Evidence that hypothalamic neurotensin signals leptin effects on feeding behavior in normal and fat-preferring rats

Neurotensin is an anti-thermogenic peptide produced by lymphatic endothelial cells

The lymphatic vasculature plays important roles in the physiology of the organs in which it resides, though a clear mechanistic understanding of how this crosstalk is mediated is lacking. Here, we performed single-cell transcriptional profiling of human and mouse adipose tissue and found that lymphatic endothelial cells highly express neurotensin (NTS/Nts). Nts expression is reduced by cold and norepinephrine in an α-adrenergic-dependent manner, suggesting a role in adipose thermogenesis. Indeed, NTS treatment of brown adipose tissue explants reduced expression of thermogenic genes. Furthermore, adenoviral-mediated overexpression and knockdown or knockout of NTS in vivo reduced and enhanced cold tolerance, respectively, an effect that is mediated by NTSR2 and ERK signaling. Inhibition of NTSR2 promoted energy expenditure and improved metabolic function in obese mice. These data establish a link between adipose tissue lymphatics and adipocytes with potential therapeutic implications.

Emerging Signaling Pathway in Arcuate Feeding-Related Neurons: Role of the Acbd7

The understanding of the mechanisms whereby energy balance is regulated is essential to the unraveling of the pathophysiology of obesity. In the last three decades, focus was put on the metabolic role played by the hypothalamic neurons expressing proopiomelanocortin (POMC) and cocaine and amphetamine regulated transcript (CART) and the neurons co-localizing agouti-related peptide (AgRP), neuropeptide Y (NPY), and gamma-aminobutyric acid (GABA). These neurons are part of the leptin-melanocortin pathway, whose role is key in energy balance regulation. More recently, the metabolic involvement of further hypothalamic uncharacterized neuron populations has been suggested. In this review, we discuss the potential homeostatic implication of hypothalamic GABAergic neurons that produce Acyl-Coa-binding domain containing protein 7 (ACBD7), precursor of the nonadecaneuropeptide (NDN), which has recently been characterized as a potent anorexigenic neuropeptide capable of relaying the leptin anorectic/thermogenic effect via the melanocortin system.

The role of food intake regulating peptides in cardiovascular regulation

Obesity is a risk factor that worsens cardiovascular events leading to higher morbidity and mortality. However, the exact mechanisms of relation between obesity and cardiovascular events are unclear. Nevertheless, it has been demonstrated that pharmacological therapy for obesity has great potential to improve some cardiovascular problems. Therefore, it is important to determine the common mechanisms regulating both food intake and blood pressure. Several hormones produced by peripheral tissues work together with neuropeptides involved in the regulation of both food intake and blood pressure. Anorexigenic (food intake lowering) hormones such as leptin, glucagon-like peptide-1 and cholecystokinin cooperate with α-melanocyte-stimulating hormone, cocaine- and amphetamine-regulated peptide as well as prolactin-releasing peptide. Curiously their collective actions result in increased sympathetic activity, especially in the kidney, which could be one of the factors responsible for the blood pressure increases seen in obesity. On the other hand, orexigenic (food intake enhancing) peptides, especially ghrelin released from the stomach and acting in the brain, cooperates with orexins, neuropeptide Y, melanin-concentrating hormone and galanin, which leads to decreased sympathetic activity and blood pressure. This paradox should be intensively studied in the future. Moreover, it is important to know that the hypothalamus together with the brainstem seem to be major structures in the regulation of food intake and blood pressure. Thus, the above mentioned regions might be essential brain components in the transmission of peripheral signals to the central effects. In this short review, we summarize the current information on cardiovascular effects of food intake regulating peptides.

To ingest or rest? Specialized roles of lateral hypothalamic area neurons in coordinating energy balance

Survival depends on an organism’s ability to sense nutrient status and accordingly regulate intake and energy expenditure behaviors. Uncoupling of energy sensing and behavior, however, underlies energy balance disorders such as anorexia or obesity. The hypothalamus regulates energy balance, and in particular the lateral hypothalamic area (LHA) is poised to coordinate peripheral cues of energy status and behaviors that impact weight, such as drinking, locomotor behavior, arousal/sleep and autonomic output. There are several populations of LHA neurons that are defined by their neuropeptide content and contribute to energy balance. LHA neurons that express the neuropeptides melanin-concentrating hormone (MCH) or orexins/hypocretins (OX) are best characterized and these neurons play important roles in regulating ingestion, arousal, locomotor behavior and autonomic function via distinct neuronal circuits. Recently, another population of LHA neurons containing the neuropeptide Neurotensin (Nts) has been implicated in coordinating anorectic stimuli and behavior to regulate hydration and energy balance. Understanding the specific roles of MCH, OX and Nts neurons in harmonizing energy sensing and behavior thus has the potential to inform pharmacological strategies to modify behaviors and treat energy balance disorders.

Peptides and food intake

The mechanisms for controlling food intake involve mainly an interplay between gut, brain, and adipose tissue (AT), among the major organs. Parasympathetic, sympathetic, and other systems are required for communication between the brain satiety center, gut, and AT. These neuronal circuits include a variety of peptides and hormones, being ghrelin the only orexigenic molecule known, whereas the plethora of other factors are inhibitors of appetite, suggesting its physiological relevance in the regulation of food intake and energy homeostasis. Nutrients generated by food digestion have been proposed to activate G-protein-coupled receptors on the luminal side of enteroendocrine cells, e.g., the L-cells. This stimulates the release of gut hormones into the circulation such as glucagon-like peptide-1 (GLP-1), oxyntomodulin, pancreatic polypeptides, peptide tyrosine tyrosine, and cholecystokinin, which inhibit appetite. Ghrelin is a peptide secreted from the stomach and, in contrast to other gut hormones, plasma levels decrease after a meal and potently stimulate food intake. Other circulating factors such as insulin and leptin relay information regarding long-term energy stores. Both hormones circulate at proportional levels to body fat content, enter the CNS proportionally to their plasma levels, and reduce food intake. Circulating hormones can influence the activity of the arcuate nucleus (ARC) neurons of the hypothalamus, after passing across the median eminence. Circulating factors such as gut hormones may also influence the nucleus of the tractus solitarius (NTS) through the adjacent circumventricular organ. On the other hand, gastrointestinal vagal afferents converge in the NTS of the brainstem. Neural projections from the NTS, in turn, carry signals to the hypothalamus. The ARC acts as an integrative center, with two major subpopulations of neurons influencing appetite, one of them coexpressing neuropeptide Y and agouti-related protein (AgRP) that increases food intake, whereas the other subpopulation coexpresses pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript that inhibits food intake. AgRP antagonizes the effects of the POMC product, α-melanocyte-stimulating hormone (α-MSH). Both populations project to areas important in the regulation of food intake, including the hypothalamic paraventricular nucleus, which also receives important inputs from other hypothalamic nuclei.

Loss of neurotensin receptor-1 disrupts the control of the mesolimbic dopamine system by leptin and promotes hedonic feeding and obesity

Neurons of the lateral hypothalamic area (LHA) control motivated behaviors such as feeding and ambulatory activity, in part by modulating mesolimbic dopamine (DA) circuits. The hormone, leptin, acts via the long form of the leptin receptor (LepRb) in the brain to signal the repletion of body energy stores, thereby decreasing feeding and promoting activity. LHA LepRb neurons, most of which contain neurotensin (Nts; LepRb(Nts) neurons) link leptin action to the control of mesolimbic DA function and energy balance. To understand potential roles for Nts in these processes, we examined mice null for Nts receptor 1 (NtsR1KO). While NtsR1KO mice consume less food than controls on a chow diet, they eat more and become obese when fed a high-fat, high-sucrose palatable diet; NtsR1KO mice also exhibit augmented sucrose preference, consistent with increased hedonic feeding in these animals. We thus sought to understand potential roles for NtsR1 in the control of the mesolimbic DA system and LHA leptin action. LHA Nts cells project to DA-containing midbrain areas, including the ventral tegmental area (VTA) and the substantia nigra (SN), where many DA neurons express NtsR1. Furthermore, in contrast to wild-type mice, intra-LHA leptin treatment increased feeding and decreased VTA Th expression in NtsR1KO mice, consistent with a role for NtsR1 signaling from LHA LepRb neurons in the suppression of food intake and control of mesolimbic DA function. Additionally, these data suggest that other leptin-regulated LHA neurotransmitters normally oppose aspects of Nts action to promote balanced responses to leptin.

Diverse roles of neurotensin agonists in the central nervous system

Neurotensin (NT) is a tridecapeptide that is found in the central nervous system (CNS) and the gastrointestinal tract. NT behaves as a neurotransmitter in the brain and as a hormone in the gut. Additionally, NT acts as a neuromodulator to several neurotransmitter systems including dopaminergic, sertonergic, GABAergic, glutamatergic, and cholinergic systems. Due to its association with such a wide variety of neurotransmitters, NT has been implicated in the pathophysiology of several CNS disorders such as schizophrenia, drug abuse, Parkinson's disease (PD), pain, central control of blood pressure, eating disorders, as well as, cancer and inflammation. The present review will focus on the role that NT and its analogs play in schizophrenia, endocrine function, pain, psychostimulant abuse, and PD.

The role of neurotensin in physiologic and pathologic processes

PURPOSE OF REVIEW

Neurotensin is a 13-amino acid peptide found in the central nervous system central nervous system and the gastrointestinal tract. Since its initial discovery in 1973, neurotensin has been shown to play a role in a wide range of physiologic and pathologic processes throughout the body. Ongoing research efforts continue to clarify the role of neurotensin in various central nervous system and gastrointestinal processes, as well as how disruption of these normal mechanisms may lead to diseases ranging from schizophrenia to colorectal cancer. The goal of this review is to provide an overview of the most recent advances in the field of neurotensin research, in the context of what has been previously published.

RECENT FINDINGS

Because of the seemingly unrelated functions of neurotensin in the central nervous system and the periphery, the scope of the articles reviewed is rather broad. Contributions continue to be made to our understanding of the downstream effects of neurotensin signaling and the complex feedback loops between neurotensin and other signaling molecules. By selective targeting or blockade of specific neurotensin receptors, investigators have identified potential drugs for use in the treatment of schizophrenia, alcoholism, chronic pain, or cancer. Neurotensin-based pharmacologic agents are being used successfully in animal models for a number of these conditions.

SUMMARY

The review highlights the wide array of biological processes in which neurotensin has a role, and summarizes the most recent advances in various fields of neurotensin research. The knowledge gained through this research has led to the development of first-in-class drugs for the treatment of various medical conditions, and it is clear that in the coming years some of these agents will be ready to move from the bench to the bedside in clinical trials.

The acute and subchronic effects of a brain-penetrating, neurotensin-1 receptor agonist on feeding, body weight and temperature

The neurotensin-1 (NT1) receptor has been implicated in mediating a number of important neurotensin effects. We have found that PD149163, a selective, brain-penetrating, NT1 receptor agonist, produces a number of therapeutic-like preclinical effects after peripheral administration including pro-cognitive, antipsychotic and anxiolytic effects. In this study, we investigated PD149163's effect on food intake and thermal regulation, two physiological processes thought to be mediated by NT1 receptors. Brown Norway rats and leptin-deficient mice (ob/ob) mice were administered subcutaneous PD149163 (0, 0.1, 0.25, or 1 mg/kg) for ten consecutive days. Weight and 24-h food intake were measured in mice and rats and core body temperature was also measured in rats. PD149163 significantly decreased food intake in rats and ob/ob mice and no tolerance was demonstrated to this effect over the course of the study. PD149163-treated animals exhibited weight loss compared to saline-treated animals. PD149163 produced hypothermia as expected but this effect did show tolerance over the course of the study, unlike feeding. The results suggest that NT1 receptor agonists are candidates for treatment of obesity and that somewhat different mechanisms are involved in NT1-induced feeding regulation and temperature regulation.

Hormonal regulation of clonal, immortalized hypothalamic neurons expressing neuropeptides involved in reproduction and feeding

The hypothalamus has been particularly difficult to study at the molecular level because of the inherent cellular heterogeneity and complexity of neuronal circuits within. We have generated a large number of immortalized, clonal cell lines through retroviral gene transfer of the oncogene SV40 T-Ag into primary murine hypothalamic neuronal cell cultures. A number of these neuronal cell lines express neuropeptides linked to the control of feeding behavior and reproduction, including neuropeptide Y (NPY) and neurotensin (NT). We review recent studies on the direct regulation of NPY gene expression by estrogen, and the leptin-mediated control of signal transduction pathways and NT transcription. These studies provide new insights into the direct control of neuropeptide synthesis by hormones and nutrients at a mechanistic level in the individual neuron, not yet possible in the whole brain. Using these novel cell models, we expect to contribute substantially to the understanding of how individual neuronal cell types control overall endocrine function, especially with regard to two of the most well-known roles of distinct peptidergic neurons; these being the control of reproduction and energy homeostasis.

Role of neuropeptides in appetite regulation and obesity--a review

Obesity represents the most prevalent nutritional problem worldwide which in the long run predisposes to development of diabetes mellitus, hypertension, endometrial carcinoma, osteoarthritis, gall stones and cardiovascular diseases. Despite significant reductions in dietary fat consumption, the prevalence of obesity is on a rise and is taking on pandemic proportions. Obesity develops when energy intake exceeds energy expenditure over time. Recently, a close evolutionary relationship between the peripheral and hypothalamic neuropeptides has become apparent. The hypothalamus being the central feeding organ mediates regulation of short-term and long-term dietary intake via synthesis of various orexigenic and anorectic neuropeptides. The structure and function of many hypothalamic peptides (neuropeptide Y (NPY), melanocortins, agouti-related peptide (AGRP), cocaine and amphetamine regulated transcript (CART), melanin concentrating hormone (MCH), orexins have been characterized in rodent models The peripheral neuropeptides such as cholecystokinin (CCK), ghrelin, peptide YY (PYY3-36), amylin, bombesin regulate important gastrointestinal functions such as motility, secretion, absorption, provide feedback to the central nervous system on availability of nutrients and may play a part in regulating food intake. The pharmacological potential of several endogenous peripheral peptides released prior to, during and/or after feeding are being explored. Long-term regulation is provided by the main circulating hormones leptin and insulin. These systems implicated in hypothalamic appetite regulation provide potential targets for treatment of obesity which could potentially pass into clinical development in the next 5 years. This review summarizes various effects and interrelationship of these central and peripheral neuropeptides in metabolism, obesity and their potential role as targets for treatment of obesity.

Leptin signaling in neurotensin neurons involves STAT, MAP kinases ERK1/2, and p38 through c‐Fos and ATF1

The adipokine leptin signals energy status to the hypothalamus, which triggers a network of neuropeptide responses. Each hypothalamic cell type expresses a unique complement of neuropeptides, receptors, and second messengers; thus each likely responds specifically to peripheral hormones. We describe here the analysis of leptin signaling in a clonal population of mouse neurotensin (NT) -expressing hypothalamic neurons, N-39. Leptin induced phosphorylation of STAT3 and MAPK ERK1/2, but not the downstream effector of PI3K, Akt, and also induced c-Fos protein. We found activation of p38 MAPK by leptin, accompanied by phosphorylation of its downstream effector ATF-1. Phosphorylation of ATF-1 is blocked by the p38 MAPK inhibitor SB 203580. We linked this signaling directly to NT transcription. Protein binding analysis indicates that both ATF-1 and c-Fos are capable of binding to the mouse NT/N gene predominantly at physiological or high concentrations of leptin. The evidence indicates activation of distinct leptin signal transduction pathways that directly result in changes in NT gene expression and links these specific neurons to the control of energy homeostasis.

Anorexigenic hormones leptin, insulin, and alpha-melanocyte-stimulating hormone directly induce neurotensin (NT) gene expression in novel NT-expressing cell models

Neurotensin (NT) is implicated in the regulation of energy homeostasis, in addition to its many described physiological functions. NT is postulated to mediate, in part, the effects of leptin in the hypothalamus. We generated clonal, immortalized hypothalamic cell lines, N-39 and N-36/1, which are the first representative NT-expressing cell models available for the investigation of NT gene regulation and control mechanisms. The cell lines express the Ob-Rb leptin receptor neuropeptide Y (NPY)-Y1, Y2, Y4, Y5 receptors, melanocortin 4 receptor, insulin receptor, and the NT receptor. NT mRNA levels are induced by approximately 1.5-fold to twofold with leptin, insulin, and alpha-melanocyte stimulating hormone treatments but not by NPY. Leptin-mediated induction of NT gene expression was biphasic at 10(-11) and 10(-7) M. The leptin responsive region was localized to within -381 to -250 bp of the 5' regulatory region of the NT gene. Furthermore, we demonstrated direct leptin-mediated signal transducers and activators of transcription (STAT) binding to this region at 10(-11) m, but not 10(-7) m leptin, in chromatin precipitation assays. Leptin-induced NT regulation was attenuated by dominant-negative STAT3 protein expression. These data support the hypothesis that NT may have a direct role in the neuroendocrine control of feeding and energy homeostasis.

The effect of neurotensin on insulin-induced proliferation of human fibroblasts

Neurotensin has been shown to influence growth in a number of cancerous and non-cancerous cells and to enhance the proliferative effects of growth factors without itself inducing proliferation. Here we show that neurotensin potentiates the proliferative effects of insulin on IMR90 human fibroblasts in a concentration and neurotensin receptor type 1-dependent manner. This potentiating effect of neurotensin was blocked by inhibitors of phospholipase C and protein kinase C, was accompanied by an increase in the level of soluble inositol phosphates and did not involve an autocrine factor. These results show that neurotensin can enhance insulin-dependent proliferation of human fibroblasts and suggest a possible role for neurotensin in tissue growth and repair.

Minireview: A hypothalamic role in energy balance with special emphasis on leptin

The hypothalamus is a major site for integration of central and peripheral signals that regulate energy homeostasis. Within the hypothalamus, neurons residing in the ARC (arcuate nucleus)-PVN (paraventricular)-PF/LH (perifornical/lateral hypothalamus) axis communicate among each other and are subjected to the influence of several peripheral factors, including leptin and insulin. Proper signaling in the hypothalamus by leptin, a long-sought peripheral factor that relays the status of fat stores, is critical to normal regulation of food intake and body weight. Leptin action in the hypothalamus is mediated by a large number of orexigenic and anorectic peptide-producing neurons of the ARC-PVN-PF/LH axis. Not only the classical JAK2 (Janus kinase 2)-STAT3 (signal transducer and activator of transcription 3) pathway, but also the phosphatidylinositol-3 kinase-phosphodiesterase 3B-cAMP pathway mediates hypothalamic leptin receptor signaling. It appears that hypothalamic leptin resistance, possibly due to defective nutritional regulation of leptin receptor expression and/or reduced STAT3 signaling in the hypothalamus, contributes to the development of obesity associated with high-fat feeding and aging. Interestingly, hypothalamic neurons may develop leptin resistance despite an intact JAK2-STAT3 signaling path. The role of suppressor of cytokine signaling 3 and other negative regulators of leptin signaling in central leptin resistance needs to be established, an important area of future investigation. Further understanding of the neural circuitry and leptin signaling in the hypothalamus is critical not only for the advancement of our knowledge on the hypothalamic role in energy balance but also for future development of drugs for the attenuation or treatment of obesity and related disorders in humans.

Éléments de physiologie et de neurobiologie de la prise alimentaire

Many methods and techniques have accumulated a considerable mass of data about the mechanisms which control food intake and energetic loss. After a presentation of the main experimental approaches in this respect, the most relevant signals sent by peripheral organs to the central nervous system are presented: Glucose, triglycerides; from adipocytes: Leptin; from pancreas: Insulin, pancreatic polypeptide, amylin, enterostatin; from digestive tract: Ghrelin, cholecystokinin, peptide Y Y 3-36. Then are considered, especially at the hypothalamic level, their interpretation by neurones whose transmitters are either neuropeptides such as: Neuropeptide Y, Agouti Related Peptide, Cocaine/Amphetamine Regulated Transcript, Melanin Concentrating Hormone, alpha Melanocyte Stimulating Hormone, orexins/hypocretins, octadecaneuropeptide, nociceptin/orphanin FQ, opioid peptides, Interleukin 1, galanin, urocortin 2, Neurotrophic ciliary factor, or monoamines such as: Glutamate, dopamine, Norepinephrine, serotonine, GABA, histamine, acetylcholine. In a last part are considered the likely relationships existing between feeding, pleasure and addiction, centered on dopamine transmission in the nucleus accumbens. After this brief synopsis one should not be surprised that this so complex system which regulates feeding may be affected by various disorders; however one may be amazed by such a scarcity of drugs to influence it; in any case, many new pharmacological strategies can be expected in the future.

Leptin signaling in the hypothalamus: emphasis on energy homeostasis and leptin resistance

Leptin, the long-sought satiety factor of adipocytes origin, has emerged as one of the major signals that relay the status of fat stores to the hypothalamus and plays a significant role in energy homeostasis. Understanding the mechanisms of leptin signaling in the hypothalamus during normal and pathological conditions, such as obesity, has been the subject of intensive research during the last decade. It is now established that leptin action in the hypothalamus in regulation of food intake and body weight is mediated by a neural circuitry comprising of orexigenic and anorectic signals, including NPY, MCH, galanin, orexin, GALP, alpha-MSH, NT, and CRH. In addition to the conventional JAK2-STAT3 pathway, it has become evident that PI3K-PDE3B-cAMP pathway plays a critical role in leptin signaling in the hypothalamus. It is now established that central leptin resistance contributes to the development of diet-induced obesity and ageing associated obesity. Central leptin resistance also occurs due to hyperleptinimia produced by exogenous leptin infusion. A defective nutritional regulation of leptin receptor gene expression and reduced STAT3 signaling may be involved in the development of leptin resistance in DIO. However, leptin resistance in the hypothalamic neurons may occur despite an intact JAK2-STAT3 pathway of leptin signaling. Thus, in addition to defective JAK2-STAT3 pathway, defects in other leptin signaling pathways may be involved in leptin resistance. We hypothesize that defective regulation of PI3K-PDE3B-cAMP pathway may be one of the mechanisms behind the development of central leptin resistance seen in obesity.

Targeted inactivation of the neurotensin type 1 receptor reveals its role in body temperature control and feeding behavior but not in analgesia

Three subtypes of neurotensin receptor have been described, two members of the heptahelical transmembrane domain G protein-coupled receptor superfamily NT-1R and NT-2R, and NT-3R unrelated to this family. We have generated NT-1R deficient (NT-1R(-/-)) mice. NT-1R(-/-) mice were born at the expected Mendelian frequency without obvious abnormalities and they were fertile. The NT-induced analgesia on the writhing induced by phenyl-p-benzoquinone administration remained at wild-type levels in the NT-1R(-/-) mice demonstrating that the NT-1R is not implicated in the analgesic effect of NT in this test. The NT-1R(-/-) mice were hyperthermic; their body temperature was not affected by intracerebroventricular (i.c.v.) administration of NT, contrasting with the hypothermia induced in NT-1R(+/+) mice. NT-1R(-/-) mice showed a small significant increase in body weight compared to the NT-1R(+/+) congeners as early as 10 weeks after birth, correlated with a higher food intake. NT-1R(-/-) mice showed similar spontaneous locomotion to the control littermates, but did not respond to i.c.v. NT-induced hypolocomotion. I.c.v. injection of NT inhibited feeding in fasted wild-type mice, but had no effect on feeding of the NT-1R(-/-) mice. I.c.v. administration of the orexigenic neuropeptide Y (NPY) stimulated feeding to the same extent in both wild-type and NT-1R(-/-) mice. This analysis of NT-1R-deficient mice shows that the NT-1R does not play a role in NT-induced analgesia, but that it is clearly implicated in thermal and feeding regulation, weight control, and NT-induced hypolocomotion.

Evidence that neurotensin mediates the central effect of leptin on food intake in rat

Recent evidence suggests that leptin's action on food intake and body weight regulation is mediated by a number of orexigenic and anorectic neuronal systems in the hypothalamus. Our previous demonstration that central injections of leptin induce hypothalamic neurotensin (NT) gene expression in association with a reduced food intake and decreased body weight in rats indicates that NT, an anorectic peptide, is involved in mediating leptin's action on feeding and body weight regulation. To begin to examine the relative role of NT in this regard we evaluated the effects of NT antiserum (NT-AS) or NT receptor antagonist, SR 48692, on the satiety action of leptin in rats. In the first experiment, 3rd cerebroventricular (i.c.v.) administration of either 1 or 5 microl of NT-AS, 30 min prior to leptin (4 microg) injection, completely blocked the effects of leptin on food deprivation (FD)-induced feeding. In the second experiment, intraperitoneal (i.p.) administration of SR 48692 (40 microg/kg) also completely prevented leptin's satiety action on FD-induced feeding. These results showing the reversal of leptin's satiety action by either NT immunoneutralization or NT-receptor antagonism support our hypothesis that NT is involved in mediating leptin's action on feeding and further suggest that this neuropeptide is a quantitatively important component of the leptin sensitive neural circuitry.

A novel neurotensin peptide analog given extracranially decreases food intake and weight in rodents

Neurotensin decreases food intake in the rat when injected into the cerebral ventricles. We tested the effect of a novel neurotensin analog (NT69L), injected intra-peritoneally (i.p.), on weight gain and food intake in rats. Sprague-Dawley rats (270 g) were injected i. p. with either saline or NT69L at 0.001 or 0.010 mg/kg. In further experiments, larger rats at a more steady state on the growth curve (400 g) were injected with either saline or 0.010 or 1 mg/kg NT69L. Food intake, water consumption and body weight were recorded daily. Weight gain was significantly reduced in the smaller rats injected with 0.001 or 0.010 mg/kg, showing only a 8.5 and 9.0% increase in original weight, respectively, as compared to a 29% increase for the controls. The larger rats injected with 1 mg/kg, had a significant reduction in body weight with a 3.0% decrease in original body weight as compared to a 2.4% increase for the controls. Food intake was significantly reduced suggesting that the weight loss observed after injection of NT69L was attributable in part to a reduction in food intake. The genetically obese Zucker rats injected with NT69L (1 mg/kg) had a significant reduction in weight gain and food intake. NT69L significantly increased blood glucose and corticosterone levels and decreased TSH and T4 in Sprague-Dawley and Zucker rats, an effect that was only transitory. NT69L also caused a decrease in norepinephrine in both the hypothalamus and nucleus accumbens, and an increase in dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and serotonin. In this study, NT69L exhibited a consistent and dramatic effect on body weight and food intake in Sprague-Dawley and obese Zucker rats, and enabled us to study the role that NT plays in weight control and the functional interactions of NT with brain amines, and metabolic and endocrinological parameters.

Effect of chronic intraperitoneal injections of leptin on hypothalamic neurotensin content and food intake

This study was intended for the investigation of the effects of chronic injections of leptin for 7 days on food intake and hypothalamic neurotensin (NT). Leptin treatment significantly reduced food intake [144.3+/-2.5 g (L) vs. 156.7+/-2.5 g (C); P=0. 002] and body weight gain [23.7 g+/-1.0 g (L) vs. 31.5+/-1.3 g (C); P=0.003]. NT concentration was lower in the lateral hypothalamus (LH) of leptin-treated rats than in the control ad libitum fed rats (-30%; P<0.05). The same diminution was observed in pair-fed rats (-27%; P<0.05). This diminution was therefore related to the decrease in food intake rather than to a direct effect of leptin. As the LH was the only area where NT was modified, it appears that among the hypothalamic nuclei involved in the regulation of feeding behavior it is the most sensitive area to a low energy depletion. Therefore, it might play a specific role in triggering the mechanisms necessary to restore body weight and/or energy balance.

Hypothalamic hypocretin/orexin and neuropeptide Y: divergent interaction with energy depletion and leptin

The aim of this study was to measure the effects of chronic leptin treatment on two orexigenic peptides present in the hypothalamus namely hypocretin/orexin and neuropeptide Y (NPY). For this purpose, recombinant murine leptin (0.2 mg/rat/day) or saline were injected intraperitoneally in Long-Evans rats for 7 consecutive days. Food intake (-8%; p < 0.002) and body weight gain (23.7 +/- 1 vs 31.5 +/- 1.3 g; p < 0.003) were significantly lower in leptin-treated rats than the saline-treated rats. NPY concentrations did not change significantly in any of the microdissected brain areas including the arcuate and paraventricular nuclei. Orexin A concentration in the lateral hypothalamus was significantly decreased by the leptin treatment (-68%; p < 0.01). A smaller decrease (-46%; p < 0.04) was also noted in saline-treated rats pairfed to the level of the leptin-treated rats. We conclude that orexin/hypocretin could be considered as a new relay for leptin in the central nervous system. Its variation in case of lower energy supply observed in pairfed rats could constitute an alerting system for the brain and therefore considered as the first step in the establishment of defense mechanisms against energy depletion.