Intraventricular insulin and leptin reduce food intake and body weight in C57BL/6J mice

As the incidence of obesity continues to increase, adequate animal models acquire increased importance for the investigation of energy homeostatic mechanisms. Understanding the central mechanism of action of the adiposity hormones, insulin and leptin, has become particularly important as researchers examine ways to treat or prevent obesity. Although the intra-3rd-ventricular (i3vt) administration of insulin reduces food intake in several species, its effects on food intake and body weight have not been previously been assessed in mice. Male C57BL/6J mice were administered insulin i3vt (0.05, 0.1 or 0.4 microU) or leptin i3vt (5 microg/1 microl) as a positive control. As it occurs in other species, i3vt insulin dose-dependently reduced 24-h food intake and body weight, and increased hypothalamic proopiomelanocortin (POMC) mRNA. Hence, genetic manipulations that influence brain insulin sensitivity in mice can now more easily be integrated with the broader literature on energy homeostasis.     

Diurnal H-reflex variation in mice

Mice exhibit diurnal variation in complex motor behaviors, but little is known about diurnal variation in simple spinally mediated functions. This study describes diurnal variation in the H-reflex (HR), a wholly spinal and largely monosynaptic reflex. Six mice were implanted with tibial nerve cuff electrodes and electrodes in the soleus and gastrocnemius muscles, for recording of ongoing and nerve-evoked electromyographic activity (EMG). Stimulation and recording were under computer control 24 h/day. During a 10-day recording period, HR amplitude varied throughout the day, usually being larger in the dark than in the light. This diurnal HR variation could not be attributed solely to differences in the net ongoing level of descending and segmental excitation to the spinal cord or stimulus intensity. HRs were larger in the dark than in the light even after restricting the evoked responses to subsets of trials having similar ongoing EMG and M-responses. The diurnal variation in the HR was out of phase with that reported previously for rats, but was in phase with that observed in monkeys. These data, supported by those in other species, suggest that the supraspinal control of the excitability of the HR pathway varies throughout the day in a species-specific pattern. This variation should be taken into account in experimental and clinical studies of spinal reflexes recorded at different times of day.     

Change in body weight after hormone replacement therapy in postmenopausal women is dependent on basal circulating leptin

Objective: To address the effect of leptin in the modulation of change in body weight after hormone replacement therapy (HRT), we prospectively examined the responses of body weight and serum leptin after estrogen–progestin replacement in postmenopausal women. Patients: Subjects consisted of 63 postmenopausal women aged 54–82 years on HRT for osteoporosis. Design: Thirty three of the subjects received 0.3 mg of conjugated equine estrogen (CEE) (group 1) while 30 were on 0.625 mg of CEE daily (group 2). All subjects also took 5 mg of medrogestone acetate and 750 mg elemental calcium supplement daily. Measurements: Fasting serum leptin was measured by RIA at baseline, 1 and 3 months after treatment. Data were expressed as mean±S.E.M. Results: Serum leptin was highly related to body weight both at baseline (r=0.40, P<0.001) and after 3 months of HRT (r=0.42, P<0.001). When divided the subjects into three equal groups according to baseline leptin levels, it was found that serum leptin significantly decreased in subjects with high baseline leptin at 3 months (−9.4±5.7%, P<0.05) while it increased in subjects whose baseline leptin levels were in the lowest tertile at 1 month (33.2±8.3%, P<0.001) and 3 month (27.8±8.3%, P<0.01). In regards to body weight, those with leptin in the highest tertile demonstrated a reduction of body weight at 3 (−1.9±0.6%, P<0.05) and 12 months (−3.2±0.5%, P<0.05) after HRT while those whose serum leptin levels were in the lowest and middle tertiles did not demonstrate change in body weight. By repeated measured analysis of variance, it was found that the decrease in body weight in subjects with high serum leptin was independent of the doses of estrogen. Conclusion: Postmenopausal hormone replacement does not cause weight gain. However, it results in a small reduction in body weight particularly in subjects with higher basal leptin concentrations.     

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.     

Diurnal rhythms of leptin and ghrelin in the systemic circulation and in the gastric mucosa are related to food intake in rats

We investigated diurnal changes in leptin and ghrelin levels in the stomach and in the systemic circulation and their relation to food intake rhythms in Wistar rats housed at 22 °C with a 12-h light/dark cycle and free access to food and water. Animals were sacrificed every 3 h over a 24-h period. Leptin and ghrelin levels in serum and in the gastric mucosa were analysed by immunoassay. Leptin mRNA levels were determined in the gastric mucosa by RT-PCR and in different adipose tissue depots (epididymal, retroperitoneal and mesenteric) by Northern blot. Ghrelin mRNA levels were determined by Northern blot. Gastric and serum leptin levels displayed similar diurnal rhythms, rising during the dark phase and decreasing gradually during the light phase. Leptin expression in the different adipose tissue depots correlated positively with circulating leptin levels (P<0.05), although there were some depot-associated differences. Leptin mRNA levels in the mesenteric depot correlated positively with food intake (P<0.05). In blood, ghrelin levels rose sharply just before the onset of the dark phase and dropped suddenly just after. In the stomach, ghrelin levels were high during the fasting period of light and low during the night, and correlated inversely with food intake, gastric contents and serum leptin levels (P<0.05). Leptin and ghrelin in the stomach and in the systemic circulation thus show diurnal variations that are influenced by food intake rhythms. The results agree with a role for ghrelin as a stimulant of meal initiation.     

Interaction of leptin and nitric oxide on food intake in broilers and Leghorns

Leptin, which is produced in proportion to adiposity, has been reported to regulate feeding behaviors. Previous researchers reported that inhibition of nitric oxide (NO) synthase (NOS) decreased food intake, while L-arginine attenuated this effect. Recently, studies showed that NO plays an important role as a mediator of feeding behavior induced by a variety of neuropeptides. We investigated whether the anorectic effect of leptin is mediated by nitric oxide in broilers and Leghorns. In the first experiment, leptin was intracerebroventricularly (ICV) administered into the right lateral ventricle of broilers and food intake monitored at 15-min intervals through 180 min postinjection. L-arginine attenuated the decrease in food intake induced by leptin. In the second experiment, leptin was coinjected ICV with NG-nitro-arginine methyl ester HC1 (L-NNA), a NOS inhibitor. In the following study, we investigated whether the decreased feeding induced by leptin (10 microg/l0 microl) is mediated by nitric oxide in chickens. Three week old chickens were administered two levels of leptin (A=aCSF, B=10 microg/l0 microl) into the right lateral ventricle, and nitrate and nitrite (nitric oxide metabolites) were monitored 30-min postinjection. The results showed leptin decreased NO formation significantly compared with the control group. These results suggest that NO interacts with leptin in the central nervous system to modulate feeding behavior in the chicken.     

Diurnal patterns of food intake and plasma corticosterone levels in lactating rats

The diurnal patterns of food intake and plasma corticosterone levels were determined in lactating Wistar-Imamichi rats maintained in a light (14 L: 10 D, lights on 0500 hr) and temperature (24±2°C) controlled animal room. Lactating mothers with four or more than eight pups showed a characteristic diurnal pattern of food intake with high rates of intake around the time of lights off. The diurnal rhythmicity of food intake seemed to disappear in late lactation in mothers with more than eight pups. The plasma corticosterone concentration on day 9 of lactation displayed a diurnal rhythm with high values at 1700 hr and 2100 hr. The rhythmicity of the corticosterone levels was abolished on day 16 of lactation and a high level was maintained throughout a 24 hr period. Since the diurnal rhythm of the corticosterone level was shifted in animals fed during the restricted period (0900–1700 hr) from days 2 to 9 of lactation, the appearance of diurnal rhythm of corticoid secretion seemed to depend on the diurnal feeding rhythm in lactation as well as in the estrous cycle.     

Effects of leptin and orexin-A on food intake and feeding related hypothalamic neurons

The lateral hypothalamic area (LHA) and the ventromedial hypothalamic nucleus (VMH) have historically been implicated in ingestive behavior, energy balance and body mass regulation. The LHA is more closely associated with the initiation of eating; whereas the VMH mediates the cessation of eating. The parvocellular part of the paraventricular nucleus (pPVN) is also included in the suppressing mechanism. Recently, two hypothalamic peptides, orexin-A and orexin-B, localized in the posterior and lateral hypothalamic perifornical region were discovered in the rat brain and they increase food intake. Leptin, a protein encoded by an obesity gene, expressed in adipose tissue and released into the blood also affects food intake. Orexin and leptin receptors have been localized in the LHA, pPVN, and VMH. The purpose of this study was to measure food intake in the rat in response to leptin and orexin-A; and to determine their electrophysiological effects on feeding related hypothalamic neurons. Results clearly show that leptin suppresses food intake whereas orexin-A increases food intake. These differences are associated with leptin and orexin-A modulatory effects on LHA, pPVN, and VMH glucose responding neurons. In the LHA, leptin inhibits a larger proportion of both glucose-sensitive neurons (GSNs) and non-GSNs. In the pPVN, leptin increases more GSNs in comparison to non-GSNs. Whereas in the VMH, leptin increases the activity of glucoreceptor neurons (GRNs) in comparison to non-GRNs. Orexin-A had opposite effects: increases activity of GSNs more than the non-GSNs in the LHA and significantly suppresses GRNs in the VMH. In the pPVN, orexin-A had no observable effects on neurons that have a low density of orexin 2 receptors. Results are discussed in terms of hypothalamic neural circuits that are sensitive to endogenous food intake inducing and reducing substances.     

Effect of intra-third ventricular administration of insulin on food intake after food deprivation

It has been suggested that insulin may participate as a signal in the overall control of feeding. To further study this possible role of insulin, food-deprived male Wistar rats were subjected to intra-third cerebro-ventricular infusions of insulin. Infusion of 0.5 and 2.0 mIU/rat at 0745 hr, and 2.0 mIU/rat of insulin at 1900 hr in 24.5 hr food-deprived rats, and 2.0 mIU/rat of insulin at 2200 hr in 4 hr food-deprived rats did not significantly affect food intake. Infusion of the high dose of 8.0 mIU/rat of insulin at 2200 hr in 4 hr food-deprived rats significantly decreased food intake with a long-delayed and long-lasting effect. This and previous evidence suggest that intra-third ventricular administration of small amounts of insulin induce a decrease of food intake only in non-food-deprived rats.     

Risperidone alters food intake, core body temperature, and locomotor activity in mice

Risperidone induces significant weight gain in female mice; however, the underlying mechanisms related to this effect are unknown. We investigated the effects of risperidone on locomotor activity, core body temperature, and uncoupling protein (UCP) and hypothalamic orexin mRNA expression. Female C57BL/6J mice were acclimated to individual housing and randomly assigned to either risperidone (4 mg/kg BW day) or placebo (PLA). Activity and body temperature were measured over 48-hour periods twice a week for 3 weeks. Food intake and body weights were measured weekly. UCP1 (BAT), UCP3 (gastrocnemius), and orexin (hypothalamus) mRNA expressions were measured using RT-PCR. Risperidone-treated mice consumed more food (p = 0.050) and gained more weight (p = 0.0001) than PLA-treated mice after 3 weeks. During the initial 2 days of treatment, there was an acute effect of treatment on activity (p = 0.046), but not body temperature (p = 0.290). During 3 weeks of treatment, average core body temperatures were higher in risperidone-treated mice compared to controls during the light phase (p = 0.0001), and tended to be higher during the dark phase (p = 0.057). Risperidone-treated mice exhibited lower activity levels than controls during the dark phase (p = 0.006); there were no differences in activity during the light phase (p = 0.47). UCP1 (p < 0.01) and UCP3 (p < 0.05) mRNA expressions were greater in risperidone-treated mice compared to controls, whereas, orexin mRNA expression was lower in risperidone-treated mice (p < 0.01). These results suggest that risperidone-induced weight gain in mice is a consequence of increased energy intake and reduced activity, while the elevation in body temperature may be a result of thermogenic effect of food intake and elevated UCP1, UCP3, and a reduced hypothalamic orexin expression.     

Dependence of food intake on acute and chronic ventricular administration of insulin

Several lines of evidences indicate that insulin affords short- and long-term neuroendocrine signals to modulate ingestive behavior. To further study a possible role of insulin in the control of food intake, male Wistar rats were subjected to various intra-third cerebro-ventricular applications of saline and insulin. Infusion of 2.0 mIU/rat of insulin at 1100 and 1900 decreased food intake in a 23.5 hr test period. Infusion of 0.5 mIU/rat of insulin between 1100 and 1200 decreased nighttime food intake during the 1st and 2nd days. Infusion of 2.0 mIU/rat/24 hr of insulin from osmotic minipumps decreased nighttime food intake throughout the active pump period and the effect persisted into the post-pump period. The results support the notion that insulin is involved in the regulation of food intake in the rat.     

Diurnal sex differences in the sleep-wake cycle of mice are dependent on gonadal function

STUDY OBJECTIVES: Sex is an important determinant of the pathophysiology of several disorders that influence and/or impair sleep-wake regulation. To date, few studies have examined either the role of sex or the gonadal hormones on sleep and wakefulness. The difficulty in performing well-controlled clinical experiments on sex and sleep underscores the need for effective animal models to investigate the influence of the gonadal hormones on sleep-wake states. This study describes the influence of sex on sleep and wakefulness in mice, the primary mammalian genetic model for sleep analysis, and tests the hypothesis that gonadal function drives sex differences in sleep-wake states. DESIGN: Electroencephalogram/electromyogram sleep-wake patterns were recorded in intact and gonadectomized male and female C57BL/6J mice maintained on a 14-hour light:10-hour dark schedule. Following a 24-hour baseline recording, mice were sleep deprived during the light phase by gentle handling and given a 10-hour recovery opportunity during the immediate dark phase. MEASUREMENTS AND RESULTS: Intact female mice spent more time awake than intact males during 24 hours of baseline recording at the expense of non-rapid eye movement (NREM) sleep. Though the recovery response of NREM sleep was similar between males and females, when examined in reference to baseline levels, females exhibited a more robust recovery response. Gonadectomy in males and females reduced or eliminated the majority of sex differences in sleep architecture and homeostasis. CONCLUSIONS: These data demonstrate that the gonadal hormones influence the amount, distribution, and intensity of sleep but do not account for all sex differences in the sleep-wake cycle.     

Reflex insulin response associated to food intake in human subjects

The occurrence of a reflex insulin discharge at the beginning of a meal, and its possible influence on intake were studied in 7 normal weight humans. Each subject was tested twice under three standard meal conditions. The evolutions of insulinemia and glycemia were recorded over an 84 min observation period, starting 2 min before food presentation. Blood was drawn continuously from an antecubital vein, and collected in 1-min samples for the first 30 min, and then in 3-min samples. The average glycemia curve was stable until some 18-20 min after meal onset. By contrast, a significant rise in plasma insulin appeared as early as the 4th min after meal onset and it is hypothesized to be preabsorptive, of cephalic and/or gastric origin. However, inter-test variations were large even in the same person. Schematically, three types of early insulin responses were observed: high and/or sustained rise, moderate and/or short increase, moderate decrease in plasma insulin. The shape of the early insulin response was not related to any meal characteristic. The potential biological and behavioral significance of the early insulin release is discussed.     

不同进食量对小鼠功能活动和生化指标的影响

目的:探讨不同进食量在不同时间内对小鼠体重、记忆力、平衡耐力和相应生化指标的影响。方法:预先计算小鼠每天平均进食量,按照100%食量,75％食量、50％食量、25％食量及0％食量分为A、B、C、D、E组。实验过程中每3d测试记忆力、平衡耐力和体重1次,第10d取血检测相应生化指标。结果:实验第3d,E组体重、平衡耐力下降;实验第6d和第9d,A组、B组、C组体重明显上升,A组、D组动物的记忆力低于B组和C组;实验第10d,D组血糖显著下降,总胆固醇及甘油三酯随进食量的减少而显著下降。结论:适度减少进食量能维持正常体力和血糖水平,保持良好的记忆力,并有助于降低血中总胆固醇和甘油三酯。     

Effects of insulin on food intake and plasma glucose level in fat-fed diabetic rats

Schedules of insulin treatment which reliably increased eating in fat-fed diabetic rats were studied for their effect on plasma glucose concentrations. An inverse correlation between intake and plasma glucose was observed in fat-fed diabetics given long-term treatment with protamine-zinc insulin (PZI); however changes in glucose did not account for the differential effect of insulin on food intakes in normal controls or normal and diabetic rats fed a low-fat food. A single injection of 1 U PZI which increased eating in fat-fed diabetics but not normal controls 17–23 hr later did not reduce glucose concentrations from hyperglycemic levels in diabetics during the same time period. Injections of regular insulin increased eating in fat-fed diabetic and normal rats in a comparable fashion, but did not reduce plasma glucose in diabetics as low as in normal animals. The results show that the effect of exogenously administered insulin on food intake in fat-fed diabetics is largely unrelated to changes in circulating glucose levels and suggest that metabolic consequences of insulin treatment other than hypoglycemia may underlie the effect of the hormone on feeding in these animals.     

Effect of chronic insulin administration on food intake and body weight in rats.

Insulin was chronically administered to rats to determine its effect on the daily changes in food intake and body weight. Animals received regular insulin via 14-day osmotic minipumps in doses of 0.0, 0.5, 1.0, 3.0, and 5.0 IU/day treated either with (+GLU) or without glutamic acid (-GLU). Previous studies have shown that glutamic acid prevents insulin aggregation in the minipumps to provide a more stable flow rate. Food intake and body weights were measured each day of treatment. Chronic insulin treatment was ineffective in promoting changes in animals receiving any dose of insulin except the highest dose. Animals receiving 5.0 IU/day insulin + GLU experienced a transient hyperphagia and weight gain followed by a suppression in food intake and body weight by Day 4 of treatment. Effects were attenuated in animals receiving insulin -GLU. Plasma insulin concentrations on Day 14 were similar for all doses, suggesting a compensation took place either in insulin degradation or endogenous insulin production. Results indicate that glutamic acid treatment enhances the effects of chronic insulin administration via osmotic minipumps.     

Possible common central pathway for resistin and insulin in regulating food intake

Aim: Adipose tissue has been the object of intense research in the field of obesity and diabetes diseases in the last decade. Examination of adipocyte‐secreted peptides led to the identification of a unique polypeptide, resistin (RSTN), which has been suggested as a link between obesity and diabetes. RSTN plays a clearly documented role in blocking insulin (INS)‐induced hypoglycaemia. As brain injection of INS affects feeding behaviour, we studied the possible interaction between INS and RSTN in food‐deprived rats, measuring effects on food intake. In addition, we examined how RSTN might affect neuropeptide Y (NPY)‐induced feeding, as studies have shown that rat RSTN can interfere with the NPY system. Methods: Overnight food‐deprived rats were injected into the third brain ventricle (3V) with either INS (10 or 20 mUI), RSTN (0.1–0.4 nmol/rat), or saline before access to food. Another group of rats was injected into the 3V with RSTN alone, NPY alone or RSTN plus NPY. Their food intake and body weight were measured. Results: Our results confirm the hypophagic effect of RSTN on food deprivation‐induced food intake, and more importantly, show that RSTN neither potentiates nor blocks the effects of INS on food intake, but does reduce the hyperphagic effect of NPY. Conclusion: The observation that RSTN does not modify feeding INS‐induced hypophagia, but does influence NPY‐induced feeding, points to the possibility that RSTN may be involved in control of food intake through an NPY‐ergic mechanism as INS.