White adipose tissue sympathetic nervous system denervation increases fat pad mass and fat cell number

Cross-talk between adipose tissue and microbiota-gut-brain-axis in brain development and neurological disorder

The gut microbiota is an important factor responsible for the physiological processes as well as pathogenesis of host. The communication between central nervous system (CNS) and microbiota occurs by different pathways i.e., chemical, neural, immune, and endocrine. Alteration in gut microbiota i.e., gut dysbiosis causes alteration in the bidirectional communication between CNS and gut microbiota and linked to the pathogenesis of neurological and neurodevelopmental disorder. Therefore, now-a-days microbiota-gut-brain-axis (MGBA) has emerged as therapeutic target for the treatment of metabolic disorder. But, experimental data available on MGBA from basic research has limited application in clinical study. In present study we first summarized molecular mechanism of microbiota interaction with brain physiology and pathogenesis via collecting data from different sources i.e., PubMed, Scopus, Web of Science. Furthermore, evidence shows that adipose tissue (AT) is active during metabolic activities and may also interact with MGBA. Hence, in present study we have focused on the relationship among MGBA, brown adipose tissue, and white adipose tissue. Along with this, we have also studied functional specificity of AT, and understanding heterogeneity among MGBA and different types of AT. Therefore, molecular interaction among them may provide therapeutic target for the treatment of neurological disorder.

Transcriptome analysis of norepinephrine-induced lipolysis in differentiated adipocytes of Bama pig

Sympathetic innervation of white adipose tissue (WAT) plays a key role in the regulation of lipid metabolism. Sympathetic activation promotes release of norepinephrine (NE), which binds to adrenergic receptors on adipocytes, promoting adipocyte lipolysis and enhanced oxidative metabolism. However, the mechanism by which sympathetic nerves regulate lipid metabolism in pig adipose tissue remains unclear. We used NE to simulate the process of sympathetic driving in pig adipocytes. RNA sequencing (RNA-seq) was used to determine the gene expression profile of pig adipocytes responding to NE stimulation. Our data suggests that the lipolytic signaling pathway is activated in pig adipocytes upon acute stimulation of NE, resulting in enhanced lipid metabolism and lipolysis, consistent with the phenomena found in humans and mice. Specifically, differentially expressed protein coding genes (PCGs) (SIRT4, SLC27A1) are mainly associated with functions that inhibit fatty acid oxidation and promote lipid synthesis. Similarly, we investigated the changes in regulatory transcripts such as long non-coding RNAs (lncRNAs) and transcripts of uncertain coding potential (TUCP) in response to NE and found that differentially expressed lncRNAs (lncG47338, lncG30660, lncG29516, lncG3790) and TUCP (TUCP_G38001) were co-expressed with target genes related to the promotion of fatty acid β-oxidation, lipolysis and oxidative metabolism, thus acting as regulators. These results indicate a broad suite of gene expression alterations in response to NE stimulation and promote the understanding of the molecular mechanisms by which NE regulates lipid metabolism in pigs.

Thermogenic adipose tissue in energy regulation and metabolic health

The ability to generate thermogenic fat could be a targeted therapy to thwart obesity and improve metabolic health. Brown and beige adipocytes are two types of thermogenic fat cells that regulate energy balance. Both adipocytes share common morphological, biochemical, and thermogenic properties. Yet, recent evidence suggests unique features exist between brown and beige adipocytes, such as their cellular origin and thermogenic regulatory processes. Beige adipocytes also appear highly plastic, responding to environmental stimuli and interconverting between beige and white adipocyte states. Additionally, beige adipocytes appear to be metabolically heterogenic and have substrate specificity. Nevertheless, obese and aged individuals cannot develop beige adipocytes in response to thermogenic fat-inducers, creating a key clinical hurdle to their therapeutic promise. Thus, elucidating the underlying developmental, molecular, and functional mechanisms that govern thermogenic fat cells will improve our understanding of systemic energy regulation and strive for new targeted therapies to generate thermogenic fat. This review will examine the recent advances in thermogenic fat biogenesis, molecular regulation, and the potential mechanisms for their failure.

Neurohormonal Changes in the Gut-Brain Axis and Underlying Neuroendocrine Mechanisms following Bariatric Surgery

Obesity is a complex, multifactorial disease that is a major public health issue worldwide. Currently approved anti-obesity medications and lifestyle interventions lack the efficacy and durability needed to combat obesity, especially in individuals with more severe forms or coexisting metabolic disorders, such as poorly controlled type 2 diabetes. Bariatric surgery is considered an effective therapeutic modality with sustained weight loss and metabolic benefits. Numerous genetic and environmental factors have been associated with the pathogenesis of obesity, while cumulative evidence has highlighted the gut-brain axis as a complex bidirectional communication axis that plays a crucial role in energy homeostasis. This has led to increased research on the roles of neuroendocrine signaling pathways and various gastrointestinal peptides as key mediators of the beneficial effects following weight-loss surgery. The accumulate evidence suggests that the development of gut-peptide-based agents can mimic the effects of bariatric surgery and thus is a highly promising treatment strategy that could be explored in future research. This article aims to elucidate the potential underlying neuroendocrine mechanisms of the gut-brain axis and comprehensively review the observed changes of gut hormones associated with bariatric surgery. Moreover, the emerging role of post-bariatric gut microbiota modulation is briefly discussed.

The Vasoactive Effect of Perivascular Adipose Tissue and Hydrogen Sulfide in Thoracic Aortas of Normotensive and Spontaneously Hypertensive Rats

The objective of this study was to investigate the vasoregulatory role of perivascular adipose tissue (PVAT) and its mutual interaction with endogenous and exogenous H₂S in the thoracic aorta (TA) of adult normotensive Wistar rats and spontaneously hypertensive rats (SHRs). In SHRs, hypertension was associated with cardiac hypertrophy and increased contractility. Regardless of the strain, PVAT revealed an anticontractile effect; however, PVAT worsened endothelial-dependent vasorelaxation. Since H₂S produced by both the vascular wall and PVAT had a pro-contractile effect in SHRs, H₂S decreased the sensitivity of adrenergic receptors to noradrenaline in Wistar rats. While H₂S had no contribution to endothelium-dependent relaxation in Wistar rats, in SHRs, H₂S produced by the vascular wall had a pro-relaxant effect. We observed a larger vasorelaxation induced by exogenous H₂S donor in SHRs than in Wistar rats. Additionally, in the presence of PVAT, this effect was potentiated. We demonstrated that PVAT of the TA aggravated endothelial function in SHRs. However, H₂S produced by the TA vascular wall had a pro-relaxation effect, and PVAT revealed anti-contractile activity mediated by the release of an unknown factor and potentiated the vasorelaxation induced by exogenous H₂S. All these actions could represent a form of compensatory mechanism to balance impaired vascular tone regulation.

The acute effect of dopamine infusion on lipid and cytokine concentrations in persons with a cervical spinal cord injury-a pilot study

STUDY DESIGN

Acute experimental study.

OBJECTIVES

To investigate the acute response of markers of lipid metabolism and interleukin (IL)-6 to dopamine infusion in people with a cervical spinal cord injury (CSCI).

SETTING

Laboratory of Wakayama Medical University, Japan.

METHODS

Ten participants, four with CSCI and six AB individuals, underwent 50 min of dopamine infusion. Blood samples were collected prior to, immediately after and 1 h following cessation of dopamine infusion for the determination of circulating catecholamine, lipid, ketone body and IL-6 concentrations.

RESULTS

The adrenaline concentration following dopamine infusion was increased by 59 ± 7% in CSCI (p = 0.038, Cohen's d effect size (ES): 1.47), while this was not changed in AB (p = 0.223). Triglycerides and acetoacetic acid concentration were increased in both groups, immediately after and 1 h post-infusion (triglycerides p ≤ 0.042, ES CSCI: 1.00, ES AB: 1.12; acetoacetic acid p ≤ 0.030; ES CSCI: 1.72, ES AB: 1.31). 3-Hydroxybutyric acid concentration was increased in CSCI only (48 ± 15%, p = 0.039, ES: 1.44; AB p = 0.115). Dopamine infusion did not affect plasma IL-6 concentration in either group (p ≥ 0.368).

CONCLUSIONS

Dopamine infusion induced a sustained increase in triglyceride and ketone body concentrations in persons with CSCI. In contrast, cytokine concentrations were not affected by dopamine infusion. These findings suggest that circulating catecholamines can stimulate metabolism in people with CSCI despite the presence of autonomic dysfunction.

Induction of Adipose Tissue Browning as a Strategy to Combat Obesity

The ongoing obesity pandemic generates a constant need to develop new therapeutic strategies to restore the energy balance. Therefore, the concept of activating brown adipose tissue (BAT) in order to increase energy expenditure has been revived. In mammals, two developmentally distinct types of brown adipocytes exist; the classical or constitutive BAT that arises during embryogenesis, and the beige adipose tissue that is recruited postnatally within white adipose tissue (WAT) in the process called browning. Research of recent years has significantly increased our understanding of the mechanisms involved in BAT activation and WAT browning. They also allowed for the identification of critical molecules and critical steps of both processes and, therefore, many new therapeutic targets. Several non-pharmacological approaches, as well as chemical compounds aiming at the induction of WAT browning and BAT activation, have been tested in vitro as well as in animal models of genetically determined and/or diet-induced obesity. The therapeutic potential of some of these strategies has also been tested in humans. In this review, we summarize present concepts regarding potential therapeutic targets in the process of BAT activation and WAT browning and available strategies aiming at them.

There and Back Again: Leptin Actions in White Adipose Tissue

Leptin is a hormone discovered almost 30 years ago with important implications in metabolism. It is primarily produced by white adipose tissue (WAT) in proportion to the amount of fat. The discovery of leptin was a turning point for two principle reasons: on one hand, it generated promising expectations for the treatment of the obesity, and on the other, it changed the classical concept that white adipose tissue was simply an inert storage organ. Thus, adipocytes in WAT produce the majority of leptin and, although its primary role is the regulation of fat stores by controlling lipolysis and lipogenesis, this hormone also has implications in other physiological processes within WAT, such as apoptosis, browning and inflammation. Although a massive number of questions related to leptin actions have been answered, the necessity for further clarification facilitates constantly renewing interest in this hormone and its pathways. In this review, leptin actions in white adipose tissue will be summarized in the context of obesity.

Apolipoprotein A-IV Enhances Fatty Acid Uptake by Adipose Tissues of Male Mice via Sympathetic Activation

Apolipoprotein A-IV (ApoA-IV) synthesized by the gut regulates lipid metabolism. Sympathetic innervation of adipose tissues also controls lipid metabolism. We hypothesized that ApoA-IV required sympathetic innervation to increase fatty acid (FA) uptake by adipose tissues and brown adipose tissue (BAT) thermogenesis. After 3 weeks feeding of either a standard chow diet or a high-fat diet (HFD), mice with unilateral denervation of adipose tissues received intraperitoneal administration of recombinant ApoA-IV protein and intravenous infusion of lipid mixture with radioactive triolein. In chow-fed mice, ApoA-IV administration increased FA uptake by intact BAT but not the contralateral denervated BAT or intact white adipose tissue (WAT). Immunoblots showed that, in chow-fed mice, ApoA-IV increased expression of lipoprotein lipase and tyrosine hydroxylase in both intact BAT and inguinal WAT (IWAT), while ApoA-IV enhanced protein levels of β3 adrenergic receptor, adipose triglyceride lipase, and uncoupling protein 1 in the intact BAT only. In HFD-fed mice, ApoA-IV elevated FA uptake by intact epididymal WAT (EWAT) but not intact BAT or IWAT. ApoA-IV increased sympathetic activity assessed by norepinephrine turnover (NETO) rate in BAT and EWAT of chow-fed mice, whereas it elevated NETO only in EWAT of HFD-fed mice. These observations suggest that, in chow-fed mice, ApoA-IV activates sympathetic activity of BAT and increases FA uptake by BAT via innervation, while in HFD-fed mice, ApoA-IV stimulates sympathetic activity of EWAT to shunt FAs into the EWAT.

A Systematic Scoping Review of Surgically Manipulated Adipose Tissue and the Regulation of Energetics and Body Fat in Animals

OBJECTIVE

Surgical manipulations of adipose tissue by removal, or partial lipectomy, have demonstrated body fat compensation and recovered body weight, suggesting that the body is able to resist changes to body composition. However, the mechanisms underlying these observations are not well understood. The purpose of this scoping review is to provide an update on what is currently known about the regulation of energetics and body fat after surgical manipulations of adipose tissue in small mammals.

METHODS

PubMed and Scopus were searched to identify 64 eligible studies. Outcome measures included body fat, body weight, food intake, and circulating biomarkers.

RESULTS

Surgeries performed included lipectomy (72%) or transplantation (12%) in mice (35%), rats (35%), and other small mammals. Findings suggested that lipectomy did not have consistent long-term effects on reducing body weight and fat because regain occurred within 12 to 14 weeks post surgery. Hence, biological feedback mechanisms act to resist long-term changes of body weight or fat. Furthermore, whether this weight and fat regain occurred because of "passive" and "active" regulation under the "set point" or "settling point" theories cannot fully be discerned because of limitations in study designs and data collected.

CONCLUSIONS

The regulation of energetics and body fat are complex and dynamic processes that require further studies of the interplay of genetic, physiological, and behavioral factors.

Adrenoceptors in white, brown, and brite adipocytes

Adrenoceptors play an important role in adipose tissue biology and physiology that includes regulating the synthesis and storage of triglycerides (lipogenesis), the breakdown of stored triglycerides (lipolysis), thermogenesis (heat production), glucose metabolism, and the secretion of adipocyte-derived hormones that can control whole-body energy homeostasis. These processes are regulated by the sympathetic nervous system through actions at different adrenoceptor subtypes expressed in adipose tissue depots. In this review, we have highlighted the role of adrenoceptor subtypes in white, brown, and brite adipocytes in both rodents and humans and have included detailed analysis of adrenoceptor expression in human adipose tissue and clonally derived adipocytes. We discuss important considerations when investigating adrenoceptor function in adipose tissue or adipocytes. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Denervation as a tool for testing sympathetic control of white adipose tissue

This review summarizes the evidence derived from studies utilizing denervation procedures to demonstrate sympathetic control of white adipose tissue metabolism and body fat mass. A majority of the work demonstrating neural control of white fat was performed in the Bartness laboratory with Siberian hamsters as the predominant experimental model. These animals experience dramatic changes in body fat mass in response to changes in photoperiod, however, the mechanisms identified in hamsters have been reproduced or further elucidated by experiments with other animal models. Evidence for the role of sympathetic innervation contributing to the control of white adipocyte lipolysis and preadipocyte proliferation is summarized. In addition, evidence from denervation experiments for neural communication between different white fat depots as well as for a feedback control loop between sensory afferents from individual fat depots and sympathetic efferents to the same or distant white fat depots is discussed.

The involvement of purinergic signalling in obesity

Obesity is a growing worldwide health problem, with an alarming increasing prevalence in developed countries, caused by a dysregulation of energy balance. Currently, no wholly successful pharmacological treatments are available for obesity and related adverse consequences. In recent years, hints obtained from several experimental animal models support the notion that purinergic signalling, acting through ATP-gated ion channels (P2X), G protein-coupled receptors (P2Y) and adenosine receptors (P1), is involved in obesity, both at peripheral and central levels. This review has drawn together, for the first time, the evidence for a promising, much needed novel therapeutic purinergic signalling approach for the treatment of obesity with a 'proof of concept' that hopefully could lead to further investigations and clinical trials for the management of obesity.

Whole-tissue 3D imaging reveals intra-adipose sympathetic plasticity regulated by NGF-TrkA signal in cold-induced beiging

Sympathetic arborizations act as the essential efferent signals in regulating the metabolism of peripheral organs including white adipose tissues (WAT). However, whether these local neural structures would be of plastic nature, and how such plasticity might participate in specific metabolic events of WAT, remains largely uncharacterized. In this study, we exploit the new volume fluorescence-imaging technique to observe the significant, and also reversible, plasticity of intra-adipose sympathetic arborizations in mouse inguinal WAT in response to cold challenge. We demonstrate that this sympathetic plasticity depends on the cold-elicited signal of nerve growth factor (NGF) and TrkA receptor. Blockage of NGF or TrkA signaling suppresses intra-adipose sympathetic plasticity, and moreover, the cold-induced beiging process of WAT. Furthermore, we show that NGF expression in WAT depends on the catecholamine signal in cold challenge. We therefore reveal the key physiological relevance, together with the regulatory mechanism, of intra-adipose sympathetic plasticity in the WAT metabolism.

Leptin and brain-adipose crosstalks

Interactions between the brain and distinct adipose depots have a key role in maintaining energy balance, thereby promoting survival in response to metabolic challenges such as cold exposure and starvation. Recently, there has been renewed interest in the specific central neuronal circuits that regulate adipose depots. Here, we review anatomical, genetic and pharmacological studies on the neural regulation of adipose function, including lipolysis, non-shivering thermogenesis, browning and leptin secretion. In particular, we emphasize the role of leptin-sensitive neurons and the sympathetic nervous system in modulating the activity of brown, white and beige adipose tissues. We provide an overview of advances in the understanding of the heterogeneity of the brain regulation of adipose tissues and offer a perspective on the challenges and paradoxes that the community is facing regarding the actions of leptin on this system.

Short photoperiod reverses obesity in Siberian hamsters via sympathetically induced lipolysis and Browning in adipose tissue

Changes in photoperiod length are transduced into neuroendocrine signals by melatonin (MEL) secreted by the pineal gland triggering seasonally adaptive responses in many animal species. Siberian hamsters, transferred from a long-day 'summer-like' photoperiod (LD) to a short-day 'winter-like' photoperiod (SD), exhibit a naturally-occurring reversal in obesity. Photoperiod-induced changes in adiposity are mediated by the duration of MEL secretion and can be mimicked by exogenously administered MEL into animals housed in LD. Evidence suggests that MEL increases the sympathetic nervous system (SNS) drive to white adipose tissue (WAT). Here, we investigated whether MEL-driven seasonally adaptive losses in body fat are associated with WAT lipolysis and browning. Hamsters were subcutaneously administered vehicle (LD+VEH) or 0.4mg/kg MEL (LD+MEL) daily for 10weeks while animals housed in SD served as a positive control. MEL and SD exposure significantly decreased the retroperitoneal (RWAT), inguinal (IWAT), epididymal (EWAT) WAT, food intake and caused testicular regression compared with the LD+VEH group. MEL/SD induced lipolysis in the IWAT and EWAT, browning of the RWAT, IWAT, and EWAT, and increased UCP1 expression in the IBAT. Additionally, MEL/SD significantly increased the number of shared MEL receptor 1a and dopamine beta-hydroxylase-immunoreactive neurons in discrete brain sites, notably the paraventricular hypothalamic nucleus, dorsomedial hypothalamic nucleus, arcuate nucleus, locus coeruleus and dorsal motor nucleus of vagus. Collectively, these findings support our hypothesis that SD-exposed Siberian hamsters undergo adaptive decreases in body adiposity due to SNS-stimulated lipid mobilization and generalized WAT browning.

A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineages

Conditional expression of diphtheria toxin receptor (DTR) is widely used for tissue-specific ablation of cells. However, diphtheria toxin (DT) crosses the blood-brain barrier, which limits its utility for ablating peripheral cells using Cre drivers that are also expressed in the central nervous system (CNS). Here we report the development of a brain-sparing DT, termed BRAINSPAReDT, for tissue-specific genetic ablation of cells outside the CNS. We prevent blood-brain barrier passage of DT through PEGylation, which polarizes the molecule and increases its size. We validate BRAINSPAReDT with regional genetic sympathectomy: BRAINSPAReDT ablates peripheral but not central catecholaminergic neurons, thus avoiding the Parkinson-like phenotype associated with full dopaminergic depletion. Regional sympathectomy compromises adipose tissue thermogenesis, and renders mice susceptible to obesity. We provide a proof of principle that BRAINSPAReDT can be used for Cre/DTR tissue-specific ablation outside the brain using CNS drivers, while consolidating the link between adiposity and the sympathetic nervous system.

Does bariatric surgery improve adipose tissue function?

Bariatric surgery is currently the most effective treatment for obesity. Not only do these types of surgeries produce significant weight loss but also they improve insulin sensitivity and whole body metabolic function. The aim of this review is to explore how altered physiology of adipose tissue may contribute to the potent metabolic effects of some of these procedures. This includes specific effects on various fat depots, the function of individual adipocytes and the interaction between adipose tissue and other key metabolic tissues. Besides a dramatic loss of fat mass, bariatric surgery shifts the distribution of fat from visceral to the subcutaneous compartment favoring metabolic improvement. The sensitivity towards lipolysis controlled by insulin and catecholamines is improved, adipokine secretion is altered and local adipose inflammation as well as systemic inflammatory markers decreases. Some of these changes have been shown to be weight loss independent, and novel hypothesis for these effects includes include changes in bile acid metabolism, gut microbiota and central regulation of metabolism. In conclusion bariatric surgery is capable of improving aspects of adipose tissue function and do so in some cases in ways that are not entirely explained by the potent effect of surgery. © 2016 World Obesity.

Rapid linkage of innate immunological signals to adaptive immunity by the brain-fat axis

Innate immunological signals induced by pathogen- and/or damage-associated molecular patterns are essential for adaptive immune responses, but it is unclear if the brain has a role in this process. Here we found that while the abundance of tumor-necrosis factor (TNF) quickly increased in the brain of mice following bacterial infection, intra-brain delivery of TNF mimicked bacterial infection to rapidly increase the number of peripheral lymphocytes, especially in the spleen and fat. Studies of various mouse models revealed that hypothalamic responses to TNF were accountable for this increase in peripheral lymphocytes in response to bacterial infection. Finally, we found that hypothalamic induction of lipolysis mediated the brain's action in promoting this increase in the peripheral adaptive immune response. Thus, the brain-fat axis is important for rapid linkage of innate immunity to adaptive immunity.

Leptin intake in suckling rats restores altered T3 levels and markers of adipose tissue sympathetic drive and function caused by gestational calorie restriction

BACKGROUND

Maternal calorie restriction during gestation in rats has been associated with altered white adipose tissue (WAT) sympathetic innervation and function in offspring. Here, we aimed to investigate whether supplementation with oral leptin (a breast milk component) throughout the lactation period may revert the aforementioned adverse programming effects.

METHODS

Three groups of male and female rats were studied at the postnatal day 25: the offspring of control dams, the offspring of 20% calorie-restricted dams during pregnancy (CR) and CR rats supplemented with physiological doses of leptin throughout lactation (CR-Leptin). Tyrosine hydroxylase (TH) levels and its immunoreactive area, and mRNA expression levels of lipid metabolism-related genes and of deiodinase iodothyronine type II (Dio2) were determined in WAT. Triiodothyronine (T3) levels were determined in the blood.

RESULTS

In CR males, leptin treatment restored the decreased TH levels and its immunoreactive area in WAT, and partially normalized expression levels of genes related to lipolysis and fatty acid oxidation (adipose triglyceride lipase, hormone-sensitive lipase, carnitine palmitoyltransferase 1b and peroxisome proliferator-activated receptor gamma coactivator 1-alpha). Leptin treatment also reverted the decreased T3 plasma levels and WAT lipoprotein lipase mRNA levels occurring in CR males and females, and the decreased Dio2 mRNA levels in CR females.

CONCLUSIONS

Leptin supplementation throughout the lactation period reverts the malprogrammed effects on WAT structure and function induced by undernutrition during pregnancy. These findings support the relevance of the intake of leptin during lactation, bearing clear characteristics of essential nutrient, and provide a strategy to treat and/or prevent the programmed trend to obesity acquired by inadequate fetal nutrition.

Increase in visceral fat per se does not induce insulin resistance in the canine model

OBJECTIVES

To determine whether a selective increase of visceral adipose tissue content will result in insulin resistance.

METHODS

Sympathetic denervation of the omental fat was performed under general inhalant anesthesia by injecting 6-hydroxydopamine in the omental fat of lean mongrel dogs (n = 11). In the conscious animal, whole-body insulin sensitivity was assessed by the minimal model (SI ) and the euglycemic hyperinsulinemic clamp (SICLAMP ). Changes in abdominal fat were monitored by magnetic resonance. All assessments were determined before (Wk0) and 2 weeks (Wk2) after denervation. Data are medians (upper and lower interquartile).

RESULTS

Denervation of omental fat resulted in increased percentage (and content) of visceral fat [Wk0: 10.2% (8.5-11.4); Wk2: 12.4% (10.4-13.6); P < 0.01]. Abdominal subcutaneous fat remained unchanged. However, no changes were found in SI [Wk0: 4.7 (mU/l)(-1) min(-1) (3.1-8.8); Wk2: 5.3 (mU/l)(-1) min(-1) (4.5-7.2); P = 0.59] or SICLAMP [Wk0: 42.0 × 10(-4) dl kg(-1) min(-1) (mU/l)(-1) (41.0-51.0); Wk2: 40.0 × 10(-4) dl kg(-1) min(-1) (mU/l) (-1) (34.0-52.0); P = 0.67].

CONCLUSIONS

Despite a selective increase in visceral adiposity in dogs, insulin sensitivity in vivo did not change, which argues against the concept that accumulation of visceral adipose tissue contributes to insulin resistance.

Neural innervation of white adipose tissue and the control of lipolysis

White adipose tissue (WAT) is innervated by the sympathetic nervous system (SNS) and its activation is necessary for lipolysis. WAT parasympathetic innervation is not supported. Fully-executed SNS-norepinephrine (NE)-mediated WAT lipolysis is dependent on β-adrenoceptor stimulation ultimately hinging on hormone sensitive lipase and perilipin A phosphorylation. WAT sympathetic drive is appropriately measured electrophysiologically and neurochemically (NE turnover) in non-human animals and this drive is fat pad-specific preventing generalizations among WAT depots and non-WAT organs. Leptin-triggered SNS-mediated lipolysis is weakly supported, whereas insulin or adenosine inhibition of SNS/NE-mediated lipolysis is strongly supported. In addition to lipolysis control, increases or decreases in WAT SNS drive/NE inhibit and stimulate white adipocyte proliferation, respectively. WAT sensory nerves are of spinal-origin and sensitive to local leptin and increases in sympathetic drive, the latter implicating lipolysis. Transsynaptic viral tract tracers revealed WAT central sympathetic and sensory circuits including SNS-sensory feedback loops that may control lipolysis.

Paradoxical adipose hyperplasia after cryolipolysis

IMPORTANCE

Cryolipolysis is the noninvasive reduction of fat with localized cutaneous cooling. Since initial introduction, over 650,000 cryolipolysis treatment cycles have been performed worldwide. We present a previously unreported, rare adverse effect following cryolipolysis: paradoxical adipose hyperplasia.

OBSERVATIONS

A man in his 40s underwent a single cycle of cryolipolysis to his abdomen. Three months following his treatment, a gradual enlargement of the treatment area was noted. This enlargement was a large, well-demarcated subcutaneous mass, slightly tender to palpation. Imaging studies revealed accumulation of adipose tissue with normal signal intensity within the treatment area.

CONCLUSIONS AND RELEVANCE

Paradoxical adipose hyperplasia is a rare, previously unreported adverse effect of cryolipolysis with an incidence of 0.0051%. No single unifying risk factor has been identified. The phenomenon seems to be more common in male patients undergoing cryolipolysis. At this time, there is no evidence of spontaneous resolution. Further studies are needed to characterize the pathogenesis and histologic findings of this rare adverse event.

Central sympathetic innervations to visceral and subcutaneous white adipose tissue

There is a link between visceral white adipose tissue (WAT) and the metabolic syndrome in humans, with health improvements produced with small visceral WAT reduction. By contrast, subcutaneous WAT provides a site for lipid storage that is rather innocuous relative to ectopic lipid storage in muscle or liver. The sympathetic nervous system (SNS) is the principal initiator for lipolysis in WAT by mammals. Nothing is known, however, about the central origins of the SNS circuitry innervating the only true visceral WAT in rodents, mesenteric WAT (MWAT), which drains into the hepatic portal vein. We tested whether the central sympathetic circuits to subcutaneous [inguinal WAT (IWAT)] and visceral WAT (MWAT) are separate or shared and whether they possess differential sympathetic drives with food deprivation in Siberian hamsters. Using two isogenic strains of pseudorabies virus, a retrograde transneuronal viral tract tracer within the same hamsters, we found some overlap (∼20-55% doubly infected neurons) between the two circuitries across the neural axis with lesser overlap proximal to the depots (spinal cord and sympathetic chain) and with more neurons involved in the innervation of IWAT than MWAT in some brain regions. Food deprivation triggered a greater sympathetic drive to subcutaneous (IWAT) than visceral (MWAT) depots. Collectively, we demonstrated both shared and separate populations of brain, spinal cord, and sympathetic chain neurons ultimately project to a subcutaneous WAT depot (IWAT) and the only visceral WAT depot in rodents (MWAT). In addition, the lipolytic stimulus of food deprivation only increased SNS drive to subcutaneous fat (IWAT).

Integrated effects of leptin in the forebrain and hindbrain of male rats

Leptin receptors (ObRs) in the forebrain and hindbrain have been independently recognized as important mediators of leptin responses. It is unclear how leptin activity in these areas is integrated. We tested whether both forebrain and hindbrain ObRs have to be activated simultaneously to change energy balance and to maintain metabolic homeostasis. Previous studies used acute leptin injections in either the third ventricle (1-5 μg) or the fourth ventricle (3-10 μg); here we used 12-day infusions of low doses of leptin in one or both ventricles (0.1 μg/24 h in third, 0.6 μg/24 h in fourth). Male Sprague Dawley rats were fitted with third and fourth ventricle cannulas, and saline or leptin was infused from Alzet pumps for 6 or 12 days. Rats that received leptin into only the third or the fourth ventricle were not different from controls that received saline in both ventricles. By contrast, rats with low-dose leptin infusions into both the third and fourth ventricle showed a dramatic 60% reduction in food intake that was reversed on day 6, a 20% weight loss that stabilized on day 6, and a 50% decrease in body fat at day 12 despite the correction of food intake. They displayed normal activity and maintained energy expenditure despite weight loss, indicating inappropriately high thermogenesis that coincided with increased signal transducer and activator of transcription 3 (STAT3) phosphorylation in the brainstem. Altogether, these findings show that with low doses of leptin, chronic activation of both hypothalamic and brainstem ObRs is required to reduce body fat.

Leptin-sensitive sensory nerves innervate white fat

Leptin, the primary white adipose tissue (WAT) adipokine, is thought to convey lipid reserve information to the brain via the circulation. Because WAT responds to environmental/internal signals in a fat pad-specific (FPS) manner, systemic signals such as leptin would fail to communicate such distinctive information. Saturation of brain leptin transport systems also would fail to convey increased lipid levels beyond that point. WAT possesses sensory innervation exemplified by proven sensory-associated peptides in nerves within the tissue and by viral sensory nerve-specific transneuronal tract tracer, H129 strain of herpes simplex virus 1 labeling of dorsal root ganglia (DRG) pseudounipolar neurons, spinal cord and central sensory circuits. Leptin as a paracrine factor activating WAT sensory innervation could supply the brain with FPS information. Therefore, we tested for and found the presence of the long form of the leptin receptor (Ob-Rb) on DRG pseudounipolar neurons immunohistochemically labeled after injections of Fluorogold, a retrograde tract tracer, into inguinal WAT (IWAT). Intra-IWAT leptin injections (300 ng) significantly elevated IWAT nerve spike rate within 5 min and persisted for at least 30 min. Intra-IWAT leptin injections also induced significant c-Fos immunoreactivity (ir), indicating neural activation across DRG pseudounipolar sensory neurons labeled with Fluorogold IWAT injections. Intraperitoneal leptin injection did not increase c-Fos-ir in DRG or the arcuate nucleus, nor did it increase arcuate signal transducer and activator of transcription 3 phosphorylation-ir. Collectively, these results strongly suggest that endogenous leptin secreted from white adipocytes functions as a paracrine factor to activate spinal sensory nerves innervating the tissue.

Neuronal Sirt1 deficiency increases insulin sensitivity in both brain and peripheral tissues

Sirt1 is a NAD(+)-dependent class III deacetylase that functions as a cellular energy sensor. In addition to its well-characterized effects in peripheral tissues, emerging evidence suggests that neuronal Sirt1 activity plays a role in the central regulation of energy balance and glucose metabolism. To assess this idea, we generated Sirt1 neuron-specific knockout (SINKO) mice. On both standard chow and HFD, SINKO mice were more insulin sensitive than Sirt1(f/f) mice. Thus, SINKO mice had lower fasting insulin levels, improved glucose tolerance and insulin tolerance, and enhanced systemic insulin sensitivity during hyperinsulinemic euglycemic clamp studies. Hypothalamic insulin sensitivity of SINKO mice was also increased over controls, as assessed by hypothalamic activation of PI3K, phosphorylation of Akt and FoxO1 following systemic insulin injection. Intracerebroventricular injection of insulin led to a greater systemic effect to improve glucose tolerance and insulin sensitivity in SINKO mice compared with controls. In line with the in vivo results, insulin-induced AKT and FoxO1 phosphorylation were potentiated by inhibition of Sirt1 in a cultured hypothalamic cell line. Mechanistically, this effect was traced to a reduced effect of Sirt1 to directly deacetylate and repress IRS-1 function. The enhanced central insulin signaling in SINKO mice was accompanied by increased insulin receptor signal transduction in liver, muscle, and adipose tissue. In summary, we conclude that neuronal Sirt1 negatively regulates hypothalamic insulin signaling, leading to systemic insulin resistance. Interventions that reduce neuronal Sirt1 activity have the potential to improve systemic insulin action and limit weight gain on an obesigenic diet.

Sympathetic denervation of one white fat depot changes norepinephrine content and turnover in intact white and brown fat depots

It is well-established that the sympathetic nervous system (SNS) regulates adipocyte metabolism and recently it has been reported that sensory afferents from white fat overlap anatomically with sympathetic efferents to white fat. The studies described here characterize the response of intact fat pads to selective sympathectomy (local 6-hydroxydopamine (6OHDA) injections) of inguinal (ING) or epididymal (EPI) fat in male NIH Swiss mice and provide in vivo evidence for communication between individual white and brown fat depots. The contralateral ING pad, both EPI pads, perirenal (PR), and mesenteric (MES) pads were significantly enlarged 4 weeks after denervating one ING pad, but only intrascapular brown adipose tissue (IBAT) increased when both ING pads were denervated. Denervation of one or both EPI pad had no effect on fat depot weights. In an additional experiment, norepinephrine turnover (NETO) was inhibited in ING, retroperitoneal (RP), MES, and IBAT 2 days after denervation of both EPI or of both ING pads. NE content was reduced to 10-30% of control values in all fat depots. There was no relation between early changes in NETO and fat pad weight 4 weeks after denervation, even though the reduction in NE content of intact fat pads was maintained. These data demonstrate that there is communication among individual fat pads, presumably through central integration of activity of sensory afferent and sympathetic efferent fibers, that changes sympathetic drive to white adipose tissue in a unified manner. In specific situations, removal of sympathetic efferents to one pad induces a compensatory enlargement of other intact depots.

Moderate caloric restriction during gestation in rats alters adipose tissue sympathetic innervation and later adiposity in offspring

Maternal prenatal undernutrition predisposes offspring to higher adiposity in adulthood. Mechanisms involved in these programming effects, apart from those described in central nervous system development, have not been established. Here we aimed to evaluate whether moderate caloric restriction during early pregnancy in rats affects white adipose tissue (WAT) sympathetic innervation in the offspring, and its relationship with adiposity development. For this purpose, inguinal and retroperitoneal WAT (iWAT and rpWAT, respectively) were analyzed in male and female offspring of control and 20% caloric-restricted (from 1-12 d of pregnancy) (CR) dams. Body weight (BW), the weight, DNA-content, morphological features and the immunoreactive tyrosine hydroxylase and Neuropeptide Y area (TH+ and NPY+ respectively, performed by immunohistochemistry) of both fat depots, were studied at 25 d and 6 m of age, the latter after 2 m exposure to high fat diet. At 6 m of life, CR males but not females, exhibited greater BW, and greater weight and total DNA-content in iWAT, without changes in adipocytes size, suggesting the development of hyperplasia in this depot. However, in rpWAT, CR males but not females, showed larger adipocyte diameter, with no changes in DNA-content, suggesting the development of hypertrophy. These parameters were not different between control and CR animals at the age of 25 d. In iWAT, both at 25 d and 6 m, CR males but not females, showed lower TH(+) and NPY(+), suggesting lower sympathetic innervation in CR males compared to control males. In rpWAT, at 6 m but not at 25 d, CR males but not females, showed lower TH(+) and NPY(+). Thus, the effects of caloric restriction during gestation on later adiposity and on the differences in the adult phenotype between internal and subcutaneous fat depots in the male offspring may be associated in part with specific alterations in sympathetic innervation, which may impact on WAT architecture.

Deletion of Nhlh2 results in a defective torpor response and reduced Beta adrenergic receptor expression in adipose tissue

Background

Mice with a targeted deletion of the basic helix-loop-helix transcription factor, Nescient Helix-Loop-Helix 2 (Nhlh2), display adult-onset obesity with significant increases in their fat depots, abnormal responses to cold exposure, and reduced spontaneous physical activity levels. These phenotypes, accompanied by the hypothalamic expression of Nhlh2, make the Nhlh2 knockout (N2KO) mouse a useful model to study the role of central nervous system (CNS) control on peripheral tissue such as adipose tissue.

Methodology

Differences in body temperature and serum analysis of leptin were performed in fasted and ad lib fed wild-type (WT) and N2KO mice. Histological analysis of white (WAT) and brown adipose tissue (BAT) was performed. Gene and protein level expression of inflammatory and metabolic markers were compared between the two genotypes.

Principal Findings

We report significant differences in serum leptin levels and body temperature in N2KO mice compared with WT mice exposed to a 24-hour fast, suggestive of a defect in both white (WAT) and brown adipose tissue (BAT) function. As compared to WT mice, N2KO mice showed increased serum IL-6 protein and WAT IL-6 mRNA levels. This was accompanied by slight elevations of mRNA for several macrophage markers, including expression of macrophage specific protein F4/80 in adipose, suggestive of macrophage infiltration of WAT in the mutant animals. The mRNAs for β3-adrenergic receptors (β3-AR), β2-AR and uncoupling proteins were significantly reduced in WAT and BAT from N2KO mice compared with WT mice.

Conclusions

These studies implicate Nhlh2 in the central control of WAT and BAT function, with lack of Nhlh2 leading to adipose inflammation and altered gene expression, impaired leptin response to fasting, all suggestive of a deficient torpor response in mutant animals.

Endocrine mechanisms of seasonal adaptation in small mammals: from early results to present understanding

Seasonal adaptation is widespread among mammals of temperate and polar latitudes. The changes in physiology, morphology and behaviour are controlled by the photoneuroendocrine system that, as a first step, translates day lengths into a hormonal signal (melatonin). Decoding of the humoral melatonin signal, i.e. responses on the cellular level to slight alterations in signal duration, represents the prerequisite for appropriate timing of winter acclimatization in photoperiodic animals. Corresponding to the diversity of affected traits, several hormone systems are involved in the regulation downstream of the neural integration of photoperiodic time measurement. Results from recent studies provide new insights into seasonal control of reproduction and energy balance. Most intriguingly, the availability of thyroid hormone within hypothalamic key regions, which is a crucial determinant of seasonal transitions, appears to be regulated by hormone secretion from the pars tuberalis of the pituitary gland. This proposed neuroendocrine pathway contradicts the common view of the pituitary as a gland that acts downstream of the hypothalamus. In the present overview of (neuro)endocrine mechanisms underlying seasonal acclimatization, we are focusing on the dwarf hamster Phodopus sungorus (long-day breeder) that is known for large amplitudes in seasonal changes. However, important findings in other mammalian species such as Syrian hamsters and sheep (short-day breeder) are considered as well.

Sensory and sympathetic nervous system control of white adipose tissue lipolysis

Circulating factors are typically invoked to explain bidirectional communication between the CNS and white adipose tissue (WAT). Thus, initiation of lipolysis has been relegated primarily to adrenal medullary secreted catecholamines and the inhibition of lipolysis primarily to pancreatic insulin, whereas signals of body fat levels to the brain have been ascribed to adipokines such as leptin. By contrast, evidence is given for bidirectional communication between brain and WAT occurring via the sympathetic nervous system (SNS) and sensory innervation of this tissue. Using retrograde transneuronal viral tract tracers, the SNS outflow from brain to WAT has been defined. Functionally, sympathetic denervation of WAT blocks lipolysis to a variety of lipolytic stimuli. Using anterograde transneuronal viral tract tracers, the sensory input from WAT to brain has been defined. Functionally, these WAT sensory nerves respond electrophysiologically to increases in WAT SNS drive suggesting a possible neural negative feedback loop to regulate lipolysis.

Getting the message across: mechanisms of physiological cross talk by adipose tissue

Obesity is associated with resistance of skeletal muscle to insulin-mediated glucose uptake, as well as resistance of different organs and tissues to other metabolic and vascular actions of insulin. In addition, the body is exquisitely sensitive to nutrient imbalance, with energy excess or a high-fat diet rapidly increasing insulin resistance, even before noticeable changes occur in fat mass. There is a growing acceptance of the fact that, as well as acting as a storage site for surplus energy, adipose tissue is an important source of signals relevant to, inter alia, energy homeostasis, fertility, and bone turnover. It has also been widely recognized that obesity is a state of low-grade inflammation, with adipose tissue generating substantial quantities of proinflammatory molecules. At a cellular level, the understanding of the signaling pathways responsible for such alterations has been intensively investigated. What is less clear, however, is how alterations of physiology, and of signaling, within one cell or one tissue are communicated to other parts of the body. The concepts of cell signals being disseminated systemically through a circulating "endocrine" signal have been complemented by the view that local signaling may similarly occur through autocrine or paracrine mechanisms. Yet, while much elegant work has focused on the alterations in signaling that are found in obesity or energy excess, there has been less attention paid to ways in which such signals may propagate to remote organs. This review of the integrative physiology of obesity critically appraises the data and outlines a series of hypotheses as to how interorgan cross talk takes place. The hypotheses presented include the "fatty acid hypothesis,", the "portal hypothesis,", the "endocrine hypothesis,", the "inflammatory hypothesis,", the "overflow hypothesis,", a novel "vasocrine hypothesis," and a "neural hypothesis," and the strengths and weaknesses of each hypothesis are discussed.

Anterograde transneuronal viral tract tracing reveals central sensory circuits from white adipose tissue

The origins of the sympathetic nervous system (SNS) innervation of white adipose tissue (WAT) have been defined using the transneuronal viral retrograde tract tracer, pseudorabies virus. Activation of this SNS innervation is acknowledged as the principal initiator of WAT lipolysis. The central control of WAT lipolysis may require neural feedback to a brain-SNS-WAT circuit via WAT afferents. Indeed, conventional tract tracing studies have demonstrated that peripheral pseudounipolar dorsal root ganglion (DRG) sensory cells innervate WAT. The central nervous system projections of WAT afferents remain uncharted, however, and form the focus of the present study. We used the H129 strain of the herpes simplex virus-1 (HSV-1), an anterograde transneuronal viral tract tracer, to define the afferent circuits projecting from WAT to the central nervous system. Siberian hamster inguinal (IWAT) or epididymal WAT was injected with H129 and the neuraxis processed for HSV-1 immunoreactivity. We found substantial overlap in the pattern of WAT sensory afferent projections with multiple SNS outflow sites along the neuraxis, suggesting the possibility of WAT sensory-SNS circuits that could regulate WAT SNS drive and thereby lipolysis. Previously, we demonstrated that systemic 2-deoxy-d-glucose (2DG) elicited increases in the SNS drive to IWAT. Here, we show that systemic 2DG administration also significantly increases multiunit spike activity arising from decentralized IWAT afferents. Collectively, these data provide structural and functional support for the existence of a sensory WAT pathway to the brain, important in the negative feedback control of lipid mobilization.

A reduction in the amount and anti-contractile effect of periadventitial mesenteric adipose tissue precedes hypertension development in spontaneously hypertensive rats

The aim of this study was to determine whether alterations in periadventitial adipose tissue and its anti-contractile effect precede hypertension development. We used 4-week-old male Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), which were pre-hypertensive. Vascular function was studied in the perfused mesenteric bed (MB, 1.5 mL/min). MB weight was lower in SHR (8.0 +/- 0.3 mg/g body weight) than in WKY (9.0 +/- 0.3 mg/g body weight) rats. Concentration-response curves to KCI (6 to 75 mmol/L) and to acetylcholine (10(-9) to 10(-5) mol/L) were similar between groups. Contractile responses to serotonin (10(-9) to 10(-5) mol/L) were significantly higher in SHR compared to WKY. 4-Aminopyridine (4-AP, 2 mmol/L), a blocker of Kv channels, induced a similar increase in perfusion pressure in both strains. However, 4-AP (2 mmol/L) significantly increased the contractile response to serotonin (10(-9) to 10(-5) mol/L) only in WKY. The anti-contractile effect of fat was confirmed by a comparison of (+) fat and (-) fat mesenteric arteries, which revealed that 4-AP significantly enhanced contractions only in (+) fat rings from WKY. These results show that alterations in visceral periadventitial fat mass and function in SHR precede hypertension, suggesting a constitutive mechanism independent of age and the hypertensive state.

Adaptation to lactation in OLETF rats lacking CCK-1 receptors: body weight, fat tissues, leptin and oxytocin

OBJECTIVE

To understand the adaptation to lactation of obese rats, by studying the interplay among the gut hormone cholecystokinin (CCK), the adiposity hormone leptin and the affiliation hormone oxytocin in modulating body mass and fat storage.

DESIGN

Strain differences were examined between Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking expression of functional CCK-1 receptors and Long Evans Tokushima Otsuka (LETO) controls, tested as nulliparous dams, at the 7 and 15th lactation day, at weaning (lactation day 22) or 8 weeks postweaning.

MEASUREMENTS

We measured body mass, fat pads (brown, retroperitoneal and inguinal) and inguinal adipocytes. Plasma levels of leptin and oxytocin were determined.

RESULTS

Fat depots of LETO female rats were larger during lactation compared to the levels found in postweaning and nulliparous female rats. LETO female rats gained weight and accumulated fat during pregnancy and lactation, returning to their normal fat levels postweaning. In contrast, OLETF female rats presented lower body weight and fat depots during the lactation period than nulliparous dams, and regained the weight and fat postweaning. Plasma leptin and oxytocin were highly correlated and followed the same pattern. OLETF leptin levels were highly correlated with fat depot and inguinal cell surface. No significant correlation was found for LETO parameters.

CONCLUSIONS

Pregnancy and lactation are energy-consuming events, which naturally induce female rats to increase food intake and accumulate fat. When challenged by the demands of rapidly growing preobese OLETF pups, OLETF dams' fat stores are reduced to lean, LETO levels. During lactation, sensitivity of the oxytocinergic neurons descending from the paraventricular nuclei to the nucleus of the solitary tract to CCK is reduced. We theorized that this pathway is not available to OLETF female rats that lack functional CCK-1 receptors to mediate the signal. The current study contributes to the understanding of the female body's adaptation to lactation.

Leptin controls adipose tissue lipogenesis via central, STAT3-independent mechanisms

Leptin (encoded by Lep) controls body weight by regulating food intake and fuel partitioning. Obesity is characterized by leptin resistance and increased endocannabinoid tone. Here we show that leptin infused into the mediobasal hypothalamus (MBH) of rats inhibits white adipose tissue (WAT) lipogenesis, which occurs independently of signal transducer and activator of transcription-3 (STAT3) signaling. Correspondingly, transgenic inactivation of STAT3 signaling by mutation of the leptin receptor (s/s mice) leads to reduced adipose mass compared to db/db mice (complete abrogation of leptin receptor signaling). Conversely, the ability of hypothalamic leptin to suppress WAT lipogenesis in rats is lost when hypothalamic phosphoinositide 3-kinase signaling is prevented or when sympathetic denervation of adipose tissue is performed. MBH leptin suppresses the endocannabinoid anandamide in WAT, and, when this suppression of endocannabinoid tone is prevented by systemic CB1 receptor activation, MBH leptin fails to suppress WAT lipogenesis. These data suggest that the increased endocannabinoid tone observed in obesity is linked to a failure of central leptin signaling to restrain peripheral endocannabinoids.

Differential sympathetic drive to adipose tissues after food deprivation, cold exposure or glucoprivation

Surplus energy is principally stored in white adipose tissue (WAT) as triacylglycerol and mobilized via lipolysis through norepinephrine (NE) released from sympathetic nervous system terminals innervating WAT. We demonstrated that central melanocortin receptor agonism provokes differential sympathetic drives across WAT pads and interscapular brown adipose tissue (IBAT). Here we tested for differential WAT and IBAT sympathetic drive to known lipolytic stimuli {glucoprivation [2-deoxy-D-glucose (2-DG)], cold exposure (5 degrees C), food deprivation (16 h), or both cold exposure and food deprivation} by measuring NE turnover (NETO). Only inguinal WAT NETO significantly increased across all stimuli. Dorsal subcutaneous WAT NETO only increased with glucoprivation. Retroperitoneal WAT NETO increased with glucoprivation, cold and cold + food deprivation, but not by food deprivation. Epididymal WAT NETO was unaffected by glucoprivation but increased with cold, cold + food deprivation or food deprivation, but to a small significant degree. IBAT NETO was unaffected by glucoprivation or food deprivation, but increased with cold and cold + food deprivation. Plasma glucose decreased with food deprivation and increased with 2-DG administration or cold exposure. Plasma glycerol was increased with food deprivation, cold, and their combination but not with 2-DG, whereas plasma free fatty acids increased with food deprivation, cold + food deprivation, and 2-DG. These data show differential sympathetic drive to WAT and BAT for four different lipolytic stimuli, exemplifying the fat pad-specific pattern of WAT sympathetic drive across lipid-mobilizing conditions and emphasizing the need to analyze multiple adipose depots for measures of NETO and likely most measures.

Lou/C obesity-resistant rat exhibits hyperactivity, hypermetabolism, alterations in white adipose tissue cellularity, and lipid tissue profiles

Lou/C obesity-resistant rat constitutes an original model to understand the phenomena of overweight and obesity. The aim of the present study was to identify metabolic causes for the outstanding leanness of Lou/C rat. To this end, the metabolic profiles (food intake, energy expenditure, and physical activity) and the cellular characteristics of white adipose tissue (lipogenesis, lipolysis, cellularity, and lipid composition) in 30-wk-old Lou/C rats were compared with age-matched Wistar rats. Lou/C rats exhibited a lower body weight (-45%), reduced adiposity (-80%), increased locomotor activity (+95%), and higher energy expenditure (+11%) than Wistar rats. Epididymal adipose tissue of Lou/C rat was twice lower than that of Wistar rat due to both a reduction in both adipocyte size (-25%) and number (three times). Basal lipolysis and sensitivity to noradrenaline were similar; however, the responsiveness to noradrenaline was lower in adipocytes from Lou/C compared with that from Wistar rats. Lipidomic analysis of plasma, adipose tissue, and liver revealed profound differences in lipid composition between the two strains. Of note, the desaturation indexes (ratio C16:1/C16:0 and C18:1/C18:0) were lower in Lou/C, indicating a blunted activity of delta-9-desaturase such as stearoyl-coenzyme A-desaturase-1. Increased physical activity, increased energy expenditure, and white adipose tissue cellularity are in good agreement with previous observations suggesting that a higher sympathetic tone in Lou/C could contribute to its lifelong leanness.

Brain-adipose tissue neural crosstalk

The preponderance of basic obesity research focuses on its development as affected by diet and other environmental factors, genetics and their interactions. By contrast, we have been studying the reversal of a naturally-occurring seasonal obesity in Siberian hamsters. In the course of this work, we determined that the sympathetic innervation of white adipose tissue (WAT) is the principal initiator of lipid mobilization not only in these animals, but in all mammals including humans. We present irrefutable evidence for the sympathetic nervous system (SNS) innervation of WAT with respect to neuroanatomy (including its central origins as revealed by transneuronal viral tract tracers), neurochemistry (norepinephrine turnover studies) and function (surgical and chemical denervation). A relatively unappreciated role of WAT SNS innervation also is reviewed--the control of fat cell proliferation as shown by selective chemical denervation that triggers adipocyte proliferation, although the precise mechanism by which this occurs presently is unknown. There is no, however, equally strong evidence for the parasympathetic innervation of this tissue; indeed, the data largely are negative severely questioning its existence and importance. Convincing evidence also is given for the sensory innervation of WAT (as shown by tract tracing and by markers for sensory nerves in WAT), with suggestive data supporting a possible role in conveying information on the degree of adiposity to the brain. Collectively, these data offer an additional or alternative view to the predominate one of the control of body fat stores via circulating factors that serve as efferent and afferent communicators.

Appetite and energy balance signals from adipocytes

Interest in the biology of white adipose tissue has risen markedly with the recent surge in obesity and its associated disorders. The tissue is no longer viewed simply as a vehicle for lipid storage; instead, it is recognized as a major endocrine and secretory organ. White adipocytes release a multiplicity of protein hormones, signals and factors, termed adipokines, with an extensive range of physiological actions. Foremost among these various adipokines is the cytokine-like hormone, leptin, which is synthesized predominantly in white fat. Leptin plays a critical role in the control of appetite and energy balance, with mutations in the genes encoding the hormone or its receptor leading to profound obesity in both rodents and man. Leptin regulates appetite primarily through an interaction with hypothalamic neuroendocrine pathways, inhibiting orexigenic peptides such as neuropeptide Y and orexin A, and stimulating anorexigenic peptides such as proopiomelanocortin. White fat also secretes several putative appetite-related adipokines, which include interleukin-6 and adiponectin, but whether these are indeed significant signals in the regulation of food intake has not been established. Through leptin and the other adipokines it is evident that adipose tissue communicates extensively with other organs and plays a pervasive role in metabolic homeostasis.

Sympathetic but not sensory denervation stimulates white adipocyte proliferation

White adipocyte proliferation is a hallmark of obesity, but it largely remains a mechanistic mystery. We and others previously demonstrated that surgical denervation of white adipose tissue (WAT) triggers increases in fat cell number, but it is unknown whether this was due to preadipocyte proliferation or maturation of existing preadipocytes that allowed them to be counted. In addition, surgical denervation severs not only sympathetic but also sensory innervation of WAT. Therefore, we tested whether sympathetic WAT denervation triggers adipocyte proliferation using 5-bromo-2'-deoxyuridine (BrdU) as a marker of proliferation and quantified BrdU-immunoreactive (ir) cells that were co-labeled with AD-3-ir, an adipocyte-specific membrane protein marker. The unilateral denervation model was used for all experiments where Siberian hamster inguinal WAT (IWAT) was unilaterally denervated, the contralateral pad was sham denervated serving as a within-animal control, and then BrdU was injected systemically for 6 days. When IWAT was surgically denervated, severing both sympathetic and sensory nerves, tyrosine hydroxylase (TH)-ir, a sympathetic nerve marker, and calcitonin gene-related peptide (CGRP)-ir, a sensory nerve marker, were significantly decreased, and BrdU+AD-3-ir adipocytes were increased approximately 300%. When IWAT was selectively sensory denervated via local microinjections of capsaicin, a sensory nerve-specific toxin, CGRP-ir, but not TH-ir, was decreased, and BrdU+AD-3-ir adipocytes were unchanged. When IWAT was selectively sympathetically denervated via local microinjections of 6-hydroxy-dopamine, a catecholaminergic-specific toxin, TH-ir, but not CGRP-ir, was significantly decreased, and BrdU+AD-3-ir adipocytes were increased approximately 400%. Collectively, these data provide the first direct evidence that sympathetic nerves inhibit white adipocyte proliferation in vivo.

Effects of central or peripheral leptin administration on norepinephrine turnover in defined fat depots

Leptin preserves lean tissue but decreases adipose tissue by increasing lipolysis and/or inhibiting lipogenesis. The sympathetic nervous system (SNS) is a primary regulator of lipolysis, but it is not known if leptin increases norepinephrine turnover (NETO) in white adipose tissue. In this study, we examined the effect of leptin administered either as a chronic physiological dose (40 microg/day for 4 days from ip miniosmotic pumps) or as an acute injection in the third ventricle (1.5 microg injected two times daily for 2 days) on NETO and the size of brown and white fat depots in male Sprague Dawley rats. NETO was determined from the decline in tissue norepinephrine (NE) during 4 h following administration of the NE synthesis inhibitor alpha-methyl-para-tryrosine. The centrally injected leptin-treated animals demonstrated more dramatic reductions in food intake, body weight, and fat pad size and an increase in NETO compared with the peripherally infused animals. Neither route of leptin administration caused a uniform increase in NETO across all fat pads tested, and in both treatment conditions leptin decreased the size of certain fat pads independent of an increase in NETO. Similar discrepancies in white fat NETO were found for rats pair fed to leptin-treated animals. These results demonstrate that leptin acting either centrally or peripherally selectively increases sympathetic outflow to white fat depots and that a leptin-induced change in fat pad weight does not require an increase in NETO.

Energy expenditure and body composition of chronically maintained decerebrate rats in the fed and fasted condition

The contribution of the caudal brainstem to adaptation to starvation was tested using chronically maintained decerebrate (CD) and neurologically intact controls. All rats were gavage fed an amount of diet that maintained weight gain in controls. CD rats were subjected to a two-stage surgery to produce a complete transection of the neuroaxis at the mesodiencephalic juncture. One week later, the rats were housed in an indirect calorimeter, and 24 h energy expenditure was measured for 4 d. One half of each of the CD and control groups was then starved for 48 h. Fed CD rats maintained a lower body temperature (35 C), a similar energy expenditure per unit fat-free mass but an elevated respiratory quotient compared with controls. They gained less weight, had 20% less lean tissue, and had 60% more fat than controls. Circulating leptin, adiponectin, and insulin were elevated, glucose was normal, but testosterone was dramatically reduced. Responses to starvation were similar in CD and controls; they reduced energy expenditure, decreased respiratory quotient, indicating lipid utilization, defended body temperature, mobilized fat, decreased serum leptin and insulin, and regulated plasma glucose. These data clearly demonstrate that the isolated caudal brainstem is sufficient to mediate many aspects of the energetic response to starvation. In intact animals, these responses may be refined by a contribution by more rostral brain areas or by communication between fore- and hind-brain. In the absence of communication from the forebrain, the caudal brainstem is inadequate for maintenance of testosterone levels or lean tissue in fed or fasted animals.

White adipose tissue sensory nerve denervation mimics lipectomy-induced compensatory increases in adiposity

The sensory innervation of white adipose tissue (WAT) is indicated by the labeling of sensory bipolar neurons in the dorsal root ganglion after retrograde dye placement into WAT. In addition, immunoreactivity (ir) for sensory-associated neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P in WAT pads also supports the notion of WAT sensory innervation. The function of this sensory innervation is unknown but could involve conveying the degree of adiposity to the brain. In tests of total body fat regulation, partial surgical lipectomy triggers compensatory increases in the mass of nonexcised WAT, ultimately resulting in restoration of total body fat levels in Siberian hamsters and other animals. The signal that triggers this compensation is unknown but could involve disruption of WAT sensory innervation that accompanies lipectomy. Therefore, a local and selective sensory denervation was accomplished by microinjecting the sensory nerve neurotoxin capsaicin bilaterally into epididymal WAT (EWAT) of Siberian hamsters, whereas controls received vehicle injections. Additional hamsters had bilateral EWAT lipectomy (EWATx) or sham lipectomy. As seen previously, EWATx resulted in significantly increased retroperitoneal WAT (RWAT) and inguinal WAT (IWAT) masses. Capsaicin treatment significantly decreased CGRP- but not tyrosine hydroxylase-ir, attesting to the diminished and selective sensory innervation. Capsaicin-treated hamsters also had increased RWAT and, to a lesser degree, IWAT mass largely mimicking the WAT mass increases seen after lipectomy. Collectively, these data suggest the possibility that information related to peripheral lipid stores may be conveyed to the brain via the sensory innervation of WAT.

Sympathetic and parasympathetic innervation of adipose tissue: metabolic implications

PURPOSE OF REVIEW

Adipose tissue is of fundamental importance for the integrative physiology of the body by serving metabolic and endocrine functions. The purpose of this review is to evaluate the functions of the autonomic innervation of adipose tissue.

RECENT FINDINGS

Different lines of evidence from studies on the sympathetic or parasympathetic innervation of adipose tissue have indicated that the autonomic nervous system modulates the fundamental properties of adipose tissue function and biology at the cellular and molecular level. This is reflected in the modulation of lipolysis/lipogenesis, local insulin sensitivity of glucose and fatty acid uptake, the expression levels of several adipokines in adipose tissue, and the modulation of fat cell number. In general, the function of the sympathetic nervous system can be described in terms of catabolism, whereas the function of the parasympathetic system can be described as anabolic.

SUMMARY

Innervation by autonomic nerves modulates glucose and fat metabolism in adipose tissue. It is very tempting to speculate on the effects of shifts in the balance between sympathetic and parasympathetic activity in adipose tissue in (patho)physiological conditions, such as lipodystrophy, type 2 diabetes mellitus, dyslipidemia and other insulin-resistant states.

Short photoperiod exposure increases adipocyte sensitivity to noradrenergic stimulation in Siberian hamsters

Siberian hamsters (Phodopus sungorus) exhibit a naturally occurring, reversible seasonal obesity with body fat peaking in long "summerlike" days (LDs) and reaching a nadir in short "winterlike" days (SDs). These SD-induced decreases in adiposity are mediated largely via sympathetic nervous system (SNS) innervation of white adipose tissue (WAT), as indicated by increased WAT norepinephrine (NE) turnover. We examined whether SDs also increase sensitivity to NE-stimulated lipolysis. This was accomplished by measuring NE- and beta3-adrenoceptor (beta3-AR) agonist (BRL-37344)-induced lipolysis (glycerol release) as well as NE-induced cAMP accumulation by inguinal, epididymal, and retroperitoneal WAT (IWAT, EWAT, and RWAT) in isolated adipocytes of LD- and SD-housed hamsters. SDs increased potency/efficacy of NE-triggered lipolysis in a temporally and fat pad-specific manner. Thus when WAT pad mass decreased most rapidly (5 wk of SDs), potency (sensitivity/EC50) and efficacy (maximal response asymptote) of NE-stimulated lipolysis were increased for all WAT pads and also at 10 wk for IWAT compared with their LD counterparts. SD enhancement of lipolysis was similar for NE and BRL-37344 in IWAT adipocytes. These results, coupled with our previous demonstration that SDs upregulate WAT beta3-AR mRNA expression, suggest that increased beta3-ARs mediated the SD-induced increased NE sensitivity. NE-stimulated adipocyte accumulation of cAMP was greater after 5 wk of SDs for IWAT and EWAT and after 10 wk of SDs for IWAT compared with LDs, with no photoperiod effect for RWAT. Therefore, the SD-induced increase in SNS drive to WAT and increased sensitivity to this drive may work together to increase lipolysis in SDs.