Rapid rewiring of arcuate nucleus feeding circuits by leptin

The fat-derived hormone leptin regulates energy balance in part by modulating the activity of neuropeptide Y and proopiomelanocortin neurons in the hypothalamic arcuate nucleus. To study the intrinsic activity of these neurons and their responses to leptin, we generated mice that express distinct green fluorescent proteins in these two neuronal types. Leptin-deficient (ob/ob) mice differed from wild-type mice in the numbers of excitatory and inhibitory synapses and postsynaptic currents onto neuropeptide Y and proopiomelanocortin neurons. When leptin was delivered systemically to ob/ob mice, the synaptic density rapidly normalized, an effect detectable within 6 hours, several hours before leptin's effect on food intake. These data suggest that leptin-mediated plasticity in the ob/ob hypothalamus may underlie some of the hormone's behavioral effects.     

Virus-assisted mapping of neural inputs to a feeding center in the hypothalamus

We report the development of a pseudorabies virus that can be used for retrograde tracing from selected neurons. This virus encodes a green fluorescent protein marker and replicates only in neurons that express the Cre recombinase and in neurons in synaptic contact with the originally infected cells. The virus was injected into the arcuate nucleus of mice that express Cre only in those neurons that express neuropeptide Y or the leptin receptor. Sectioning of the brains revealed that these neurons receive inputs from neurons in other regions of the hypothalamus, as well as the amygdala, cortex, and other brain regions. These data suggest that higher cortical centers modulate leptin signaling in the hypothalamus. This method of neural tracing may prove useful in studies of other complex neural circuits.     

Trophic action of leptin on hypothalamic neurons that regulate feeding

In adult mammals, the adipocyte-derived hormone leptin acts on the brain to reduce food intake by regulating the activity of neurons in the arcuate nucleus of the hypothalamus (ARH). Here, we report that neural projection pathways from the ARH are permanently disrupted in leptin-deficient (Lepob/Lepob) mice and leptin treatment in adulthood does not reverse these neuroanatomical defects. However, treatment of Lepob/Lepob neonates with exogenous leptin rescues the development of ARH projections, and leptin promotes neurite outgrowth from ARH neurons in vitro. These results suggest that leptin plays a neurotrophic role during the development of the hypothalamus and that this activity is restricted to a neonatal critical period that precedes leptin's acute regulation of food intake in adults.     

运动对高脂饮食大鼠下丘脑SOCS-3和BDNF以及瘦素抵抗的影响

目的：观察运动对高脂饮食大鼠血清和下丘脑瘦素（Leptin）以及下丘脑 瘦素长型受体（OB-Rb） 、促黑皮素受体4（MC4R）、细胞因子信号转导抑制因子-3（SOCS-3） mRNA表达和脑源性神经营养因子（ BDNF）的影响,探讨适宜运动对高脂饮食大鼠预防肥胖的部分中枢机制。方法：雄性SD鼠24只,随机分为 正常对照组（C组）,高脂模型组（H组）和高脂 60min 运动组（HE组）,每组8只。高脂模型组和高脂 60min 运动组大鼠喂饲高脂饲料,高脂饮食运动组大鼠进行60min的无负重游泳运动。持续10周。结果： 10周运动后,高脂模型组大鼠较正常对照组大鼠体重、Lee''S指数、体脂、脂体比均显著增高(p<0.05), 血清瘦素水平显著升高(p<0.05),下丘脑内OB-Rb、MC4R mRNA表达量显著降低(p<0.05),SOCS-3 mRNA表 达量显著升高(p<0.05),下丘脑BDNF含量显著降低(p<0.05);高脂60min运动组较高脂模型组大鼠体重显 著降低(p<0.01),Lee''S指数、体脂、脂体比均显著降低(p<0.05),血清瘦素水平显著升高(p<0.05),下 丘脑OB-Rb、MC4R、leptin mRNA表达量显著升高(p<0.05),下丘脑SOCS-3 mRNA表达量显著降低(p<0.05) ,下丘脑BDNF含量显著升高(p<0.05)。结论：长期适宜的运动可通过降低下丘脑SOCS-3的表达,增加下丘 脑Leptin 与受体OB-Rb的结合,降低了瘦素抵抗,激活下丘脑含 MC4R 受体的神经元,从而刺激 BDNF 的 释放,从而起到预防高脂饮食引起肥胖的作用。     

Hypothalamic mTOR signaling regulates food intake

The mammalian Target of Rapamycin (mTOR) protein is a serine-threonine kinase that regulates cell-cycle progression and growth by sensing changes in energy status. We demonstrated that mTOR signaling plays a role in the brain mechanisms that respond to nutrient availability, regulating energy balance. In the rat, mTOR signaling is controlled by energy status in specific regions of the hypothalamus and colocalizes with neuropeptide Y and proopiomelanocortin neurons in the arcuate nucleus. Central administration of leucine increases hypothalamic mTOR signaling and decreases food intake and body weight. The hormone leptin increases hypothalamic mTOR activity, and the inhibition of mTOR signaling blunts leptin's anorectic effect. Thus, mTOR is a cellular fuel sensor whose hypothalamic activity is directly tied to the regulation of energy intake.     

Severely impaired adipsin expression in genetic and acquired obesity

Adipsin, a serine protease homolog, is synthesized and secreted by adipose cells and is found in the bloodstream. The expression of adipsin messenger RNA (mRNA) and protein was analyzed in rodents during metabolic perturbations and in several experimental models of obesity. Adipsin mRNA abundance is increased in adipose tissue during fasting in normal rats and in diabetes due to streptozotocin-induced insulin deficiency. Adipsin mRNA abundance decreased during the continuous infusion of glucose, which induces a hyperglycemic, hyperinsulinemic state that is accompanied by an increased adipose mass; it is suppressed (greater than 100-fold) in two strains of genetically obese mice (db/db and ob/ob), compared to their congenic counterparts, and is also reduced when obesity is induced chemically by injection of monosodium glutamate into newborn mice. Circulating adipsin protein is decreased in these animal models of obesity, as determined by immunoblotting with antisera to adipsin. Little change in adipsin expression is observed in a model of obesity obtained by pure overfeeding of normal rats (cafeteria model). These data suggest a possible role for adipsin in the above-mentioned disordered metabolic states, and raise the possibility that adipsin expression may be used to distinguish obesities that arise from certain genetic or metabolic defects from those that result from pure overfeeding.     

Nicotine decreases food intake through activation of POMC neurons

Smoking decreases appetite, and smokers often report that they smoke to control their weight. Understanding the neurobiological mechanisms underlying the anorexic effects of smoking would facilitate the development of novel treatments to help with smoking cessation and to prevent or treat obesity. By using a combination of pharmacological, molecular genetic, electrophysiological, and feeding studies, we found that activation of hypothalamic α3β4 nicotinic acetylcholine receptors leads to activation of pro-opiomelanocortin (POMC) neurons. POMC neurons and subsequent activation of melanocortin 4 receptors were critical for nicotinic-induced decreases in food intake in mice. This study demonstrates that nicotine decreases food intake and body weight by influencing the hypothalamic melanocortin system and identifies critical molecular and synaptic mechanisms involved in nicotine-induced decreases in appetite.     

早期Ⅱ型糖尿病肾病小鼠模型的建立

[目的]在自发性II型糖尿病小鼠（db／db）基础上建立1种II型糖尿病肾病小鼠模型,为糖尿病肾病新药研发提供高效优质的服务平台。[方法]用II型糖尿病小鼠（db／db）,分别在其4周龄和8周龄进行左侧单肾切除手术．待其康复1周后,再将动物按周龄大小分成2组,另外2组对应周龄的db／db小鼠进行假手术,作为阴性对照组。每2周测定空腹6小时血糖浓度和体重,每4周收集尿液,测定24h微量尿白蛋白总量。[结果]8周龄阴性对照组小鼠与其对应进行单侧肾切除的小鼠空腹6h血糖和体重并无明显差异,但24h微量尿白蛋白总量显著增高,4周龄阴性对照组小鼠与其对应进行单侧肾切除的小鼠相比,其空腹6h血糖和24h微量尿白蛋白总量并无显著增高。[结论]在db／db小鼠8周龄进行单侧肾脏切除可以加速db／db小鼠糖尿病肾病的发生和发展。     

Optical imaging of neuronal populations during decision-making

We investigated decision-making in the leech nervous system by stimulating identical sensory inputs that sometimes elicit crawling and other times swimming. Neuronal populations were monitored with voltage-sensitive dyes after each stimulus. By quantifying the discrimination time of each neuron, we found single neurons that discriminate before the two behaviors are evident. We used principal component analysis and linear discriminant analysis to find populations of neurons that discriminated earlier than any single neuron. The analysis highlighted the neuron cell 208. Hyperpolarizing cell 208 during a stimulus biases the leech to swim; depolarizing it biases the leech to crawl or to delay swimming.     

Role of brain insulin receptor in control of body weight and reproduction

Insulin receptors (IRs) and insulin signaling proteins are widely distributed throughout the central nervous system (CNS). To study the physiological role of insulin signaling in the brain, we created mice with a neuron-specific disruption of the IR gene (NIRKO mice). Inactivation of the IR had no impact on brain development or neuronal survival. However, female NIRKO mice showed increased food intake, and both male and female mice developed diet-sensitive obesity with increases in body fat and plasma leptin levels, mild insulin resistance, elevated plasma insulin levels, and hypertriglyceridemia. NIRKO mice also exhibited impaired spermatogenesis and ovarian follicle maturation because of hypothalamic dysregulation of luteinizing hormone. Thus, IR signaling in the CNS plays an important role in regulation of energy disposal, fuel metabolism, and reproduction.     

Adipsin and complement factor D activity: an immune-related defect in obesity

Adipsin is a serine protease that is secreted by adipocytes into the bloodstream; it is deficient in several animal models of obesity, representing a striking example of defective gene expression in this disorder. Recombinant mouse adipsin was purified and its biochemical and enzymatic properties were studied in order to elucidate the function of this protein. Activated adipsin has little or no proteolytic activity toward most substrates but has the same activity as human complement factor D, cleaving complement factor B when it is complexed with activated complement component C3. Like authentic factor D, adipsin can activate the alternative pathway of complement, resulting in red blood cell lysis. Decreased (58 to 80 percent) complement factor D activity, relative to lean controls, was observed as a common feature of several experimental models of obesity, including the ob/ob, db/db, and monosodium glutamate (MSG)-injected mouse and the fa/fa rat. These results suggest that adipsin and the alternative pathway of complement may play an unexpected but important role in the regulation of systemic energy balance in vivo.     

Modulation of brain reward circuitry by leptin

Leptin, a hormone secreted by fat cells, suppresses food intake and promotes weight loss. To assess the action of this hormone on brain reward circuitry, changes in the rewarding effect of lateral hypothalamic stimulation were measured after leptin administration. At five stimulation sites near the fornix, the effectiveness of the rewarding electrical stimulation was enhanced by chronic food restriction and attenuated by intracerebroventricular infusion of leptin. In contrast, the rewarding effect of stimulating neighboring sites was insensitive to chronic food restriction and was enhanced by leptin in three of four cases. These opposing effects of leptin may mirror complementary changes in the rewarding effects of feeding and of competing behaviors.     

Selective recording and stimulation of individual identified neurons in freely behaving Aplysia

A neuroethological technique is described for selective recording and stimulation of an individual neuron in freely behaving Aplysia by means of a fine wire glued into the connective tissue sheath above the identified cell body. A whole-nerve cuff electrode simultaneously monitored functionally related multiunit axon activity. For biophysical analysis the soma was impaled with a microelectrode when the ganglion was subsequently exposed. The technique is illustrated for several identified neurons involved in different behaviors.     

Neurobiology. Death leads to brain neuron birth

Although scientists have provided mounting evidence in the past few years that new neurons can be produced in some areas of the adult brain, the neocortex--the region most concerned with such higher brain functions as memory and learning--did not seem capable of such regeneration. Now, in the 22 June issue of Nature, neuroscientists report that when they induced certain neurons in the neocortex of adult mice to self-destruct, the loss triggered the formation of replacement neurons by brain stem cells. If similar regeneration of brain neurons can be triggered in humans, the findings could open the door for treatments that might restore memory in Alzheimer's disease, for example, or undo the damage wreaked by spinal cord injury.     

损毁弓状核对大鼠骨微构筑学的影响

目的研究损毁大鼠下丘脑弓状核(ARC)对骨微构筑学的影响。方法新生雌性Sprague-Dawley(SD)大鼠12只,用同窝对照的方法,按体质量从轻到重编号,用抽签法随机分为实验组和对照组,每组6只。实验组大鼠于出生后第1、3、5、7、9天皮下注射10%谷氨酸单钠(MSG)4g/kg B.W,对照组同法注射等体积生理盐水。各组大鼠皆存活至200d,以3%戊巴比妥钠腹腔麻醉,用4%多聚甲醛经左心室行全身灌注,取脑作下丘脑弓状核冠状面切片,HE染色。取各组大鼠左侧胫骨,用2.5%戊二醛固定,然后将胫骨近端作矢状面锯开,用作扫描电镜研究。另取右侧胫骨和第四腰椎,常规脱钙,石蜡包埋,矢状面连续切片,胶原特殊染色,用于显示骨小梁结构。用图象分析仪对弓状核正中隆起切面和骨组织进行照片和计量。结果MSG大鼠弓状核神经细胞数量显著减少,骨的微构筑学出现明显破坏,发生了明显骨质疏松。结论(1)损毁大鼠下丘脑弓状核可导致骨微构筑学明显破坏,出现明显骨质疏松,首次命名为大鼠脑源性骨质疏松。(2)ARC参与骨代谢的调控。     

The obesity-associated FTO gene encodes a 2-oxoglutarate-dependent nucleic acid demethylase

Variants in the FTO (fat mass and obesity associated) gene are associated with increased body mass index in humans. Here, we show by bioinformatics analysis that FTO shares sequence motifs with Fe(II)- and 2-oxoglutarate-dependent oxygenases. We find that recombinant murine Fto catalyzes the Fe(II)- and 2OG-dependent demethylation of 3-methylthymine in single-stranded DNA, with concomitant production of succinate, formaldehyde, and carbon dioxide. Consistent with a potential role in nucleic acid demethylation, Fto localizes to the nucleus in transfected cells. Studies of wild-type mice indicate that Fto messenger RNA (mRNA) is most abundant in the brain, particularly in hypothalamic nuclei governing energy balance, and that Fto mRNA levels in the arcuate nucleus are regulated by feeding and fasting. Studies can now be directed toward determining the physiologically relevant FTO substrate and how nucleic acid methylation status is linked to increased fat mass.     

Brain lesions in an infant rhesus monkey treated with monsodium glutamate

In an infant rhesus monkey brain damage resulted from subcutaneously administered monosodium glutamate. Although a relatively high dose of monosodium glutamate was used, the infant was asymptomatic for a 3-hour observation period during which time hypothalamic neurons were undergoing a process of acute cell death. With the electron microscope it was observed that dendrites and cell bodies of neurons are the tissue components primarily affected in brain damage induced by monosodium glutamate.     

Impaired respiratory and body temperature control upon acute serotonergic neuron inhibition

Physiological homeostasis is essential for organism survival. Highly responsive neuronal networks are involved, but their constituent neurons are just beginning to be resolved. To query brain serotonergic neurons in homeostasis, we used a neuronal silencing tool, mouse RC::FPDi (based on the synthetic G protein-coupled receptor Di), designed for cell type-specific, ligand-inducible, and reversible suppression of action potential firing. In mice harboring Di-expressing serotonergic neurons, administration of the ligand clozapine-N-oxide (CNO) by systemic injection attenuated the chemoreflex that normally increases respiration in response to tissue carbon dioxide (CO(2)) elevation and acidosis. At the cellular level, CNO suppressed firing rate increases evoked by CO(2) acidosis. Body thermoregulation at room temperature was also disrupted after CNO triggering of Di; core temperatures plummeted, then recovered. This work establishes that serotonergic neurons regulate life-sustaining respiratory and thermoregulatory networks, and demonstrates a noninvasive tool for mapping neuron function.     

初生肉仔鸡血清和下丘脑摄食调节相关激素的发育规律与品种特点

 【目的】研究初生肉仔鸡血清和下丘脑摄食调节相关激素的发育规律并进行品种间比较。【方法】观测了北京油鸡和AA鸡在孵出后0、1、3、5、7、9和11 d的采食量,血清和下丘脑的胰岛素和瘦素及下丘脑NPY和α-MSH水平的变化。【结果】北京油鸡和AA鸡的生长规律基本一致,但前者的ADFI和ADG极显著低于后者（P＜0.01）。北京油鸡血清胰岛素随日龄的波动较大,而AA鸡除0 d外,其它日龄维持在7.5 μIU•ml-1左右。北京油鸡血清瘦素在各个日龄间无明显差异,而AA鸡1和3 d血清瘦素显著高于0 d（P≤0.03）。北京油鸡下丘脑瘦素随日龄增长呈下降趋势,而AA鸡1 d下丘脑瘦素高于0 d（P＜0.01）,而后有所降低。2个品种的下丘脑胰岛素和NPY随日龄的变化趋势一致。下丘脑胰岛素在出壳后前5 d的水平较高,而后有所下降。下丘脑NPY随日龄增长而上升,其中7 d最高。北京油鸡下丘脑α-MSH在出壳后前7 d的水平较低,而后有所升高,而AA鸡下丘脑α-MSH随日龄增长而降低,达5 d最低,而后又上升。相关分析表明,血清瘦素、下丘脑胰岛素、瘦素和NPY与ADFI的相关性较强,而血清胰岛素和下丘脑α-MSH与ADFI的相关性不强。【结论】血清和下丘脑的摄食相关激素的发育规律因品种和指标不同而异,胰岛素、瘦素、NPY和α-MSH在雏鸡开食过程中可能发挥着一定作用,但其具体调节机制仍需进一步研究。