Differential regulation of agouti-related protein and neuropeptide Y in hypothalamic neurons following a stressful event

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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Altered Expression of Agouti-Related Protein and Its Colocalization with Neuropeptide Y in the Arcuate Nucleus of the Hypothalamus during Lactation*

Endocrinology ◽

10.1210/endo.140.6.6829 ◽

1999 ◽

Vol 140 (6) ◽

pp. 2645-2650 ◽

Cited By ~ 59

Author(s):

Peilin Chen ◽

Chien Li ◽

Carrie Haskell-Luevano ◽

Roger D. Cone ◽

M. Susan Smith

Keyword(s):

In Situ Hybridization ◽

Food Intake ◽

Neuropeptide Y ◽

Arcuate Nucleus ◽

Mrna Levels ◽

Related Protein ◽

Altered Expression ◽

Caudal Portion ◽

Agouti Related Protein

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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Neither Agouti-Related Protein nor Neuropeptide Y Is Critically Required for the Regulation of Energy Homeostasis in Mice

Molecular and Cellular Biology ◽

10.1128/mcb.22.14.5027-5035.2002 ◽

2002 ◽

Vol 22 (14) ◽

pp. 5027-5035 ◽

Cited By ~ 296

Author(s):

Su Qian ◽

Howard Chen ◽

Drew Weingarth ◽

Myrna E. Trumbauer ◽

Dawn E. Novi ◽

...

Keyword(s):

Body Weight ◽

Neuropeptide Y ◽

Energy Homeostasis ◽

Arcuate Nucleus ◽

Body Weight Gain ◽

Physiological Role ◽

Related Protein ◽

Double Knockout ◽

Orexigenic Peptide ◽

Agouti Related Protein

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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Paraventricular Nucleus Administration of Calcitonin Gene-Related Peptide Inhibits Food Intake and Stimulates the Hypothalamo-Pituitary-Adrenal Axis

Endocrinology ◽

10.1210/en.2002-220902 ◽

2003 ◽

Vol 144 (4) ◽

pp. 1420-1425 ◽

Cited By ~ 42

Author(s):

Waljit S. Dhillo ◽

Caroline J. Small ◽

Preeti H. Jethwa ◽

Sabina H. Russell ◽

James V. Gardiner ◽

...

Keyword(s):

Food Intake ◽

Hpa Axis ◽

Male Rats ◽

Mrna Levels ◽

Related Protein ◽

Melanocyte Stimulating Hormone ◽

Calcitonin Gene ◽

Agouti Related Protein ◽

Prior Administration

Abstract Calcitonin gene-related protein (CGRP) inhibits food intake and stimulates the hypothalamo-pituitary-adrenal (HPA) axis after intracerebroventricular injection in rats. However, the hypothalamic site and mechanism of action are unknown. We investigated the effects of intraparaventricular nucleus administration (iPVN) of CGRP on food intake and the HPA axis in rats and the effect of CGRP on the release of hypothalamic neuropeptides in vitro. In addition, we investigated the effects of food deprivation on hypothalamic CGRP expression. CGRP dose-dependently reduced food intake in the first hour after iPVN injection in fasted male rats (saline, 5.1 ± 0.8 g; 0.3 nmol CGRP, 1.1 ± 0.5 g; P < 0.001 vs. saline). iPVN injection of CGRP8–37 (a CGRP1 receptor antagonist) alone had no effect on food intake. However, the reduction in food intake by iPVN CGRP was attenuated by prior administration of CGRP8–37 [CGRP8–37 (10 nmol)/CGRP (0.3 nmol), 3.0 ± 0.8 g; P < 0.05 vs. 0.3 nmol CGRP]. CGRP (100 nm) stimulated the release of α-melanocyte stimulating hormone, cocaine- and amphetamine-related transcript, corticotropin-releasing hormone, and arginine vasopressin from hypothalamic explants to 127 ± 19%, 148 ± 10%, 158 ± 17%, and 198 ± 21% of basal levels, respectively (P < 0.05 vs. basal), but did not alter the release of either neuropeptide Y or agouti-related protein. Hypothalamic CGRP mRNA levels in 24-h fasted rats were increased to 130 ± 8% of control levels [CGRP mRNA (arbitrary units), 4.75 ± 0.4; controls, 3.65 ± 0.34; P < 0.05]. Our data suggest that CGRP administered to the PVN inhibits food intake and stimulates the HPA axis.

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Endogenous Melanocortin Antagonist in Fish: Structure, Brain Mapping, and Regulation by Fasting of the Goldfish Agouti-Related Protein Gene

Endocrinology ◽

10.1210/en.2003-0453 ◽

2003 ◽

Vol 144 (10) ◽

pp. 4552-4561 ◽

Cited By ~ 94

Author(s):

José Miguel Cerdá-Reverter ◽

Richard Ector Peter

Keyword(s):

Energy Balance ◽

Food Intake ◽

Brain Mapping ◽

Arcuate Nucleus ◽

Mrna Levels ◽

Central Administration ◽

Related Protein ◽

Melanocortin Peptides ◽

Agouti Related Protein ◽

Tuberal Nucleus

Agouti-related protein (AGRP) is a naturally occurring antagonist of melanocortin. In mammals, central AGRP expression is restricted to the arcuate nucleus in which it plays a key role in the control of energy balance by antagonizing melanocortin effects at melanocortin 4 receptors. In goldfish, melanocortin 4 receptor is profusely expressed within the main brain areas for the control of energy balance, and central administration of agonist or antagonist analogs inhibits or stimulates food intake, respectively. Here we demonstrate that the goldfish genome has a homologous gene to mammalian AGRP. Detailed brain mapping by in situ hybridization shows that AGRP is exclusively expressed in the ventrobasal hypothalamic lateral tuberal nucleus, the teleostean homolog of the arcuate nucleus. Fasting up-regulates its mRNA levels in the lateral tuberal nucleus. In the periphery, AGRP is expressed in several tissues including ovary, muscle, and ventral skin, suggesting that AGRP might regulate peripheral actions of melanocortin peptides. The results provide the first evidence for an endogenous melanocortin antagonist in nontetrapod species and suggest that hypothalamic overexpression during fasting might regulate the inhibitory effects of melanocortin peptides on food intake in goldfish.

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Chronic Central Infusion of Ghrelin Increases Hypothalamic Neuropeptide Y and Agouti-Related Protein mRNA Levels and Body Weight in Rats

Diabetes ◽

10.2337/diabetes.50.11.2438 ◽

2001 ◽

Vol 50 (11) ◽

pp. 2438-2443 ◽

Cited By ~ 410

Author(s):

J. Kamegai ◽

H. Tamura ◽

T. Shimizu ◽

S. Ishii ◽

H. Sugihara ◽

...

Keyword(s):

Body Weight ◽

Neuropeptide Y ◽

Mrna Levels ◽

Related Protein ◽

Agouti Related Protein

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Fasting Induces a Large, Leptin-Dependent Increase in the Intrinsic Action Potential Frequency of Orexigenic Arcuate Nucleus Neuropeptide Y/Agouti-Related Protein Neurons

Endocrinology ◽

10.1210/en.2004-1397 ◽

2005 ◽

Vol 146 (3) ◽

pp. 1043-1047 ◽

Cited By ~ 159

Author(s):

Kanji A. Takahashi ◽

Roger D. Cone

Keyword(s):

Action Potential ◽

Neuropeptide Y ◽

Arcuate Nucleus ◽

Related Protein ◽

Action Potential Frequency ◽

Agouti Related Protein ◽

Potential Frequency

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Signal Transducer and Activator of Transcription-3 Is Required in Hypothalamic Agouti-Related Protein/Neuropeptide Y Neurons for Normal Energy Homeostasis

Endocrinology ◽

10.1210/en.2007-0945 ◽

2008 ◽

Vol 149 (7) ◽

pp. 3346-3354 ◽

Cited By ~ 55

Author(s):

Lijie Gong ◽

Fayi Yao ◽

Kristin Hockman ◽

Henry H. Heng ◽

Gregory J. Morton ◽

...

Keyword(s):

Neuropeptide Y ◽

Energy Homeostasis ◽

Leptin Receptor ◽

Metabolic Effects ◽

Cytokine Signaling ◽

Mrna Levels ◽

Signal Transducer ◽

Related Protein ◽

Fat Cell ◽

Agouti Related Protein

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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Glucose injection reduces neuropeptide Y and agouti-related protein expression in the arcuate nucleus: A possible physiological role in eating behavior

Molecular Brain Research ◽

10.1016/j.molbrainres.2004.12.017 ◽

2005 ◽

Vol 135 (1-2) ◽

pp. 69-80 ◽

Cited By ~ 22

Author(s):

Guo-Qing Chang ◽

Olga Karatayev ◽

Zoya Davydova ◽

Katherine Wortley ◽

Sarah F. Leibowitz

Keyword(s):

Protein Expression ◽

Neuropeptide Y ◽

Eating Behavior ◽

Arcuate Nucleus ◽

Physiological Role ◽

Related Protein ◽

Glucose Injection ◽

Agouti Related Protein

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Contribution of Noradrenergic and Adrenergic Cell Groups of the Brainstem and Agouti-Related Protein-Synthesizing Neurons of the Arcuate Nucleus to Neuropeptide-Y Innervation of Corticotropin-Releasing Hormone Neurons in Hypothalamic Paraventricular Nucleus of the Rat

Endocrinology ◽

10.1210/en.2007-0732 ◽

2007 ◽

Vol 148 (11) ◽

pp. 5442-5450 ◽

Cited By ~ 43

Author(s):

Tamás Füzesi ◽

Gábor Wittmann ◽

Zsolt Liposits ◽

Ronald M. Lechan ◽

Csaba Fekete

Keyword(s):

Neuropeptide Y ◽

Paraventricular Nucleus ◽

Arcuate Nucleus ◽

Protein A ◽

Hypothalamic Paraventricular Nucleus ◽

Related Protein ◽

Cell Groups ◽

Hypothalamic Arcuate Nucleus ◽

Agouti Related Protein ◽

Pituitary Adrenal Axis

CRH-synthesizing neurons in the hypothalamic paraventricular nucleus (PVN) integrate neuronal and hormonal inputs and serve as a final common pathway to regulate the hypothalamic-pituitary-adrenal axis. One of the neuronal regulators of CRH neurons is neuropeptide Y (NPY) contained in axons that densely innervate CRH neurons. The three main sources of NPY innervation of the PVN are the hypothalamic arcuate nucleus and the noradrenergic and adrenergic neurons of the brainstem. To elucidate the origin of the NPY-immunoreactive (NPY-IR) innervation to hypophysiotropic CRH neurons, quadruple-labeling immunocytochemistry for CRH, NPY, dopamine-β-hydroxylase, and phenylethanolamine-N-methyltransferase was performed. Approximately 63% of NPY-IR varicosities on the surface of CRH neurons were catecholaminergic (22% noradrenergic and 41% adrenergic), and 37% of NPY-IR boutons were noncatecholaminergic. By triple-labeling immunofluorescence detection of NPY, CRH, and agouti-related protein, a marker of NPY axons projecting from the arcuate nucleus, the noncatecholaminergic, NPY-ergic axon population was shown to arise primarily from the arcuate nucleus. When NPY was administered chronically into the cerebral ventricle of fed animals, a dramatic reduction of CRH mRNA was observed in the PVN (NPY vs. control integrated density units, 23.9 ± 2.7 vs. 77.09 ± 15.9). We conclude that approximately two thirds of NPY-IR innervation to hypophysiotropic CRH neurons originates from catecholaminergic neurons of the brainstem, whereas the remaining one third arises from the arcuate nucleus. The catecholaminergic NPY innervation seems to modulate the activation of CRH neurons in association with glucoprivation and infection, whereas the NPY input from the arcuate nucleus may contribute to inhibition of CRH neurons during fasting.

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