Pathophysiological significance of the obese gene product, leptin, in ventromedial hypothalamus (VMH)-lesioned rats: evidence for loss of its satiety effect in VMH-lesioned rats

Intracellular interplay between cholecystokinin and leptin signalling for satiety control in rats

Cholecystokinin (CCK) and leptin are satiety-controlling peptides, yet their interactive roles remain unclear. Here, we addressed this issue using in vitro and in vivo models. In rat C6 glioma cells, leptin pre-treatment enhanced Ca²⁺ mobilization by a CCK agonist (CCK-8s). This leptin action was reduced by Janus kinase inhibitor (AG490) or PI3-kinase inhibitor (LY294002). Meanwhile, leptin stimulation alone failed to mobilize Ca²⁺ even in cells overexpressing leptin receptors (C6-ObRb). Leptin increased nuclear immunoreactivity against phosphorylated STAT3 (pSTAT3) whereas CCK-8s reduced leptin-induced nuclear pSTAT3 accumulation in these cells. In the rat ventromedial hypothalamus (VMH), leptin-induced action potential firing was enhanced, whereas nuclear pSTAT3 was reduced by co-stimulation with CCK-8s. To further analyse in vivo signalling interplay, a CCK-1 antagonist (lorglumide) was intraperitoneally injected in rats following 1-h restricted feeding. Food access was increased 3-h after lorglumide injection. At this timepoint, nuclear pSTAT3 was increased whereas c-Fos was decreased in the VMH. Taken together, these results suggest that leptin and CCK receptors may both contribute to short-term satiety, and leptin could positively modulate CCK signalling. Notably, nuclear pSTAT3 levels in this experimental paradigm were negatively correlated with satiety levels, contrary to the generally described transcriptional regulation for long-term satiety via leptin receptors.

Inflammatory cytokines, appetite-regulating hormones, and energy metabolism in patients with gastrointestinal cancer

This study investigated energy metabolism and its association with inflammatory cytokines and appetite- regulating hormones in patients with gastrointestinal cancer. Subjects were inpatients scheduled to undergo therapeutic intervention for diagnosed gastrointestinal cancer. Nutritional status on admission was assessed based on anthropometric measurements, nutrition screening results, food intake rate (energy intake/energy provided in hospital food), and biochemical test results. Fat-free mass (FFM) was measured using the bioelectrical impedance analysis. Resting energy expenditure (REE) and respiratory quotient were measured with indirect calorimetry, and basal energy expenditure (BEE) was calculated using the Harris-Benedict equation. A total 51 patients with gastrointestinal cancer were enrolled (17 with esophageal cancer, 15 with gastric cancer, and 19 with colorectal cancer); 16 had stage I disease, 11 had stage II, 13 had stage III, and 11 had stage IV. The levels of inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α increased significantly with cancer stage progression (P<0.001; Jonckheere-Terpstra trend test). The REE/body weight and the REE/FFM tended to increase with cancer stage progression (P=0.064 and P=0.053, respectively; Jonckheere-Terpstra trend test). FFM showed a significant negative correlation with the level of TNF-α (P=0.008; Spearman's correlation coefficient). Also, food intake rate showed a significant negative correlation with levels of IL-6 and TNF-α (P<0.001). The level of active ghrelin was positively correlated with that of IL-6 and energy metabolism (P=0.004 and 0.016, respectively) and negatively correlated with food intake rate (P=0.035), which suggests a state of ghrelin resistance. In conclusion, this study confirmed increases in the levels of inflammatory cytokines with the progression of gastrointestinal cancer and suggested the possible association of such increases with decreased FFM and the increased energy metabolism. However, the increased levels of active ghrelin failed to compensate for cachexia in cancer patients.

Hypothalamic mechanisms associated with corticotropin-releasing factor-induced anorexia in chicks

Central administration of corticotropin-releasing factor (CRF), a 41-amino acid peptide, is associated with potent anorexigenic effects in rodents and chickens. However, the mechanism underlying this effect remains unclear. Hence, the objective of the current study was to elucidate the hypothalamic mechanisms that mediate CRF-induced anorexia in 4 day-old Cobb-500 chicks. After intracerebroventricular (ICV) injection of 0.02 nmol of CRF, CRF-injected chicks ate less than vehicle chicks while no effect on water intake was observed at 30 min post-injection. In subsequent experiments, the hypothalamus samples were processed at 60 min post-injection. The CRF-injected chicks had more c-Fos immunoreactive cells in the arcuate nucleus (ARC), dorsomedial nucleus (DMN), ventromedial hypothalamus (VMH), and paraventricular nucleus (PVN) of the hypothalamus than vehicle-treated chicks. CRF injection was associated with decreased whole hypothalamic mRNA abundance of neuropeptide Y receptor sub-type 1 (NPYR1). In the ARC, CRF-injected chicks expressed more CRF and CRF receptor sub-type 2 (CRFR2) mRNA but less agouti-related peptide (AgRP), NPY, and NPYR1 mRNA than vehicle-injected chicks. CRF-treated chicks expressed greater amounts of CRFR2 and mesotocin mRNA than vehicle chicks in the PVN and VMH, respectively. In the DMN, CRF injection was associated with reduced NPYR1 mRNA. In conclusion, the results provide insights into understanding CRF-induced hypothalamic actions and suggest that the anorexigenic effect of CRF involves increased CRFR2-mediated signaling in the ARC and PVN that overrides the effects of NPY and other orexigenic factors.

Corticotrophin-releasing factor mediates vasoactive intestinal peptide-induced hypophagia and changes in plasma parameters

Vasoactive intestinal peptide (VIP) and corticotrophin-releasing factor (CRF) are anorexigenic neuropeptides that act in the hypothalamus to regulate food intake. Intracerebroventricular (ICV) microinjection of VIP promotes increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone, indicating that VIP activates hypothalamic-pituitary-adrenal axis. The aim of this study was to evaluate the interaction between VIP and CRF, by verifying the effects of ICV administration of VIP on the activity of neurons and CRF mRNA expression in paraventricular nucleus of hypothalamus (PVN). In addition, it was evaluated the effects of pretreatment with CRF type 1 receptor (CRFR1) antagonist (Antalarmin, ANT) or CRF type 2 receptor (CRFR2) antagonist (Antisauvagine-30, AS30) on VIP-induced changes on food intake and plasma parameters of male rats. Compared to Saline group, VIP increased not only the number of Fos-related antigens (FRA)-immunoreactive neurons in the PVN but also CRF mRNA levels in this nucleus. Both ANT and AS30 treatment attenuated the inhibition of food intake promoted by VIP, ANT showing a more pronounced effect. Both antagonists also attenuated VIP-induced reduction and enhancement of free fatty acids and corticosterone plasma levels, respectively, and only AS30 was able to attenuate the hyperglycemia. These results suggest that CRF is an important mediador of VIP effects on energy balance, and CRFR1 and CRFR2 are involved in these responses.

The Melanin-concentrating Hormone System in Human, Rodent and Avian Brain

Melanin-concentrating hormone (MCH) is a cyclic 19 amino acid orexigenic hypothalamic peptide. MCH is located in the lateral and dorsal hypothalamus, as well as in the zona incerta. In mammals MCH increases food intake, contributes to regulation of energy balance, temperature, reproductive function, endocrine homeostasis and biological rhythms. Several studies have proved the significance of MCH in obesity, diabetes and depression.

Although the peptide is well-characterized in mouse models, much less is known about its functions in avians. In birds the MCH system especially in the lateral and basal hypothalamus has important connections to the limbic system and it coordinates the vegetative and endocrine functions, as well as the emotional behaviour. Pharmacological modulation of MCH system could contribute to the therapy of eating disorders and improve agricultural efficiency regarding avians. Reviewing the current knowledge on MCH system in human, rodents and avians may stimulate a new wave of studies in the field.

Food intake regulation in late pregnancy and early lactation

The dip in food intake, which starts in late pregnancy and continues into early lactation, has traditionally been interpreted as a depression in intake due to physical constraints. However, the rôle of physical constraints on intake has been overemphasized, particularly in early lactation. There is mounting evidence that the presence and mobilization of body reserves in early lactation play an important rôle in regulating intake at this time.

Conceptually, the dip in intake in early lactation observed when cows have access to non-limiting foods can be accounted for by assuming that the cow has a desired level of body reserves. When the cow is not compromised, the changes with time in body reserves and the dip in intake represent the normal case and provide the basis against which to assess true depressions in intake which may occur when the cow is compromised by limiting nutrition or environment.

The regulation of body reserves and intake in the periparturient cow is orchestrated through nervous and hormonal signals. Likely factors that are involved in intake regulation are reproductive hormones, neuropeptides, adrenergic signals, insulin and insulin resistance and leptin. Furthermore, oxidation of NEFA in the liver may result in feedback signals that reduce intake. The relative importance of these is discussed. A better understanding of the physiological signals involved in intake regulation and their interrelations with body weight regulation may provide important indicators of the degree of compromise that periparturient cows may experience.

The role of polycarbonate monomer bisphenol-A in insulin resistance

Bisphenol A (BPA) is a synthetic unit of polycarbonate polymers and epoxy resins, the types of plastics that could be found in essentially every human population and incorporated into almost every aspect of the modern human society. BPA polymers appear in a wide range of products, from liquid storages (plastic bottles, can and glass linings, water pipes and tanks) and food storages (plastics wraps and containers), to medical and dental devices. BPA polymers could be hydrolyzed spontaneously or in a photo- or temperature-catalyzed process, providing widespread environmental distribution and chronic exposure to the BPA monomer in contemporary human populations. Bisphenol A is also a xenoestrogen, an endocrine-disrupting chemical (EDC) that interferes with the endocrine system mimicking the effects of an estrogen and could potentially keep our endocrine system in a constant perturbation that parallels endocrine disruption arising during pregnancy, such as insulin resistance (IR). Gestational insulin resistance represents a natural biological phenomenon of higher insulin resistance in peripheral tissues of the pregnant females, when nutrients are increasingly being directed to the embryo instead of being stored in peripheral tissues. Gestational diabetes mellitus may appear in healthy non-diabetic females, due to gestational insulin resistance that leads to increased blood sugar levels and hyperinsulinemia (increased insulin production from the pancreatic beta cells). The hypothesis states that unnoticed and constant exposure to this environmental chemical might potentially lead to the formation of chronic low-level endocrine disruptive state that resembles gestational insulin resistance, which might contribute to the development of diabetes. The increasing body of evidence supports the major premises of this hypothesis, as exemplified by the numerous publications examining the association of BPA and insulin resistance, both epidemiological and mechanistic. However, to what extent BPA might contribute to the development of diabetes in the modern societies still remains unknown. In this review, I discuss the chemical properties of BPA and the sources of BPA contamination found in the environment and in human tissues. I provide an overview of mechanisms for the proposed role of bisphenol A in insulin resistance and diabetes, as well as other related diseases, such as cardiovascular diseases. I describe the transmission of BPA effects to the offspring and postulate that gender related differences might originate from differences in liver enzyme levels, such as UDP-glucuronosyltransferase, which is involved in BPA processing and its elimination from the organism. I discuss the molecular mechanisms of BPA action through nuclear and membrane-bound ER receptors, non-monotonic dose response, epigenetic modifications of the DNA and propose that chronic exposure to weak binders, such as BPA, may mimic the effects of strong binders, such as estrogens.

Hypothalamic AMP-Activated Protein Kinase Regulates Biphasic Insulin Secretion from Pancreatic β Cells during Fasting and in Type 2 Diabetes

Glucose-stimulated insulin secretion (GSIS) by pancreatic β cells is biphasic. However, the physiological significance of biphasic GSIS and its relationship to diabetes are not yet fully understood. This study demonstrated that impaired first-phase GSIS follows fasting, leading to increased blood glucose levels and brain glucose distribution in humans. Animal experiments to determine a possible network between the brain and β cells revealed that fasting-dependent hyperactivation of AMP-activated protein kinase in the hypothalamus inhibited first-phase GSIS by stimulating the α-adrenergic pancreatic nerve. Furthermore, abnormal excitability of this brain-β cell neural axis was involved in diabetes-related impairment of first-phase GSIS in diabetic animals. Finally, pancreatic denervation improved first-phase GSIS and glucose tolerance and ameliorated severe diabetes by preventing β cell loss in diabetic animals. These results indicate that impaired first-phase GSIS is critical for brain distribution of dietary glucose after fasting. Furthermore, β cells in individuals with diabetes mistakenly sense that they are under conditions that mimic prolonged fasting. The present study provides additional insight into both β cell physiology and the pathogenesis of β cell dysfunction in type 2 diabetes.

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Fasting-induced hypothalamic AMPK activation inhibited first-phase GSIS by stimulating the α-adrenergic nerve.

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The brain-pancreas neural axis was involved in β cell dysfunction and glucose intolerance in diabetes.

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Pancreatic denervation improved first-phase GSIS, glucose tolerance and β cell survival in type 2 diabetic animals.

Glucose-stimulated insulin secretion (GSIS) from pancreatic β cells is biphasic. Furthermore, first-phase GSIS is inhibited in type 2 diabetes. This study revealed that fasting reduced first-phase GSIS by signaling via the brain-pancreatic β cell neural axis, which is essential for maintaining glucose supply to the brain at re-feeding after fasting. Abnormal excitability of this neural axis was also associated with impaired first-phase GSIS in type 2 diabetes. Surgical pancreatic denervation improved diabetes in an animal study. The present data reveal that diabetic β cells exist under conditions that mimic starvation and provide a therapeutic potency of pancreatic denervation against diabetes.

Metabolic signals in sleep regulation: recent insights

Sleep and energy balance are essential for health. The two processes act in concert to regulate central and peripheral homeostasis. During sleep, energy is conserved due to suspended activity, movement, and sensory responses, and is redirected to restore and replenish proteins and their assemblies into cellular structures. During wakefulness, various energy-demanding activities lead to hunger. Thus, hunger promotes arousal, and subsequent feeding, followed by satiety that promotes sleep via changes in neuroendocrine or neuropeptide signals. These signals overlap with circuits of sleep-wakefulness, feeding, and energy expenditure. Here, we will briefly review the literature that describes the interplay between the circadian system, sleep-wake, and feeding-fasting cycles that are needed to maintain energy balance and a healthy metabolic profile. In doing so, we describe the neuroendocrine, hormonal/peptide signals that integrate sleep and feeding behavior with energy metabolism.

The Orphan G Protein-Coupled Receptor Gene GPR178 Is Evolutionary Conserved and Altered in Response to Acute Changes in Food Intake

G protein-coupled receptors (GPCRs) are a class of integral membrane proteins mediating physiological functions fundamental for survival, including energy homeostasis. A few years ago, an amino acid sequence of a novel GPCR gene was identified and named GPR178. In this study, we provide new insights regarding the biological significance of Gpr178 protein, investigating its evolutionary history and tissue distribution as well as examining the relationship between its expression level and feeding status. Our phylogenetic analysis indicated that GPR178 is highly conserved among all animal species investigated, and that GPR178 is not a member of a protein family. Real-time PCR and in situ hybridization revealed wide expression of Gpr178 mRNA in both the brain and periphery, with high expression density in the hypothalamus and brainstem, areas involved in the regulation of food intake. Hence, changes in receptor expression were assessed following several feeding paradigms including starvation and overfeeding. Short-term starvation (12–48h) or food restriction resulted in upregulation of Gpr178 mRNA expression in the brainstem, hypothalamus and prefrontal cortex. Conversely, short-term (48h) exposure to sucrose or Intralipid solutions downregulated Gpr178 mRNA in the brainstem; long-term exposure (10 days) to a palatable high-fat and high-sugar diet resulted in a downregulation of Gpr178 in the amygdala but not in the hypothalamus. Our results indicate that hypothalamic Gpr178 gene expression is altered during acute exposure to starvation or acute exposure to palatable food. Changes in gene expression following palatable diet consumption suggest a possible involvement of Gpr178 in the complex mechanisms of feeding reward.

Gene-environment interactions controlling energy and glucose homeostasis and the developmental origins of obesity

Obesity and type 2 diabetes mellitus (T2DM) often occur together and affect a growing number of individuals in both the developed and developing worlds. Both are associated with a number of other serious illnesses that lead to increased rates of mortality. There is likely a polygenic mode of inheritance underlying both disorders, but it has become increasingly clear that the pre- and postnatal environments play critical roles in pushing predisposed individuals over the edge into a disease state. This review focuses on the many genetic and environmental variables that interact to cause predisposed individuals to become obese and diabetic. The brain and its interactions with the external and internal environment are a major focus given the prominent role these interactions play in the regulation of energy and glucose homeostasis in health and disease.

FTO knockdown in rat ventromedial hypothalamus does not affect energy balance

Single nucleotide polymorphisms (SNPs) clustered in the first intron of the fat mass and obesity‐associated (FTO) gene has been associated with obesity. FTO expression is ubiquitous, with particularly high levels in the hypothalamic area of the brain. To investigate the region‐specific role of FTO, AAV technology was applied to knockdown FTO in the ventromedial hypothalamus (VMH). No effect of FTO knockdown was observed on bodyweight or parameters of energy balance. Animals were exposed twice to an overnight fast, followed by a high‐fat high‐sucrose (HFHS) diet for 1 week. FTO knockdown did not result in a different response to the diets. A region‐specific role for FTO in the VMH in the regulation of energy balance could not be found.

Knocking down expression of the obesity‐associated gene FTO in rat ventromedial hypothalamus did not affect energy balance.

20 years of leptin: role of leptin in energy homeostasis in humans

The hyperphagia, low sympathetic nervous system tone, and decreased circulating concentrations of bioactive thyroid hormones that are common to states of congenital leptin deficiency and hypoleptinemia following and during weight loss suggest that the major physiological function of leptin is to signal states of negative energy balance and decreased energy stores. In weight-reduced humans, these phenotypes together with pronounced hypometabolism and increased parasympathetic nervous system tone create the optimal circumstance for weight regain. Based on the weight loss induced by leptin administration in states of leptin deficiency (obese) and observed similarity of phenotypes in states of congenital and dietary-induced states of hypoleptinemia (reduced obese), it has been suggested that exogenous leptin could potentially be useful in initiating, promoting, and sustaining weight reduction. However, the responses of human beings to exogenous leptin administration are dependent not only on extant energy stores but also on energy balance. Leptin administration to humans at usual weight has little, if any, effect on body weight while leptin administration during weight loss mitigates hunger, especially if given in supraphysiological doses during severe caloric restriction. Leptin repletion is most effective following weight loss by dietary restriction. In this state of weight stability but reduced energy stores, leptin at least partially reverses many of the metabolic, autonomic, neuroendocrine, and behavioral adaptations that favor weight regain. The major physiological function of leptin is to signal states of negative energy balance and decreased energy stores. Leptin, and pharmacotherapies affecting leptin signaling pathways, is likely to be most useful in sustaining weight loss.

Ventromedial hypothalamus-specific Ptpn1 deletion exacerbates diet-induced obesity in female mice

Protein-tyrosine phosphatase 1B (PTP1B) regulates food intake (FI) and energy expenditure (EE) by inhibiting leptin signaling in the hypothalamus. In peripheral tissues, PTP1B regulates insulin signaling, but its effects on CNS insulin action are largely unknown. Mice harboring a whole-brain deletion of the gene encoding PTP1B (Ptpn1) are lean, leptin-hypersensitive, and resistant to high fat diet-induced (HFD-induced) obesity. Arcuate proopiomelanocortin (POMC) neuron-specific deletion of Ptpn1 causes a similar, but much milder, phenotype, suggesting that PTP1B also acts in other neurons to regulate metabolism. Steroidogenic factor-1-expressing (SF-1-expressing) neurons in the ventromedial hypothalamus (VMH) play an important role in regulating body weight, FI, and EE. Surprisingly, Ptpn1 deletion in SF-1 neurons caused an age-dependent increase in adiposity in HFD-fed female mice. Although leptin sensitivity was increased and FI was reduced in these mice, they had impaired sympathetic output and decreased EE. Immunohistochemical analysis showed enhanced leptin and insulin signaling in VMH neurons from mice lacking PTP1B in SF-1 neurons. Thus, in the VMH, leptin negatively regulates FI, promoting weight loss, whereas insulin suppresses EE, leading to weight gain. Our results establish a novel role for PTP1B in regulating insulin action in the VMH and suggest that increased insulin responsiveness in SF-1 neurons can overcome leptin hypersensitivity and enhance adiposity.

Recombinant adeno-associated virus: efficient transduction of the rat VMH and clearance from blood

To promote the efficient and safe application of adeno-associated virus (AAV) vectors as a gene transfer tool in the central nervous system (CNS), transduction efficiency and clearance were studied for serotypes commonly used to transfect distinct areas of the brain. As AAV2 was shown to transduce only small volumes in several brain regions, this study compares the transduction efficiency of three AAV pseudotyped vectors, namely AAV2/1, AAV2/5 and AAV2/8, in the ventromedial nucleus of the hypothalamus (VMH). No difference was found between AAV2/1 and AAV2/5 in transduction efficiency. Both AAV2/1 and AAV2/5 achieved a higher transduction rate than AAV2/8. One hour after virus administration to the brain, no viral particles could be traced in blood, indicating that no or negligible numbers of virions crossed the blood-brain barrier. In order to investigate survival of AAV in blood, clearance was determined following systemic AAV administration. The half-life of AAV2/1, AAV2/2, AAV2/5 and AAV2/8 was calculated by determining virus clearance rates from blood after systemic injection. The half-life of AAV2/2 was 4.2 minutes, which was significantly lower than the half-lives of AAV2/1, AAV2/5 and AAV2/8. With a half-life of more than 11 hours, AAV2/8 particles remained detectable in blood significantly longer than AAV2/5. We conclude that application of AAV in the CNS is relatively safe as no AAV particles are detectable in blood after injection into the brain. With a half-life of 1.67 hours of AAV2/5, a systemic injection with 1×10⁹ genomic copies of AAV would be fully cleared from blood after 2 days.

Deficient leptin signaling ameliorates systemic lupus erythematosus lesions in MRL/Mp-Fas lpr mice

Leptin is secreted by adipocytes, the placenta, and the stomach. It not only controls appetite through leptin receptors in the hypothalamus, it also regulates immunity. In the current study, we produced leptin-deficient MRL/Mp-Fas(lpr) mice to investigate the potential role of leptin in autoimmunity. C57BL/6J-ob/ob mice were backcrossed with MRL/Mp-Fas(lpr) mice, which develop human systemic lupus erythematosus (SLE)-like lesions. The effects of leptin deficiency on various SLE-like manifestations were investigated in MRL/Mp-Fas(lpr) mice. The regulatory T cell population in the spleen was analyzed by flow cytometry, and the effects of leptin on regulatory T cells and Th17 cells were evaluated in vitro. Compared with leptin-producing MRL/Mp-Fas(lpr) mice, leptin-deficient MRL/Mp-Fas(lpr) mice showed less marked splenomegaly and a particularly low population of CD3(+)CD4(-)CD8(-)B220(+) T cells (lpr cells). Their serum concentrations of Abs to dsDNA were lower, and renal histological changes at age 20 wk were ameliorated. Regulatory T cells were increased in the spleens of leptin-deficient MRL/Mp-Fas(lpr) mice. Leptin suppressed regulatory T cells and enhanced Th17 cells in vitro. In conclusion, blockade of leptin signaling may be of therapeutic benefit in patients with SLE and other autoimmune diseases.

Relationship between serum leptin level and disease activity in patients with systemic sclerosis

To determine the relationship between serum leptin levels and disease activity in systemic sclerosis (SSc). A total of 60 subjects (30 controls and 30 patients) were included. The inflammatory markers and leptin levels were evaluated and body mass index (BMI) was measured for both groups. The assessment of the skin involvement was performed based on the modified Rodnan skin score (mRSS). Disease activity was evaluated according to the Valentini scleroderma disease activity index. There was a significant difference between the patient and control groups in terms of BMI (p < 0.05); however there was no difference with regards to age and gender (p > 0.05). Valentini scores and mRSS were determined to be significantly higher in active patients (n = 14) than in inactive patients (n = 16) (p < 0.05). No significant difference was determined between groups in terms of leptin levels (p > 0.05). However, leptin levels were significantly lower in active patients than in inactive patients (p < 0.05). We found a significant positive correlation between serum leptin and BMI (p < 0.05), and leptin and serum C3 levels (p < 0.05); no relationship was detected between leptin and other parameters. Leptin can be used as an activity marker in SSc. Further studies, including larger series, should be carried out to clarify this relationship.

Ventromedial hypothalamic lesions enhance small intestinal cell proliferation in mice

SUMMARY

BACKGROUND

We have found previously that ventromedial hypothalamic lesions (VMH) enhance cell proliferation in the visceral organs through vagal hyperactivity in rats. The goal of the current study was to determine the characteristics and nature of cell proliferation in the small intestine in VMH-lesioned mice.

METHODS

The weight and length of the small intestine, thickness of the mucosal and muscle layers, number of proliferating cell nuclear antigen (PCNA)-positive cells, and mitotic cell count in the mucosal layer in VMH-lesioned and Sham VMH-lesioned mice were determined at 7 days after the operation.

RESULTS

The weight and length of the small intestine in VMH-lesioned mice were significantly greater than those in Sham VMH-lesioned mice, by 11.6% and 15.0%, respectively. The thicknesses of the mucosal and muscle layers of the small intestine in VMH-lesioned mice were also significantly greater than those in Sham VMH-lesioned mice, by 12.7% and 12.5%, respectively. PCNA-positive cells and mitotic cells in the mucosal layer were densely present in crypts in VMH-lesioned mice, and were significantly increased by 31.9% and 71.7%, respectively, compared to Sham VMH-lesioned mice.

CONCLUSIONS

These results demonstrate that VMH lesions in mice enhance cell proliferation in the mucosal layers and cause cell hypertrophy or cell proliferation in the muscle layers of the small intestine, which increases the weight and length of the small intestine. VMH lesions in mice may be a new tool for identifying growth factors and related genes involved in enlarging the small intestine mainly through cell proliferation.

Inhibition of immobilization stress-induced anorexia, behavioral deficits, and plasma corticosterone secretion by injected leptin in rats

Leptin, originally identified as an anti-obesity hormone, also has an important role in the regulation of mood and emotion. The present study was designed to monitor effects of injected leptin on immobilization stress-induced anorexia, behavioral deficits, and plasma corticosterone secretion in rats. Exposure to 2 h immobilization stress decreased food intake and body weight in saline-injected animals. Animals exposed to open field, elevated plus maze, and light-dark transition tests the day following immobilization exhibited anxiety-like behavior. Leptin injected at doses of 0.1 and 0.5 mg/kg also decreased food intake and body weight in unstressed animals and elicited anxiolytic effects at dose of 0.5 mg/kg, monitored on the following day. Immobilization-induced decreases in food intake, body weight, as well as stress-induced behavioral deficits in the open field, elevated plus maze, and light-dark transition test were reversed by exogenous leptin in a dose-dependent (0.1-0.5 mg/kg) manner. Acute exposure to 2 h immobilization produced a fourfold rise in plasma levels of corticosterone. Animals injected with leptin at a dose of 0.1 mg/kg, but not at dose of 0.5 mg/kg, exhibited a marginal increase in plasma corticosterone. Immobilization-induced increases of plasma corticosterone were reversed by leptin injected at doses of 0.1 or 0.5 mg/kg. The data suggest that exogenous leptin can reduce stress perception, resulting in an inhibition of stress effects on the activity of hypothalamic-pituitary-adrenal axis and behavior. The reported pharmacological effects of leptin represent an innovative approach for the treatment of stress-related disorders.

Exercise and obesity in fibromyalgia: beneficial roles of IGF-1 and resistin?

Introduction

Severe fatigue is a major health problem in fibromyalgia (FM). Obesity is common in FM, but the influence of adipokines and growth factors is not clear. The aim was to examine effects of exercise on fatigue, in lean, overweight and obese FM patients.

Methods

In a longitudinal study, 48 FM patients (median 52 years) exercised for 15 weeks. Nine patients were lean (body mass index, BMI 18.5 to 24.9), 26 overweight (BMI 25 to 29.9) and 13 obese. Fatigue was rated on a 0 to 100 mm scale (fibromyalgia impact questionnaire [FIQ] fatigue) and multidimensional fatigue inventory (MFI-20) general fatigue (MFIGF). Higher levels in FIQ fatigue and MFIGF indicate greater degree of fatigue. Free and total IGF-1, neuropeptides, adipokines were determined in serum and cerebrospinal fluid (CSF).

Results

Baseline FIQ fatigue correlated negatively with serum leptin (r = -0.345; P = 0.016) and nerve growth factor (NGF; r = -0.412; P = 0.037). In lean patients, baseline MFIGF associated negatively with serum resistin (r = -0.694; P = 0.038). FIQ Fatigue associated negatively with CSF resistin (r = -0.365; P = 0.073). Similarly, FIQ fatigue (r = -0.444; P = 0.026) and MFIGF correlated negatively with CSF adiponectin (r = -0.508; P = 0.01). In lean patients, FIQ fatigue (P = 0.046) decreased after 15 weeks. After 30 weeks, MFIGF decreased significantly in lean (MFIGF: P = 0.017), overweight (MFIGF: P = 0.001), and obese patients (MFIGF: P = 0.016). After 15 weeks, total IGF-1 increased in lean (P = 0.043) patients. ∆Total IGF-1 differed significantly between lean and obese patients (P = 0.010). ∆Total IGF-1 related negatively with ∆MFIGF after 15 weeks (r = -0.329; P = 0.050). After 30 weeks, ∆FIQ fatigue negatively correlated with ∆NGF (r = -0.463; P = 0.034) and positively with ∆neuropeptide Y (NPY) (r = 0.469; P = 0.032). Resistin increased after 30 weeks (P = 0.034). ∆MFIGF correlated negatively with ∆resistin (r = -0.346; P = 0.031), being strongest in obese patients (r = -0.815; P = 0.007). In obese patients, ∆FIQ fatigue after 30 weeks correlated negatively with ∆free IGF-1 (r = -0.711; P = 0.032).

Conclusions

Exercise reduced fatigue in all FM patients, this effect was achieved earlier in lean patients. Baseline levels of resistin in both serum and CSF associated negatively with fatigue. Resistin was increased after the exercise period which correlated with decreased fatigue. Changes in IGF-1 indicate similar long-term effects in obese patients. This study shows reduced fatigue after moderate exercise in FM and indicates the involvement of IGF-1 and resistin in these beneficial effects.

Trial registration

ClinicalTrials.gov: NCT00643006

Functional magnetic resonance imaging analysis of food-related brain activity in patients with lipodystrophy undergoing leptin replacement therapy

CONTEXT

Lipodystrophy is a disease characterized by a paucity of adipose tissue and low circulating concentrations of adipocyte-derived leptin. Leptin-replacement therapy improves eating and metabolic disorders in patients with lipodystrophy.

OBJECTIVE

The aim of the study was to clarify the pathogenic mechanism of eating disorders in lipodystrophic patients and the action mechanism of leptin on appetite regulation.

SUBJECTS AND INTERVENTIONS

We investigated food-related neural activity using functional magnetic resonance imaging in lipodystrophic patients with or without leptin replacement therapy and in healthy controls. We also measured the subjective feelings of appetite.

RESULTS

Although there was little difference in the enhancement of neural activity by food stimuli between patients and controls under fasting, postprandial suppression of neural activity was insufficient in many regions of interest including amygdala, insula, nucleus accumbens, caudate, putamen, and globus pallidus in patients when compared with controls. Leptin treatment effectively suppressed postprandial neural activity in many of these regions of interest, whereas it showed little effect under fasting in patients. Consistent with these results, postprandial formation of satiety feeling was insufficient in patients when compared with controls, which was effectively reinforced by leptin treatment.

CONCLUSIONS

This study demonstrated the insufficiency of postprandial suppression of food-related neural activity and formation of satiety feeling in lipodystrophic patients, which was effectively restored by leptin. The findings in this study emphasize the important pathological role of leptin in eating disorders in lipodystrophy and provide a clue to understanding the action mechanism of leptin in human, which may lead to development of novel strategies for prevention and treatment of obesity.

Type 2 corticotropin-releasing factor receptor in the ventromedial nucleus of hypothalamus is critical in regulating feeding and lipid metabolism in white adipose tissue

Ventromedial nucleus of hypothalamus (VMH) plays a critical role in regulating feeding and energy metabolism. The nucleus expresses high levels of the type 2 corticotropin-releasing factor receptor (CRFR2) and receives prominent innervation of nerve fibers containing Urocortin 3 (Ucn 3), an endogenous ligand of the receptor. In the present study, we showed that mice deficient in Ucn 3 had elevated basal feeding and increased nocturnal food intake after overnight fasting compared with the wild-type (WT) littermates. The Ucn 3 null mice also had lower circulating insulin levels compared with those of the WT mice. Interestingly, the mutant mice maintained a comparable body weight with the WT littermates. Mice with reduced CRFR2 expression in the VMH by small hairpin RNA knockdown (KD) recapitulated feeding phenotypes observed in the Ucn 3 null mice. However, VMH CRFR2 KD mice gained significantly more weight than control mice. The weight gain was due to an accumulation of white adipose tissue (WAT) accompanied by reduced plasma free fatty acids and glycerol levels, increased respiratory quotients, and improved glucose tolerance. On the other hand, plasma insulin levels were comparable with the receptor KD and control mice. Furthermore, the expression of several genes, including hormone-sensitive lipase, was significantly reduced in the WAT of VMH CRFR2 KD mice compared with controls. These results indicate that Ucn 3 signaling through CRFR2 is a critical molecular mediator in the VMH in regulating feeding and lipid metabolism in WAT.

Prevention of fasting-mediated bone marrow atrophy by leptin administration

Leptin is an adipokine that regulates body weight. In the current study, we demonstrate that continuous injection of leptin prevents the lymphocyte reduction observed in fasted mice, especially the immature B cell populations in the bone marrow. Although leptin administration reduced apoptotic cells in the bone marrow of fasted mice, it did not prevent glucocorticoid-mediated apoptosis in vitro. Bone marrow atrophy has also been shown in the leptin receptor-deficient db/db mice. In order to investigate the mechanisms underlying these processes, we transplanted bone marrow cells from db/db or control (+m/+m) mice into C.B-17/lcr-scid/scid mice. We found that the spleen and bone marrow B cell populations were completely reconstituted when db/db and +m/+m cells were transplanted into scid mice. Our findings suggest that direct interactions between leptin and bone marrow cells are not essential for the development of B cells in a metabologically normal environment.

Hypothalamic obesity after craniopharyngioma: mechanisms, diagnosis, and treatment

Obesity is a common complication after craniopharyngioma therapy, occurring in up to 75% of survivors. Its weight gain is unlike that of normal obesity, in that it occurs even with caloric restriction, and attempts at lifestyle modification are useless to prevent or treat the obesity. The pathogenesis of this condition involves the inability to transduce afferent hormonal signals of adiposity, in effect mimicking a state of CNS starvation. Efferent sympathetic activity drops, resulting in malaise and reduced energy expenditure, and vagal activity increases, resulting in increased insulin secretion and adipogenesis. Lifestyle intervention is essentially useless in this syndrome, termed "hypothalamic obesity." Pharmacologic treatment is also difficult, consisting of adrenergics to mimic sympathetic activity, or suppression of insulin secretion with octreotide, or both. Recently, bariatric surgery (Roux-en-Y gastric bypass, laparoscopic gastric banding, truncal vagotomy) have also been attempted with variable results. Early and intensive management is required to mitigate the obesity and its negative consequences.

Cell proliferation in visceral organs induced by ventromedial hypothalamic (VMH) lesions: Development of electrical VMH lesions in mice and resulting pathophysiological profiles

We have found that ventromedial hypothalamic (VMH) lesions produced by electrocoagulation induce cell proliferation in visceral organs through vagal hyperactivity, and also stimulate regeneration of partially resected liver in rats. To facilitate identification of proliferative and/or regenerative factors at the gene level, we developed electrical production of VMH lesions in mice, for which more genetic information is available compared to rats, and examined the pathophysiological profiles in these mice. Using ddy mice, we produced VMH lesions with reference to the previously reported method in rats. We then examined the pathophysiological profiles of the VMH-lesioned mice. Electrical VMH lesions in mice were produced using the following coordinates: 1.6 mm posterior to the bregma, anteriorly; 0.5 mm lateral to the midsagittal line, transversely; and 0.2 mm above the base of the skull, vertically, with 1 mA of current intensity and 10 s duration. The VMH-lesioned mice showed similar metabolic characteristics to those of VMH-lesioned rats, including body weight gain, increased food intake, increased percentage body fat, and elevated serum insulin and leptin. However, there were some differences in short period of hyperphagia, and in normal serum lipids compared to those of VMH-lesioned rats. The mice showed a similar cell proliferation in visceral organs, including stomach, small intestine, liver, and, exocrine and endocrine pancreas. In conclusion, procedures for development of VMH lesions in mice by electrocoagulation were developed and the VMH-lesioned mice showed pathophysiological profiles similar to those of VMH-lesioned rats, particularly in cell proliferation in visceral organs. These findings have not been observed previously in gold thioglucose-induced VMH-lesioned mice. This model may be a new tool for identifying factors involved in cell proliferation or regeneration in visceral organs.

Food restriction alters neuronal morphology in the hypothalamic ventromedial nucleus of male rats

Several lines of evidence have implicated the hypothalamic ventromedial nucleus (VMH) in the control of caloric homeostasis. For example, the activity of VMH neurons depends on energy availability. We tested the hypothesis that energy balance may involve the remodeling of the dendritic arbor of VMH neurons. We compared two groups of animals: one group had ad libitum access to food, and the other experienced 10-d restricted access to food. As expected, the food-deprived group lost body weight and had reduced levels of glucose, insulin, and leptin. VMH neurons were visualized after Golgi impregnation, and dendrite length was measured. Food deprivation had differential effects on VMH neurons. In particular, within the ventrolateral VMH, for neurons with long primary dendrites (LPDs) that extended in the lateral, but not medial, direction, the LPDs were 31% shorter. These same neurons exhibited a 32% reduction in the number of other dendrites without a change in soma size. In contrast, within the dorsomedial VMH, for neurons with medially, but not laterally, extended LPDs, the soma area was reduced by 28%. However, neurons in the dorsomedial VMH did not display a change in the length or number of dendrites, regardless of LPD direction. Thus, although structural changes during calorie depletion occur in both the dorsomedial and ventrolateral VMH, only the latter exhibits a remodeled dendritic arbor. These results also suggest that the direction of the LPD may be an important marker of neuronal function in the VMH.

The role of proopiomelanocortin (POMC) neurones in feeding behaviour

The precursor protein, proopiomelanocortin (POMC), produces many biologically active peptides via a series of enzymatic steps in a tissue-specific manner, yielding the melanocyte-stimulating hormones (MSHs), corticotrophin (ACTH) and β-endorphin. The MSHs and ACTH bind to the extracellular G-protein coupled melanocortin receptors (MCRs) of which there are five subtypes. The MC3R and MC4R show widespread expression in the central nervous system (CNS), whilst there is low level expression of MC1R and MC5R. In the CNS, cell bodies for POMC are mainly located in the arcuate nucleus of the hypothalamus and the nucleus tractus solitarius of the brainstem. Both of these areas have well defined functions relating to appetite and food intake. Mouse knockouts (ko) for pomc, mc4r and mc3r all show an obese phenotype, as do humans expressing mutations of POMC and MC4R. Recently, human subjects with specific mutations in β-MSH have been found to be obese too, as have mice with engineered β-endorphin deficiency. The CNS POMC system has other functions, including regulation of sexual behaviour, lactation, the reproductive cycle and possibly central cardiovascular control. However, this review will focus on feeding behaviour and link it in with the neuroanatomy of the POMC neurones in the hypothalamus and brainstem.

Effects of nutrition on neuro-endocrine stress responses

PURPOSE OF REVIEW

Past studies in humans and animals have shown that low blood glucose concentrations due to fasting negatively interfere with the ability to mount a hypothalamus-pituitary-adrenal (HPA) axis response to psychological stress or to pharmacological activation, respectively. This contradicts the classical view of the proposed primary glucocorticoid function of providing the individual with energy in fight-or-flight situations.

RECENT FINDINGS

Not many studies have followed up on this phenomenon in recent years, but our understanding of how appetite and satiety is regulated has significantly improved. Many of the neuropeptides involved in regulation of energy homeostasis interact with key areas of the HPA axis. The majority of orexigenic peptides have been shown to activate the HPA axis, while some anorexic peptides negatively modulate HPA axis activation and others also stimulate it.

SUMMARY

The effects of orexigenic peptides on the HPA axis are incompatible with the phenomenon of blunted HPA axis activity in states of low energy available, while the fact that some anorexigenic peptides activate the HPA axis might point to a permissive role. In conclusion, current data insufficiently explain negative HPA axis modulation by low glucose levels.

Delayed satiety-like actions and altered feeding microstructure by a selective type 2 corticotropin-releasing factor agonist in rats: intra-hypothalamic urocortin 3 administration reduces food intake by prolonging the post-meal interval

Brain corticotropin-releasing factor/urocortin (CRF/Ucn) systems are hypothesized to control feeding, with central administration of 'type 2' urocortins producing delayed anorexia. The present study sought to identify the receptor subtype, brain site, and behavioral mode of action through which Ucn 3 reduces nocturnal food intake in rats. Non-food-deprived male Wistar rats (n=176) were administered Ucn 3 into the lateral (LV) or fourth ventricle, or into the ventromedial or paraventricular nuclei of the hypothalamus (VMN, PVN) or the medial amygdala (MeA), regions in which Ucn 3 is expressed in proximity to CRF(2) receptors. LV Ucn 3 suppressed ingestion during the third-fourth post-injection hours. LV Ucn 3 anorexia was reversed by cotreatment with astressin(2)-B, a selective CRF(2) antagonist and not observed following equimole subcutaneous or fourth ventricle administration. Bilateral intra-VMN and intra-PVN infusion, more potently than LV infusion, reduced the quantity (57-73%) and duration of ingestion (32-68%) during the third-fourth post-infusion hours. LV, intra-PVN and intra-VMN infusion of Ucn 3 slowed the eating rate and reduced intake by prolonging the post-meal interval. Intra-VMN Ucn 3 reduced feeding bout size, and intra-PVN Ucn 3 reduced the regularity of eating from pellet to pellet. Ucn 3 effects were behaviorally specific, because minimal effective anorectic Ucn 3 doses did not alter drinking rate or promote a conditioned taste aversion, and site-specific, because intra-MeA Ucn 3 produced a nibbling pattern of more, but smaller meals without altering total intake. The results implicate the VMN and PVN of the hypothalamus as sites for Ucn 3-CRF(2) control of food intake.

Diminished hypothalamic bdnf expression and impaired VMH function are associated with reduced SF-1 gene dosage

In the central nervous system, steroidogenic factor 1 (SF-1) is required for terminal differentiation of neurons within the ventromedial hypothalamus (VMH). Given the importance of this brain region in regulating physiological homeostasis including energy balance, we asked how sf-1 gene dosage affects VMH function. Despite an apparent normal VMH cytoarchitecture, sf-1 heterozygous (+/-) mice exhibited diet-induced obesity when they were group housed with hyperphagia and impaired sympathetic activity. On the basis of previous findings suggesting brain-derived neurotrophic factor (bdnf) as an SF-1 target gene, we assessed the colocalization of SF-1 and BDNF expressing neurons, as well as expression of the four exon-specific bdnf promoter transcripts in the VMH. Indeed, a subset of neurons located primarily in the ventrolateral VMH coexpress SF-1 and BDNF, and in contrast to other brain regions, bdnf I, II, and IV but not III are found. Consistent with these findings, cellular assays showed that SF-1 is able to activate exon I and IV promoters. More important, levels of bdnf I and IV in the VMH were reduced in heterozygous mice similar to levels observed in fasted wild-type mice. Collectively, we propose that a reduction in the sf-1 gene dosage directly affects BDNF levels in the VMH and disrupts normal hypothalamic function.

Injections of leptin into rat ventromedial hypothalamus increase adipocyte apoptosis in peripheral fat and in bone marrow

The accumulation of fat cells (adipocytes) in bone marrow is now thought to be a factor contributing to age-related bone loss. Women with osteoporosis have higher numbers of marrow adipocytes than women with healthy bone, and bone formation rate is inversely correlated with adipocyte number in bone tissue biopsies from both men and women. Adipogenic differentiation of bone marrow stromal cells increases with age, but the factors regulating populations of mature adipocytes are not well understood. Leptin is thought to regulate adipose tissue mass via its receptors in the ventromedial hypothalamus (VMH). We have therefore tested the hypothesis that stimulation of leptin receptors in the VMH regulates adipocyte number in bone marrow. Results indicate that unilateral twice-daily injections of leptin into the rat VMH for only 4 or 5 days cause a significant reduction in the number of adipocytes in peripheral fat pads and bone marrow and indeed eliminate adipocytes almost entirely from bone marrow of the proximal tibia. Osteoblast surface is not affected with leptin treatment. Apoptosis assays performed on bone marrow samples from control and treated rats have revealed a significant increase in protein concentration of the apoptosis marker caspase-3 with leptin treatment. We conclude that stimulation of leptin receptors in the VMH significantly decreases the adipocyte population in bone marrow, primarily through apoptosis of marrow adipocytes. Elimination of marrow adipocytes via this central pathway may represent a useful strategy for the treatment and prevention of osteoporosis.

Leptin signaling

The discovery of leptin was a major breakthrough in our understanding of the role of adipose tissue as a storage and secretory organ. Leptin was initially thought to act mainly to prevent obesity; however, studies have demonstrated profound effects of leptin in the response to fasting, regulation of neuroendocrine and immune systems, hematopoiesis, bone and brain development. This review will focus on the signaling pathways which mediate these diverse effects of leptin in the brain and other physiologic systems.

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

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

Leptin prevents obesity induced by a high-fat diet after diet-induced weight loss in the marsupial S. crassicaudata

The aims of this study were to determine in the marsupial Sminthopsis crassicaudata, the effects of leptin on food intake, body weight, tail width (a reflection of fat stores), and leptin mRNA, after caloric restriction followed by refeeding ad libitum with either a standard or high-fat preferred diet. S. crassicaudata (n = 32), were fed standard laboratory diet (LabD; 1.01 kcal/g, 20% fat) ad libitum fo 3 days. On days 4-10, animals received LabD at 75% of basal intake and then (days 11-25) were fed either LabD or a choice of LabD and mealworms (MW; 2.99 kcal/g, 30% fat); during this time, half the animals (n = 8) in each group received either leptin (2.5 mg/kg) or PBS intraperitoneally two times daily. On day 26, animals were killed and fat was removed for assay of leptin mRNA. At baseline, body weight, tail width, and food intake were similar in each group. After caloric restriction, body weight (P < 0.001) and tail width (P < 0.001) decreased. On return to ad libitum feeding in the PBS-treated animals, body weight and tail width returned to baseline in the LabD-fed animals (P < 0.001) and increased above baseline in the MW-fed animals (P < 0.001). In the LabD groups, tail width (P < 0.001) and body weight (P < 0.001) decreased after leptin compared with PBS. In the MW groups, the increase in tail width (P < 0.001) and body weight (P = 0.001) were attenuated after leptin compared with PBS. The expression of leptin mRNA in groups fed MW were greater in PBS than in leptin-treated animals (P < 0.05). Therefore, after diet-induced weight loss, leptin prevents a gain in fat mass in S. crassicaudata; this has potential implications for the therapeutic use of leptin.

Cardiovascular responses evoked by leptin acting on neurons in the ventromedial and dorsomedial hypothalamus

Leptin, a circulating hormone produced by adipose tissue, is believed to act on the hypothalamus to increase sympathetic vasomotor activity, in addition to its well-known effects on appetite and energy expenditure. In this study, we determined the cardiovascular effects of direct application of leptin to specific cell groups within the hypothalamus that are known to be activated by circulating leptin. In rats anesthetized with urethane, microinjections of leptin (16 ng in 20 nL solution) were made into the ventromedial hypothalamic nucleus, dorsomedial hypothalamic nucleus, and paraventricular nucleus. Compared with vehicle solution, microinjections of leptin into the ventromedial hypothalamic nucleus evoked significant increases in arterial pressure and renal sympathetic nerve activity, but not heart rate. In contrast, microinjections of leptin into the dorsomedial hypothalamic nucleus evoked significant increases in arterial pressure and heart rate but not renal sympathetic nerve activity, whereas microinjections of leptin into the paraventricular nucleus had no significant effect on any of the measured cardiovascular variables. These results indicate that the ventromedial and dorsomedial hypothalamic regions might be important sites at which leptin activation leads to increases in sympathetic vasomotor activity and heart rate, as occurs in obesity-related hypertension.

Ventromedial hypothalamus lesions induce jejunal epithelial cell hyperplasia through an increase in gene expression of cyclooxygenase

BACKGROUND

We demonstrated that ventromedial hypothalamus (VMH) lesions facilitate DNA synthesis, which reflects cell proliferation in abdominal organs, including the liver, pancreas, stomach, small intestine and large intestine, all of which are amply innervated by the vagal nerve.

OBJECTIVE

To investigate which area DNA synthesis facilitates and what factors contribute to cell proliferation in the small intestine in VMH-lesioned rats.

DESIGN

At 7 days after VMH lesions or sham operations, a segment of rat jejunum was taken for histological examination. A part of the jejunum was also removed from VMH-lesioned and sham-operated rats after 3 days and examined for 5-bromo-2'-deoxyuridine (BrdU) incorporation. At 6, 12 and 24 h after VMH lesions, the proximal intestine was removed from individual rats, from the pylorus to the mid-jejunum. Total RNA was extracted from these tissues of each rat, and the levels of epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha mRNA were determined using reverse-transcription polymerase chain reaction. Cyclooxygenase (COX)-1 and -2 mRNA levels were determined using Northern blotting.

RESULTS

: Jejunal villi in VMH-lesioned rats were markedly enlarged compared to those of sham-operated rats and jejunal crypts in VMH-lesioned rats more markedly incorporated BrdU. Northern blot analysis revealed an increase in COX-1 mRNA after 6, 12 and 24 h in the jejunum of VMH-lesioned rats. COX-2 mRNA was decreased 6 and 12 h after VMH lesioning; however, it was significantly increased 24 h after VMH lesions in comparison to sham-operated rats. The levels of EGF and TGF-alpha mRNA were unchanged in VMH lesioned rats.

CONCLUSION

VMH lesions induced enlargement of jejunal villi and increased the gene expression of COX-1 in the small intestine. Prostaglandins, probably E(2), induced by COX-1 may be one candidate factor responsible for the cell proliferation of the small intestinal epithelium in these rats.

The therapeutic potential of somatostatin receptor ligands in the treatment of obesity and diabetes

Since the development of synthetic somatostatin analogues, several therapeutic applications for somatostatin receptor agonist molecules have been defined. Established applications for somatostatin analogue treatment include pituitary tumours (growth hormone and thyrotropin-secreting adenomas), neuroendocrine tumours of the pancreas and gastrointestinal tract (so-called carcinoid tumours, vasoactive intestinal tumours) and gastroenterological conditions (pancreatitis, gastrointestinal bleedings, refractory diarrhoeas, pancreatic and intestinal fistulas, diarrhoea in AIDS). Further areas for development of somatostatin analogue therapy include obesity, polycystic ovary syndrome and diabetes mellitus, dysmetabolic conditions that are often interrelated. The challenge for the future will be to transform results from clinical trials conducted in heterogeneous clinical situations into novel options of somatostatin analogue use. Since obesity and diabetes mellitus both are disorders of marked heterogeneity, the subgroup of patients that will benefit most from somatostatin analogue treatment has yet to be defined. In addition, the development of more universal ligands covering all of the known somatostatin receptor molecules as well as receptor subtype specific agents is currently underway. The establishment of slow-release depot formulations of octreotide and lanreotide has already provided a more acceptable and consistent delivery mechanism. Use of biodegradable polymer microsphere formulations provides the basis for the development of novel applications, which include hyperinsulinaemia, obesity and polycystic ovary syndrome as components of the dysmetabolic syndrome. The most developed thus far is the use of octreotide in hyperinsulinaemic forms of obesity and in distinct stages of diabetic retinopathy.

Enhanced responses of the chorda tympani nerve to sugars in the ventromedial hypothalamic obese rat

Sweet taste sensitivity in obese rats with lesions of the ventromedial hypothalamus (VMH) was studied by examining chorda tympani nerve responses to various taste stimuli including sugars. In the early progressive phase of obesity (2 wk after creating VMH lesions), there was no significant difference in the nerve responses to any taste stimulus between sham-operated and VMH-lesioned rats. In contrast, in the late phase of obesity (15-18 wk after VMH lesions), the magnitude of responses to sugars (except for fructose) was prominently greater than that in age-matched controls. High-fat diet-induced obese rats and streptozotocin-diabetic rats also showed greater chorda tympani nerve responses to sugars as was observed in VMH-lesioned obese rats, indicating that VMH lesions might not be specifically related to the enhanced gustatory neural responses to sugars. Although it has been demonstrated that the enhanced responses of the chorda tympani nerve to sugars in genetically diabetic db/db mice is largely attributable to the lack of the direct suppressive effect of leptin on the taste receptor cells, plasma leptin levels were not correlated with the changes in chorda tympani responsiveness to sugars in these models of obesity and diabetes. Accordingly, our results suggest that some chronic factors, including high blood glucose, inefficiency of insulin action, or leptin resistance may be related to the enhancement of chorda tympani nerve responses to sugars.

Effects of continuous lumbar intrathecal infusion of leptin in rats on weight regulation

Intracranial leptin alters food consumption and body weight. To systematically characterize the effects of extended continuous spinal intrathecal delivery on such regulation, female rats received continuous lumbar spinal infusion (14 days) through catheters connected to osmotic minipumps of a vehicle or one of several doses of recombinant murine leptin (0.03-10 microg/day). The following observations were made. (1) Leptin resulted in a dose-dependent suppression in body weight and food consumption at doses above 0.3 microg/day. (2) Food consumption was initially reduced. Weight fell for 7 days and then plateaued at a level proportional to dose. (3) The ratio of food consumed to body weight was constant for control animals across the study. Leptin-infused rats slowed the initial fall in weight by increasing food consumption, such that the food to body weight ratio returned to that of control values. Rats were thus regulating food consumption to sustain body weight as defined by leptin dose. (4) On day 14, cisternal cerebrospinal fluid was obtained and leptin measured. Concentrations covaried in a log linear fashion with infusion dose. Body weight and food consumption covaried similarly with cisternal leptin concentrations across dose groups. Our data suggest that steady state infusions of leptin induce a degree of appetite suppression that leads to a steady state level of body weight loss and not simply to a simple block of consumatory behavior. The unexpected potency of the observed effects of intrathecal leptin relative to doses that are required after i.c.v. delivery suggests that at least a portion of the effects of intrathecal leptin may reflect a medullary action. The observed correlation of cisternal leptin levels with the behavioral effects is also consistent with a reliable distribution of the infused leptin to target supraspinal sites.

Use of somatostatin receptor ligands in obesity and diabetic complications

Somatostatin (SMS) is a potent inhibitory molecule. It inhibits both exocrine and endocrine secretory functions of the pancreas, suppresses growth hormone secretion and reduces the level of insulin-like growth factor-1. Long-acting somatostatin analogues were currently investigated for potential clinical benefits in two settings: (a) control of hyperinsulinaemia in obesity and (b) control of an excess of pro-angiogenic factors in diabetes-associated retinal complications. In two randomized, controlled trials the long-acting somatostatin analogue octreotide retarded progression of the microvascular complications in pre-proliferative and advanced stages of diabetic retinopathy. Inhibition of the early phase of insulin secretion by use of octreotide in patients with hypothalamic obesity resulted in weight loss and improved quality of life. Efficacy of octreotide correlated to residual beta-cell activity prior to the treatment. Obesity and diabetes mellitus are the most common chronic metabolic disorders in the world. The use of somatostatin analogues addressing the various hormonal imbalances of these disorders may provide a novel concept for their pharmacological treatment.

Leptin inhibits stress-induced apoptosis of T lymphocytes

Leptin, which is secreted by adipocytes, the placenta and the stomach, not only controls appetite through leptin receptors in the hypothalamus but also regulates cell-mediated immunity. In this study we have demonstrated that continuous injection of leptin prevents the reduction in lymphocyte numbers normally observed in fasted and steroid-injected mice. Consistent with leptin-induced protection, we observed up-regulation of the bcl-xL gene as a result of signal transduction via leptin receptors on lymphocytes. We suggest that leptin might contribute to the recovery of immune suppression in malnourished mice by inhibiting lymphocyte apoptosis.

GABAergic nature of hypothalamic leptin target neurones in the ventromedial arcuate nucleus

Leptin is an adipose tissue-derived cytokine hormone, which reduces body weight via interactions with hypothalamic neurones. Leptin receptors capable of activating the JAK-STAT signal transduction pathway are expressed at high levels in the hypothalamus, particularly in the arcuate nucleus. In order to identify the chemical mediators of leptin's action in the hypothalamus, we have examined whether GABA neurones of the hypothalamic arcuate nucleus contain leptin receptors and the leptin-activated transcription factor STAT3. GABAergic neurones, as visualized by antisera to the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) and GABA, were demonstrated in the ventromedial and ventrolateral parts of the arcuate nucleus. GABA neurones in the ventromedial arcuate nucleus were shown to contain leptin receptor immunoreactivity, as revealed using an antiserum generated to a sequence common to all isoforms of the leptin receptor (Ob-R), as well as an antiserum generated to the carboxy-terminal end of the long leptin receptor (Ob-Rb), and immunoreactivity for the leptin-induced signal transduction molecule STAT3. Ventromedial GABA neurones were also shown to contain neuropeptide Y, whereas ventrolateral proopiomelanocortin-containing neurones lacked GAD and GABA immunoreactivity. Levels of mRNA for GAD65, GAD67 and the vesicular GABA transporter (VGAT) were analysed in the arcuate nucleus of leptin-deficient ob/ob mice and lean control mice by in situ hybridization. No significant differences in GAD65, GAD67 or VGAT mRNA were detected in the arcuate nucleus of ob/ob mice as compared to lean control mice. The presence of leptin receptor and STAT3 in GABAergic arcuate neurones, but absence of changes in gene transcription for GAD and VGAT mRNA suggests, that leptin does not transcriptionally regulate the expression of proteins involved in GABAergic transmission in arcuate neurones. However, mechanisms other than transcriptional regulation for leptin to influence arcuate GABA neurones may exist.

Down-regulated STAT3 messenger ribonucleic acid and STAT3 protein in the hypothalamic arcuate nucleus of the obese leptin-deficient (ob/ob) mouse

Leptin is a weight-reducing hormone produced by adipose tissue, which reduces food intake via hypothalamic leptin receptors and the JAK-STAT signaling pathway. In vivo studies have shown that leptin activates specifically STAT3 in the hypothalamus. We have studied the cellular localization of STAT3 messenger RNA (mRNA) and STAT3 protein in the mouse mediobasal hypothalamus using, respectively, in situ hybridization and immunohistochemistry. Strong STAT3 mRNA and STAT3 immunoreactivity was demonstrated in neurons located in the ventral part of the mouse arcuate nucleus. Comparison of STAT3 mRNA levels in the arcuate nucleus of lean control mice and obese leptin-deficient ob/ob mice showed that the levels of STAT3 mRNA in the arcuate nucleus were significantly lower (31% less in ob/ob mice), compared with control mice. Hybridization with a probe specific for STAT3alpha mRNA showed that the down-regulated STAT3 expression in the arcuate nucleus of ob/ob mice is represented by STAT3alpha. There was a marked difference in numbers and intensity of STAT3-immunoreactive cell bodies, with virtually no STAT3-immunoreactive cell bodies in the mediobasal hypothalamus of ob/ob mice, compared with control mice. Direct double-labeling immunofluorescence histochemistry of sections from control mice, combining a goat antiserum raised against a peptide sequence present in all leptin receptor isoforms (Ob-R) or a guinea pig anti-serum generated to a peptide sequence specific for Ob-Rb with rabbit STAT3 antiserum, demonstrated colocalization of STAT3 and Ob-R as well as colocalization of STAT3 and Ob-Rb, in many cell bodies of the arcuate nucleus. The results suggest that circulating leptin acts via leptin receptor-/STAT3-containing neurons in the ventral arcuate nucleus and that congenital leptin deficiency, as seen in obese ob/ob mice, results in a down-regulation of STAT3 mRNA and protein levels.

The hypothalamus and the regulation of energy homeostasis: lifting the lid on a black box

The hypothalamus is the focus of many peripheral signals and neural pathways that control energy homeostasis and body weight. Emphasis has moved away from anatomical concepts of 'feeding' and 'satiety' centres to the specific neurotransmitters that modulate feeding behaviour and energy expenditure. We have chosen three examples to illustrate the physiological roles of hypothalamic neurotransmitters and their potential as targets for the development of new drugs to treat obesity and other nutritional disorders. Neuropeptide Y (NPY) is expressed by neurones of the hypothalamic arcuate nucleus (ARC) that project to important appetite-regulating nuclei, including the paraventricular nucleus (PVN). NPY injected into the PVN is the most potent central appetite stimulant known, and also inhibits thermogenesis; repeated administration rapidly induces obesity. The ARC NPY neurones are stimulated by starvation, probably mediated by falls in circulating leptin and insulin (which both inhibit these neurones), and contribute to the increased hunger in this and other conditions of energy deficit. They therefore act homeostatically to correct negative energy balance. ARC NPY neurones also mediate hyperphagia and obesity in the ob/ob and db/db mice and fa/fa rat, in which leptin inhibition is lost through mutations affecting leptin or its receptor. Antagonists of the Y5 receptor (currently thought to be the NPY 'feeding' receptor) have anti-obesity effects. Melanocortin-4 receptors (MC4-R) are expressed in various hypothalamic regions, including the ventromedial nucleus and ARC. Activation of MC4-R by agonists such as alpha-melanocyte-stimulating hormone (a cleavage product of pro-opiomelanocortin which is expressed in ARC neurones) inhibits feeding and causes weight loss. Conversely, MC4-R antagonists such as 'agouti' protein and agouti gene-related peptide (AGRP) stimulate feeding and cause obesity. Ectopic expression of agouti in the hypothalamus leads to obesity in the AVY mouse, while AGRP is co-expressed by NPY neurones in the ARC. Synthetic MC4-R agonists may ultimately find use as anti-obesity drugs in human subjects Orexins-A and -B, derived from prepro-orexin, are expressed in specific neurones of the lateral hypothalamic area (LHA). Orexin-A injected centrally stimulates eating and prepro-orexin mRNA is up regulated by fasting and hypoglycaemia. The LHA is important in receiving sensory signals from the gut and liver, and in sensing glucose, and orexin neurones may be involved in stimulating feeding in response to falls in plasma glucose.

Integration of metabolism and intake regulation: a review focusing on periparturient animals

There has been great interest in dry matter intake regulation in lactating dairy cattle to enhance performance and improve animal health and welfare. Predicting voluntary dry matter intake (VDMI) is complex and influenced by numerous factors relating to the diet, management, housing, environment and the animal. The objective of this review is to identify and discuss important metabolic factors involved in the regulation of VDMI and their integration with metabolism. We have described the adaptations of intake and metabolism and discussed mechanisms of intake regulation. Furthermore we have reviewed selected metabolic signals involved in intake regulation. A substantial dip in VDMI is initiated in late pregnancy and continues into early lactation. This dip has traditionally been interpreted as caused by physical constraints, but this role is most likely overemphasized. The dip in intake coincides with changes in reproductive status, fat mass, and metabolic changes in support of lactation, and we have described metabolic signals that may play an equally important role in intake regulation. These signals include nutrients, metabolites, reproductive hormones, stress hormones, leptin, insulin, gut peptides, cytokines, and neuropeptides such as neuropeptide Y, galanin, and corticotrophin-releasing factor. The involvement of these signals in the periparturient dip in intake is discussed, and evidence supporting the integration of the regulation of intake and metabolism is presented. Still, much research is needed to clarify the complex regulation of VDMI in lactating dairy cows, particularly in the periparturient animal.