Leptin In Rats Research Articles

Melatonin and estradiol effects on food intake, body weight, and leptin in ovariectomized rats

Objective The study in ovariectomized (Ovx) rats, as a model of menopausal status, of the effects of melatonin (M) and/or estradiol (E), associated or not with food restriction, on body weight (BW) and serum leptin levels. Methods Female SD rats (200–250 g) were Ovx and treated with E, M, E + M or its diluents. Control sham-Ovx rats were treated with E–M diluents. After 7 weeks being fed ad libitum, the animals were exposed for 7 more weeks to a 30% food restriction. We measured: food intake, BW, nocturnal and diurnal urinary excretion of sulphatoxymelatonin (aMT6s), leptin in midday and midnight blood samples, glucose, total cholesterol, LDL, HDL and triglycerides. Results Day/night rhythm of aMT6s excretion was preserved in all cases. The increase of aMT6s excretion in M-treated animals basically affected the nocturnal period. In animals fed ad libitum, E fully prevented Ovx-induced increase of BW, leptin and cholesterol. Melatonin reduced food intake and partially prevented the increase of BW and cholesterol, without changing leptin levels. Under food restriction, M was the most effective treatment in reducing BW and cholesterol. Leptin levels were similar in M, E or E + M treated rats, and lower than in untreated Ovx rats. Conclusions Our result gives a preliminary experimental basis for a post-menopausal co-treatment with estradiol and melatonin. It could combine the effectiveness of estradiol (not modified by melatonin) with the positive effects of melatonin (improvement of sleep quality, prevention of breast cancer, etc.). The possible beneficial effects of melatonin which could justify its use, need to be demonstrated in clinical trials.

Nitric Oxide Synthase Inhibition Prevents Leptin Induced Gn-RH Release in Prepubertal and Peripubertal Female Rats

The aim of the present paper was to study the role of NO as a mediator of leptin action at the hypothalamic level during sexual maturation. First, we analyzed the effect of different leptin concentrations (10 (-13), 10 (-11) and 10 (-9) M) on Gn-RH release from anterior preoptic area and medio basal hypothalamus (APOA-MBH) of prepubertal (15 days old) and peripubertal (30 days old) female rats. Leptin 10 (-13) M was the most effective concentration in releasing Gn-RH in both groups of animals. Since glutamate (GLU) and GABA are involved in the hypothalamic control of Gn-RH neurons and also in the neuroendocrine mechanism of puberty, in a second serie of experiments, we evaluated the effect of a competitive inhibitor of nitric oxide synthase (NOS), N-monomethyl-L-arginine (NMMA) on Gn-RH, GLU and GABA release in response to leptin. Co incubation of APOA-MBH with NMMA 0.5 mM, completely blocked Gn-RH and GLU release induced by leptin 10 (-13) M in prepubertal and peripubertal rats. NMMA also blocked the stimulation of GABA release in prepubertal rats, as well as the inhibition of GABA release induced by leptin in peripubertal rats. It can be proposed that the different effect of NO on GABA release, could be related to ontogenic changes, e.g, maturation of receptors and/or interneuronal connections during sexual development. Present results provide evidence that leptin acts at the hypothalamic level to stimulate NO release, which in turn modifies the release of amino acid neurotransmitters involved in Gn-RH control.

Obesity Reduced the Gene Expressions of Leptin Receptors in Hypothalamus and Liver

The expression of leptin receptor (OB-R) is downregulated by leptin in some cell lines. This study investigated the expressions of leptin receptors at central nerve system and peripheral site in a dietary model of obesity. Rats in the 8 week high-diet and control group were classified based on body weight gain into obese and control groups. Serum leptin and insulin concentrations were measured and gene expressions of short form of leptin receptor (OB-Ra) and long form (OB-Rb) in hypothalamus and liver were detected by RT-PCR. The levels of serum leptin in obese rats were increased compared with control rats (p<0.05). The levels of OB-Ra and OB-Rb gene expressions in both hypothalamus and liver in obese rats were reduced significantly (p<0.01). Serum leptin concentrations of obese rats had a significant negative relationship with both of OB-Ra or OB-Rb gene expression levels in hypothalamus and liver (p<0.01). On the other hand, serum insulin levels had no relationship with OB-Ra or OB-Rb gene expression levels in neither liver nor hypothalamus. Rats with diet-induced obesity have hyperleptinemia and reduced expressions of leptin receptors in hypothalamus and liver. The results suggest that a leptin downregulated OB-R expression is one of leptin resistant mechanisms for maintaining obesity.

Maternal leptin treatment during lactation programs the thyroid function of adult rats

Recently, we showed that both maternal malnutrition during lactation and leptin treatment during the neonatal period program thyroid function. In this study we evaluate whether maternal leptin treatment during lactation programs thyroid function of the offspring in the adulthood. The dams were divided into 2 groups: Lep-daily sc single injected with 8 μg/100 g of body weight with recombinant rat leptin during the last 3 days of lactation and control group (C) that received the same volume of saline. The 180 day-old animals received a single i.p. injection of 125I (2.22 × 10 4 Bq) and they were killed 2 h after the injection. Triiodothyronine (T3), thyroxine (T4), thyrotropin (TSH) and leptin concentrations were measured by radioimmunoassay. The milk of leptin-treated mothers on the last day of treatment had higher leptin ( p < 0.05) concentration. The pups of the leptin-treated mothers had at 21 days an unchanged T3, T4 and leptin serum concentrations with higher TSH ( p < 0.05). The offspring of Lep mothers had at 180 days a higher T3 ( p < 0.05) with normal thyroid 125I uptake, T4 and TSH serum concentrations compared to the controls. So, the mother's hyperleptinaemia during lactation programs to a higher T3 serum concentration on the offspring, probably by a higher leptin transfer through the milk.

Improvement of chronic heart failure by dexamethasone is not associated with downregulation of leptin in rats

To demonstrate the hypothesis that dexamethasone (Dex) could improve chronic heart failure (CHF) by inhibiting the downstream signaling transduction of leptin but had no influence on the upregulation of leptin and its receptor in myocardium. CHF was induced by left coronary artery ligation for 6 weeks. CHF rats were treated with Dex 50 mg.kg/d. Hemodynamics, histology, reactive oxygen species (ROS)-related parameters, and leptin concentrations in serum were measured. The mRNA expression of matrix metalloproteinases (MMP)2/9, tissue inhibitor of metalloproteinases (TIMP)1/2, tumor necrosis factor (TNF)-alpha, and OB-Rb were measured by RT-PCR. In the CHF rats, hemodynamic functions were deteriorated, which was accompanied with myocardium remodeling and histological changes. CHF rats showed hyperleptinemia and excessive ROS in the serum, and the upregulation of MMP-2/9, TNF-alpha, and leptin receptor mRNA and downregulation of TIMP-1/2 mRNA in the myocardium compared with the sham operation group. Dex treatment significantly ameliorated CHF in association with the reversion of the abnormalities of MMP-2/9, TIMP-1/2, TNF-alpha, and ROS. But Dex had no influence on the hyperleptinemia and the upregulated leptin and its receptor in the myocardium during CHF. Dex improves CHF by inhibiting TNF-alpha, MMP-2, MMP-9, and ROS. Dex had no effects on upregulated leptin and its receptor expression and hyperleptinemia induced by CHF.

Differing effects of acute and chronic stressors on plasma osteocalcin and leptin in rats

Stressor activation of the sympathetic nervous system and the hypothalamic–pituitary–adrenal axis can have profound effects on bone and also appetite and metabolism. We tested in rats the response of plasma osteocalcin (pOC, a bone biomarker that is acutely stress responsive), corticosterone, and leptin to (1) ethanol consumption (5% w/v) in a liquid diet (compared with ad libitum and pair-fed rats), (2) acute restraint, and (3) acute (once, 1 h) and (4) chronic (1 h/day for 7 weeks) social aggression. Basal pOC concentration did not differ with ethanol diet or social interaction, but was elevated by both foot restraint immobilization (Imo) and restraint in wire mesh cylinders (WMR). As previously reported for chronic Imo, ingestion of ethanol blunted the pOC response to Imo. Plasma corticosterone concentration was increased by acute WMR and acute social interaction but was unaltered by chronic social interaction. Plasma leptin concentration was markedly increased by Imo in ad libitum fed, but only slightly in ethanol or pair-fed rats. In contrast, the data reflect significant differences between acute and chronic stressor effects since chronic social stress had little effect on pOC or plasma corticosterone, but tended to decrease leptin level in relation to dominance. Lack of significant impact of prolonged ethanol intake or social aggression suggests physiological adaptation.

Hypothalamic Arcuate Nucleus Mediates the Sympathetic and Arterial Pressure Responses to Leptin

Leptin is an adipocyte-derived hormone that plays an important role in the regulation of energy homeostasis through its action in the central nervous system. Leptin decreases body weight by promoting satiety and increasing thermogenesis via increasing sympathetic nerve activity (SNA) to brown adipose tissue. Leptin also increases renal SNA and arterial pressure. The arcuate nucleus is considered as a major nucleus for leptin action on energy homeostasis. We tested whether leptin action in the arcuate nucleus simultaneously activates SNA to brown adipose tissue and the kidney. The sympathetic and cardiovascular responses to intra-arcuate injection of leptin were compared with those evoked by intracerebroventricular administration of leptin in rat. Intracerebroventricular administration of leptin (10 mug) caused a significant increase in SNA to brown adipose tissue and the kidney. Intracerebroventricular leptin also increased mean arterial pressure. Direct injection of leptin (500 ng) into the arcuate nucleus increased both brown adipose tissue (254+/-49%; P<0.001 versus vehicle) and renal SNA (111+/-31%; P<0.001 versus vehicle). Microinjection of leptin into the arcuate nucleus also produced a substantial increase in mean arterial pressure (from 82+/-3 to 100+/-7 mm Hg; P=0.02). These data demonstrate that leptin action in the arcuate nucleus of the hypothalamus is important for the control of sympathetic outflow to both brown adipose tissue and the kidney. These results also suggest that the cardiovascular effects of leptin might be evoked by the action of this hormone in the arcuate nucleus of the hypothalamus.

Preparation of Leptin Antagonists by Site‐Directed Mutagenesis of Human, Ovine, Rat, and Mouse Leptin's Site III

Six muteins of human, ovine, rat, and mouse leptins mutated to Ala in amino acids 39-41 or 39-42 were prepared by site-directed mutagenesis of the putative site III, which does not affect binding but is necessary for receptor activation, then expressed, solubilized in 4.5 M urea, at pH 11.3 in presence of cysteine, refolded and purified to homogeneity by anion-exchange chromatography on Q-Sepharose or combination of anion-exchange chromatography followed by gel filtration. The overall yields were 400-800 mg from 5 L of fermentation. All proteins were >98% pure as evidenced by SDS-PAGE and contained at least 95% monomers as documented by gel-filtration chromatography under nondenaturing conditions. Circular dichroism analysis revealed that all six muteins have identical secondary structure characteristic of nonmutated leptins, namely 52-63% of alpha helix content. All muteins formed a 1:1 complex with chicken leptin binding domain, (chLBD) and bound chLBD or membrane-embedded leptin receptor with affinity identical to WT leptins. Muteins were devoid of any biological activity in several bioassays but were potent competitive antagonists. Some muteins were pegylated using 40 kDa PEG. Although pegylation decreased the in vitro activity, increasing circulation half-life can recompensate this deficit, so pegylated antagonists are expected to be more potent in vivo.

TIME‐DEPENDENT TRANSITION FROM H2O2–EXTRACELLULAR SIGNAL‐REGULATED KINASE‐ TO O2−–NITRIC OXIDE‐DEPENDENT MECHANISMS IN THE STIMULATORY EFFECT OF LEPTIN ON RENAL Na+/K+‐ATPase IN THE RAT

1. Recent studies suggest that leptin, a peptide hormone secreted by white adipose tissue, is involved in the pathogenesis of arterial hypertension, in part by regulating renal sodium handling. Previously, we have demonstrated that in normal rats leptin has a time-dependent effect on renal Na(+)/K(+)-ATPase that drives tubular sodium reabsorption. Short-term leptin infusion results in a transient decrease in Na(+)/K(+)-ATPase activity, whereas prolonged administration stimulates the enzyme. 2. In the present study, we investigated whether these acute effects of leptin are preserved in rats with experimentally induced chronic hyperleptinaemia. 3. Hyperleptinaemia was induced by administration of exogenous leptin (0.25 mg/kg twice daily, s.c., for 7 days). Acute effects of leptin in anaesthetized control (normoleptinaemic) and hyperleptinaemic animals was investigated. Leptin was infused into the abdominal aorta proximally to the renal arteries for 0.5, 1, 2 or 3 h. 4. Leptin (1 microg/min per kg) had a time-dependent effect on renal Na(+)/K(+)-ATPase in both the control and hyperleptinaemic groups. The inhibitory effect observed after 0.5 h infusion was impaired in the hyperleptinaemic group. However, in both groups this effect was abolished by the Janus kinase inhibitor tyrphostin AG490 (100 nmol/min per kg), as well as by the phosphatidylinositol 3-kinase inhibitors wortmannin (10 nmol/min per kg) and LY294002 (1 micromol/min per kg). 5. The stimulatory effect of leptin on Na(+)/K(+)-ATPase activity was observed after 3 h of infusion and was of similar magnitude in control and hyperleptinaemic groups. In the control group, the stimulatory effect of leptin was abolished by the NADPH oxidase inhibitor apocynin (1 micromol/min per kg), the H(2)O(2) scavenger catalase (1 mg/min per kg) and the extracellular signal-regulated kinase (ERK) inhibitor PD98059 (100 nmol/min per kg). In contrast, in the hyperleptinaemic group, the stimulatory effect of leptin was abolished by the cGMP analogue 8-bromo-cGMP (100 nmol/min per kg) and by the superoxide dismutase mimetic tempol (100 micromol/min per kg) but was not affected by catalase or PD98059. 6. Leptin increased urinary H(2)O(2) excretion and ERK phosphorylation in the renal tissue only in the control group. 7. The results suggest that the acute stimulatory effect of leptin on renal Na(+)/K(+)-ATPase is mediated by divergent mechanisms depending on the chronic leptin level (i.e. by H(2)O(2)-dependent stimulation of ERK in normoleptinaemic animals and by superoxide-dependent impairment of the nitric oxide-cGMP pathway in hyperleptinaemic rats).

Leptin Antagonist Reveals an Uncoupling between Leptin Receptor Signal Transducer and Activator of Transcription 3 Signaling and Metabolic Responses with Central Leptin Resistance

Leptin-resistant rats have reduced leptin receptors and signaling and are refractory to exogenous leptin. However, it is unclear how leptin-mediated hypothalamic signal transducer and activator of transcription 3 (STAT3) signaling relates to the loss of physiological responsiveness. We hypothesized that if leptin resistance is associated with leptin receptors that are no longer functionally coupled to leptin responses, then a leptin antagonist should be less effective in leptin-resistant compared with leptin-responsive rats. Hypothalamic leptin resistance was induced in lean rats with a recombinant adeno-associated viral (rAAV) vector encoding leptin by intracerebroventricular injection. Following development of leptin resistance, at day 153, these rats and control rats were infused centrally either with vehicle or a rat leptin antagonist for 14 days. Food intake, body weight, adiposity, and uncoupling protein 1 expression increased with antagonist infusion in controls but elevated only marginally in leptin-resistant rats. Basal hypothalamic STAT3 signaling remained unchanged with antagonist infusion in control rats despite the pronounced orexigenic response in these animals. STAT3 phosphorylation in rats pretreated with rAAV-leptin to induce leptin resistance was elevated 2-fold. Paradoxically, in these leptin-resistant rats, the antagonist fully reversed the 2-fold elevated phosphorylated STAT3, but it evoked minimal physiological responses. These data reveal an uncoupling between leptin receptor activation and metabolic responses with central leptin resistance.

Regulation of corticotropin-releasing factor and its types 1 and 2 receptors by leptin in rats subjected to treadmill running-induced stress

The present study was conducted to investigate the long-term effects of subchronic elevation of central leptin levels on the expression of corticotropin-releasing factor (CRF) and its types 1 and 2 receptors in the brain of rats subjected to treadmill running-induced stress. PBS or recombinant murine leptin was infused continuously for a period of 5 days into the third ventricle of rats with the aid of osmotic minipumps at a delivery rate of 2 mug/day. On the fifth day of infusion, rats were killed under resting conditions or after a session of treadmill running, which is known to induce a stress response in rats. Leptin treatment significantly decreased food intake, body weight, white adipose tissue weight, glucose and insulin plasma contents, and blunted the treadmill running-induced elevation in plasma levels of corticosterone. Leptin infusion prevented stress-induced de novo synthesis of CRF in the paraventricular hypothalamic nucleus (PVN), which was measured using the intronic probe for CRF heteronuclear RNA. The induction of the type 1 CRF receptor (CRF(1)R) in the PVN and supraoptic nucleus in running rats was also significantly blunted by leptin. In contrast, leptin treatment strongly increased the expression of type 2 CRF receptor (CRF(2)R) in the ventromedial hypothalamic nucleus (VMH). The present results suggest that subchronic elevation of central levels of leptin blunts treadmill running-induced activation of the hypothalamic-pituitary-adrenal axis through the inhibition of activation of the CRFergic PVN neurons, and potentially enhances the anorectic CRF effects via the stimulation of expression of CRF(2)R in the VMH.

훈련방법의 차이가 흰쥐의 혈액성분과 랩틴농도에 미치는 영향

본 연구는 비슷한 강도의 규칙적인 수영과 트레드밀 훈련이 흰쥐의 체중, 지방량, 혈중 triglyceride, insulin, 및 랩틴 호르몬 변화에 미치는 영향을 살펴보고 운동이 비만에 미치는 영향을 과학적으로 분석하고자 하였다. 본 연구의 결과로 규칙적인 훈련은 체중과 지방량을 감소시킬 뿐만이 아니라 혈중 triglyceride, insulin, 및 랩틴 호르몬을 감소시킴으로 비만 예방에 큰 효과가 있는 것으로 알려졌으며, 같은 기간의 비슷한 강도의 운동에서 수영 훈련 보다는 트레드밀 위에서 달리는 운동이 비만 예방에 더 큰 효과가 있는 것으로 나타났다. 추후 서로 다른 운동을 부여하여 운동생리학적인 변화를 비교할 뿐만이 아니라 이러한 원인을 규명하는 기전적인 연구가 진행되어져야 한다고 본다. The purpose of this study is to evaluate the different type of exercise training on the changes of blood variables and leptin in SD rats. For this study, SD rats were divided into three groups: control group (CG: n=10), swim trained group (SG: n=10), and treadmill trained group (TG: n=10). The animals were housed in a pathogen-free animal facility (<TEX>$22-24^{\circ}C$</TEX>, 50-60% relative humidity, 08:00-20:00 lighting hours) at D university animal center, Pusan, Korea). Food and water were available ad libitum. The trained rats underwent a 8-wk endurance swim training (5 times/wk) in water at <TEX>$26-29^{\circ}C$</TEX> (SG) and treadmill training (5 times/wk) in DAEJONG treadmill for 60 min. All data were expressed as mean and standard deviation by using SPSS package program (ver 10.0). The result through the statistical analysis of this data were summarized as follows: 1. In the weight changes, there were significant differences among CG, SG and TG(p<.05) after regular swim and treadmill training. TG showed the lowest weight than the other groups. 2. In the epididymal & perirenal adipose tissue levels, there were significant differences among CG, SG and TG(p<.05) after regular swim and treadmill training. TG showed the lowest adipose tissue levels than the other groups. 3. In the triglyceride changes, For the SG and TG, there were significantly decreased after regular swim and treadmill training. TG showed the lowest triglyceride levels than the other groups. 4. In the insulin hormone, For the SG and TG, there were significantly decreased after regular swim and treadmill training. TG showed the lowest insulin levels than the other groups. 5. In the leptin changes, For the SG and TG, there were significantly decreased after regular swim and treadmill training. TG was the lowest than the other groups. Based on the results, Regular swim and treadmill training decrease body weight, epididymal & perirenal adipose tissue levels significantly, this is caused but by decreased triglycerides, insulin, and leptin hormone levels not by the other factors. Regular treadmill training decreased insulin hormone levels compare to swim training, however there was no direct insulin effect on the weight changes. and it might be the direct effect of leptin hormones.

Mechanisms of Sympathetic Activation in Obesity-Related Hypertension

Obesity prevalence is soaring in industrialized countries and progressively increasing in the developing world. Altered patterns of nutrition and reduction in work-related energy expenditure have led to obesity becoming a truly global health issue. The central thermodynamic formulation for the origins of obesity, a mismatched energy balance equation, with an excess of dietary calorie intake over body energy expenditure, is a first step in the understanding of this phenomenon but leaves the diverse causal issues unexplored. Dietary calorie intake is modified by multiple social, economic, and cultural issues. Similarly, the reduction in energy expenditure in recent decades has complex origins, deriving from demographic and social change, which includes third-world transition from a labor-intensive agricultural economy to an industrial base, the introduction of household labor-saving devices, the popularity of transportation modes not reliant on physical effort, and from changed recreational habits, particularly in childhood (computer games instead of physical games). The prevalence of childhood obesity is escalating, having whimsically but not entirely unrealistically been attributed to “potato chips and computer chips.” Obesity and hypertension are intimately associated, and both very commonly coexist in individual patients with insulin resistance, hyperinsulinemia, and hyperlipidemia, this clustering of adverse health factors1 being designated the metabolic syndrome. The pathophysiological mechanisms by which obesity leads to hypertension remain uncertain. Understanding these processes might, perhaps, provide a more rational basis for drug treatment of obesity-related hypertension. Attempts at reduction in body weight, although pivotal in the treatment of obesity-related hypertension, more often than not fail, so that antihypertensive drug therapy is often needed. This review analyses the proposition that obesity is characterized by activation of the sympathetic nervous system and that obesity-related hypertension is, in fact, neurogenic, being initiated and sustained by neural mechanisms. At one time, this idea would have been held to fly in the …

Abstracts for Oral Presentation

Abstracts for Oral Presentation

Ghrelin and sleep-wake regulation

peptides play a key role in the regulation of sleep-wake behavior ([11][1]). There are many hints that also the endogenous ligand of the growth hormone (GH) secretagogue (GHS) receptor ghrelin participates in the regulation of vigilance states. In a previous editorial focus ([10][2]) I wrote that

Primary Prevention by Nutrition Intervention in Infancy and Childhood

Foreword Contributors Introduction Infant Nutrition and Primary Prevention: Current and Future Perspectives: Lucas, A. Sampson, H.A. Reduction in Risk of Cardiovascular Diseases Nutritional Interventions in Infancy and Childhood for Prevention of Atherosclerosis and the Metabolic Syndrome: Singhal, A. Childhood Obesity: Potential Mechanisms for the Development of an Epidemic: Maffeis, C. Prenatal and Postnatal Development of Obesity: Primary Prevention Trials and Observational Studies: Kroke, A. Childhood Diabetes Mellitus with Emphasis on Perinatal Factors: Laron, Z. Prevention of Atopy, Allergy and Infectious Diseases The Gut Microbiota and Potential Health Effects of Intervention: Bjorksten, B. The Relationship of Breastfeeding to the Development of Atopic Disorders: Zeiger, R.S. Friedman, N.J. Prevention of Atopy and Allergic Disease: Type of Infant Formula: Sampson, H.A. Introduction of Solid Foods: von Berg, A. Other Potentially Preventable Diseases Osteoporosis: Is Primary Prevention Possible? Fewtrell, M.S. Nutrition and Cancer Prevention: Targets, Strategies, and the Importance of Early Life Interventions: Hursting, S.D. Cantwell, M.M. Sansbury, L.B. Forman, M.R. LC-PUFAs: Influence on Multiple Health Outcome Long-Chain Polyunsaturated Fatty Acids in Early Life: Effects on Multiple Health Outcomes. A Critical Review of Current Status, Gaps and Knowledge: Fewtrell, M.S. Perinatal PUFA Intake Affects Leptin and Oral Tolerance in Neonatal Rats and Possibly Immunoreactivity in Intrauterine Growth Retardation in Man: Hanson, L.A. Korotkova, M. Hahn-Zoric, M. Zaman, S. Malik, A. Ashraf, R. Amu, S. Padyukov, L. Telemo, E. Strandvik, B. The Crucial Role of Dietary n-6 Polyunsaturated Fatty Acids in Excessive Adipose Tissue Development: Relationship to Childhood Obesity: Massiera, F. Guesnet, P. Ailhaud, G. Impact of Nutrition on Health Mechanism Aspects -Omics for Prevention: Gene, Protein and Metabolite Profiling to Better Understand Individual Disposition to Disease: Affolter, M. Bergonzelli, G.E. Blaser, K. Blum-Sperisen, S. Corthesy, B. Fay, L.B. Garcia-Rodenas, C. Lopes, L.V. Marvin-Guy, L. Mercenier, A. Mutch, D.M. Panchaud, A. Raymond, F. Schmidt-Weber, C. Schumann, A. Spertini, F. Williamson, G. Kussmann, M. Concluding Remarks.

Perinatal overfeeding in rats results in increased levels of plasma leptin but unchanged cerebrospinal leptin in adulthood

To study the effect of perinatal programming and overfeeding on the hypothalamic control mechanisms of food intake in adult rats. Neonatal programming effects on body weight, food intake, central and peripheral leptin levels, hypothalamic neuropeptides, leptin receptors and central leptin responsiveness in adult rats. Plasma and cerebrospinal fluid (CSF) leptin levels were analyzed using radioimmunoassay. Neuropeptide mRNA levels were analyzed using in situ hybridization. Leptin receptor mRNA levels were analyzed using reverse transcriptase-polymerase chain reaction. Perinatally overfed rats growing up in small litters (SL) maintain their obese and hyperleptinemic phenotype in adulthood. However, leptin levels in CSF are abnormally low considering the plasmatic hyperleptinemia. In contrast to the already reported changes in perinatally overfed juvenile rats, perinatally overfed adult rats did not show any alteration in the expression of leptin receptor isoforms and evaluated neuropeptides. Moreover, SL adult rats showed a normal sensitivity regarding the inhibitory effect of intracerebroventricular leptin administration on food intake. Perinatal overfeeding does not induce alterations in either the anorectic response to central leptin administration or expression of leptin receptors and neuropeptides in adulthood. The leptin resistance to peripheral leptin in SL adult rats may be related to impaired leptin transport across the blood-brain barrier.

Increased Leptin Expression in the Dorsal Vagal Complex Suppresses Adiposity without Affecting Energy Intake and Metabolic Hormones

Increased leptin transgene expression locally in hypothalamic sites suppresses weight and energy intake, enhances thermogenic energy expenditure, and differentially modulates metabolic hormones for an extended period. We evaluated whether a similar localized expression of leptin transgene in the dorsal vagal complex (DVC) in the caudal brain stem that also displays the biologically relevant leptin receptor would reproduce these varied responses and thus demonstrate functional connectivity between the hypothalamus and DVC. Adult female rats were microinjected with a recombinant adeno-associated virus encoding either rat leptin or green fluorescent protein gene (control) in the DVC. Food intake and body weight were monitored weekly, and metabolic variables were analyzed at the end of 10 weeks. Increased leptin transgene expression in the DVC suppressed the time-related increase in body weight accompanied by a transient decrease in food intake at week 1 post-injection and little effect on thermogenic energy expenditure. That suppression of weight was due to decreased adiposity is shown by the markedly suppressed white adipose tissue-derived hormones, leptin and adiponectin. Circulating concentrations of pancreatic insulin, gastric ghrelin, and glucose levels were unchanged. This segregation of the varied effects of leptin expression in hypothalamic sites vs. DVC endorses the view that among the various endocrine organs under sympathetic nervous system control, only those leptin-activated neural circuits in the hypothalamus that suppress weight and adiposity on a long-term basis transverse through DVC en route to white adipose tissue.

Changes in liver PPARα mRNA expression in response to two levels of high-safflower-oil diets correlate with changes in adiposity and serum leptin in rats and mice

The ligand-dependent transcription factor peroxisome proliferator-activated receptor α (PPARα) is known to be activated by common fatty acids and to regulate the expression of genes of various lipid oxidation pathways and transport. High-fat diets provide more fatty acids, which presumably could enhance lipid catabolism through up-regulation of PPARα signaling. However, high intake of fat could also lead to obesity. To examine PPARα signaling in high-fat feeding and obesity, this study examined the hepatic mRNA expression of PPARα and some of its target genes in Wistar rats and C57BL/6J mice fed two levels (20% or 30% wt/wt) of high-safflower-oil (SFO; oleic-acid-rich) diets until animals showed significantly higher body weight (13 weeks for rats and 22 weeks for mice) than those of control groups fed a 5% SFO diet. At the end of these respective feeding periods, only the rats fed 30% SFO and the mice fed 20% SFO among the two groups fed high-fat diets showed significantly higher body weight, white adipose tissue weight, serum leptin and mRNA expression of PPARα ( P<.05) compared to the respective control groups. Despite elevated acyl-CoA (a PPARα target gene) protein and activity in both groups fed high-fat diets, the mRNA expression level of most PPARα target genes examined correlated mainly to PPARα mRNA levels and not to fat intake or liver lipid levels. The observation that the liver PPARα mRNA expression in groups fed high-fat diets was significantly higher only in obese animals with elevated serum leptin implied that obesity and associated hyperleptinemia might have a stronger impact than dietary SFO intake per se on PPARα-regulated mRNA expression in the liver.

Effects of central leptin infusion on the reward-potentiating effect of d-amphetamine

It was previously reported that chronic food restriction and maintenance of rats at 75–80% of initial body weight enhanced the reward-potentiating effect of d-amphetamine in the lateral hypothalamic self-stimulation (LHSS) paradigm. Moreover, the enhancement reversed in parallel with body weight recovery when ad libitum access to food was reinstated. The present study tested the hypothesis that hypoleptinemia during food restriction is necessary for expression of enhanced drug reward. In Experiment 1, intracerebroventricular (i.c.v.) infusion of leptin (0.5 μg/0.5 μl/hr for 8 days) in food-restricted rats did not alter the rewarding effect of d-amphetamine (0.5 mg/kg, i.p.). Considering that i.c.v. leptin may not diffuse into deep brain regions where direct effects on drug reward sensitivity may be exerted, effects of acute bilateral microinjection of leptin (0.5 μg) in ventral tegmental area and nucleus accumbens were tested in Experiment 2 and found to have no effect. In Experiment 3, chronic i.c.v. leptin infusion in ad libitum fed rats decreased food intake and body weight and enhanced the rewarding effect of d-amphetamine. Sensitivity to d-amphetamine returned to normal as body weight recovered following cessation of leptin infusion. This result suggests that weight loss, whether from hormone-induced appetite suppression or experimenter-imposed food restriction, is sufficient to enhance drug reward sensitivity. Experiment 4 tested whether food restriction in the absence of body weight loss alters drug reward sensitivity. Rats received chronic i.c.v. infusion of the orexigenic melanocortin receptor antagonist, SHU9119 (0.02 μg/0.5 μl/hr for 12 days), and a subset were pair-fed to vehicle-infused controls. Although these subjects ingested ∼50% of the amount of food ingested by free-feeding SHU9119-infused rats, they displayed no weight loss and no change in sensitivity to d-amphetamine. Together, results of this study support the importance of weight loss, but not leptin, in the enhancement of drug reward sensitivity.