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Intense exercise and food restriction cause similar hypothalamic neuropeptide Y increases in rats.

Neuropeptide Y (NPY) is a potent central appetite stimulant whose concentrations rise markedly in hypothalamic appetite-regulating regions in food-deprived rats. To determine whether increased energy expenditure also affects hypothalamic NPY, we studied the effects of intense physical exercise in rats (n = 10) running voluntarily on a large-diameter exercise wheel. Running was initiated by restricting food intake but stabilized at an average of 8 km/day when food intake was matched to that in 11 nonexercised, freely fed controls [23.9 +/- 1.9 (SE) g/day vs. 24.7 +/- 1.3 g/day; P > 0.5]. Running expended approximately 40% of daily energy intake, and weight gain was significantly inhibited. A separate group (n = 10) of nonexercised rats was food restricted (approximately 15 g/day) to match the weights of the exercised rats. The rats were killed after 40 days, when both experimental groups weighed 30% less than controls (P < 0.01). Hypothalamic NPY concentrations showed significant (P < 0.01) increases of 30-70% in specific regions (arcuate and dorsomedial nuclei and medial preoptic and lateral hypothalamic areas) in both the running and food-restricted groups, compared with controls. There were no significant differences between the two experimental groups in NPY concentrations in any hypothalamic region. These findings suggest that negative energy balance, whether caused by reduced energy intake or increased expenditure, increases hypothalamic NPYergic activity. As NPY acts on the hypothalamus to increase body weight, these data support the postulated homeostatic role of NPY in maintaining nutritional state.

Animals↗

Alterations in hypothalamic NPY and CRF in anorexic tumor-bearing rats.

Regional hypothalamic concentrations of neuropeptide Y (NPY) and corticotropin-releasing factor (CRF), respectively a stimulant and an inhibitor of feeding behavior, were investigated in hypothalamic nuclei in rats carrying the Yoshida sarcoma. Tumor-bearing rats (n = 10), non-tumor-bearing controls (n = 10), and food-restricted rats (n = 10), which did not carry tumors but were pair-fed to match the reduced food intake of the tumor-bearing group, were studied after 10 days. NPY concentrations in the arcuate nucleus (ARC, the main site of NPY synthesis) were significantly increased above controls (P < 0.01) in both tumor-bearing and food-restricted groups. However, NPY concentrations in the paraventricular nucleus (PVN, an NPY-sensitive site of NPY release) showed opposing changes, with a 25% decrease (P = 0.052) in the tumor-bearing but a 48% increase (P < 0.01) in the food-restricted group. CRF concentrations in both the PVN and the ARC were significantly reduced (P < 0.01) in the food-restricted group, but remained close to control values in the tumor-bearing group (P not significant). Changes in hypothalamic appetite-regulating neuropeptides in cancer anorexia, which may result from the action of cytokines produced by a host defense response or the tumor itself, may account for reduced feeding. Such changes may include impaired activity of NPY or failure of CRF activity to be suppressed after underfeeding and weight loss.

Adipose Tissue↗

Attenuation of leptin-mediated effects by monosodium glutamate-induced arcuate nucleus damage.

Leptin is a protein secreted by adipocytes that is important in regulating appetite and adiposity. Recent studies have suggested the presence of leptin receptors in the arcuate nucleus of the hypothalamus (ANH). Neonatal administration of monosodium glutamate (MSG) damages the ANH, resulting in obesity and neuroendocrine dysfunction. Neonatal administration of MSG was utilized to test the hypothesis that the anatomic site for many of leptin's actions is the ANH. Female control (n = 6) and MSG-treated rats (n = 7) were implanted for 14 days with osmotic minipumps containing phosphate-buffered saline or leptin (1 mg.kg-1.day-1). Leptin suppressed (P < 0.05) body weight gain in controls but did not suppress weight gain in MSG-treated rats. Leptin decreased (P < 0.05) fat depots in controls but had no effect in MSG-treated rats. Night feeding was suppressed (P < 0.05) in leptin-treated control rats. MSG-treated rats showed a suppression in food intake that was of a smaller magnitude and appeared later in the course of leptin treatment. These findings suggest that leptin mediates some physiological actions related to fat mobilization via receptors located in the ANH.

Adipose Tissue↗

Programmed obesity in intrauterine growth-restricted newborns: modulation by newborn nutrition.

The degree of nutrient enhancement during the newborn period may modulate programming of appetite-regulating hormones, body composition, and propensity to adult obesity in intrauterine growth-restricted (IUGR) newborns. Pregnant rats received, from day 10 to term gestation and throughout lactation, ad libitum food (AdLib) or 50% food restriction (FR) to produce IUGR newborns. AdLib vs. FR offspring were studied at day 1, and, to create two distinct groups of newborn catch-up growth (immediate, delayed) among the IUGR newborns, cross-fostering techniques were employed. The four groups of pups at 3 wk were IUGR immediate catch-up growth (FR/AdLib), IUGR delayed catch-up growth (FR/FR), control (AdLib/AdLib), and lactation FR control (AdLib/FR). From 3 wk to 9 mo, all offspring had AdLib rat chow. Maternal FR during pregnancy resulted in IUGR pups (6.0 +/- 0.3 vs. 7.1 +/- 0.3 g, P < 0.01) with decreased leptin (0.66 +/- 0.03 vs. 1.63 +/- 0.12 ng/ml, P < 0.001) and increased ghrelin (0.43 +/- 0.03 vs. 0.26 +/- 0.02 ng/ml, P < 0.001). Maternal FR during lactation (FR/FR) further impaired IUGR offspring growth at 3 wk. However, by 9 mo, these pups attained normal body weight, percent body fat, and plasma leptin levels. Conversely, IUGR offspring nursed by AdLib dams (FR/AdLib) exhibited rapid catch-up growth at 3 wk and continued accelerated growth, resulting in increased weight, percent body fat, and plasma leptin levels. Thus the degree of newborn nutrient enhancement and timing of IUGR newborn catch-up growth may determine the programming of orexigenic hormones and offspring obesity.

Animals↗

Size at birth, postnatal growth and risk of obesity.

Epidemiological studies over the last 15 years have shown that size at birth, early postnatal catch-up growth and excess childhood weight gain are associated with an increased risk of adult cardiovascular disease and type 2 diabetes. At the same time, rising rates of obesity and overweight in children, even at pre-school ages, have shifted efforts towards the identification of very early factors that predict risk of subsequent obesity, which may allow early targeted interventions. Overall, higher birth weight is positively associated with subsequent greater body mass index in childhood and later life; however, the relationship is complex. Higher birth weight is associated with greater subsequent lean mass, rather than fat mass. In contrast, lower birth weight is associated with a subsequent higher ratio of fat mass to lean mass, and greater central fat and insulin resistance. This paradoxical effect of lower birth weight is at least partly explained by the observation that infants who have been growth restrained in utero tend to gain weight more rapidly, or 'catch up', during the early postnatal period, which leads to increased central fat deposition. There is still debate as to whether there are critical early periods for obesity: does excess weight gain during infancy, childhood or even very early neonatal life have a greater impact on long-term fat deposition and insulin resistance? Early identification of childhood obesity risk will be aided by identification of maternal and fetal genes that regulate fetal nutrition and growth, and postnatal genes that regulate appetite, energy expenditure and the partitioning of energy intake into fat or lean tissue growth.

Birth Weight↗

Obesity-associated hypertension: new insights into mechanisms.

Obesity is strongly associated with hypertension and cardiovascular disease. Several central and peripheral abnormalities that can explain the development or maintenance of high arterial pressure in obesity have been identified. These include activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system. Obesity is also associated with endothelial dysfunction and renal functional abnormalities that may play a role in the development of hypertension. The continuing discovery of mechanisms regulating appetite and metabolism is likely to lead to new therapies for obesity-induced hypertension. Better understanding of leptin signaling in the hypothalamus and the mechanisms of leptin resistance should facilitate therapeutic approaches to reverse the phenomenon of selective leptin resistance. Other hunger and satiety signals such as ghrelin and peptide YY are potentially attractive therapeutic strategies for treatment of obesity and its complications. These recent discoveries should lead to novel strategies for treatment of obesity and hypertension.

Adiponectin↗

Variability and discontinuity of the pathognomonic systemic effects caused by Walker 256 tumor progression in rats.

Cancer pathognomonic systemic effects (PSE) have high individual variability. For this reason present data were collected daily and synchronized considering four main points: inoculation day, onset of PSE, aggravation and death. The subclinical period free of PSE ranged between 15.7 +/- 2.2 days, the clinical period was less variable, 8.9 +/- 0.5 days, divided in a moderate and a grave phase of nearly the same length. PSE involved disturbances of fundamental homeostatic regulations: appetite, sodium, water, immune, etc. PSE triggering correlated highly with survival (r2 = 0.95, P < 0.01), but poorly with primary tumor growth, and it was anticipated by metastases from 20.5 +/- 2.6 to 10.6 +/- 1.1 days (P < 0.01). After multifocal simultaneous inoculations, PSE triggering was anticipated to 4.2 +/- 0.2 days (marked reduction of individual variability), in the presence of small total-tumor masses, absence of macroscopic metastases, and without changes in the following clinical period features. PSE triggering seems to be a major prognostic indicator probably related to multifocal tumor growth.

Animals↗

Galanin and cognition.

Since the neuropeptide galanin's discovery in 1983, information has accumulated that implicates it in a wide range of functions, including pain sensation, stress responses, appetite regulation, and learning and memory. This article reviews the evidence for specific functions of galanin in cognitive processes. Consistencies as well as gaps in the literature are organized around basic questions of methodology and theory. This review shows that although regularities are evident in the observed behavioral effects of galanin across several methods for measuring learning and memory, generalization from these findings is tempered with concerns about confounds and a restricted range of testing conditions. Furthermore, it is revealed that many noncognitive behavioral constructs that are relevant for assessing potential roles for galanin in cognition have not been thoroughly examined. The review concludes by laying out how future theory and experimental work can overcome these concerns and confidently define the nature of the association of galanin with particular cognitive constructs.

Behavior↗

Food restriction-like effects of dietary dehydroepiandrosterone. Hypothalamic neurotransmitters and metabolites in male C57BL/6 and (C57BL/6 x DBA/2)F1 mice.

Dehydroepiandrosterone (DHEA) is a precursor of sex hormones in mammals. Dietary DHEA serves to prevent or inhibit various diseases and also lengthens life spans of animals. Moreover, dietary DHEA inhibits food intake in certain strains of mice. We administered DHEA (0.45% w/w of food) to C57BL/6 (B6) and (B6 x DBA/2)F1 (BDF1) mice for 5 weeks. Food intake was inhibited in both strains of mice during the first week. Thereafter, B6, but not BDF1, mice consumed less food. Because hypothalamic serotonin and/or dopamine regulate appetite, satiety and other behaviors, the hypothesis tested was that hypothalamic concentration of serotonin, dopamine and/or their metabolites are affected differentially in B6 and BDF1 mice fed DHEA. In another study, mice were fed the AIN-76A diet with or without DHEA for 1 and 7 days or were pair-fed to DHEA-fed mice for 7 days. On Day 1 of DHEA feeding (acute effects) hypothalamic levels of serotonin, dopamine, and metabolites were unchanged in B6 mice, but levels of dopamine were increased and levels of dopamine metabolites were decreased in BDF1 mice. On Day 7 of DHEA feeding, levels of serotonin were increased in BDF1 but not B6 mice. On Day 7 of pair-feeding there were decreased levels of hypothalamic dopamine metabolites in BDF1 but not B6 mice. Paraventricular nuclei of BDF1 mice had decreased levels of serotonin but not of dopamine in all groups. Serum levels of DHEA and its metabolite, 5-androstene-3beta,17beta-diol, correlated significantly only with serotonin concentrations in BDF1 mice. The salient findings of these experiments are that DHEA inhibits food intake to a greater extent in B6 than in BDF1 mice. However, alterations of hypothalamic neurotransmitters were greater in BDF1 than in B6 mice. Because BDF1 and B6 mice share B6 genes, relevant gene(s) derived from DBA/2 mice might mediate the different responses detected.

3,4-Dihydroxyphenylacetic Acid↗

Central nervous and metabolic effects of intranasally applied leptin.

In obesity, due to the resistance of leptin receptors at the blood brain barrier, increased peripheral leptin levels cannot act appropriately at brain sites relevant for appetite regulation. In this study, we focused on the intranasal application of leptin. This mode of administration provides a promising tool for a direct access of peptides to the brain by circumventing the blood brain barrier. Male Wistar rats were treated daily with 0.1 or 0.2 mg/kg leptin intranasally for 4 wk. Compared with controls, leptin-treated animals gained significantly less weight and exhibited significantly reduced food and water intake. Corticotropin-releasing factor mRNA expression in the paraventricular nucleus showed a tendency for up-regulation by leptin; neuropeptide Y mRNA expression in the arcuate nucleus was decreased. In the central nucleus of the amygdala, corticotropin-releasing factor mRNA was significantly elevated in leptin-treated animals, suggesting a role in affective and/or emotional aspects of food intake. Serum leptin levels were unchanged, indicating a direct action of leptin in the central nervous system without prior access to the periphery. The intranasal application thus represents a useful tool to administer leptin in a noninvasive way with rapid permeation into the central nervous system.

Administration, Intranasal↗

Central relaxin-3 administration causes hyperphagia in male Wistar rats.

Relaxin-3 (INSL-7) is a recently discovered member of the insulin superfamily. Relaxin-3 mRNA is expressed in the nucleus incertus of the brainstem, which has projections to the hypothalamus. Relaxin-3 binds with high affinity to the LGR7 receptor and to the previously orphan G protein-coupled receptor GPCR135. GPCR135 mRNA is expressed predominantly in the central nervous system, particularly in the paraventricular nucleus (PVN). The presence of relaxin-3 and these receptors in the PVN led us to investigate the effect of central administration of relaxin-3 on food intake in male Wistar rats. The receptor involved in mediating these effects was also investigated. Intracerebroventricular injections of human relaxin-3 (H3) to satiated rats significantly increased food intake 1 h post administration in the early light phase [0.96 +/- 0.16 g (vehicle) vs. 1.81 +/- 0.21 g (180 pmol H3), P < 0.05] and the early dark phase [2.95 +/- 0.45 g (vehicle) vs. 4.39 +/- 0.39 g (180 pmol H3), P < 0.05]. Intra-PVN H3 administration significantly increased 1-h food intake in satiated rats in the early light phase [0.34 +/- 0.16 g (vehicle) vs. 1.23 +/- 0.30 g (18 pmol H3), P < 0.05] and the early dark phase [4.43 +/- 0.32 g (vehicle) vs. 6.57 +/- 0.42 g (18 pmol H3), P < 0.05]. Feeding behavior increased after intra-PVN H3. Equimolar doses of human relaxin-2, which binds the LGR7 receptor but not GPCR135, did not increase feeding. Hypothalamic neuropeptide Y, proopiomelanocortin, or agouti-related peptide mRNA expression did not change after acute intracerebroventricular H3. These results suggest a novel role for relaxin-3 in appetite regulation.

Animals↗

Reduction in adiposity affects the extent of afferent projections to growth hormone-releasing hormone and somatostatin neurons and the degree of colocalization of neuropeptides in growth hormone-releasing hormone and somatostatin cells of the ovine hypothalamus.

Various neuropeptides and neurotransmitters affect GH secretion by acting on GHRH and somatostatin (SRIF) cells. GH secretion is also affected by alteration in adiposity, which could be via modulation of GHRH and SRIF cells. We quantified colocalization of neuropeptides in GHRH and SRIF cells and afferent projections to these cells in lean (food restricted) and normally fed sheep (n=4/group). The number of GHRH-immunoreactive (IR) cells in the arcuate nucleus was higher in lean animals, but the number of SRIF-IR cells in the periventricular nucleus was similar in the two groups. A subpopulation of GHRH-IR cells colocalized neuropeptide Y in lean animals, but this was not seen in normally fed animals. GHRH/galanin (GAL) colocalization was higher in lean animals with no difference in numbers of GHRH/tyrosine hydroxylase or GHRH/GAL-like peptide cells. SRIF/enkephalin colocalization was lower in lean animals. The percentage of GHRH neurons receiving SRIF input was similar in lean and normally fed animals, but more GHRH cells received input from enkephalin afferents in normally fed animals. The percentage of SRIF cells receiving GHRH, neuropeptide Y, GAL, and orexin afferents was higher in lean animals. These findings provide an anatomical evidence of central mechanism(s) by which appetite-regulating peptides and dopamine could regulate GH secretion. Increased input to SRIF cells in lean animals may be inhibitory and permissive of increased GH. The appearance of NPY in GHRH cells of lean animals may be a mechanism for regulation of increasing GH secretion with reduced adiposity.

Adipose Tissue↗

Leptin acts on metabolism in a photoperiod-dependent manner, but has no effect on reproductive function in the seasonally breeding Siberian hamster (Phodopus sungorus).

Leptin may play a role in appetite regulation and metabolism, but its reproductive role is less clear. In photoperiodic Siberian hamsters, seasonal changes in fatness, leptin gene expression, and metabolism occur synchronously with activation or suppression of reproduction, analogous to puberty. Here, we test the hypothesis that seasonal changes in leptin secretion mediate the photoperiodic regulation of reproduction. Mature male and ovariectomized estrogen-treated female Siberian hamsters were kept in long (LD; 16 h of light, 8 h of darkness) or short days (SD; 8 h of light, 16 h of darkness) for 8 weeks, and recombinant murine leptin (15 microg/day) was infused for 2 weeks via osmotic minipumps. SD hamsters exhibited significant weight and fat losses, reduced serum leptin and food intake, and suppressed pituitary LH concentration. Leptin did not suppress food intake over the 2-week treatment on either photoperiod, but significantly reduced fat reserves in SD hamsters. Leptin had no significant effect on pituitary LH concentrations in either sex or photoperiod or on testicular size and testosterone concentrations in males. These results suggest hamsters are more responsive to leptin on SD than on LD and that effects on food intake and fat loss can be dissociated in this species. Our data suggest that leptin does not mediate photoperiodic reproductive changes.

Animals↗

Expression of the leptin receptor during germ cell development in the mouse testis.

Leptin, a recently identified hormonal product of the ob gene, is known to regulate appetite, body metabolism, and reproductive functions. We investigated the expression of the leptin receptor (Ob-R) in testes from different age groups. The messenger RNA for Ob-R was found in testes from all age groups using RT-PCR. Using immunohistochemistry, we observed age- and stage-dependent distribution of the Ob-R in mouse testis. In testis of 5-day-old mice, its expression was mainly in type A spermatogonia. In the 20- and 30-day-old testis, Ob-R expression was in the spermatocytes; in the adult testis, it was specific to spermatocytes in stages IX and X of the cycle of the seminiferous epithelium. Five main immunoreactive proteins were detected using Western blot (220, 120, 90, 66, and 46 kDa). The 120-kDa protein was evident only in 20-day-old and older testes, whereas the 90-kDa band was present only in the 5- and 10-day-old testis. Leptin treatment induced phosphorylation of signal transducer and activator of transcription-3 in cultured seminiferous tubules from adult and 5-day-old testes. Our results show for the first time age- and stage-specific localization of a functional Ob-R in testicular germ cells. We hypothesize a direct role for leptin, through phosphorylation of signal transducer and activator of transcription-3, in proliferation and differentiation of germ cells, which may partially explain the infertility observed in leptin-deficient mice.

Aging↗

Cerebrospinal fluid ghrelin is negatively associated with body mass index.

Ghrelin is a 28 amino acid peptide hormone, predominantly expressed in the gastric epithelium and, at a lower level, in the hypothalamus. Although several lines of evidence indicate that ghrelin has a role in appetite regulation, nevertheless the regulation and role of central ghrelin levels remain unclear. To further characterize the role of ghrelin in the regulation of body adiposity, we investigated the association between fasting cerebrospinal fluid (CSF) ghrelin levels and body mass index (BMI) in humans. We consecutively enrolled 19 adults (aged 21-76 yr, 15 females and 4 males), including 4 obese, 7 overweight and 8 lean subjects, who underwent spinal anesthesia during surgery for non-malignant conditions. We found a negative association between fasting CSF ghrelin levels and BMI (r = -0.48, p = 0.035) and a trend towards lower (by 16%) fasting CSF ghrelin levels in the obese (p = 0.06 for the difference between lean and obese subjects). In conclusion, we found a negative association between fasting CSF ghrelin levels and BMI in humans. Our data suggest that central ghrelin may have a role in the regulation of body adiposity in humans, which requires further study to be fully elucidated.

Adult↗

The gut and regulation of body weight.

Signals generated by the gastrointestinal tract are able to regulate appetite and influence body weight. Ghrelin is an orexigenic peptide produced by the stomach. Satiety signals derived from the intestine and pancreas include peptide YY, pancreatic polypeptide, glucagon-like peptide 1, oxyntomodulin, and cholecystokinin. Signals from the gut and adipose tissue are integrated in the central nervous system to provide energy homeostasis. Knowledge of the body's control of appetite is important because we strive to combat obesity in man.

Animals↗

Independent circadian and sleep/wake regulation of adipokines and glucose in humans.

Leptin and adiponectin play important physiological roles in regulating appetite, food intake, and energy balance and have pathophysiological roles in obesity and anorexia nervosa. To assess the relative contributions of day/night patterns in behaviors (sleep/wake cycle and food intake) and of the endogenous circadian pacemaker on observed day/night patterns of adipokines, in six healthy subjects we measured circulating leptin, soluble leptin receptor, adiponectin, glucose, and insulin levels throughout a constant routine protocol (38 h of wakefulness with constant posture, temperature, and dim light, as well as identical snacks every 2 h) and throughout sleep and fasting periods before and after the constant routine. There were significant endogenous circadian rhythms in leptin, glucose, and insulin, with peaks around the usual time of awakening. Sleep/fasting resulted in additional systematic decreases in leptin, glucose, and insulin, whereas wakefulness/food intake resulted in a systematic increase in leptin. Thus, the day/night pattern in leptin is likely caused by combined effects from the endogenous circadian pacemaker and day/night patterns in behaviors. Our data imply that alterations in the sleep/wake schedule would lead to an increased daily range in circulating leptin, with lowest leptin upon awakening, which, by influencing food intake and energy balance, could be implicated in the increased prevalence of obesity in the shift work population.

Adiponectin↗

Effect of gastric bypass and gastric banding on proneurotensin levels in morbidly obese patients.

CONTEXT: Neurotensin is produced mainly in the N cells of the ileum and has a role in appetite regulation; levels are decreased in obese subjects and increase after bariatric surgery. Mature neurotensin is very unstable, with a short half-life. OBJECTIVE: The objective of this study was to compare baseline and postoperative levels of the more stable neurotensin precursor, proneurotensin/neuromedin (pro-NT/NMN), in patients after gastric banding, gastric bypass, and nonoperated controls, respectively, during long-term follow-up. DESIGN AND SETTING: This was a prospective observational study in a university hospital. PARTICIPANTS AND MAIN OUTCOME MEASURES: Overnight fasting plasma pro-NT/NMN concentrations were measured with a new sandwich immunoassay in morbidly obese subjects at baseline and 6, 12, and 24 months after gastric banding (n = 8), Roux-en-Y gastric bypass (n = 5), and in nonoperated controls (n = 7). RESULTS: After gastric bypass and banding, body weight decreased by (mean +/- sd) 29.5 +/- 5.5 and 22.8 +/- 5.9 kg, respectively. The decrease after 3 and 6 months was more pronounced after gastric bypass compared with gastric banding (P < 0.05). Plasma pro-NT/NMN levels in patients after gastric bypass increased from 246.3 +/- 174.3 pmol/liter on admission to 748.3 +/- 429.6 pmol/liter after 24 months (P < 0.01). In contrast, in patients with gastric banding, pro-NT/NMN concentrations remained stable (207.3 +/- 60.5 pmol/liter at admission, 226.6 +/- 116.8 pmol/liter after 24 months). Neither body weight nor plasma pro-NT/NMN levels changed in nonoperated controls. CONCLUSION: Plasma pro-NT/NMN levels show a more pronounced increase after gastric bypass compared with gastric banding, suggesting that specific bariatric surgical procedures result in distinct alterations of gastrointestinal hormone metabolism. The more stable precursor pro-NT/NMN provides a new tool to quantify neurotensin levels in clinical practice.

Adult↗