Effects of "Bioactive" amino acids leucine, glutamate, arginine and tryptophan on feed intake and mRNA expression of relative neuropeptides in broiler chicks

ABSTRACT: Feed intake control is vital to ensuring optimal nutrition and achieving full potential for growth and development in poultry. The aim of the present study was to investigate the effects of L-leucine, L-glutamate, L-tryptophan and L-arginine on feed intake and the mRNA expression levels of hypothalamic Neuropeptide involved in feed intake regulation in broiler chicks. Leucine, glutamate, tryptophan or arginine was intra-cerebroventricularly (ICV) administrated to 4d-old broiler chicks respectively and the feed intake were recorded at various time points. Quantitative PCR was performed to determine the hypothalamic mRNA expression levels of Neuropeptide Y (NPY), agouti related protein (AgRP), pro-opiomelanocortin (POMC), melanocortin receptor 4 (MC4R) and corticotrophin releasing factor (CRF). Our results showed that ICV administration of L-leucine (0.15 or 1.5 mumol) significantly (P < 0.05) increased feed intake up to 2 h post-administration period and elevated both hypothalamic NPY and AgRP mRNA expression levels. In contrast, ICV administration of L-glutamate (1.6 mumol) significantly (P < 0.05) decreased feed intake 0.25, 0.5 and 2 h post-injection, and increased hypothalamic CRF and MC4R mRNA expression levels. Meanwhile, both L-tryptophan (10 or 100 mug) and L-arginine (20 or 200 mug) had no significant effect on feed intake. These findings suggested that L-leucine and L-glutamate could act within the hypothalamus to influence food intake, and that both orexigenic and anorexigenic Neuropeptide genes might contribute directly to these effects.     

动物食欲调节的中枢信号通路

下丘脑是动物食欲调节的中枢，外周食欲信号在下丘脑中经食欲调节网络整合，产生饱感或饥饿。其中，以 ５′－磷酸腺苷激活的蛋白激酶（ＡＭＰＫ）调控位点上的 ＡＭＰＫ-ＡＣＣ-ＣＰＴ１和 ＵＣＰ２-ＦＯＸＯ１-ｐＣＲＥＢ信号通路以及雷帕霉素靶蛋白（ｍＴＯＲ）调控位点上的 ＰＩ３Ｋ-Ａｋｔ-ｍＴＯＲ和 ｍＴＯＲ-４ＥＢＰ１／ｐ７０Ｓ６Ｋ-ＮＰＹ／ＡｇＲＰ信号通路尤为重要。ＡＭＰＫ和 ｍＴＯＲ在 ＡＭＰＫ-ＴＳＣ ｍＴＯＲ通路、固醇类调节因子绑定蛋白（ＳＲＥＢＰ）基因表达和吞噬启动激酶（Ｕｌｋ１）活性通路上存在互作。外周营养和能量信号传输到下丘脑后，经过这些网络的传输和分析，作用于下丘脑中的食欲相关肽，最终调控动物的采食行为。     

下丘脑-垂体-肾上腺轴参与动物采食调控的研究进展

采食是动物维持生命活动的基本生理过程，是动物生长发育的基础。畜禽采食量的高低直接影响到营养物质的摄入量及生产性能的发挥。在畜牧业生产中，影响采食的因素很多，而应激是其中一个非常重要的影响因素。动物机体的应激反应主要由下丘脑-垂体-肾上腺（HPA）轴来调控。下丘脑、垂体和肾上腺皮质通过释放促肾上腺皮质激素释放激素（CRH）、促肾上腺皮质激素（ACTH）和糖皮质激素（GC）这3种应激激素来协同调控动物的应激反应。应激激素对采食行为的调节是一个非常复杂的过程，主要通过稳态和非稳态途径来调节采食，可以双向调控食物的摄入量。稳态途径指的是通过调控机体能量稳态而调控采食。CRH和ACTH通过抑制下丘脑促食欲肽的表达而抑制采食；而GC在中枢和外周发挥着完全相反的作用。非稳态途径指的是通过影响中脑奖赏系统调控采食的愉悦感，是近年来食欲调控研究的热点，越来越多的研究证明了应激激素与奖赏系统的联系。作者针对应激激素调控采食的最新研究报道进行综述，以期为生产实践中新型的采食调控技术研发提供一定的参考。     

Distribution of orexin B and its relationship with GnRH in the pig hypothalamus

Increasing evidence suggests that orexins--hypothalamic neuropeptides--act as neurotransmitters or neuromediators in the brain, regulating autonomic and neuroendocrine functions. Orexins are closely associated with gonadotropin-releasing hormone (GnRH) neurons in the preoptic area and alter luteinizing hormone (LH) release, suggesting that they regulate reproduction. Here, we investigated the distribution of orexin B (immunohistochemical technique) and the relationship between orexin B and GnRH containing fibres and neurons in the pig hypothalamus using double immunofluorescence and laser-scanning confocal microscopy. Orexin B immunoreactive neurons were mainly localized in the perifornical area (PeF), dorsomedial hypothalamic nucleus (DMH), zona incerta (ZI) and the posterior hypothalamic area (PH), with a sparser distribution in the preoptic and anterior hypothalamic area. Immunoreactive fibres were distributed throughout the central nervous system. Approximately 30% GnRH neurons were in close contact with orexin B immunoreactive fibres, among these approximately 6% of GnRH neurons co-localized with orexin B perikarya in the region between the caudal preoptic area and the anterior hypothalamic area. Orexin B may regulate reproduction by altering LH release in the hypothalamus.     

A rat model for the energetic regulation of gonadotropin secretion: role of the glucose-sensing mechanism in the brain

Energy availability has been considered to regulate gonadal activity by modulating the release of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) at various reproductive phases, such as lactation and puberty in domestic as well as wild animals. Experimental models with rats and sheep have demonstrated that fasting or glucoprivation suppresses pulsatile LH release. From those experiments, the information on energy deficiency is considered to be detected by specific central sensors and conveyed to the hypothalamus to regulate LH release as well as food intake. Noradrenergic neurons, originating in the medulla oblongata and projecting to the hypothalamic paraventricular nucleus (PVN), is reported to be one of the pathways mediating the response of LH release to energy deficiency. The other component is considered to be an energy-sensing mechanism in the brain. Glucose or other oxidizable fuels may function as a metabolic signal to regulate LH release. Previous studies suggest the presence of a glucose-sensing mechanism in the rat hindbrain. From our previous results in the rat, the ependymocytes lining the wall of the cerebroventricle could possibly serve as a glucose sensor to regulate GnRH/LH release. Greater understanding of the nature of the energy-sensing mechanism in the brain will contribute to the nutritional manipulation of reproductive performance in domestic animals in various conditions.     

Short‐term ingestion of deoxynivalenol in naturally contaminated feed alters piglet performance and gut hormone secretion

The mycotoxin deoxynivalenol (DON) generally exists in cereals and affects human and animal health. The aim of this study is to analyze the impacts of DON in naturally contaminated feed on piglet growth performance and intestinal hormone secretion in the short term. We randomly divided 5‐week‐old piglets into four groups: Control, DON 1,000, DON 2,000 and DON 3,000 groups. Piglets received a feed naturally contaminated with DON (approximately 400, 1,000, 2,000 or 3,000 μg/kg) for 21 days. Body weight showed no significant difference following exposure to DON. The balance of anti‐oxidation and oxidation was disrupted by DON after 21 days. The concentration of tumor necrosis factor‐alpha (TNF‐α) and cyclooxgenase‐2 (COX‐2) significantly increased (p < .001) in all DON‐treated groups. Gut anorexigenic hormone secretion of peptide YY (PYY) and cholecystokinin (CCK) had a time‐ and dose‐dependent relationship with DON exposure; however, there was no effect on orexigenic hormone ghrelin secretion. Changes of histomorphology in the jejunum were observed in DON‐treated groups, including villi flattening and fusion, and apical necrosis of villi. These results indicated that DON could suppress piglet growth performance and alter gut hormone secretion in the short term.     

胃泌酸调节素研究进展

胃泌酸调节素(OXM)是由小肠L细胞分泌的一种肽类激素,它能够透过血脑屏障到达下丘脑弓状核,与其特异性受体结合后发出饱感信号终止动物进食.胃泌酸调节素对动物食欲的调节和内环境稳态的稳定,是通过抑制胃酸分泌、降低采食量、增加能量消耗及动员脂肪分解等生物学功能实现的.论文综述了近年来国内外学者对胃泌酸调节素在来源及结构、生物学功能和作用机理3个方面的研究成果,并阐述了对其进行进一步研究的发展方向.     

食物摄入与下丘脑能量平衡

能量平衡（energy balance）是能量摄入与能量消耗相平衡的过程。动物机体在处于能量平衡时才能维持正常的生命活动。下丘脑中的多个与摄食相关的神经核团，在神经和体液的调节下发挥关键作用，并构成了复杂而精密的神经网络。本文将从影响下丘脑能量平衡的神经核团、神经肽、神经投射和外周激素等方面，对食物摄入与下丘脑能量平衡进行论述。     

妊娠期奶山羊下丘脑GnRH和OT免疫反应双标记细胞的分布

为了探讨促性腺激素释放激素（GnRH）和催产素（OT）是否在下丘脑细胞中共存,采用免疫组织化学双标记法对妊娠期奶山羊下丘脑中GnRH与OT的分布进行了检测。结果显示：室旁核、视上核、视前交叉上核、弓状核、下丘脑外侧区、乳头体内侧核、乳头体后核等核团（区）有GnRH和OT免疫反应双标记细胞,在妊娠的不同时期,GnRH和OT免疫反应双标记细胞数量有显著差异。这些结果为GnRH与OT相互调节提供了形态学证据。     

Central role of the melanocortin-4 receptors in appetite regulation after endotoxin

Melanocortin-4 receptors (MC4R) are key factors in the depression of appetite during disease. This study was designed to determine the role of agouti-related protein (AgRP) in the effect of endotoxin (lipopolysaccharide, LPS) on appetite. Sheep received an intracerebroventricular injection of either saline or AgRP (0.5 nmol/kg of BW) 1 h before intravenous injection of either saline or LPS (0.6 microg/kg of BW) at time 0 and again at 4 h. Agouti-related protein prevented the reduction in feed intake due to LPS (P < 0.05). In a second experiment, AgRP gene expression was unaffected at 3 h and increased (P < 0.01) at 6 h after LPS. Immunohistochemical evidence indicated that there was an increase in the percentage of AgRP neurons with c-Fos immunoreactive nuclei 6 h after sheep were injected with LPS (P < 0.04) and a corresponding decrease in a-melanocyte-stimulating hormone neurons coexpressing c-Fos (P < 0.001). In situ hybridization provided evidence for an increase in AgRP gene expression and a decrease in proopiomelanocortin gene expression 6 h after LPS (P < 0.05). In a final experiment, physiological elevation of orexigenic agents by short-term fasting kept feed intake at the same level as controls, in spite of the presence of LPS, similar to the effects of AgRP in Exp. 1. The AgRP inhibition of the MC4R prevents appetite inhibition in response to LPS and well after LPS inhibition of feed intake, both AgRP and a-melanocyte-stimulating hormone may change in a pattern that favors appetite increases. These studies support the notion of the MC4R as a critical component of the mechanism for appetite suppression due to endotoxin.     

Mechanisms controlling feed intake in ruminants: a review

The purpose of this paper is to review our understanding of the involvement of central and peripheral factors in the control of feed intake in ruminants. The regulation of body weight under various states of energy need depends on an animal's ability to control feed intake to meet these needs. In the central nervous system (CNS), the ventromedial and lateral hypothalamus appear to be the areas involved in satiety and hunger, respectively; other important areas are the paraventricular nucleus and rostral brain areas. Intracerebroventricular injection of neurotransmitters, alpha- and beta-adrenergic agonists, 5-hydroxytryptamine and gamma aminobutyric acid (GABA) agonists, has stimulated feeding in ruminants; intravenous administration of benzodiazepines stimulated feed intake in sheep and cattle, possibly by increasing GABA levels in the brain. Neuropeptides of the opioid and cholecystokinin families have reciprocal hunger-stimulating and satiety-eliciting effects when administered centrally in sheep. Further, concentrations of these neuropeptides in specific areas of the hypothalamus have been shown to change with the state of hunger-satiety of sheep. In the periphery, none of the hormones associated with the pituitary, adrenal gland, pancreas or gastrointestinal tract has been shown to have significant effects on the control of feed intake. In addition, the physical properties of the ingested feed in the gastrointestinal tract, while possibly influencing the rate or pattern of feeding, do not appear to be primary factors in the control of feed intake under many feeding conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recent advances in the central control of intake in ruminants.

Neuropeptide Y (NPY) is a strong stimulant of feed intake in sheep as well as in rodents. The information available indicates that it functions in vivo in the modulation of feeding within the central nervous system, more specifically, within the hypothalamus, and probably within the paraventricular nucleus. Injected NPY can override a variety of satiating factors, including those arising from normal feed intake, artificial distension of the reticulorumen, and intraruminal infusion of sodium propionate. Even so, these satiating factors are able to reduce feeding in the face of at least one dosage of exogenous NPY. Neuropeptide Y has specificity in regard to ingestive behavior in rats. It stimulates feeding and drinking but does not alter grooming behavior. It also preferentially enhances carbohydrate appetite. The possibility that specific appetites are influenced by NPY has not been investigated in ruminants. Finally, further investigations of NPY should enhance our knowledge of feed intake and energy balance regulation and its linkage with reproductive physiology.     

Distribution of the androgen receptor in the diencephalon and the pituitary gland in goats: Co-localisation with corticotrophin releasing hormone, arginine vasopressin and corticotrophs

Previously it has been shown that androgen suppresses transportation-induced increases in plasma adrenocorticotropic hormone (ACTH), possibly by suppressing the secretion of corticotrophin releasing hormone (CRH) or arginine vasopressin (AVP) from the hypothalamus, or secretion of ACTH from the pituitary gland. The aim of the present study was to examine androgen target sites in the caprine diencephalon and pituitary gland using immunohistochemical methods. The androgen receptor (AR) was expressed strongly in the bed nucleus of the stria terminalis, the medial preoptic area, the arcuate nucleus, the ventromedial hypothalamic nucleus and the suprachiasmatic nucleus in the diencephalon. Between 8% and 11% of CRH and AVP neurons in the paraventricular hypothalamic nucleus (PVN) expressed AR. In the pituitary gland, 7.1% of corticotrophs expressed AR. The results are consistent with the proposal that androgen acts directly and indirectly on CRH and/or AVP neurons in the PVN. The possibility of a direct action of androgen on the corticotrophs in the pituitary gland was also considered.     

Orexin‐B‐like immunoreactivity in pituitary αMSH‐producing cells and median eminence GnRH‐containing fibres of the flat‐tailed house gecko

We examined the distribution of the orexin‐like peptides in the pituitary and median eminence of the flat‐tailed house gecko (Hemidactylus platyurus) using immunohistochemistry. Orexin‐B‐like, but not orexin‐A‐like, immunoreactivity was detected in the pituitary, specifically in the pars intermedia, and these cells corresponded to alpha‐melanocyte‐stimulating hormone (αMSH)‐producing cells. Orexin‐B and αMSH secreted from pars intermedia may modulate secretion of adenohypophyseal cells in the pars distalis. In the median eminence, orexin‐B‐immunoreactive puncta and fibres were observed, and these structures corresponded to gonadotropin‐releasing hormone (GnRH)‐immunoreactive puncta and fibres. Orexin‐B secreted from GnRH‐containing neurons in the hypothalamus may affect thyrotropin‐releasing hormone‐containing neurons resulting in modulation of αMSH secretion of melanotrophs in the pars intermedia.     

Cortisol treatment reduces ghrelin signaling and food intake in tilapia, Oreochromis mossambicus

It is well known that after a stressor, levels of plasma cortisol rise, inducing physiological changes within the animal that are directed toward maintaining homeostasis. Less well understood is the role of cortisol in regulating food intake in teleosts. This study investigated the effect of cortisol on food intake and regulation of the neuroendocrine appetite-stimulating hormones, neuropeptide Y (NPY) and ghrelin, in tilapia (Oreochromis mossambicus). Male and female tilapia were randomly assigned to one of the following treatments: unhandled control, vehicle-injected control, or cortisol (2 μg/g BW). Food intake was determined 24 h after injection during a 1-h feeding trial. Cortisol reduced food intake (P < 0.001). An identical study was conducted to measure the effects of 24-h cortisol treatment on the endocrine regulators of food intake. Cortisol reduced stomach expression of ghrelin mRNA (P < 0.05) and plasma concentrations of ghrelin (P < 0.05). In the hypothalamus/optic tectum cortisol reduced levels of GHSR1a-LR (biologically active ghrelin receptor) mRNA. In the telencephalon/preoptic area cortisol significantly reduced levels of NPY and GHSR1b-LR (biologically inactive ghrelin receptor) mRNA. These findings suggest that anorexigenic actions of cortisol may be mediated via two separate pathways: (1) reducing circulating ghrelin levels as well as GHSR1a-LR expression in the hypothalamus/optic tectum and/or (2) suppressing NPY expression in the telencephalon/preoptic area.     

A test of the lipostat theory in a seasonal (ovine) model under natural conditions reveals a close relationship between adiposity and melanin concentrating hormone expression

A study was undertaken in Corriedale ewes to test the lipostat theory using data obtained from a model of seasonal change in food intake and body composition. The theory predicts adipose-derived factors signal to the brain and vice versa, to maintain homeostasis. It is held that leptin acts on cells in the brain to regulate food intake and energy expenditure, through “first order” neurons in the arcuate nucleus (ARC). These cells are thought to receive information that is relayed to “second order” neurons, to regulate food intake and other functions. In this study, groups (n = 4–5) of ovariectomized ewes were maintained under natural conditions and sampled at various points across the year. Food intake, body composition and indices of metabolic function were measured prior to collection of brains for in situ hybridization analysis. Expression of genes encoding for neuropeptide Y (NPY), pro-opiomelanocortin (POMC), orexin (ORX), melanin concentrating hormone (MCH) and leptin receptor (ObRb) was quantified. NPY gene expression was high when food intake was also high but, across the year, changes in NPY and POMC gene expression did not correspond predictably to plasma leptin levels or leptin receptor gene expression. Negative correlation was found between adiposity (omental and whole body fat) and gene expression of MCH and ORX, suggesting that changes in expression of genes for “second order” orexigenic peptides are closely linked to changes of metabolic state, even when similar relationships cannot be shown for expression of genes in “first order” neurons. These data provide support for the lipostat theory.     

Correlation analysis of hypothalamic mRNA levels of appetite regulatory neuropeptides and several metabolic parameters in 28‐day‐old layer chickens

Various lines of evidence suggest that appetite‐related neuropeptides in the hypothalamus are regulated by adiposity signals such as leptin and insulin in mammals. In the present study, we examined age‐dependent changes in the weight of abdominal fat and hypothalamic mRNA levels of neuropeptide Y (NPY, an orexigenic neuropeptide) and proopiomelanocortin (POMC, a precursor of anorexigenic neuropeptides) in growing chickens at 7, 14, 21 and 28 days of age. Hypothalamic NPY mRNA levels were significantly (P < 0.05) decreased after 14 days of age, whereas hypothalamic POMC mRNA levels were significantly (P < 0.05) increased at 28 days of age. The percentage of abdominal fat was significantly increased after 14 days of age in chickens. We next examined the correlation of hypothalamic NPY and POMC mRNA levels and several parameters at 28 days of age. There were no significant correlations between hypothalamic mRNA levels of NPY or POMC and the percentage of abdominal fat. These findings suggest that the gene expressions of NPY and POMC do not depend on adiposity in chickens, at least in 28‐day‐old layer chickens.     

Effect of capsaicin on cholecystokinin and neuropeptide Y expressions in the brain of high-fat diet fed rats

Capsaicin, one of the pungent principles of hot pepper, has been reported to cause a cessation of increases in body weight and fat gain induced by high-fat feeding. Especially, in body weight and feeding control, cholecystokinin (CCK) has been well known as a satiety signal and neuropeptide Y (NPY) has been described as one of the most potent orexigenic signals. This study was carried out to investigate the effect of capsaicin on CCK- and NPY- immunoreactivities (IR) in the brain of high-fat fed rats. The animals were divided into normal-fat diet (NF), high-fat diet (HF) and high-fat diet containing capsaicin (HF-CAP) groups. Mean body weight gain (MBWG) of HF group was higher than that of NF group. However, in HF-CAP group, MBWG was lower than that of HF group. CCK-IR in suprachiasmatic nucleus (SCN), paraventricular nucleus (PVN), median eminence (ME), arcuate nucleus (ARC) and amygdala was not prominent in all the groups. In cerebral cortex, CCK-IR was more reduced in HF-CAP group than in the other groups. In the HF-CAP group, NPY-IR in the hypothalamic nuclei, amygdala and cerebral cortex was more poorly found than in the NF and HF groups. It is concluded that (1) NPY-IR may react more sensitively on capsaicin than CCK-IR, (2) no rapid increase of body weight in capsaicin treated rats may result from the diminished food intake through the low expression of NPY in hypothalamus in HF-CAP group.     

Neuroendocrine mechanism mediating energetic regulation of gonadotropin release in female rats

Energy level is a critical factor controlling gonadal activity at various phases of reproduction. A female rat model has revealed that fasting‐induced luteinizing hormone (LH) suppression is mediated by a specific neural pathway, such as noradrenergic neurons originating in the A2 region and projecting to the hypothalamic paraventricular nucleus and corticotropin‐releasing hormone neurons. The pathway is shared with that mediating glucoprivic suppression of LH pulses. Among the peripheral signals altered by energy deficiency, glucose could be a signal molecule conveying the peripheral information to the brain to regulate feeding and gonadotropin‐releasing hormone/LH release through the noradrenergic pathway during undernutrition. The brain detects the energy availability to control feeding and reproductive function at various phases of an animal’s life. It is most likely that the central glucose‐sensing mechanism could be similar to the pancreatic one, involving a glucokinase‐mediated process to detect glucose availability. Further studies are needed to elucidate the mechanism integrating the energy signals.