Hypothalamic implants of dilute estradiol fail to reduce feeding in ovariectomized rats

To investigate further the site where estradiol (E(2)) inhibits food intake, we tested the effects on feeding of subcutaneous and intrahypothalamic implants of 10% E(2) benzoate in cholesterol (CHOL) or CHOL alone. E(2) was implanted subcutaneously in Silastic tubes, and intrahypothalamically via bilateral 29-gauge cannulas into the paraventricular nucleus (PVN) or the medial preoptic area (MPA) of ovariectomized (OVX) Sprague-Dawley and Long-Evans rats. Three-day implant periods followed 3-day baseline periods. Rats were allowed ad libitum access to chow and tap water, and food intake and body weight were measured each day. Subcutaneous 10% E(2) implants in Sprague-Dawley rats reduced food intake 21% on Day 2 and 34% on Day 3 (P's<.01) and decreased 3-day body weight gain 11 g (P<.05). In contrast, 10% E(2) implants in the PVN of Sprague-Dawley rats did not change food intake or body weight. Implants of 10% or 20% E(2) in the MPA also failed to decrease food intake. MPA implants of 10% E(2) decreased body weight gain 8 g (P<.05), but MPA implants of 20% E(2) decreased weight gain only 4 g (P>.05). To determine whether the strain of rat affected our negative results on food intake, we implanted 10% E(2) into the PVN of Long-Evans rats. Again, PVN E(2) did not decrease food intake significantly in comparison to the pretest baseline. PVN E(2) did, however, decrease body weight gain 5 g and decreased food intake 6% compared to rats with implants of CHOL (both P<.05), but these effects appeared to be due to an increase in feeding in the CHOL group in comparison to their baseline. Finally, CHOL and E(2) implants did not impair the responsivity of the PVN because acute implants of norepinephrine (NE) into the PVN of E(2)- or CHOL-treated Long-Evans rats significantly increased food intake. Our results do not support the hypothesis that E(2)'s actions in either the PVN or the MPA are sufficient to account for its inhibitory effects on feeding.     

Central vs. peripheral effects of estrogen on food intake and lipoprotein lipase activity in ovariectomized rats

The effects of implants of estradiol benzoate (EB) into either the ventromedial nucleus (VMH-EB) or the paraventricular nucleus (PVN-EB) of the hypothalamus were compared to the effects of peripheral EB (Per-EB) replacement in ovariectomized rats. After three days of hormone treatment, the Per-EB group and the PVN-EB group exhibited a decrease in food intake and body weight. Adipose tissue lipoprotein lipase activity was generally suppressed for the Per-EB, PVN-EB, and VMH-EB groups in the left and right parametrial and retroperitoneal fat pads. The finding that the VMH-EB and PVN-EB groups experienced similar peripheral stimulation but differed on the food intake and body weight measures would suggest that these measures are not entirely under peripheral control. The findings support the hypothesis that estrogen exerts its effects via multiple mechanisms, both central and peripheral. In addition, the PVN is shown to be an important site for further research on the modulation of feeding and metabolism by estrogen.     

Repeated hypothalamic stimulation with neuropeptide Y increases daily carbohydrate and fat intake and body weight gain in female rats

Neuropeptide Y (NPY), repeatedly injected in the hypothalamic paraventricular nucleus (PVN), produces dramatic obesity and overeating in female rats maintained on a single nutritionally complete diet. In the present study, we investigated whether these effects could also be obtained in animals with a choice of three pure macronutrients: protein, carbohydrate, and fat. Female rats with indwelling PVN cannulas were injected with NPY (235 pmol) or its saline vehicle every 8 hr for 6 days. A third group was left undisturbed. Consumption of each macronutrient and body weight were measured every 24 hr for 6 days preinjection, 6 days during injections, and 21 days after the injections were terminated. Relative to vehicle or preinjection rates of body weight gain (approximately 1.5 g/day), NPY dramatically enhanced weight gain to a rate of 9.3 g/day and more than doubled total daily food intake. This augmentation was accounted for by increases in carbohydrate intake (+26.4 kcal/day) and fat intake (+48.5 kcal/day), with no significant potentiation of protein consumption. When the NPY injections were terminated, body weight and macronutrient intake returned to control levels within 1 or 2 weeks. These findings are consistent with a role for NPY in hypothalamic mechanisms of macronutrient intake and body weight regulation and suggest that disturbances in brain NPY may contribute to the development of eating and weight disorders.     

Sleep, brain energy levels, and food intake

Background

The feeling of hunger and feeding, a wake–state-dependent behavior, is regulated by specific centers within the hypothalamus. While paraventricular nucleus (PVN), arcuate nucleus (ARC), and dorso- and ventromedial hypothalamus (DMH/VMH) regulate feeding, the lateral hypothalamus (LH) is associated both with feeding and wake/REM sleep regulation. In order to examine the effects of sleep and wakefulness on food intake and body weight, we also measured hypothalamic ATP concentrations, which are known to be involved in feeding behavior and sleep–wake regulation.

Methods

In rats, food intake and body weight was measured during a 24-h light–dark cycle and during 6 h of sleep deprivation (SD) performed by gentle handling. Tissue samples from the PVN, ARC/DMH/VMH, and LH were collected after 6 h of SD and from time-matched diurnal controls. ATP was measured by luciferin-luciferase bioluminescence assay.

Results

Across the 24-h light–dark period, rats consumed approximately 28.13±4.48 g of food and gained 5.22±1.65 g with a positive correlation between food intake and body weight. During SD, while food intake increased significantly +147.31±6.13%, they lost weight significantly (–93.29±13.64%) when compared to undisturbed controls. SD resulted in a significant decrease in ATP levels only in LH (–44.60±21.13%) with no change in PVN, ARC/DMH/VMH region when compared with undisturbed controls.

Conclusion

The results indicate a strong overall correlation between ATP concentrations in the LH and individual food intake and suggest a sleep–wake dependent neuronal control of food intake and body weight.     

Effects of stereoisomers of estradiol on food intake, body weight and hoarding behavior in female rats

The effects of 17-alpha and 17-beta estradiol on food intake, body weight and hoarding behavior in ovariectomised rats were investigated. For five days, ten animals received subcutaneous injections of both isomers (10 micrograms/kg/day) in a counterbalanced design. Hoarding tests were conducted on the last three days of each 5-day injection period. 17-Alpha estradiol significantly reduced food intake but was without effect on body weight. 17-Beta estradiol reduced food intake significantly more than the alpha form and also significantly reduced body weight. These differential effects suggest that stereoisomers of estradiol may be acting on separate regulatory systems. The treatments did not change hoarding activity compared to pre-treatment levels.     

Ghrelin、melanotan-Ⅱ以及胆囊收缩素对下丘脑双侧室旁核损伤大鼠摄食的影响

目的探讨大鼠下丘脑双侧室旁核(PVN)损伤引起的过食和肥胖的产生机制。方法 Wistar雄性大鼠36只,通过电损伤下丘脑双侧PVN使大鼠产生过食和肥胖,检测ghrelin、melanotan-II(MT-II,一种合成的α-黑色素细胞刺激素——α-MSH的结构同源体)以及胆囊收缩素-8(CCK-8)摄食作用的改变。结果双侧PVN损伤后大鼠的体重和摄食量明显增加,显示出过食和肥胖,手术后1周,外周给与Ghrelin,3～4h后PVN损伤组比伪损伤组的摄食量增加明显,Ghrelin显示出更强的刺激摄食的作用;中枢给予MT-Ⅱ可明显抑制24h节食大鼠的食物摄取,然而PVN损伤后MT-II对24h节食大鼠摄食的抑制作用减弱甚至消失;外周给予CCK-8可明显抑制大鼠各时间段的摄食作用,PVN损伤组和伪损伤组之间未见明显差异。结论大鼠下丘脑双侧PVN损伤引起的过食和肥胖可能与增强的ghrelin对摄食的刺激作用和(或)α-MSH受体的破坏有关。     

Melatonin enhances NADPH-diaphorase activities in the hypothalamus of maternally-separated rats

Maternal separation or social isolation is a risk factor in the development of mammalian species affecting both physical and mental growth, and food intake regulation. Melatonin has been known to regulate body weight on various species including rodents. We investigated the effect of melatonin treatment on the expression of nitric oxide synthase, which may involved in food intake regulation, in the brain of maternally separated-rats using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Melatonin (10 mg/kg i.p.) was injected to 14-day-old maternally-separated rats for 7 days. Maternally-separated rats with melatonin administration showed significantly higher staining intensities of NADPH-d-positive neurons in the paraventricular nucleus (PVN) and in lateral hypothalamic area (LHA) than maternally-separated without melatonin administration (P < 0.05). Body weight of melatonin treated rats significantly increased at the 6th and 7th day compared to that of rats without melatonin treatment (P < 0.05). These results indicate that melatonin may be associated with increase body weight via NOS in the hypothalamic areas in maternally-separated or socially isolated rats.     

Effects of chronic intrahypothalamic infusion of insulin on food intake and diurnal meal patterning in the rat

In Experiment 1, rats were chronically infused with insulin (2.7, 27, or 270 ng/hr) or 0.9% saline into the ventromedial (VMH), medial perifornical (PF), or lateral (LH) hypothalamus. VMH infusions of insulin caused a significant, dose-dependent decrease in food intake and body weight; PF infusion of insulin was less effective, but significant; whereas LH infusions of insulin were ineffective. In Experiment 2, rats were chronically infused with insulin (0.54 ng/hr) or 0.9% saline into the VMH, paraventricular (PVN), or posterior (PN) hypothalamic nucleus. Subjects that received VMH or PN infusions of insulin failed to regain weight lost as a result of surgery even 2 weeks after infusion; subjects that received PVN infusions of insulin regained their preoperative weights faster than did controls. All of the groups that received insulin significantly increased their daytime food intake during the infusion period and decreased their night food intake slightly; 24-hr food intake remained unchanged.     

Chronic weight loss in lean and obese rats with a brain-enhanced chemical delivery system for estradiol

Studies were undertaken to determine the effects on body weight and food intake of a chemical delivery system which preferentially delivers estradiol (E2) to the brain and there serves as a source for the sustained release of the steroid. We injected intravenously various doses of this estradiol-chemical delivery system (E2-CDS), E2-valerate (E2-VAL) or the dimethyl sulfoxide (DMSO) vehicle to young lean male rats and monitored body weight and 24 hr food intake for 39 days postinjection. E2-VAL caused a transient reduction in food intake and body weight gain. By contrast, a single injection of E2-CDS caused a chronic, dose-dependent reduction in the rate of body weight gain. In these lean rats, the duration of reduced body weight gain was not correlated with the observed transient reduction in food intake. In aged, obese male rats, E2-CDS caused a marked and chronic dose-dependent reduction in body weight. In contrast to lean rats, E2-CDS caused a long-term reduction in food intake in obese rats. To evaluate the importance of the E2-CDS-induced reduction in food intake in the observed persistent weight loss in obese rats, E2-CDS was administered to a group of obese rats and a second group which received the DMSO vehicle was pair-fed an equivalent amount of food daily. The resulting weight loss in both groups was equivalent. These results show that the enhanced delivery of E2 to the brain with the E2-CDS causes sustained reduction in the rate of body weight gain in lean rats and persistent weight loss in obese animals.     

Use of peripheral blood transcriptome biomarkers for epilepsy prediction

Fenfluramine reduces hunger and promotes body weight loss by increasing central serotonin (5-HT) signaling. More recently, neuropeptides have been linked to the regulation of feeding behavior, metabolism and body weight. To examine possible interactions between 5-HT and neuropeptides in appetite control, fenfluramine (200 nmol/0.5 μl/side) was administered directly into the hypothalamic paraventricular nuclei (PVN) of male rats. Bilateral fenfluramine produced significant hypophagia and increased expression of PVN corticotropin releasing factor (CRF) mRNA and neuropeptide Y (NPY) mRNA in the arcuate nucleus within the first hour after drug administration. Fenfluramine's effects on feeding behavior and mRNA expression were blocked by PVN injections of a 5-HT(1-2) receptor antagonist, metergoline (15 nmol/0.5 μl/side). These data suggest that 5-HT neurons targeting hypothalamic paraventricular CRF neurons may participate in an appetite control circuit for reducing food intake.     

Galanin in the PVN increases nutrient intake and changes peripheral hormone levels in the rat

In self-selection feeding paradigms, rats display differential patterns of nutrient (protein, carbohydrate or fat) intake. Factors known to influence this selection include brain peptides as well as circadian parameters. In this series of experiments we investigated the role of PVN galanin in nutrient intake during the early and late dark periods in the rat. Rats were allowed to select between three isocaloric diets enriched in protein, carbohydrate or fat. Following a 2-week adaptation period, the animals' 24-h intake was monitored for 4 weeks. Galanin was injected into the PVN and food intake was measured 1, 2 and 24 h post-injection. Galanin significantly increased the 1 h total food intake but it failed to increase the intake of any particular nutrient. Galanin had no effect 2 or 24 h post-injection. Analysis of the data grouped by preference based on the rats 24 h baseline selection patterns over the 4-week period revealed that galanin seem to increase the preferred nutrient. That is, galanin preferentially increased the intake of the carbohydrate- or fat-rich diet in animals with high (over 40% of the total food intake) 24-h baselines in this particular nutrient. Finally, analysis of the plasma hormone levels after paraventricular galanin administration revealed a significant increase in noradrenaline levels, a small reduction in plasma insulin with no effects on adrenaline, glucose or corticosterone. The data revealed that galanin in the PVN influences both food intake and metabolic functioning. PVN galanin significantly increases sympathetic outflow and seems to stimulate the intake of the individual rat's preferred macronutrient.     

Paraventricular hypothalamic clonidine increases rather than decreases susceptibility to activity-based anorexia in the rat.

Anorexia has been related to reduced activity of the paraventricular hypothalamic (PVN) noradrenergic-feeding system. In this study we determined whether clonidine (an alpha 2-adrenergic agonist) infused into the PVN reduced susceptibility to activity-based anorexia (ABA) in the rat. In Experiment 1, clonidine (6 doses) was chronically infused into the PVN of male Sprague-Dawley rats. All animals were exposed to ABA (1.5 hr/day food access; 22.5 hr/day running wheel access) until a 25% body weight loss was reached. Dose-related increases in susceptibility to ABA and decreases in food intake were observed. In Experiment 2, for which heavier animals and 3 doses of clonidine were used, we found no difference in food intake and wheel activity but increased susceptibility to ABA. Chronic clonidine infused into the PVN does not produce hyperphagia and exacerbates rather than attenuates susceptibility to ABA.     

Enhanced anorexigenic signaling in lean obesity resistant syndecan-3 null mice

Obesity is associated with increased risk of diabetes, cardiovascular disease and several types of cancers. The hypothalamus is a region of the brain critical in the regulation of body weight. One of the critical and best studied hypothalamic circuits is comprised of the melanocortinergic orexigenic agouti-related protein (AgRP) and anorexigenic α-melanocyte stimulating hormone (α-MSH) neurons. These neurons project axons to the same hypothalamic target neurons and balance each other's activity leading to body weight regulation. We previously showed that the brain proteoglycan syndecan-3 regulates feeding behavior and body weight, and syndecan-3 null (SDC-3(-/-)) mice are lean and obesity resistant. Here we show that the melanocortin agonist Melanotan II (MTII) potently suppresses food intake and activates the hypothalamic paraventricular nuclei (PVN) in SDC-3(-/-) mice based on c-fos immunoreactivity. Interestingly, we determined that the AgRP neuropeptide is reduced in the PVN of SDC-3(-/-) mice compared to wild type mice. In contrast, neuropeptide Y, coexpressed in the AgRP neuron, is not differentially expressed nor is the counteracting neuropeptide α-MSH. These findings are unprecedented and indicate that AgRP protein localization can be selectively regulated within the hypothalamus resulting in altered neuropeptide response and tone.     

Food intake and adipose tissue lipoprotein lipase activity after hypothalamic estradiol benzoate implants in rats

Unilateral implants of estradiol benzoate in the ventromedial hypothalamus (VMH) reduced food intake in ovariectomized rats. The implants did not produce cornification of the vaginal epithelium. Furthermore, the reduction in food intake was observed in the absence of changes in adipose tissue lipoprotein lipase activity or cytoplasmic progestin receptor levels. These results suggest that, while estradiol may normally act at both central and peripheral sites to affect food intake and body weight, estrogenic stimulation of just the VMH may be sufficient to reduce food intake in ovariectomized rats.     

Variation of fat intake with estrous cycle, ovariectomy and estradiol replacement in hamsters (Mesocricetus auratus) eating a fractionated diet

Intakes of fats, proteins, and carbohydrates were measured daily for a 3 month period in female hamsters maintained on a fractionated diet consisting of the dietary constituents, dextrose, fat and soybean meal. In the first study, hamsters showed variations in body weight and fat intake across the estrous cycle and following ovariectomy, with elevations during diestrous and after ovariectomy when endogenous estrogens are reduced. In the second study, the effects of exogenous estradiol or cholesterol on intake patterns of ovariectomized hamsters were determined. Hamsters lost weight and decreased fat intake when implanted with a silastic containing estradiol and gained weight and increased fat intake when exposed to cholesterol treatment. In neither of the two studies were the intakes of protein or carbohydrates significantly affected by the animals' hormonal status. These results suggest that in the hamster, estrogenic effects on food intake are specific to some dietary constituents and not to others.     

Effects of long-term ingestion of aspartame on hypothalamic neuropeptide Y, plasma leptin and body weight gain and composition

The aim of this study was to determine the effects of the chronic ingestion of aspartame (ASP) on brain neuropeptide Y (NPY) concentrations, plasma hormones, food intake and body fat. Two groups of male Long-Evans rats, fed on a control (C) well-balanced diet, had to drink either a 0.1% ASP solution or water for a period of 14 weeks starting at weaning. Food intake and body weight were weekly recorded. At the end of the experiment, fat pads were sampled, leptin and insulin were measured in the plasma and NPY in several microdissected brain areas. Substituting ASP for water led to lower body weight (-8%; P<.004) and lower fat depot weight (-20%; P<.01) with no differences in energy intake or plasma insulin concentrations. Plasma leptin was significantly reduced by 34% (P<.05). Leptin concentrations were well-correlated with final body weight (r=.47; P<.025) and fat pad mass (r=.53; P<.01). NPY concentrations were 23% lower (P<.03) in the arcuate nucleus of ASP rats with no differences in other brain areas. The beneficial effects on body composition could be related to the decreased effects of NPY on lipid and energy metabolism, independently of insulin. The reasons for the NPY decrease (regulatory or toxicological) are not obvious. The constitutive amino acids of the ASP molecule might participate in the NPY regulation.     

Electroconvulsive shock effects on food and water intake as a function of prior deprivational state

Two experiments, each using approximately 30 male and 30 female hooded rats, examined the effects of electroconvulsive shock (ECS) on water intake as a function of the water deprivation state of the animal and food intake and body weight as a function of food deprivation state. In Experiment 1, half the animals were subjected to water deprivation prior to ECS or sham ECS, and the other half were watered ad lib; in Experiment 2, food deprivation was the pre-ECS manipulation. As predicted, ECS produced a decrease in water intake in the ad lib watered animals but not in the deprived ones. A similar treatment by deprivation interaction was not found for food intake or body weight. In the males, food intake was decreased for one day by the treatment but recovered to a normal level two days following ECS; however, such an effect of ECS on food intake did not occur in the females. Since food and water intake was not differentially affected by ECS and sham ECS in deprived animals, previous cautions regarding ECS effects on motivational states may not be germane to many studies using appetitive conditioning paradigms.     

Insulin infusion during a nocturnal fast suppresses the subsequent day-time intake

Much recent evidence suggests a dual and opposite action of insulin on food intake and body weight. Peripherally administered, long acting insulin stimulates weight gain and food intake. On the contrary intracerebroventricularly infused insulin decreases food intake and body weight. It has been suggested that the shift from the nocturnal hyperinsulinism and hyperphagia to the day-time hypoinsulinism and hypophagia depended on the action of insulin on the brain during the night. It has also been hypothesized that the absence of nocturnal hyperinsulinism due to fasting was partly responsible for the hyperphagia observed during the subsequent day-time. In the present experiment, insulin was infused intravenously at various low doses (0.01, 0.025, 0.05 U/hr) during a nocturnal fast. Its effects on the following diurnal free food intake were investigated. It was shown that the experimentally elevated plasma insulin induced a dose-dependent reduction in the day-time feeding response. It was concluded that this reduction is due to the chronic action on the brain of the high plasma insulin level induced by the infusion during the nocturnal fast.     

PVN-hindbrain pathway involved in the hypothalamic hyperphagia-obesity syndrome

This study examined the involvement of caudal brainstem projections of the hypothalamic paraventricular nucleus (PVN) in the medial hypothalamic (MH) hyperphagia-obesity syndrome. Experiment 1 demonstrated that a unilateral parasagittal knife cut in the MH combined with a contralateral coronal knife cut in either the ventrolateral pons (vP) or ventrolateral medulla (vM) significantly increased food intake and body weight in adult female rats. Overeating and overweight were also produced by a unilateral MH knife cut combined with a contralateral oblique cut under the nucleus of the solitary tract and dorsal motor nucleus of the vagus complex (NST/DX). In contrast, an MH cut x dorsolateral medullary cut combination did not increase food intake or body weight compared to a MH cut alone or sham surgery. Experiment 2 demonstrated that the hyperphagia/obesity effect of MH x vP knife cuts was comparable to that obtained with bilateral PVN lesions, but less than that produced by bilateral MH knife cuts. Bilateral vP cuts also increased body weight but the effect was less than that obtained with the other experimental treatments. Feeding the rats a high-fat diet rather than chow potentiated the hyperphagia and obesity syndromes produced by the various lesion conditions. Taken together, these findings suggest that the medial hypothalamic hyperphagia and obesity syndrome is due, in part, to damage to PVN projections to the caudal brainstem, the NST/DX complex in particular. The functional significance of this PVN-hindbrain "feeding" pathway and the identity of extra-PVN components of the hyperphagia-obesity syndrome remain to be established.     

Vanadate stimulates in vivo glucose uptake in brain and arrests food intake and body weight gain in rats

Vanadate, administered via drinking fluid (0.2-0.8 mg/ml in 80 mM NaCl), attenuated food intake and strongly suppressed body weight gain in normally-fed or 20-hour food-deprived rats. At 0.8 mg/ml for 4 days, oral vanadate significantly stimulated the rate of hexose uptake by brain tissue. When microinjected into the lateral cerebral ventricle at a dose of 82 nmol, vanadate strongly and specifically suppressed food intake and body weight gain in 20-hour food deprived rats previously maintained on tap water. This inhibitory effect was reversed by coadministration of 3-O-methyl glucose. Collectively, the results suggest that vanadate is capable of blocking food intake by a specific effect in the central nervous system that involves stimulation of local glucose uptake.