Role of dorsomedial hypothalamic neuropeptide Y in energy homeostasis

RF-amide related peptide-3 (RFRP-3): a novel neuroendocrine regulator of energy homeostasis, metabolism, and reproduction

A hypothalamic neuropeptide, RF-amide related peptide-3 (RFRP-3), the mammalian ortholog of the avian gonadotropin-inhibitory hormone (GnIH) has inhibitory signals for reproductive axis via G-protein coupled receptor 147 in mammals. Moreover, RFRP-3 has orexigenic action but the mechanism involved in energy homeostasis and glucose metabolism is not yet known. Though, the RFRP-3 modulates orexigenic action in co-operation with other neuropeptides, which regulates metabolic cues in the hypothalamus. Administration of GnIH/RFRP-3 suppresses plasma luteinizing hormone, at the same time stimulates feeding behavior in birds and mammals. Likewise, in the metabolically deficient conditions, its expression is up-regulated suggests that RFRP-3 contributes to the integration of energy balance and reproduction. However, in many other metabolic conditions like induced diabetes and high-fat diet obesity, etc. its role is still not clear while, RFRP-3 induces the glucose homeostasis by adipocytes is reported. The physiological role of RFRP-3 in metabolic homeostasis and the metabolic effects of RFRP-3 signaling in pharmacological studies need a detailed discussion. Further studies are required to find out whether RFRP-3 is associated with restricted neuroendocrine function observed in type II diabetes mellitus, aging, or sub-fertility. In this context, the current review is focused on the role of RFRP-3 in the above-mentioned mechanisms. Studies from search engines including PubMed, Google Scholar, and science.gov are included after following set inclusion/exclusion criteria. As a developing field few mechanisms are still inconclusive, however, based on the available information RFRP-3 seems to be a putative tool in future treatment strategies towards metabolic disease.

Should I Lay or Should I Grow: Photoperiodic Versus Metabolic Cues in Chickens

While photoperiod has been generally accepted as the primary if not the exclusive cue to stimulate reproduction in photoperiodic breeders such as the laying hen, current knowledge suggests that metabolism, and/or body composition can also play an influential role to control the hypothalamic-pituitary gonadal (HPG)-axis. This review thus intends to first describe how photoperiodic and metabolic cues can impact the HPG axis, then explore and propose potential common pathways and mechanisms through which both cues could be integrated. Photostimulation refers to a perceived increase in day-length resulting in the stimulation of the HPG. While photoreceptors are present in the retina of the eye and the pineal gland, it is the deep brain photoreceptors (DBPs) located in the hypothalamus that have been identified as the potential mediators of photostimulation, including melanopsin (OPN4), neuropsin (OPN5), and vertebrate-ancient opsin (VA-Opsin). Here, we present the current state of knowledge surrounding these DBPs, along with their individual and relative importance and, their possible downstream mechanisms of action to initiate the activation of the HPG axis. On the metabolic side, specific attention is placed on the hypothalamic integration of appetite control with the stimulatory (Gonadotropin Releasing Hormone; GnRH) and inhibitory (Gonadotropin Inhibitory Hormone; GnIH) neuropeptides involved in the control of the HPG axis. Specifically, the impact of orexigenic peptides agouti-related peptide (AgRP), and neuropeptide Y (NPY), as well as the anorexigenic peptides pro-opiomelanocortin (POMC), and cocaine-and amphetamine regulated transcript (CART) is reviewed. Furthermore, beyond hypothalamic control, several metabolic factors involved in the control of body weight and composition are also presented as possible modulators of reproduction at all three levels of the HPG axis. These include peroxisome proliferator-activated receptor gamma (PPAR-γ) for its impact in liver metabolism during the switch from growth to reproduction, adiponectin as a potential modulator of ovarian development and follicular maturation, as well as growth hormone (GH), and leptin (LEP).

Perinatal exposure to endocrine disrupting compounds and the control of feeding behavior-An overview

Endocrine disrupting compounds (EDC) are ubiquitous environmental contaminants that can interact with steroid and nuclear receptors or alter hormone production. Many studies have reported that perinatal exposure to EDC including bisphenol A, PCB, dioxins, and DDT disrupt energy balance, body weight, adiposity, or glucose homeostasis in rodent offspring. However, little information exists on the effects of perinatal EDC exposure on the control of feeding behaviors and meal pattern (size, frequency, duration), which may contribute to their obesogenic properties. Feeding behaviors are controlled centrally through communication between the hindbrain and hypothalamus with inputs from the emotion and reward centers of the brain and modulated by peripheral hormones like ghrelin and leptin. Discrete hypothalamic nuclei (arcuate nucleus, paraventricular nucleus, lateral and dorsomedial hypothalamus, and ventromedial nucleus) project numerous reciprocal neural connections between each other and to other brain regions including the hindbrain (nucleus tractus solitarius and parabrachial nucleus). Most studies on the effects of perinatal EDC exposure examine simple crude food intake over the course of the experiment or for a short period in adult models. In addition, these studies do not examine EDC's impacts on the feeding neurocircuitry of the hypothalamus-hindbrain, the response to peripheral hormones (leptin, ghrelin, cholecystokinin, etc.) after refeeding, or other feeding behavior paradigms. The purpose of this review is to discuss those few studies that report crude food or energy intake after perinatal EDC exposure and to explore the need for deeper investigations in the hypothalamic-hindbrain neurocircuitry and discrete feeding behaviors.

Hypothalamus and thermogenesis: Heating the BAT, browning the WAT

Brown adipose tissue (BAT) has been also considered as the main thermogenic organ responsible of maintenance body temperature through heat production. However, a new type of thermogenic fat has been characterized during the last years, the beige or brite fat, that is developed from white adipose tissue (WAT) in response to different stimuli by a process known as browning. The activities of brown and beige adipocytes ameliorate metabolic disease, including obesity in mice and correlate with leanness in humans. Many genes and pathways that regulate brown and beige adipocyte biology have now been identified, providing a variety of promising therapeutic targets for metabolic disease. The hypothalamus is the main central place orchestrating the outflow signals that drive the sympathetic nerve activity to BAT and WAT, controlling heat production and energy homeostasis. Recent data have revealed new hypothalamic molecular mechanisms, such as hypothalamic AMP-activated protein kinase (AMPK), that control both thermogenesis and browning. This review provides an overview of the factors influencing BAT and WAT thermogenesis, with special focus on the integration of peripheral information on hypothalamic circuits controlling thermoregulation.

Neuropeptide Y: An Anti-Aging Player?

Accumulating evidence suggests that neuropeptide Y (NPY) has a role in aging and lifespan determination. In this review, we critically discuss age-related changes in NPY levels in the brain, together with recent findings concerning the contribution of NPY to, and impact on, six hallmarks of aging, specifically: loss of proteostasis, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing, cellular senescence, and mitochondrial dysfunction. Understanding how NPY contributes to, and counteracts, these hallmarks of aging will open new avenues of research on limiting damage related to aging.

Optogenetic activation of leptin- and glucose-regulated GABAergic neurons in dorsomedial hypothalamus promotes food intake via inhibitory synaptic transmission to paraventricular nucleus of hypothalamus

OBJECTIVE

The dorsomedial hypothalamus (DMH) has been considered an orexigenic nucleus, since the DMH lesion reduced food intake and body weight and induced resistance to diet-induced obesity. The DMH expresses feeding regulatory neuropeptides and receptors including neuropeptide Y (NPY), cocaine- and amphetamine-regulated transcript (CART), cholecystokinin (CCK), leptin receptor, and melanocortin 3/4 receptors. However, the principal neurons generating the orexigenic function in the DMH remain to be defined. This study aimed to clarify the role of the DMH GABAergic neurons in feeding regulation by using optogenetics and electrophysiological techniques.

METHODS

We generated the mice expressing ChRFR-C167A, a bistable chimeric channelrhodopsin, selectively in GABAergic neurons of DMH via locally injected adeno-associated virus 2. Food intake after optogenetic activation of DMH GABAergic neurons was measured. Electrophysiological properties of DMH GABAergic neurons were measured using slice patch clamp.

RESULTS

Optogenetic activation of DMH GABAergic neurons promoted food intake. Leptin hyperpolarized and lowering glucose depolarized half of DMH GABAergic neurons, suggesting their orexigenic property. Optical activation of axonal terminals of DMH GABAergic neurons at the paraventricular nucleus of hypothalamus (PVN), where anorexigenic neurons are localized, increased inhibitory postsynaptic currents on PVN neurons and promoted food intake.

CONCLUSION

DMH GABAergic neurons are regulated by metabolic signals leptin and glucose and, once activated, promote food intake via inhibitory synaptic transmission to PVN.

Changes in brain peptides associated with reproduction and energy homeostasis in photosensitive and photorefractory migratory redheaded buntings

Present study examined the expression of brain peptides associated with the reproduction and energy homeostasis (GnRH/GnIH, NPY/VIP), and assessed their possible functional association in the photosensitive (non-breeding, pre-breeding), photostimulated (breeding) and photorefractory (post-breeding) migratory redheaded buntings (Emberiza bruniceps), using double-labeled immunohistochemistry. Particularly, we measured immunoreactive (-ir) cell numbers, per cent cell area and cell optical density (OD) in the preoptic area (GnRH-I), midbrain (GnRH-II), paraventricular nucleus (GnIH), dorsomedial hypothalamus, DMH and infundibular complex, INc (NPY and VIP), and lateral septal organ (VIP) of buntings kept under natural photoperiods at the wintering latitude (26°55'N). There was a significant seasonal difference in GnRH-I, not GnRH-II, with reduced -ir cells in the photosensitive and photorefractory buntings, and notably with increased cell OD between the refractory and non-breeding states with no increase in testis size. Also, increased cell OD of GnIH neurons in non-breeding state indicated its role in the maintenance of small testes during the post-refractory period. Overall, seasonal changes in GnRH-I and GnIH were found consistent with their suggested roles in reproductive regulation of absolute photorefractory birds. Further, there was a significant seasonal change in cell OD of NPY neurons in DMH, not the INc. In contrast, VIP immunoreactivity was seasonally altered, with a significantly higher VIP-ir cells in breeding than the pre-breeding state. Finally, close proximity between perikarya with fibres suggested functional interactions between the GnRH and GnIH, and NPY and VIP. Thus, seasonal plasticity of brain peptides is perhaps the part of neural regulation of seasonal reproduction and associated energy homeostasis in migratory songbirds.

Central transthyretin acts to decrease food intake and body weight

Transthyretin (TTR) is a blood and cerebrospinal fluid transporter of thyroxine and retinol. Gene expression profiling revealed an elevation of Ttr expression in the dorsomedial hypothalamus (DMH) of rats with exercise-induced anorexia, implying that central TTR may also play a functional role in modulating food intake and energy balance. To test this hypothesis, we have examined the effects of brain TTR on food intake and body weight and have further determined hypothalamic signaling that may underlie its feeding effect in rats. We found that intracerebroventricular (icv) administration of TTR in normal growing rats decreased food intake and body weight. This effect was not due to sickness as icv TTR did not cause a conditioned taste aversion. ICV TTR decreased neuropeptide Y (NPY) levels in the DMH and the paraventricular nucleus (P < 0.05). Chronic icv infusion of TTR in Otsuka Long-Evans Tokushima Fatty rats reversed hyperphagia and obesity and reduced DMH NPY levels. Overall, these results demonstrate a previously unknown anorectic action of central TTR in the control of energy balance, providing a potential novel target for treating obesity and its comorbidities.

The brain and brown fat

Brown adipose tissue (BAT) is a specialized organ responsible for thermogenesis, a process required for maintaining body temperature. BAT is regulated by the sympathetic nervous system (SNS), which activates lipolysis and mitochondrial uncoupling in brown adipocytes. For many years, BAT was considered to be important only in small mammals and newborn humans, but recent data have shown that BAT is also functional in adult humans. On the basis of this evidence, extensive research has been focused on BAT function, where new molecules, such as irisin and bone morphogenetic proteins, particularly BMP7 and BMP8B, as well as novel central factors and new regulatory mechanisms, such as orexins and the canonical ventomedial nucleus of the hypothalamus (VMH) AMP- activated protein kinase (AMPK)-SNS-BAT axis, have been discovered and emerged as potential drug targets to combat obesity. In this review we provide an overview of the complex central regulation of BAT and how different neuronal cell populations co-ordinately work to maintain energy homeostasis.

Cetaceans evolution: insights from the genome sequences of common minke whales

Background

Whales have captivated the human imagination for millennia. These incredible cetaceans are the only mammals that have adapted to life in the open oceans and have been a source of human food, fuel and tools around the globe. The transition from land to water has led to various aquatic specializations related to hairless skin and ability to regulate their body temperature in cold water.

Results

We present four common minke whale (Balaenoptera acutorostrata) genomes with depth of ×13 ~ ×17 coverage and perform resequencing technology without a reference sequence. Our results indicated the time to the most recent common ancestors of common minke whales to be about 2.3574 (95% HPD, 1.1521 – 3.9212) million years ago. Further, we found that genes associated with epilation and tooth-development showed signatures of positive selection, supporting the morphological uniqueness of whales.

Conclusions

This whole-genome sequencing offers a chance to better understand the evolutionary journey of one of the largest mammals on earth.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1213-1) contains supplementary material, which is available to authorized users.

Neuropeptide Y attenuates anxiety- and depression-like effects of cholecystokinin-4 in mice

We investigated the involvement of neuropeptide Y (NPY) in the modulation of cholecystokinin-4 (CCK-4)-evoked anxiety and depression. Adult male mice were injected with vehicle, CCK-4, NPY, NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY or antagonist BIBP3226, via intracerebroventricular route, and subjected to social interaction or forced swim test (FST) for the evaluation of anxiety- and depression-like phenotypes, respectively. To assess the interactions between the two systems, if any, NPYergic agents were administered prior to CCK-4 and the animals were subjected to these behavioral tests. Treatment with CCK-4 or BIBP3226 dose-dependently reduced social interaction time, while NPY or [Leu(31), Pro(34)]-NPY produced opposite effect. CCK-4 treatment increased immobility time in FST. This effect was reversed by NPY and [Leu(31), Pro(34)]-NPY, although BIBP3226 per se did not alter the immobility time. In a combination study, the anxiogenic or depressive effects of CCK-4 were attenuated by NPY or [Leu(31), Pro(34)]-NPY and potentiated by BIBP3226. The brains of CCK-4 treated rats were processed for NPY immunohistochemistry. Following CCK-4 treatment, the nucleus accumbens shell (AcbSh), ventral part of lateral division of the bed nucleus of stria terminalis (BSTLV), hypothalamic paraventricular nucleus and locus coeruleus showed a reduction in NPY-immunoreactive fibers. Population of NPY-immunopositive cells was also decreased in the AcbSh, BSTLV, prefrontal cortex and hypothalamic arcuate nucleus (ARC). However, NPY-immunoreaction in the fibers of the ARC and cells of the central nucleus of amygdala was unchanged. We conclude that, inhibition of NPY signaling in the brain by CCK-4 might be causal to anxiety- and depression-like behaviors.

Anorexigenic effects of central adrenomedullin are associated with hypothalamic changes in juvenile Gallus gallus

Adrenomedullin (AM), a 52 residue neuropeptide, is associated with anorexia in mammals and has a poorly understood central mechanism of action. Thus, this study focused on elucidating AM's central mechanism of action in an alternative vertebrate model, the chick (Gallus gallus). In Experiment 1, chicks centrally injected with AM dose-dependently reduced food but not water intake. In Experiment 2, those chicks that received central AM had increased c-Fos immunoreactivity in the magnocellular division of the paraventricular nucleus (PaMC), ventromedial hypothalamus (VMH) and doromedial hypothalamus (DM). The lateral hypothalamic area, parvocellular division of the paraventricular hypothalamus and the arcuate nucleus were not affected. In Experiment 3, antagonism of corticotrophin releasing factor (CRF) receptors did not affect AM-associated anorexia. In Experiment 4, a comprehensive behavior analysis was conducted and AM-treated chicks pecked less, moved more, jumped more and spent more time in deep rest. In conclusion, exogenous AM induced anorexia is associated with activation of the PaMC, VMH and DM of the hypothalamus, is not CRF dependent, and affects behaviors unrelated to food intake in chicks.

Examination of the influence of leptin and acute metabolic challenge on RFRP-3 neurons of mice in development and adulthood

BACKGROUND

The neuropeptide RFamide-related peptide-3 (RFRP-3; mammalian ortholog to gonadotropin-inhibiting hormone) can inhibit luteinizing hormone (LH) release and increases feeding, but the regulation and development of RFRP-3 neurons remains poorly characterized, especially in mice.

METHODS AND RESULTS

We first confirmed that peripheral injections of murine RFRP-3 peptide could markedly suppress LH secretion in adult mice, as in other species. Second, given RFRP-3's reported orexigenic properties, we performed double-label in situ hybridization for metabolic genes in Rfrp neurons of mice. While Rfrp neurons did not readily coexpress neuropeptide Y, thyrotropin-releasing hormone, or MC4R, a small subset of Rfrp neurons did express the leptin receptor in both sexes. Surprisingly, we identified no changes in Rfrp expression or neuronal activation in adult mice after acute fasting. However, we determined that Rfrp mRNA levels in the dorsal-medial nucleus were significantly reduced in adult obese (Ob) mice of both sexes. Given the lower Rfrp levels observed in adult Ob mice, we asked whether leptin might also regulate RFRP-3 neuron development. Rfrp gene expression changed markedly over juvenile development, correlating with the timing of the juvenile 'leptin surge' known to govern hypothalamic feeding circuit development. However, the dramatic developmental changes in juvenile Rfrp expression did not appear to be leptin driven, as the pattern and timing of Rfrp neuron development were unaltered in Ob juveniles.

CONCLUSION

Leptin status modulates RFRP-3 expression in adulthood, but is not required for normal development of the RFRP-3 system. Leptin's regulation of adult RFRP-3 neurons likely occurs primarily via indirect signaling, and may be secondary to obesity, as only a small subset of RFRP-3 neurons express the long form of the leptin receptor (LepRb).

Overexpression of neuropeptide Y in the dorsomedial hypothalamus causes hyperphagia and obesity in rats

We sought to determine a role for NPY overexpression in the dorsomedial hypothalamus (DMH) in obesity etiology using the rat model of adeno-associated virus (AAV)-mediated expression of NPY (AAVNPY) in the DMH. Rats received bilateral DMH injections of AAVNPY or control vector and were fed on regular chow. Five-week postviral injection, half the rats from each group were switched to access to a high-fat diet for another 11 weeks. We examined variables including body weight, food intake, energy efficiency, meal patterns, glucose tolerance, fat mass, plasma insulin, plasma leptin, and hypothalamic gene expression. Rats with DMH NPY overexpression had increased food intake and body weight and lowered metabolic efficiency. The hyperphagia was mediated through increased meal size during the dark. Although these rats had normal blood glucose, their plasma insulin levels were increased in both basal and glucose challenge conditions. While high-fat diet induced hyperphagia, obesity, and hyperinsulinemia, these effects were amplified in rats with DMH NPY overexpression. Arcuate Npy, agouti-related protein and proopiomelanocortin expression was appropriately regulated in response to positive energy balance. These results indicate that DMH NPY overexpression can cause hyperphagia and obesity and DMH NPY may have actions in glucose homeostasis.

Dorsomedial hypothalamic NPY modulation of adiposity and thermogenesis

In addition to controlling food intake, the dorsomedial hypothalamus (DMH) plays an important role in thermoregulation. Within the DMH, a number of neuropeptides and receptors have been found and their roles in controlling energy balance are being investigated. We recently found that the orexigenic neuropeptide Y (NPY) in the DMH has specific actions on body adiposity and thermogenesis using a viral-mediated manipulation of NPY in the DMH. Knockdown of NPY in the DMH promotes the development of brown adipocytes in white adipose tissue and increases brown adipocyte activity. DMH NPY knockdown also causes increased thermogenesis and energy expenditure. Finally, DMH NPY knockdown prevents high-fat diet-induced obesity and improves glucose homeostasis. This review focuses on the role of DMH NPY in modulating body adiposity and thermogenesis.

Cocaine- and amphetamine-regulated transcript (CART) peptide immunoreactivity in feeding- and reward-related brain areas of young OLETF rats

Cocaine- and amphetamine-regulated transcript (CART) peptide is expressed in brain areas involved in the control of appetite, drug reward and homeostatic regulation and it has an overall anorexigenic effect. Recently, we have shown that CART peptide immunoreactivity was significantly reduced in the rostral part of the nucleus accumbens and in the rostro-medial part of the nucleus of the solitary tract in adult CCK-1 receptor deficient obese diabetic Otsuka Long Evans Tokushima Fatty (OLETF) rats compared to Long Evans Tokushima Otsuka (LETO) lean controls. It is not clear, however, whether altered CART expression is caused primarily by the deficiency in CCK-1 signaling or whether is related to the obese and diabetic phenotype of the OLETF strain which develops at a later age. Therefore, in the present study, CART-immunoreaction in feeding-related areas of the brain was compared in young, age-matched (6-7 weeks old) non-obese, non-diabetic OLETF rats and in LETO controls. We found that, young, non-diabetic OLETF rats revealed unaltered distribution of CART-peptide expressing neurons and axons throughout the brain when compared to age-matched LETO rats. In contrast to previous results observed in the obese diabetic adult rats, intensity of CART immunoreaction did not differ in the areas related to control of food-intake and reward in the young OLETFs compared to young LETO rats. Our findings suggest that factors secondary to obesity and/or diabetes rather than impaired CCK-1 receptor signaling may contribute to altered CART expression in the OLETF strain.

Cerebrospinal fluid neuropeptide Y-like immunoreactivity correlates with impulsive aggression in human subjects

BACKGROUND

Neurochemical studies have pointed to a modulatory role in human aggression for a number of central neurotransmitters; some (e.g., serotonin) appear to play an inhibitory role, while others (e.g., vasopressin) appear to play a facilitator role in the modulation of aggression. While recent animal studies of neuropeptide Y (NPY) have suggested a facilitator role for central NPY in the modulation of aggression, no human studies of central NPY have yet been reported regarding aggression.

METHODS

Basal lumbar cerebrospinal fluid (CSF) was obtained from 60 physically healthy subjects with personality disorder (PD) (n=40) and from healthy volunteers (n=20). These samples were then assessed for CSF NPY-like immunoreactivity (NPY-LI) and other neurotransmitter-related species in CSF and correlated with measures of aggression and impulsivity.

RESULTS

Cerebrospinal fluid NPY-LI was higher in PD subjects compared with healthy volunteers and in subjects with intermittent explosive disorder compared with those without intermittent explosive disorder. In PD subjects, CSF NPY-LI was directly correlated with composite measures of aggression and impulsivity and a composite measure of impulsive aggression. Group differences in CSF NPY-LI concentration were accounted for by measures of impulsive aggression.

CONCLUSIONS

These data suggest a direct relationship between CSF NPY-immunoreactivity concentration and measures of impulsive aggression in human subjects. This adds to the complex picture of the central neuromodulatory role of impulsive aggression in human subjects.

Dorsomedial hypothalamic NPY and energy balance control

Neuropeptide Y (NPY) is a potent hypothalamic orexigenic peptide. Within the hypothalamus, Npy is primarily expressed in the arcuate nucleus (ARC) and the dorsomedial hypothalamus (DMH). While the actions of ARC NPY in energy balance control have been well studied, a role for DMH NPY is still being unraveled. In contrast to ARC NPY that serves as one of downstream mediators of actions of leptin in maintaining energy homeostasis, DMH NPY is not under the control of leptin. Npy gene expression in the DMH is regulated by brain cholecystokinin (CCK) and other yet to be identified molecules. The findings of DMH NPY overexpression or induction in animals with increased energy demands and in certain rodent models of obesity implicate a role for DMH NPY in maintaining energy homeostasis. In support of this view, adeno-associated virus (AAV)-mediated overexpression of NPY in the DMH causes increases in food intake and body weight and exacerbates high-fat diet-induced hyperphagia and obesity. Knockdown of NPY in the DMH via AAV-mediated RNAi ameliorates hyperphagia, obesity and glucose intolerance of Otsuka Long-Evans Tokushima Fatty rats in which DMH NPY overexpression has been proposed to play a causal role. NPY knockdown in the DMH also prevents high-fat diet-induced hyperphagia, obesity and impaired glucose homeostasis. A detailed examination of actions of DMH NPY reveals that DMH NPY specifically affects nocturnal meal size and produces an inhibitory action on within meal satiety signals. In addition, DMH NPY modulates energy expenditure likely through affecting brown adipocyte formation and thermogenic activity. Overall, the recent findings provide clear evidence demonstrating critical roles for DMH NPY in energy balance control, and also imply a potential role for DMH NPY in maintaining glucose homeostasis.

Roles of dorsomedial hypothalamic cholecystokinin signaling in the controls of meal patterns and glucose homeostasis

A role for dorsomedial hypothalamus (DMH) cholecystokinin (CCK) signaling in feeding control has been proposed. Administration of CCK into the DMH reduces food intake and OLETF rats lacking CCK1 receptors (CCK1R) become hyperphagic and obese. We hypothesized that site specific replenishment of CCK1R in the DMH of OLETF rats would attenuate aspects of their feeding deficits. Recombinant vectors of adeno-associated viral (AAV)-mediated expression of CCK1R (AAVCCK1R) were bilaterally delivered into the DMH of OLETF. OLETF rats with AAVCCK1R injections demonstrated a 65% replenishment of Cck1r mRNA expression in the DMH relative to lean LETO control rats. Although this level of replenishment did not significantly affect overall food intake or body weight through 14 weeks following viral injections, meal patterns were partially normalized in OLETF rats receiving AAVCCK1R with a significant decrease in dark cycle meal size and a small but significant decrease in daily food intake in the meal analysis chambers. Importantly, the elevation in blood glucose level of OLETF rats was attenuated by the AAVCCK1R injections (p=0.03), suggesting a role for DMH CCK signaling in glucose homeostasis. In support of this role, administration of CCK into the DMH of intact rats enhanced glucose tolerance, as this occurred through activation of CCK1R but not CCK2R signaling. In conclusion, partial replenishment of CCK1R in the DMH of OLETF rats, although insufficient for altering overall food intake and body weight, normalizes meal pattern changes and reduces blood glucose levels. Our study also shows a novel role of DMH CCK signaling in glucose homeostasis.

The arcuate nucleus and neuropeptide Y contribute to the antitumorigenic effect of calorie restriction

Calorie restriction (CR) is known to have profound effects on tumor incidence. A typical consequence of CR is hunger, and we hypothesized that the neuroendocrine response to CR might in part mediate CR's antitumor effects. We tested CR under appetite suppression using two models: neuropeptide Y (NPY) knockout mice and monosodium glutamate-injected mice. While CR was protective in control mice challenged with a two-stage skin carcinogenesis model, papilloma development was neither delayed nor reduced by CR in the monosodium glutamate-treated and NPY knockout mice. Adiponectin levels were also not increased by CR in the appetite-suppressed mice. We propose that some of CR's beneficial effects cannot be separated from those imposed on appetite, and that NPY neurons in the arcuate nucleus of the hypothalamus are involved in the translation of reduced intake to downstream physiological and functional benefits.

Noradrenergic projections to the ventromedial hypothalamus regulate fat metabolism during endurance exercise

The regulation of energy metabolism by the central nervous system during endurance exercise was examined. We conducted respiratory gas analysis by functionally paralyzing the ventromedial hypothalamus (VMH), the lateral hypothalamic area, and the paraventricular nucleus of the hypothalamus with local anaesthetic (lidocaine) during treadmill running at a velocity that allowed for efficient fatty acid oxidation. Our results showed that only the lidocaine treatment of the VMH attenuated fatty acid oxidation during endurance exercise. The monoaminergic neural activities at these nuclei during in vivo microdialysis in rats under the same conditions indicated a significant increase in the extracellular concentration of noradrenaline in all nuclei. Similarly, a significant increase in dopamine occurred at some points during exercise, but no change in serotonin concentration occurred regardless of exercise. Disruption of noradrenergic projections to the VMH by 6-hydroxydopamine attenuated the enhancement of fat oxidation during running. Blocker treatments clarified that noradrenergic inputs to the VMH are mediated by β-adrenoceptors. These data indicate that information about peripheral tissues status is transmitted via noradrenergic projections originating in the medulla oblongata, which may be an important contribution by the VMH and its downstream mechanisms to enhanced fatty acid oxidation during exercise.

High-fat diet offsets the long-lasting effects of running-wheel access on food intake and body weight in OLETF rats

We have previously demonstrated that running-wheel access normalizes the food intake and body weight of Otsuka Long-Evens Tokushima Fatty (OLETF) rats. Following 6 wk of running-wheel access beginning at 8 wk of age, the body weight of OLETF rats remains reduced, demonstrating a lasting effect on their phenotype. In contrast, access to a high-fat diet exacerbates the hyperphagia and obesity of OLETF rats. To determine whether diet modulates the long-term effects of exercise, we examined the effects of high-fat diet on food intake and body weight in OLETF rats that had prior access to running wheels for 4 wk. We found that 4 wk of running exercise significantly decreased food intake and body weight of OLETF rats. Consistent with prior results, 4 wk of exercise also produced long-lasting effects on food intake and body weight in OLETF rats fed a regular chow. When running wheels were relocked, OLETF rats stabilized at lower levels of body weight than sedentary OLETF rats. However, access to a high-fat diet offset these effects. When OLETF rats were switched to a high-fat diet following wheel relocking, they significantly increased food intake and body weight, so that they reached levels similar to those of sedentary OLETF rats fed a high-fat diet. Gene expression determination of hypothalamic neuropeptides revealed changes that appeared to be appropriate responses to the effects of diet and running exercise. Together, these results demonstrate that high-fat diet modulates the long-lasting effects of exercise on food intake and body weight in OLETF rats.

Hypothalamic obesity in patients with craniopharyngioma: profound changes of several weight regulatory circuits

One of the most striking examples of dysfunctional hypothalamic signaling of energy homeostasis is observed in patients with hypothalamic lesions leading to hypothalamic obesity (HO). This drastic condition is frequently seen in patients with craniopharyngioma (CP), an embryological tumor located in the hypothalamic and/or pituitary region, frequently causing not only hypopituitarism, but also leading to damage of medial hypothalamic nuclei due to the tumor and its treatment. HO syndrome in CP patients is characterized by fatigue, decreased physical activity, uncontrolled appetite, and morbid obesity, and is associated with insulin and leptin resistance. Mechanisms leading to the profoundly disturbed energy homeostasis are complex. This review summarizes different aspects of important clinical studies as well as data obtained in rodent studies. In addition a model is provided describing how medial hypothalamic lesion can interact simultaneously with several weight-regulating circuitries.

Plasma neuropeptide Y levels differ in distinct diabetic conditions

Neuropeptide Y (NPY) is an important hormone in appetite regulation. Although the contribution of NPY to metabolic disease has been previously demonstrated, there are only a few reports addressing NPY plasma levels under distinct diabetic conditions. In this study we evaluated NPY plasma levels in diabetes mellitus type 2 (DM2) patients with (n=34) and without (n=34) diabetic polyneuropathy (PNP) and compared these with age and gender matched healthy controls (n=34). We also analyzed NPY plasma levels in gestational diabetes mellitus (GDM) patients with age and pregnancy-week matched controls with normal glucose tolerance (NGT). NPY concentration was determined using a commercially available radioimmunoassay kit. In addition, metabolic parameters of DM2 and GDM patients were recorded. One-way ANOVA tests with appropriate post hoc corrections showed elevated levels of NPY in DM2 patients with and without PNP when compared with those of healthy controls (122.32±40.86 and 117.33±29.92 vs. 84.65±52.17 pmol/L; p<0.001, p<0.005, respectively). No significant difference was observed between diabetic patients with and without PNP. The NPY levels were similar in the GDM group and in pregnant women with NGT (74.87±14.36 vs. 84.82±51.13 pmol/L, respectively). Notably, the NPY concentration correlated positively with insulin levels in DM2 patients (R=0.35, p<0.01). Our data suggest a potential involvement of circulating NPY in DM2 pathology.

Deficits in gastrointestinal responses controlling food intake and body weight

The gastrointestinal tract serves as a portal sensing incoming nutrients and relays mechanical and chemosensory signals of a meal to higher brain centers. Prolonged consumption of dietary fat causes adaptive changes within the alimentary, metabolic, and humoral systems that promote a more efficient process for energy metabolism from this rich source, leading to storage of energy in the form of adipose tissue. Furthermore, prolonged ingestion of dietary fats exerts profound effects on responses to signals involved in termination of a meal. This article reviews the effects of ingested fat on gastrointestinal motility, hormone release, and neuronal substrates. It focuses on changes in sensitivity to satiation signals resulting from chronic ingestion of high-fat diet, which may lead to disordered appetite and dysregulation of body weight.

Meal patterns and hypothalamic NPY expression during chronic social stress and recovery

In the present study, we examined meal patterns during and after exposure to the visible burrow system (VBS), a rodent model of chronic social stress, to determine how the microstructure of food intake relates to the metabolic consequences of social subordination. Male Long-Evans rats were housed in mixed-sex VBS colonies (4 male, 2 female) for 2 wk, during which time a dominance hierarchy formed [1 dominant male (DOM) and 3 subordinate males (SUB)], and then male rats were individually housed for a 3-wk recovery period. Controls were individually housed with females during the 2-wk VBS period and had no changes in ingestive behavior compared with a habituation period. During the hierarchy-formation phase of VBS housing, DOM and SUB had a reduced meal frequency, whereas SUB also had a reduced meal size. However, during the hierarchy-maintenance phase of VBS housing, DOM meal patterns did not differ from controls, whereas SUB continued to display a reduced food intake via less frequent meals. During recovery, DOM had comparable meal patterns to controls, whereas SUB had an increased meal size. Hypothalamic neuropeptide Y (NPY) mRNA levels were not different between these groups during the experimental period. Together, the results suggest that exposure to chronic social stress alters ingestive behavior both acutely and in the long term, which may influence the metabolic changes that accompany bouts of stress and recovery; however, these differences in meal patterns do not appear to be mediated by hypothalamic NPY.

Rutecarpine ameliorates bodyweight gain through the inhibition of orexigenic neuropeptides NPY and AgRP in mice

Orexigenic neuropeptides NPY and AgRP play major roles in feeding and are closely related to obesity and diabetic metabolic syndrome. This study explored the inhibitory effect of rutecarpine on feeding and obesity in high-fat-diet-induced (C57BL/6) and leptin-deficient (ob/ob) obese mice. Both mice strains developed obesity, but the obesity was inhibited by the reduced food intake resulting from rutecarpine treatment (0.01%, p<0.01). Blood cholesterol, non-fasting glucose, insulin, and leptin levels were reduced, compared with the control group. Rutecarpine inhibited the expression of NPY and AgRP in the arcuate nucleus (ARC) of the hypothalamus and suppressed the expression of both neuropeptides in N29-4 neuronal cells. These results indicate that rutecarpine ameliorates obesity by inhibiting food intake, which involves inhibited expression of the orexigenic neuropeptides NPY and AgRP.

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.

Oestrogen modulates hypothalamic control of energy homeostasis through multiple mechanisms

The control of energy homeostasis in women is correlated with the anorectic effects of oestrogen, which can attenuate body weight gain and reduce food intake in rodent models. This review investigates the multiple signalling pathways and cellular targets that oestrogen utilises to control energy homeostasis in the hypothalamus. Oestrogen affects all of the hypothalamic nuclei that control energy homeostasis. Oestrogen controls the activity of hypothalamic neurones through gene regulation and neuronal excitability. Oestrogen's primary cellular pathway is the control of gene transcription through the classical oestrogen receptors (ERs) (ERalpha and ERbeta) with ERalpha having the primary role in energy homeostasis. Oestrogen also controls energy homeostasis through membrane-mediated events via membrane-associated ERs or a novel, putative membrane ER that is coupled to G-proteins. Therefore, oestrogen is coupled to at least two receptors with multiple signalling and transcriptional pathways to mediate immediate and long-term anorectic effects. Ultimately, it is the interactions of all the receptor-mediated processes in hypothalamus and other areas of the central nervous system that will determine the anorectic effects of oestrogen and its control of energy homeostasis.

Neuropeptide y receptor selective ligands in the treatment of obesity

Obesity is a serious public health problem throughout the world, affecting both developed societies and developing countries. The central nervous system has developed a meticulously interconnected circuitry in order to keep us fed and in an adequate nutritional state. One of these consequences is that an energy-dense environment favors the development of obesity. Neuropeptide Y (NPY) is one of the most abundant and widely distributed peptides in the central nervous system of both rodents and humans and has been implicated in a variety of physiological actions. Within the hypothalamus, NPY plays an essential role in the control of food intake and body weight. Centrally administered NPY causes robust increases in food intake and body weight and, with chronic administration, can eventually produce obesity. NPY activates a population of at least six G protein-coupled Y receptors. NPY analogs exhibit varying degrees of affinity and specificity for these Y receptors. There has been renewed speculation that ligands for Y receptors may be of benefit for the treatment of obesity. This review highlights the therapeutic potential of Y(1), Y(2), Y(4), and Y(5) receptor agonists and antagonists as additional intervention to treat human obesity.