Anterograde transneuronal viral tract tracing reveals central sensory circuits from brown fat and sensory denervation alters its thermogenic responses

An atlas of brain-bone sympathetic neural circuits in mice

There is clear evidence that the sympathetic nervous system (SNS) mediates bone metabolism. Histological studies show abundant SNS innervation of the periosteum and bone marrow-these nerves consist of noradrenergic fibers that immunostain for tyrosine hydroxylase, dopamine beta-hydroxylase, or neuropeptide Y. Nonetheless, the brain sites that send efferent SNS outflow to the bone have not yet been characterized. Using pseudorabies (PRV) viral transneuronal tracing, we report, for the first time, the identification of central SNS outflow sites that innervate bone. We find that the central SNS outflow to bone originates from 87 brain nuclei, sub-nuclei, and regions of six brain divisions, namely the midbrain and pons, hypothalamus, hindbrain medulla, forebrain, cerebral cortex, and thalamus. We also find that certain sites, such as the raphe magnus (RMg) of the medulla and periaqueductal gray (PAG) of the midbrain, display greater degrees of PRV152 infection, suggesting that there is considerable site-specific variation in the levels of central SNS outflow to the bone. This comprehensive compendium illustrating the central coding and control of SNS efferent signals to bone should allow for a greater understanding of the neural regulation of bone metabolism, and importantly and of clinical relevance, mechanisms for central bone pain.

Increased Suicide Mortality and Reduced Life Expectancy Associated With Ambient Heat Exposure

INTRODUCTION

Ambient heat exposure is a risk factor for suicide in many regions of the world. However, little is known about the extent to which life expectancy has been shortened by heat-related suicide deaths. This study aimed to evaluate the short-term effects of heat on suicide mortality and quantify the reduced life expectancy associated with heat in China.

METHODS

A time-stratified, case-crossover analysis in 2023 was performed during the warm season (May to September) from 2016 to 2020 to assess the short-term association between extreme heat (the 95th percentile of mean temperature) and suicide mortality in Anhui Province, China. A subgroup analysis was performed according to sex, age, marital status, suicide type, and region. The attributable fraction and years of life lost due to heat were calculated, and the heat-related life expectancy loss was estimated.

RESULTS

This study included 9,642 suicide deaths, with an average age of 62.4 years and 58.8% of suicides in males. Suicide risk was associated with an 80.7% increase (95% confidence interval [CI]: 21.4%-68.9%) after exposure to extreme heat (30.6°C) in comparison to daily minimum temperature (7.9°C). Subgroup analysis revealed that heat-related suicide risk was more prominent in the married population than in the unmarried population. Heat was estimated to be associated with 31.7% (95% CI: 18.0%-43.2%) of the suicides, corresponding to 7.0 years of loss in life expectancy for each decedent.

CONCLUSIONS

Heat exposure was associated with an increased risk of suicide and reduced life expectancy. However, further prospective studies are required to confirm this relationship.

Differential responses to UCP1 ablation in classical brown versus beige fat, despite a parallel increase in sympathetic innervation

In the cold, the absence of the mitochondrial uncoupling protein 1 (UCP1) results in hyper-recruitment of beige fat, but classical brown fat becomes atrophied. Here we examine possible mechanisms underlying this phenomenon. We confirm that in brown fat from UCP1-knockout (UCP1-KO) mice acclimated to the cold, the levels of mitochondrial respiratory chain proteins were diminished; however, in beige fat, the mitochondria seemed to be unaffected. The macrophages that accumulated massively not only in brown fat but also in beige fat of the UCP1-KO mice acclimated to cold did not express tyrosine hydroxylase, the norepinephrine transporter (NET) and monoamine oxidase-A (MAO-A). Consequently, they could not influence the tissues through the synthesis or degradation of norepinephrine. Unexpectedly, in the cold, both brown and beige adipocytes from UCP1-KO mice acquired an ability to express MAO-A. Adipose tissue norepinephrine was exclusively of sympathetic origin, and sympathetic innervation significantly increased in both tissues of UCP1-KO mice. Importantly, the magnitude of sympathetic innervation and the expression levels of genes induced by adrenergic stimulation were much higher in brown fat. Therefore, we conclude that no qualitative differences in innervation or macrophage character could explain the contrasting reactions of brown versus beige adipose tissues to UCP1-ablation. Instead, these contrasting responses may be explained by quantitative differences in sympathetic innervation: the beige adipose depot from the UCP1-KO mice responded to cold acclimation in a canonical manner and displayed enhanced recruitment, while the atrophy of brown fat lacking UCP1 may be seen as a consequence of supraphysiological adrenergic stimulation in this tissue.

Self-harm and interpersonal violence due to high temperature from the global burden of disease study 2019: A 30-year assessment

BACKGROUND

The impact of global warming on health due to climate change is increasingly studied, but the global burden of self-harm and interpersonal violence attributable to high temperature is still limited. This study aimed to systematically assess the burden of self-harm and interpersonal violence attributable to high temperature globally or by region and climate zone from 1990 to 2019.

METHODS

We obtained the global, regional, and national deaths, disability-adjusted life years (DALYs), age-standardized mortality rates (ASMR), and age-standardized disability-adjusted life year rates (ASDR) of self-harm and interpersonal violence due to high temperature from 1990 to 2019 through the Global Burden of Disease Study (GBD) 2019. The burden of self-harm and interpersonal violence due to high temperature was estimated by age, sex, climate zone, the socio-demographic index (SDI), and the healthcare access and quality index (HAQ). Average annual percentage changes (AAPCs) in ASMR and ASDR were calculated for 1990-2019 using the Joinpoint model.

RESULTS

From 1990 to 2019, the global deaths and DALYs related to self-harm and interpersonal violence due to high temperature increased from 20,002 (95% UI, 9243 to 41,928) and 1,107,216 (95% UI, 512,062 to 2,319,477) to 26,459 (95% UI, 13,574 to 47,265) and 1,382,487 (95% UI, 722,060 to 2,474,441), respectively. However, the ASMR and ASDR showed varying degrees of decreasing trends, with decreases of 13.36% and 12.66%, respectively. The ASMR was high and declining in low and low-middle SDI regions, particularly in tropical and subtropical regions. In addition, SDI and HAQ index were negatively correlated with ASMR in 204 countries and regions.

CONCLUSIONS

The global burden of self-harm and interpersonal violence attributed to high temperature has decreased over the past 30 years, but the number of deaths and DALYs continues to rise. Climate change continues to make heat stress a significant risk factor for self-harm and interpersonal violence worldwide.

An Atlas of Brain-Bone Sympathetic Neural Circuits

There is clear evidence that the sympathetic nervous system (SNS) mediates bone metabolism. Histological studies show abundant SNS innervation of the periosteum and bone marrow--these nerves consist of noradrenergic fibers that immunostain for tyrosine hydroxylase, dopamine beta hydroxylase, or neuropeptide Y. Nonetheless, the brain sites that send efferent SNS outflow to bone have not yet been characterized. Using pseudorabies (PRV) viral transneuronal tracing, we report, for the first time, the identification of central SNS outflow sites that innervate bone. We find that the central SNS outflow to bone originates from 87 brain nuclei, sub-nuclei and regions of six brain divisions, namely the midbrain and pons, hypothalamus, hindbrain medulla, forebrain, cerebral cortex, and thalamus. We also find that certain sites, such as the raphe magnus (RMg) of the medulla and periaqueductal gray (PAG) of the midbrain, display greater degrees of PRV152 infection, suggesting that there is considerable site-specific variation in the levels of central SNS outflow to bone. This comprehensive compendium illustrating the central coding and control of SNS efferent signals to bone should allow for a greater understanding of the neural regulation of bone metabolism, and importantly and of clinical relevance, mechanisms for central bone pain.

Sensory nerve and neuropeptide diversity in adipose tissues

Both brown and white adipose tissues (BAT/WAT) are innervated by the peripheral nervous system, including efferent sympathetic nerves that communicate from the brain/central nervous system out to the tissue, and afferent sensory nerves that communicate from the tissue back to the brain and locally release neuropeptides to the tissue upon stimulation. This bidirectional neural communication is important for energy balance and metabolic control, as well as maintaining adipose tissue health through processes like browning (development of metabolically healthy brown adipocytes in WAT), thermogenesis, lipolysis, and adipogenesis. Decades of sensory nerve denervation studies have demonstrated the particular importance of adipose sensory nerves for brown adipose tissue and WAT functions, but far less is known about the tissue's sensory innervation compared to the better-studied sympathetic nerves and their neurotransmitter norepinephrine. In this review, we cover what is known and not yet known about sensory nerve activities in adipose, focusing on their effector neuropeptide actions in the tissue.

Adipose Tissue-Derived Extracellular Vesicles: A Promising Biomarker and Therapeutic Strategy for Metabolic Disorders

Adipose tissue plays an important role in systemic energy metabolism, and its dysfunction can lead to severe metabolic disorders. Various cells in adipose tissue communicate with each other to maintain metabolic homeostasis. Extracellular vesicles (EVs) are recognized as novel medium for remote intercellular communication by transferring various bioactive molecules from parental cells to distant target cells. Increasing evidence suggests that the endocrine functions of adipose tissue and even the metabolic homeostasis are largely affected by different cell-derived EVs, such as insulin signaling, lipolysis, and metabolically triggered inflammation regulations. Here, we provide an overview focused on the role of EVs released by different cell types of adipose tissue in metabolic diseases and their possible molecular mechanisms and highlight the potential applications of EVs as biomarkers and therapeutic targets. Moreover, the current EVs-based therapeutic strategies have also been discussed. This trial is registered with NCT05475418.

Prevention of suicides associated with global warming: perspectives from early career psychiatrists

Climate change poses significant challenges to global mental health, with potential consequences including increased rates of suicide and mental health disorders. Early Career Psychiatrists (ECPs) play a crucial role in addressing these challenges. The Climate Psychiatry Alliance, a group of psychiatrists dedicated to improving mental health amidst climate change, recognizes the importance of cultivating climate-aware ECPs. Training ECPs to become confident climate-aware clinicians enables them to effectively treat patients experiencing anxiety, depression, and PTSD in the context of climate-related distress. Together with other mental health professionals, ECPs can contribute to efforts by implementing strategies for monitoring and treating mental health problems arising from climate events. Additionally, they can raise awareness about the psychological consequences and risks of suicide associated with climate change. Collaboration among ECPs from various regions is essential in developing community-based approaches and reducing vulnerabilities. ECPs must prioritize supporting vulnerable populations by advocating for increased funding for mental health support and research in affected areas. Long-term solutions to address the mental health impacts of climate change and global warming should be pursued to mitigate future suicidality. Integrating climate considerations into local mental health programs and expanding psychological support services is crucial. By promoting emotional resilience and self-awareness, ECPs can contribute to building a more climate-resilient and mentally healthy society.

The nervous system and adipose tissues: a tale of dialogues

White, beige, and brown adipose tissues play a crucial role in maintaining energy homeostasis. Due to the heterogeneous and diffuse nature of fat pads, this balance requires a fine and coordinated control of many actors and therefore permanent dialogues between these tissues and the central nervous system. For about two decades, many studies have been devoted to describe the neuro-anatomical and functional complexity involved to ensure this dialogue. Thus, if it is now clearly demonstrated that there is an efferent sympathetic innervation of different fat depots controlling plasticity as well as metabolic functions of the fat pad, the crucial role of sensory innervation capable of detecting local signals informing the central nervous system of the metabolic state of the relevant pads is much more recent. The purpose of this review is to provide the current state of knowledge on this subject.

The metabolic and functional roles of sensory nerves in adipose tissues

Homeostatic regulation of adipose tissue is critical for the maintenance of energy balance and whole-body metabolism. The peripheral nervous system provides bidirectional neural communication between the brain and adipose tissue, thereby providing homeostatic control. Most research on adipose innervation and nerve functions has been limited to the sympathetic nerves and their neurotransmitter norepinephrine. In recent years, more work has focused on adipose sensory nerves, but the contributions of subsets of sensory nerves to metabolism and the specific roles contributed by sensory neuropeptides are still understudied. Advances in imaging of adipose innervation and newer tissue denervation techniques have confirmed that sensory nerves contribute to the regulation of adipose functions, including lipolysis and browning. Here, we summarize the historical and latest findings on the regulation, function and plasticity of adipose tissue sensory nerves that contribute to metabolically important processes such as lipolysis, vascular control and sympathetic axis cross-talk.

Investigations of brain-wide functional and structural networks of dopaminergic and CamKIIα-positive neurons in VTA with DREADD-fMRI and neurotropic virus tracing technologies

BACKGROUND

The ventral tegmental area (VTA) contains heterogeneous cell populations. The dopaminergic neurons in VTA play a central role in reward and cognition, while CamKIIα-positive neurons, composed mainly of glutamatergic and some dopaminergic neurons, participate in the reward learning and locomotor activity behaviors. The differences in brain-wide functional and structural networks between these two neuronal subtypes were comparatively elucidated.

METHODS

In this study, we applied a method combining Designer Receptors Exclusively Activated by Designer Drugs (DREADD) and fMRI to assess the cell type-specific modulation of whole-brain neural networks. rAAV encoding the cre-dependent hM3D was injected into the right VTA of DAT-cre or CamKIIα-cre transgenic rats. The global brain activities elicited by DREADD stimulation were then detected using BOLD-fMRI. Furthermore, the cre-dependent antegrade transsynaptic viral tracer H129ΔTK-TT was applied to label the outputs of VTA neurons.

RESULTS

We found that DREADD stimulation of dopaminergic neurons induced significant BOLD signal changes in the VTA and several VTA-related regions including mPFC, Cg and Septum. More regions responded to selective activation of VTA CamKIIα-positive neurons, resulting in increased BOLD signals in VTA, Insula, mPFC, MC_R (Right), Cg, Septum, Hipp, TH_R, PtA_R, and ViC_R. Along with DREADD-BOLD analysis, further neuronal tracing identified multiple cortical (MC, mPFC) and subcortical (Hipp, TH) brain regions that are structurally and functionally connected by VTA dopaminergic and CamKIIα-positive neurons.

CONCLUSIONS

Our study dissects brain-wide structural and functional networks of two neuronal subtypes in VTA and advances our understanding of VTA functions.

Transneuronal Circuit Analysis with Pseudorabies Viruses

Our ability to understand the function of the nervous system is dependent upon defining the connections of its constituent neurons. Development of methods to define connections within neural networks has always been a growth industry in the neurosciences. Transneuronal spread of neurotropic viruses currently represents the best means of defining synaptic connections within neural networks. The method exploits the ability of viruses to invade neurons, replicate, and spread through the intimate synaptic connections that enable communication among neurons. Since the method was first introduced in the 1970s, it has benefited from an increased understanding of the virus life cycle, the function of viral genomes, and the ability to manipulate the viral genome in support of directional spread of virus and the expression of transgenes. In this article, we review these advances in viral tracing technology and the ways in which they may be applied for functional dissection of neural networks. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Retrograde infection of CNS circuits by peripheral injection of virus Basic Protocol 2: Transneuronal analysis by intracerebral injection Alternate Protocol 1: Transneuronal analysis with multiple recombinant strains Alternate Protocol 2: Conditional replication and spread of PRV Alternate Protocol 3: Conditional reporters of PRV infection and spread Alternate Protocol 4: Reporters of neural activity in polysynaptic circuits Support Protocol 1: Growing and titering a PRV viral stock Support Protocol 2: Immunohistochemical processing and detection Support Protocol 3: Dual-immunofluorescence localization.

Potential links between brown adipose tissue, circadian dysregulation, and suicide risk

Circadian desynchronizations are associated with psychiatric disorders as well as with higher suicidal risk. Brown adipose tissue (BAT) is important in the regulation of body temperature and contributes to the homeostasis of the metabolic, cardiovascular, skeletal muscle or central nervous system. BAT is under neuronal, hormonal and immune control and secrets batokines: i.e., autocrine, paracrine and endocrine active substances. Moreover, BAT is involved in circadian system. Light, ambient temperature as well as exogen substances interact with BAT. Thus, a dysregulation of BAT can indirectly worsen psychiatric conditions and the risk of suicide, as one of previously suggested explanations for the seasonality of suicide rate. Furthermore, overactivation of BAT is associated with lower body weight and lower level of blood lipids. Reduced body mass index (BMI) or decrease in BMI respectively, as well as lower triglyceride concentrations were found to correlate with higher risk of suicide, however the findings are inconclusive. Hyperactivation or dysregulation of BAT in relation to the circadian system as a possible common factor is discussed. Interestingly, substances with proven efficacy in reducing suicidal risk, like clozapine or lithium, interact with BAT. The effects of clozapine on fat tissue are stronger and might differ qualitatively from other antipsychotics; however, the significance remains unclear. We suggest that BAT is involved in the brain/environment homeostasis and deserves attention from a psychiatric point of view. Better understanding of circadian disruptions and its mechanisms can contribute to personalized diagnostic and therapy as well as better assessment of suicide risk.

The Physiology of Neurogenic Obesity: Lessons from Spinal Cord Injury Research

BACKGROUND

A spinal cord injury (SCI) from trauma or disease impairs sensorimotor pathways in somatic and autonomic divisions of the nervous system, affecting multiple body systems. Improved medical practices have increased survivability and life expectancy after SCI, allowing for the development of extensive metabolic comorbidities and profound changes in body composition that culminate in prevalent obesity.

SUMMARY

Obesity is the most common cardiometabolic component risk in people living with SCI, with a diagnostic body mass index cutoff of 22 kg/m2 to account for a phenotype of high adiposity and low lean mass. The metameric organization of specific divisions of the nervous system results in level-dependent pathology, with resulting sympathetic decentralization altering physiological functions such as lipolysis, hepatic lipoprotein metabolism, dietary fat absorption, and neuroendocrine signaling. In this manner, SCI provides a unique opportunity to study in vivo the "neurogenic" components of certain pathologies that otherwise are not readily observable in other populations. We discuss the unique physiology of neurogenic obesity after SCI, including the altered functions mentioned above as well as structural changes such as reduced skeletal muscle and bone mass and increased lipid deposition in the adipose tissue, skeletal muscle, bone marrow, and liver.

KEY MESSAGE

The study of neurogenic obesity after SCI gives us a unique neurological perspective on the physiology of obesity. The lessons learned from this field can guide future research and advancements to inform the study of obesity in persons with and without SCI.

Monosynaptic restriction of the anterograde herpes simplex virus strain H129 for neural circuit tracing

Identification of synaptic partners is a fundamental task for systems neuroscience. To date, few reliable techniques exist for whole brain labeling of downstream synaptic partners in a cell-type-dependent and monosynaptic manner. Herein, we describe a novel monosynaptic anterograde tracing system based on the deletion of the gene UL6 from the genome of a cre-dependent version of the anterograde Herpes Simplex Virus 1 strain H129. Given that this knockout blocks viral genome packaging and thus viral spread, we reasoned that co-infection of a HSV H129 ΔUL6 virus with a recombinant adeno-associated virus expressing UL6 in a cre-dependent manner would result in monosynaptic spread from target cre-expressing neuronal populations. Application of this system to five nonreciprocal neural circuits resulted in labeling of neurons in expected projection areas. While some caveats may preclude certain applications, this system provides a reliable method to label postsynaptic partners in a brain-wide fashion.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

Skeletal interoception in bone homeostasis and pain

Accumulating evidence indicates that interoception maintains proper physiological status and orchestrates metabolic homeostasis by regulating feeding behaviors, glucose balance, and lipid metabolism. Continuous skeletal remodeling consumes a tremendous amount of energy to provide skeletal scaffolding, support muscle movement, store vital minerals, and maintain a niche for hematopoiesis, which are processes that also contribute to overall metabolic balance. Although skeletal innervation has been described for centuries, recent work has shown that skeletal metabolism is tightly regulated by the nervous system and that skeletal interoception regulates bone homeostasis. Here, we provide a general discussion of interoception and its effects on the skeleton and whole-body metabolism. We also discuss skeletal interoception-mediated regulation in the context of pathological conditions and skeletal pain as well as future challenges to our understanding of these process and how they can be leveraged for more effective therapy.

Brain-to-BAT - and Back?: Crosstalk between the Central Nervous System and Thermogenic Adipose Tissue in Development and Therapy of Obesity

The body of mammals harbors two distinct types of adipose tissue: while cells within the white adipose tissue (WAT) store surplus energy as lipids, brown adipose tissue (BAT) is nowadays recognized as the main tissue for transforming chemical energy into heat. This process, referred to as 'non-shivering thermogenesis', is facilitated by the uncoupling of the electron transport across mitochondrial membranes from ATP production. BAT-dependent thermogenesis acts as a safeguarding mechanism under reduced ambient temperature but also plays a critical role in metabolic and energy homeostasis in health and disease. In this review, we summarize the evolutionary structure, function and regulation of the BAT organ under neuronal and hormonal control and discuss its mutual interaction with the central nervous system. We conclude by conceptualizing how better understanding the multifaceted communicative links between the brain and BAT opens avenues for novel therapeutic approaches to treat obesity and related metabolic disorders.

Interactions between central nervous system and peripheral metabolic organs

According to Descartes, minds and bodies are distinct kinds of "substance", and they cannot have causal interactions. However, in neuroscience, the two-way interaction between the brain and peripheral organs is an emerging field of research. Several lines of evidence highlight the importance of such interactions. For example, the peripheral metabolic systems are overwhelmingly regulated by the mind (brain), and anxiety and depression greatly affect the functioning of these systems. Also, psychological stress can cause a variety of physical symptoms, such as bone loss. Moreover, the gut microbiota appears to play a key role in neuropsychiatric and neurodegenerative diseases. Mechanistically, as the command center of the body, the brain can regulate our internal organs and glands through the autonomic nervous system and neuroendocrine system, although it is generally considered to be outside the realm of voluntary control. The autonomic nervous system itself can be further subdivided into the sympathetic and parasympathetic systems. The sympathetic division functions a bit like the accelerator pedal on a car, and the parasympathetic division functions as the brake. The high center of the autonomic nervous system and the neuroendocrine system is the hypothalamus, which contains several subnuclei that control several basic physiological functions, such as the digestion of food and regulation of body temperature. Also, numerous peripheral signals contribute to the regulation of brain functions. Gastrointestinal (GI) hormones, insulin, and leptin are transported into the brain, where they regulate innate behaviors such as feeding, and they are also involved in emotional and cognitive functions. The brain can recognize peripheral inflammatory cytokines and induce a transient syndrome called sick behavior (SB), characterized by fatigue, reduced physical and social activity, and cognitive impairment. In summary, knowledge of the biological basis of the interactions between the central nervous system and peripheral organs will promote the full understanding of how our body works and the rational treatment of disorders. Thus, we summarize current development in our understanding of five types of central-peripheral interactions, including neural control of adipose tissues, energy expenditure, bone metabolism, feeding involving the brain-gut axis and gut microbiota. These interactions are essential for maintaining vital bodily functions, which result in homeostasis, i.e., a natural balance in the body's systems.

The connectome from the cerebral cortex to skeletal muscle using viral transneuronal tracers: a review

Connectomics has developed from an initial observation under an electron microscope to the present well-known medical imaging research approach. The emergence of the most popular transneuronal tracers has further advanced connectomics research. Researchers use the virus trans-nerve tracing method to trace the whole brain, mark the brain nerve circuit and nerve connection structure, and construct a complete nerve conduction pathway. This review assesses current methods of studying cortical to muscle connections using viral neuronal tracers and demonstrates their application in disease diagnosis and prognosis.

Seasonal changes and decrease of suicides and suicide attempts in France over the last 10 years

The objective of this study was to examine the evolution of suicides and suicide attempts over the last 10 years in France. We analyzed the number of deaths by suicide and suicide attempts in metropolitan France (2009-2018) from French national databases, on a daily, weekly or monthly basis. Seasonal variation in suicide rates was modeled using a cosinor function. Based on this model, we determined the association of suicides and suicide attempts with geographic characteristics, age, gender, means used and psychiatric disorders. The number of suicides and suicide attempts decreased over the last ten years in France (mean decrease of 14.49% and 11.69% per year). We observed a significant and recurrent seasonal pattern of suicides and suicide attempts in France, with a peak in spring. The suicide and suicide attempt rates were higher in the northern departments of France. Suicides were more frequent for men (75%) and middle-age individuals (45-54 years old), while suicide attempts were more frequent for women (62%) and young adults and middle-age individual (15-19 and 40-49 years old). Nearly two-thirds of the patients who attempted suicide suffered from comorbid psychiatric disorders. Mood disorders was the most frequent comorbid psychiatric disorder (54%). Voluntary drug intoxication was the most common means of suicide attempt (80%), and hanging was the most common means of suicide (54%). The number of suicides and suicide attempts decreased in France over the last 10 years, with large and recurrent seasonal variations. These findings could be used to alert and adjust prevention policies, as well as developing preventive strategies such as chronotherapeutics.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

Exploring multiple pathways and mediation effects of urban environmental factors for suicide prevention

Public health is threatened by air pollution and high temperature, especially in urban areas and areas impacted by climate change. Well-designed urban forms have co-benefits on promoting human health and mediating atmospheric environment-related threats (e.g., high temperature and air pollution). Previous studies overlooked these mediating effects of urban form on suicide mortality. This study used partial least squares modeling and countywide data in Taiwan to identify the crucial influences and pathways of urban environment, socioeconomic status, and diseases on suicide mortality. The model considered the impact of the characteristics of urban form (i.e., urban development intensity, land mix, and urban sprawl), urban industrial status (i.e., industrial level), urban greening (i.e., green coverage), disease (i.e., important diseases morbidity of human immunodeficiency virus [HIV], cerebrovascular disease [CVD], chronic liver disease and cirrhosis [CLDC], nephritis, nephrotic syndrome and nephrosis [NNSN], malignant tumor [MT]), socioeconomic status (i.e., income level and aging population rate), and the atmospheric environment (i.e., air pollution and high temperature) on suicide mortality. Optimizing land mix and minimizing urban development intensity and urban sprawl have been found to reduce suicide mortality. The mediating effect of urban form on suicide mortality originated from air pollution and high temperature, and mediating air pollution was greater than high temperature. Furthermore, industrial level, important diseases (HIV, CVD, CLDC, NNSN, and MT) morbidity, an aging population rate, air pollution, and high temperature were associated with an increase in suicide mortality, whereas green coverage and income level were associated with a reduction in suicide rates. The findings demonstrate that appropriate urban policy and urban planning may lower suicide mortality, be useful strategies for suicide prevention, and be a foundation for building a healthy city. Moreover, this study provides clarity on the complex relationship of suicide and the urban environment while identifying crucial factors.

Orexin receptor type 2 agonism inhibits thermogenesis in brown adipose tissue by attenuating afferent innervation

Orexin signaling has been associated with energy expenditure and brown adipose tissue (BAT) function. However, conflicting data exist in the field about how orexin signaling regulates BAT thermogenesis. In this study, we show that a specific orexin receptor type 2 (OX2R) agonist [Ala11, D-Leu15]-OxB (OB-Ala) inhibited intrascapular brown adipose tissue (iBAT) thermogenesis by reducing sympathetic output to iBAT. This effect is mediated by OX2Rs located on afferent nerve endings innervating iBAT instead of brown adipocyte itself. Microinjection of OB-Ala into iBAT inhibited iBAT thermogenesis in mice upon cold exposure and neuronal activity in the paraventricular nucleus. Findings suggest that OB-Ala could inhibit iBAT thermogenesis by attenuating sensory input thereby inhibiting the sympathetic-sensory iBAT feedback loop. Our study uncovers a novel primary action site of orexin in the regulation of energy balance.

Dopamine receptor 2 downregulation and brain-derived neurotrophic factor upregulation in the paraventricular nucleus are correlated with brown adipose tissue thermogenesis in rats with bilateral substantia nigra lesions

The thermogenesis resulting from brown adipose tissue (BAT)-induced energy consumption is an important method of energy regulation. It has been reported that brain-derived neurotrophic factor (BDNF)-positive neurons in the paraventricular nucleus (PVN) can regulate adaptive thermogenesis in interscapular brown adipose tissue (IBAT), but the upstream regulatory mechanism is still unclear. Our previous studies have found that a large number of dopamine (DA) receptors (DRs) are expressed on BDNF-positive neurons in the PVN and that the substantia nigra (SN) can directly project to the PVN (forming the SN-PVN pathway). Therefore, we speculate that DA in the SN can regulate the expression of BDNF via DRs and then affect IBAT thermogenesis. In this study, bilateral SN lesions were induced in rats with 6-hydroxydopamine (6-OHDA), and the altered expression of DRs and BDNF in the PVN and the metabolic changes in IBAT were studied via double immunofluorescence and western blotting. The results showed that BDNF-positive neurons in the PVN expressed DR 1 (D1) and DR 2 (D2) and were surrounded by a large number of tyrosine hydroxylase (TH)-positive nerve fibers. Compared with the control group, the 6-OHDA group exhibited significantly fewer TH-positive neurons and significantly lower TH expression in the SN, but body weight, IBAT weight and food consumption did not differ between the groups. In the PVN, BDNF expression was upregulated in the 6-OHDA group, while D2 and TH expression was downregulated. In IBAT, the expression of uncoupling protein-1 (UCP-1), phosphorylated hormone-sensitive lipase (p-HSL), TH and β3-adrenergic receptor (β3-AR) was increased, while the expression of fatty acid synthase (FAS) was decreased. The IBAT cell diameter was also decreased in the 6-OHDA group. The results suggest that the SN-PVN pathway may be an upstream neural pathway that can affect BDNF expression in the PVN and that DRs may mediate its regulatory effects. This study expands our understanding of the relationship between DA and obesity.

Sensory Circumventricular Organs, Neuroendocrine Control, and Metabolic Regulation

The central nervous system is critical in metabolic regulation, and accumulating evidence points to a distributed network of brain regions involved in energy homeostasis. This is accomplished, in part, by integrating peripheral and central metabolic information and subsequently modulating neuroendocrine outputs through the paraventricular and supraoptic nucleus of the hypothalamus. However, these hypothalamic nuclei are generally protected by a blood-brain-barrier limiting their ability to directly sense circulating metabolic signals—pointing to possible involvement of upstream brain nuclei. In this regard, sensory circumventricular organs (CVOs), brain sites traditionally recognized in thirst/fluid and cardiovascular regulation, are emerging as potential sites through which circulating metabolic substances influence neuroendocrine control. The sensory CVOs, including the subfornical organ, organum vasculosum of the lamina terminalis, and area postrema, are located outside the blood-brain-barrier, possess cellular machinery to sense the metabolic interior milieu, and establish complex neural networks to hypothalamic neuroendocrine nuclei. Here, evidence for a potential role of sensory CVO-hypothalamic neuroendocrine networks in energy homeostasis is presented.

HSV-1 H129-Derived Anterograde Neural Circuit Tracers: Improvements, Production, and Applications

Anterograde viral tracers are powerful and essential tools for dissecting the output targets of a brain region of interest. They have been developed from herpes simplex virus 1 (HSV-1) strain H129 (H129), and have been successfully applied to map diverse neural circuits. Initially, the anterograde polysynaptic tracer H129-G4 was used by many groups. We then developed the first monosynaptic tracer, H129-dTK-tdT, which was highly successful, yet improvements are needed. Now, by inserting another tdTomato expression cassette into the H129-dTK-tdT genome, we have created H129-dTK-T2, an updated version of H129-dTK-tdT that has improved labeling intensity. To help scientists produce and apply our H129-derived viral tracers, here we provide the protocol describing our detailed and standardized procedures. Commonly-encountered technical problems and their solutions are also discussed in detail. Broadly, the dissemination of this protocol will greatly support scientists to apply these viral tracers on a large scale.

Sensory neurons expressing calcitonin gene-related peptide α regulate adaptive thermogenesis and diet-induced obesity

Objectives

Heat-sensory neurons from the dorsal root ganglia (DRG) play a pivotal role in detecting the cutaneous temperature and transmission of external signals to the brain, ensuring the maintenance of thermoregulation. However, whether these thermoreceptor neurons contribute to adaptive thermogenesis remains elusive. It is also unknown whether these neurons play a role in obesity and energy metabolism.

Methods

We used genetic ablation of heat-sensing neurons expressing calcitonin gene-related peptide α (CGRPα) to assess whole-body energy expenditure, weight gain, glucose tolerance, and insulin sensitivity in normal chow and high-fat diet-fed mice. Exvivo lipolysis and transcriptional characterization were combined with adipose tissue-clearing methods to visualize and probe the role of sensory nerves in adipose tissue. Adaptive thermogenesis was explored using infrared imaging of intrascapular brown adipose tissue (iBAT), tail, and core temperature upon various stimuli including diet, external temperature, and the cooling agent icilin.

Results

In this report, we show that genetic ablation of heat-sensing CGRPα neurons promotes resistance to weight gain upon high-fat diet (HFD) feeding and increases energy expenditure in mice. Mechanistically, we found that loss of CGRPα-expressing sensory neurons was associated with reduced lipid deposition in adipose tissue, enhanced expression of fatty acid oxidation genes, higher exvivo lipolysis in primary white adipocytes, and increased mitochondrial respiration from iBAT. Remarkably, mice lacking CGRPα sensory neurons manifested increased tail cutaneous vasoconstriction at room temperature. This exacerbated cold perception was not associated with reduced core temperature, suggesting that heat production and heat conservation mechanisms were engaged. Specific denervation of CGRPα neurons in intrascapular BAT did not contribute to the increased metabolic rate observed upon global sensory denervation.

Conclusions

Taken together, these findings highlight an important role of cutaneous thermoreceptors in regulating energy metabolism by triggering counter-regulatory responses involving energy dissipation processes including lipid fuel utilization and cutaneous vasodilation.

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Removal of sensory spinal neurons expressing CGRPα mitigates diet-induced obesity.

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CGRPα afferents antagonize adaptive thermogenesis in brown adipose tissue.

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Loss of CGRPα afferents leads to enhanced cold perception and vasoconstriction.

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Specific adipose denervation of CGRPα afferents does not modulate energy metabolism.

Peripheral Innervation in the Regulation of Glucose Homeostasis

Precise regulation of circulating glucose is crucial for human health and ensures a sufficient supply to the brain, which relies almost exclusively on glucose for metabolic energy. Glucose homeostasis is coordinated by hormone-secreting endocrine cells in the pancreas, as well as glucose utilization and production in peripheral metabolic tissues including the liver, muscle, and adipose tissue. Glucose-regulatory tissues receive dense innervation from sympathetic, parasympathetic, and sensory fibers. In this review, we summarize the functions of peripheral nerves in glucose regulation and metabolism. Dynamic changes in peripheral innervation have also been observed in animal models of obesity and diabetes. Together, these studies highlight the importance of peripheral nerves as a new therapeutic target for metabolic disorders.

Brown Adipose Tissue: A Metabolic Regulator in a Hypothalamic Cross Talk?

Since the discovery of functionally competent, energy-consuming brown adipose tissue (BAT) in adult humans, much effort has been devoted to exploring this tissue as a means for increasing energy expenditure to counteract obesity. However, despite promising effects on metabolic rate and insulin sensitivity, no convincing evidence for weight-loss effects of cold-activated human BAT exists to date. Indeed, increasing energy expenditure would naturally induce compensatory feedback mechanisms to defend body weight. Interestingly, BAT is regulated by multiple interactions with the hypothalamus from regions overlapping with centers for feeding behavior and metabolic control. Therefore, in the further exploration of BAT as a potential source of novel drug targets, we discuss the hypothalamic orchestration of BAT activity and the relatively unexplored BAT feedback mechanisms on neuronal regulation. With a holistic view on hypothalamic-BAT interactions, we aim to raise ideas and provide a new perspective on this circuit and highlight its clinical relevance.

Functional characterization of human brown adipose tissue metabolism

Brown adipose tissue (BAT) has long been described according to its histological features as a multilocular, lipid-containing tissue, light brown in color, that is also responsive to the cold and found especially in hibernating mammals and human infants. Its presence in both hibernators and human infants, combined with its function as a heat-generating organ, raised many questions about its role in humans. Early characterizations of the tissue in humans focused on its progressive atrophy with age and its apparent importance for cold-exposed workers. However, the use of positron emission tomography (PET) with the glucose tracer [18F]fluorodeoxyglucose ([18F]FDG) made it possible to begin characterizing the possible function of BAT in adult humans, and whether it could play a role in the prevention or treatment of obesity and type 2 diabetes (T2D). This review focuses on the in vivo functional characterization of human BAT, the methodological approaches applied to examine these features and addresses critical gaps that remain in moving the field forward. Specifically, we describe the anatomical and biomolecular features of human BAT, the modalities and applications of non-invasive tools such as PET and magnetic resonance imaging coupled with spectroscopy (MRI/MRS) to study BAT morphology and function in vivo, and finally describe the functional characteristics of human BAT that have only been possible through the development and application of such tools.

Increased energy expenditure and activated β3-AR-cAMP-PKA signaling pathway in the interscapular brown adipose tissue of 6-OHDA-induced Parkinson's disease model rats

To explore the possible mechanism of weight loss in Parkinson's disease (PD). Bilateral injections of 6-hydroxydopamine (6-OHDA) into substantia nigra (SN) were performed to induce the PD model rats. The rotarod test, food intake, body weight, and interscapular brown adipose tissue (IBAT) weight were recorded 6 weeks postoperation. HE staining was performed to observe the morphology of multilocular adipose cells in IBAT. Immunohistochemistry and western blot were used to determine the protein levels of tyrosine hydroxylase (TH) in the SN, and the levels of uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), phosphorylated-hormone sensitive lipase (p-HSL), HSL, TH, β3-adrenergic receptor (β3-AR), cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA) in IBAT. After treatment with 6-OHDA for 6 weeks, 6-OHDA rats exhibited decreased TH expression in SN accompanied with shortened staying time on the rotating rod. This motor impairment paralleled with no significant alteration in body mass, IBAT weight, and food intake until the end of the experimental protocol. However, the decreasing diameter of the single fat vesicle in IBAT was observed in the 6-OHDA group. Meanwhile, compared with the control group, the protein expression of UCP1, PGC-1α, p-HSL, TH, β3-AR, cAMP, and PKA in IBAT were increased significantly in the 6-OHDA group, whereas no obvious change in the expression of HSL. The present study suggested an increased energy expenditure and activation of the β3-AR-cAMP-PKA signaling pathway in the IBAT after the destruction of the dopamine system in the SN of the rat.

Neuroendocrine Regulation of Energy Metabolism Involving Different Types of Adipose Tissues

Despite tremendous research efforts to identify regulatory factors that control energy metabolism, the prevalence of obesity has been continuously rising, with nearly 40% of US adults being obese. Interactions between secretory factors from adipose tissues and the nervous system innervating adipose tissues play key roles in maintaining energy metabolism and promoting survival in response to metabolic challenges. It is currently accepted that there are three types of adipose tissues, white (WAT), brown (BAT), and beige (BeAT), all of which play essential roles in maintaining energy homeostasis. WAT mainly stores energy under positive energy balance, while it releases fuels under negative energy balance. Thermogenic BAT and BeAT dissipate energy as heat under cold exposure to maintain body temperature. Adipose tissues require neural and endocrine communication with the brain. A number of WAT adipokines and BAT batokines interact with the neural circuits extending from the brain to cooperatively regulate whole-body lipid metabolism and energy homeostasis. We review neuroanatomical, histological, genetic, and pharmacological studies in neuroendocrine regulation of adipose function, including lipid storage and mobilization of WAT, non-shivering thermogenesis of BAT, and browning of BeAT. Recent whole-tissue imaging and transcriptome analysis of differential gene expression in WAT and BAT yield promising findings to better understand the interaction between secretory factors and neural circuits, which represents a novel opportunity to tackle obesity.

Molecular pathways linking adipose innervation to insulin action in obesity and diabetes mellitus

Adipose tissue comprises adipocytes and many other cell types that engage in dynamic crosstalk in a highly innervated and vascularized tissue matrix. Although adipose tissue has been studied for decades, it has been appreciated only in the past 5 years that extensive arborization of nerve fibres has a dominant role in regulating the function of adipose tissue. This Review summarizes the latest literature, which suggests that adipocytes signal to local sensory nerve fibres in response to perturbations in lipolysis and lipogenesis. Such adipocyte signalling to the central nervous system causes sympathetic output to distant adipose depots and potentially other metabolic tissues to regulate systemic glucose homeostasis. Paracrine factors identified in the past few years that mediate such adipocyte-neuron crosstalk are also reviewed. Similarly, immune cells and endothelial cells within adipose tissue communicate with local nerve fibres to modulate neurotransmitter tone, blood flow, adipocyte differentiation and energy expenditure, including adipose browning to produce heat. This understudied field of neurometabolism related to adipose tissue biology has great potential to reveal new mechanistic insights and potential therapeutic strategies for obesity and type 2 diabetes mellitus.

Intact innervation is essential for diet-induced recruitment of brown adipose tissue

The possibility that recruitment and activation of brown adipose tissue (BAT) thermogenesis could be beneficial for curtailing obesity development in humans prompts a need for a better understanding of the control of these processes [that are often referred to collectively as diet-induced thermogenesis (DIT)]. Dietary conditions are associated with large changes in blood-borne factors that could be responsible for BAT recruitment, but BAT is also innervated by the sympathetic nervous system. To examine the significance of the innervation for DIT recruitment, we surgically denervated the largest BAT depot, i.e., the interscapular BAT depot in mice and exposed the mice at thermoneutrality to a high-fat diet versus a chow diet. Denervation led to an alteration in feeding pattern but did not lead to enhanced obesity, but obesity was achieved with a lower food intake, as denervation increased metabolic efficiency. Conclusively, denervation totally abolished the diet-induced increase in total UCP1 protein levels observed in the intact mice, whereas basal UCP1 expression was not dependent on innervation. The denervation of interscapular BAT did not discernably hyper-recruit other BAT depots, and no UCP1 protein could be detected in the principally browning-competent inguinal white adipose tissue depot under any of the examined conditions. We conclude that intact innervation is essential for diet-induced thermogenesis and that circulating factors cannot by themselves initiate recruitment of brown adipose tissue under obesogenic conditions. Therefore, the processes that link food intake and energy storage to activation of the nervous system are those of significance for the further understanding of diet-induced thermogenesis.

The Importance of Peripheral Nerves in Adipose Tissue for the Regulation of Energy Balance

Brown and white adipose tissues are essential for maintenance of proper energy balance and metabolic health. In order to function efficiently, these tissues require both endocrine and neural communication with the brain. Brown adipose tissue (BAT), as well as the inducible brown adipocytes that appear in white adipose tissue (WAT) after simulation, are thermogenic and energy expending. This uncoupling protein 1 (UCP1)-mediated process requires input from sympathetic nerves releasing norepinephrine. In addition to sympathetic noradrenergic signaling, adipose tissue contains sensory nerves that may be important for relaying fuel status to the brain. Chemical and surgical denervation studies of both WAT and BAT have clearly demonstrated the role of peripheral nerves in browning, thermogenesis, lipolysis, and adipogenesis. However, much is still unknown about which subtypes of nerves are present in BAT versus WAT, what nerve products are released from adipose nerves and how they act to mediate metabolic homeostasis, as well as which cell types in adipose are receiving synaptic input. Recent advances in whole-depot imaging and quantification of adipose nerve fibers, as well as other new research findings, have reinvigorated this field of research. This review summarizes the history of research into adipose innervation and brain⁻adipose communication, and also covers landmark and recent research on this topic to outline what we currently know and do not know about adipose tissue nerve supply and communication with the brain.

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.

Brown adipose tissue plays a central role in systemic inflammation-induced sleep responses

We previously identified brown adipose tissue (BAT) as a source of sleep-inducing signals. Pharmacological activation of BAT enhances sleep while sleep loss leads to increased BAT thermogenesis. Recovery sleep after sleep loss is diminished in mice that lack uncoupling protein 1 (UCP-1), and also in wild-type (WT) mice after sensory denervation of the BAT. Systemic inflammation greatly affects metabolism and the function of adipose tissue, and also induces characteristic sleep responses. We hypothesized that sleep responses to acute inflammation are mediated by BAT-derived signals. To test this, we determined the effects of systemic inflammation on sleep and body temperature in UCP-1 knockout (KO) and WT mice. Intraperitoneal injections of lipopolysaccharide, tumor necrosis factor-α, interleukin-1 beta and clodronate containing liposomes were used to induce systemic inflammation. In WT animals, non-rapid-eye movement sleep (NREMS) was elevated in all four inflammatory models. All NREMS responses were completely abolished in UCP-1 KO animals. Systemic inflammation elicited an initial hypothermia followed by fever in WT mice. The hypothermic phase, but not the fever, was abolished in UCP-1 KO mice. The only recognized function of UCP-1 is to promote thermogenesis in brown adipocytes. Present results indicate that the presence of UCP-1 is necessary for increased NREMS but does not contribute to the development of fever in systemic inflammation.

Sensory denervation of inguinal white fat modifies sympathetic outflow to white and brown fat in Siberian hamsters

White adipose tissue (WAT) and brown adipose tissue (BAT) have sympathetic nervous system (SNS) and sensory innervations. Previous studies from our laboratory revealed central neuroanatomical evidence of WAT sensory and BAT SNS crosstalk with double labeling of inguinal WAT (IWAT) sensory and interscapular BAT (IBAT) SNS neurons. We previously demonstrated that WAT lipolysis increases IBAT temperature, but this effect is absent when IWAT afferents are surgically denervated, which severs both sensory and SNS nerves. It is possible that WAT sensory feedback can regulate SNS drive to itself and other WAT and BAT depots, and thus contribute to the existence of differential SNS outflow to fat during different energy challenges. Here we selectively denervated IWAT sensory nerves in Siberian hamsters using capsaicin and measured norepinephrine turnover (NETO) i.e., SNS drive to WAT and BAT depots, IBAT uncoupling protein 1 (UCP1) expression, body mass, fat mass, blood glucose, and food consumed after a 24-h cold exposure. IWAT sensory denervation decreased both IWAT and IBAT NETO and IBAT UCP1 expression. IWAT sensory denervation, however, increased mesenteric WAT (MWAT) NETO after the 24-h cold exposure and did not modify epididymal WAT (EWAT) and retroperitoneal WAT (RWAT) NETO compared with respective controls. Body mass, fat mass, blood glucose, and food consumed were unchanged across groups. RWAT and EWAT mass decreased in capsaicin-injected hamsters, but did not in the vehicle hamsters. These results functionally demonstrate the existence of IWAT sensory and IBAT SNS crosstalk and that a disruption in this sensory-SNS feedback mechanism modifies SNS drive to IWAT, IBAT, and MWAT, but not EWAT and RWAT.

Brown and beige adipose tissues: phenotype and metabolic potential in mice and men

With the recent rediscovery of brown fat in adult humans, our outlook on adipose tissue biology has undergone a paradigm shift. While we attempt to identify, recruit, and activate classic brown fat stores in humans, identification of beige fat has also raised the possibility of browning our white fat stores. Whether such transformation of human white fat depots can be achieved to enhance the whole body oxidative potential remains to be seen. Evidence to date, however, largely points toward a major oxidative role only for classic brown fat depots, at least in rodents. White fat stores seem to provide the main fuel for sustaining thermogenesis via lipolysis. Interestingly, molecular markers consistent with both classic brown and beige fat identity can be observed in human supraclavicular depot, thereby complicating the discussion on beige fat in humans. Here, we review the recent advances made in our understanding of brown and beige fat in humans and mice. We further provide an overview of their plausible physiological relevance to whole body energy metabolism.

Brown adipose tissue activation in a rat model of Parkinson's disease

Loss of body weight and fat mass is one of the nonmotor symptoms of Parkinson's disease (PD). Weight loss is due primarily to reduced energy intake and increased energy expenditure. Whereas inadequate energy intake in PD patients is caused mainly by appetite loss and impaired gastrointestinal absorption, the underlying mechanisms for increased energy expenditure remain largely unknown. Brown adipose tissue (BAT), a key thermogenic tissue in humans and other mammals, plays an important role in thermoregulation and energy metabolism; however, it has not been tested whether BAT is involved in the negative energy balance in PD. Here, using the 6-hydroxydopamine (6-OHDA) rat model of PD, we found that the activity of sympathetic nerve (SN), the expression of Ucp1 in BAT, and thermogenesis were increased in PD rats. BAT sympathetic denervation blocked sympathetic activity and decreased UCP1 expression in BAT and attenuated the loss of body weight in PD rats. Interestingly, sympathetic denervation of BAT was associated with decreased sympathetic tone and lipolysis in retroperitoneal and epididymal white adipose tissue. Our data suggeste that BAT-mediated thermogenesis may contribute to weight loss in PD.

Role of calcitonin gene-related peptide in energy metabolism

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by alternative tissue-specific splicing of the primary transcript of the CALC genes. CGRP is widely distributed in the central and peripheral nervous system, as well as in several organs and tissues. The presence of CGRP in the liver and brown and white adipose tissue suggests an effect of this neuropeptide on regulation of energy homeostasis.

METHODS

In this review, we summarize the current knowledge of the effect of CGRP on the control of energy metabolism, primarily focusing on food intake, thermoregulation and lipid metabolism in adipose tissue, liver and muscle.

RESULTS

CGRP induces anorexia, stimulating anorexigenic neuropeptide and/or inhibiting orexigenic neuropeptide expression, through cAMP/PKA pathway activation. CGRP also induces energy expenditure, increasing the skin temperature and brown adipose tissue thermogenesis. It has been also suggested that information related to peripheral lipid stores may be conveyed to the brain via CGRP-sensory innervation from adipose tissue. More recently, it was demonstrated that mice lacking αCGRP are protected from obesity induced by high-fat diet and that CGRP regulates the content of lipid in liver, muscle and adipose tissue.

CONCLUSIONS

It is unclear the receptor responsible by CGRP effects, as well as whether this neuropeptide acts directly or indirectly in liver, muscle and adipose tissue.

The role of the brown adipose tissue in β3-adrenergic receptor activation-induced sleep, metabolic and feeding responses

Brown adipose tissue (BAT) is regulated by the sympathetic nervous system via β3-adrenergic receptors (β3-AR). Here we tested the hypothesis that pharmacological stimulation of β3-ARs leads to increased sleep in mice and if this change is BAT dependent. In wild-type (WT) animals, administration of CL-316,243, a selective β3-AR agonist, induced significant increases in non-rapid-eye movement sleep (NREMS) lasting for 4–10 h. Simultaneously, electroencephalographic slow-wave activity (SWA) was significantly decreased and body temperature was increased with a delay of 5–6 h. In uncoupling protein 1 (UCP-1) knockout mice, the middle and highest doses of the β3-AR agonist increased sleep and suppressed SWA, however, these effects were significantly attenuated and shorter-lasting as compared to WT animals. To determine if somnogenic signals arising from BAT in response to β3-AR stimulation are mediated by the sensory afferents of BAT, we tested the effects of CL-316,243 in mice with the chemical deafferentation of the intra-scapular BAT pads. Sleep responses to CL-316,243 were attenuated by ~50% in intra-BAT capsaicin-treated mice. Present findings indicate that the activation of BAT via β3-AR leads to increased sleep in mice and that this effect is dependent on the presence of UCP-1 protein and sleep responses require the intact sensory innervation of BAT.

Bidirectional crosstalk between the sensory and sympathetic motor systems innervating brown and white adipose tissue in male Siberian hamsters

The brain networks connected to the sympathetic motor and sensory innervations of brown (BAT) and white (WAT) adipose tissues were originally described using two transneuronally transported viruses: the retrogradely transported pseudorabies virus (PRV), and the anterogradely transported H129 strain of herpes simplex virus-1 (HSV-1 H129). Further complexity was added to this network organization when combined injections of PRV and HSV-1 H129 into either BAT or WAT of the same animal generated sets of coinfected neurons in the brain, spinal cord, and sympathetic and dorsal root ganglia. These neurons are well positioned to act as sensorimotor links in the feedback circuits that control each fat pad. We have now determined the extent of sensorimotor crosstalk between interscapular BAT (IBAT) and inguinal WAT (IWAT). PRV152 and HSV-1 H129 were each injected into IBAT or IWAT of the same animal: H129 into IBAT and PRV152 into IWAT. The reverse configuration was applied in a different set of animals. We found single-labeled neurons together with H129+PRV152 coinfected neurons in multiple brain sites, with lesser numbers in the sympathetic and dorsal root ganglia that innervate IBAT and IWAT. We propose that these coinfected neurons mediate sensory-sympathetic motor crosstalk between IBAT and IWAT. Comparing the relative numbers of coinfected neurons between the two injection configurations showed a bias toward IBAT-sensory and IWAT-sympathetic motor feedback loops. These coinfected neurons provide a neuroanatomical framework for functional interactions between IBAT thermogenesis and IWAT lipolysis that occurs with cold exposure, food restriction/deprivation, exercise, and more generally with alterations in adiposity.

Separate and shared sympathetic outflow to white and brown fat coordinately regulates thermoregulation and beige adipocyte recruitment

White adipose tissue (WAT) and brown adipose tissue (BAT) are innervated and regulated by the sympathetic nervous system (SNS). It is not clear, however, whether there are shared or separate central SNS outflows to WAT and BAT that regulate their function. We injected two isogenic strains of pseudorabies virus, a retrograde transneuronal viral tract tracer, with unique fluorescent reporters into interscapular BAT (IBAT) and inguinal WAT (IWAT) of the same Siberian hamsters to define SNS pathways to both. To test the functional importance of SNS coordinated control of BAT and WAT, we exposed hamsters with denervated SNS nerves to IBAT to 4°C for 16-24 h and measured core and fat temperatures and norepinephrine turnover (NETO) and uncoupling protein 1 (UCP1) expression in fat tissues. Overall, there were more SNS neurons innervating IBAT than IWAT across the neuroaxis. However, there was a greater percentage of singly labeled IWAT neurons in midbrain reticular nuclei than singly labeled IBAT neurons. The hindbrain had ~30-40% of doubly labeled neurons while the forebrain had ~25% suggesting shared SNS circuitry to BAT and WAT across the brain. The raphe nucleus, a key region in thermoregulation, had ~40% doubly labeled neurons. Hamsters with IBAT SNS denervation maintained core body temperature during acute cold challenge and had increased beige adipocyte formation in IWAT. They also had increased IWAT NETO, temperature, and UCP1 expression compared with intact hamsters. These data provide strong neuroanatomical and functional evidence of WAT and BAT SNS cross talk for thermoregulation and beige adipocyte formation.

Control of brown and beige fat development

Brown and beige adipocytes expend chemical energy to produce heat and are therefore important in regulating body temperature and body weight. Brown adipocytes develop in discrete and relatively homogenous depots of brown adipose tissue, whereas beige adipocytes are induced to develop in white adipose tissue in response to certain stimuli - notably, exposure to cold. Fate-mapping analyses have identified progenitor populations that give rise to brown and beige fat cells, and have revealed unanticipated cell-lineage relationships between vascular smooth muscle cells and beige adipocytes, and between skeletal muscle cells and brown fat. In addition, non-adipocyte cells in adipose tissue, including neurons, blood vessel-associated cells and immune cells, have crucial roles in regulating the differentiation and function of brown and beige fat.

Lipolysis sensation by white fat afferent nerves triggers brown fat thermogenesis

Objective

Metabolic challenges, such as a cold environment, stimulate sympathetic neural efferent activity to white adipose tissue (WAT) to drive lipolysis, thereby increasing the availability of free fatty acids as one source of fuel for brown adipose tissue (BAT) thermogenesis. WAT is also innervated by sensory nerve fibers that network to metabolic brain areas; moreover, activation of these afferents is reported to increase sympathetic nervous system outflow. However, the endogenous stimuli sufficient to drive WAT afferents during metabolic challenges as well as their functional relation to BAT thermogenesis remain unknown.

Method

We tested if local WAT lipolysis directly activates WAT afferent nerves, and then assessed whether this WAT sensory signal affected BAT thermogenesis in Siberian hamsters (Phodopus sungorus).

Results

2-deoxyglucose, a sympathetic nervous system stimulant, caused β-adrenergic receptor dependent increases in inguinal WAT (IWAT) afferent neurophysiological activity. In addition, direct IWAT injections of the β₃-AR agonist CL316,243 dose-dependently increased: 1) phosphorylation of IWAT hormone sensitive lipase, an indicator of SNS-stimulated lipolysis, 2) expression of the neuronal activation marker c-Fos in dorsal root ganglion neurons receiving sensory input from IWAT, and 3) IWAT afferent neurophysiological activity, an increase blocked by antilipolytic agent 3,5-dimethylpyrazole. Finally, we demonstrated that IWAT afferent activation by lipolysis triggers interscapular BAT thermogenesis through a neural link between these two tissues.

Conclusions

These data suggest IWAT lipolysis activates local IWAT afferents triggering a neural circuit from WAT to BAT that acutely induces BAT thermogenesis.

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Glucoprivation-induced lipolysis activates sensory nerves from white fat via β-adrenoreceptors.

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Lipolysis sensation by local afferent nerves innervating white fat is proposed.

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Lipid products of lipolysis are sufficient to activate sensory nerves from white fat.

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Stimulation of white fat afferents by lipolysis increases brown fat temperature.

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Findings illustrate functional neural connectivity between white and brown fat.

Adipose Tissue and Energy Expenditure: Central and Peripheral Neural Activation Pathways

Increasing energy expenditure is an appealing therapeutic target for the prevention and reversal of metabolic conditions such as obesity or type 2 diabetes. However, not enough research has investigated how to exploit pre-existing neural pathways, both in the central nervous system (CNS) and peripheral nervous system (PNS), in order to meet these needs. Here, we review several research areas in this field, including centrally acting pathways known to drive the activation of sympathetic nerves that can increase lipolysis and browning in white adipose tissue (WAT) or increase thermogenesis in brown adipose tissue (BAT), as well as other central and peripheral pathways able to increase energy expenditure of these tissues. In addition, we describe new work investigating the family of transient receptor potential (TRP) channels on metabolically important sensory nerves, as well as the role of the vagus nerve in regulating energy balance.