The brain endocannabinoid system in the regulation of energy balance

Nicotine exposure during breastfeeding alters the expression of endocannabinoid system biomarkers in female but not in male offspring at adulthood

Early nicotine exposure compromises offspring's phenotype at long-term in both sexes. We hypothesize that offspring exposed to nicotine during breastfeeding show deregulated central and peripheral endocannabinoid system (ECS), compromising several aspects of their metabolism. Lactating rats received nicotine (NIC, 6 mg/Kg/day) or saline from postnatal day (PND) 2 to 16 through implanted osmotic minipumps. Offspring were analyzed at PND180. We evaluated protein expression of N-acylphosphatidylethanolamide-phospholipase D (NAPE-PLD), fatty acid amide hydrolase (FAAH), diacylglycerol lipase (DAGL), monoacylglycerol lipase (MAGL) and cannabinoid receptors (CB1 and/or CB2) in lateral hypothalamus, paraventricular nucleus of the hypothalamus, liver, visceral adipose tissue (VAT), adrenal and thyroid. NIC offspring from both sexes did not show differences in hypothalamic ECS markers. Peripheral ECS markers showed no alterations in NIC males. In contrast, NIC females had lower liver DAGL and CB1, higher VAT DAGL, higher adrenal NAPE-PLD and higher thyroid FAAH. Endocannabinoids biosynthesis was affected by nicotine exposure during breastfeeding only in females; alterations in peripheral tissues suggest lower action in liver and higher action in VAT, adrenal and thyroid. Effects of nicotine exposure during lactation on ECS markers are sex- and tissue-dependent. This characterization helps understanding the phenotype of the adult offspring in this model and may contribute to the development of new pharmacological targets for the treatment of several metabolic diseases that originate during development.

Lipid endocannabinoids in energy metabolism, stress and developmental programming

The endocannabinoid system (ECS) regulates brain development and function, energy metabolism and stress in a sex-, age- and tissue-dependent manner. The ECS comprises mainly the bioactive lipid ligands anandamide (AEA) and 2-aracdonoylglycerol (2-AG), cannabinoid receptors 1 and 2 (CB1 and CB2), and several metabolizing enzymes. The endocannabinoid tonus is increased in obesity, stimulating food intake and a preference for fat, reward, and lipid accumulation in peripheral tissues, as well as favoring a positive energy balance. Energy balance and stress responses share adaptive mechanisms regulated by the ECS that seem to underlie the complex relationship between feeding and emotional behavior. The ECS is also a key regulator of development. Environmental insults (diet, toxicants, and stress) in critical periods of developmental plasticity, such as gestation, lactation and adolescence, alter the ECS and may predispose individuals to the development of chronic diseases and behavioral changes in the long term. This review is focused on the ECS and the developmental origins of health and disease (DOHaD).

Effects of endocannabinoids on feed intake, stress response and whole-body energy metabolism in dairy cows

Endocannabinoids, particularly anandamide (AEA) and 2-arachidonoylglycerol (2-AG), are instrumental in regulating energy homeostasis and stress response. However, little is known about the endocannabinoid system (ECS) in ruminants, although EC could improve dairy health and productivity, at least by increasing feed intake. In this study, we report if intraperitoneal (i.p.) AEA and 2-AG administration affects feed intake, whole-body macronutrient metabolism, isolation and restraint stress, and whether diet composition modulates circulating endocannabinoid concentrations in cows. Twenty Simmental cows in late lactation were fed a grass silage and a corn silage based diet. On each diet, cows received daily i.p. injections with either AEA (5 µg/kg; n = 7), 2-AG (2.5 µg/kg; n = 6) or saline (n = 7) for 8 days. Endocannabinoid administration for 5 days under free-ranging (non-stressed) conditions had no effect on feed intake or energy balance, but attenuated the stress-induced suppression of feed intake when housing changed to individual tie-stalls without social or tactile interaction. Endocannabinoids increased whole-body carbohydrate oxidation, reduced fat oxidation, and affected plasma non-esterified fatty acid concentrations and fatty acid contents of total lipids. There was no effect of endocannabinoids on plasma triglyceride concentrations or hepatic lipogenesis. Plasma AEA concentrations were not affected by diet, however, plasma 2-AG concentrations tended to be lower on the corn silage based diet. In conclusion, endocannabinoids attenuate stress-induced hypophagia, increase short-term feed intake and whole-body carbohydrate oxidation and decrease whole-body fat oxidation in cows.

A Role for Peripheral Anandamide and 2-Arachidonoylglycerol in Short-Term Food Intake and Orexigenic Hypothalamic Responses in a Species with Continuous Nutrient Delivery

The endocannabinoid system (ECS) plays a pivotal role in the complex control and regulation of food intake. Pharmacological ECS activation could improve health in energy-deficient stages by increasing food intake, at least in intermittent feeders. However, knowledge of the mechanism regulating appetite in species with continued nutrient delivery is incomplete. The objectives of this pilot study were to investigate the effect of the intraperitoneal (i.p.) administration of the endocannabinoids (ECs) anandamide (AEA) and 2-arachidonoylglycerol (2-AG) on food intake, plasma EC concentrations and hypothalamic orexigenic signaling, and to study how the circulatory EC tone changes in response to short-term food deprivation in dairy cows, a species with continuous nutrient delivery. The administration of EC resulted in higher food intake during the first hour after treatment. Plasma AEA concentrations were significantly increased 2.5 h after AEA injection, whereas plasma 2-AG concentrations remained unchanged 2.5 h after 2-AG injection. The hypothalamic immunoreactivity of cannabinoid receptor 1, agouti-related protein, and orexin-A was not affected by either treatment; however, neuropeptide Y and agouti-related protein mRNA abundances were downregulated in the arcuate nucleus of AEA-treated animals. Short-term food deprivation increased plasma 2-AG, while plasma AEA remained unchanged. In conclusion, i.p.-administered 2-AG and AEA increase food intake in the short term, but only AEA accumulates in the circulation. However, plasma 2-AG concentrations are more responsive to food deprivation than AEA.

Cerebral μ-opioid and CB1 receptor systems have distinct roles in human feeding behavior

Eating behavior varies greatly between individuals, but the neurobiological basis of these trait-like differences in feeding remains poorly understood. Central μ-opioid receptors (MOR) and cannabinoid CB₁ receptors (CB₁R) regulate energy balance via multiple neural pathways, promoting food intake and reward. Because obesity and eating disorders have been associated with alterations in the brain's opioid and endocannabinoid signaling, the variation in MOR and CB₁R system function could potentially underlie distinct eating behavior phenotypes. In this retrospective positron emission tomography (PET) study, we analyzed [¹¹C]carfentanil PET scans of MORs from 92 healthy subjects (70 males and 22 females), and [¹⁸F]FMPEP-d₂ scans of CB₁Rs from 35 subjects (all males, all also included in the [¹¹C]carfentanil sample). Eating styles were measured with the Dutch Eating Behavior Questionnaire (DEBQ). We found that lower cerebral MOR availability was associated with increased external eating-individuals with low MORs reported being more likely to eat in response to environment's palatable food cues. CB₁R availability was associated with multiple eating behavior traits. We conclude that although MORs and CB₁Rs overlap anatomically in brain regions regulating food reward, they have distinct roles in mediating individual feeding patterns. Central MOR system might provide a pharmacological target for reducing individual's excessive cue-reactive eating behavior.

Stress Related Shift Toward Inflammaging in Cosmonauts After Long-Duration Space Flight

Space flight exerts a specific conglomerate of stressors on humans that can modulate the immune system. The mechanism remains to be elucidated and the consequences for cosmonauts in the long term are unclear. Most of the current research stems from short-term spaceflights as well as pre- and post-flight analyses due to operational limitations. Immune function of 12 cosmonauts participating in a long-duration (>140 days) spaceflight mission was monitored pre-, post-, and on two time-points in-flight. While the classical markers for stress such as cortisol in saliva where not significantly altered, blood concentrations of the endocannabinoid system (ECS) were found to be highly increased in-flight indicating a biological stress response. Moreover, subjects showed a significant rise in white blood cell counts. Neutrophils, monocytes and B cells increased by 50% whereas NK cells dropped by nearly 60% shortly after landing. Analysis of blood smears showed that lymphocyte percentages, though unchanged pre- and post-flight were elevated in-flight. Functional tests on the ground revealed stable cellular glutathione levels, unaltered baseline and stimulated ROS release in neutrophils but an increased shedding of L-selectin post-flight. In vitro stimulation of whole blood samples with fungal antigen showed a highly amplified TNF and IL-1β response. Furthermore, a significant reduction in CD4⁺CD25⁺CD27^low regulatory T cells was observed post-flight but returned to normal levels after one month. Concomitantly, high in-flight levels of regulatory cytokines TGF-β, IL-10 and IL-1ra dropped rapidly after return to Earth. Finally, we observed a shift in the CD8⁺ T cell repertoire toward CD8⁺ memory cells that lasted even one month after return to Earth. Conclusion: Long-duration spaceflight triggered a sustained stress dependent release of endocannabinoids combined with an aberrant immune activation mimicking features of people at risk for inflammation related diseases. These effects persisted in part 30 days after return to Earth. The currently available repertoire of in-flight testing as well as the post-flight observation periods need to be expanded to tackle the underlying mechanism for and consequences of these immune changes in order to develop corresponding mitigation strategies based on a personalized approach for future interplanetary space explorations.

Fatty Acid Metabolites as Novel Regulators of Non-shivering Thermogenesis

Fatty acids are essential contributors to adipocyte-based non-shivering thermogenesis by acting as activators of uncoupling protein 1 and serving as fuel for mitochondrial heat production. Novel evidence suggests a contribution to this thermogenic mechanism by their conversion to bioactive compounds. Mammalian cells produce a plethora of oxylipins and endocannabinoids, some of which have been identified to affect the abundance or thermogenic activity of brown and brite adipocytes. These effectors are produced locally or at distant sites and signal toward thermogenic adipocytes via a direct interaction with these cells or indirectly via secondary mechanisms. These interactions are evoked by the activation of receptor-mediated pathways. The endogenous production of these compounds is prone to modulation by the dietary intake of the respective precursor fatty acids. The effect of nutritional interventions on uncoupling protein 1-derived thermogenesis may thus at least in part be conferred by the production of a supportive oxylipin and endocannabinoid profile. The manipulation of this system in future studies will help to elucidate the physiological potential of these compounds as novel, endogenous regulators of non-shivering thermogenesis.

Modulations of Neuroendocrine Stress Responses During Confinement in Antarctica and the Role of Hypobaric Hypoxia

The Antarctic continent is an environment of extreme conditions. Only few research stations exist that are occupied throughout the year. The German station Neumayer III and the French-Italian Concordia station are such research platforms and human outposts. The seasonal shifts of complete daylight (summer) to complete darkness (winter) as well as massive changes in outside temperatures (down to -80°C at Concordia) during winter result in complete confinement of the crews from the outside world. In addition, the crew at Concordia is subjected to hypobaric hypoxia of ∼650 hPa as the station is situated at high altitude (3,233 m). We studied three expedition crews at Neumayer III (sea level) (n = 16) and two at Concordia (high altitude) (n = 15) to determine the effects of hypobaric hypoxia on hormonal/metabolic stress parameters [endocannabinoids (ECs), catecholamines, and glucocorticoids] and evaluated the psychological stress over a period of 11 months including winter confinement. In the Neumayer III (sea level) crew, EC and n-acylethanolamide (NAE) concentrations increased significantly already at the beginning of the deployment (p < 0.001) whereas catecholamines and cortisol remained unaffected. Over the year, ECs and NAEs stayed elevated and fluctuated before slowly decreasing till the end of the deployment. The classical stress hormones showed small increases in the last third of deployment. By contrast, at Concordia (high altitude), norepinephrine concentrations increased significantly at the beginning (p < 0.001) which was paralleled by low EC levels. Prior to the second half of deployment, norepinephrine declined constantly to end on a low plateau level, whereas then the EC concentrations increased significantly in this second period during the overwintering (p < 0.001). Psychometric data showed no significant changes in the crews at either station. These findings demonstrate that exposition of healthy humans to the physically challenging extreme environment of Antarctica (i) has a distinct modulating effect on stress responses. Additionally, (ii) acute high altitude/hypobaric hypoxia at the beginning seem to trigger catecholamine release that downregulates the EC response. These results (iii) are not associated with psychological stress.

Is transcranial direct current stimulation an effective modality in reducing food craving? A systematic review and meta-analysis

Non-invasive electrical stimulation of the brain has recently been extensively investigated to regulate food craving. However, the existing literature is controversial and there are some important questions which need to be addressed about clinical and technical factors contributing to efficacy of this method. A systematic search was performed in reliable scientific databases, and 15 eligible studies were identified. The pooled standardized mean differences for the effects of transcranial direct current stimulation (tDCS) on Visual Analogue Scale, energy intake and food craving questionnaire were -0.78 [-1.12, -0.44], -0.91 [-1.38, -0.44], -0.54 [-0.85, -0.24], respectively. Subgroup analysis showed that the most important factors associated with the impact of tDCS on food craving were the population under study, current intensity of stimulation, and number of stimulation sessions. The findings of this study support a significant impact of neuromodulation of dorsolateral prefrontal cortex (DLPFC) on energy intake and food craving using tDCS. It is recommended that multisession bilateral stimulation of the DLPFC with the current intensity of 2 mA be used to reduce food craving.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

Contribution of adaptive thermogenesis to the hypothalamic regulation of energy balance

Obesity and its related disorders are among the most pervasive diseases in contemporary societies, and there is an urgent need for new therapies and preventive approaches. Given (i) our poor social capacity to correct unhealthy habits, and (ii) our evolutionarily genetic predisposition to store excess energy as fat, the current environment of caloric surplus makes the treatment of obesity extremely difficult. During the last few decades, an increasing number of methodological approaches have increased our knowledge of the neuroanatomical basis of the control of energy balance. Compelling evidence underlines the role of the hypothalamus as a homeostatic integrator of metabolic information and its ability to adjust energy balance. A greater understanding of the neural basis of the hypothalamic regulation of energy balance might indeed pave the way for new therapeutic targets. In this regard, it has been shown that several important peripheral signals, such as leptin, thyroid hormones, oestrogens and bone morphogenetic protein 8B, converge on common energy sensors, such as AMP-activated protein kinase to modulate sympathetic tone on brown adipose tissue. This knowledge may open new ways to counteract the chronic imbalance underlying obesity. Here, we review the current state of the art on the role of hypothalamus in the regulation of energy balance with particular focus on thermogenesis.

Neuronal systems and circuits involved in the control of food intake and adaptive thermogenesis

With the still-growing prevalence of obesity worldwide, major efforts are made to understand the various behavioral, environmental, and genetic factors that promote excess fat gain. Obesity results from an imbalance between energy intake and energy expenditure, which emphasizes the importance of deciphering the mechanisms behind energy balance regulation to understand its physiopathology. The control of energy balance is assured by brain systems/circuits capable of generating adequate ingestive and thermogenic responses to maintain the stability of energy reserves, which implies a proper integration of the homeostatic signals that inform about the status of the energy stores. In this article, we overview the organization and functionality of key neuronal circuits or pathways involved in the control of food intake and energy expenditure. We review the role of the corticolimbic (executive and reward) and autonomic systems that integrate their activities to regulate energy balance. We also describe the mechanisms and pathways whereby homeostatic sensing is achieved in response to variations of homeostatic hormones, such as leptin, insulin, and ghrelin, while putting some emphasis on the prominent importance of the mechanistic target of the rapamycin signaling pathway in coordinating the homeostatic sensing process.

Hypothalamic control of brown adipose tissue thermogenesis

It has long been known, in large part from animal studies, that the control of brown adipose tissue (BAT) thermogenesis is insured by the central nervous system (CNS), which integrates several stimuli in order to control BAT activation through the sympathetic nervous system (SNS). SNS-mediated BAT activity is governed by diverse neurons found in brain structures involved in homeostatic regulations and whose activity is modulated by various factors including oscillations of energy fluxes. The characterization of these neurons has always represented a challenging issue. The available literature suggests that the neuronal circuits controlling BAT thermogenesis are largely part of an autonomic circuitry involving the hypothalamus, brainstem and the SNS efferent neurons. In the present review, we recapitulate the latest progresses in regards to the hypothalamic regulation of BAT metabolism. We briefly addressed the role of the thermoregulatory pathway and its interactions with the energy balance systems in the control of thermogenesis. We also reviewed the involvement of the brain melanocortin and endocannabinoid systems as well as the emerging role of steroidogenic factor 1 (SF1) neurons in BAT thermogenesis. Finally, we examined the link existing between these systems and the homeostatic factors that modulate their activities.

Cognitive and autonomic determinants of energy homeostasis in obesity

Obesity ensues from an imbalance between energy intake and expenditure that results from gene-environment interactions, which favour a positive energy balance. A society that promotes unhealthy food and encourages sedentary lifestyle (that is, an obesogenic environment) has become a major contributory factor in excess fat deposition in individuals predisposed to obesity. Energy homeostasis relies upon control of energy intake as well as expenditure, which is in part determined by the themogenesis of brown adipose tissue and mediated by the sympathetic nervous system. Several areas of the brain that constitute cognitive and autonomic brain systems, which in turn form networks involved in the control of appetite and thermogenesis, also contribute to energy homeostasis. These networks include the dopamine mesolimbic circuit, as well as the opioid, endocannabinoid and melanocortin systems. The activity of these networks is modulated by peripheral factors such as hormones derived from adipose tissue and the gut, which access the brain via the circulation and neuronal signalling pathways to inform the central nervous system about energy balance and nutritional status. In this Review, I focus on the determinants of energy homeostasis that have emerged as prominent factors relevant to obesity.

Interaction between the cholecystokinin and endogenous cannabinoid systems in cued fear expression and extinction retention

Post-traumatic stress disorder (PTSD) is thought to develop, in part, from improper inhibition of fear. Accordingly, one of the most effective treatment strategies for PTSD is exposure-based psychotherapy. Ideally, neuroscience would inform adjunct therapies that target the neurotransmitter systems involved in extinction processes. Separate studies have implicated the cholecystokinin (CCK) and endocannabinoid systems in fear; however, there is a high degree of anatomical colocalization between the cannabinoid 1 receptor (Cnr1) and CCK in the basolateral amygdala (BLA), a brain region critical for emotion regulation. Although most research has focused on GABA and GABAergic plasticity as the mechanism by which Cnr1 mediates fear inhibition, we hypothesize that a functional interaction between Cnr1 and CCKB receptor (CCKBR) is critical for fear extinction processes. In this study, systemic pharmacological manipulation of the cannabinoid system modulated cued fear expression in C57BL/6J mice after consolidation of auditory fear conditioning. Knockout of the CCKBR, however, had no effect on fear- or anxiety-like behaviors. Nonetheless, administration of a Cnr1 antagonist increased freezing behavior during a cued fear expression test in wild-type subjects, but had no effect on freezing behavior in CCKBR knockout littermates. In addition, we found that Cnr1-positive fibers form perisomatic clusters around CCKBR-positive cell bodies in the BLA. These CCKBR-positive cells comprise a molecularly heterogenous population of excitatory and inhibitory neurons. These findings provide novel evidence that Cnr1 contributes to cued fear expression via an interaction with the CCK system. Dysfunctional Cnr1-CCKBR interactions might contribute to the etiology of, or result from, fear-related psychiatric disease.

The endocannabinoid system: directing eating behavior and macronutrient metabolism

For many years, the brain has been the primary focus for research on eating behavior. More recently, the discovery of the endocannabinoids (EC) and the endocannabinoid system (ECS), as well as the characterization of its actions on appetite and metabolism, has provided greater insight on the brain and food intake. The purpose of this review is to explain the actions of EC in the brain and other organs as well as their precursor polyunsaturated fatty acids (PUFA) that are converted to these endogenous ligands. The binding of the EC to the cannabinoid receptors in the brain stimulates food intake, and the ECS participates in systemic macronutrient metabolism where the gastrointestinal system, liver, muscle, and adipose are involved. The EC are biosynthesized from two distinct families of dietary PUFA, namely the n-6 and n-3. Based on their biochemistry, these PUFA are well known to exert considerable physiological and health-promoting actions. However, little is known about how these different families of PUFA compete as precursor ligands of cannabinoid receptors to stimulate appetite or perhaps down-regulate the ECS to amend food intake and prevent or control obesity. The goal of this review is to assess the current available research on ECS and food intake, suggest research that may improve the complications associated with obesity and diabetes by dietary PUFA intervention, and further reveal mechanisms to elucidate the relationships between substrate for EC synthesis, ligand actions on receptors, and the physiological consequences of the ECS. Dietary PUFA are lifestyle factors that could potentially curb eating behavior, which may translate to changes in macronutrient metabolism, systemically and in muscle, benefiting health overall.

The PVH as a site of CB1-mediated stimulation of thermogenesis by MC4R agonism in male rats

The present study was designed to investigate the involvement of the cannabinoid receptor 1 (CB1) in the stimulating effects of the melanocortin-4 receptor (MC4R) agonism on whole-body and brown adipose tissue (BAT) thermogenesis. In a first series of experiments, whole-body and BAT thermogenesis were investigated in rats infused in the third ventricle of the brain with the MC4R agonist melanotan II (MTII) and the CB1 agonist δ9-tetrahydrocannabinol (δ(9)-THC) or the CB1 antagonist AM251. Whole-body thermogenesis was measured by indirect calorimetry and BAT thermogenesis assessed from interscapular BAT (iBAT) temperature. δ(9)-THC blunted the effects of MTII on energy expenditure and iBAT temperature, whereas AM251 tended to potentiate the MTII effects. δ(9)-THC also blocked the stimulating effect of MTII on (14)C-bromopalmitate and (3)H-deoxyglucose uptakes in iBAT. Additionally, δ(9)-THC attenuated the stimulating effect of MTII on the expression of peroxisome proliferator-activated receptor-γ coactivator 1-α (Pgc1α), type II iodothyronine deiodinase (Dio2), carnitine palmitoyltransferase 1B (Cpt1b), and uncoupling protein 1 (Ucp1). In a second series of experiments, we addressed the involvement of the paraventricular hypothalamic nucleus (PVH) in the CB1-mediated effects of MTII on iBAT thermogenesis, which were assessed following the infusion of MTII in the PVH and δ(9)-THC or AM251 in the fourth ventricle of the brain. We demonstrated the ability of δ(9)-THC to blunt MTII-induced iBAT temperature elevation. δ(9)-THC also blocked the PVH effect of MTII on (14)C-bromopalmitate uptake as well as on Pgc1α and Dio2 expression in iBAT. Altogether the results of this study demonstrate the involvement of the PVH in the CB1-mediated stimulating effects of the MC4R agonist MTII on whole-body and BAT thermogenesis.

Differential Expression of Brain Cannabinoid Receptors between Repeatedly Stressed Males and Females may Play a Role in Age and Gender-Related Difference in Traumatic Brain Injury: Implications from Animal Studies

Inconsistent gender differences in the outcome of TBI have been reported. The mechanism is unknown. In a recent male animal study, repeated stress followed by TBI had synergistic effects on brain gene expression and caused greater behavioral deficits. Because females are more likely to develop anxiety after stress and because anxiety is mediated by cannabinoid receptors (CBRs) (CB₁ and CB₂), there is a need to compare CB₁ and CB₂ expression in stressed males and females. CB₁ and CB₂ mRNA expression was determined in the amygdala, hippocampus, prefrontal cortex (PFC), and hypothalamus of adolescent male and female rats after 3 days of repeated tail-shock stress using qPCR. PFC CB₁ and CB₂ protein levels were determined using Western blot techniques. Both gender and stress had significant effects on brain CB₁ mRNA expression levels. Overall, females showed significantly higher CB₁ and CB₂ mRNA levels in all brain regions than males (p < 0.01). Repeated stress reduced CB₁ mRNA levels in the amygdala, hippocampus, and PFC (p < 0.01, each). A gender × stress interaction was found in CB₁ mRNA level in the hippocampus (p < 0.05), hypothalamus (p < 0.01), and PFC (p < 0.01). Within-sex one-way ANOVA analysis showed decreased CB₁ mRNA in the hippocampus, hypothalamus, and PFC of stressed females (p < 0.01, each) but increased CB₁ mRNA levels in the hypothalamus of stressed males (p < 01). There was a gender and stress interaction in prefrontal CB₁ receptor protein levels (p < 0.05), which were decreased in stressed females only (p < 0.05). Prefrontal CB₂ protein levels were decreased in both male and female animals after repeated stress (p < 0.05, each). High basal levels of CBR expression in young naïve females could protect against TBI damage whereas stress-induced CBR deficits could predict a poor outcome of TBI in repeatedly stressed females. Further animal studies could help evaluate this possibility.

Concurrent pharmacological modification of cannabinoid-1 and glucagon-like peptide-1 receptor activity affects feeding behavior and body weight in rats fed a free-choice, high-carbohydrate diet

To extend preliminary studies on the effects on food intake of the combined use of cannabinoid (CB) 1 and glucagon-like peptide-1 (GLP-1) receptor agonists and antagonists, the effect of these drugs on the feeding behavior in rats maintained on a free-choice, high-carbohydrate diet was investigated over a longer period of time. Rats were fed a standard diet for 3 days and then fed with both the standard and the high-sucrose chow. After 4 days of the high-calorie diet, the following combination treatments were administered daily by an intraperitoneal injection for the next 3 days: 1 mg/kg AM 251 (a CB1 receptor antagonist) or 1 mg/kg WIN 55,212-2 (a CB1 receptor agonist) together with 3 µg/kg exendin-4 (Ex-4, a GLP-1 receptor agonist) or 160 µg/kg exendin (9-39) [Ex (9-39), a GLP-1 receptor antagonist]. The total daily caloric intake and body weight were significantly reduced in rats treated with Ex-4 and AM 251 or WIN 55,212-2 compared with either of the drugs injected alone and the saline-injected controls. Both drug combinations selectively inhibited ingestion of the high-sucrose chow. Although Ex (9-39) administration did not significantly affect food consumption, it resulted in a marked body weight gain, indicating that the GLP-1 receptor antagonist caused a positive energy balance. It is concluded that AM 251 or WIN 55,212-2 and Ex-4, injected together, exert additive, inhibitory effects on the consumption of high-sugar food.

Cannabinoid-hypocretin cross-talk in the central nervous system: what we know so far

Emerging findings suggest the existence of a cross-talk between hypocretinergic and endocannabinoid systems. Although few studies have examined this relationship, the apparent overlap observed in the neuroanatomical distribution of both systems as well as their putative functions strongly point to the existence of such cross-modulation. In agreement, biochemical and functional studies have revealed the existence of heterodimers between CB1 cannabinoid receptor and hypocretin receptor-1, which modulates the cellular localization and downstream signaling of both receptors. Moreover, the activation of hypocretin receptor-1 stimulates the synthesis of 2-arachidonoyl glycerol culminating in the retrograde inhibition of neighboring cells and suggesting that endocannabinoids could contribute to some hypocretin effects. Pharmacological data indicate that endocannabinoids and hypocretins might have common physiological functions in the regulation of appetite, reward and analgesia. In contrast, these neuromodulatory systems seem to play antagonistic roles in the regulation of sleep/wake cycle and anxiety-like responses. The present review attempts to piece together what is known about this interesting interaction and describes its potential therapeutic implications.

High fat diet and body weight have different effects on cannabinoid CB(1) receptor expression in rat nodose ganglia

Energy balance is regulated, in part, by the orexigenic signaling pathways of the vagus nerve. Fasting-induced modifications in the expression of orexigenic signaling systems have been observed in vagal afferents of lean animals. Altered basal cannabinoid (CB1) receptor expression in the nodose ganglia in obesity has been reported. Whether altered body weight or a high fat diet modifies independent or additive changes in CB1 expression is unknown. We investigated the expression of CB1 and orexin 1 receptor (OX-1R) in the nodose ganglia of rats fed ad libitum or food deprived (24h), maintained on low or high fat diets (HFD), with differing body weights. Male Wistar rats were fed chow or HFD (diet-induced obese: DIO or diet-resistant: DR) or were body weight matched to the DR group but fed chow (wmDR). CB1 and OX-1R immunoreactivity were investigated and CB1 mRNA density was determined using in situ hybridization. CB1 immunoreactivity was measured in fasted rats after sulfated cholecystokinin octapeptide (CCK8s) administration. In chow rats, fasting did not modify the level of CB1 mRNA. More CB1 immunoreactive cells were measured in fed DIO, DR and wmDR rats than chow rats; levels increased after fasting in chow and wmDR rats but not in DIO or DR rats. In HFD fasted rats CCK8s did not reduce CB1 immunoreactivity. OX-1R immunoreactivity was modified by fasting only in DR rats. These data suggest that body weight contributes to the proportion of neurons expressing CB1 immunoreactivity in the nodose ganglion, while HFD blunts fasting-induced increases, and CCK-induced suppression of, CB1-immunoreactivity.

Understanding the brown adipocyte as a contributor to energy homeostasis

Brown adipocytes are specialized cells capable of undergoing thermogenesis, a phenomenon regulated by the sympathetic nervous system, due to the presence of uncoupling protein 1 (UCP1). The recent demonstrations of their presence in adult humans, and the discovery that brown adipocytes can be derived from distinct precursors and express specific genes depending on their anatomic location, have sparked intense interest in enhancing the current understanding of their biology and relevance to human energy homeostasis. We provide an overview of the latest advances related to the developmental origins of brown adipocytes, discuss their regulation and function in both rodents and humans, and offer a critical perspective on the relevance of brown adipocyte-mediated thermogenesis in human physiology.

Effects of glucagon-like peptide-1 receptor stimulation and blockade on food consumption and body weight in rats treated with a cannabinoid CB1 receptor agonist WIN 55,212-2

Background

Glucagon-like peptide-1 (GLP-1) and endocannabinoids are involved in appetite control. Recently we have demonstrated that cannabinoid (CB)1 receptor antagonist and GLP-1 receptor agonist synergistically suppress food intake in the rat. The aim of the present study was to determine the effects of GLP-1 receptor stimulation or blockade on feeding behavior in rats treated with WIN 55,212-2, a CB1 receptor agonist.

Material/Methods

Experiments were performed on adult male Wistar rats. In the first experiment the effects of increasing doses (0.5–4.0 mg/kg) of WIN 55,212-2 injected intraperitoneally on 24-hour food consumption were tested. In further experiments a GLP-1 receptor antagonist, exendin (9-39), and WIN 55,212-2 or a GLP-1 receptor agonist, exendin-4, and WIN 55,212-2 were injected intraperitoneally at subthreshold doses (that alone did not change food intake and body weight) to investigate whether these agents may interact to affect food intake in rats.

Results

WIN 55,212-2 administered at low doses (0.5–2 mg/kg) did not markedly change 24-hour food consumption; however, at the highest dose, daily food intake was inhibited. Combined administration of WIN 55,212-2 and exendin (9-39) did not change the amount of food consumed compared to either the control group or to each agent injected alone. Combined injection of WIN 55,212-2 and exendin-4 at subthreshold doses resulted in a significant decrease in food intake and body weight in rats.

Conclusions

Stimulation of the peripheral CB1 receptor by its agonist WIN 55,212-2 can induce anorexigenic effects or potentiate, even at a subthreshold dose, the effects of exendin-4, a known anorectic agent. Hence, this dual action of the cannabinoid system should be considered in the medical use of CB1 agonists.

Distribution of type 1 cannabinoid receptor-expressing neurons in the septal-hypothalamic region of the mouse: colocalization with GABAergic and glutamatergic markers

Type 1 cannabinoid receptor (CB1) is the principal mediator of retrograde endocannabinoid signaling in the brain. In this study, we addressed the topographic distribution and amino acid neurotransmitter phenotype of endocannabinoid-sensitive hypothalamic neurons in mice. The in situ hybridization detection of CB1 mRNA revealed high levels of expression in the medial septum (MS) and the diagonal band of Broca (DBB), moderate levels in the preoptic area and the hypothalamic lateroanterior (LA), paraventricular (Pa), ventromedial (VMH), lateral mammillary (LM), and ventral premammillary (PMV) nuclei, and low levels in many other hypothalamic regions including the suprachiasmatic (SCh) and arcuate (Arc) nuclei. This regional distribution pattern was compared with location of γ-aminobutyric acid (GABA)ergic and glutamatergic cell groups, as identified by the expression of glutamic acid decarboxylase 65 (GAD65) and type 2 vesicular glutamate transporter (VGLUT2) mRNAs, respectively. The MS, DBB, and preoptic area showed overlaps between GABAergic and CB1-expressing neurons, whereas hypothalamic sites with moderate CB1 signals, including the LA, Pa, VMH, LM, and PMV, were dominated by glutamatergic neurons. Low CB1 mRNA levels were also present in other glutamatergic and GABAergic regions. Dual-label in situ hybridization experiments confirmed the cellular co-expression of CB1 with both glutamatergic and GABAergic markers. In this report we provide a detailed anatomical map of hypothalamic glutamatergic and GABAergic systems whose neurotransmitter release is controlled by retrograde endocannabinoid signaling from hypothalamic and extrahypothalamic target neurons. This neuroanatomical information contributes to an understanding of the role that the endocannabinoid system plays in the regulation of endocrine and metabolic functions.

Control and physiological determinants of sympathetically mediated brown adipose tissue thermogenesis

Brown adipose tissue (BAT) represents a remarkable heat-producing tissue. The thermogenic potential of BAT is conferred by uncoupling protein 1, a protein found uniquely in brown adipocytes. BAT activity and capacity is controlled by the sympathetic nervous system (SNS), which densely innervates brown fat depots. SNS-mediated BAT thermogenesis is essentially governed by hypothalamic and brainstem neurons. BAT activity is also modulated by brain energy balance pathways including the very significant brain melanocortin system, suggesting a genuine involvement of SNS-mediated BAT thermogenesis in energy homeostasis. The use of positron emission tomography/computed tomography scanning has revealed the presence of well-defined BAT depots in the cervical, clavicular, and paraspinal areas in adult humans. The prevalence of these depots is higher in subjects exposed to low temperature and is also higher in women compared to men. Moreover, the prevalence of BAT decreases with age and body fat mass, suggesting that BAT could be involved in energy balance regulation and obesity in humans. This short review summarizes recent progress made in our understanding of the control of SNS-mediated BAT thermogenesis and of the determinants of BAT prevalence or detection in humans.

Involvement of the opioid system in the orexigenic and hedonic effects of melanin-concentrating hormone

Melanin-concentrating hormone (MCH) exerts an orexigenic effect that resembles that of opioids, suggesting that the MCH and opioid systems could interact in controlling the food intake behavior. Three series of experiments were conducted in male Wistar rats: 1) to test the ability of the κ-, μ-, and δ-opioid receptor antagonists binaltorphimine (nor-BNI-κ), β-funaltrexamine (β-FNA-μ), and naltrindole (NTI-δ), respectively, to block the stimulating effects of MCH on food intake; 2) to verify the ability of MCH to induce a positive hedonic response to a sweet stimulus when injected into the nucleus accumbens shell (NAcSh) or right lateral ventricle (LV) of the brain; and 3) to assess the ability of nor-BNI, β-FNA, and NTI to block the effects of MCH on the hedonic response to a sweet stimulus. Nor-BNI, NTI (0, 10 and 40 nmol), and β-FNA (0, 10 and 50 nmol) were administered into the LV prior to injecting MCH (2.0 nmol). To assess the hedonic response, rats were implanted with an intraoral cannula allowing for the infusion of a sweet solution into the oral cavity. Food intake was assessed in sated rats during the first 3 h following the MCH or vehicle (i.e., artificial cerebrospinal fluid) injection. The hedonic response to a sweet stimulus was assessed by examining facial mimics, following the intraoral administration of a sucrose solution. Blockade of each of the three opioid receptors by selective antagonists prevented MCH-induced feeding. Furthermore, MCH-injections into the NAcSh and right LV resulted in enhanced hedonic responses. Finally, antagonism of the three opioid receptors blunted the LV-injected, MCH-induced, facial-liking expressions in response to an intraoral sweet stimulus. Overall, the present study provides evidence to link the MCH and opioid systems in the food intake behavior.

Energy balance regulation by endocannabinoids at central and peripheral levels

Dysregulation of the endocannabinoid system (ECS) is a universal and, perhaps, causative feature of obesity. Central nervous system (CNS) circuits that regulate food intake were initially believed to be the targets for dysregulation. However, it is increasingly evident that endocannabinoids affect food intake, energy expenditure and substrate metabolism by acting on peripheral sites. Cannabinoid type 1 receptor (CB1r) antagonists can effectively treat obesity and associated metabolic alterations but, unfortunately, cause and exacerbate mood disorders. Drugs restricted to act on peripheral CB1rs might be safer and more effective, retaining the anti-obesity effects but lacking the adverse neurodepressive reactions. This review summarizes the emerging roles of the ECS in energy balance and discusses future pharmacological approaches for developing peripherally restricted CB1r antagonists.

Reward, dopamine and the control of food intake: implications for obesity

The ability to resist the urge to eat requires the proper functioning of neuronal circuits involved in top-down control to oppose the conditioned responses that predict reward from eating the food and the desire to eat the food. Imaging studies show that obese subjects might have impairments in dopaminergic pathways that regulate neuronal systems associated with reward sensitivity, conditioning and control. It is known that the neuropeptides that regulate energy balance (homeostatic processes) through the hypothalamus also modulate the activity of dopamine cells and their projections into regions involved in the rewarding processes underlying food intake. It is postulated that this could also be a mechanism by which overeating and the resultant resistance to homoeostatic signals impairs the function of circuits involved in reward sensitivity, conditioning and cognitive control.

The pathophysiology of cardiac cachexia

PURPOSE OF REVIEW

Cardiac cachexia, the loss of lean body mass that affects a large proportion of patients with chronic heart failure, is associated with increased morbidity and mortality. The pathophysiology of cardiac cachexia is complex and multifactorial, but recent studies are providing new information that is helping to clarify the pathophysiology and new targets for treatment.

RECENT FINDINGS

New attention is being paid to developing a definition as well as a clinically relevant way to diagnose this syndrome. The adverse clinical effects of cachexia are being emphasized by new research on the obesity paradox, suggesting that cardiac cachexia is such a detrimental process that obesity actually confers a survival benefit. This information is useful in developing practical approaches to managing body weight and lean tissue in chronic heart failure patients and may provide therapeutic targets. New mechanisms and pathways that mediate cardiac cachexia are being identified and appear to act by increasing energy requirements, reducing energy intake, impairing nutrient absorption, and causing metabolic alterations.

SUMMARY

Recent studies have helped to better delineate multifactorial mechanisms in the pathophysiology of cardiac cachexia that may lead to more effective treatments to address this common and important syndrome in patients with chronic heart failure.

Tea catechins' affinity for human cannabinoid receptors

Among the many known health benefits of tea catechins count anti-inflammatory and neuroprotective activities, as well as effects on the regulation of food intake. Here we address cannabimimetic bioactivity of catechin derivatives occurring in tea leaves as a possible cellular effector of these functionalities. Competitive radioligand binding assays using recombinant human cannabinoid receptors expressed in Chem-1 and CHO cells identified (-)-epigallocatechin-3-O-gallate, EGCG (K(i)=33.6 microM), (-)-epigallocatechin, EGC (K(i)=35.7 microM), and (-)-epicatechin-3-O-gallate, ECG (K(i)=47.3 microM) as ligands with moderate affinity for type 1 cannabinoid receptors, CB1. Binding to CB2 was weaker with inhibition constants exceeding 50 microM for EGC and ECG. The epimers (+)-catechin and (-)-epicatechin exhibited negligible affinities for both CB1 and CB2. It can be concluded that central nervous cannabinoid receptors may be targeted by selected tea catechins but signaling via peripheral type receptors is less likely to play a major role in vivo.

Obesity: genes, brain, gut, and environment

Obesity, which is assuming alarming proportions, has been attributed to genetic factors, hypothalamic dysfunction, and intestinal gut bacteria and an increase in the consumption of energy-dense food. Obesity predisposes to the development of type 2 diabetes mellitus, hypertension, coronary heart disease, and certain forms of cancer. Recent studies have shown that the intestinal bacteria in obese humans and mice differ from those in lean that could trigger a low-grade systemic inflammation. Consumption of a calorie-dense diet that initiates and perpetuates obesity could be due to failure of homeostatic mechanisms that regulate appetite, food consumption, and energy balance. Hypothalamic factors that regulate energy needs of the body, control appetite and satiety, and gut bacteria that participate in food digestion play a critical role in the onset of obesity. Incretins, cholecystokinin, brain-derived neurotrophic factor, leptin, long-chain fatty acid coenzyme A, endocannabinoids and vagal neurotransmitter acetylcholine play a role in the regulation of energy intake, glucose homeostasis, insulin secretion, and pathobiology of obesity and type 2 diabetes mellitus. Thus, there is a cross-talk among the gut, liver, pancreas, adipose tissue, and hypothalamus. Based on these evidences, it is clear that management of obesity needs a multifactorial approach.

Palatable high-energy diet decreases the expression of cannabinoid type 1 receptor messenger RNA in specific brain regions in the rat

In laboratory rodents, a palatable high-energy diet (PHED) is usually consumed in a higher quantity than a standard laboratory diet, leading to the development of an obese phenotype. The central effects of PHED are not fully understood. Nonetheless, the long-term consumption of PHED can decrease cannabinoid type 1 receptor (CB1R) protein density in particular brain regions. However, little is known about the diet-dependent regulation of the brain expression of CB1R mRNA. The present study aimed to investigate the effects of the long-term consumption of PHED and short-term (12 h) food deprivation on the brain expression of CB1R mRNA. For 13 weeks, rats were fed a standard laboratory chow or PHED presented as a free choice of chow, shortcake biscuits and pork spread. In total, the food intake of PHED rats was higher than that of chow-fed animals. Expectedly, PHED rats demonstrated higher body weight than chow-fed animals. The difference in body weight between PHED- and chow-fed rats was as result of the fat but not the lean mass. PHED-fed rats had significantly higher plasma levels of leptin and insulin and significantly higher levels of expression of suppressor of cytokine signalling 3 (SOCS-3) in the arcuate hypothalamic nucleus. The long-term consumption of PHED significantly decreased the levels of CB1R mRNA expression in the cingulate (Cg) cortex, ventromedial hypothalamic nucleus and the descending/autonomic divisions of the parvocellular hypothalamic nucleus (PVH), the ventrolateral parvocellular PVH and, to a lesser extent, the dorsomedial parvocellular PVH. Acute food deprivation decreased the levels of CB1R transcript in the Cg and ventrolateral parvocellular PVH. Altogether, the present results demonstrate that long-term PHED leads to an increase in the hypothalamic expression of SOCS-3 mRNA and a decrease in expression of CB1R mRNA in the Cg cortex and specific hypothalamic regions.