Stimulation of food intake in rats by centrally administered hypothalamic growth hormone-releasing factor

Hypothalamic growth hormone-releasing factors (GRFs) have been purified recently from human pancreatic (hp) tumours and from rat hypothalamus (rh). GRF peptides have strong homology with peptides of the glucagon, vasoactive intestinal polypeptide and PHI-27 family. Aside from their potent actions on release of somatotropin, no other biological actions of GRFs have been reported. GRF has been localized in neurones bordering the ventromedial hypothalamic nucleus, a region associated frequently with experimental analysis of feeding behaviour. We now report that intracerebroventricularly (i.c.v.)-administered rhGRF and hpGRF(1-40) in doses of 0.2, 2.0 and 20.0 pmol, produced an increase in food intake in hungry rats. This effect seemed to be specific to GRF as i.c.v. injections of a structurally related but physiologically inactive peptide in the same doses had no effect on feeding. In addition, peripheral injections of rhGRF or growth hormone had no effect on food intake, suggesting that the present effects may be mediated centrally. Injections (i.c.v.) of rhGRF (0.2, 2.0 and 20.0 pmol) had no effect on general activity, suggesting that GRF does not produce nonspecific arousal.     

Vasopressin alters female sexual behaviour by acting on the brain independently of alterations in blood pressure

Subcutaneous (s.c.) administration of Arg-vasopressin (AVP) prolongs retention of a learned behaviour and elevates arterial blood pressure. Intracerebroventricular (i.c.v.) injection of a thousandfold lower dose of AVP than needed with s.c. injection produces the same behavioural effect, suggesting that AVP acts on the brain to control behaviour. However, as i.c.v. injection of AVP also elevates arterial blood pressure, it was suggested that AVP, and perhaps other peptides as well, influences behaviour indirectly by eliciting a peripheral response, for example blood pressure changes, rather than by acting directly on the brain. The suprachiasmatic nuclei (SCN) of the hypothalamus, a source of vasopressin production, inhibit sexual receptivity in oestradiol-17 beta-treated ovariectomized rats during the light phase of the daily lighting cycle, leading to speculation that vasopressin might inhibit sexual behaviour. Here we report that i.c.v. injections of AVP (1, 4 or 10 ng) inhibit sexual behaviour in receptive rats. This behavioural response is prevented by i.c.v. injection of an antiserum to AVP 30 min before AVP injection. Subcutaneous injection of a high dose of AVP (1 microgram) has no behavioural effect but elevates arterial blood pressure within 30 min of administration. Intracerebroventricular injection of a behaviourally effective dose of AVP (1 ng) has no effect on blood pressure. The results provide direct evidence that AVP can alter behaviour by an action on the brain and independently of its effect on blood pressure.     

An anorexic lipid mediator regulated by feeding.

Oleylethanolamide (OEA) is a natural analogue of the endogenous cannabinoid anandamide. Like anandamide, OEA is produced in cells in a stimulus-dependent manner and is rapidly eliminated by enzymatic hydrolysis, suggesting a function in cellular signalling. However, OEA does not activate cannabinoid receptors and its biological functions are still unknown. Here we show that, in rats, food deprivation markedly reduces OEA biosynthesis in the small intestine. Administration of OEA causes a potent and persistent decrease in food intake and gain in body mass. This anorexic effect is behaviourally selective and is associated with the discrete activation of brain regions (the paraventricular hypothalamic nucleus and the nucleus of the solitary tract) involved in the control of satiety. OEA does not affect food intake when injected into the brain ventricles, and its anorexic actions are prevented when peripheral sensory fibres are removed by treatment with capsaicin. These results indicate that OEA is a lipid mediator involved in the peripheral regulation of feeding.     

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.     

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。     

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.     

八肽胆囊收缩素抗血清翻转针刺耐受的电生理学研究

动物整体水平研究证实，八肽胆囊收缩素抗血清（ＣＣＫ－ＡＳ）可翻转电针耐受，而ＣＣＫ－ＡＳ本身不影响基础痛阈。本文采用记录神经元放电的方法证明：脑室注射ＣＣＫ－ＡＳ能翻转对长时间电针产生耐受效应的大鼠丘脑束旁核痛兴奋神经元（ＰＥＮ）和痛抑制神经元（ＰＩＮ）的电活动，使电针镇痛效应重新出现。而脑室注射正常兔血清（ＮＲＳ）对产生电针耐受效应的ＰＥＮ和ＰＩＮ的电活动无影响。从细胞水平得到的这一结果与整体水平研究的证据相一致。提示，内源性ＣＣＫ－８参与电针耐受可能是电针镇痛受到拮抗的机制之一。这一发现同时为临床医学实践提供了进一步的依据。     

PYY modulation of cortical and hypothalamic brain areas predicts feeding behaviour in humans

The ability to maintain adequate nutrient intake is critical for survival. Complex interrelated neuronal circuits have developed in the mammalian brain to regulate many aspects of feeding behaviour, from food-seeking to meal termination. The hypothalamus and brainstem are thought to be the principal homeostatic brain areas responsible for regulating body weight. However, in the current 'obesogenic' human environment food intake is largely determined by non-homeostatic factors including cognition, emotion and reward, which are primarily processed in corticolimbic and higher cortical brain regions. Although the pleasure of eating is modulated by satiety and food deprivation increases the reward value of food, there is currently no adequate neurobiological account of this interaction between homeostatic and higher centres in the regulation of food intake in humans. Here we show, using functional magnetic resonance imaging, that peptide YY3-36 (PYY), a physiological gut-derived satiety signal, modulates neural activity within both corticolimbic and higher-cortical areas as well as homeostatic brain regions. Under conditions of high plasma PYY concentrations, mimicking the fed state, changes in neural activity within the caudolateral orbital frontal cortex predict feeding behaviour independently of meal-related sensory experiences. In contrast, in conditions of low levels of PYY, hypothalamic activation predicts food intake. Thus, the presence of a postprandial satiety factor switches food intake regulation from a homeostatic to a hedonic, corticolimbic area. Our studies give insights into the neural networks in humans that respond to a specific satiety signal to regulate food intake. An increased understanding of how such homeostatic and higher brain functions are integrated may pave the way for the development of new treatment strategies for obesity.     

5-羟色胺在F344大鼠下丘脑释放及其免疫调节作用

在F344雄性大鼠腹腔注射血蓝蛋白(KLH),研究T 细胞依赖抗原初始免疫反应对中枢神经系统5 羟色胺(5 HT)代谢的影响。当免疫刺激大鼠4天后,其下丘脑匀浆5 羟色胺水平出现降低,同时应用在体脑微透析技术研究发现清醒大鼠腹腔注射血蓝蛋白4天后,其下丘脑前叶细胞外液的5 羟色胺水平增加。为了评价在免疫反应中大鼠下丘脑5 羟色胺释放效应,本文应用氯苯丙胺(PCA)选择性预先耗竭5 羟色胺释放,并测定这些动物在注射血蓝蛋白后抗体产生情况。结果显示在应用氯苯丙胺预处理的血蓝蛋白免疫动物特异抗体IgM和IgG与未用氯苯丙胺预处理的动物比较均有明显增加(P<0.01)。上述资料表明,对于T 细胞依赖抗原,其初始抗体产生的量是由位于下丘脑5 羟色胺神经终端抑制性递质释放所调节。     

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.     

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.     

Changes in hypothalamic preproenkephalin A mRNA following stress and opiate withdrawal

The median eminence of the pituitary is rich in opioid receptors, and exogenous opioids have major effects on the release of adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), prolactin, growth hormone (GH) and thyrotropin. Stress results in similar changes in anterior pituitary hormone secretion. Enkephalin immunoreactivity has been reported in the medial parvocellular neurons of the hypothalamic paraventricular nucleus which project to the median eminence, the site where hypothalamic releasing factors are secreted into the portal blood and thence to the anterior pituitary gland. The endocrine response to stressful stimuli might therefore, at least in part, be mediated through the activation of hypothalamic enkephalinergic neurons. We show that two stressful stimuli, opiate withdrawal and intraperitoneal injection of hypertonic saline, both result in very rapid and marked increases in enkephalin mRNA in the parvocellular paraventricular nucleus. The activation of hypothalamic enkephalin neurons may be important in the neuroendocrine response to stress.     

Effect of nocistatin in pain modulation

Using tail-flick latency as the nociceptive index and von Frey hair to measure the mechanical allodynia, the aim of the present study is to determine whether nocistatin, injected intracerebroventricularly (i.c.v.), would reverse the anti-morphine effect of orphanin FQ (OFQ), and, injected i.c.v. or intrathecally (Lt.), would inhibit the mechanical allodynia in a L5 and L6 spinal nerve ligation model of neuropathic pain in rats. The results show that i.c.v. injection of nocistatin produces no significant changes in the TFL, nor does it affect morphine analgesia. In addition, i.c.v. or i.t. nocistatin produces no significant changes in withdrawal threshold of the nerve-lesioned hind paw. However, nocistatin significantly reverses the antagonistic effect of OFQ on morphine analgesia when it was coinjected i.c.v. with OFQ. The results suggest that nocistatin can reverse the anti-morphine effect of OFQ in rat brain, but cannot inhibit the mechanical allodynia of neuropathic pain in rat brain and spinal cord.     

Leptin activates anorexigenic POMC neurons through a neural network in the arcuate nucleus

The administration of leptin to leptin-deficient humans, and the analogous Lepob/Lepob mice, effectively reduces hyperphagia and obesity. But common obesity is associated with elevated leptin, which suggests that obese humans are resistant to this adipocyte hormone. In addition to regulating long-term energy balance, leptin also rapidly affects neuronal activity. Proopiomelanocortin (POMC) and neuropeptide-Y types of neurons in the arcuate nucleus of the hypothalamus are both principal sites of leptin receptor expression and the source of potent neuropeptide modulators, melanocortins and neuropeptide Y, which exert opposing effects on feeding and metabolism. These neurons are therefore ideal for characterizing leptin action and the mechanism of leptin resistance; however, their diffuse distribution makes them difficult to study. Here we report electrophysiological recordings on POMC neurons, which we identified by targeted expression of green fluorescent protein in transgenic mice. Leptin increases the frequency of action potentials in the anorexigenic POMC neurons by two mechanisms: depolarization through a nonspecific cation channel; and reduced inhibition by local orexigenic neuropeptide-Y/GABA (gamma-aminobutyric acid) neurons. Furthermore, we show that melanocortin peptides have an autoinhibitory effect on this circuit. On the basis of our results, we propose an integrated model of leptin action and neuronal architecture in the arcuate nucleus of the hypothalamus.     

Characterization of cDNA and genomic clones encoding the precursor to rat hypothalamic growth hormone-releasing factor

Growth hormone-releasing factor (GHRF) is a hypothalamic peptide which positively regulates the synthesis and secretion of growth hormone in the anterior pituitary. The amino-acid sequence of a 43-residue GHRF peptide isolated from rat hypothalamus was recently determined. Immunocytochemical techniques have been used to localize GHRF-containing cell bodies and nerve fibres largely to the medial-basal region of the rat hypothalamus. The rat has also been used extensively as an animal model to study the effects of GHRF on growth hormone synthesis and secretion and on somatic growth. To pursue questions concerning the biosynthesis of GHRF, the expression of the ghrf gene, and its regulation in the hypothalamus by neural and hormonal influences, we have now isolated and characterized both complementary DNA and genomic clones encoding rat hypothalamic GHRF. The rat ghrf gene spans nearly 10 kilobases (kb) of rat genomic DNA, contains 5 exons and encodes a 104-amino-acid precursor to the rat GHRF peptide. Comparison with previously characterized human ghrf cDNA and genomic clones has allowed patterns of conservation of amino-acid and nucleotide sequences between the human and rat GHRFs to be determined.     

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.     

精氨酸加压素免疫阳性神经元在中菊头蝠(Rhinolophus affinis)脑中的分布

精氨酸加压素(arginine vasopressin,AVP)属于垂体后叶激素家族,它与神经内分泌的调节、心血管功能的调节、血压调节、学习和记忆以及生殖等生理功能密切相关.AVP在不同哺乳动物中枢神经系统内的分布方式和传输路径存在明显差异.本实验采用免疫组织化学ABC法系统观察了AVP免疫阳性神经元和免疫阳性神经纤维在中菊头蝠(Rhinolophus affinis)脑中的形态特征和分布特点.结果显示AVP免疫阳性神经元和免疫阳性神经纤维明显可见于中菊头蝠下丘脑室旁核、视上核、视交叉上核、下丘脑外侧区、正中隆起和垂体后叶,其细胞形态与其它哺乳动物相应结构的细胞特征类似,提示AVP神经元在哺乳动物下丘脑中的分布具有高度的保守性,AVP在中菊头蝠下丘脑可能有着与其它哺乳动物类似的功能.室周视前区、终纹床核和前脑外侧束也有少量AVP免疫阳性(immunoreactive arginine-vasopressin,AVP-ir)神经元分布,而在海马、隔核、杏仁核和侧间隔等边缘核团没有发现与大鼠等哺乳动物相应结构类似的分布,这可能与蝙蝠的视觉退化有关.     

运动与瘦素的研究进展

瘦素（ leptin）是脂肪组织分泌的一种蛋白质类激素,主要作用在下丘脑,具有调节体脂代谢、能量平衡等功能,瘦素水平的高低对肥胖、2-型糖尿病等疾病起到调节作用。血清瘦素可通过血脑屏障与下丘脑的瘦素受体结合,激活 JAK2-STAT3等信号转导通路,进而改变中枢神经系统中一系列神经肽的表达。通过收集大量近年来关于不同运动形式、运动强度、运动时间等情况对血浆瘦素水平影响的文献,总结分析出一次性运动、非一次性运动对血浆瘦素水平和能量代谢的影响,以及目前研究存在的问题,加深对瘦素功能和机理的分子水平认知,并展望了今后的研究前景。