Gut hormone PYY(3-36) physiologically inhibits food intake

Food intake is regulated by the hypothalamus, including the melanocortin and neuropeptide Y (NPY) systems in the arcuate nucleus. The NPY Y2 receptor (Y2R), a putative inhibitory presynaptic receptor, is highly expressed on NPY neurons in the arcuate nucleus, which is accessible to peripheral hormones. Peptide YY(3-36) (PYY(3-36)), a Y2R agonist, is released from the gastrointestinal tract postprandially in proportion to the calorie content of a meal. Here we show that peripheral injection of PYY(3-36) in rats inhibits food intake and reduces weight gain. PYY(3-36) also inhibits food intake in mice but not in Y2r-null mice, which suggests that the anorectic effect requires the Y2R. Peripheral administration of PYY(3-36) increases c-Fos immunoreactivity in the arcuate nucleus and decreases hypothalamic Npy messenger RNA. Intra-arcuate injection of PYY(3-36) inhibits food intake. PYY(3-36) also inhibits electrical activity of NPY nerve terminals, thus activating adjacent pro-opiomelanocortin (POMC) neurons. In humans, infusion of normal postprandial concentrations of PYY(3-36) significantly decreases appetite and reduces food intake by 33% over 24 h. Thus, postprandial elevation of PYY(3-36) may act through the arcuate nucleus Y2R to inhibit feeding in a gut-hypothalamic pathway.     

UCP2 mediates ghrelin's action on NPY/AgRP neurons by lowering free radicals

The gut-derived hormone ghrelin exerts its effect on the brain by regulating neuronal activity. Ghrelin-induced feeding behaviour is controlled by arcuate nucleus neurons that co-express neuropeptide Y and agouti-related protein (NPY/AgRP neurons). However, the intracellular mechanisms triggered by ghrelin to alter NPY/AgRP neuronal activity are poorly understood. Here we show that ghrelin initiates robust changes in hypothalamic mitochondrial respiration in mice that are dependent on uncoupling protein 2 (UCP2). Activation of this mitochondrial mechanism is critical for ghrelin-induced mitochondrial proliferation and electric activation of NPY/AgRP neurons, for ghrelin-triggered synaptic plasticity of pro-opiomelanocortin-expressing neurons, and for ghrelin-induced food intake. The UCP2-dependent action of ghrelin on NPY/AgRP neurons is driven by a hypothalamic fatty acid oxidation pathway involving AMPK, CPT1 and free radicals that are scavenged by UCP2. These results reveal a signalling modality connecting mitochondria-mediated effects of G-protein-coupled receptors on neuronal function and associated behaviour.     

Leptin-regulated endocannabinoids are involved in maintaining food intake

Leptin is the primary signal through which the hypothalamus senses nutritional state and modulates food intake and energy balance. Leptin reduces food intake by upregulating anorexigenic (appetite-reducing) neuropeptides, such as alpha-melanocyte-stimulating hormone, and downregulating orexigenic (appetite-stimulating) factors, primarily neuropeptide Y. Genetic defects in anorexigenic signalling, such as mutations in the melanocortin-4 (ref. 5) or leptin receptors, cause obesity. However, alternative orexigenic pathways maintain food intake in mice deficient in neuropeptide Y. CB1 cannabinoid receptors and the endocannabinoids anandamide and 2-arachidonoyl glycerol are present in the hypothalamus, and marijuana and anandamide stimulate food intake. Here we show that following temporary food restriction, CB1 receptor knockout mice eat less than their wild-type littermates, and the CB1 antagonist SR141716A reduces food intake in wild-type but not knockout mice. Furthermore, defective leptin signalling is associated with elevated hypothalamic, but not cerebellar, levels of endocannabinoids in obese db/db and ob/ob mice and Zucker rats. Acute leptin treatment of normal rats and ob/ob mice reduces anandamide and 2-arachidonoyl glycerol in the hypothalamus. These findings indicate that endocannabinoids in the hypothalamus may tonically activate CB1 receptors to maintain food intake and form part of the neural circuitry regulated by leptin.     

AMP-kinase regulates food intake by responding to hormonal and nutrient signals in the hypothalamus

Obesity is an epidemic in Western society, and causes rapidly accelerating rates of type 2 diabetes and cardiovascular disease. The evolutionarily conserved serine/threonine kinase, AMP-activated protein kinase (AMPK), functions as a 'fuel gauge' to monitor cellular energy status. We investigated the potential role of AMPK in the hypothalamus in the regulation of food intake. Here we report that AMPK activity is inhibited in arcuate and paraventricular hypothalamus (PVH) by the anorexigenic hormone leptin, and in multiple hypothalamic regions by insulin, high glucose and refeeding. A melanocortin receptor agonist, a potent anorexigen, decreases AMPK activity in PVH, whereas agouti-related protein, an orexigen, increases AMPK activity. Melanocortin receptor signalling is required for leptin and refeeding effects on AMPK in PVH. Dominant negative AMPK expression in the hypothalamus is sufficient to reduce food intake and body weight, whereas constitutively active AMPK increases both. Alterations of hypothalamic AMPK activity augment changes in arcuate neuropeptide expression induced by fasting and feeding. Furthermore, inhibition of hypothalamic AMPK is necessary for leptin's effects on food intake and body weight, as constitutively active AMPK blocks these effects. Thus, hypothalamic AMPK plays a critical role in hormonal and nutrient-derived anorexigenic and orexigenic signals and in energy balance.     

糖皮质激素性骨质疏松大鼠弓状核β-内啡肽免疫反应神经元的变化

目的：观察地塞米松（DEX）致雄性大鼠骨质疏松后,其下丘脑弓状核β-内啡肽（β-endorphin,β-EP）免疫反应神经元的变化。方法：选用4月龄健康雄性SD大鼠16只,采用随机数字表法将大鼠随机分为2组,模型组给予地塞米松磷酸钠注射液以0．1mg／100g体重,肌肉注射,2次／周,连续8周。对照组肌肉注射等量生理盐水,8周后处死取材。通过检测大鼠胫骨上段骨组织形态计量学的变化判断骨代谢的情况;采用免疫组织化学方法观察弓状核β-EP免疫反应神经元的变化。结果：与对照组相比,模型组大鼠骨小梁面积百分数、骨小梁宽度和骨小梁数量明显减小（P〈0．05）,骨小梁分离度明显增大（P〈0．01）;模型组大鼠下丘脑弓状核β-EP免疫反应阳性神经元的数量明显减少（p〈0．05）。结论：弓状核β-EP免疫反应阳性神经元数量的减少可能与糖皮质激素性骨盾疏松的形成具有密切的美系。     

尼莫地平和银杏叶提取物对谷氨酸神经毒性的对抗作用：形态学观察

用形态学的方法观察了尼莫地平和银杏叶提取物（含黄酮甙类２４％和内酯３．４％）对谷氨酸神经毒性的影响。结果发现谷氨酸导致新生小鼠下丘脑弓状核变性、坏死，钙通道拮抗剂尼莫地平及血小板激活因子受体拮抗剂银杏叶提取物均可剂量依赖性地抑制谷氨酸引起的神经元损伤。结果提示钙离子超载及血小板激活因子的激活与谷氨酸的神经毒性作用有关     

A role for ghrelin in the central regulation of feeding

Ghrelin is an acylated peptide that stimulates the release of growth hormone from the pituitary. Ghrelin-producing neurons are located in the hypothalamus, whereas ghrelin receptors are expressed in various regions of the brain, which is indicative of central-and as yet undefined-physiological functions. Here we show that ghrelin is involved in the hypothalamic regulation of energy homeostasis. Intracerebroventricular injections of ghrelin strongly stimulated feeding in rats and increased body weight gain. Ghrelin also increased feeding in rats that are genetically deficient in growth hormone. Anti-ghrelin immunoglobulin G robustly suppressed feeding. After intracerebroventricular ghrelin administration, Fos protein, a marker of neuronal activation, was found in regions of primary importance in the regulation of feeding, including neuropeptide Y6 (NPY) neurons and agouti-related protein (AGRP) neurons. Antibodies and antagonists of NPY and AGRP abolished ghrelin-induced feeding. Ghrelin augmented NPY gene expression and blocked leptin-induced feeding reduction, implying that there is a competitive interaction between ghrelin and leptin in feeding regulation. We conclude that ghrelin is a physiological mediator of feeding, and probably has a function in growth regulation by stimulating feeding and release of growth hormone.     

Partial leptin deficiency and human adiposity.

The adipocyte-derived hormone leptin is crucial for energy homeostasis in mammals; mice and humans without it suffer from a voracious appetite and extreme obesity. The effect on energy balance of variations in plasma leptin above a minimal threshold is uncertain, however, particularly in humans. Here we examine a group of individuals who are genetically partially deficient in leptin, and show that differences in circulating leptin levels within the range found in normal human populations can directly influence the laying down of fat tissue (adiposity).     

Melanin-concentrating hormone is the cognate ligand for the orphan G-protein-coupled receptor SLC-1.

The underlying causes of obesity are poorly understood but probably involve complex interactions between many neurotransmitter and neuropeptide systems involved in the regulation of food intake and energy balance. Three pieces of evidence indicate that the neuropeptide melanin-concentrating hormone (MCH) is an important component of this system. First, MCH stimulates feeding when injected directly into rat brains; second, the messenger RNA for the MCH precursor is upregulated in the hypothalamus of genetically obese mice and in fasted animals; and third, mice lacking MCH eat less and are lean. MCH antagonists might, therefore, provide a treatment for obesity. However, the development of such molecules has been hampered because the identity of the MCH receptor has been unknown until now. Here we show that the 353-amino-acid human orphan G-protein-coupled receptor SLC-1 expressed in HEK293 cells binds MCH with sub-nanomolar affinity, and is stimulated by MCH to mobilize intracellular Ca2+ and reduce forskolin-elevated cyclic AMP levels. We also show that SLC-1 messenger RNA and protein is expressed in the ventromedial and dorsomedial nuclei of the hypothalamus, consistent with a role for SLC-1 in mediating the effects of MCH on feeding.     

BDNF controls dopamine D3 receptor expression and triggers behavioural sensitization

Brain-derived neurotrophic factor (BDNF), like other neurotrophins, is a polypeptidic factor initially regarded to be responsible for neuron proliferation, differentiation and survival, through its uptake at nerve terminals and retrograde transport to the cell body. A more diverse role for BDNF has emerged progressively from observations showing that it is also transported anterogradely, is released on neuron depolarization, and triggers rapid intracellular signals and action potentials in central neurons. Here we report that BDNF elicits long-term neuronal adaptations by controlling the responsiveness of its target neurons to the important neurotransmitter, dopamine. Using lesions and gene-targeted mice lacking BDNF, we show that BDNF from dopamine neurons is responsible for inducing normal expression of the dopamine D3 receptor in nucleus accumbens both during development and in adulthood. BDNF from corticostriatal neurons also induces behavioural sensitization, by triggering overexpression of the D3 receptor in striatum of hemiparkinsonian rats. Our results suggest that BDNF may be an important determinant of pathophysiological conditions such as drug addiction, schizophrenia or Parkinson's disease, in which D3 receptor expression is abnormal.     

Deciphering a neuronal circuit that mediates appetite

Hypothalamic neurons that co-express agouti-related protein (AgRP), neuropeptide?Y and γ-aminobutyric acid (GABA) are known to promote feeding and weight gain by integration of various nutritional, hormonal, and neuronal signals. Ablation of these neurons in mice leads to cessation of feeding that is accompanied by activation of Fos in most regions where they project. Previous experiments have indicated that the ensuing starvation is due to aberrant activation of the parabrachial nucleus (PBN) and it could be prevented by facilitating GABA(A) receptor signalling in the PBN within a critical adaptation period. We speculated that loss of GABA signalling from AgRP-expressing neurons (AgRP neurons) within the PBN results in unopposed excitation of the PBN, which in turn inhibits feeding. However, the source of the excitatory inputs to the PBN was unknown. Here we show that glutamatergic neurons in the nucleus tractus solitarius (NTS) and caudal serotonergic neurons control the excitability of PBN neurons and inhibit feeding. Blockade of serotonin (5-HT(3)) receptor signalling in the NTS by either the chronic administration of ondansetron or the genetic inactivation of Tph2 in caudal serotonergic neurons that project to the NTS protects against starvation when AgRP neurons are ablated. Likewise, genetic inactivation of glutamatergic signalling by the NTS onto N-methyl D-aspartate-type glutamate receptors in the PBN prevents starvation. We also show that suppressing glutamatergic output of the PBN reinstates normal appetite after AgRP neuron ablation, whereas it promotes weight gain without AgRP neuron ablation. Thus we identify the PBN as a hub that integrates signals from several brain regions to bidirectionally modulate feeding and body weight.     

Central nervous system control of food intake

New information regarding neuronal circuits that control food intake and their hormonal regulation has extended our understanding of energy homeostasis, the process whereby energy intake is matched to energy expenditure over time. The profound obesity that results in rodents (and in the rare human case as well) from mutation of key signalling molecules involved in this regulatory system highlights its importance to human health. Although each new signalling pathway discovered in the hypothalamus is a potential target for drug development in the treatment of obesity, the growing number of such signalling molecules indicates that food intake is controlled by a highly complex process. To better understand how energy homeostasis can be achieved, we describe a model that delineates the roles of individual hormonal and neuropeptide signalling pathways in the control of food intake and the means by which obesity can arise from inherited or acquired defects in their function.     

Glucose sensing by POMC neurons regulates glucose homeostasis and is impaired in obesity

A subset of neurons in the brain, known as 'glucose-excited' neurons, depolarize and increase their firing rate in response to increases in extracellular glucose. Similar to insulin secretion by pancreatic beta-cells, glucose excitation of neurons is driven by ATP-mediated closure of ATP-sensitive potassium (K(ATP)) channels. Although beta-cell-like glucose sensing in neurons is well established, its physiological relevance and contribution to disease states such as type 2 diabetes remain unknown. To address these issues, we disrupted glucose sensing in glucose-excited pro-opiomelanocortin (POMC) neurons via transgenic expression of a mutant Kir6.2 subunit (encoded by the Kcnj11 gene) that prevents ATP-mediated closure of K(ATP) channels. Here we show that this genetic manipulation impaired the whole-body response to a systemic glucose load, demonstrating a role for glucose sensing by POMC neurons in the overall physiological control of blood glucose. We also found that glucose sensing by POMC neurons became defective in obese mice on a high-fat diet, suggesting that loss of glucose sensing by neurons has a role in the development of type 2 diabetes. The mechanism for obesity-induced loss of glucose sensing in POMC neurons involves uncoupling protein 2 (UCP2), a mitochondrial protein that impairs glucose-stimulated ATP production. UCP2 negatively regulates glucose sensing in POMC neurons. We found that genetic deletion of Ucp2 prevents obesity-induced loss of glucose sensing, and that acute pharmacological inhibition of UCP2 reverses loss of glucose sensing. We conclude that obesity-induced, UCP2-mediated loss of glucose sensing in glucose-excited neurons might have a pathogenic role in the development of type 2 diabetes.     

Interaction between neuropeptide Y and noradrenaline on central catecholamine neurons

Despite their widespread occurrence in the central nervous system, interactions between co-localized transmitters and their receptors remain poorly understood. Noradrenergic neurons of the nucleus locus coeruleus contain the peptide co-transmitter neuropeptide Y (refs 1,2). In locus coeruleus cells, stimulation of alpha2-adrenoceptors 3,4 or opioid mu-receptors 5,6 increases a potassium conductance and thereby leads to hyperpolarization and inhibition of spontaneous firing. Coupling between these receptors and the inward rectifying K+ channels involves a pertussis toxin-sensitive GTP-binding protein (Gi or Go)7. Here we investigate whether the neuropeptide Y and alpha2-receptors of locus coeruleus neurons interact with one another. When administered alone, neuropeptide Y reduces the discharge of action potentials, probably by increasing the permeability of the membrane to potassium ions through the activation of a G protein; this effect is reduced in the presence of alpha2-adrenoceptor antagonists. Moreover, the peptide selectively increases the hyperpolarizing effect of alpha2-agonists, but does not enhance responses to opioid mu-agonists. We suggest that noradrenaline and its co-transmitter neuropeptide Y stimulate separate receptors, which influence each other in a specific way.     

Encoding of conditioned fear in central amygdala inhibitory circuits

The central amygdala (CEA), a nucleus predominantly composed of GABAergic inhibitory neurons, is essential for fear conditioning. How the acquisition and expression of conditioned fear are encoded within CEA inhibitory circuits is not understood. Using in vivo electrophysiological, optogenetic and pharmacological approaches in mice, we show that neuronal activity in the lateral subdivision of the central amygdala (CEl) is required for fear acquisition, whereas conditioned fear responses are driven by output neurons in the medial subdivision (CEm). Functional circuit analysis revealed that inhibitory CEA microcircuits are highly organized and that cell-type-specific plasticity of phasic and tonic activity in the CEl to CEm pathway may gate fear expression and regulate fear generalization. Our results define the functional architecture of CEA microcircuits and their role in the acquisition and regulation of conditioned fear behaviour.     

Expression detection and partial cloning of porcine leptin receptor (OBR) gene

The product of the obesity gene, called leptin, is an important regulator of adiposity, which mainly functions via its regulation of feed intake and energy metabolism. Both obesity gene (ob gene) and leptin receptor gene ( OBR gene) are thought to play a major role in controlling of body fat mass as well as body weight. The result of RT-PCR shows that levels of pig OBRmRNA are higher in hypothalamus, lung and liver, and lower expression can be detected in other tissues. Total RNA purified from 11 different organs and tissues have been hybridized with pig OBR cDNA probes. The hybridization signals are shown in 7 organs and tissues. 4.1 and 3.8 kb bands were observed from hypothalamus, whereas 3.8 and 3.5 kb bands were observed in other tissues instead. The nearly complete sequence of the extracellular domain of pig OBR gene was obtained. The homology of sequence is 89.2% between pig and human, 80.3% between pig and mouse. Alignment of the predicted amino acid sequence of OBR in pig, human and mouse shows that the overall identity is 86.5% between pig and human, 76.6% between pig and mouse. Two WSXWS motifs were found at aa₃₁₃ and aa₆₁₆.     

石杉碱甲对急性炎症小鼠室旁核和脑干c-Fos和GFAP表达的影响

目的:探讨石杉碱甲对急性炎症小鼠下丘脑室旁核和脑干神经元c-Fos和星形胶质细胞(astrocytes,AST)胶质原纤维酸性蛋白(glial fiberillany acidic protein,GFAP)表达的影响.方法:①采用蛋清致小鼠足趾肿胀模型,检测致炎后30min,1h,2h的小鼠足容积并计算肿胀度;②免疫组化技术检测孤束核、迷走背核及室旁核神经元c-Fos及星形胶质细胞GFAP的表达.结果:①与生理盐水组比较,不同浓度的石杉碱甲均可明显抑制蛋清致小鼠足肿胀(P<0.05或P<0.01).②与对照组相比,致炎组小鼠孤束核和室旁核内Fos免疫阳性神经元(Fos-immunoreactive neurons,Fos-IR)及GFAP免疫阳性星形胶质细胞(GFAP-immunoreactive astrocytes,GFAP-IR)数目均明显增多(P<0.01),而迷走背核增加不显著(P>0.05).与致炎组相比,石杉碱甲给药组孤束核、迷走背核及室旁核内Fos-IR神经元及GFAP-IR星形胶质细胞数目均明显增多(P<0.01).结论:石杉碱甲对蛋清致小鼠足肿胀有明显的抗炎作用;石杉碱甲能够显著增强急性炎症小鼠孤束核、迷走背核及室旁核内神经元和星形胶质细胞的活动.     

A role for lateral hypothalamic orexin neurons in reward seeking

The lateral hypothalamus is a brain region historically implicated in reward and motivation, but the identity of the neurotransmitters involved are unknown. The orexins (or hypocretins) are neuropeptides recently identified as neurotransmitters in lateral hypothalamus neurons. Although knockout and transgenic overexpression studies have implicated orexin neurons in arousal and sleep, these cells also project to reward-associated brain regions, including the nucleus accumbens and ventral tegmental area. This indicates a possible role for these neurons in reward function and motivation, consistent with previous studies implicating these neurons in feeding. Here we show that activation of lateral hypothalamus orexin neurons is strongly linked to preferences for cues associated with drug and food reward. In addition, we show that chemical activation of lateral hypothalamus orexin neurons reinstates an extinguished drug-seeking behaviour. This reinstatement effect was completely blocked by prior administration of an orexin A antagonist. Moreover, administration of the orexin A peptide directly into the ventral tegmental area also reinstated drug-seeking. These data reveal a new role for lateral hypothalamus orexin neurons in reward-seeking, drug relapse and addiction.