthermore, the response to NPY and naloxone was additive, suggesting that peripheral naloxone and PVN NPY activate different neuronal populations in the CNA. Three other brain regions, the nucleus of the solitary tract, the ventrolateral medulla, and the supraoptic nucleus, all showed increases in cFos-IR in this study, but these changes came only as a result of increased food intake after PVN-injected NPY. The current data suggest that the CNA is a site important for the integration of the NPY and opioid systems.

Effect of naltrexone on feeding, neuropeptide Y and uncoupling protein gene expression during lactation.

Neuropeptide Y increases feeding and decreases measures of brown adipose tissue thermogenesis. In lactating rats, increased feeding, increased hypothalamic neuropeptide Y neuroactivity and decreased thermogenesis occur. Naltrexone is an opioid receptor antagonist which decreases neuropeptide Y-induced feeding and reverse neuropeptide Y-induced decreases in brown adipose tissue thermogenesis. We hypothesized that opioid receptors are involved in neuropeptide Y neuroactivity during lactation. To see if naltrexone would alter feeding neuropeptide Y gene expression in the arcuate nucleus, neuropeptide Y levels in the paraventricular nucleus, and uncoupling protein gene expression in brown adipose tissue of lactating rats, osmotic minipumps pre-filled with either 0.9% saline or naltrexone (70 micrograms/h) were implanted subcutaneously in 47 female Sprague-Dawley rats weighing 309 +/- 5 g. Half these rats were studied on days 10-16 of lactation, and the other half were studied 7 days after lactation. After 48 h, neuropeptide Y mRNA levels and uncoupling protein mRNA levels were determined using specific cDNA probes. Neuropeptide Y peptide levels in the paraventricular nucleus were measured by radioimmunoassay. Naltrexone decreased food intake by 26% in the postlactating rats, but had no effect on feeding in the lactating animals. Lactation resulted in significantly increased arcuate neuropeptide Y mRNA, decreased neuropeptide Y levels in the paraventricular nucleus and decreased brown adipose tissue uncoupling protein mRNA levels. Naltrexone did not influence any of these parameters. Thus, the alterations in neuropeptide Y neuroactivity and brown fat thermogenesis which occur in lactation is not altered by generalized opioid receptor blockade.

Regional hypothalamic differences in neuropeptide Y-induced feeding and energy substrate utilization

Previous research has shown that both the paraventricular nucleus (PVN) of the hypothalamus and the perifornical hypothalamus (PFH) are sites at which microinjection of neuropeptide Y (NPY) can induce eating. The PVN has also been shown to be responsive to the effects of exogenous NPY on energy substrate utilization. Therefore, the objective of the present study was to further characterize and compare the effects of NPY on whole-body calorimetry and feeding after microinjection into either the PVN or the PFH. The metabolic effects of NPY (19.5-78 pmol) were determined using an open-circuit calorimeter by measuring the volumes of oxygen consumed and carbon dioxide expired in order to compute respiratory quotients (RQs). Following NPY injection into the PVN ( n = 10) or PFH ( n = 10), RQs and locomotor activity were monitored over three hours. Additional groups of rats with PVN ( n = 10) or PFH ( n = 10) cannulae were tested for their feeding responses to these same doses of peptide. While NPY injections into the PVN evoked dose-dependent increases in RQ within 30–40 min of treatment, PFH NPY did not alter RQ at any of the doses tested. Locomotor activity was unaffected by NPY in either site. NPY administration into both the PVN and PFH stimulated eating, although the PFH was found to be the more sensitive in terms of absolute amount of food consumed. These findings support the hypothesis that the PVN may regulate metabolic processes that either produce or coincide with NPY-induced feeding. This contrasts with the PFH, which appears to mediate only the feeding-stimulatory actions of NPY.

Behavioral effects of naloxone on neuropeptide Y-induced feeding

We evaluated the effect of naloxone on neuropeptide Y (NPY)-induced feeding behavior using two methods; operant chambers and observational analysis. In the first study rats were trained on a FR 80 (first pellet) FR 3 (subsequent pellets) reinforcement schedule. Following training, rats were injected with NPY (intraventricular, 5 (ig) and various doses of naloxone (subcutaneous, 0, 0.1, 0.3, 1, 3, and 10 mg/kg). NPY significantly increased the number of pellets consumed during the one hour session and naloxone (1, 3, and 10 mg/kg) blocked this effect. NPY failed to alter the time to the first response, but did decrease the time needed to complete the first ratio (FR 80). Naloxone (3 and 10 mg/kg) increased the latency to the first response and blocked NPY's effect on completion of the first ratio. In the second study, we observed rats continually following injection of saline, NPY (5 μg ICV) and/or naloxone (l mg/kg SC). NPY increased food intake during the 1-h session and naloxone blocked this effect. NPY decreased the latency to eat, but naloxone failed to significantly antagonize this effect. The amount of time spent eating was greater in the NPY group compared to the saline group and naloxone antagonized this effect. Lag sequential analysis indicated that NPY induced a move-eat-move behavioral sequence that disappeared following naloxone administration. These data lend support to the notion that opioids are involved in maintenance of NPY-induced feeding but affect meal initiation in a minor way. Only relatively high doses of naloxone (3 and 10 mg/kg) altered NPY-induced changes in meal initiation.

Antisense to NPY-Y1 demonstrates that Y1 receptors in the hypothalamus underlie NPY hypothermia and feeding in rats.

Neuropeptide Y (NPY) is a highly potent endogenous peptide which when injected into the medial hypothalamus causes spontaneous eating behaviour and an intense fall in body temperature (Tb). This study used antisense oligodeoxynucleotides (ODNs) to determine whether the Y1 subtype of NPY receptor could underlie these remarkable physiological responses. In the unrestrained rat, the ventromedial hypothalamus (VMH) which is highly reactive to NPY was injected with antisense for NPY (aNPY), Y1 receptors (aNPY-Y1) and mismatched controls (mNPY; mNPY-Y1). After cannulae were implanted bilaterally in the brain of 19 rats, 0.4 or 0.8 microgram per 0.8 microliter of the phosphorothioate synthesised ODNs were delivered to the VMH of the rats at 12 h intervals over 2 d. Only the lower dose of aNPY-Y1, but not aNPY, evoked an intense phasic rise in the Tb following each micro-injection. Simultaneously, 0.4 microgram per 0.8 microliter of aNPY-Y1, but not aNPY, suppressed feeding behaviour after a sequence of micro-injections and on the following day. Body weights and locomotor activity of the rats likewise declined concomitantly with the hyperthermia and hypophagia caused by the Y1 receptor antisense. Neither of the control ODNs for NPY or Y1 receptors injected similarly in the VMH of the rats exerted any effects on these measures. These results clearly provide convincing evidence that in the VMH the Y1 subtype of NPY receptor mediates, in part, the neuronal mechanisms responsible for spontaneous feeding and hypothermia produced by native NPY when applied directly to this structure. The concurrent decline in body weight and activity caused by aNPY-Y1 could be caused by the episodes of hyperthermia.

Ineffectiveness of hypothalamic serotonin to block neuropeptide Y-induced feeding

A variety of recent research has suggested that the feeding associated with enhanced neuropeptide Y (NPY) activity within the hypothalamus may operate in part by interacting antagonistically with other neural processes responsive to serotonin (5-hydroxytryptamine or 5-HT). To test this possibility further, experiments were performed to determine if the magnitude of feeding produced by injecting NPY into the paraventricular nucleus (PVN) or the perifornical hypothalamus (PFH) was diminished by coinjections of 5-HT into these two sites or peripheral injections of the 5-HT agonist, d-fenfluramine. Adult male Sprague-Dawley rats were implanted unilaterally with stainless steel cannulae aimed to terminate either in the PVN or the PFH. In both studies, NPY (235 pmol) produced significant feeding in both sites either 1 or 2 h after injection when compared to saline. This enhanced feeding response was significantly greater in the PFH 2 h after injection (40% in the central study; 70% in the peripheral study). Coinjection of 5-HT (6.3, 12.5, or 25.0 nmol) into either site had no effect on the induction of this NPY-induced feeding response. However, peripherally injected d-fenfluramine (0.32, 0.63, or 1.25 mg/kg) produced strong dose-dependent attenuation of both 1- and 2-h food intake elicited by 235 pmol NPY in either site, with the PFH being proportionately more sensitive to this effect. Viewed together, these results suggest that the feeding-suppressant effects of systemic fenfluramine on hypothalamic NPY-induced feeding may operate largely via peripheral mechanisms and/or central ones that have little to do with its 5-HT agonistic effects within the PVN or PFH.

Effects of opioid antagonists naloxone and naltrexone on neuropeptide Y-induced feeding and brown fat thermogenesis in the rat. Neural site of action.

Neuropeptide Y administered intracerebroventricularly and into the paraventricular nucleus of the hypothalamus stimulates feeding and decreases brown adipose tissue thermogenesis. Although specific neuropeptide Y antagonists are not yet available, previous studies had shown that the opioid antagonist naloxone blocked neuropeptide Y-induced feeding when both drugs were injected intracerebroventricularly. We wanted to find out if naloxone injected into specific brain sites would block neuropeptide Y effects on feeding and brown fat thermogenesis. Rats were double injected in specific brain sites with neuropeptide Y and either naloxone or naltrexone (a congener of naloxone). Food intake and brown fat measures were assessed. Naloxone or naltrexone in the paraventricular nucleus weakly decreased paraventricular nucleus neuropeptide Y-induced feeding and did not affect neuropeptide Y-induced reductions in brown fat activity. Peripheral naloxone blocked intracerebroventricular neuropeptide Y-induced feeding and brown fat alterations. Fourth ventricular naloxone decreased paraventricular nucleus neuropeptide Y-induced feeding, and naltrexone given into the nucleus of the solitary tract blocked paraventricular nucleus neuropeptide Y-induced alterations in feeding and brown fat. These data indicate that neuropeptide Y in the paraventricular nucleus may act on feeding and brown fat thermogenesis through opioidergic pathways in the nucleus of the solitary tract.

The effect of central blockade of kappa-opioid receptors on neuropeptide Y-induced feeding in the rat

Neuropeptide Y (NPY) and the endogenousK-opioid receptor ligand, dynorphin (dyn), stimulate feeding when injected centrally in the rat. Norbinaltorphimine (norBNI, 25 nmol) reduced the feeding response to NPY (2.4 nmol) by 67% (P < 0.02). An additive effect of dynorphin and NPY was seen on food intake (saline0.8 ± 0.1,dyn1.9 ± 0.4,and the NPY9.7 ± 2.2). A component of NPY-induced feeding maycor* be mediated byK-opioid neuronal systems.

Analysis of neuropeptide Y-induced feeding: Dissociation of Y 1 and Y 2 receptor effects on natural meal patterns

To differentiate NPY receptor subtypes, Y 1 and Y 2, in terms of their impact on feeding behavior, the intact molecule NPY(1–36) and the 3 fragments, NPY(2–36), the Y 1 agonist [Leu 31,Pro 34]NPY, and the Y 2 agonist NPY(13–36), were injected (100 pmol/0.3 μl) into the hypothalamic paraventricular nucleus (PVN) of freely feeding rats. A computer-automated data acquisition system was employed in these experiments to permit a detailed analysis of feeding over the 12-h nocturnal cycle, in animals maintained on pure macronutrient diets. The results demonstrate that: 1) NPY(1–36) potentiates feeding behavior, primarily carbohydrate ingestion, by increasing the size and duration of the first meal after injection, rather than by affecting meal number or feeding rate, suggesting that NPY acts through mechanisms of satiety. The potentiation of carbohydrate intake occurs in association with a suppression of protein intake, which is strongest during the second meal after injection and which further increases the proportion of carbohydrate in the diet. No changes in fat ingestion are seen. 2) NPY(2–36), with the N-terminal tyrosine residue deleted, is equally potent to NPY(1–36) in potentiating carbohydrate intake and increasing meal size; however, it is less selective than NPY(1–36), producing an additional, smaller increase in consumption of protein. 3) The stimulatory effect of these peptides on carbohydrate intake and meal size is similarly observed, with somewhat reduced potency, after PVN injection of the selective Y 1 agonist [Leu 31,Pro 34]NPY which, like NPY(1–36), also reduces protein intake. 4) The Y 2 receptor agonist, NPY(13–36), causes a decrease in the ingestion of carbohydrate, a smaller decline in protein intake, and a reduction in meal size. It is proposed that hypothalamic Y 1 receptors mediate the stimulatory effect of NPY on carbohydrate intake and meal size, while Y 2 receptors have the opposite effect of suppressing carbohydrate intake, possibly by altering presynaptic release of monoamines known to influence nutrient ingestion.

Pertussis toxin inhibits neuropeptide Y-induced feeding in rats

Neuropeptide Y (NPY) is the most powerful peptide drug stimulating feeding in rats. Rats with paraventricular hypothalamic (PVH) cannulae were used to investigate the mechanisms involved in NPY-induced feeding. Consistent with previous reports, injection of 2 μg of NPY into the PVH significantly increased the cumulative food intake over 1-, 2- and 4-hr periods. Ad lib feeding decreased significantly two days after pertussis toxin (PT) administration, but recovered to nearly normal levels on the fourth day. PT had no immediate effect on NPY-induced feeding; however, four days after PT was injected NPY (2 μg) did not increase the food intake compared to control. In vitro investigations showed that isoproterenol-stimulated adenylate cyclase activity in the hypothalamus of control rats was inhibited by NPY. In PT-treated rats, however, no inhibition of cAMP production was observed. These results suggest that cAMP may mediate NPY-induced feeding and that a PT-sensitive G protein may be involved in this signal transduction.

Peripheral and central satiety factors in neuropeptide Y-induced feeding in rats.

In the first study, injection of NPY into the hypothalamic paraventricular nucleus (PVN) caused a robust feeding effect that was attenuated by intravenous infusions of glucose, but not fructose. It is suggested that increased blood glucose has a direct central effect on NPY feeding mechanisms. In a second study, and contrary to a previous report, peripheral administration of CCK-8 had a marked satiety effect in NPY-treated rats. Thus, NPY-induced feeding is, at least for a short time, possibly subject to the satiating action of prandially-released CCK. In a final study, NPY was shown to be without effect on gastric emptying of a solid test meal.