Neuropeptide Y and corticotropin-releasing hormone concentrations within specific hypothalamic regions of lean but not ob/ob mice respond to food-deprivation and refeeding

Refeeding after caloric restriction reverses altered liver glucose release

CONTEXT

Caloric restriction increases liver glucose release (LGR), but it is not known if this is a permanent condition.

OBJECTIVE

To investigate if refeeding after caloric restriction reverses the high LGR.

MATERIALS AND METHODS

Rats were organised in six-pups litters (GC); 12-pups litters with either 50% caloric restriction from 21 to 80 days of age (GR) or fed at will from 50 to 80 days of age (GRL). Liver perfusion was made at the age of 80 days.

RESULTS

LGR was higher in the GR both during basal and adrenaline-stimulated conditions. Refeeding after caloric restriction decreased it to values close to those of GC rats.

DISCUSSION

The altered LGR of GR rats was reversed by refeeding (group GRL). The influence of hypothalamic neuropetides on these hepatic changes is suggested.

CONCLUSIONS

Enhanced LGR under caloric restriction is not programmed by early feeding; instead, it is determined by the current nutritional conditions.

Do Bodybuilders Use Evidence-Based Nutrition Strategies to Manipulate Physique?

Competitive bodybuilders undergo strict dietary and training practices to achieve an extremely lean and muscular physique. The purpose of this study was to identify and describe different dietary strategies used by bodybuilders, their rationale, and the sources of information from which these strategies are gathered. In-depth interviews were conducted with seven experienced (10.4 ± 3.4 years bodybuilding experience), male, natural bodybuilders. Participants were asked about training, dietary and supplement practices, and information resources for bodybuilding strategies. Interviews were transcribed verbatim and analyzed using qualitative content analysis. During the off-season, energy intake was higher and less restricted than during the in-season to aid in muscle hypertrophy. There was a focus on high protein intake with adequate carbohydrate to permit high training loads. To create an energy deficit and loss of fat mass, energy intake was gradually and progressively reduced during the in-season via a reduction in carbohydrate and fat intake. The rationale for weekly higher carbohydrate refeed days was to offset declines in metabolic rate and fatigue, while in the final “peak week” before competition, the reasoning for fluid and sodium manipulation and carbohydrate loading was to enhance the appearance of leanness and vascularity. Other bodybuilders, coaches and the internet were significant sources of information. Despite the common perception of extreme, non-evidence-based regimens, these bodybuilders reported predominantly using strategies which are recognized as evidence-based, developed over many years of experience. Additionally, novel strategies such as weekly refeed days to enhance fat loss, and sodium and fluid manipulation, warrant further investigation to evaluate their efficacy and safety.

Intermittent Moderate Energy Restriction Improves Weight Loss Efficiency in Diet-Induced Obese Mice

Background

Intermittent severe energy restriction is popular for weight management. To investigate whether intermittent moderate energy restriction may improve this approach by enhancing weight loss efficiency, we conducted a study in mice, where energy intake can be controlled.

Methods

Male C57/Bl6 mice that had been rendered obese by an ad libitum diet high in fat and sugar for 22 weeks were then fed one of two energy-restricted normal chow diets for a 12-week weight loss phase. The continuous diet (CD) provided 82% of the energy intake of age-matched ad libitum chow-fed controls. The intermittent diet (ID) provided cycles of 82% of control intake for 5–6 consecutive days, and ad libitum intake for 1–3 days. Weight loss efficiency during this phase was calculated as (total weight change) ÷ [(total energy intake of mice on CD or ID)–(total average energy intake of controls)]. Subsets of mice then underwent a 3-week weight regain phase involving ad libitum re-feeding.

Results

Mice on the ID showed transient hyperphagia relative to controls during each 1–3-day ad libitum feeding period, and overall ate significantly more than CD mice (91.1±1.0 versus 82.2±0.5% of control intake respectively, n = 10, P<0.05). There were no significant differences between CD and ID groups at the end of the weight loss or weight regain phases with respect to body weight, fat mass, circulating glucose or insulin concentrations, or the insulin resistance index. Weight loss efficiency was significantly greater with ID than with CD (0.042±0.007 versus 0.018±0.001 g/kJ, n = 10, P<0.01). Mice on the CD exhibited significantly greater hypothalamic mRNA expression of proopiomelanocortin (POMC) relative to ID and control mice, with no differences in neuropeptide Y or agouti-related peptide mRNA expression between energy-restricted groups.

Conclusion

Intermittent moderate energy restriction may offer an advantage over continuous moderate energy restriction, because it induces significantly greater weight loss relative to energy deficit in mice.

Central nervous system neuropeptide Y signaling via the Y1 receptor partially dissociates feeding behavior from lipoprotein metabolism in lean rats

Elevated plasma triglyceride (TG) levels contribute to an atherogenic dyslipidemia that is associated with obesity, diabetes, and metabolic syndrome. Numerous models of obesity are characterized by increased central nervous system (CNS) neuropeptide Y (NPY) tone that contributes to excess food intake and obesity. Previously, we demonstrated that intracerebroventricular (icv) administration of NPY in lean fasted rats also elevates hepatic production of very low-density lipoprotein (VLDL)-TG. Thus, we hypothesize that elevated CNS NPY action contributes to not only the pathogenesis of obesity but also dyslipidemia. Here, we sought to determine whether the effects of NPY on feeding and/or obesity are dissociable from effects on hepatic VLDL-TG secretion. Pair-fed, icv NPY-treated, chow-fed Long-Evans rats develop hypertriglyceridemia in the absence of increased food intake and body fat accumulation compared with vehicle-treated controls. We then modulated CNS NPY signaling by icv injection of selective NPY receptor agonists and found that Y1, Y2, Y4, and Y5 receptor agonists all induced hyperphagia in lean, ad libitum chow-fed Long-Evans rats, with the Y2 receptor agonist having the most pronounced effect. Next, we found that at equipotent doses for food intake NPY Y1 receptor agonist had the most robust effect on VLDL-TG secretion, a Y2 receptor agonist had a modest effect, and no effect was observed for Y4 and Y5 receptor agonists. These findings, using selective agonists, suggest the possibility that the effect of CNS NPY signaling on hepatic VLDL-TG secretion may be relatively dissociable from effects on feeding behavior via the Y1 receptor.

Pre- and postprandial effects on ghrelin signaling in the brain and on the GH/IGF-I axis in the Mozambique tilapia (Oreochromis mossambicus)

The discovery of ghrelin (GRLN) has broadened our understanding of the regulation of energy homeostasis in vertebrates. In addition to stimulating growth hormone release from the pituitary, GRLN has been implicated as a hunger signal stimulating food intake in mammals and goldfish. Indeed, GRLN levels rise preprandial and fall following a meal. The current study investigated pre- and postprandial changes (3 h before and after a meal) in GRLN signaling in the tilapia (Oreochromis mossambicus). Significant elevations in preprandial brain mRNA levels of the GRLN receptor (GHS-R1a) and GRLN were observed; though not significant brain neuropeptide Y (NPY) mRNA levels did increase preprandially. GHS-R1b, and NPY mRNA levels were reduced significantly 3 h after a meal; whereas GHS-R1a levels were unaltered postprandially. Brain ghrelin mRNA levels exhibited a transient significant increase 1 h postprandially. Tilapia that missed the scheduled feeding exhibited no changes in brain GHS-R1a, GRLN and NPY postprandial mRNA levels; whereas GHS-R1b mRNA levels were significantly reduced 1 and 3 h postprandially. Brain GHSR preprocessed RNA (heteronuclear mRNA) levels were significantly elevated 3 h preprandially. GHS-R hnRNA levels were significantly elevated 1h postprandial in fed and fasted tilapia. No preprandial rise in plasma GRLN was observed. Following a meal, plasma GRLN levels were significantly elevated; whereas there was no change in tilapia missing the scheduled feeding. Stomach mRNA levels of GRLN rose preprandially and remained unchanged following a meal. In animals that missed the scheduled feeding stomach GRLN levels dropped significantly 1 h following a meal. There was no change in plasma growth hormone levels in the fed fish, although there was a significant rise in the fasted fish 1h after the scheduled feeding. Postprandial levels of plasma IGF-I were elevated in both fed and fasted tilapia. These results suggest that brain derived GRLN is likely driving day-to-day appetite through GHS-R1a and NPY; while systemic GRLN may play a role in postprandial metabolism.

Absence of effects of short-term fasting on plasma ghrelin and brain expression of ghrelin receptors in the tilapia, Oreochromis mossambicus

Ghrelin is an important endocrine peptide that links the gastrointestinal system and brain in the regulation of food intake and energy expenditure. In human, rat, and goldfish plasma levels of ghrelin and GH are elevated in fasted animals, suggesting that ghrelin is an orexigenic signal and a driving force behind the elevated plasma levels of GH during fasting. Ghrelin's orexigenic action is mediated by the ghrelin receptor (GHS-R1a and GHS-R1b) which is localized on neuropeptide Y (NPY) neurons in the brain. Studies were undertaken to investigate the effect of short-term fasting on plasma ghrelin and brain expression of GHS-R1a, GHS-R1b, and NPY in the tilapia. Fasting for 7 days had no effect on plasma ghrelin concentrations, whereas significant increases in plasma levels of GH were observed on day 3. Fasting significantly reduced plasma levels of IGF-I on days 3 and 7, and of glucose on days 3, 5, and 7. Brain expression of ghrelin and GHS-R1b were significantly elevated in fasted fish on day 3, but were significantly reduced on day 5. This reduction was likely due to a significant increase in the expression in the fed controls on day 5 compared to day 0. No change was detected in the expression of GHS-R1a or NPY in the brain. These results indicate that ghrelin is not acting as a hunger signal in short-term fasted tilapia and is not responsible for the elevated levels of plasma GH.

Hungry for life: How the arcuate nucleus and neuropeptide Y may play a critical role in mediating the benefits of calorie restriction

Laboratory studies consistently demonstrate extended lifespan in animals on calorie restriction (CR), where total caloric intake is reduced by 10-40% but adequate nutrition is otherwise maintained. CR has been further shown to delay the onset and severity of chronic diseases associated with aging such as cancer, and to extend the functional health span of important faculties like cognition. Less understood are the underlying mechanisms through which CR might act to induce such alterations. One theory postulates that CR's beneficial effects are intimately tied to the neuroendocrine response to low energy availability, of which the arcuate nucleus in the hypothalamus plays a pivotal role. Neuropeptide Y (NPY), a neurotransmitter in the front line of the arcuate response to low energy availability, is the primary hunger signal affected by CR and therefore may be a critical mechanism for lifespan extension.

Oxytocin deficiency mediates hyperphagic obesity of Sim1 haploinsufficient mice

Single-minded 1 (Sim1) encodes a transcription factor essential for formation of the hypothalamic paraventricular nucleus (PVN). Sim1 haploinsufficiency is associated with hyperphagic obesity and increased linear growth in humans and mice, similar to the phenotype of melanocortin 4 receptor (Mc4r) mutations. PVN neurons in Sim1(+/-) mice are hyporesponsive to the melanocortin agonist melanotan II. PVN neuropeptides oxytocin (Oxt), TRH and CRH inhibit feeding when administered centrally. Consequently, we hypothesized that altered PVN neuropeptide expression mediates the hyperphagia of Sim1(+/-) mice. To test this hypothesis, we measured hypothalamic expression of PVN neuropeptides in Sim1(+/-) and wild-type mice. Oxt mRNA and peptide were decreased by 80% in Sim1(+/-) mice, whereas TRH, CRH, arginine vasopressin (Avp), and somatostatin mRNAs were decreased by 20-40%. Sim1(+/-) mice also showed abnormal regulation of Oxt but not CRH mRNA in response to feeding state. A selective Mc4r agonist activated PVN Oxt neurons in wild-type mice, supporting involvement of these neurons in melanocortin feeding circuits. To test whether Oxt itself regulates feeding, we measured the effects of central administration of an Oxt receptor antagonist or repeated doses of Oxt on food intake of Sim1(+/-) and wild-type mice. Sim1(+/-) mice were hypersensitive to the orexigenic effect of the Oxt receptor antagonist. Oxt decreased the food intake and weight gain of Sim1(+/-) mice at a dose that did not affect wild-type mice. Our results support the importance of Oxt neurons in feeding regulation and suggest that reduced Oxt neuropeptide is one mechanism mediating the hyperphagic obesity of Sim1(+/-) mice.

Type-dependent differential expression of neuropeptide Y in chicken hypothalamus (Gallus domesticus)

Neuropeptide Y (NPY) is one of the most important orexigenic agents in central regulation of feeding behavior, body weight and energy homeostasis in domestic chickens. To examine differences in the hypothalamic NPY between layer-type and meat-type of chickens, which are two divergent kinds of the domestic chickens in feeding behavior and body weight, we detected mRNA levels of NPY in hypothalamic infundibular nucleus (IN), paraventricular nucleus (PVN) and lateral hypothalamic area (LHA) of these two types of chickens using one-step real time RT-PCR. The meat-type chicken had more food daily (about 1.7 folds) and greater body weights (about 1.5 folds) and brain weights than the layer-type chicken at the age of 14 d. In the meat-type of chicken, NPY mRNA levels of the IN and PVN were significantly greater than those of the LHA, and were not significantly different between the IN and PVN. However, in the layer-type of chicken, NPY mRNA levels were significantly greater in the IN than those in the LHA and PVN, and were not significantly different between the PVN and LHA. In all these hypothalamic regions, the layer-type of chicken had significantly higher NPY mRNA levels than the meat-type chicken did. These results suggest the expression of NPY in the hypothalamus has a type-dependent pattern in domestic chickens.

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.

Regulation of hypothalamic NPY by diet and smoking

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

Gonadotropin-releasing hormone-II messenger ribonucleic acid and protein content in the mammalian brain are modulated by food intake

GnRH-II is the most evolutionarily conserved member of the GnRH peptide family. In mammals, GnRH-II has been shown to regulate reproductive and feeding behaviors. In female musk shrews, GnRH-II treatment increases mating behaviors and decreases food intake. Although GnRH-II-containing neurons are known to reside in the midbrain, the neural sites of GnRH-II action are undetermined, as is the degree to which GnRH-II is regulated by energy availability. To determine whether GnRH-II function is affected by changes in food intake, we analyzed the levels of GnRH-II mRNA in the midbrain and GnRH-II protein in numerous target regions. Adult musk shrews were ad libitum fed, food restricted, or food restricted and refed for varying durations. Compared with ad libitum levels, food restriction decreased, and 90 min of refeeding reinstated, GnRH-II mRNA levels in midbrain and GnRH-II peptide in several target areas including the medial habenula and ventromedial nucleus. Refeeding for 90 min also reinstated female sexual behavior in underfed shrews. In male shrews, abundant GnRH-II peptide was present in all sites assayed, including the preoptic area, a region with only low GnRH-II in females. In contrast to females, food restriction did not affect GnRH-II protein in male brains or inhibit their mating behavior. Our results further define the relationship between GnRH-II, energy balance, and reproduction, and suggest that food restriction may inhibit female reproduction by reducing GnRH-II output to several brain nuclei. We postulate that this highly conserved neuropeptide functions similarly in other mammals, including humans, to fine-tune reproductive efforts with periods of sufficient energy resources.

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.

Developmental increases in hypothalamic neuropeptide Y content with the embryonic age of meat- and layer-type chicks

We determined central neuropeptide Y (NPY) content of meat- and layer-type chicks at embryonic days 7, 14, 20, and at post-hatching day 1. The central NPY was detectable at day 7; hypothalamic NPY content developmentally increased with a similar pattern but a different level between both types of chicks. These results were discussed with respect to feeding behavior early period after hatching.

Neuropeptide Y content in the hypothalamic paraventricular nucleus responds to fasting and refeeding in broiler chickens

To examine the neural mechanism by which hypothalamic neuropeptide Y (NPY) regulates energy homeostasis and feeding behavior in commercial broilers, we measured NPY content in several hypothalamic regions of birds that were fasted and then refed. After fasting for 48 and 72 h, body weight significantly decreased, and food intake significantly increased during the subsequent refeeding. The lost body weight was not restored to ad libitum feeding levels even after 3 days of refeeding. Plasma glucose concentration and body fat content significantly decreased and plasma non-esterified fatty acid (NEFA) concentration significantly increased after 48- and 72-h fasting. Refeeding for 24 h restored plasma metabolites and body fat content to pre-fasting levels. NPY content in the paraventricular nucleus (PVN) and infundibular nucleus significantly increased during fasting, and NPY content of the PVN was restored to pre-fasting levels after 24-h refeeding. However, there was no significant change in the NPY content of the lateral hypothalamic area during fasting or refeeding. The present results of changes in the hypothalamic NPY content during fasting and refeeding support the hypothesis that NPY plays a central role in regulation of energy homeostasis, with especially important effect on feeding behavior and body weight in broiler chickens.

The therapeutic potential of nicotine and nicotinic agonists for weight control

Transdermal nicotine patches have been successfully introduced as a safe and powerful aid to smoking cessation; this has contributed to the rising interest in additional therapeutic applications for nicotine and synthetic nicotinic agonists. Nicotine and nicotinic agonists may have a therapeutic potential for a variety of disorders, including Alzheimer's and Parkinson's diseases, depression, attention deficit disorder, Tourette's syndrome and ulcerative colitis. These interests are partially fuelled by the urgent need of the tobacco industry to find new niches for nicotine in a world bound eventually to retire from cigarette smoking. At the same time, there is an increased interest in developing drugs for fighting obesity, a growing affliction of industrialised nations. This review presents data on the potential of nicotine, and in particular synthetic nicotinic agonists, for controlling body weight. Nicotinic agonists may become relatively safe, effective and inexpensive alternatives for several optional drugs currently being developed for treating human obesity, including beta-3-adrenergic agonists, leptin and its agonists, and neuropeptide Y antagonists.

Integration of hypothalamic feeding and metabolic signals: focus on neuropeptide Y

Research is reviewed on effects of neuropeptide Y (NPY) on energy substrate utilization and central interactions among NPY, serotonin and urocortin, particularly in neurons of the paraventricular nucleus of the hypothalamus.

Abnormal response of the neuropeptide Y-deficient mouse reproductive axis to food deprivation but not lactation

Neuropeptide Y (NPY) plays a key role in both food intake and GnRH secretion. Food deprivation elevates hypothalamic NPY activity and suppresses LH and gonadal steroid secretion. Similarly, lactation up-regulates NPY expression as food consumption increases and estrous cycles cease. These observations suggest that NPY coordinates reproductive suppression in response to energy deficiency; if so, the reproductive axis of NPY knockout (KO) mice should be impervious to lactation and food deprivation. We monitored food consumption, body weight, and estrous cyclicity during lactation in NPY KO mice with large and small litters. NPY KO mice with either litter size resembled wild types (WTs) in weight regulation and food consumption. Large-litter mothers had longer anestrous periods and smaller pups at weaning, but NPY KOs and WTs did not differ in either respect. We also examined the LH response of NPY KO mice to 48 h without food. Basal levels of LH in ovariectomized NPY KO animals decreased in response to fasting, but LH levels in intact and estrogen-treated ovariectomized NPY KO animals did not. In contrast, WTs consistently showed fasting-induced suppression of LH. Our findings suggest that other systems can sustain the hyperphagia of lactation and NPY alone is not responsible for suppressing cyclicity during lactation. Nevertheless, the suppression of basal LH release that accompanies food deprivation in normal female mice appears to require the steroid-dependent actions of NPY.

Orexin-A immunoreactivity and prepro-orexin mRNA expression in hyperphagic rats induced by hypothalamic lesions and lactation

Orexins are endogenous neuropeptides that potently facilitate appetite and food consumption. In the present study, we examined orexin immunoreactivity and prepro-orexin mRNA expression in the lateral hypothalamus by immunohistochemistry and competitive reverse transcription-polymerase chain reaction (RT-PCR) methods in different models of hyperphagia in rats. Hyperphagia was induced by lesions of either the ventromedial hypothalamus (VMHL) or the paraventricular nucleus (PVNL), and we also compared lactating rats to nonlactating controls. Both VMHL and PVNL increased food intake and body weight compared to shams. On day 7 post lesion, serum leptin and insulin concentrations exhibited 3.2- and 2.8-fold increases in VMHL rats, and nonsignificant 1.8- and 1.8-fold increases in PVNL rats; there were significant decreases (48% and 33%) in lactating rats on day 12 postpartum compared to controls, respectively. Serum glucose concentrations were not significantly changed compared to controls in these rats. Quantification by image analysis suggests that VMHL significantly decreased the number and mean staining intensity of orexin-A immunoreactive neurones compared to those in the sham-lesioned group; while PVNL did not change orexin-A immunoreactivity. Competitive RT-PCR analysis showed that VMHL significantly decreased the prepro-orexin mRNA expression compared to those in the sham-lesioned group, and PVNL did not change it. Lactating rats on days 11-12 of lactation had significantly greater number and mean staining intensity of orexin-A immunoreactive neurones, prepro-orexin mRNA expression food intake and body weight than nonlactating postpartum rats. Thus, changes in orexin-A immunoreactivity and prepro-orexin mRNA expression were not consistent between the hyperphagia models. These results suggest that the hyperphagia from VMHL or PVNL and lactating rats differ in their involvement of orexin-A, and the change in circulating leptin and insulin concentrations may be involved in the change of orexin-A immunoreactivity in these rats.

Hypothalamic NPY, AGRP, and POMC mRNA responses to leptin and refeeding in mice

Food deprivation (FD) increases hypothalamic neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNA levels and decreases proopiomelanocortin (POMC) mRNA levels; refeeding restores these levels. We determined the time course of changes in hypothalamic NPY, AGRP, and POMC mRNA levels on refeeding after 24 h FD in C57BL mice by in situ hybridization. After 24 h deprivation, mice were refed with either chow or a palatable mash containing no calories or were injected with murine leptin (100 microg) without food. Mice were perfused 2 or 6 h after treatment. Food deprivation increased hypothalamic NPY mRNA (108 +/- 6%) and AGRP mRNA (78 +/- 7%) and decreased hypothalamic POMC mRNA (-15 +/- 1%). Refeeding for 6 h, but not 2 h, was sufficient to reduce (but not restore) NPY mRNA, did not affect AGRP mRNA, and restored POMC mRNA levels to ad libitum control levels. Intake of the noncaloric mash had no effect on mRNA levels, and leptin administration after deprivation (at a dose sufficient to reduce refeeding in FD mice) was not sufficient to affect mRNA levels. These results suggest that gradual postabsorptive events subsequent to refeeding are required for the restoration of peptide mRNA to baseline levels after food deprivation in mice.

Long-term undernutrition followed by short-term refeeding effects on the corticotropin-releasing hormone containing neurones in the paraventricular nucleus: an immunohistochemical study in sheep

The effect of nutritional level on the immunoreactivity of corticotropin-releasing hormone (CRH) in neurones of the hypothalamic paraventricular nucleus was described in sheep, a ruminant, whose feeding strategy differs from that of monogastric species. Two groups of ewes were underfed (40%), or fed at maintenance (100%) for 167 days, after which one-half of each group was killed or ad libitum refed (at least 150% of maintenance) for 4 days before killing. The presence of CRH in the paraventricular nucleus was examined by immunohistochemistry. The number of CRH immunoreactive neurones was increased in underfed ewes, but without modification of the plasma concentration of cortisol, indicating that the rise of CRH was not released in the portal blood nor linked to the pituitary-adrenal axis. Refeeding did not modify significantly the number of CRH immunoreactive neurones in the nucleus although these neurones were increased, only in refed ewes that were previously underfed. These data differ from those for rats and mice where CRH expression is decreased or not modified by underfeeding which could reflect different effects of undernutrition on CRH immunoreactive neurones in monogastric compared to ruminants species.

Orexins/hypocretins in the ob/ob mouse: hypothalamic gene expression, peptide content and metabolic effects

Orexins (forms A and B) belong to a new family of peptides that, as neuropeptide Y (NPY), stimulate food intake when centrally injected. The ob/ob mouse is a well-characterized model of hyperphagia and obesity associated with strong metabolic disturbances and a central dysregulation of peptides involved in the control of feeding. In the present report, we investigated the hypocretin (Hcrt)/orexin (OX) peptide pathway in lean and ob/ob mice. Prepro-Hcrt/OX mRNA expression, measured by in situ hybridization was restricted to the lateral hypothalamus area. It was significantly decreased in ob/ob mice (-18%; p<0.01). When estimated by real time RT-PCR in the whole hypothalamus, this decrease amounted to 65% (p<0.001). Hcrt-1/OX-A peptide concentrations, measured by RIA in microdissected hypothalamic nuclei were high in the lateral hypothalamus (LH) and lower in the arcuate (ARC) and paraventricular nuclei (PVN). In ob/ob mice, OX-A levels were significantly lower than in lean mice in the LH (-34%; p<0.02) and in the PVN (-72%; p<0.005). Acute intracerebroventricular injection of Hcrt-1/OX-A (1-10 nmol) stimulated feeding in lean, but not in ob/ob mice, whereas Hcrt-2/OX-B (1-10 nmol) had the opposite effect. Acute third ventricle (i3vt) injections of Hcrt/OX peptides in ob/ob mice transiently increased their metabolic rate and stimulated lipid substrate utilization. These findings provide direct evidence that Hcrt/OX peptides are down-regulated in the hypothalamus of ob/ob mice, contrary to the NPY system. The present data argues that Hcrt/OX peptides are not primarily responsible for the metabolic syndrome of the ob/ob mice. The diminution in the OX tone might participate in a counterregulatory system necessary to limit the adverse effects of NPY on food intake and body weight.

Appetite suppression based on selective inhibition of NPY receptors

AIM

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

RESULTS

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

CONCLUSIONS

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

Neuropeptide Y stimulates food consumption through multiple receptors in goldfish

In this study, the acute effects of brain intracerebroventricular (icv) injections of mammalian neuropeptide Y (NPY) Y1 ([31Leu,34Pro]NPY), Y2 (NPY2-36) and Y5 ([D-32Trp]NPY) receptor subtype agonists on food intake in goldfish were examined. Icv injection of Y1 and Y5 receptor agonists in dosages of 1 and 5 ng/g exhibited dose-dependent effects on food intake; however, higher dosages of both receptor subtypes had desensitising effects on food intake, and caused a decrease in food intake in comparison to the lower dosages. At 10 and 20 ng/g, Y1 receptor agonist-treated fish exhibited feeding significantly lower than intact and saline-injected fish; fish treated with the same dosages of Y5 agonist exhibited food intake similar to intact and saline-injected fish. Y2 agonist had no effects on food intake. Co-icv administration of Y1 and Y5 agonists in dosages of 1 and 5 ng/g caused enhanced food intake that was additive of the individual doses alone. However, desensitising one receptor did not influence the responsiveness of the other. Co-icv injection of Y1 receptor agonist in desensitizing high dosages (10 and 15 ng/g) with Y5 receptor agonist in lower doses (1 and 5 ng/g, respectively) or vice versa, resulted in a food intake similar to the dosages of Y1 and Y5 receptor agonists at 1 and 5 ng/g given alone. Overall, this study demonstrates that NPY acts centrally through Y1 and Y5 receptors to stimulate food intake in goldfish. The Y1 and Y5 receptors appear to act independently in the stimulation of food intake in goldfish.

Effects of food deprivation and refeeding on neuropeptide Y (NPY) mRNA levels in goldfish

In mammals, NPY is a key factor in the regulation of feeding behavior. In the present study, the effects of refeeding for 1-3 h in 72-75-h food deprived (FD) goldfish on the levels of NPY mRNA in telencephalon-preoptic (TEL-POA), hypothalamus (HYP) and optic tectum-thalamus (OT-THAL) were examined, using Northern blot analysis. Goldfish FD for 72 h exhibited a significant increase in NPY mRNA levels in all brain regions. At 1 h after 72-h FD (73-h FD), NPY mRNA was significantly increased in TEL-POA and OT-THAL, but remained the same as 72-h FD fish in HYP. At 3 h after 72-h FD (75 h), all brain regions exhibited a significant increase in NPY mRNA levels. However, subsequent refeeding for 1-3 h rapidly and completely reversed the effects of FD in all brain regions, reaching fed levels within 1-3 h of refeeding. Serum GH levels were highest in 72-h FD fish, but decreased significantly over 1-3 h after 72-h FD; whereas, refeeding reversed the increase in serum GH levels only at 3 h after refeeding. Taken together, these results further support that NPY is a physiological brain transducer involved in the regulation of daily appetite and feeding in goldfish.

Leptin rapidly inhibits hypothalamic neuropeptide Y secretion and stimulates corticotropin-releasing hormone secretion in adrenalectomized mice

Leptin may rapidly inhibit food intake by altering the secretion of hypothalamic neuropeptides such as neuropeptide Y (NPY), a stimulator of food intake, and/or corticotropin-releasing hormone (CRH), an inhibitor of food intake. We measured concentrations of NPY and CRH in specific hypothalamic regions [i.e., arcuate nucleus (ARC), paraventricular nucleus (PVN), ventromedial nucleus and dorsomedial nucleus] of 7- to 8-wk-old lean and ob/ob mice at 1 or 3 h after intracerebroventricular leptin administration. No rapid-onset effects of leptin on hypothalamic NPY or CRH concentrations were observed in intact mice. The addition of leptin to hypothalamic preparations from intact mice also did not alter NPY or CRH secretion. Glucocorticoids may oppose leptin actions. Consistent with this, leptin administration to adrenalectomized mice markedly reduced CRH concentrations in the ARC within 3 h after injection. This rapid reduction in CRH concentration in the ARC after leptin administration is more likely due to stimulated CRH release from this region than to decreased synthesis/transport from the PVN because leptin stimulates CRH synthesis in the PVN. Within 20 min after exposure to leptin, NPY secretion from hypothalamic preparations obtained from adrenalectomized mice was lowered by 27% and CRH secretion was elevated by 51%. The current study demonstrates that leptin rapidly influences the secretion of hypothalamic NPY and CRH and that these actions of leptin within the hypothalamus are restrained by the presence of endogenous corticosterone.

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.

Regulation of food intake by neuropeptide Y in goldfish

In mammals, neuropeptide Y (NPY) is a potent orexigenic factor. In the present study, third brain ventricle (intracerebroventricular) injection of goldfish NPY (gNPY) caused a dose-dependent increase in food intake in goldfish, and intracerebroventricular administration of NPY Y1-receptor antagonist BIBP-3226 decreased food intake; the actions of gNPY were blocked by simultaneous injection of BIBP-3226. Goldfish maintained on a daily scheduled feeding regimen display an increase in NPY mRNA levels in the telencephalon-preoptic area and hypothalamus shortly before feeding; however, a decrease occured in optic tectum-thalamus. In both fed and unfed fish, brain NPY mRNA levels decreased after scheduled feeding. Restriction in daily food ration intake for 1 wk or food deprivation for 72 h resulted in increased brain NPY mRNA levels. Results from these studies demonstrate that NPY is a physiological brain signal involved in feeding behavior in goldfish, mediating its effects, at least in part, through Y1-like receptors in the brain.

Neuroendocrine mechanisms regulating food intake and body weight

In the field of obesity research, two separate lines of study have emerged which explore the mechanism by which food intake is regulated: short-term control of food intake, and the central regulation of energy balance. The former studies the satiety response during consumption of meals, whereby satiety signalling originating in the gut is transduced into a neural signal that modulates satiety pathways in the brainstem. This review describes a neuroanatomically based model in which leptin and insulin signalling in the hypothalamus governs long-term regulation of energy balance via mechanisms that are integrated with satiety hormone signalling in the brainstem. The functional outcome of this integration is a cumulative meal-to-meal regulation of food intake, that over relatively long intervals serves to maintain stable adipose stores. Our model provides a context within which continued investigation of neuroendocrine mechanisms that control food intake and body weight can be explored, and has potential application to our current understanding of clinical obesity and its treatment.