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1
Williams, Gareth, Joanne A. Harrold, and David J. Cutler. "The hypothalamus and the regulation of energy homeostasis: lifting the lid on a black box." Proceedings of the Nutrition Society 59, no. 3 (August 2000): 385–96. http://dx.doi.org/10.1017/s0029665100000434.
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The hypothalamus is the focus of many peripheral signals and neural pathways that control energy homeostasis and body weight. Emphasis has moved away from anatomical concepts of ‘feeding’ and ‘satiety’ centres to the specific neurotransmitters that modulate feeding behaviour and energy expenditure. We have chosen three examples to illustrate the physiological roles of hypothalamic neurotransmitters and their potential as targets for the development of new drugs to treat obesity and other nutritional disorders. Neuropeptide Y (NPY) is expressed by neurones of the hypothalamic arcuate nucleus (ARC) that project to important appetite-regulating nuclei, including the paraventricular nucleus (PVN). NPY injected into the PVN is the most potent central appetite stimulant known, and also inhibits thermogenesis; repeated administration rapidly induces obesity. The ARC NPY neurones are stimulated by starvation, probably mediated by falls in circulating leptin and insulin (which both inhibit these neurones), and contribute to the increased hunger in this and other conditions of energy deficit. They therefore act homeostatically to correct negative energy balance. ARC NPY neurones also mediate hyperphagia and obesity in the ob/ob and db/db mice and fa/fa rat, in which leptin inhibition is lost through mutations affecting leptin or its receptor. Antagonists of the Y5 receptor (currently thought to be the NPY ‘feeding’ receptor) have anti-obesity effects. Melanocortin-4 receptors (MC4-R) are expressed in various hypothalamic regions, including the ventromedial nucleus and ARC. Activation of MC4-R by agonists such as α-melanocyte-stimulating hormone (a cleavage product of pro-opiomelanocortin which is expressed in ARC neurones) inhibits feeding and causes weight loss. Conversely, MC4-R antagonists such as ‘agouti’ protein and agouti gene-related peptide (AGRP) stimulate feeding and cause obesity. Ectopic expression of agouti in the hypothalamus leads to obesity in the AVY mouse, while AGRP is co-expressed by NPY neurones in the ARC. Synthetic MC4-R agonists may ultimately find use as anti-obesity drugs in human subjects Orexins-A and -B, derived from prepro-orexin, are expressed in specific neurones of the lateral hypothalamic area (LHA). Orexin-A injected centrally stimulates eating and prepro-orexin mRNA is up regulated by fasting and hypoglycaemia. The LHA is important in receiving sensory signals from the gut and liver, and in sensing glucose, and orexin neurones may be involved in stimulating feeding in response to falls in plasma glucose.
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Denis, R. G. P., C. Bing, S. Brocklehurst, J. A. Harrold, R. G. Vernon, and G. Williams. "Diurnal changes in hypothalamic neuropeptide and SOCS-3 expression: effects of lactation and relationship with serum leptin and food intake." Journal of Endocrinology 183, no. 1 (October 2004): 173–81. http://dx.doi.org/10.1677/joe.1.05659.
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Rats normally eat about 85% of their food at night. Lactation increases food intake 3- to 4-fold, but the diurnal pattern of food intake persists. The mechanisms responsible for the diurnal and lactation-induced changes in food intake are still unresolved, hence we have further investigated the possible roles of serum leptin and hypothalamic expression of neuropeptide Y (NPY), agouti-related peptide (AgRP) and pro-opiomelanocortin (POMC) in rats. Suppressor of cytokine signalling-3 (SOCS-3) acts as a feedback inhibitor of leptin signalling in the hypothalamus, hence changes in expression of SOCS-3 were also investigated. Changes in expression of NPY, AgRP or POMC alone could not account for the diurnal changes in intake and their alteration by lactation. However, there were increased AgRP mRNA:POMC mRNA ratios at night and also during lactation, which were very similar to estimated changes in food intake. Such changes in expression may result in dominance of the orexigenic AgRP peptide over the appetite-suppressing POMC-derived peptides, and so could contribute to the hyperphagia in these states. Diurnal and lactation-related changes in the AgRP mRNA:POMC mRNA ratio and food intake are not due to changes in leptin alone. However, hypoleptinaemia, possibly through increased expression of NPY, may contribute to the hyperphagia of lactation. In the dark, expression of SOCS-3 was decreased in non-lactating rats; lactation decreased SOCS-3 expression in both light and dark phases. However, such changes are likely to enhance the ability of leptin-responsive neurones to transmit the leptin signal, and so are unlikely to contribute to either the nocturnal increase in appetite or the hyperphagia of lactation.
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Joly, A., R. Denis, J. Castel, R. Palmiter, C. Magnan, and S. Luquet. "O35 Rôle des Neurones NPY/AgRP dans le contrôle de la balance énergétique." Diabetes & Metabolism 36 (March 2010): A10. http://dx.doi.org/10.1016/s1262-3636(10)70039-2.
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Joly, A., R. Denis, J. Castel, C. Cansell, C. Magnan, and S. Luquet. "035 Implication des neurones NPY/AgRP dans le contrôle de la partition des flux énergétiques en périphérie." Diabetes & Metabolism 37, no. 1 (March 2011): A9. http://dx.doi.org/10.1016/s1262-3636(11)70523-7.
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Feng, Bing, Frank Greenway, Jerney Harms, Hesong Liu, Chunmei Wang, Pingwen Xu, and Yanlin He. "OR23-3 Hunger Hormone Asprosin Activates Orexigenic Neurons via SK Currents." Journal of the Endocrine Society 6, Supplement_1 (November 1, 2022): A19. http://dx.doi.org/10.1210/jendso/bvac150.039.
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Abstract Neurons that co-express the orexigenic agouti-related protein (AgRP) and neuropeptide Y (NPY) are indispensable for normal feeding behavior. Firing activities of AgRP/NPY neurons dynamically fluctuate with energy status and coordinate appropriate feeding behavior to meet nutritional demands. We previously demonstrated that asprosin, a recently discovered fasting-induced glucogenic and orexigenic hormone, crosses the blood-brain barrier and directly activates the orexigenic AgRP/NPY neurons via a cyclic cAMP-dependent pathway. However, intrinsic mechanisms on how asprosin regulates AgRP/NPY neural activities during the fed-to-fasted transition are not fully understood. In the satiated mice with low circulating levels of asprosin, we found that AgRP/NPY neurons expressed high levels of the small conductance calcium-activated potassium channel 3 (SK3) and were inhibited by SK3-mediated potassium currents. Conversely, in 24 hour-fasting mice with high levels of asprosin, AgRP/NPY neurons expressed low levels of SK3 and were activated via inhibition of SK3-mediated potassium currents. Notably, the stimulatory effects of asprosin on AgRP/NPY neurons were blunted in mice with SK3 selectively deleted in the AgRP/NPY neurons, further supporting a mediating role of SK3. Moreover, we also identified protein tyrosine phosphatase receptor δ (Ptprd), a membrane-bound phosphatase receptor, as the orexigenic asprosin-receptor. Deletion of Ptprd in AgRP/NPY neurons abolished asprosin's stimulatory effect on SK3-mediated currents and protected mice from diet-induced obesity. Lastly, increased circulating levels of asprosin promoted hyperphagia, body weight gain, and glucose intolerance. On the other hand, anti-asprosin antibody treatment decreased food intake and body weight by inhibiting AgRP/NPY and other orexigenic hypothalamic neurons via SK currents stimulation. In summary, our data support a model that asprosin acts on Ptprd expressed by AgRP/NPY neurons to inhibit SK3 current, further activating AgRP/NPY neurons to increase food intake and body weight. Our findings also provided preclinical evidence that asprosin-neutralizing antibodies could be used to treat obesity. Presentation: Monday, June 13, 2022 11:45 a.m. - 12:00 p.m.
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Oh, Youjin, Eun-Seon Yoo, Sang Hyeon Ju, Eunha Kim, Seulgi Lee, Seyun Kim, Kevin Wickman, and Jong-Woo Sohn. "GIRK2 potassium channels expressed by the AgRP neurons decrease adiposity and body weight in mice." PLOS Biology 21, no. 8 (August 18, 2023): e3002252. http://dx.doi.org/10.1371/journal.pbio.3002252.
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It is well known that the neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons increase appetite and decrease thermogenesis. Previous studies demonstrated that optogenetic and/or chemogenetic manipulations of NPY/AgRP neuronal activity alter food intake and/or energy expenditure (EE). However, little is known about intrinsic molecules regulating NPY/AgRP neuronal excitability to affect long-term metabolic function. Here, we found that the G protein-gated inwardly rectifying K+ (GIRK) channels are key to stabilize NPY/AgRP neurons and that NPY/AgRP neuron-selective deletion of the GIRK2 subunit results in a persistently increased excitability of the NPY/AgRP neurons. Interestingly, increased body weight and adiposity observed in the NPY/AgRP neuron-selective GIRK2 knockout mice were due to decreased sympathetic activity and EE, while food intake remained unchanged. The conditional knockout mice also showed compromised adaptation to coldness. In summary, our study identified GIRK2 as a key determinant of NPY/AgRP neuronal excitability and driver of EE in physiological and stress conditions.
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Goldstone, Anthony P., Unga A. Unmehopa, Stephen R. Bloom, and Dick F. Swaab. "Hypothalamic NPY and Agouti-Related Protein Are Increased in Human Illness But Not in Prader-Willi Syndrome and Other Obese Subjects." Journal of Clinical Endocrinology & Metabolism 87, no. 2 (February 1, 2002): 927–37. http://dx.doi.org/10.1210/jcem.87.2.8230.
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Animal studies have demonstrated the importance of orexigenic NPY and agouti-related protein (AGRP) hypothalamic neurons, which are inhibited by the adipocyte hormone leptin, in the regulation of body weight and neuroendocrine secretion. We have examined NPY and AGRP neurons in postmortem human hypothalami from controls, Prader-Willi syndrome and other obese subjects, using quantitative immunocytochemistry (ICC) and in situ hybridization, to identify causes of leptin resistance in human obesity. Using combined ICC and in situ hybridization, AGRP, but not POMC, was colocalized with NPY in infundibular nucleus neurons. Infundibular nucleus (including median eminence) NPY ICC staining or mRNA expression, and AGRP ICC staining, increased with premorbid illness duration. NPY ICC staining and mRNA expression were reduced in obese subjects, but AGRP ICC staining was unchanged, correcting for illness duration. This suggests normal responses of NPY and AGRP neurons to peripheral signals, such as leptin and insulin, in human illness and obesity. The pathophysiology of obesity and illness-associated anorexia appear to lie in downstream or separate neuronal circuits, but the infundibular neurons may mediate neuroendocrine responses to illness. The implications for pharmacological treatment of human obesity are discussed.
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Bugarith, Kishor, Thu T. Dinh, Ai-Jun Li, Robert C. Speth, and Sue Ritter. "Basomedial Hypothalamic Injections of Neuropeptide Y Conjugated to Saporin Selectively Disrupt Hypothalamic Controls of Food Intake." Endocrinology 146, no. 3 (March 1, 2005): 1179–91. http://dx.doi.org/10.1210/en.2004-1166.
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Neuropeptide Y (NPY) conjugated to saporin (NPY-SAP), a ribosomal inactivating toxin, is a newly developed compound designed to selectively target and lesion NPY receptor-expressing cells. We injected NPY-SAP into the basomedial hypothalamus (BMH), just dorsal to the arcuate nucleus (ARC), to investigate its neurotoxicity and to determine whether ARC NPY neurons are required for glucoprivic feeding. We found that NPY-SAP profoundly reduced NPY Y1 receptor and αMSH immunoreactivity, as well as NPY, Agouti gene-related protein (AGRP), and cocaine and amphetamine-related transcript mRNA expression in the BMH. NPY-SAP lesions were localized to the injection site with no evidence of retrograde transport by hindbrain NPY neurons with BMH terminals. These lesions impaired responses to intracerebroventricular (icv) leptin (5 μg/5 μl·d) and ghrelin (2 μg/5 μl), which are thought to alter feeding primarily by actions on ARC NPY/AGRP and proopiomelanocortin/cocaine and amphetamine-related transcript neurons. However, the hypothesis that NPY/AGRP neurons are required downstream mediators of glucoprivic feeding was not supported. Although NPY/AGRP neurons were destroyed by NPY-SAP, the lesion did not impair either the feeding or the hyperglycemic response to 2-deoxy-d-glucose-induced blockade of glycolysis use. Similarly, responses to glucagon-like peptide-1 (GLP-1, 5 μg/3 μl icv), NPY (5 μg/3 μl icv), cholecystokinin octapeptide (4 μg/kg ip), and β-mercaptoacetate (68 mg/kg ip) were not altered by the NPY-SAP lesion. Thus, NPY-SAP destroyed NPY receptor-expressing neurons in the ARC and selectively disrupted controls of feeding dependent on those neurons but did not disrupt peptidergic or metabolic controls dependent upon circuitry outside the BMH.
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Fraley, G. S., and S. Ritter. "Immunolesion of Norepinephrine and Epinephrine Afferents to Medial Hypothalamus Alters Basal and 2-Deoxy-d-Glucose-Induced Neuropeptide Y and Agouti Gene-Related Protein Messenger Ribonucleic Acid Expression in the Arcuate Nucleus." Endocrinology 144, no. 1 (January 1, 2003): 75–83. http://dx.doi.org/10.1210/en.2002-220659.
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Abstract Neuropeptide Y (NPY) and agouti gene-related protein (AGRP) are orexigenic peptides of special importance for control of food intake. In situ hybridization studies have shown that NPY and AGRP mRNAs are increased in the arcuate nucleus of the hypothalamus (ARC) by glucoprivation. Other work has shown that glucoprivation stimulates food intake by activation of hindbrain glucoreceptor cells and requires the participation of rostrally projecting norepinephrine (NE) or epinephrine (E) neurons. Here we determine the role of hindbrain catecholamine afferents in glucoprivation-induced increase in ARC NPY and AGRP gene expression. The selective NE/E immunotoxin saporin-conjugated antidopamineβ-hydroxylase (anti-dβh) was microinjected into the medial hypothalamus and expression of AGRP and NPY mRNA was analyzed subsequently in the ARC under basal and glucoprivic conditions using 33P-labeled in situ hybridization. Saporin-conjugated anti-dβh virtually eliminated dβh-immunoreactive terminals in the ARC without causing nonspecific damage. These lesions significantly increased basal but eliminated 2-deoxy-d-glucose-induced increases in AGRP and NPY mRNA expression. Results indicate that hindbrain catecholaminergic neurons contribute to basal NPY and AGRP gene expression and mediate the responsiveness of NPY and AGRP neurons to glucose deficit. Our results also suggest that catecholamine neurons couple potent orexigenic neural circuitry within the hypothalamus with hindbrain glucose sensors that monitor brain glucose supply.
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Phillips, Colin T., and Richard D. Palmiter. "Role of Agouti-Related Protein-Expressing Neurons in Lactation." Endocrinology 149, no. 2 (November 1, 2007): 544–50. http://dx.doi.org/10.1210/en.2007-1153.
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Hypothalamic neurons that express agouti-related protein (AgRP) and neuropeptide Y (NPY) are thought to be important for regulation of feeding, especially under conditions of negative energy balance. The expression of NPY and AgRP increases during lactation and may promote the hyperphagia that ensues. We explored the role of AgRP neurons in reproduction and lactation, using a mouse model in which AgRP-expressing neurons were selectively ablated by the action of diphtheria toxin. We show that ablation of AgRP neurons in neonatal mice does not interfere with pregnancy, parturition, or lactation, suggesting that early ablation allows compensatory mechanisms to become established. However, ablation of AgRP neurons after lactation commences results in rapid starvation, indicating that both basal feeding and lactation-induced hyperphagia become dependent on AgRP neurons in adulthood. We also show that constitutive inactivation of Npy and Agrp genes does not prevent pregnancy or lactation, nor does it protect lactating dams from diphtheria toxin-induced starvation.
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Olofsson, Louise E., Andrew A. Pierce, and Allison W. Xu. "Functional requirement of AgRP and NPY neurons in ovarian cycle-dependent regulation of food intake." Proceedings of the National Academy of Sciences 106, no. 37 (September 2, 2009): 15932–37. http://dx.doi.org/10.1073/pnas.0904747106.
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In female mammals including rodents and humans, feeding decreases during the periovulatory period of the ovarian cycle, which coincides with a surge in circulating estrogen levels. Ovariectomy increases food intake, which can be normalized by estrogen treatment at a dose and frequency mimicking those during the estrous cycle. Furthermore, administration of estrogen to rodents potently inhibits food intake. Despite these well-known effects of estrogen, neuronal subtypes that mediate estrogen's anorexigenic effects have not been identified. In this study, we show that changes in hypothalamic expression of agouti-related protein (Agrp) and neuropeptide Y (Npy) coincide with the cyclic changes in feeding across the estrous cycle. These cyclic changes in feeding are abolished in mice with degenerated AgRP neurons even though these mice cycle normally. Central administration of 17β-estradiol (E2) decreases food intake in controls but not in mice lacking the AgRP neurons. Furthermore, E2 treatment suppresses fasting-induced c-Fos activation in AgRP and NPY neurons and blunts the refeeding response. Surprisingly, although estrogen receptor alpha (ERα) is the key mediator of estrogen's anorexigenic effects, we find that expression of ERα is completely excluded from AgRP and NPY neurons in the mouse hypothalamus, suggesting that estrogen may regulate these neurons indirectly via presynaptic neurons that express ERα. This study indicates that neurons coexpressing AgRP and NPY are functionally required for the cyclic changes in feeding across estrous cycle and that AgRP and NPY neurons are essential mediators of estrogen's anorexigenic function.
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Coutinho, Eulalia A., Melanie Prescott, Sabine Hessler, Christopher J. Marshall, Allan E. Herbison, and Rebecca E. Campbell. "Activation of a Classic Hunger Circuit Slows Luteinizing Hormone Pulsatility." Neuroendocrinology 110, no. 7-8 (October 21, 2019): 671–87. http://dx.doi.org/10.1159/000504225.
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Introduction: The central regulation of fertility is carefully coordinated with energy homeostasis, and infertility is frequently the outcome of energy imbalance. Neurons in the hypothalamus expressing neuropeptide Y and agouti-related peptide (NPY/AgRP neurons) are strongly implicated in linking metabolic cues with fertility regulation. Objective: We aimed here to determine the impact of selectively activating NPY/AgRP neurons, critical regulators of metabolism, on the activity of luteinizing hormone (LH) pulse generation. Methods: We employed a suite of in vivo optogenetic and chemogenetic approaches with serial measurements of LH to determine the impact of selectively activating NPY/AgRP neurons on dynamic LH secretion. In addition, electrophysiological studies in ex vivo brain slices were employed to ascertain the functional impact of activating NPY/AgRP neurons on gonadotropin-releasing hormone (GnRH) neurons. Results: Selective activation of NPY/AgRP neurons significantly decreased post-castration LH secretion. This was observed in males and females, as well as in prenatally androgenized females that recapitulate the persistently elevated LH pulse frequency characteristic of polycystic ovary syndrome (PCOS). Reduced LH pulse frequency was also observed when optogenetic stimulation was restricted to NPY/AgRP fiber projections surrounding GnRH neuron cell bodies in the rostral preoptic area. However, electrophysiological studies in ex vivo brain slices indicated these effects were likely to be indirect. Conclusions: These data demonstrate the ability of NPY/AgRP neuronal signaling to modulate and, specifically, reduce GnRH/LH pulse generation. The findings suggest a mechanism by which increased activity of this hunger circuit, in response to negative energy balance, mediates impaired fertility in otherwise reproductively fit states, and highlight a potential mechanism to slow LH pulsatility in female infertility disorders, such as PCOS, that are associated with hyperactive LH secretion.
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Gong, Lijie, Fayi Yao, Kristin Hockman, Henry H. Heng, Gregory J. Morton, Kiyoshi Takeda, Shizuo Akira, Malcolm J. Low, Marcelo Rubinstein, and Robert G. MacKenzie. "Signal Transducer and Activator of Transcription-3 Is Required in Hypothalamic Agouti-Related Protein/Neuropeptide Y Neurons for Normal Energy Homeostasis." Endocrinology 149, no. 7 (April 10, 2008): 3346–54. http://dx.doi.org/10.1210/en.2007-0945.
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Signal transducer and activator of transcription (Stat)-3 signals mediate many of the metabolic effects of the fat cell-derived hormone, leptin. In mice, brain-specific depletion of either the long form of the leptin receptor (Lepr) or Stat3 results in comparable obese phenotypes as does replacement of Lepr with an altered leptin receptor locus that codes for a Lepr unable to interact with Stat3. Among the multiple brain regions containing leptin-sensitive Stat3 sites, cells expressing feeding-related neuropeptides in the arcuate nucleus of the hypothalamus have received much of the focus. To determine the contribution to energy homeostasis of Stat3 expressed in agouti-related protein (Agrp)/neuropeptide Y (Npy) arcuate neurons, Stat3 was deleted specifically from these cells, and several metabolic indices were measured. It was found that deletion of Stat3 from Agrp/Npy neurons resulted in modest weight gain that was accounted for by increased adiposity. Agrp/Stat3-deficient mice also showed hyperleptinemia, and high-fat diet-induced hyperinsulinemia. Stat3 deletion in Agrp/Npy neurons also resulted in altered hypothalamic gene expression indicated by increased Npy mRNA and decreased induction of suppressor of cytokine signaling-3 in response to leptin. Agrp mRNA levels in the fed or fasted state were unaffected. Behaviorally, mice without Stat3 in Agrp/Npy neurons were mildly hyperphagic and hyporesponsive to leptin. We conclude that Stat3 in Agrp/Npy neurons is required for normal energy homeostasis, but Stat3 signaling in other brain areas also contributes to the regulation of energy homeostasis.
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Kas, Martien J. H., Adrie W. Bruijnzeel, Jurgen R. Haanstra, Victor M. Wiegant, and Roger A. H. Adan. "Differential regulation of agouti-related protein and neuropeptide Y in hypothalamic neurons following a stressful event." Journal of Molecular Endocrinology 35, no. 1 (August 2005): 159–64. http://dx.doi.org/10.1677/jme.1.01819.
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Stress affects eating behaviour in rodents and humans, suggesting that the regulation of energy balance and the stress response are coupled physiological processes. Neuropeptide Y (NPY) and agouti-related protein (AgRP) are potent food-stimulating neuropeptides that are highly co-localised in arcuate nucleus neurons of the hypothalamus. Recent studies have shown that NPY and AgRP mRNA levels in these neurons respond similarly to fasting and leptin, indicating functional redundancy of the neuropeptide systems in these orexigenic neurons. However, we have found that NPY and AgRP mRNA expression in arcuate nucleus neurons are dissociated immediately following a stressful event. Two hours following a brief session of inescapable foot shocks, AgRP mRNA levels are down-regulated (P < 0.0001). In contrast, NPY mRNA levels are up-regulated (P < 0.0001). To provide physiological relevance for this acute down-regulation of AgRP, an inverse agonist of melanocortin receptors, we have shown that acute intracerebroventricular injection of a melanocortin receptor agonist, α-melanocyte-stimulating hormone (α-MSH), caused a significantly stronger activation of the hypothalamus–pituitary–adrenal-cortical (HPA) axis following a stressful event than in controls. Thus, AgRP and NPY mRNA levels in similar arcuate nucleus neurons are differentially regulated following a stressful event. This may contribute to increased sensitivity for α-MSH to activate the HPA axis following a repeated stressful experience.
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van de Wall, Esther, Rebecca Leshan, Allison W. Xu, Nina Balthasar, Roberto Coppari, Shun Mei Liu, Young Hwan Jo, et al. "Collective and Individual Functions of Leptin Receptor Modulated Neurons Controlling Metabolism and Ingestion." Endocrinology 149, no. 4 (December 27, 2007): 1773–85. http://dx.doi.org/10.1210/en.2007-1132.
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Two known types of leptin-responsive neurons reside within the arcuate nucleus: the agouti gene-related peptide (AgRP)/neuropeptide Y (NPY) neuron and the proopiomelanocortin (POMC) neuron. By deleting the leptin receptor gene (Lepr) specifically in AgRP/NPY and/or POMC neurons of mice, we examined the several and combined contributions of these neurons to leptin action. Body weight and adiposity were increased by Lepr deletion from AgRP and POMC neurons individually, and simultaneous deletion in both neurons (A+P LEPR-KO mice) further increased these measures. Young (periweaning) A+P LEPR-KO mice exhibit hyperphagia and decreased energy expenditure, with increased weight gain, oxidative sparing of triglycerides, and increased fat accumulation. Interestingly, however, many of these abnormalities were attenuated in adult animals, and high doses of leptin partially suppress food intake in the A+P LEPR-KO mice. Although mildly hyperinsulinemic, the A+P LEPR-KO mice displayed normal glucose tolerance and fertility. Thus, AgRP/NPY and POMC neurons each play mandatory roles in aspects of leptin-regulated energy homeostasis, high leptin levels in adult mice mitigate the importance of leptin-responsiveness in these neurons for components of energy balance, suggesting the presence of other leptin-regulated pathways that partially compensate for the lack of leptin action on the POMC and AgRP/NPY neurons.
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Qian, Su, Howard Chen, Drew Weingarth, Myrna E. Trumbauer, Dawn E. Novi, Xiaoming Guan, Hong Yu, et al. "Neither Agouti-Related Protein nor Neuropeptide Y Is Critically Required for the Regulation of Energy Homeostasis in Mice." Molecular and Cellular Biology 22, no. 14 (July 15, 2002): 5027–35. http://dx.doi.org/10.1128/mcb.22.14.5027-5035.2002.
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ABSTRACT Agouti-related protein (AgRP), a neuropeptide abundantly expressed in the arcuate nucleus of the hypothalamus, potently stimulates feeding and body weight gain in rodents. AgRP is believed to exert its effects through the blockade of signaling by α-melanocyte-stimulating hormone at central nervous system (CNS) melanocortin-3 receptor (Mc3r) and Mc4r. We generated AgRP-deficient (Agrp−/− ) mice to examine the physiological role of AgRP. Agrp−/− mice are viable and exhibit normal locomotor activity, growth rates, body composition, and food intake. Additionally, Agrp−/− mice display normal responses to starvation, diet-induced obesity, and the administration of exogenous leptin or neuropeptide Y (NPY). In situ hybridization failed to detect altered CNS expression levels for proopiomelanocortin, Mc3r, Mc4r, or NPY mRNAs in Agrp−/− mice. As AgRP and the orexigenic peptide NPY are coexpressed in neurons of the arcuate nucleus, we generated AgRP and NPY double-knockout (Agrp−/− ;Npy−/− ) mice to determine whether NPY or AgRP plays a compensatory role in Agrp−/− or NPY-deficient (Npy−/− ) mice, respectively. Similarly to mice deficient in either AgRP or NPY, Agrp−/− ;Npy−/− mice suffer no obvious feeding or body weight deficits and maintain a normal response to starvation. Our results demonstrate that neither AgRP nor NPY is a critically required orexigenic factor, suggesting that other pathways capable of regulating energy homeostasis can compensate for the loss of both AgRP and NPY.
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Zhang, Juan, Yunting Zhou, Cheng Chen, Feiyuan Yu, Yun Wang, Jiang Gu, Lian Ma, and Guyu Ho. "ERK1/2 mediates glucose-regulated POMC gene expression in hypothalamic neurons." Journal of Molecular Endocrinology 54, no. 2 (January 26, 2015): 125–35. http://dx.doi.org/10.1530/jme-14-0330.
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Hypothalamic glucose-sensing neurons regulate the expression of genes encoding feeding-related neuropetides POMC, AgRP, and NPY – the key components governing metabolic homeostasis. AMP-activated protein kinase (AMPK) is postulated to be the molecular mediator relaying glucose signals to regulate the expression of these neuropeptides. Whether other signaling mediator(s) plays a role is not clear. In this study, we investigated the role of ERK1/2 using primary hypothalamic neurons as the model system. The primary neurons were differentiated from hypothalamic progenitor cells. The differentiated neurons possessed the characteristic neuronal cell morphology and expressed neuronal post-mitotic markers as well as leptin-regulated orexigenic POMC and anorexigenic AgRP/NPY genes. Treatment of cells with glucose dose-dependently increased POMC and decreased AgRP/NPY expression with a concurrent suppression of AMPK phosphorylation. In addition, glucose treatment dose-dependently increased the ERK1/2 phosphorylation. Blockade of ERK1/2 activity with its specific inhibitor PD98059 partially (approximately 50%) abolished glucose-induced POMC expression, but had little effect on AgRP/NPY expression. Conversely, blockade of AMPK activity with its specific inhibitor produced a partial (approximately 50%) reversion of low-glucose-suppressed POMC expression, but almost completely blunted the low-glucose-induced AgRP/NPY expression. The results indicate that ERK1/2 mediated POMC but not AgRP/NPY expression. Confirming the in vitro findings, i.c.v. administration of PD98059 in rats similarly attenuated glucose-induced POMC expression in the hypothalamus, but again had little effect on AgRP/NPY expression. The results are indicative of a novel role of ERK1/2 in glucose-regulated POMC expression and offer new mechanistic insights into hypothalamic glucose sensing.
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Chen, Peilin, Chien Li, Carrie Haskell-Luevano, Roger D. Cone, and M. Susan Smith. "Altered Expression of Agouti-Related Protein and Its Colocalization with Neuropeptide Y in the Arcuate Nucleus of the Hypothalamus during Lactation*." Endocrinology 140, no. 6 (June 1, 1999): 2645–50. http://dx.doi.org/10.1210/endo.140.6.6829.
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Abstract During lactation, the levels of neuropeptide Y (NPY), which plays an important role in mediating food intake, are significantly elevated in a number of hypothalamic areas, including the arcuate nucleus (ARH). To identify additional hypothalamic systems that might be important in mediating the increase in food intake and alterations in energy homeostasis during lactation, the present studies examined the expression of agouti-related protein (AGRP), a recently described homologue of the skin agouti protein. AGRP is found in the hypothalamus and has been suggested to play an important role in the regulation of food intake. In the first experiment, animals were studied during diestrus of the estrous cycle, a stage of the cycle when estrogen levels are basal and similar to lactation, or during days 12–13 postpartum. Lactating animals had their litters adjusted to eight pups on day 2 postpartum. Brain tissue sections were used to measure AGRP messenger RNA (mRNA) levels by in situ hybridization. AGRP mRNA signal was found mostly in the ventromedial portion of the ARH, which has been shown to contain a high density of NPY neurons. A significant increase in AGRP mRNA content was observed in the mid- to caudal portion of the ARH of lactating animals compared with diestrous females. No difference was found in the rostral portion of the ARH. In the second experiment, double-label in situ hybridization for AGRP and NPY was performed in lactating animals to determine the extent of colocalization of the two peptides in the ARH, using 35S-labeled and digoxigenin-labeled antisense complementary RNA probes. It was found that almost all of the NPY-positive neurons throughout the ARH also expressed AGRP mRNA signal. Furthermore, AGRP expression was confined almost exclusively to NPY-positive neurons. Thus, the present study showed that during lactation, AGRP gene expression was significantly elevated in a subset of the AGRP neurons in the ARH. The high degree of colocalization of AGRP and NPY, coupled with previous reports from our laboratory demonstrating increased NPY expression in the ARH in response to suckling, suggests that AGRP and NPY are coordinately regulated and may be involved in the increase in food intake during lactation.
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Turi, Gergely F., Zsolt Liposits, Suzanne M. Moenter, Csaba Fekete, and Erik Hrabovszky. "Origin of Neuropeptide Y-Containing Afferents to Gonadotropin-Releasing Hormone Neurons in Male Mice." Endocrinology 144, no. 11 (November 1, 2003): 4967–74. http://dx.doi.org/10.1210/en.2003-0470.
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Abstract The origin of neuropeptide Y (NPY) afferents to GnRH neurons was investigated in male mice. Neonatal lesioning of the hypothalamic arcuate nuclei (ARC) with monosodium glutamate markedly reduced the number of NPY fibers in the preoptic area as well as the frequency of their contacts with perikarya and proximal dendrites of GnRH neurons. Dual-label immunofluorescence studies to determine the precise contribution of the ARC to the innervation of GnRH neurons by NPY axons were carried out on transgenic mice in which enhanced green fluorescent protein was expressed under the control of the GnRH promoter (GnRH-enhanced green fluorescent protein mice). The combined application of red Cy3 and blue AMCA fluorochromogenes established that 49.1 ± 7.3% of NPY axons apposed to green GnRH neurons also contained agouti-related protein (AGRP), a selective marker for NPY axons arising from the ARC. Immunoelectronmicroscopic analysis detected symmetric synapses between AGRP fibers and GnRH-immunoreactive perikarya. Additional triple-fluorescence experiments revealed the presence of dopamine-β-hydroxylase immunoreactivity within 25.4 ± 3.3% of NPY afferents to GnRH neurons. This enzyme marker enabled the selective labeling of NPY pathways ascending from noradrenergic/adrenergic cell populations of the brain stem, thus defining a second important source for NPY-containing fibers regulating GnRH cells. The absence of both topographic markers (AGRP and dopamine-β-hydroxylase) within 26% of NPY contacts suggests that additional sources of NPY fibers to GnRH neurons exist. Future studies will address distinct functions of the two identified NPY systems in the afferent neuronal regulation of the GnRH system.
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Kurita, Hideharu, Kai Y. Xu, Yuko Maejima, Masanori Nakata, Katsuya Dezaki, Putra Santoso, Yifei Yang, et al. "Arcuate Na+,K+-ATPase senses systemic energy states and regulates feeding behavior through glucose-inhibited neurons." American Journal of Physiology-Endocrinology and Metabolism 309, no. 4 (August 15, 2015): E320—E333. http://dx.doi.org/10.1152/ajpendo.00446.2014.
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Feeding is regulated by perception in the hypothalamus, particularly the first-order arcuate nucleus (ARC) neurons, of the body's energy state. However, the cellular device for converting energy states to the activity of critical neurons in ARC is less defined. We here show that Na+,K+-ATPase (NKA) in ARC senses energy states to regulate feeding. Fasting-induced systemic ghrelin rise and glucose lowering reduced ATP-hydrolyzing activity of NKA and its substrate ATP level, respectively, preferentially in ARC. Lowering glucose concentration (LG), which mimics fasting, decreased intracellular NAD(P)H and increased Na+ concentration in single ARC neurons that subsequently exhibited [Ca2+]i responses to LG, showing that they were glucose-inhibited (GI) neurons. Third ventricular injection of the NKA inhibitor ouabain induced c-Fos expression in agouti-related protein (AgRP) neurons in ARC and evoked neuropeptide Y (NPY)-dependent feeding. When injected focally into ARC, ouabain stimulated feeding and mRNA expressions for NPY and AgRP. Ouabain increased [Ca2+]i in single NPY/AgRP neurons with greater amplitude than in proopiomelanocortin neurons in ARC. Conversely, the specific NKA activator SSA412 suppressed fasting-induced feeding and LG-induced [Ca2+]i increases in ARC GI neurons. NPY/AgRP neurons highly expressed NKAα3, whose knockdown impaired feeding behavior. These results demonstrate that fasting, via ghrelin rise and LG, suppresses NKA enzyme/pump activity in ARC and thereby promotes the activation of GI neurons and NPY/AgRP-dependent feeding. This study identifies ARC NKA as a hypothalamic sensor and converter of metabolic states to key neuronal activity and feeding behaviour, providing a new target to treat hyperphagic obesity and diabetes.
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Briggs, Dana I., Pablo J. Enriori, Moyra B. Lemus, Michael A. Cowley, and Zane B. Andrews. "Diet-Induced Obesity Causes Ghrelin Resistance in Arcuate NPY/AgRP Neurons." Endocrinology 151, no. 10 (September 8, 2010): 4745–55. http://dx.doi.org/10.1210/en.2010-0556.
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Circulating ghrelin is decreased in obesity, and peripheral ghrelin does not induce food intake in obese mice. We investigated whether ghrelin resistance was a centrally mediated phenomenon involving dysregulated neuropeptide Y (NPY) and agouti-related peptide (AgRP) circuits. We show that diet-induced obesity (DIO) (12 wk) suppresses the neuroendocrine ghrelin system by decreasing acylated and total plasma ghrelin, decreasing ghrelin and Goat mRNA in the stomach, and decreasing expression of hypothalamic GHSR. Peripheral (ip) or central (intracerebroventricular) ghrelin injection was able to induce food intake and arcuate nucleus Fos immunoreactivity in chow-fed but not high-fat diet-fed mice. DIO decreased expression of Npy and Agrp mRNA, and central ghrelin was unable to promote expression of these genes. Ghrelin did not induce AgRP or NPY secretion in hypothalamic explants from DIO mice. Injection of NPY intracerebroventricularly increased food intake in both chow-fed and high-fat diet-fed mice, indicating that downstream NPY/AgRP neural targets are intact and that defective NPY/AgRP function is a primary cause of ghrelin resistance. Ghrelin resistance in DIO is not confined to the NPY/AgRP neurons, because ghrelin did not stimulate growth hormone secretion in DIO mice. Collectively, our data suggests that DIO causes ghrelin resistance by reducing NPY/AgRP responsiveness to plasma ghrelin and suppressing the neuroendocrine ghrelin axis to limit further food intake. Ghrelin has a number of functions in the brain aside from appetite control, including cognitive function, mood regulation, and protecting against neurodegenerative diseases. Thus, central ghrelin resistance may potentiate obesity-related cognitive decline, and restoring ghrelin sensitivity may provide therapeutic outcomes for maintaining healthy aging.
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Goto, Motomitsu, Hiroshi Arima, Minemori Watanabe, Masayuki Hayashi, Ryouichi Banno, Ikuko Sato, Hiroshi Nagasaki, and Yutaka Oiso. "Ghrelin Increases Neuropeptide Y and Agouti-Related Peptide Gene Expression in the Arcuate Nucleus in Rat Hypothalamic Organotypic Cultures." Endocrinology 147, no. 11 (November 1, 2006): 5102–9. http://dx.doi.org/10.1210/en.2006-0104.
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Ghrelin, which was identified from the rat stomach, is a potent stimulant for food intake. Several lines of evidence suggest that the orexigenic action of ghrelin is mediated via the neuropeptide Y (NPY) neurons in the arcuate nucleus, although the detailed mechanisms by which ghrelin stimulates NPY neurons are not clear. In this study, we examined the gene regulation of NPY and agouti-related peptide (AGRP), another orexigenic peptide synthesized in the NPY neurons, in the arcuate nucleus by ghrelin in hypothalamic organotypic cultures. Incubation of the hypothalamic explants with ghrelin significantly increased NPY and AGRP mRNA expression in the presence, but not absence, of dexamethasone. Glucocorticoids were also necessary for ghrelin action in vivo because an intracerebroventricular injection of ghrelin significantly increased NPY and AGRP mRNA expression in the arcuate nucleus only in sham-operated, but not in adrenalectomized rats. The stimulatory effects of ghrelin on gene expression were not blocked by a sodium channel blocker tetrodotoxin in the organotypic cultures. Ghrelin also increased NPY heteronuclear (hn) RNA expression, the first transcript that has been used as an indicator for gene transcription. The stimulatory effects of ghrelin on NPY gene expression were abolished in the presence of cycloheximide, which blocks translation, suggesting that de novo protein synthesis is required for ghrelin action. These data suggest that ghrelin stimulates NPY and AGRP gene expression independently of action potentials only in the presence of glucocorticoids. Furthermore, our data demonstrate stimulatory action of ghrelin on NPY gene transcription, which requires de novo protein synthesis.
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Zheng, Huiyuan, Michele M. Corkern, Scott M. Crousillac, Laurel M. Patterson, Curtis B. Phifer, and Hans-Rudolf Berthoud. "Neurochemical phenotype of hypothalamic neurons showing Fos expression 23 h after intracranial AgRP." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 282, no. 6 (June 1, 2002): R1773—R1781. http://dx.doi.org/10.1152/ajpregu.00019.2002.
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Agouti-related protein (AgRP) is coexpressed with neuropeptide Y (NPY) in a population of neurons in the arcuate nucleus (ARC) of the hypothalamus and stimulates food intake for up to 7 days if injected intracerebroventricularly. The prolonged food intake stimulation does not seem to depend on continued competition at the melanocortin-4 receptor (MC4R), because the relatively specific MC4R agonist MTII regains its ability to suppress food intake 24 h after AgRP injection. Intracerebroventricular AgRP also stimulates c-Fos expression 24 h after injection in several brain areas, so the neurons exhibiting delayed Fos expression might be particularly important in feeding behavior. Thus we aimed to identify the neurochemical phenotype of some of these neurons in select hypothalamic areas, using double-label immunohistochemistry. AgRP-injected rats ingested significantly more chow (10.2 ± 0.6 g) vs. saline controls (3.4 ± 0.7 g) in the first 9 h (light phase) after injection. In the lateral hypothalamus (particularly the perifornical area) 23 h after injection, AgRP induced significantly more Fos vs. saline in orexin-A (OXA) neurons (25.6 ± 4.9 vs. 4.8 ± 3.1%), but not in melanin-concentrating hormone (MCH) or cocaine- and amphetamine-regulated transcript (CART) neurons. In the ARC, AgRP induced significantly more Fos in CART (40.6 ± 5.9 vs. 13.4 ± 1.8%) but not NPY neurons. In the paraventricular nucleus, there was no significant difference in Fos expression induced by AgRP vs. saline in oxytocin and CART neurons. We conclude that the long-lasting hyperphagia induced by AgRP is correlated with and possibly partially mediated by hyperactive OXA neurons in the lateral hypothalamus and CART neurons in the ARC, but not by NPY and MCH neurons. The substantial increase in light-phase food intake by AgRP supports a role for the arousing effects of OXA. Activation of CART neurons in the ARC (which likely coexpress proopiomelanocortin) could indicate attempts to activate counterregulatory decreases in food intake.
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Qiu, Jian, Martha A. Bosch, Chungang Zhang, Oline K. Rønnekleiv, and Martin J. Kelly. "Estradiol Protects Neuropeptide Y/Agouti-Related Peptide Neurons against Insulin Resistance in Females." Neuroendocrinology 110, no. 1-2 (June 19, 2019): 105–18. http://dx.doi.org/10.1159/000501560.
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When it comes to obesity, men exhibit a higher incidence of metabolic syndrome than women in early adult life, but this sex advantage wanes in postmenopausal women. A key diagnostic of the metabolic syndrome is insulin resistance in both peripheral tissues and brain, especially in the hypothalamus. Since the anorexigenic hormone 17β-estradiol (E2) regulates food intake in part by inhibiting the excitability of the hypothalamic neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons, we hypothesized that E2 would protect against insulin resistance in NPY/AgRP neurons with diet-induced obesity (DIO). Therefore, we did whole-cell recordings and single cell quantitative polymerase chain reaction in arcuate NPYGFP neurons from both female and male mice to test the efficacy of insulin with DIO. The resting membrane potential and input resistance of NPY/AgRP neurons were significantly increased in DIO versus control-diet fed males. Most notably, the efficacy of insulin to activate KATP channels in NPY/AgRP neurons was significantly attenuated, although the KATP channel opener diazoxide was fully effective in NPY/AgRP neurons from DIO males, indicating that the KATP channels were expressed and functional. In contrast, insulin was fully efficacious to activate KATP channels in DIO females, and the response was reversed by the KATP channel blocker tolbutamide. However, the ability of insulin to activate KATP channels was abrogated with ovariectomy but fully restored with E2 replacement. Insulin resistance in obese males was likely mediated by an increase in suppressor of cytokine signaling-3 (SOCS-3), protein tyrosine phosphatase B (PTP1B) and T-cell protein tyrosine phosphatase (TCPTP) activity, since the expression of all 3 mRNAs were upregulated in the obese males but not in females. As proof of principle, pre-incubation of hypothalamic slices from DIO males with the PTP1B/TCPTP inhibitor CX08005 completely rescued the effects of insulin. Therefore, E2 protects NPY/AgRP neurons in females against insulin resistance through, at least in part, attenuating phosphatase activity. The neuroprotective effects of E2 may explain sex differences in the expression of metabolic syndrome that disappears with the loss of E2 in aging.
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Morrison, Christopher D., Gregory J. Morton, Kevin D. Niswender, Richard W. Gelling, and Michael W. Schwartz. "Leptin inhibits hypothalamic Npy and Agrp gene expression via a mechanism that requires phosphatidylinositol 3-OH-kinase signaling." American Journal of Physiology-Endocrinology and Metabolism 289, no. 6 (December 2005): E1051—E1057. http://dx.doi.org/10.1152/ajpendo.00094.2005.
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Phosphatidylinositol 3-OH-kinase (PI3K) and STAT3 are signal transduction molecules activated by leptin in brain areas controlling food intake. To investigate their role in leptin-mediated inhibition of hypothalamic neuropeptide Y ( Npy) and agouti-related peptide ( Agrp) gene expression, male Sprague-Dawley rats ( n = 5/group) were either fed ad libitum or subjected to a 52-h fast. At 12-h intervals, the PI3K inhibitor LY-294002 (LY, 1 nmol) or vehicle was injected intracerebroventricularly (ICV) as a pretreatment, followed 1 h later by leptin (3 μg icv) or vehicle. Fasting increased hypothalamic Npy and Agrp mRNA levels ( P < 0.05), and ICV leptin administration prevented this increase. As predicted, LY pretreatment blocked this inhibitory effect of leptin, such that Npy and Agrp levels in LY-leptin-treated animals were similar to fasted controls. By comparison, leptin-mediated activation of hypothalamic STAT3 signaling, as measured by induction of both phospho-STAT3 immunohistochemistry and suppressor of cytokine signaling-3 ( Socs3) mRNA, was not significantly attenuated by ICV LY pretreatment. Because NPY/AgRP neurons project to the hypothalamic paraventricular nucleus (PVN), we next investigated whether leptin activation of PVN neurons is similarly PI3K dependent. Compared with vehicle, leptin increased the number of c-Fos positive cells within the parvocellular PVN ( P = 0.001), and LY pretreatment attenuated this effect by 35% ( P = 0.043). We conclude that leptin requires intact PI3K signaling both to inhibit hypothalamic Npy and Agrp gene expression and activate neurons within the PVN. In addition, these data suggest that leptin activation of STAT3 is insufficient to inhibit expression of Npy or Agrp in the absence of PI3K signaling.
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Gyengesi, Erika, Zhong-Wu Liu, Giuseppe D'Agostino, Geliang Gan, Tamas L. Horvath, Xiao-Bing Gao, and Sabrina Diano. "Corticosterone Regulates Synaptic Input Organization of POMC and NPY/AgRP Neurons in Adult Mice." Endocrinology 151, no. 11 (November 1, 2010): 5395–402. http://dx.doi.org/10.1210/en.2010-0681.
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Changes in circulating hormones, such as leptin and ghrelin, induce alterations in synaptic input organization and electrophysiological properties of neurons of the arcuate nucleus of the hypothalamus. To assess whether changes in circulating glucocorticoids also alter synaptic arrangement and membrane potential properties, we studied the effect of adrenalectomy (ADX) and corticosterone replacement in mice on the proopiomelanocortin (POMC) and neuropeptide Y (NPY)/agouti-related protein (AgRP) neurons of the hypothalamic arcuate nucleus. ADX reduced the number of symmetric, putative inhibitory synapses onto POMC neurons and the number of asymmetric, putative excitatory synapses onto NPY/AgRP neurons. Corticosterone replacement in ADX mice to levels similar to sham-operated animals restored the number of synapses onto POMC and NPY/AgRP neurons to that seen in sham-operated controls. The alterations in the synaptic arrangement in ADX mice were not due to their decrease in food intake as evidenced by the synaptic analysis of the pair-fed control animals. In line with the altered synaptic input organization, a depolarization of POMC membrane potential and a hyperpolarization of NPY/AgRP membrane potential were observed in ADX mice compared with their sham-operated controls. All of these changes reverted upon corticosterone replacement. These results reveal that the known orexigenic action of corticosteroids is mediated, at least in part, by synaptic changes and altered excitability of the melanocortin system.
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Jones, Edward S., Nicolas Nunn, Adam P. Chambers, Søren Østergaard, Birgitte S. Wulff, and Simon M. Luckman. "Modified Peptide YY Molecule Attenuates the Activity of NPY/AgRP Neurons and Reduces Food Intake in Male Mice." Endocrinology 160, no. 11 (May 10, 2019): 2737–47. http://dx.doi.org/10.1210/en.2019-00100.
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Abstract To study the effects of an analog of the gut-produced hormone peptide YY (PYY3-36), which has increased selectivity for the Y2 receptor; specifically, to record its effects on food intake and on hypothalamic neuropeptide Y/agouti-related peptide (NPY/AgRP) neuron activity. NNC0165-1273, a modified form of the peptide hormone PYY3-36 with potent selectivity at Y2 receptor (>5000-fold over Y1, 1250-fold over Y4, and 650-fold over Y5 receptor), was tested in vivo and in vitro in mouse models. NNC0165-1273 has fivefold lower relative affinity for Y2 compared with PYY3-36, but >250-, 192-, and 400-fold higher selectivity, respectively, for the Y1, Y4, and Y5 receptors. NNC0165-1273 produced a reduction in nighttime feeding at a dose at which PYY3-36 loses efficacy. The normal behavioral satiety sequence observed suggests that NNC0165-1273 is not nauseating and, instead, reduces food intake by producing early satiety. Additionally, NNC0165-1273 blocked ghrelin-induced cFos expression in NPY/AgRP neurons. In vitro electrophysiological recordings showed that, opposite to ghrelin, NNC0165-1273 hyperpolarized NPY/AgRP neurons and reduced action potential frequency. Administration of NNC0165-1273 via subcutaneous osmotic minipump caused a dose-dependent decrease in body weight and fat mass in an obese mouse model. Finally, NNC0165-1273 attenuated the feeding response when NPY/AgRP neurons were activated using ghrelin or more selectively with designer receptors. NNC0165-1273 is nonnauseating and stimulates a satiety response through, at least in part, a direct action on hypothalamic NPY/AgRP neurons. Modification of PYY3-36 to produce compounds with increased affinity to Y2 receptors may be useful as antiobesity therapies in humans.
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Sánchez, Edith, Praful S. Singru, Runa Acharya, Monica Bodria, Csaba Fekete, Ann Marie Zavacki, Antonio C. Bianco, and Ronald M. Lechan. "Differential Effects of Refeeding on Melanocortin-Responsive Neurons in the Hypothalamic Paraventricular Nucleus." Endocrinology 149, no. 9 (May 8, 2008): 4329–35. http://dx.doi.org/10.1210/en.2008-0411.
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To explore the effect of refeeding on recovery of TRH gene expression in the hypothalamic paraventricular nucleus (PVN) and its correlation with the feeding-related neuropeptides in the arcuate nucleus (ARC), c-fos immunoreactivity (IR) in the PVN and ARC 2 h after refeeding and hypothalamic TRH, neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNA levels 4, 12, and 24 h after refeeding were studied in Sprague-Dawley rats subjected to prolonged fasting. Despite rapid reactivation of proopiomelanocortin neurons by refeeding as demonstrated by c-fos IR in ARC α-MSH-IR neurons and ventral parvocellular subdivision PVN neurons, c-fos IR was present in only 9.7 ± 1.1% hypophysiotropic TRH neurons. Serum TSH levels remained suppressed 4 and 12 h after the start of refeeding, returning to fed levels after 24 h. Fasting reduced TRH mRNA compared with fed animals, and similar to TSH, remained suppressed at 4 and 12 h after refeeding, returning toward normal at 24 h. AGRP and NPY gene expression in the ARC were markedly elevated in fasting rats, AGRP mRNA returning to baseline levels 12 h after refeeding and NPY mRNA remaining persistently elevated even at 24 h. These data raise the possibility that refeeding-induced activation of melanocortin signaling exerts differential actions on its target neurons in the PVN, an early action directed at neurons that may be involved in satiety, and a later action on hypophysiotropic TRH neurons involved in energy expenditure, potentially mediated by sustained elevations in AGRP and NPY. This response may be an important homeostatic mechanism to allow replenishment of depleted energy stores associated with fasting.
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Teubner, Brett J. W., Erin Keen-Rhinehart, and Timothy J. Bartness. "Third ventricular coinjection of subthreshold doses of NPY and AgRP stimulate food hoarding and intake and neural activation." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 302, no. 1 (January 2012): R37—R48. http://dx.doi.org/10.1152/ajpregu.00475.2011.
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We previously demonstrated that 3rd ventricular (3V) neuropeptide Y (NPY) or agouti-related protein (AgRP) injection potently stimulates food foraging/hoarding/intake in Siberian hamsters. Because NPY and AgRP are highly colocalized in arcuate nucleus neurons in this and other species, we tested whether subthreshold doses of NPY and AgRP coinjected into the 3V stimulates food foraging, hoarding, and intake, and/or neural activation [c-Fos immunoreactivity (c-Fos-ir)] in hamsters housed in a foraging/hoarding apparatus. In the behavioral experiment, each hamster received four 3V treatments by using subthreshold doses of NPY and AgRP for all behaviors: 1) NPY, 2) AgRP, 3) NPY+AgRP, and 4) saline with a 7-day washout period between treatments. Food foraging, intake, and hoarding were measured 1, 2, 4, and 24 h and 2 and 3 days postinjection. Only when NPY and AgRP were coinjected was food intake and hoarding increased. After identical treatment in separate animals, c-Fos-ir was assessed at 90 min and 14 h postinjection, times when food intake (0–1 h) and hoarding (4–24 h) were uniquely stimulated. c-Fos-ir was increased in several hypothalamic nuclei previously shown to be involved in ingestive behaviors and the central nucleus of the amygdala (CeA), but only in NPY+AgRP-treated animals (90 min and 14 h: magno- and parvocellular regions of the hypothalamic paraventricular nucleus and perifornical area; 14 h only: CeA and sub-zona incerta). These results suggest that NPY and AgRP interact to stimulate food hoarding and intake at distinct times, perhaps released as a cocktail naturally with food deprivation to stimulate these behaviors.
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Sheffer-Babila, Sharone, Yan Sun, Davelene D. Israel, Shun-Mei Liu, Genevieve Neal-Perry, and Streamson C. Chua. "Agouti-related peptide plays a critical role in leptin's effects on female puberty and reproduction." American Journal of Physiology-Endocrinology and Metabolism 305, no. 12 (December 15, 2013): E1512—E1520. http://dx.doi.org/10.1152/ajpendo.00241.2013.
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Deficient leptin signaling causes infertility via reduced activity of GnRH neurons, causing a hypogonadal state in both rodents and humans. Because GnRH neurons do not express leptin receptors, leptin's effect on GnRH neurons must be indirect. Neurons within the hypothalamic arcuate nucleus that coexpress AGRP and NPY are considered to be important intermediate neurons involved in leptin regulation of GnRH neurons. Previously, we reported that the absence of AGRP and haploinsufficiency of MC4R in leptin receptor mutant ( Lepr db/db ) females result in restoration of fertility and lactation despite the persistence of obesity and insulin resistance. The overarching hypothesis in the present study is that the absence or reduction of leptin's inhibition of AGRP/NPY neurons leads to suppression of GnRH release in cases of leptin signaling deficiency. Since TAC2 (NKB)-TAC3R signaling plays a role in puberty maturation and is modulated by metabolic status, the other aim of this study is to test whether TAC2/NKB neurons in ARC regulated by melanocortinergic signals herein affect leptin's action on puberty and reproduction. Our data showed that AGRP deficiency in Lepr db/db females restores normal timing of vaginal opening and estrous cycling, although uterine weight gain and mammary gland development are morphologically delayed. Nonetheless, Agrp−/− Lepr db/db females are fertile and sustain adequate nutrition of pups with lactation to weaning age. AGRP deficiency results in advanced vaginal opening in wild-type female mice. The postpubertal increase in hypothalamic TAC2 mRNA was not observed in Lepr db/db females, whereas AGRP deficiency restored it in Lepr db/ db females. Additionally, MC4R activation with MTII induced FOS expression in TAC2 neurons, supporting the concept of melanocortinergic regulation of TAC2 neurons. These studies suggest that AGRP imposes an inhibitory effect on puberty and that TAC2 neurons may transmit melanocortinergic inhibition of GnRH neurons.
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Rønnekleiv, Oline K., Jian Qiu, and Martin J. Kelly. "Arcuate Kisspeptin Neurons Coordinate Reproductive Activities with Metabolism." Seminars in Reproductive Medicine 37, no. 03 (May 2019): 131–40. http://dx.doi.org/10.1055/s-0039-3400251.
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AbstractHypothalamic control of fertility is the quintessential homeostatic function. However, fertility is metabolically demanding; so, there must be coordination between energy states and reproductive functions. Because gonadotropin-releasing hormone (GnRH) neurons are devoid of many of the critical metabolic hormone receptors for sensing nutrient levels, it has long been recognized that the sensing of energy stores had to be done by neurons presynaptic to GnRH neurons. Some of the obvious players have been the anorexigenic proopiomelanocortin (POMC) and orexigenic neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons, both of which are in close apposition to the median eminence, a circumventricular organ. Indeed, POMC and NPY/AgRP neurons are inversely regulated by glucose and metabolic hormones including insulin and leptin. However, their synaptic connections with GnRH neurons are sparse and/or GnRH neurons are lacking the postsynaptic receptors to mediate the appropriate physiological response. Kisspeptin neurons were discovered in the early part of this century and subsequently shown to project to and control GnRH neuronal excitability. In fact, more recently the arcuate kisspeptin neurons have been identified as the command neurons driving pulsatile release of GnRH. Subsequently, it was shown that arcuate kisspeptin neurons express not only steroid hormone receptors but also metabolic hormone receptors such that similar to POMC neurons, they are excited by insulin and leptin. Therefore, based on the premise that arcuate kisspeptin neurons are the key neurons coordinating energy states with reproduction, we will review not only how these vital neurons control pulsatile GnRH release but how they control energy homeostasis through their synaptic connections with POMC and NPY/AgRP neurons and ultimately how E2 can regulate their excitability.
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Bi, Sheng, Benjamin M. Robinson, and Timothy H. Moran. "Acute food deprivation and chronic food restriction differentially affect hypothalamic NPY mRNA expression." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 285, no. 5 (November 2003): R1030—R1036. http://dx.doi.org/10.1152/ajpregu.00734.2002.
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Although acute food deprivation and chronic food restriction both result in body weight loss, they produce different metabolic states. To evaluate how these two treatments affect hypothalamic peptide systems involved in energy homeostasis, we compared patterns of hypothalamic neuropeptide Y (NPY), agouti-related protein (AgRP), proopiomelanocotin (POMC), and leptin receptor gene expression in acutely food-deprived and chronically food-restricted rats. Both acute food deprivation and chronic food restriction reduced body weight and circulating leptin levels and resulted in increased arcuate NPY and decreased arcuate POMC gene expression. Arcuate AgRP mRNA levels were only elevated in acutely deprived rats. NPY gene expression was increased in the compact subregion of the dorsomedial hypothalamus (DMH) in response to chronic food restriction, but not in response to acute food deprivation. Leptin receptor expression was not affected by either treatment. Double in situ hybridization histochemistry revealed that, in contrast to the situation in the arcuate nucleus, NPY and leptin receptor mRNA-expressing neurons were not colocalized in the DMH. Together, these data suggest that arcuate and DMH NPY gene expression are differentially regulated. DMH NPY-expressing neurons do not appear to be under the direct control of leptin signaling.
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Smith, A. W., M. A. Bosch, E. J. Wagner, O. K. Rønnekleiv, and M. J. Kelly. "The membrane estrogen receptor ligand STX rapidly enhances GABAergic signaling in NPY/AgRP neurons: role in mediating the anorexigenic effects of 17β-estradiol." American Journal of Physiology-Endocrinology and Metabolism 305, no. 5 (September 1, 2013): E632—E640. http://dx.doi.org/10.1152/ajpendo.00281.2013.
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Besides its quintessential role in reproduction, 17β-estradiol (E2) is a potent anorexigenic hormone. E2 and the selective Gq-coupled membrane estrogen receptor (Gq-mER) ligand STX rapidly increase membrane excitability in proopiomelanocortin (POMC) neurons by desensitizing the coupling of GABAB receptors to G protein-coupled inwardly rectifying K+ channels (GIRKs), which upon activation elicit a hyperpolarizing outward current. However, it is unknown whether E2 and STX can modulate GABAB signaling in neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons. We used single-cell RT-PCR and whole cell patch clamping with selective pharmacological reagents to show that NPY/AgRP cells of mice express the GABAB-R1 and -R2 receptors and are hyperpolarized by the GABAB agonist baclofen in an E2-dependent manner. In males, E2 rapidly attenuated the coupling of GABAB receptors to GIRKs, which was blocked by the general PI3K inhibitors wortmannin and LY-294002 or the selective p110β subunit inhibitor TGX-221. The ERα-selective agonist propyl pyrazole triol mimicked the effects of E2. STX, in contrast, enhanced the GABAB response in males, which was abrogated by the estrogen receptor (ER) antagonist ICI 182,780. In gonadectomized mice of both sexes, E2 enhanced or attenuated the GABAB response in different NPY/AgRP cells. Coperfusing wortmannin with E2 or simply applying STX always enhanced the GABAB response. Thus, in NPY/AgRP neurons, activation of the Gq-mER by E2 or STX enhances the GABAergic postsynaptic response, whereas activation of ERα by E2 attenuates it. These findings demonstrate a clear functional dichotomy of rapid E2 membrane-initiated signaling via ERα vs. Gq-mER in a CNS neuron vital for regulating energy homeostasis.
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Vulliémoz, Nicolas R., Ennian Xiao, Linna Xia-Zhang, Sharon L. Wardlaw, and Michel Ferin. "Central Infusion of Agouti-Related Peptide Suppresses Pulsatile Luteinizing Hormone Release in the Ovariectomized Rhesus Monkey." Endocrinology 146, no. 2 (February 1, 2005): 784–89. http://dx.doi.org/10.1210/en.2004-1093.
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Abstract Agouti-related peptide (AGRP), an endogenous melanocortin receptor antagonist, is a powerful orexigenic peptide when infused centrally. AGRP and neuropeptide Y (NPY), another orexigenic peptide, are colocated within the same neurons in the arcuate nucleus. Both NPY and AGRP mRNA expression increases during food restriction, a condition that is known to suppress the GnRH pulse generator and reproductive function. Although NPY has been shown previously to suppress LH secretion in the ovariectomized monkey, data on AGRP are lacking. In this study, we examined the effect of AGRP infusion into the third ventricle on pulsatile LH release in five adult monkeys. The 8-h protocol included a 3-h intraventricular saline infusion to establish baseline pulsatile LH release, followed by a 5-h infusion of AGRP (83–132) [5 μg/h (n = 1) or 10 μg/h (n = 4)]. In separate experiments, each animal received an 8-h saline treatment as a control. Blood samples were collected every 15 min for LH measurements. Cortisol levels were measured every 45 min. AGRP infusion significantly decreased LH pulse frequency (from a baseline of 0.74 ± 0.07 pulse/h to 0.36 ± 0.12 during AGRP infusion; P < 0.01) and mean LH concentrations (to 41.1 ± 7.5% of baseline by h 5 of AGRP infusion; P < 0.001). LH pulse amplitude was not modified by AGRP treatment. AGRP infusion also significantly increased cortisol release, as previously reported. The data demonstrate that central administration of AGRP inhibits pulsatile LH release in the monkey and suggest that AGRP, like NPY, may mediate the effect of a negative energy balance on the reproductive system by suppressing the GnRH pulse generator.
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Tang-Christensen, Mads, Niels Vrang, Sylvia Ortmann, Martin Bidlingmaier, Tamas L. Horvath, and Matthias Tschöp. "Central Administration of Ghrelin and Agouti-Related Protein (83–132) Increases Food Intake and Decreases Spontaneous Locomotor Activity in Rats." Endocrinology 145, no. 10 (October 1, 2004): 4645–52. http://dx.doi.org/10.1210/en.2004-0529.
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Abstract Ghrelin was recently identified as an endogenous ligand of the GH secretagogue receptor. The novel peptide hormone is produced by gastric A-like cells, and circulating levels rise before feeding, suggestive of ghrelin as an endogenous hunger factor. ghrelin stimulates food intake and promotes adiposity after peripheral or central administration, likely by activating hypothalamic neurons expressing the orexigenic neuropeptides neuropeptide Y (NPY) and agouti-related protein (AGRP). To examine whether ghrelin-induced feeding resembles NPY and AGRP [AGRP fragment (83–132)] induced orexia, we compared the short- and long-term orexigenic capacity of the three peptides. A single intracerebroventricular injection of ghrelin (0.2, 1.0, and 5.0 μg) increased food intake in a dose-dependent manner. A prolonged and uncompensated increase in feeding was seen after the highest dose of ghrelin. The prolonged effects on feeding (+72 h) closely resembled those of AGRP (83–132) but not NPY. Surprisingly, ghrelin injections reduced overall locomotor activity by 20% during the first 24-h observation period. AGRP (83–132) had similar effects on locomotor behavior, whereas NPY had no effect. In summary, ghrelin causes long-term increases of food intake and, like AGRP, plays a previously unknown role as a suppressor of spontaneous physical activity. Expanding the current model of food intake control to include mechanisms regulating physical activity may promote our understanding of two major etiological factors causing obesity.
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Sominsky, Luba, Ilvana Ziko, Thai-Xinh Nguyen, Julie Quach, and Sarah J. Spencer. "Hypothalamic effects of neonatal diet: reversible and only partially leptin dependent." Journal of Endocrinology 234, no. 1 (July 2017): 41–56. http://dx.doi.org/10.1530/joe-16-0631.
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Early life diet influences metabolic programming, increasing the risk for long-lasting metabolic ill health. Neonatally overfed rats have an early increase in leptin that is maintained long term and is associated with a corresponding elevation in body weight. However, the immediate and long-term effects of neonatal overfeeding on hypothalamic anorexigenic pro-opiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP)/neuropeptide Y (NPY) circuitry, and if these are directly mediated by leptin, have not yet been examined. Here, we examined the effects of neonatal overfeeding on leptin-mediated development of hypothalamic POMC and AgRP/NPY neurons and whether these effects can be normalised by neonatal leptin antagonism in male Wistar rats. Neonatal overfeeding led to an acute (neonatal) resistance of hypothalamic neurons to exogenous leptin, but this leptin resistance was resolved by adulthood. While there were no effects of neonatal overfeeding on POMC immunoreactivity in neonates or adults, the neonatal overfeeding-induced early increase in arcuate nucleus (ARC) AgRP/NPY fibres was reversed by adulthood so that neonatally overfed adults had reduced NPY immunoreactivity in the ARC compared with controls, with no further differences in AgRP immunoreactivity. Short-term neonatal leptin antagonism did not reverse the excess body weight or hyperleptinaemia in the neonatally overfed, suggesting factors other than leptin may also contribute to the phenotype. Our findings show that changes in the availability of leptin during early life period influence the development of hypothalamic connectivity short term, but this is partly resolved by adulthood indicating an adaptation to the metabolic mal-programming effects of neonatal overfeeding.
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Bewick, Gavin A., Waljit S. Dhillo, Sarah J. Darch, Kevin G. Murphy, James V. Gardiner, Preeti H. Jethwa, Wing May Kong, Mohammed A. Ghatei, and Stephen R. Bloom. "Hypothalamic Cocaine- and Amphetamine-Regulated Transcript (CART) and Agouti-Related Protein (AgRP) Neurons Coexpress the NOP1 Receptor and Nociceptin Alters CART and AgRP Release." Endocrinology 146, no. 8 (August 1, 2005): 3526–34. http://dx.doi.org/10.1210/en.2004-1659.
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Abstract Nociceptin or orphanin FQ (N/OFQ) and its receptor NOP1 are expressed in hypothalamic nuclei involved in energy homeostasis. N/OFQ administered by intracerebroventricular or arcuate nucleus (ARC) injection increases food intake in satiated rats. The mechanisms by which N/OFQ increases food intake are unknown. We hypothesized that N/OFQ may regulate hypothalamic neurons containing peptides involved in the control of food intake such as cocaine- and amphetamine-regulated transcript (CART), αMSH, neuropeptide Y (NPY), and agouti-related protein (AgRP). We investigated the ability of N/OFQ to alter the release of CART, αMSH, NPY, and AgRP using ex vivo medial basal hypothalamic explants. Incubation of hypothalamic explants with N/OFQ (1, 10, 100 nm) resulted in significant changes in CART and AgRP release. One hundred nanomoles N/OFQ caused a 33% decrease in release of CART (55–102) immunoreactivity (IR) and increased release of AgRP-IR to 163% but produced no change in either αMSH-IR or NPY-IR. Double immunocytochemistry/in situ hybridization demonstrated that CART-IR and NOP1 mRNA are colocalized throughout the hypothalamus, in particular in the paraventricular nucleus, lateral hypothalamus, zona incerta, and ARC, providing an anatomical basis for N/OFQ action on CART release. Dual in situ hybridization demonstrated that AgRP neurons in the ARC also express the NOP1 receptor. Our data suggest that nociceptin via the NOP1 receptor may increase food intake by decreasing the release of the anorectic peptide CART and increasing the release of the orexigenic peptide AgRP.
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Teaney, Nicole A., and Nicole E. Cyr. "Sirtuin 1 Regulates Synapsin 1 in POMC-Producing N43-5 Neurons via FOXO1." Journal of the Endocrine Society 5, Supplement_1 (May 1, 2021): A56—A57. http://dx.doi.org/10.1210/jendso/bvab048.114.
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Abstract The nutrient-sensor protein Sirtuin 1 (Sirt1; silent mating type information regulation 2 homolog 1) has been shown to have significant and opposing effects on insulin resistance, leptin resistance, and body weight in the periphery and the brain. In the hypothalamic arcuate nucleus (ARC) of the brain, Sirt1 increases in the obese state and acts to promote weight gain as well as insulin and leptin resistance by increasing the orexigenic neuropeptides Agouti-related protein (AgRP) and neuropeptide Y (NPY), and in a distinct set of ARC neurons, by decreasing POMC and thus its anorexigenic derivative alpha-melanocyte stimulating hormone (alpha-MSH) (1). Sirt1’s actions on these neuropeptides are mediated at least in part by the deacetylation of the transcription factor forkhead box O1 (FOXO1). Another mechanism by which Sirt1 regulates body weight appears to be through mediating changes in the synapses of these neuropeptide-producing ARC neurons. For example, a previous study demonstrated that Sirt1 inhibition with the specific Sirt1 inhibitor, Ex-527, decreased AgRP-NPY inhibitory synaptic input on POMC neurons, which suggests that the obesity-induced increase in ARC Sirt1 would increase AgRP-NPY inhibition of POMC neurons thus promoting weight gain (2). The present study investigated how Sirt1 regulates synapses specifically in POMC-producing N43-5 neurons. Results reveal that inhibition of Sirt1 with Ex-527 significantly increased the presynaptic marker Synapsin 1 (Syn1) in N43-5 neurons. Furthermore, we investigated whether the Sirt1 target, FOXO1, mediates these synaptic changes. FOXO1 overexpression significantly decreased Syn1 and transfection of mutant FOXO1 significantly increased Syn1. Overall, our results suggest that Sirt1 regulates synapses of POMC neurons and does so in a manner that differs from Sirt1’s regulation of AgRP-NPY neuronal synapses. Future work will elucidate the mechanisms and consequences of Sirt1 and FOXO1 regulation of POMC neuron synapses under different nutritional conditions in vitro and in vivo. (1) Cyr, N. E., Steger, J. S., Toorie, A. M., Yang, J. Z., Stuart, R., Nillni, E. A. (2014). Central Sirt1 Regulates Body Weight and Energy Expenditure Along With the POMC-Derived Peptide α-MSH and the Processing Enzyme CPE Production in Diet-Induced Obese Male Rats, Endocrinology, 155(7), 2423–2435. (2) Dietrich, M. O., Antunes, C., Geliang, G., Liu, Z., Borok, E., Nie, Y., . . . Horvath, T. L. (2010). Agrp neurons mediate Sirt1’s action on the melanocortin system and energy balance: Roles for Sirt1 in neuronal firing and synaptic plasticity. The Journal of Neuroscience, 30(35), 11815–11825.
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Desai, Mina, Monica G. Ferrini, Guang Han, Kavita Narwani, and Michael G. Ross. "Maternal High Fat Diet Programs Male Mice Offspring Hyperphagia and Obesity: Mechanism of Increased Appetite Neurons via Altered Neurogenic Factors and Nutrient Sensor AMPK." Nutrients 12, no. 11 (October 29, 2020): 3326. http://dx.doi.org/10.3390/nu12113326.
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Maternal high-fat (HF) is associated with offspring hyperphagia and obesity. We hypothesized that maternal HF alters fetal neuroprogenitor cell (NPC) and hypothalamic arcuate nucleus (ARC) development with preferential differentiation of neurons towards orexigenic (NPY/AgRP) versus anorexigenic (POMC) neurons, leading to offspring hyperphagia and obesity. Furthermore, these changes may involve hypothalamic bHLH neuroregulatory factors (Hes1, Mash1, Ngn3) and energy sensor AMPK. Female mice were fed either a control or a high fat (HF) diet prior to mating, and during pregnancy and lactation. HF male newborns were heavier at birth and exhibited decreased protein expression of hypothalamic bHLH factors, pAMPK/AMPK and POMC with increased AgRP. As adults, these changes persisted though with increased ARC pAMPK/AMPK. Importantly, the total NPY neurons were increased, which was consistent with the increased food intake and adult fat mass. Further, NPCs from HF newborn hypothalamic tissue showed similar changes with preferential NPC neuronal differentiation towards NPY. Lastly, the role of AMPK was further confirmed with in vitro treatment of Control NPCs with pharmacologic AMPK modulators. Thus, the altered ARC development of HF offspring results in excess appetite and reduced satiety leading to obesity. The underlying mechanism may involve AMPK/bHLH pathways.
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Mercer, Julian G., Kim M. Moar, Alexander W. Ross, Nigel Hoggard, and Peter J. Morgan. "Photoperiod regulates arcuate nucleus POMC, AGRP, and leptin receptor mRNA in Siberian hamster hypothalamus." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 278, no. 1 (January 1, 2000): R271—R281. http://dx.doi.org/10.1152/ajpregu.2000.278.1.r271.
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Siberian hamsters decreased body weight by 30% during 18 wk in short day (SD) vs. long day (LD) controls. Subsequent imposed food deprivation (FD; 24 h) caused a further 10% decrease. In the hypothalamic arcuate nucleus (ARC), SDs reduced proopiomelanocortin (POMC) gene expression and agouti-related protein (AGRP) mRNA was elevated, changes that summate to reduced catabolic drive through the melanocortin receptors. There was no effect of photoperiod on neuropeptide Y (NPY), melanin concentrating hormone, orexin, or corticotropin-releasing factor mRNAs. Superimposed FD increased AGRP gene expression and caused a localized elevation of NPY mRNA in the ARC. Both adipose tissue leptin and ARC leptin receptor (OB-Rb) mRNAs were downregulated in SDs, whereas FD increased OB-Rb gene expression. Thus OB-Rb mRNA is differentially regulated by acute and chronic changes in plasma leptin in this species. In a separate experiment in LDs, AGRP gene expression was increased by 24 or 48 h FD, whereas POMC mRNA was downregulated in the caudal ARC. AGRP and NPY mRNAs were extensively coexpressed in the ARC, and their differential regulation by photoperiod and FD is suggestive of transcript-specific regulation at the level of individual neurons.
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Gil-Campos, Mercedes, Concepción María Aguilera, Ramón Cañete, and Angel Gil. "Ghrelin: a hormone regulating food intake and energy homeostasis." British Journal of Nutrition 96, no. 2 (August 2006): 201–26. http://dx.doi.org/10.1079/bjn20061787.
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Regulation of energy homeostasis requires precise coordination between peripheral nutrient-sensing molecules and central regulatory networks. Ghrelin is a twenty-eight-amino acid orexigenic peptide acylated at the serine 3 position mainly with an n-octanoic acid, which is produced mainly in the stomach. It is the endogenous ligand of the growth hormone secretagogue (GHS) receptors. Since plasma ghrelin levels are strictly dependent on recent food intake, this hormone plays an essential role in appetite and meal initiation. In addition, ghrelin is involved in the regulation of energy homeostasis. The ghrelin gene is composed of four exons and three introns and renders a diversity of orexigenic peptides as well as des-acyl ghrelin and obestatin, which exhibit anorexigenic properties. Ghrelin stimulates the synthesis of neuropeptide Y (NPY) and agouti-related protein (AgRP) in the arcuate nucleus neurons of the hypothalamus and hindbrain, which in turn enhance food intake. Ghrelin-expressing neurons modulate the action of both orexigenic NPY/AgRP and anorexigenic pro-opiomelanocortin neurons. AMP-activated protein kinase is activated by ghrelin in the hypothalamus, which contributes to lower intracellular long-chain fatty acids, and this appears to be the molecular signal for the expression of NPY and AgRP. Recent data suggest that ghrelin has an important role in the regulation of leptin and insulin secretion and vice versa. The present paper updates the effects of ghrelin on the control of energy homeostasis and reviews the molecular mechanisms of ghrelin synthesis, as well as interaction with GHS receptors and signalling. Relationships with leptin and insulin in the regulation of energy homeostasis are addressed.
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Fekete, Csaba, Praful S. Singru, Edith Sanchez, Sumit Sarkar, Marcelo A. Christoffolete, Rogerio S. Riberio, William M. Rand, Charles H. Emerson, Antonio C. Bianco, and Ronald M. Lechan. "Differential Effects of Central Leptin, Insulin, or Glucose Administration during Fasting on the Hypothalamic-Pituitary-Thyroid Axis and Feeding-Related Neurons in the Arcuate Nucleus." Endocrinology 147, no. 1 (January 1, 2006): 520–29. http://dx.doi.org/10.1210/en.2005-0956.
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The reductions in circulating levels of leptin, insulin, and glucose with fasting serve as important homeostasis signals to neurons of the hypothalamic arcuate nucleus that synthesize neuropeptide Y (NPY)/agouti-related protein (AGRP) and α-MSH/cocaine and amphetamine-regulated transcript. Because the central administration of leptin is capable of preventing the inhibitory effects of fasting on TRH mRNA in hypophysiotropic neurons primarily through effects on the arcuate nucleus, we determined whether the continuous administration of 30 mU/d insulin or 648 μg/d glucose into the cerebrospinal fluid by osmotic minipump might also have similar effects on the hypothalamic-pituitary-thyroid axis. As anticipated, the intracerebroventricular infusion of leptin reduced fasting-induced elevations in NPY and AGRP mRNA and increased proopiomelanocortin and cocaine and amphetamine-regulated transcript mRNA in the arcuate nucleus. In addition, leptin prevented fasting-induced reduction in pro-TRH mRNA levels in the paraventricular nucleus and in circulating thyroid hormone levels. In contrast, whereas insulin increased proopiomelanocortin mRNA and both insulin and glucose reduced NPY mRNA in arcuate nucleus neurons, neither prevented the fasting-induced suppression in hypophysiotropic TRH mRNA or circulating thyroid hormone levels. We conclude that insulin and glucose only partially replicate the central effects of leptin and may not be essential components of the hypothalamic-pituitary-thyroid regulatory system during fasting.
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Rafiei, Neda, Caitlin S. Mitchell, Caitlin R. Tedesco, Jessica Chen, Eun A. Choi, Stephanie Roughley, Philip Jean-Richard-dit-Bressel, et al. "Chemogenetic activation ofarcuate nucleus NPY and NPY/AgRP neurons increases feeding behaviour in mice." Neuropeptides 107 (October 2024): 102454. http://dx.doi.org/10.1016/j.npep.2024.102454.
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Hahn, Tina M., John F. Breininger, Denis G. Baskin, and Michael W. Schwartz. "Coexpression of Agrp and NPY in fasting-activated hypothalamic neurons." Nature Neuroscience 1, no. 4 (August 1998): 271–72. http://dx.doi.org/10.1038/1082.
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Landry, Taylor, Daniel Shookster, Alec Chaves, Katrina Free, Tony Nguyen, and Hu Huang. "Exercise increases NPY/AgRP and TH neuron activity in the hypothalamus of female mice." Journal of Endocrinology 252, no. 3 (March 1, 2022): 167–77. http://dx.doi.org/10.1530/joe-21-0250.
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Recent evidence identifies a potent role for aerobic exercise to modulate the activity of hypothalamic neurons related to appetite; however, these studies have been primarily performed in male rodents. Since females have markedly different neuronal mechanisms regulating food intake, the current study aimed to determine the effects of acute treadmill exercise on hypothalamic neuron populations involved in regulating appetite in female mice. Mature, untrained female mice were exposed to acute sedentary, low- (10 m/min), moderate- (14 m/min), and high (18 m/min)-intensity treadmill exercise in a randomized crossover design. Mice were fasted 10 h before exercise, and food intake was monitored for 48 h after bouts. Immunohistochemical detection of cFOS was performed 3 h post-exercise to determine the changes in hypothalamic neuropeptide Y (NPY)/agouti-related peptide (AgRP), pro-opiomelanocortin (POMC), tyrosine hydroxylase (TH), and SIM1-expressing neuron activity concurrent with the changes in food intake. Additionally, stains for pSTAT3tyr705 and pERKthr202/tyr204 were performed to detect exercise-mediated changes in intracellular signaling. Briefly, moderate- and high-intensity exercises increased 24-h food intake by 5.9 and 19%, respectively, while low-intensity exercise had no effects. Furthermore, increases in NPY/AgRPARC, SIM1PVN, and TH neuron activity were observed 3 h after high-intensity exercise, with no effects on POMCARC neurons. While no effects of exercise on pERKthr202/tyr204 were observed, pSTAT3tyr705 was elevated specifically in NPY/AgRP neurons 3 h post-exercise. Overall, aerobic exercise increased the activity of several appetite-stimulating neuron populations in the hypothalamus of female mice, which may provide insight into previously reported sexual dimorphisms in post-exercise feeding.
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Johnson, Miranda D., Sebastien G. Bouret, Ambrose A. Dunn-Meynell, Christina N. Boyle, Thomas A. Lutz, and Barry E. Levin. "Early postnatal amylin treatment enhances hypothalamic leptin signaling and neural development in the selectively bred diet-induced obese rat." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 311, no. 6 (December 1, 2016): R1032—R1044. http://dx.doi.org/10.1152/ajpregu.00326.2016.
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Selectively bred diet-induced obese (DIO) rats become obese on a high-fat diet and are leptin resistant before becoming obese. Compared with diet-resistant (DR) neonates, DIO neonates have impaired leptin-dependent arcuate (ARC) neuropeptide Y/agouti-related peptide (NPY/AgRP) and α-melanocyte-stimulating hormone (α-MSH; from proopiomelanocortin (POMC) neurons) axon outgrowth to the paraventricular nucleus (PVN). Using phosphorylation of STAT3 (pSTAT3) as a surrogate, we show that reduced DIO ARC leptin signaling develops by postnatal day 7 (P7) and is reduced within POMC but not NPY/AgRP neurons. Since amylin increases leptin signaling in adult rats, we treated DIO neonates with amylin during postnatal hypothalamic development and assessed leptin signaling, leptin-dependent ARC-PVN pathway development, and metabolic changes. DIO neonates treated with amylin from P0–6 and from P0–16 increased ARC leptin signaling and both AgRP and α-MSH ARC-PVN pathway development, but increased only POMC neuron number. Despite ARC-PVN pathway correction, P0–16 amylin-induced reductions in body weight did not persist beyond treatment cessation. Since amylin enhances adult DIO ARC signaling via an IL-6-dependent mechanism, we assessed ARC-PVN pathway competency in IL-6 knockout mice and found that the AgRP, but not the α-MSH, ARC-PVN pathway was reduced. These results suggest that both leptin and amylin are important neurotrophic factors for the postnatal development of the ARC-PVN pathway. Amylin might act as a direct neurotrophic factor in DIO rats to enhance both the number of POMC neurons and their α-MSH ARC-PVN pathway development. This suggests important and selective roles for amylin during ARC hypothalamic development.
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Baldini, Giulia, and Kevin D. Phelan. "The melanocortin pathway and control of appetite-progress and therapeutic implications." Journal of Endocrinology 241, no. 1 (April 2019): R1—R33. http://dx.doi.org/10.1530/joe-18-0596.
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The initial discovery that ob/ob mice become obese because of a recessive mutation of the leptin gene has been crucial to discover the melanocortin pathway to control appetite. In the melanocortin pathway, the fed state is signaled by abundance of circulating hormones such as leptin and insulin, which bind to receptors expressed at the surface of pro-opiomelanocortin (POMC) neurons to promote processing of POMC to the mature hormone α-melanocyte-stimulating hormone (α-MSH). The α-MSH released by POMC neurons then signals to decrease energy intake by binding to melanocortin-4 receptor (MC4R) expressed by MC4R neurons to the paraventricular nucleus (PVN). Conversely, in the ‘starved state’ activity of agouti-related neuropeptide (AgRP) and of neuropeptide Y (NPY)-expressing neurons is increased by decreased levels of circulating leptin and insulin and by the orexigenic hormone ghrelin to promote food intake. This initial understanding of the melanocortin pathway has recently been implemented by the description of the complex neuronal circuit that controls the activity of POMC, AgRP/NPY and MC4R neurons and downstream signaling by these neurons. This review summarizes the progress done on the melanocortin pathway and describes how obesity alters this pathway to disrupt energy homeostasis. We also describe progress on how leptin and insulin receptors signal in POMC neurons, how MC4R signals and how altered expression and traffic of MC4R change the acute signaling and desensitization properties of the receptor. We also describe how the discovery of the melanocortin pathway has led to the use of melanocortin agonists to treat obesity derived from genetic disorders.
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van den Top, Marco, Kevin Lee, Andrew D. Whyment, Andrew M. Blanks, and David Spanswick. "Orexigen-sensitive NPY/AgRP pacemaker neurons in the hypothalamic arcuate nucleus." Nature Neuroscience 7, no. 5 (April 18, 2004): 493–94. http://dx.doi.org/10.1038/nn1226.
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Luquet, Serge, Colin T. Phillips, and Richard D. Palmiter. "NPY/AgRP neurons are not essential for feeding responses to glucoprivation." Peptides 28, no. 2 (February 2007): 214–25. http://dx.doi.org/10.1016/j.peptides.2006.08.036.
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Oh, Youjin, and Jong-Woo Sohn. "Role of specific GIRK channel subunits in arcuate NPY/AgRP neurons." IBRO Reports 6 (September 2019): S400—S401. http://dx.doi.org/10.1016/j.ibror.2019.07.1275.
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