Increased threshold concentrations of neuropeptide Y for a stimulatory effect on food intake in obese Zucker rats--changes in the microstructure of the feeding behavior

NPYR modulation: Potential for the next major advance in obesity and type 2 diabetes management?

The approval of the glucagon-like peptide 1 (GLP-1) mimetics semaglutide and liraglutide for management of obesity, independent of type 2 diabetes (T2DM), has initiated a resurgence of interest in gut-hormone derived peptide therapies for the management of metabolic diseases, but side-effect profile is a concern for these medicines. However, the recent approval of tirzepatide for obesity and T2DM, a glucose-dependent insulinotropic polypeptide (GIP), GLP-1 receptor co-agonist peptide therapy, may provide a somewhat more tolerable option. Despite this, an increasing number of non-incretin alternative peptides are in development for obesity, and it stands to reason that other hormones will take to the limelight in the coming years, such as peptides from the neuropeptide Y family. This narrative review outlines the therapeutic promise of the neuropeptide Y family of peptides, comprising of the 36 amino acid polypeptides neuropeptide Y (NPY), peptide tyrosine-tyrosine (PYY) and pancreatic polypeptide (PP), as well as their derivatives. This family of peptides exerts a number of metabolically relevant effects such as appetite regulation and can influence pancreatic beta-cell survival. Although some of these actions still require full translation to the human setting, potential therapeutic application in obesity and type 2 diabetes is conceivable. However, like GLP-1 and GIP, the endogenous NPY, PYY and PP peptide forms are subject to rapid in vivo degradation and inactivation by the serine peptidase, dipeptidyl-peptidase 4 (DPP-4), and hence require structural modification to prolong circulating half-life. Numerous protective modification strategies are discussed in this regard herein, alongside related impact on biological activity profile and therapeutic promise.

Neuropeptide Y and Peptide YY in Association with Depressive Symptoms and Eating Behaviours in Adolescents across the Weight Spectrum: From Anorexia Nervosa to Obesity

Neuropeptide Y (NPY) and peptide YY (PYY) are involved in metabolic regulation. The purpose of the study was to assess the serum levels of NPY and PYY in adolescents with anorexia nervosa (AN) or obesity (OB), as well as in a healthy control group (CG). The effects of potential confounders on their concentrations were also analysed. Eighty-nine adolescents were included in this study (AN = 30, OB = 30, and CG = 29). Anthropometric measurements and psychometric assessment of depressive symptoms, eating behaviours, body attitudes, and fasting serum levels of NPY and PYY were analysed. The AN group presented severe depressive symptoms, while the OB group held different attitudes towards the body. The levels of NPY were lower in the AN and OB groups as compared with the CG. The PYY levels were higher in the OB group than in the AN group and the CG. The severity of eating disorder symptoms predicted fasting serum concentrations of NPY. Lower levels of NPY in AN, as well as in OB suggests the need to look for a common link in the mechanism of this effect. Higher level of PYY in OB may be important in explaining complex etiopathogenesis of the disease. The psychopathological symptoms may have an influence on the neurohormones regulating metabolism.

Obesity causes selective and long-lasting desensitization of AgRP neurons to dietary fat

Body weight is regulated by interoceptive neural circuits that track energy need, but how the activity of these circuits is altered in obesity remains poorly understood. Here we describe the in vivo dynamics of hunger-promoting AgRP neurons during the development of diet-induced obesity in mice. We show that high-fat diet attenuates the response of AgRP neurons to an array of nutritionally-relevant stimuli including food cues, intragastric nutrients, cholecystokinin and ghrelin. These alterations are specific to dietary fat but not carbohydrate or protein. Subsequent weight loss restores the responsiveness of AgRP neurons to exterosensory cues but fails to rescue their sensitivity to gastrointestinal hormones or nutrients. These findings reveal that obesity triggers broad dysregulation of hypothalamic hunger neurons that is incompletely reversed by weight loss and may contribute to the difficulty of maintaining a reduced weight.

Abnormalities in Glucose Metabolism, Appetite-Related Peptide Release, and Pro-nflammatory Cytokines Play a Central Role in Appetite Disorders in Peritoneal Dialysis

Background: Appetite disorders are frequent and scantly studied in peritoneal dialysis (PD) patients and are associated with malnutrition and cardiovascular complications. Objective: We investigated the relationship between uremic insulin resistance, pro-inflammatory cytokines, and appetite-related peptides release (ARPr) with eating-behavior disorders in PD patients. Methods: We included 42 PD patients (12 suffering anorexia, 12 obese with high food-intake, and 18 asymptomatic) and 10 controls. We measured blood levels of ARPr including orexigens [neuropeptide-Y (NPY), ghrelin, and nitric-oxide], anorexigens [cholecystokinin, insulin, corticotropin-releasing factor, leptin, and adiponectin (Ad)], and cytokines (TNF-α, sTNFα-R2, and IL-6) both at baseline and after administering a standard-food stimulus (SFS). We also measured the expression of TNF-α, leptin and Ad-encoding mRNAs in abdominal adipose tissue. We compared these markers with eating motivation measured by a Visual Analog Scale (VAS). Results: Anorexics showed both little appetite, measured by a VAS, and low levels of orexigens that remained constant after SFS, coupled with high levels of anorexigens at baseline and after SFS. Obeses showed higher appetite, increased baseline levels of orexigens, lower baseline levels of anorexigens and cytokines and two peaks of NPY after SFS. The different patterns of ARPr and cytokines pointed to a close relationship with uremic insulin resistance. In fact, the euglycemic-hyperglycemic clamp reproduced these disorders. In anorexics, TNF-α fat expression was increased. In obese patients, leptin expression in fat tissue was down-regulated and showed correlation with the appetite. Conclusion: In PD, appetite is governed by substances that are altered at baseline and abnormally released. Such modulators are controlled by insulin metabolism and cytokines and, while anorexics display inflammatory predominance, obese patients predominantly display insulin resistance.

Dopamine-induced hypophagia is mediated by D1 and 5HT-2c receptors in chicken

The present study was designed to examine the effects of intracerebroventricular (ICV) injection of Dopamine (10, 20 and 40 nmol), L-DOPA (dopamine precursor; 62.5, 125 and 250 nmol), 6-OHDA (dopamine inhibitor; 75, 150 and 300 nmol), SCH 23390 (D1 antagonist; 2.5, 5 and 10 nmol), AMI-193 (D2 antagonist; 2.5, 5 and 10 nmol), NGB2904 (D3 antagonist; 3.2, 6.4 and 12.8 nmol), L-741 T742 (D4 antagonist; 1.5, 3 and 6 nmol) on food intake in FD3 chickens. At following, birds were ICV injected using 8-OH-DPAT (5-HT1A agonist; 15.25 nmol) and SB242084 (5-HT2C antagonist; 1.5 μg) prior dopamine (40 nmol) injection. Cumulative food intake was determined until 3 h post-injection. According to the results, dopamine significantly decreased food intake in chickens (p<0.05). The inhibitory effect of dopamine on food intake was decreased by SCH 23390 pretreatment (P<0.05), but AMI-193, NGB2904 and L-741, 742 had no effect on food intake induced by dopamine. In addition, hypophagic effect of dopamine was attenuated by SB242084 (P<0.05), but 8-OH-DPAT had no effect. These results suggest that dopamine decrease food intake via D1 receptor and there is an interaction between dopaminergic and serotonergic systems via 5-HT2C receptor in chickens.

Dehydroepiandrosterone (DHEA) blocks the increase in food intake caused by neuropeptide Y (NPY) in the Zucker rat

Recent studies have demonstrated that neuropeptide Y (NPY) reduced the neural production of dehydroepiandrosterone (DHEA) in frog hypothalamic explants. The objective of this study was to assess if DHEA can block the NPY induced increase in food intake in lean and obese Zucker rats. Rats were given one of the following four treatments: sterile water/dimethylsulfoxide (DMSO), NPY/DMSO, water/DHEA, and NPY/DHEA. Immediately after administration of their respective treatment, rats were exposed to macronutrients for 4 h and food intake was monitored. NPY caused a significant increase in total calories consumed compared to control. Co-administration of DHEA along with NPY blocked this NPY dependent effect. These results suggest that DHEA blocks the over-eating in satiated rats induced by NPY. Measurement of changes in regional hypothalamic and raphe monoamine neurotransmitters known to affect food intake suggested a possible role of serotonin fluctuations in the ventromedial hypothalamus (VMH) guiding this behaviour.

Up-regulation of Neuropeptide Y Receptors in the Hypothalamus of Monosodium Glutamate-lesioned Sprague-Dawley Rats

Monosodium-glutamate (MSG) is neurotoxic for brain regions devoid of blood-brain barrier when it is injected at high doses during the neonatal period. Neuropeptide Y (NPY) neurons in the arcuate nucleus are particularly sensitive to MSG treatment. But, despite of the large decrease of this potent orexigenic peptide, feeding behavior is only slightly affected. We hypothesized that the hypothalamic NPY receptor system might be modified in these rats. The present study characterizes hypothalamic NPY and NPY receptors in normal and MSG-treated rats. MSG-treated rats were lighter (p < 0.01) and ate 17% less than the control rats (p < 0.01). NPY levels in the mediobasal and mediodorsal hypothalamus were reduced in MSG-treated rats compared to normal rats (-26% and -43%, p < 0.05 and p < 0.01, respectively). Combined hypothalamic Y1 and Y5 NPY receptor density was increased in MSG-treated rats compared to normal rats (+25%, p < 0.04), but affinity remained unaltered. Blockade with a selective Y1 antagonist showed that the Y1 receptor subtype represented more than 90% of the combined Y1 and Y5 receptor populations. The up-regulation of the NPY receptors is an element necessary to maintain food intake at a sufficient level to allow survival and growth of the lesioned rats.

Addition of sucralose enhances the release of satiety hormones in combination with pea protein

SCOPE

Exposing the intestine to proteins or tastants, particularly sweet, affects satiety hormone release. There are indications that each sweetener has different effects on this release, and that combining sweeteners with other nutrients might exert synergistic effects on hormone release.

METHODS AND RESULTS

STC-1 cells were incubated with acesulfame-K, aspartame, saccharine, sucralose, sucrose, pea, and pea with each sweetener. After a 2-h incubation period, cholecystokinin(CCK) and glucagon-like peptide 1 (GLP-1) concentrations were measured. Using Ussing chamber technology, the mucosal side of human duodenal biopsies was exposed to sucrose, sucralose, pea, and pea with each sweetener. CCK and GLP-1 levels were measured in basolateral secretions. In STC-1 cells, exposure to aspartame, sucralose, sucrose, pea, and pea with sucralose increased CCK levels, whereas GLP-1 levels increased after addition of all test products. Addition of sucrose and sucralose to human duodenal biopsies did not affect CCK and GLP-1 release; addition of pea stimulated CCK and GLP-1 secretion.

CONCLUSION

Combining pea with sucrose and sucralose induced even higher levels of CCK and GLP-1. Synchronous addition of pea and sucralose to enteroendocrine cells induced higher levels of CCK and GLP-1 than addition of each compound alone. This study shows that combinations of dietary compounds synergize to enhance satiety hormone release.

The role of neuropeptide Y in energy homeostasis

When administered into the brain, NPY acts at Y1 and Y5 receptors to increase food intake. The response occurs with a short latency and is quite robust, such that exogenous NPY is generally considered to be the most potent of a growing list of orexigenic compounds that act in the brain. The role of endogenous NPY is not so straightforward, however. Evidence from diverse types of experiments suggests that rather than initiating behavioral eating per se, endogenous NPY elicits autonomic responses that prepare the individual to better cope with consuming a calorically large meal.

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

Intraduodenal administration of intact pea protein effectively reduces food intake in both lean and obese male subjects

BACKGROUND

Human duodenal mucosa secretes increased levels of satiety signals upon exposure to intact protein. However, after oral protein ingestion, gastric digestion leaves little intact proteins to enter the duodenum. This study investigated whether bypassing the stomach, through intraduodenal administration, affects hormone release and food-intake to a larger extent than orally administered protein in both lean and obese subjects.

METHODS

Ten lean (BMI:23.0±0.7 kg/m²) and ten obese (BMI:33.4±1.4 kg/m²) healthy male subjects were included. All subjects randomly received either pea protein solutions (250 mg/kg bodyweight in 0.4 ml/kg bodyweight of water) or placebo (0.4 ml/kg bodyweight of water), either orally or intraduodenally via a naso-duodenal tube. Appetite-profile, plasma GLP-1, CCK, and PYY concentrations were determined over a 2 h period. After 2 h, subjects received an ad-libitum meal and food-intake was recorded.

RESULTS

CCK levels were increased at 10(p<0.02) and 20(p<0.01) minutes after intraduodenal protein administration (IPA), in obese subjects, compared to lean subjects, but also compared to oral protein administration (OPA)(p<0.04). GLP-1 levels increased after IPA in obese subjects after 90(p<0.02) to 120(p<0.01) minutes, compared to OPA. Food-intake was reduced after IPA both in lean and obese subjects (-168.9±40 kcal (p<0.01) and -298.2±44 kcal (p<0.01), respectively), compared to placebo. Also, in obese subjects, food-intake was decreased after IPA (-132.6±42 kcal; p<0.01), compared to OPA.

CONCLUSIONS

Prevention of gastric proteolysis through bypassing the stomach effectively reduces food intake, and seems to affect obese subjects to a greater extent than lean subjects. Enteric coating of intact protein supplements may provide an effective dietary strategy in the prevention/treatment of obesity.

Responsiveness of obese Zucker rats to [D-Trp34]-NPY supports the targeting of Y5 receptor for obesity treatment

The increased synthesis and release of neuropeptide Y (NPY) in the hypothalamus participate in the development of overeating and obesity in the Zucker fa/fa rat. The orexigenic effects of NPY are mediated through the Y1 and Y5 receptors. The substitution of [D-Trp34] in the NPY amino-acid sequence increases selectivity without lowering potency at the Y5 receptor. In the present study, to address the role of the NPY Y5 receptor in obesity, we investigated the acute effect of [D-Trp 34]-NPY in lean and obese Zucker rats. Obese rats were markedly hyperphagic (27.1 +/- 0.6 vs. 18.7 +/- 0.4 (lean) g/day; p < 0.01). Injection of [D-Trp34]-NPY in the lateral brain ventricle at a dose of 16 microg stimulated food intake to the same extent in both lean (p < 0.01) and obese (p < 0.01) rats 1 h after injection. This effect was still observed after 6 h (p < 0.01). These results indicate, therefore, that the obese rats are responsive to [D-Trp34]-NPY. They support the role of the neuropeptide Y5 receptor in the regulation of food intake and suggest that NPY Y5 antagonism might be useful for treating obesity.

Effects of hindbrain melanin-concentrating hormone and neuropeptide Y administration on licking for water, saccharin, and sucrose solutions

Melanin-concentrating hormone (MCH) and neuropeptide Y (NPY) are orexigenic peptides found in hypothalamic neurons that project throughout the forebrain and hindbrain. The effects of fourth ventricle (4V) infusions of NPY (5 microg) and MCH (5 microg) on licking for water, 4 mM saccharin, and sucrose (0.1 and 1.0 M) solutions were compared to identify the contributions of each peptide to hindbrain-stimulated feeding. NPY increased mean meal size only for the sucrose solutions, suggesting that caloric feedback or taste quality is pertinent to the orexigenic effect; MCH infusions under identical testing conditions failed to produce increases for any tastant. A second experiment also observed no intake or licking effects after MCH doses up to 15 microg, supporting the conclusion that MCH-induced orexigenic responses require forebrain stimulation. A third experiment compared the 4V NPY results with those obtained after NPY infusions (5 microg) into the third ventricle (3V). In contrast to the effects observed after the 3V NPY injections and previously reported forebrain intracerebroventricular (ICV) NPY infusion studies, 4V NPY failed to increase meal frequency for any taste solution or ingestion rate in the early phases of the sucrose meals. Overall, 4V NPY responses were limited to intrameal behavioral processes, whereas forebrain ICV NPY stimulation elicited both consummatory and appetitive responses. The dissociation between MCH and NPY effects observed for 4V injections is consistent with reports that forebrain ICV injections of MCH and NPY produced nearly dichotomous effects on the pattern of licking microstructure, and, collectively, the results indicate that the two peptides have separate sites of feeding action in the brain.

Involvement of cocaine-amphetamine regulated transcript in the differential feeding responses to nociceptin/orphanin FQ in dark agouti and Wistar Ottawa Karlsburg W rats

Wistar Ottawa Karlsburg W (WOKW) rats and their controls, dark agouti (DA), present different features: in particular, DA rats are lean, while the WOKW are obese and present symptoms of hypertension, dyslipidemia, hyperinsulinemia, and impaired glucose tolerance. The present study tested the hypothesis that these two strains would demonstrate different sensitivity to nociceptin/orphanin FQ (N/OFQ). N/OFQ was injected into the lateral brain ventricle (LBV) of sated DA and WOKW rats, and corticosterone levels in both strains were measured after LBV injection of N/OFQ. LBV N/OFQ injections dose-dependently produced a significant increase in food intake (4 h) in DA rats, but not in WOKW. However, corticosterone levels were increased by N/OFQ to a greater degree in WOKW than in DA rats. Gene sequencing and gene expression of ORL1 receptor and cocaine-amphetamine regulated transcript (Cart) peptide were evaluated to study the difference in N/OFQ-induced feeding behavior in the two strains. WOKW rats had a different amino acid sequence of Cart peptide and a significantly higher expression of Cart in the hypothalamus. The present data show that DA and WOKW rats demonstrate different sensitivity to N/OFQ, and suggest that Cart peptide might be the underlying mechanism of this difference.

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

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

Physiology and gene regulation of the brain NPY Y1 receptor

Neuropeptide Y (NPY) is one of the most prominent and abundant neuropeptides in the mammalian brain where it interacts with a family of G-protein coupled receptors, including the Y(1) receptor subtype (Y(1)R). NPY-Y(1)R signalling plays a prominent role in the regulation of several behavioural and physiological functions including feeding behaviour and energy balance, sexual hormone secretion, stress response, emotional behaviour, neuronal excitability and ethanol drinking. Y(1)R expression is regulated by neuronal activity and peripheral hormones. The Y(1)R gene has been isolated from rodents and humans and it contains multiple regulatory elements that may participate in the regulation of its expression. Y(1)R expression in the hypothalamus is modulated by changes in energetic balance induced by a wide variety of conditions (fasting, pregnancy, hyperglycaemic challenge, hypophagia, diet induced obesity). Estrogens up-regulate responsiveness to NPY to stimulate preovulatory GnRH and gonadotropin surges by increasing Y(1)R gene expression both in the hypothalamus and the pituitary. Y(1)R expression is modulated by different kinds of brain insults, such as stress and seizure activity, and alteration in its expression may contribute to antidepressant action. Chronic modulation of GABA(A) receptor function by benzodiazepines or neuroactive steroids also affects Y(1)R expression in the amygdala, suggesting that a functional interaction between the GABA(A) receptor and Y(1)R mediated signalling may contribute to the regulation of emotional behaviour. In this paper, we review the state of the art concerning Y(1)R function and gene expression, including our personal contribution to many of the subjects mentioned above.

Orosensory stimulation is sufficient and postingestive negative feedback is not necessary for neuropeptide Y to increase sucrose intake

Although central administration of neuropeptide Y (NPY) has a potent orexic effect, it is not clear how NPY changes the potency of peripheral feedbacks from the gut to prolong eating and increase meal size. It has been suggested that NPY increases the stimulating effect of orosensory sweet stimuli or that it decreases the inhibitory effect of postingestive stimuli. To clarify this issue, we compared the orexic effect of NPY (2 microg) injected into the third ventricle of the brain on the volume and microstructure of intake of 0.8M sucrose during sham feeding (SF) and real feeding (RF) in male Sprague Dawley rats. The rationale for this comparison is that orosensory stimulation occurs in SF and RF, but postingestive negative feedback is present only in RF. NPY increased the volume ingested and the rate and number of clusters of licking significantly more in SF than in RF. This demonstrates that orosensory sucrose stimulation is sufficient and postingestive negative feedback is not necessary for the orexic effect of NPY under these experimental conditions.

Feeding response to a potent prolactin-releasing peptide agonist in lean and obese Zucker rats

Prolactin (PRL)-releasing peptide (PrRP) is a new peptide present in the hypothalamus and in the circulation that may be involved in the regulation of feeding behavior. In the present experiment, we measured it in a well-known model of obesity, the Zucker rat. We also measured the reactivity of this animal in terms of food intake after the intraperitoneal (I.P.) or central injection of PrRP-13, a potent PrRP agonist. Plasma PrRP levels were 35% lower in obese fa/fa than in the lean rats (p<0.005). I.P. injections of PrRP-13 (10 mg/kg) stimulated food intake in lean and had no effect in obese rats (p<0.001). Intracerebral injections of PrRP-13 had no effects in both genotypes. Altogether, these results do not support a role for PrRP in the hyperphagia and obesity syndrome of the Zucker rat.

NPY presynaptic actions are reduced in the hypothalamic mpPVN of obese (fa/fa), but not lean, Zucker rats in vitro

1. Neuropeptide Y (NPY) profoundly enhances feeding when injected intracerebroventricularly, or directly into hypothalamic nuclei, such as the paraventricular nucleus (PVN). Paradoxically, NPY has a reduced action on feeding in obese Zucker rats relative to lean Zucker rats, although the obese rats have much higher levels of hypothalamic NPY expression. GABAergic inputs to a subpopulation of medial parvocellular PVN (mpPVN) neurons are sensitive to NPY. Here, we tested the hypothesis that the blunted eating response to NPY observed in obese Zucker rats will be reflected in a reduced NPY action at mpPVN GABAergic synapses. 2. 'Blind' whole-cell patch-clamp recordings made from mpPVN neurons in acute brain slices of lean and obese Zucker rats revealed GABAergic inhibitory postsynaptic currents (IPSC) responses which were inhibited by NPY. While the maximum response in the obese Zucker rats was significantly less than in lean Zucker or Sprague-Dawley rats, there was no difference in the EC(50). 3. Experiments using blocking concentrations of Y(1)- or Y(5)-receptor antagonists revealed no differences between lean and obese Zucker rats in the contributions of either of these receptors to the total NPY response in mpPVN. 4. NPY is less effective at the mpPVN GABA synapse in obese than in lean Zucker rats. This is not associated with a change in the proportion of Y(1) or Y(5) receptors mediating the NPY response, and is consistent with the downregulation of NPY receptors or a reduction in receptor-effector coupling, and with the reduced sensitivity of obese rats to NPY.

Differential response to NPY of PVH and dopamine-responsive VMH neurons in overweight rats

Neuronal responses to neuropeptide Y and dopamine were recorded in brain slices of hypothalamic paraventricular (PVH) and ventromedial (VMH) nuclei in normal and hyperphagic overweight rats reared in small litters of three pups. NPY significantly activated PVH neurons of normal rats, but inhibited neurons of overweight rats. In the VMH, a significantly higher coincidence of inhibition induced by NPY and dopamine was found in overweight rats. Similar neuronal responses were evoked by a NPY Y5 receptor agonist. Effects of NPY could be blocked by a Y1 receptor antagonist. The altered response of PVH neurons to the feeding-inducing NPY and the increased inhibition by NPY and dopamine in the VMH might contribute to the persisting hyperphagia and overweight of postnatally overnourished rats.

Chronic neuropeptide Y infusion during lactation suppresses pup growth and reduces the length of lactational infertility in rats

In lactating rats, food restriction potentiates the already high levels of hypothalamic neuropeptide Y (NPY). To investigate the role that high levels of NPY might play in the prolongation of lactational infertility that typically accompanies a food restricted lactation we investigated the effects of chronic central infusions of NPY in ad libitum-fed lactating females. First, we compared the effects of intracerebroventricular (icv) infusion of NPY from Days 12-19 postpartum at a dose of 14.4 microg/day with a similar treatment in nonlactating females. In subsequent experiments we examined the effects of NPY infusions into the lateral ventricle at doses of 6 or 20 mug/day or unilaterally into the medial preoptic area at a dose of 1 microg/day from either Days 12-19 or 7-21 postpartum. Effects on food intake; female body weight; and, where appropriate, litter weight and length of lactational diestrus were compared between NPY and vehicle-treated females. As expected NPY infusion produced a robust increase in body weight and food intake in nonlactating females that was accompanied by a suppression of cyclicity. By contrast NPY treatment in lactating rats resulted in a marked decrease in litter growth and an earlier termination of lactational diestrus.

Opposite regulation of hypothalamic orexin and neuropeptide Y receptors and peptide expressions in obese Zucker rats

Many hyothalamic neuropeptides are involved in the regulation of food intake and body weight. The orexins (OX) which are synthesized in the lateral hypothalamus are among the most recently characterized whereas neuropeptide Y (NPY) belongs to a group of "older" peptides extensively studied for their effects on feeding behavior. Both stimulate food ingestion in rodents. In this experiment, we measured the expressions of these peptides as well as of their receptors (OX1-R and OX2-R, Y1 and Y5) in the hypothalamus of obese hyperphagic and lean Zucker rats by real-time RT-PCR using the TaqMan apparatus. NPY mRNA expression in the obese rats was significantly increased by a factor of 10 (P < 0.002) whereas expressions of the Y1 and Y5 receptors were decreased by 25% (P < 0.01) and 50% (P < 0.002), respectively. Their prepro-orexin mRNA expression was more than twofold decreased (P < 0.01) and expressions of their OX receptors 1 and 2 mRNA were five- and fourfold increased (P < 0.05), respectively. An inverse phenomenon was therefore noted between the two peptides: for NPY, increased levels and downregulation of receptors; and for OX, diminished levels with upregulation of receptors. The reasons for these changes might be linked to the absence of leptin signaling as similar profiles are found in the ob/ob mice. For orexins at least, other factors such as hyperglycemia might be involved. Based on anatomical considerations, a direct effect of NPY or of other brain peptides such as CRH cannot be excluded. We conclude that the diminution in the OX tone might participate in a counterregulatory system necessary to limit the noxious effects of NPY on food intake and body weight.

Central and peripheral dysregulation of melanin-concentrating hormone in obese Zucker rats

Melanin concentrating hormone (MCH) is a peptide synthesized in the lateral hypothalamus which stimulates food ingestion and leptin secretion in rodents. In this experiment, we measured the expressions of MCH as well as of its receptor (SLC-1) in the hypothalamus of obese hyperphagic and lean Zucker rats by quantitative real time RT-PCR. MCH mRNA expression in the obese rats was significantly increased by a factor of five (P<0.01) whereas expression of SLC-1 was decreased by more than 50% (P<0.05). Circulating levels of leptin and MCH were increased in the plasma of obese Zucker rats when compared to lean rats (38-fold and 1.7-fold, respectively, P<0.001 and P<0.01). However, individual MCH levels were not directly correlated to leptin levels in the lean (functional leptin receptor) or in the obese (non-functional leptin receptor) Zucker rats. These results indicate that the absence of leptin signaling in rats is associated with an increased hypothalamic expression and circulating release of MCH, contributing to their obesity syndrome.

Dietary composition during fetal and neonatal life affects neuropeptide Y functioning in adult offspring

The aim of this study was to examine the impact of maternal diet during the gestation and lactation periods on the neuropeptide Y (NPY) system in adult offspring. Male Long-Evans rats were obtained from dams fed either on a well-balanced diet (C), a high carbohydrate diet (HC) or a high-fat diet (HF) and fed themselves on the well-balanced diet for their whole life. At 6 months of age, their feeding response to various doses of NPY injected in the lateral brain ventricle was measured in one group and NPY concentrations in microdissected nuclei of the hypothalamic were measured in a second group. The HF rats were lighter than the two other groups (P<0.001). The control rats showed a typical dose-dependent feeding response to NPY. The HC rats showed a continuous increase in the response, starting at the intermediate dose (1.0 microg) only while the HF rats had a maximal response at the lowest dose (0.5 microg). The HF rats ate twice as much as the HC rats at the lowest dose tested 1 h after injection (4.4+/-0.6 vs. 2.7+/-0.4 g; P<0.05), showing therefore the greatest sensitivity to NPY. This change in the sensitivity was not related to hypothalamic NPY concentration as it was not modified in the arcuate and paraventricular nuclei. The diet imposed on the mother could have long-lasting effects on body weight regulation of the offsprings and alter the NPY system likely through modifications at the receptor level.

Neuropeptides and obesity

This review focuses on the expression, content, and release of neuropeptides and on their role in the development of obesity in animal models with single-gene mutations. The balance between neuropeptides that contribute to the control of feeding behavior is profoundly and variously altered in these models, supporting the concept of the existence of several types of obesity. The hypothalamic neuropeptide Y (NPY) and the pro-opiomelanocortin (POMC) systems are the networks most studied in relation to energy intake. Both receive information about the nutritional status and the level of energy storage through insulin and leptin signaling mediated by specific receptors located on POMC and NPY neurons present predominantly in the arcuate nucleus (ARC). When leptin signaling is defective, through a defect in either the receptor (Zucker fa/fa rat, cp/cp rat, and db/db mouse) or in the peptide itself (ob/ob mouse), the NPY system is upregulated as shown by mRNA overexpression and increased peptide release, whereas the content and/or release of some inhibitory peptides (neurotensin, cholecystokinin) are diminished. For the POMC system, there is a complex interaction between the tonic inhibition of food intake exerted by alpha-melanocyte-stimulating hormone (alpha-MSH) and the Agouti-related protein at the level of the type 4 melanocortin receptor. The latter peptide is coexpressed with NPY in the ARC. Corticotropin-releasing factor (CRF) is the link between food intake and environmental factors. It not only inhibits food intake and prevents weight gain, likely through hypothalamic effects, but also activates the hypothalamo-pituitary axis and therefore contributes to energy storage in adipose tissue. The factors that prod the CRF system toward the hypothalamic or hypothalamo-pituitary axis system remain to be more clearly defined (comodulators, connections between limbic system and ARC, cellular location, and type of receptors, etc. ). The pathways used by all of these neuromodulators include numerous brain areas, but some interest has returned to the classic ones such as the ventromedial and lateral hypothalamic areas because of the recent discovery of some peptides (orexins and melanin-concentrating hormone for the lateral hypothalamus) and receptors (CRF type 2 in the ventromedial hypothalamus). All of these pathways are redundant and function in a coordinated manner and sometimes by the novel expression of a peptide in an unusual area. The importance of such a phenomenon in obesity remains to be determined. Even if single-gene mutations are exceptions in human obesity, the study of genetic animal models of obesity has greatly contributed to the understanding of the regulation of feeding behavior and will allow researchers to develop new drug treatments for obesity that have to be associated with drastic changes in lifestyle (feeding, work habits, and physical activity) for a complete efficiency.

The pharmacology of neuropeptide Y (NPY) receptor-mediated feeding in rats characterizes better Y5 than Y1, but not Y2 or Y4 subtypes

Thirteen neuropeptide Y (NPY) agonists were administered intracerebroventricularly (i.c.v.) in rats (full dose-response curves) to estimate their half-effective dose (ED50) on feeding. These values were compared to their binding affinities (IC50) for rat NPY receptor subtypes Y1, Y2, Y4 and Y5 in vitro. Correlations between in vivo ED50 and in vitro IC50 were strong for the Y5 (r = 0.87; P < 0.01), weak for the Y1 (r = 0.48; P < 0.04) and non-significant for the Y2 and Y4 receptor subtypes. In vitro, h[D-Trp32]NPY was found to be a Y5-selective ligand and a full agonist in Y5-expressing cells. In vivo, it dose-dependently stimulated feeding, but failed to induce the full maximal response observed with pNPY. It did not antagonize pNPY-induced feeding and overfeeding in 24 h fasted rats. These findings demonstrate a role for the Y5, or possibly Y5 in combination with Y1, but not Y2 or Y4 receptor subtypes in feeding. No evidence was found for the existence of an additional, as yet undescribed, NPY feeding receptor.

Behavioral deficits in monosodium glutamate rats: specific changes in the structure of feeding behavior

We studied the feeding rhythms and feeding patterns of adult Long-Evans rats treated with monosodium glutamate (MSG) in their early post-natal period. This treatment is known to induce neuronal degeneration in the arcuate nucleus (ARC), a major hypothalamic site implicated in the regulation of feeding. Neonatal rats were treated intraperitoneally with MSG or saline (controls) alone on the first days of life. At age of 6 months, male control and male MSG rats were placed in our automatic feeding system, and the structure of feeding behavior and diurnal feeding rhythms were analysed. On a 24 hours basis, MSG rats ate less than control rats (-24%). This hypophagia resulted from a mild diurnal hyperphagia (+6%) and a pronounced nocturnal hypophagia (-34%). This hypophagia was the main consequence of a decrease of meal size in MSG rats (-37%) and was associated with an increase in meal duration (+52%). It was also associated with a total disappearance of the two feeding peaks that normally occur at light and dark onset in the rat (-90% 2 h after dark onset and -49% 2 h before light onset). These results indicate that neonatal treatment with MSG induces important changes in feeding patterns and feeding rhythms in the adulthood. These changes might be related to the disappearance of neurotransmitters located in the arcuate nucleus.

A potent neuropeptide Y antagonist, 1229U91, suppressed spontaneous food intake in Zucker fatty rats

Neuropeptide Y (NPY) is one of the most potent orexigenic substances known. 1229U91 was found to be a potent and selective NPY antagonist. To elucidate a physiological role of NPY in hyperphagia in obese animals, we studied the effect of 1229U91 on spontaneous food intake in obese and lean Zucker rats. The food intake of Zucker rats was suppressed by intracerebroventricular administration of 1229U91 more potently in obese than in lean animals without abnormal behavior (31.7 and 67.3% inhibition at doses of 10 and 30 micrograms, respectively, in Zucker fatty rats and 22.2% inhibition at 30 micrograms in lean rats). This compound markedly suppressed NPY-induced food intake at 30 micrograms but did not affect galanin-induced food intake, suggesting that the feeding suppression seen in Zucker fatty and lean rats is pharmacologically and behaviorally specific. These results suggest that NPY is involved in feeding behavior in Zucker fatty rats and that NPY contributes to feeding to a greater degree in Zucker fatty than in lean rats. The hyperphagia in Zucker fatty rats may be due to the abnormal overactivation of the NPYergic system.

Neuropeptide Y in the magnocellular hypothalamic neurons of obese Zucker rats

The obesity syndrome in Zucker rats is associated with an elevated neuropeptide Y (NPY) content in the hypothalamus. It is recognized that the axons of NPY-ergic neurons arriving from the arcuate nucleus and the midbrain are the major source of NPY in this area. In magnocellular hypothalamic neurosecretory neurons (MCN) of normal rats NPY is expressed only in response to hyperosmotic stimulation. This study used immunohistochemistry with colchicine treatment aimed at MCN to compare NPY localization in obese (fa/fa) and in lean (Fa/Fa) Zucker rats. It was found that the obese (fa/fa), in contrast to the lean (Fa/Fa) Zucker rat, displays NPY immunoreactivity in numerous MCN of the paraventricular, supraoptic as well as accessory neurosecretory nuclei. This finding suggests local synthesis of NPY in the MCN of obese (fa/fa) rats and involvement of hydro-osmotic disorders in the Zucker syndrome of obesity.

Neuropeptide Y release in the paraventricular nucleus of Long-Evans rats treated with leptin

Neuropeptide Y (NPY) and leptin are actually two of the most potent peptides involved in the regulation of food intake with their respective stimulatory and inhibitory actions. The infusion of each peptide has a significant influence on the mRNA expression of the other in the adipose tissue for leptin and in the arcuate nucleus of the hypothalamus for NPY. To confirm this functional interaction, we measured the in vivo release of hypothalamic neuropeptide Y in awake fasted and refed Long-Evans rats after intraperitoneal (I.P.) injection of leptin. For this purpose, we used the push-pull perfusion technique with the cannula placed above the right paraventricular nucleus. I.P. leptin significantly inhibited food intake during the two hours of food access (-50%; p < 0.02). NPY release was not modified by leptin alone. But, when food was present, it slightly but significantly increased (p < 0.03 or less) and remained at a sustained level in the leptin-treated rats whereas it decreased in the control saline-injected group (p < 0.04). Thus, leptin did not acutely regulate NPY release and other food-related factors are probably involved as mediators of its anorexigenic effects.

Changes in the microstructure of feeding after administration of enterostatin into the paraventricular nucleus and the amygdala

The effects of enterostatin (ENT) injected into the paraventricular nucleus (PVN) and the amygdala (AMYG) on the microstructure of feeding was studied by using an automated feeding apparatus. In rats adapted to a 6-h meal feeding regime, ENT reduced the size and duration of the first meal after injection in both the PVN and the AMYG. Similar effects were observed when ENT was given at the beginning of the dark cycle in rats fed ad libitum although the onset of feeding was also delayed in this situation. The number of meals and the size of subsequent meals was unaffected by ENT but the eating rate within the first meal was reduced after ENT injection into the AMYG of meal-fed rats. Enterostatin injected into the AMYG at a dose that suppressed feeding did not produce a conditioned taste aversion. ENT given centrally therefore appears to reduce food intake by delaying the initiation of feeding and/or advancing meal termination suggesting that it affects both appetite and satiation mechanisms.

Physiological regulation of hypothalamic neuropeptide Y release in lean and obese rats

The paraventricular nucleus (PVN) of the hypothalamus is an important site for the regulation of feeding behavior. Neuropeptide Y (NPY) injected into this nucleus strongly stimulates food intake. In the current study we measured NPY release in the PVN of unrestrained rats through the push-pull technique. The rats were placed in their habitual environment and conditions of life. NPY release was augmented by > 40% (P < 0.01) in Long-Evans rats deprived of food for 12 h. It returned to the baseline as measured in ad libitum-fed rats 90 min after food access. Its stimulation by 55 mM KCl in refed animals indicated that the whole stock of NPY was not used during a short fast. During the light-dark transition, when feeding behavior is initiated. NPY release in lean Zucker rats showed a peak 20 min after lights off and then declined. It corresponded well with the first feeding episodes. In the obese Zucker rats, this peak was absent. NPY release was totally anarchic but at a high level. The feeding behavior of the obese rats was not as time delimited as in the lean rats. This study performed in very physiological conditions therefore indicates that NPY release could drive feeding behavior in the normal life. Its dysregulation in obese rats could participate in overeating and absence of feeding rhythm measured in these rats and speed up the development of their obesity.

Bilateral hypothalamic dopamine infusion in male Zucker rat suppresses feeding due to reduced meal size

Lateral hypothalamic area dopamine activity (LHA-DA) appears to play a contributory role in regulating food intake, in particular, meal size. In this study we examined our hypothesis that bilateral LHA-DA injection induced depression of food intake via reduced meal size. Dopamine (11 mg/ml) or vehicle was infused into bilateral LHA at 0.5 microliter/h via two osmotic minipumps in six study or six control obese male Zucker rats for 13 days, respectively. Meal size, meal number, as well as food intake were continuously measured before, during, and after dopamine infusion. Intra-LHA-DA infusion significantly depressed food intake. The decreased food intake was solely caused by a significant and profound reduction in meal size. There was a modest compensatory rise in meal number that gradually increased food intake so that it reached control level on 10th dopamine infusion day. However, feeding pattern did not normalize until dopamine infusion ceased. The findings support our hypothesis that LHA-DA may participate in regulating meal size. Data also demonstrate that meal size and meal number are regulated in a reciprocal and independent manner to compensate for each other.

Enhanced feeding response to neuropeptide Y in hypothalamic neuropeptide Y-depleted rats

Monosodium glutamate is neurotoxic for the arcuate nucleus and more generally for all circumventricular organs when injected in newborn rats. Neuropeptide Y, a potent stimulator of food intake, is mainly synthesized in the arcuate nucleus. In the present experiment, we determined the hypothalamic status and the feeding response to intracerebroventricular neuropeptide Y in adult rats neonatally treated with monosodium glutamate. Marked neuropeptide Y decreases were measured in the arcuate nucleus and in the paraventricular nuclei in monosodium glutamate-treated rats (-40%; P < 0.01). Adult rats neonatally treated with monosodium glutamate weighed significantly less (-8%; P < 0.01) and ate less (-10%; P < 0.01) than the control rats. Neuropeptide Y injections in a lateral brain ventricle stimulated food intake in control and monosodium glutamate-treated rats in a dose-dependent manner (P < 0.001). Whatever the time after drug injection (2, 4, 6 and 8 h) and the injected dose (0.5, 1 and 5 micrograms), feeding responses were always greater in monosodium glutamate-treated rats (about 2 times greater starting with the lowest dose (0.5 microgram): 9.3 +/- 1.0 (monosodium glutamate) vs. 5.3 +/- 0.7 (control) g/2 h, P < 0.01). Calculated minimal effective doses were also always smaller in monosodium glutamate-treated rats than in control animals (P < 0.01). Neuropeptide Y increased meal duration, meal size and decreased latency to initiate feeding in monosodium glutamate-treated rats (P < 0.01) and control rats (P < 0.01). For each dose of neuropeptide Y, effects were more pronounced on meal size (+70%) and meal duration (+25%) in monosodium glutamate-treated rats than in control rats. Therefore, monosodium glutamate-treated rats were more sensitive to exogenous neuropeptide Y. Decreased food intake in the monosodium glutamate-treated rats was associated with a decrease in neuropeptide Y concentrations in the arcuate-paraventricular axis. This confirms the functional role of this peptidergic pathway in eating behavior.

Brain peptides and obesity: pharmacologic treatment

Obesity results from an imbalance between nutrient ingestion and metabolism, with more calories being ingested than utilized. The brain plays an important role in coordinating these complex behavioral and physiological functions, operating through multiple neurochemical systems with distinct properties. This review focuses on two hypothalamic peptide systems, neuropeptide Y (NPY) and galanin (GAL), that illustrate how the brain operates through different mechanisms to control the body's nutrient stores, in different states or conditions. These peptides have different behavioral and physiological effects and are, themselves, differentially responsive to feedback signals from circulating steroids, peptides, and nutrients. They can be distinguished by their relation to natural feeding patterns and endogenous hormones and by their specificity of action in relation to natural biological rhythms. The neuroanatomical substrates involved in these actions of NPY and GAL are also distinct. The neurocircuit mediating NPY's actions originates in the arcuate nucleus and terminates in the medial portion of the paraventricular nucleus; the GAL-containing neurons, in contrast, are concentrated in the lateral portion of the paraventricular nucleus, in addition to the medial preoptic area, which contribute to local GAL innervation as well as projections to the median eminence. Regarding their distinct functions, the evidence suggests that the NPY system is more closely related to patterns of carbohydrate ingestion and carbohydrate utilization, channeling nutrients towards the synthesis of fat. It is most strongly activated at the start of the active feeding cycle or after weaning, in close association with the adrenal steroid, corticosterone. The GAL system, in contrast, is more closely associated with patterns of fat consumption and signals related to fat oxidation. This peptide system is most active during the middle of the feeding cycle or immediately after puberty, in close association with the gonadal steroids. The gene expression and synthesis of these peptides in their respective neuronal cell groups is inhibited by circulating insulin and altered by dietary nutrients. Disturbances in sensitivity to insulin and steroid feedback regulation in the brain are believed to be involved in producing abnormal patterns of peptide function that result in overeating and body weight gain.

Nitric oxide mediates hyperphagia of obese Zucker rats: relation to specific changes in the microstructure of feeding behavior

The presence of a nitric oxide synthetase (NOS) was demonstrated in the rat brain. It has been demonstrated recently that NOS-inhibitors reduce food intake in mammals and this suggest that nitric oxide (NO) might be a physiological mediator involved in the mechanisms controlling feeding behavior. Actually, there is no information about the acute central and peripheral effects of NOS-inhibitors on feeding behavior in obese and lean Zucker rats. That is why we investigated the acute dose-dependent activity of NG-Nitro-Arginine-Methyl-Ester (L-NAME) on food intake and feeding behavior in these rats. When given peripherally in the obese rats, L-NAME produced a dose-dependent decrease in food intake (p<0.001). The calculated MED and the ED 50 were 0.50 mg/kg IP and 3.46 mg/kg IP, respectively. These effects could not be reproduced in the lean Zucker rats whatever the dose used (p=0.59). The anorectic properties of L-NAME were very well translated into the microstructure of the feeding behavior. Time spent to eat (p<0.001), meal duration (p<0.01) and meal number (p<0.01) were reduced in the obese rats. Interestingly, L-NAME produced the same effects in the lean rats, but meal size increased in a compensatory manner. Central administration of L-NAME reproduced the same effects in the obese rats, but lean rats still remained insensitive. Central aminergic and/or peptidergic defects associated with the expression of hyperphagia might explain the differences observed between these lean and the obese animals. These results indicate a role of nitric oxide in the expression of hyperphagia and show that it might be a physiological mediator involved in the mechanisms controlling feeding behavior.

Putative neuropeptide Y antagonist failed to decrease overeating in obese Zucker rats

A central dysregulation of several neuropeptides could be at the origin of the marked hyperphagia of the obese Zucker rat, a well-known animal model used for the study of obesity. Neuropeptide Y (NPY), which stimulates food intake and increases early in life in obese rats, plays a major role in the development of this hyperphagia. The aim of our experiment was to test a proposed NPY antagonist namely PYX-2 in obese hyperphagic Zucker rats in order to know if it could be an interesting drug for limiting their food intakes. Four doses of PYX-2 (50-1000 pmol) were injected in a counterbalanced order in the lateral brain ventricles of 10 adult male Zucker rats. Food intake was recorded 0.5, 1, 2, 3, 6, and 23 h after PYX-2 injection and compared either to the rat's spontaneous food intake or to the food intake following injection of artificial CSF (vehicle) only. It was not modified by any dose of PYX-2 whatever the time considered (1 h after injection: 4.3 +/- 0.5 (1000 pmol) vs 4.6 +/- 0.8 (CSF) g; 23 h period: 27.0 +/- 1.9 (1000 pmol) vs 26.6 +/- 2.9 (CSF) g; N.S.). Thus, PYX-2, the putative NPY antagonist, totally failed to inhibit food intake in the obese rats. The absence of effect of PYX-2 on food intake can be explained by the structure of PYX-2, a modified 27-36 amino acid sequence that may not be recognized by the Y1-type NPY receptors which are involved in the regulation of feeding behavior.