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Olszewski PK, Waas JR, Brooks LL, Herisson F, Levine AS. Oxytocin receptor blockade reduces acquisition but not retrieval of taste aversion and blunts responsiveness of amygdala neurons to an aversive stimulus. Peptides 2013; 50:36-41. [PMID: 24063812 DOI: 10.1016/j.peptides.2013.09.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 09/13/2013] [Accepted: 09/13/2013] [Indexed: 10/26/2022]
Abstract
When gastrointestinal sickness induced by toxin injection is associated with exposure to novel food, the animal acquires a conditioned taste aversion (CTA). Malaise is accompanied by a surge in oxytocin release and in oxytocin neuronal activity; however, it is unclear whether oxytocin is a key facilitator of aversion or merely its marker. Herein we investigated whether blockade of the oxytocin receptor with the blood-brain barrier penetrant oxytocin receptor antagonist L-368,899 is detrimental for the acquisition and/or retrieval of lithium chloride (LiCl)-dependent CTA to a saccharin solution in mice. We also examined whether L-368,899 given prior to LiCl affects neuronal activity defined through c-Fos immunohistochemistry in select brain sites facilitating CTA acquisition. L-368,899 given prior to LiCl caused a 30% increase in saccharin solution intake in a two-bottle test, but when the antagonist was administered before the two-bottle test, it failed to diminish the retrieval of an existing CTA. LiCl administration increased c-Fos expression in the hypothalamic paraventricular and supraoptic nuclei, area postrema, nucleus of the solitary tract and basolateral and central (CNA) nuclei of the amygdala. L-368,899 injected before LiCl reduced the number of c-Fos positive CNA neurons and brought it down to levels similar to those observed in mice treated only with L-368,899. We conclude that oxytocin is one of the key components in acquisition of LiCl-induced CTA and the aversive response can be alleviated by the oxytocin receptor blockade. Oxytocin receptor antagonism blunts responsiveness of CNA to peripherally injected LiCl.
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Stice E, Figlewicz DP, Gosnell BA, Levine AS, Pratt WE. The contribution of brain reward circuits to the obesity epidemic. Neurosci Biobehav Rev 2012; 37:2047-58. [PMID: 23237885 DOI: 10.1016/j.neubiorev.2012.12.001] [Citation(s) in RCA: 176] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 11/21/2012] [Accepted: 12/03/2012] [Indexed: 12/22/2022]
Abstract
One of the defining characteristics of the research of Ann E. Kelley was her recognition that the neuroscience underlying basic learning and motivation processes also shed significant light upon mechanisms underlying drug addiction and maladaptive eating patterns. In this review, we examine the parallels that exist in the neural pathways that process both food and drug reward, as determined by recent studies in animal models and human neuroimaging experiments. We discuss contemporary research that suggests that hyperphagia leading to obesity is associated with substantial neurochemical changes in the brain. These findings verify the relevance of reward pathways for promoting consumption of palatable, calorically dense foods, and lead to the important question of whether changes in reward circuitry in response to intake of such foods serve a causal role in the development and maintenance of some cases of obesity. Finally, we discuss the potential value for future studies at the intersection of the obesity epidemic and the neuroscience of motivation, as well as the potential concerns that arise from viewing excessive food intake as an "addiction". We suggest that it might be more useful to focus on overeating that results in frank obesity, and multiple health, interpersonal, and occupational negative consequences as a form of food "abuse".
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Lowe MR, Levine AS. Eating Motives and the Controversy over Dieting: Eating Less Than Needed versus Less Than Wanted. ACTA ACUST UNITED AC 2012; 13:797-806. [PMID: 15919830 DOI: 10.1038/oby.2005.90] [Citation(s) in RCA: 174] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Anti-dieting sentiment has grown in recent years. Critics of restrained eating suggest that it evokes counter-regulatory responses that render it ineffective or even iatrogenic. However, restrained eaters are not in negative energy balance and overweight individuals show reduced eating problems when losing weight by dieting. A distinction is often drawn between physiological and psychological hunger, and neuroscience research has shown that there is a neurophysiological reality underlying this distinction. The brain has a homeostatic system (activated by energy deficits) and a hedonic system (activated by the presence of palatable food). The omnipresence of highly palatable food in the environment may chronically activate the hedonic appetite system, producing a need to actively restrain eating not just to lose weight but to avoid gaining it. Just as restricting energy intake below homeostatic needs produces physiological deprivation, restricting intake of palatable foods may produce "perceived deprivation" despite a state of energy balance. In summary, the motivation to eat more than one needs appears to be every bit as real, and perhaps every bit as powerful, as the motivation to eat when energy deprived.
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Alsiö J, Olszewski PK, Levine AS, Schiöth HB. Feed-forward mechanisms: addiction-like behavioral and molecular adaptations in overeating. Front Neuroendocrinol 2012; 33:127-39. [PMID: 22305720 DOI: 10.1016/j.yfrne.2012.01.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2011] [Revised: 11/24/2011] [Accepted: 01/13/2012] [Indexed: 12/23/2022]
Abstract
Food reward, not hunger, is the main driving force behind eating in the modern obesogenic environment. Palatable foods, generally calorie-dense and rich in sugar/fat, are thus readily overconsumed despite the resulting health consequences. Important advances have been made to explain mechanisms underlying excessive consumption as an immediate response to presentation of rewarding tastants. However, our understanding of long-term neural adaptations to food reward that oftentimes persist during even a prolonged absence of palatable food and contribute to the reinstatement of compulsive overeating of high-fat high-sugar diets, is much more limited. Here we discuss the evidence from animal and human studies for neural and molecular adaptations in both homeostatic and non-homeostatic appetite regulation that may underlie the formation of a "feed-forward" system, sensitive to palatable food and propelling the individual from a basic preference for palatable diets to food craving and compulsive, addiction-like eating behavior.
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Olszewski PK, Rozman J, Jacobsson JA, Rathkolb B, Strömberg S, Hans W, Klockars A, Alsiö J, Risérus U, Becker L, Hölter SM, Elvert R, Ehrhardt N, Gailus-Durner V, Fuchs H, Fredriksson R, Wolf E, Klopstock T, Wurst W, Levine AS, Marcus C, Hrabě de Angelis M, Klingenspor M, Schiöth HB, Kilimann MW. Neurobeachin, a regulator of synaptic protein targeting, is associated with body fat mass and feeding behavior in mice and body-mass index in humans. PLoS Genet 2012; 8:e1002568. [PMID: 22438821 PMCID: PMC3305408 DOI: 10.1371/journal.pgen.1002568] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Accepted: 01/16/2012] [Indexed: 01/08/2023] Open
Abstract
Neurobeachin (Nbea) regulates neuronal membrane protein trafficking and is required for the development and functioning of central and neuromuscular synapses. In homozygous knockout (KO) mice, Nbea deficiency causes perinatal death. Here, we report that heterozygous KO mice haploinsufficient for Nbea have higher body weight due to increased adipose tissue mass. In several feeding paradigms, heterozygous KO mice consumed more food than wild-type (WT) controls, and this consumption was primarily driven by calories rather than palatability. Expression analysis of feeding-related genes in the hypothalamus and brainstem with real-time PCR showed differential expression of a subset of neuropeptide or neuropeptide receptor mRNAs between WT and Nbea+/− mice in the sated state and in response to food deprivation, but not to feeding reward. In humans, we identified two intronic NBEA single-nucleotide polymorphisms (SNPs) that are significantly associated with body-mass index (BMI) in adult and juvenile cohorts. Overall, data obtained in mice and humans suggest that variation of Nbea abundance or activity critically affects body weight, presumably by influencing the activity of feeding-related neural circuits. Our study emphasizes the importance of neural mechanisms in body weight control and points out NBEA as a potential risk gene in human obesity. Body weight and energy balance are under very complex neural, endocrine, and metabolic control. Correspondingly, recent research suggests that hundreds of genes contribute to human obesity and that only a small proportion of them have as yet been identified. Neurobeachin (Nbea) is a protein specifically expressed in nerve and endocrine cells and is important for neurotransmission, apparently by influencing the synaptic targeting of membrane proteins. Here, we show that heterozygous knockout mice, expressing Nbea at 50% of normal levels, display increased adipose tissue mass, abnormal feeding behavior, and modified expression of specific genes in the brainstem and hypothalamus known to be important for body weight control. Moreover, we find that NBEA gene polymorphisms are associated with body-mass index in adult and juvenile human cohorts. Our results demonstrate that variation of Nbea activity critically affects body weight, presumably by influencing the activity of feeding-related neural circuits. They emphasize the importance of neural mechanisms in body weight control, and they identify NBEA as a potential genetic risk factor in human obesity.
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Rask-Andersen M, Almén MS, Olausen HR, Olszewski PK, Eriksson J, Chavan RA, Levine AS, Fredriksson R, Schiöth HB. Functional coupling analysis suggests link between the obesity gene FTO and the BDNF-NTRK2 signaling pathway. BMC Neurosci 2011; 12:117. [PMID: 22087873 PMCID: PMC3248879 DOI: 10.1186/1471-2202-12-117] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Accepted: 11/16/2011] [Indexed: 11/24/2022] Open
Abstract
Background The Fat mass and obesity gene (FTO) has been identified through genome wide association studies as an important genetic factor contributing to a higher body mass index (BMI). However, the molecular context in which this effect is mediated has yet to be determined. We investigated the potential molecular network for FTO by analyzing co-expression and protein-protein interaction databases, Coxpresdb and IntAct, as well as the functional coupling predicting multi-source database, FunCoup. Hypothalamic expression of FTO-linked genes defined with this bioinformatics approach was subsequently studied using quantitative real time-PCR in mouse feeding models known to affect FTO expression. Results We identified several candidate genes for functional coupling to FTO through database studies and selected nine for further study in animal models. We observed hypothalamic expression of Profilin 2 (Pfn2), cAMP-dependent protein kinase catalytic subunit beta (Prkacb), Brain derived neurotrophic factor (Bdnf), neurotrophic tyrosine kinase, receptor, type 2 (Ntrk2), Signal transducer and activator of transcription 3 (Stat3), and Btbd12 to be co-regulated in concert with Fto. Pfn2 and Prkacb have previously not been linked to feeding regulation. Conclusions Gene expression studies validate several candidates generated through database studies of possible FTO-interactors. We speculate about a wider functional role for FTO in the context of current and recent findings, such as in extracellular ligand-induced neuronal plasticity via NTRK2/BDNF, possibly via interaction with the transcription factor CCAAT/enhancer binding protein β (C/EBPβ).
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Mitra A, Kotz CM, Kim EM, Grace MK, Kuskowski MA, Billington CJ, Levine AS. Effects of butorphanol on feeding and neuropeptide Y in the rat. Pharmacol Biochem Behav 2011; 100:575-80. [PMID: 21925202 DOI: 10.1016/j.pbb.2011.08.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2011] [Revised: 08/01/2011] [Accepted: 08/11/2011] [Indexed: 10/17/2022]
Abstract
Butorphanol ([BT] an opioid receptor agonist/antagonist) is different from other opioid agonists in that a single dose of BT can elicit up to 12 g of chow intake in a satiated rat whereas most opioid agonists induce a mild feeding response (2-3 g). Here, we first examined whether the effectiveness of BT to elicit feeding was affected by dose, method of infusion and possible tachyphylaxis following administration. Secondly, we examined whether BT administration influenced hypothalamic NPY gene expression and peptide levels. A single dose administration of BT (4 mg/kg) significantly increased food intake at 2, 3 and 6 h after administration. However following repeated injections of BT at 4 mg/kg, the cumulative long-term intake of BT-treated rats did not differ from that of controls, indicating that the animals compensate for the increased feeding following BT injection by decreased feeding at a later time. An ascending dose schedule of repeated BT injections resulted in additional feeding. NPY gene expression in the ARC was influenced by how much food had been consumed, but not by BT. The amount of food consumed and the level of NPY mRNA were inversely correlated. This is consistent with NPY's role in normal feeding. BT treatment did not affect either NPY or leptin RIA levels. We conclude that the feeding produced by BT is sensitive to dose and dosing paradigm. Further, its mechanism of action does not appear to be mediated by NPY or leptin pathways.
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Mitra A, Klockars A, Gosnell BA, Le Grevès M, Olszewski PK, Levine AS, Schiöth HB. Expression levels of genes encoding melanin concentrating hormone (MCH) and MCH receptor change in taste aversion, but MCH injections do not alleviate aversive responses. Pharmacol Biochem Behav 2011; 100:581-6. [PMID: 21925200 DOI: 10.1016/j.pbb.2011.08.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2011] [Revised: 08/01/2011] [Accepted: 08/11/2011] [Indexed: 12/24/2022]
Abstract
Melanin concentrating hormone (MCH) stimulates feeding driven by energy needs and reward and modifies anxiety behavior. Orexigenic peptides of similar characteristics, including nociceptin/orphanin FQ, Agouti-related protein and opioids, increase consumption also by reducing avoidance of potentially tainted food in animals displaying a conditioned taste aversion (CTA). Herein, using real-time PCR, we assessed whether expression levels of genes encoding MCH and its receptor, MCHR1, were affected in CTA in the rat. We also investigated whether injecting MCH intracerebroventricularly (ICV) during the acquisition and retrieval of LiCl-induced CTA, would alleviate aversive responses. MCHR1 gene was upregulated in the hypothalamus and brain stem of aversive animals, MCH mRNA was significantly higher in the hypothalamus, whereas a strong trend suggesting upregulation of MCH and MCHR1 genes was detected in the amygdala. Despite these expression changes associated with aversion, MCH injected prior to the induction of CTA with LiCl as well as later, during the CTA retrieval upon subsequent presentations of the aversive tastant, did not reduce the magnitude of CTA. We conclude that MCH and its receptor form an orexigenic system whose expression is affected in CTA. This altered MCH expression may contribute to tastant-targeted hypophagia in CTA. However, changing the MCH tone in the brain by exogenous peptide was insufficient to prevent the onset or facilitate extinction of LiCl-induced CTA. This designates MCH as one of many accessory molecules associated with shaping an aversive response, but not a critical one for LiCl-dependent CTA to occur.
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Cedernaes J, Olszewski PK, Almén MS, Stephansson O, Levine AS, Fredriksson R, Nylander O, Schiöth HB. Comprehensive analysis of localization of 78 solute carrier genes throughout the subsections of the rat gastrointestinal tract. Biochem Biophys Res Commun 2011; 411:702-7. [DOI: 10.1016/j.bbrc.2011.07.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 07/02/2011] [Indexed: 01/07/2023]
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Olszewski PK, Fredriksson R, Eriksson JD, Mitra A, Radomska KJ, Gosnell BA, Solvang MN, Levine AS, Schiöth HB. Fto colocalizes with a satiety mediator oxytocin in the brain and upregulates oxytocin gene expression. Biochem Biophys Res Commun 2011; 408:422-6. [PMID: 21514276 DOI: 10.1016/j.bbrc.2011.04.037] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Accepted: 04/07/2011] [Indexed: 12/31/2022]
Abstract
Single nucleotide polymorphisms in the fat mass and obesity-associated (FTO) gene have been associated with obesity in humans. Alterations in Fto expression in transgenic animals affect body weight, energy expenditure and food intake. Fto, a nuclear protein and proposed transcription co-factor, has been speculated to affect energy balance through a functional relationship with specific genes encoding feeding-related peptides. Herein, we employed double immunohistochemistry and showed that the majority of neurons synthesizing a satiety mediator, oxytocin, coexpress Fto in the brain of male and female mice. We then overexpressed Fto in a murine hypothalamic cell line and, using qPCR, detected a 50% increase in the level of oxytocin mRNA. Expression levels of several other feeding-related genes, including neuropeptide Y (NPY) and Agouti-related protein (AgRP), were unaffected by the FTO transfection. Addition of 10 and 100 nmol oxytocin to the cell culture medium did not affect Fto expression in hypothalamic cells. We conclude that Fto, a proposed transcription co-factor, influences expression of the gene encoding a satiety mediator, oxytocin.
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Olszewski PK, Radomska KJ, Ghimire K, Klockars A, Ingman C, Olszewska AM, Fredriksson R, Levine AS, Schiöth HB. Fto immunoreactivity is widespread in the rodent brain and abundant in feeding-related sites, but the number of Fto-positive cells is not affected by changes in energy balance. Physiol Behav 2011; 103:248-53. [PMID: 21295049 DOI: 10.1016/j.physbeh.2011.01.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2010] [Revised: 01/14/2011] [Accepted: 01/24/2011] [Indexed: 10/18/2022]
Abstract
A single nucleotide polymorphism in the FTO gene is associated with obesity in humans. Evidence gathered in animals mainly relates energy homeostasis to the central FTO mRNA levels, but our knowledge of the Fto protein distribution and regulation is limited. Fto, a demethylase and transcriptional coactivator, is thought to regulate expression of other genes. Herein, we examined Fto immunoreactivity (IR) in the mouse and rat brain with emphasis on sites governing energy balance. We also studied whether energy status affects central Fto IR. We report that Fto IR, limited to nuclear profiles, is widespread in the brain, in- and outside feeding circuits; it shows a very similar distribution in feeding-related sites in mice and rats. Several areas regulating energy homeostasis display enhanced intensity of Fto staining: the arcuate, paraventricular, supraoptic, dorsomedial, ventromedial nuclei, and dorsal vagal complex. Some regions mediating feeding reward, including the bed nucleus of the stria terminalis, have ample Fto IR. We found that differences in energy status between rats fed ad libitum, deprived or refed following deprivation, did not affect the number of Fto-positive nuclei in 10 sites governing consumption for energy or reward. We conclude that Fto IR, widespread in the rodent brain, is particularly abundant in feeding circuits, but the number of Fto-positive neurons is unaffected by changes in energy balance.
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Olszewski PK, Klockars A, Olszewska AM, Fredriksson R, Schiöth HB, Levine AS. Molecular, immunohistochemical, and pharmacological evidence of oxytocin's role as inhibitor of carbohydrate but not fat intake. Endocrinology 2010; 151:4736-44. [PMID: 20685878 PMCID: PMC2946140 DOI: 10.1210/en.2010-0151] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Oxytocin (OT) facilitates feeding termination stemming from high osmolality, stomach distention, and malaise. Recent knockout (KO) studies suggested a crucial function for OT in carbohydrate intake: OT-/- mice had increased preference for carbohydrates, including sucrose, but not fat (Intralipid). In striking contrast, sugar appetite was unaffected in the OT receptor KO mouse; data from wild-type animals have been insufficient. Therefore, we examined the involvement of OT in the regulation of sucrose vs. fat intake in C57BL/6 mice that served as a background KO strain. We exposed mice to a meal of sucrose or Intralipid and determined that the percentage of c-Fos-immunoreactive paraventricular hypothalamic OT neurons was elevated at termination of intake of either of the tastants, but this increase was 2-fold higher in sucrose-fed mice. A 48-h exposure to sucrose compared with Intralipid caused up-regulation of OT mRNA, whereas inherent individual preferences for sucrose vs. fat were not associated with differences in baseline OT expression as established with quantitative PCR. We found that L-368,899, an OT receptor antagonist, increased sugar intake when sucrose was presented alone or concurrently with Intralipid; it had no effect on Intralipid or total calorie consumption. L-368,899 affected Fos immunoreactivity in the paraventricular hypothalamus, arcuate nucleus, amygdala, and nucleus of the solitary tract, areas involved in aversion, satiety, and reward. This pattern serves as neuroanatomical basis of OT's complex role in food intake, including sucrose intake. The current findings expand our knowledge on OT and suggest that it acts as a carbohydrate-specific inhibitor of feeding.
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Olszewski PK, Grace MK, Fard SS, Le Grevès M, Klockars A, Massi M, Schiöth HB, Levine AS. Central nociceptin/orphanin FQ system elevates food consumption by both increasing energy intake and reducing aversive responsiveness. Am J Physiol Regul Integr Comp Physiol 2010; 299:R655-63. [PMID: 20427724 PMCID: PMC3774471 DOI: 10.1152/ajpregu.00556.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Accepted: 04/23/2010] [Indexed: 11/22/2022]
Abstract
Nociceptin/orphanin FQ (N/OFQ), the nociceptin opioid peptide (NOP) receptor ligand, increases feeding when injected centrally. Initial data suggest that N/OFQ blocks the development of a conditioned taste aversion (CTA). The current project further characterized the involvement of N/OFQ in the regulation of hunger vs. aversive responses in rats by employing behavioral, immunohistochemical, and real-time PCR methodology. We determined that the same low dose of the NOP antagonist [Nphe(1)]N/OFQ(1-13)NH(2) delivered via the lateral ventricle diminishes both N/OFQ- and deprivation-induced feeding. This anorexigenic effect did not stem from aversive consequences, as the antagonist did not cause the development of a CTA. When [Nphe(1)]N/OFQ(1-13)NH(2) was administered with LiCl, it moderately delayed extinction of the LiCl-induced CTA. Injection of LiCl + antagonist compared with LiCl alone generated an increase in c-Fos immunoreactivity in the central nucleus of the amygdala. The antagonist alone elevated Fos immunoreactivity in the paraventricular nucleus of the hypothalamus, nucleus of the solitary tract, and central nucleus of the amygdala. Hypothalamic NOP mRNA levels were decreased during energy intake restriction induced by aversion, as well as in non-CTA rats food-restricted to match CTA-reduced consumption. Brain stem NOP was upregulated only in aversion. Prepro-N/OFQ mRNA showed a trend toward upregulation in restricted rats (P = 0.068). We conclude that the N/OFQ system promotes feeding by affecting the need to replenish lacking calories and by reducing aversive responsiveness. It may belong to mechanisms that shift a balance between the drive to ingest energy and avoidance of potentially tainted food.
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Mitra A, Gosnell BA, Schiöth HB, Grace MK, Klockars A, Olszewski PK, Levine AS. Chronic sugar intake dampens feeding-related activity of neurons synthesizing a satiety mediator, oxytocin. Peptides 2010; 31:1346-52. [PMID: 20399242 PMCID: PMC3175817 DOI: 10.1016/j.peptides.2010.04.005] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Revised: 04/06/2010] [Accepted: 04/07/2010] [Indexed: 01/08/2023]
Abstract
Increased tone of orexigens mediating reward occurs upon repeated consumption of sweet foods. Interestingly, some of these reward orexigens, such as opioids, diminish activity of neurons synthesizing oxytocin, a nonapeptide that promotes satiety and feeding termination. It is not known, however, whether consumption-related activity of the central oxytocin system is modified under chronic sugar feeding reward itself. Therefore, we examined how chronic consumption of a rewarding high-sucrose (HS) vs. bland cornstarch (CS) diet affected the activity of oxytocin cells in the hypothalamus at the time of meal termination. Schedule-fed (2h/day) rats received either a HS or CS powdered diet for 20 days. On the 21st day, they were given the same or the opposite diet, and food was removed after the main consummatory activity was completed. Animals were perfused 60 min after feeding termination and brains were immunostained for oxytocin and the marker of neuronal activity, c-Fos. The percentage of c-Fos-positive oxytocin cells in the hypothalamic paraventricular nucleus was significantly lower in rats chronically exposed to the HS than to the CS diet, regardless of which diet they received on the final day. A similar pattern was observed in the supraoptic nucleus. We conclude that the chronic rather than acute sucrose intake reduces activity of the anorexigenic oxytocin system. These findings indicate that chronic consumption of sugar blunts activity of pathways that mediate satiety. We speculate that a reduction in central satiety signaling precipitated by regular intake of foods high in sugar may lead to generalized overeating.
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Wang C, Bomberg E, Billington CJ, Levine AS, Kotz CM. Brain-derived neurotrophic factor (BDNF) in the hypothalamic ventromedial nucleus increases energy expenditure. Brain Res 2010; 1336:66-77. [PMID: 20398635 PMCID: PMC4452019 DOI: 10.1016/j.brainres.2010.04.013] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2010] [Revised: 03/30/2010] [Accepted: 04/02/2010] [Indexed: 10/19/2022]
Abstract
Brain-derived neurotrophic factor (BDNF) decreases food intake and body weight, but few central sites of action have been identified for its effect on energy expenditure. The hypothalamic ventromedial nucleus (VMH) is important in regulating energy metabolism. Our previous work indicated that BDNF in the VMH reduced food intake. The purposes of the study were to determine: 1) if BDNF in the VMH increases energy expenditure (EE); 2) if BDNF-enhanced thermogenesis results from increased spontaneous physical activity (SPA) and resting metabolic rate (RMR); and 3) if VMH BDNF thermogenic effects are mediated by uncoupling protein 1 (UCP1) in brown adipose tissue (BAT). BDNF (0.5 microg) was injected into the VMH of male Sprague-Dawley rats and oxygen consumption, carbon dioxide production, food intake and SPA were measured for 24h in an indirect calorimeter. Animals were sacrificed 4h after BDNF injection, and BAT UCP1 gene expression was measured with quantitative real-time polymerase chain reaction. BDNF significantly decreased food and water intake, and body weight gain. Heat production and RMR were significantly elevated for 9h immediately after BDNF injection. BDNF increased SPA and EE during SPA (aEE) within 9h after injection although BDNF had no effect on 0-24h SPA and aEE. BDNF did not induce a significant increase in BAT UCP1 expression. In conclusion, VMH BDNF reduces body weight by decreasing food intake and increasing EE consequent to increased SPA and RMR, suggesting that the VMH is an important site of BDNF action to influence energy balance.
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Olszewski PK, Klockars A, Schiöth HB, Levine AS. Oxytocin as feeding inhibitor: maintaining homeostasis in consummatory behavior. Pharmacol Biochem Behav 2010; 97:47-54. [PMID: 20595062 DOI: 10.1016/j.pbb.2010.05.026] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2010] [Revised: 05/12/2010] [Accepted: 05/26/2010] [Indexed: 12/13/2022]
Abstract
Initial studies showed that the anorexigenic peptide oxytocin (OT) regulates gastric motility, responds to stomach distention and to elevated osmolality, and blocks consumption of toxic foods. Most recently, it has been proposed to act as a mediator of general and carbohydrate-specific satiety and regulator of body weight. In the current review, we discuss the function of OT as a homeostatic inhibitor of consumption, capable of mitigating multiple aspects of ingestive behavior and energy metabolism.
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Almén MS, Jacobsson JA, Shaik JHA, Olszewski PK, Cedernaes J, Alsiö J, Sreedharan S, Levine AS, Fredriksson R, Marcus C, Schiöth HB. The obesity gene, TMEM18, is of ancient origin, found in majority of neuronal cells in all major brain regions and associated with obesity in severely obese children. BMC MEDICAL GENETICS 2010; 11:58. [PMID: 20380707 PMCID: PMC2858727 DOI: 10.1186/1471-2350-11-58] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Accepted: 04/09/2010] [Indexed: 11/10/2022]
Abstract
BACKGROUND TMEM18 is a hypothalamic gene that has recently been linked to obesity and BMI in genome wide association studies. However, the functional properties of TMEM18 are obscure. METHODS The evolutionary history of TMEM18 was inferred using phylogenetic and bioinformatic methods. The gene's expression profile was investigated with real-time PCR in a panel of rat and mouse tissues and with immunohistochemistry in the mouse brain. Also, gene expression changes were analyzed in three feeding-related mouse models: food deprivation, reward and diet-induced increase in body weight. Finally, we genotyped 502 severely obese and 527 healthy Swedish children for two SNPs near TMEM18 (rs6548238 and rs756131). RESULTS TMEM18 was found to be remarkably conserved and present in species that diverged from the human lineage over 1500 million years ago. The TMEM18 gene was widely expressed and detected in the majority of cells in all major brain regions, but was more abundant in neurons than other cell types. We found no significant changes in the hypothalamic and brainstem expression in the feeding-related mouse models. There was a strong association for two SNPs (rs6548238 and rs756131) of the TMEM18 locus with an increased risk for obesity (p = 0.001 and p = 0.002). CONCLUSION We conclude that TMEM18 is involved in both adult and childhood obesity. It is one of the most conserved human obesity genes and it is found in the majority of all brain sites, including the hypothalamus and the brain stem, but it is not regulated in these regions in classical energy homeostatic models.
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Gosnell BA, Mitra A, Avant RA, Anker JJ, Carroll ME, Levine AS. Operant responding for sucrose by rats bred for high or low saccharin consumption. Physiol Behav 2010; 99:529-33. [PMID: 20096717 DOI: 10.1016/j.physbeh.2010.01.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/21/2009] [Accepted: 01/11/2010] [Indexed: 11/28/2022]
Abstract
The use of rats differing in the intake of sweet substances has highlighted some interesting parallels between taste preferences and drug self-administration. For example, rats selectively bred to consume high (HiS) or low (LoS) amounts of a 0.1% saccharin solution (when compared to water consumption), show corresponding differences across several measures of cocaine self-administration (HiS>LoS). In this study, we measured whether the two strains also differ when response requirements are imposed for obtaining a sucrose reinforcer. Male HiS and LoS rats were measured for operant responding for sucrose pellets under fixed-ratio (FR) schedules of 1, 3, 5 and 10 and under a progressive-ratio (PR) schedule, during which the response requirement for each successive pellet increased exponentially. The effect of systemic naltrexone (0.3, 1 and 3mg/kg) on PR responding for sucrose pellets was also tested. Under all FR and PR schedules, the number of pellets obtained by the LoS rats were significantly lower than those obtained by the HiS rats. Although the LoS weighed more than the HiS rats, this difference does not appear to explain differences in operant behavior. No strain differences in the effect of naltrexone were observed; the 3mg/kg dose reduced the number of pellets obtained in both strains. Measures of locomotor activity taken prior to operant trials suggest that the differences in responding were not due to differences in general activity levels. These studies provide further characterization of the HiS and LoS rat lines by demonstrating that motivation to consume sucrose is greater in HiS than in LoS rats.
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Sreedharan S, Shaik JHA, Olszewski PK, Levine AS, Schiöth HB, Fredriksson R. Glutamate, aspartate and nucleotide transporters in the SLC17 family form four main phylogenetic clusters: evolution and tissue expression. BMC Genomics 2010; 11:17. [PMID: 20059771 PMCID: PMC2824716 DOI: 10.1186/1471-2164-11-17] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Accepted: 01/08/2010] [Indexed: 11/12/2022] Open
Abstract
Background The SLC17 family of transporters transports the amino acids: glutamate and aspartate, and, as shown recently, also nucleotides. Vesicular glutamate transporters are found in distinct species, such as C. elegans, but the evolutionary origin of most of the genes in this family has been obscure. Results Our phylogenetic analysis shows that the SLC17 family consists of four main phylogenetic clades which were all present before the divergence of the insect lineage. One of these clades has not been previously described and it is not found in vertebrates. The clade containing Slc17a9 had the most restricted evolutionary history with only one member in most species. We detected expression of Slc17a1-17a4 only in the peripheral tissues but not in the CNS, while Slc17a5- Slc17a9 are highly expressed in both the CNS and periphery. Conclusions The in situ hybridization studies on vesicular nucleotide transporter revealed high expression throughout the cerebral cortex, certain areas in the hippocampus and in specific nuclei of the hypothalamus and thalamus. Some of the regions with high expression, such as the medial habenula and the dentate gyrus of the hippocampus, are important sites for purinergic neurotransmission. Noteworthy, other areas relying on purine-mediated signaling, such as the molecular layer of the dentate gyrus and the periaqueductal gray, lack or have a very low expression of Slc17a9, suggesting that there could be another nucleotide transporter in these regions.
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Olszewski PK, Fredriksson R, Olszewska AM, Stephansson O, Alsiö J, Radomska KJ, Levine AS, Schiöth HB. Hypothalamic FTO is associated with the regulation of energy intake not feeding reward. BMC Neurosci 2009; 10:129. [PMID: 19860904 PMCID: PMC2774323 DOI: 10.1186/1471-2202-10-129] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2009] [Accepted: 10/27/2009] [Indexed: 11/10/2022] Open
Abstract
Background Polymorphism in the FTO gene is strongly associated with obesity, but little is known about the molecular bases of this relationship. We investigated whether hypothalamic FTO is involved in energy-dependent overconsumption of food. We determined FTO mRNA levels in rodent models of short- and long-term intake of palatable fat or sugar, deprivation, diet-induced increase in body weight, baseline preference for fat versus sugar as well as in same-weight animals differing in the inherent propensity to eat calories especially upon availability of diverse diets, using quantitative PCR. FTO gene expression was also studied in organotypic hypothalamic cultures treated with anorexigenic amino acid, leucine. In situ hybridization (ISH) was utilized to study FTO signal in reward- and hunger-related sites, colocalization with anorexigenic oxytocin, and c-Fos immunoreactivity in FTO cells at initiation and termination of a meal. Results Deprivation upregulated FTO mRNA, while leucine downregulated it. Consumption of palatable diets or macronutrient preference did not affect FTO expression. However, the propensity to ingest more energy without an effect on body weight was associated with lower FTO mRNA levels. We found that 4-fold higher number of FTO cells displayed c-Fos at meal termination as compared to initiation in the paraventricular and arcuate nuclei of re-fed mice. Moreover, ISH showed that FTO is present mainly in hunger-related sites and it shows a high degree of colocalization with anorexigenic oxytocin. Conclusion We conclude that FTO mRNA is present mainly in sites related to hunger/satiation control; changes in hypothalamic FTO expression are associated with cues related to energy intake rather than feeding reward. In line with that, neurons involved in feeding termination express FTO. Interestingly, baseline FTO expression appears linked not only with energy intake but also energy metabolism.
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Clancy K, Hamm M, Levine AS, Wilkins J. Organics: Evidence of Health Benefits Lacking. Science 2009; 325:676. [DOI: 10.1126/science.325_676a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Jewett DC, Hahn TW, Smith TR, Fiksdal BL, Wiebelhaus JM, Dunbar AR, Filtz CR, Novinska NL, Levine AS. Effects of sibutramine and rimonabant in rats trained to discriminate between 22- and 2-h food deprivation. Psychopharmacology (Berl) 2009; 203:453-9. [PMID: 18854986 DOI: 10.1007/s00213-008-1350-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2008] [Accepted: 09/20/2008] [Indexed: 11/24/2022]
Abstract
OBJECTIVE The objective of the study was to evaluate whether sibutramine and rimonabant, drugs that decrease food intake in human and non-human animals, affect the discriminative stimulus effects associated with acute food deprivation ("hunger"). MATERIALS AND METHODS Rats were trained to discriminate between 22- and 2-h food deprivation in a two-lever choice procedure. After rats acquired the discrimination, subjects were food-restricted for 22 h and administered with sibutramine (0.32-10 mg/kg, p.o.) or rimonabant (0.32-10 mg/kg, s.c.) before a generalization test session. RESULTS Sibutramine (3.2 mg/kg) produced significant decreases in 22-h deprivation-appropriate responding, response rates (resulting in lever pressing rates similar to those following 2-h food deprivation), and food intake measured 1 h after the generalization test. A larger sibutramine dose eliminated responding and significantly reduced food intake. Rimonabant did not alter the discriminative stimulus effects of 22-h food deprivation, but rimonabant did significantly reduce both response rates and food intake. CONCLUSION Sibutramine appears to decrease food intake by reducing hunger sensations associated with food deprivation. In contrast, rimonabant does not alter the discrimination of acute food deprivation. The use of food-deprivation discrimination techniques may be useful in identifying the role of specific neuroactive compounds in eating stimulated by a sense of hunger and may aid in medication development for more effective treatments for obesity and other eating-related conditions.
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Olszewski PK, Shaw TJ, Grace MK, Höglund CE, Fredriksson R, Schiöth HB, Levine AS. Complexity of neural mechanisms underlying overconsumption of sugar in scheduled feeding: involvement of opioids, orexin, oxytocin and NPY. Peptides 2009; 30:226-33. [PMID: 19022308 PMCID: PMC2657876 DOI: 10.1016/j.peptides.2008.10.011] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2008] [Revised: 10/19/2008] [Accepted: 10/20/2008] [Indexed: 11/23/2022]
Abstract
A regular daily meal regimen, as opposed to ad libitum consumption, enforces eating at a predefined time and within a short timeframe. Hence, it is important to study food intake regulation in animal feeding models that somewhat reflect this pattern. We investigated the effect of scheduled feeding on the intake of a palatable, high-sugar diet in rats and attempted to define central mechanisms - especially those related to opioid signaling--responsible for overeating sweet foods under such conditions. We found that scheduled access to food, even as challenging as 20 min per day, does not prevent overconsumption of a high-sucrose diet compared to a standard one. An opioid receptor antagonist, naloxone, at 0.3-1 mg/kg b. wt., decreased the intake of the sweet diet, whereas higher doses were required to reduce bland food consumption. Real-time PCR analysis revealed that expression of hypothalamic and brainstem genes encoding opioid peptides and receptors did not differ in sucrose versus regular diet-fed rats, which suggests that scheduled intake of sweet food produces only a transient change in the opioid tone. Intake of sugar was also associated with upregulation of orexin and oxytocin genes in the hypothalamus and NPY in the brainstem. We conclude that scheduled consumption of sugar diets is associated with activity of a complex network of neuroregulators involving opioids, orexin, oxytocin and NPY.
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Beckman TR, Shi Q, Levine AS, Billington CJ. Amygdalar opioids modulate hypothalamic melanocortin-induced anorexia. Physiol Behav 2008; 96:568-73. [PMID: 19136019 DOI: 10.1016/j.physbeh.2008.12.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Revised: 11/18/2008] [Accepted: 12/10/2008] [Indexed: 11/17/2022]
Abstract
We wanted to assess the possibility that opioid activity in the central amygdala (CeA) could modulate the feeding inhibition of melanocortin stimulation of the paraventricular hypothalamus (PVN). The melanocortin system is important in both the acute regulation of satiety and feeding behavior and in the integration of long-term appetite signals. Melanotan II (MTII) is a synthetic MC3R and MC4R agonist which reduces food intake when given intracerebroventricularly (ICV) and into the PVN. Tyr-D-Ala-Gly-(me) Phe-Gly-ol (DAMGO), a micro-opioid receptor agonist, increases food intake, while opioid antagonists, like naltrexone (NTX), inhibit food intake after injection into many brain sites involved in appetite regulation, including the CeA. In food-deprived male Sprague-Dawley rats, co-injected intra-PVN MTII partially blocked the orexigenic effect of co-injected intra-CeA DAMGO. Intra-CeA NTX co-injected with intra-PVN MTII reduced food intake significantly more than either alone. NTX administered intra-CeA reduced c-Fos-immunoreactivity (IR) in nucleus accumbens neurons significantly compared to the intra-PVN MTII treated animals, animals co-injected intra-PVN with MTII and intra-CeA with NTX animals, and control animals. Intra-PVN MTII induced c-Fos-IR in significantly more PVN neurons than observed in control animals. Intra-CeA NTX co-injected with intra-PVN MTII induced c-Fos-IR significantly in PVN neurons relative to control and intra-CeA NTX animals. Such data support the significance of opioid action within the CeA as a modulator of the feeding regulation action of melanocortins within the PVN, occurring within the context of a larger appetitive network.
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MESH Headings
- Amygdala/drug effects
- Amygdala/metabolism
- Analgesics, Opioid/metabolism
- Animals
- Appetite Regulation/drug effects
- Appetite Regulation/physiology
- Drug Interactions
- Eating/drug effects
- Eating/physiology
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacology
- Food Deprivation
- Hormones/pharmacology
- Male
- Melanocortins/metabolism
- Naltrexone/pharmacology
- Neural Pathways/physiology
- Neurotransmitter Agents/pharmacology
- Paraventricular Hypothalamic Nucleus/drug effects
- Paraventricular Hypothalamic Nucleus/metabolism
- Peptides, Cyclic/pharmacology
- Rats
- Rats, Sprague-Dawley
- Receptor, Melanocortin, Type 3/drug effects
- Receptor, Melanocortin, Type 3/metabolism
- Receptor, Melanocortin, Type 4/drug effects
- Receptor, Melanocortin, Type 4/metabolism
- Receptors, Opioid, mu/drug effects
- Receptors, Opioid, mu/metabolism
- alpha-MSH/analogs & derivatives
- alpha-MSH/pharmacology
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