Diet-induced obesity leads to the development of leptin resistance in vagal afferent neurons

Sex-Specific Effect of a High-Energy Diet on Body Composition, Gut Microbiota, and Inflammatory Markers in Rats

Background/Objectives: A high-energy-density (HED) diet promotes body weight gain, fat accumulation, and gut dysbiosis, contributing to obesity. The aim of this study was to characterize the initial response to HED diet consumption, as well as identify any sex differences in body composition, systemic inflammation, gut microbiome, and fecal fat excretion in rats. Methods: Male and female Sprague-Dawley rats were fed a low-energy-density (LED) diet for 10 days and were then switched to an HED diet for four weeks. Food intake, body weight, and body composition were measured routinely. Serum samples were collected to measure inflammatory cytokines/chemokines. Fecal samples were collected for microbiome analysis and lipid content. Results: After the HED diet, all rats gained body weight and fat mass, with males exhibiting increased susceptibility to weight gain. Males displayed either a diet-induced obesity phenotype (DIO-P) or a diet-resistant (DR) phenotype, as characterized by their differential body weight gain. Males showed elevated TGF-β levels, while females exhibited increases in Interferon gamma-inducible protein 10 (IP-10), regulated on activation, normal T cell expressed and secreted (RANTES) protein, and basic fibroblast growth factor (FGFb). Changes in gut microbiota composition revealed a reduction in beneficial species, like Bacteroides uniformis and Parabacteroides distasonis, and an increase in species such as Akkermansia muciniphila. Sex differences in fat metabolism were shown in the greater fecal fat excretion observed in males. Conclusions: Our study demonstrates that short-term consumption of a high-energy diet elicits notable sex-specific differences in body weight, body composition, inflammatory markers, gut microbiota, and fat excretion in Sprague-Dawley rats. While we recognize that this study has a small sample size and a short-term intervention, our findings highlight the critical role of sex as a biological variable in diet-induced obesity research.

Select microbial metabolites in the small intestinal lumen regulate vagal activity via receptor-mediated signaling

The vagus nerve is proposed to enable communication between the gut microbiome and the brain, but activity-based evidence is lacking. We find that mice reared germ-free exhibit decreased vagal tone relative to colonized controls, which is reversed via microbiota restoration. Perfusing antibiotics into the small intestines of conventional mice, but not germ-free mice, acutely decreases vagal activity which is restored upon re-perfusion with intestinal filtrates from conventional, but not germ-free, mice. Microbiome-dependent short-chain fatty acids, bile acids, and 3-indoxyl sulfate indirectly stimulate vagal activity in a receptor-dependent manner. Serial perfusion of each metabolite class activates both shared and distinct neuronal subsets with varied response kinetics. Metabolite-induced and receptor-dependent increases in vagal activity correspond with the activation of brainstem neurons. Results from this study reveal that the gut microbiome regulates select metabolites in the intestinal lumen that differentially activate vagal afferent neurons, thereby enabling the microbial modulation of chemosensory signals for gut-brain communication.

Autonomic neuromodulation for cardiomyopathy associated with metabolic syndrome - Prevention of precursors for heart failure with preserved ejection fraction

Metabolic syndrome (MetS) induces a systemic inflammatory state which can lead to cardiomyopathy, manifesting clinically as heart failure (HF) with preserved ejection fraction (HFpEF). MetS components are intricately linked to the pathophysiologic processes of myocardial remodeling. Increased sympathetic nervous system activity, which is noted as an upstream factor of MetS, has been linked to adverse myocardial structural changes. Since renal denervation and vagus nerve stimulation have a sympathoinhibitory effect, attention has been paid to the cardioprotective effects of autonomic neuromodulation. In this review, the pathophysiology underlying the relationship between MetS and HF is elucidated, and the evidence regarding autonomic neuromodulation in HFpEF is summarized.

Vagus Nerve and Gut-Brain Communication

The vagus nerve, as an important component of the gut-brain axis, plays a crucial role in the communication between the gut and brain. It influences food intake, fat metabolism, and emotion by regulating the gut-brain axis, which is closely associated with the development of gastrointestinal, psychiatric, and metabolism-related disorders. In recent years, significant progress has been made in understanding the vagus-mediated regulatory pathway, highlighting its profound implications in the development of many diseases. Here, we summarize the latest advancements in vagus-mediated gut-brain pathways and the novel interventions targeting the vagus nerve. This will provide valuable insights for future research on treatment of obesity and gastrointestinal and depressive disorders based on vagus nerve stimulation.

Disrupted autonomic pathways in spinal cord injury: Implications for the immune regulation

Spinal Cord Injury (SCI) disrupts critical autonomic pathways responsible for the regulation of the immune function. Consequently, individuals with SCI often exhibit a spectrum of immune dysfunctions ranging from the development of damaging pro-inflammatory responses to severe immunosuppression. Thus, it is imperative to gain a more comprehensive understanding of the extent and mechanisms through which SCI-induced autonomic dysfunction influences the immune response. In this review, we provide an overview of the anatomical organization and physiology of the autonomic nervous system (ANS), elucidating how SCI impacts its function, with a particular focus on lymphoid organs and immune activity. We highlight recent advances in understanding how intraspinal plasticity that follows SCI may contribute to aberrant autonomic activity in lymphoid organs. Additionally, we discuss how sympathetic mediators released by these neuron terminals affect immune cell function. Finally, we discuss emerging innovative technologies and potential clinical interventions targeting the ANS as a strategy to restore the normal regulation of the immune response in individuals with SCI.

Cholinergic Neurotransmission Controls Orexigenic Endocannabinoid Signaling in the Gut in Diet-Induced Obesity

The brain bidirectionally communicates with the gut to control food intake and energy balance, which becomes dysregulated in obesity. For example, endocannabinoid (eCB) signaling in the small-intestinal (SI) epithelium is upregulated in diet-induced obese (DIO) mice and promotes overeating by a mechanism that includes inhibiting gut-brain satiation signaling. Upstream neural and molecular mechanism(s) involved in overproduction of orexigenic gut eCBs in DIO, however, are unknown. We tested the hypothesis that overactive parasympathetic signaling at the muscarinic acetylcholine receptors (mAChRs) in the SI increases biosynthesis of the eCB, 2-arachidonoyl-sn-glycerol (2-AG), which drives hyperphagia via local CB1Rs in DIO. Male mice were maintained on a high-fat/high-sucrose Western-style diet for 60 d, then administered several mAChR antagonists 30 min prior to tissue harvest or a food intake test. Levels of 2-AG and the activity of its metabolic enzymes in the SI were quantitated. DIO mice, when compared to those fed a low-fat/no-sucrose diet, displayed increased expression of cFos protein in the dorsal motor nucleus of the vagus, which suggests an increased activity of efferent cholinergic neurotransmission. These mice exhibited elevated levels of 2-AG biosynthesis in the SI, that was reduced to control levels by mAChR antagonists. Moreover, the peripherally restricted mAChR antagonist, methylhomatropine bromide, and the peripherally restricted CB1R antagonist, AM6545, reduced food intake in DIO mice for up to 24 h but had no effect in mice conditionally deficient in SI CB1Rs. These results suggest that hyperactivity at mAChRs in the periphery increases formation of 2-AG in the SI and activates local CB1Rs, which drives hyperphagia in DIO.

The Influence of Acute and Chronic Exercise on Appetite and Appetite Regulation in Patients with Prediabetes or Type 2 Diabetes Mellitus-A Systematic Review

This systematic review aims to analyze the effects of acute and chronic exercise on appetite and appetite regulation in patients with abnormal glycemic control. PubMed, Web of Science, and the Cochrane Central Register of Controlled Trials were searched for eligible studies. The included studies had to report assessments of appetite (primary outcome). Levels of appetite-regulating hormones were analyzed as secondary outcomes (considered, if additionally reported). Seven studies with a total number of 211 patients with prediabetes or type 2 diabetes mellitus (T2DM) met the inclusion criteria. Ratings of hunger, satiety, fullness, prospective food consumption, nausea, and desire to eat, as well as levels of (des-)acylated ghrelin, glucagon-like peptide 1, glucose-dependent insulinotropic peptide, pancreatic polypeptide, peptide tyrosine tyrosine, leptin, and spexin were considered. Following acute exercise, the effects on appetite (measured up to one day post-exercise) varied, while there were either no changes or a decrease in appetite ratings following chronic exercise, both compared to control conditions (without exercise). These results were accompanied by inconsistent changes in appetite-regulating hormone levels. The overall risk of bias was low. The present results provide more evidence for an appetite-reducing rather than an appetite-increasing effect of (chronic) exercise on patients with prediabetes or T2DM. PROSPERO ID: CRD42023459322.

Bariatric Surgery and New-Onset Substance Use Disorders: A Systematic review and Meta-analysis

Increasing evidence suggests that bariatric surgery (BS) patients are at risk for substance abuse disorders (SUD). The purpose of this systematic review and meta-analysis was to determine the relationship between BS and the development of new-onset substance abuse disorder (SUDNO) in bariatric patients. On October 31, 2023, we reviewed the scientific literature following PRISMA guidelines. A total of 3242 studies were analyzed, 7 met the inclusion criteria. The pooled incidence of SUDNO was 4.28%. Patients' characteristics associated with SUDNO included preoperative mental disorders, high pre-BS BMI, and public health insurance. Surgical factors associated with new SUDNOs included severe complications in the peri- or postoperative period. The occurrence of SUDNOs is a non-negligeable complication after BS. Predisposing factors may be identified and preventive actions undertaken.

Existing and Future Strategies to Manipulate the Gut Microbiota With Diet as a Potential Adjuvant Treatment for Psychiatric Disorders

Nutrition and diet quality play key roles in preventing and slowing cognitive decline and have been linked to multiple brain disorders. This review compiles available evidence from preclinical studies and clinical trials on the impact of nutrition and interventions regarding major psychiatric conditions and some neurological disorders. We emphasize the potential role of diet-related microbiome alterations in these effects and highlight commonalities between various brain disorders related to the microbiome. Despite numerous studies shedding light on these findings, there are still gaps in our understanding due to the limited availability of definitive human trial data firmly establishing a causal link between a specific diet and microbially mediated brain functions and symptoms. The positive impact of certain diets on the microbiome and cognitive function is frequently ascribed with the anti-inflammatory effects of certain microbial metabolites or a reduction of proinflammatory microbial products. We also critically review recent research on pro- and prebiotics and nondietary interventions, particularly fecal microbiota transplantation. The recent focus on diet in relation to brain disorders could lead to improved treatment outcomes with combined dietary, pharmacological, and behavioral interventions.

Nutrition at the Intersection between Gut Microbiota Eubiosis and Effective Management of Type 2 Diabetes

Nutrition is one of the most influential environmental factors in both taxonomical shifts in gut microbiota as well as in the development of type 2 diabetes mellitus (T2DM). Emerging evidence has shown that the effects of nutrition on both these parameters is not mutually exclusive and that changes in gut microbiota and related metabolites such as short-chain fatty acids (SCFAs) and branched-chain amino acids (BCAAs) may influence systemic inflammation and signaling pathways that contribute to pathophysiological processes associated with T2DM. With this background, our review highlights the effects of macronutrients, carbohydrates, proteins, and lipids, as well as micronutrients, vitamins, and minerals, on T2DM, specifically through their alterations in gut microbiota and the metabolites they produce. Additionally, we describe the influences of common food groups, which incorporate varying combinations of these macronutrients and micronutrients, on both microbiota and metabolic parameters in the context of diabetes mellitus. Overall, nutrition is one of the first line modifiable therapies in the management of T2DM and a better understanding of the mechanisms by which gut microbiota influence its pathophysiology provides opportunities for optimizing dietary interventions.

The impact of lipopolysaccharide on cerebrovascular function and cognition resulting from obesity-induced gut dysbiosis

Obesity is a worldwide epidemic coinciding with a concomitant increase in the incidence of neurodegenerative diseases, particularly dementia. Obesity is characterised by increased adiposity, chronic low-grade systemic inflammation, and oxidative stress, which promote endothelial dysfunction. Endothelial dysfunction reduces cerebrovascular function leading to reduced cerebral blood flow and, eventually, cognitive decline, thus predisposing to a neurodegenerative disease. Obesity is also characterised by gut dysbiosis and a subsequent increase in the lipopolysaccharide which increasingly activates toll-like receptor 4 (TLR4) and further promotes chronic low-grade systemic inflammation. This also disrupts the crosstalk within the gut-brain axis, thus influencing the functions of the central nervous system, including cognition. However, the mechanisms by which obesity-related increases in oxidative stress, inflammation and endothelial dysfunction are driven by, or associated with, increased systemic lipopolysaccharide leading to reduced cerebrovascular function and cognition, beyond normal ageing, have not been elucidated. Hence, this review examines how increased concentrations of lipopolysaccharide and the subsequent increased TLR4 activation observed in obesity exacerbate the development of obesity-induced reductions in cerebrovascular function and cognition.

Transfer of microbiota from lean donors in combination with prebiotics prevents excessive weight gain and improves gut-brain vagal signaling in obese rats

Gastrointestinal (GI) microbiota plays an active role in regulating the host's immune system and metabolism, as well as certain pathophysiological processes. Diet is the main factor modulating GI microbiota composition and studies have shown that high fat (HF) diets induce detrimental changes (dysbiosis) in the GI bacterial makeup. HF diet induced dysbiosis has been associated with structural and functional changes in gut-brain vagally mediated signaling system, associated with overeating and obesity. Although HF-driven changes in microbiota composition are sufficient to alter vagal signaling, it is unknown if improving microbiota composition after diet-induced obesity has been established can ameliorate gut-brain signaling and metabolic outcomes. In this study, we evaluated the effect of lean gut microbiota transfer in obese, vagally compromised, rats on gut-brain communication, food intake, and body weight. Male rats were maintained on regular chow or 45% HF diet for nine weeks followed by three weeks of microbiota depletion using antibiotics. The animals were then divided into four groups (n = 10 each): LF - control fed regular chow, LF-LF - chow fed animals that received microbiota from chow fed donors, HF-LF - HF fed animals that received microbiota from chow fed donors, and HF-HF - HF fed animals that received microbiota from HF fed donors. HF-LF animals received inulin as a prebiotic to aid the establishment of the lean microbiome. We found that transferring a LF microbiota to HF fed animals (HF-LF) reduced caloric intake during the light phase when compared with HF-HF rats and prevented additional excessive weight gain. HF-LF animals displayed an increase in postprandial activation of both primary sensory neurons innervating the GI tract and brainstem secondary neurons. We concluded from these data that improving microbiota composition in obese rats is sufficient to ameliorate gut-brain communication and restore normal feeding patterns which was associated with a reduction in weight gain.

Butterflies in the gut: the interplay between intestinal microbiota and stress

Psychological stress is a global issue that affects at least one-third of the population worldwide and increases the risk of numerous psychiatric disorders. Accumulating evidence suggests that the gut and its inhabiting microbes may regulate stress and stress-associated behavioral abnormalities. Hence, the objective of this review is to explore the causal relationships between the gut microbiota, stress, and behavior. Dysbiosis of the microbiome after stress exposure indicated microbial adaption to stressors. Strikingly, the hyperactivated stress signaling found in microbiota-deficient rodents can be normalized by microbiota-based treatments, suggesting that gut microbiota can actively modify the stress response. Microbiota can regulate stress response via intestinal glucocorticoids or autonomic nervous system. Several studies suggest that gut bacteria are involved in the direct modulation of steroid synthesis and metabolism. This review provides recent discoveries on the pathways by which gut microbes affect stress signaling and brain circuits and ultimately impact the host's complex behavior.

Neonatal overnutrition, but not neonatal undernutrition, disrupts CCK-induced hypophagia and neuron activation of the nucleus of the solitary tract and paraventricular nucleus of hypothalamus of male Wistar rats

Metabolic programming may be induced by reduction or enhancement of litter size, which lead to neonatal over or undernutrition, respectively. Changes in neonatal nutrition can challenge some regulatory processes in adulthood, such as the hypophagic effect of cholecystokinin (CCK). In order to investigate the effects of nutritional programming on the anorexigenic function of CCK in adulthood, pups were raised in small (SL, 3 pups per dam), normal (NL, 10 pups per dam), or large litters (LL, 16 pups per dam), and on postnatal day 60, male rats were treated with vehicle or CCK (10 µg/Kg) for the evaluation of food intake and c-Fos expression in the area postrema (AP), nucleus of solitary tract (NTS), and paraventricular (PVN), arcuate (ARC), ventromedial (VMH), and dorsomedial (DMH) nuclei of the hypothalamus. Overnourished rats showed increased body weight gain that was inversely correlated with neuronal activation of PaPo, VMH, and DMH neurons, whereas undernourished rats had lower body weight gain, inversely correlated with increased neuronal activation of PaPo only. SL rats showed no anorexigenic response and lower neuron activation in the NTS and PVN induced by CCK. LL exhibited preserved hypophagia and neuron activation in the AP, NTS, and PVN in response to CCK. CCK showed no effect in c-Fos immunoreactivity in the ARC, VMH, and DMH in any litter. These results indicate that anorexigenic actions, associated with neuron activation in the NTS and PVN, induced by CCK were impaired by neonatal overnutrition. However, these responses were not disrupted by neonatal undernutrition. Thus, data suggest that an excess or poor supply of nutrients during lactation display divergent effects on programming CCK satiation signaling in male adult rats.

Bioelectronic medicine: Preclinical insights and clinical advances

The nervous system maintains homeostasis and health. Homeostatic disruptions underlying the pathobiology of many diseases can be controlled by bioelectronic devices targeting CNS and peripheral neural circuits. New insights into the regulatory functions of the nervous system and technological developments in bioelectronics drive progress in the emerging field of bioelectronic medicine. Here, we provide an overview of key aspects of preclinical research, translation, and clinical advances in bioelectronic medicine.

The gut-brain axis: spatial relationship between spinal afferent nerves and 5-HT-containing enterochromaffin cells in mucosa of mouse colon

Cross talk between the gastrointestinal tract and brain is of significant relevance for human health and disease. However, our understanding of how the gut and brain communicate has been limited by a lack of techniques to identify the precise spatial relationship between extrinsic nerve endings and their proximity to specific cell types that line the inner surface of the gastrointestinal tract. We used an in vivo anterograde tracing technique, previously developed in our laboratory, to selectively label single spinal afferent axons and their nerve endings in mouse colonic mucosa. The closest three-dimensional distances between spinal afferent nerve endings and axonal varicosities to enterochromaffin (EC) cells, which contain serotonin (5-hydroxytryptamine; 5-HT), were then measured. The mean distances (± standard deviation) between any varicosity along a spinal afferent axon or its nerve ending, and the nearest EC cell, were 5.7 ± 6.0 μm (median: 3.6 μm) and 26.9 ± 18.6 μm (median: 24.1 μm), respectively. Randomization of the spatial location of EC cells revealed similar results to this actual data. These distances are ∼200-1,000 times greater than those between pre- and postsynaptic membranes (15-25 nm) that underlie synaptic transmission in the vertebrate nervous system. Our findings suggest that colonic 5-HT-containing EC cells release substances to activate centrally projecting spinal afferent nerves likely via diffusion, as such signaling is unlikely to occur with the spatial fidelity of a synapse.NEW & NOTEWORTHY We show an absence of close physical contact between spinal afferent nerves and 5-HT-containing EC cells in mouse colonic mucosa. Similar relative distances were observed between randomized EC cells and spinal afferents compared with actual data. This spatial relationship suggests that substances released from colonic 5-HT-containing EC cells are unlikely to act via synaptic transmission to neighboring spinal afferents that relay sensory information from the gut lumen to the brain.

Role of diet and its effects on the gut microbiome in the pathophysiology of mental disorders

There is emerging evidence that diet has a major modulatory influence on brain-gut-microbiome (BGM) interactions with important implications for brain health, and for several brain disorders. The BGM system is made up of neuroendocrine, neural, and immune communication channels which establish a network of bidirectional interactions between the brain, the gut and its microbiome. Diet not only plays a crucial role in shaping the gut microbiome, but it can modulate structure and function of the brain through these communication channels. In this review, we summarize the evidence available from preclinical and clinical studies on the influence of dietary habits and interventions on a selected group of psychiatric and neurologic disorders including depression, cognitive decline, Parkinson's disease, autism spectrum disorder and epilepsy. We will particularly address the role of diet-induced microbiome changes which have been implicated in these effects, and some of which are shared between different brain disorders. While the majority of these findings have been demonstrated in preclinical and in cross-sectional, epidemiological studies, to date there is insufficient evidence from mechanistic human studies to make conclusions about causality between a specific diet and microbially mediated brain function. Many of the dietary benefits on microbiome and brain health have been attributed to anti-inflammatory effects mediated by the microbial metabolites of dietary fiber and polyphenols. The new attention given to dietary factors in brain disorders has the potential to improve treatment outcomes with currently available pharmacological and non-pharmacological therapies.

Role of the gut-brain axis in energy and glucose metabolism

The gastrointestinal tract plays a role in the development and treatment of metabolic diseases. During a meal, the gut provides crucial information to the brain regarding incoming nutrients to allow proper maintenance of energy and glucose homeostasis. This gut-brain communication is regulated by various peptides or hormones that are secreted from the gut in response to nutrients; these signaling molecules can enter the circulation and act directly on the brain, or they can act indirectly via paracrine action on local vagal and spinal afferent neurons that innervate the gut. In addition, the enteric nervous system can act as a relay from the gut to the brain. The current review will outline the different gut-brain signaling mechanisms that contribute to metabolic homeostasis, highlighting the recent advances in understanding these complex hormonal and neural pathways. Furthermore, the impact of the gut microbiota on various components of the gut-brain axis that regulates energy and glucose homeostasis will be discussed. A better understanding of the gut-brain axis and its complex relationship with the gut microbiome is crucial for the development of successful pharmacological therapies to combat obesity and diabetes.

Mechanisms of reduced leptin-mediated satiety signaling during obesity

BACKGROUND/OBJECTIVES

Disrupted leptin signaling in vagal afferent neurons contributes to hyperphagia and obesity. Thus, we tested the hypothesis that intrinsic negative regulators of leptin signaling, suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) underlie dysfunctional leptin-mediated vagal afferent satiety signaling during obesity.

METHODS

Experiments were performed on standard chow-fed control mice, high-fat fed (HFF), or low-fat fed (LFF) mice. SOCS3 and PTP1B expression were quantified using western blot and quantitative PCR. Nodose ganglion neuronal excitability and jejunal afferent sensitivity were measured by patch clamp and extracellular afferent recordings, respectively.

RESULTS

Increased expression of SOCS3 and PTP1B were observed in the jejunum of HFF mice. Prolonged incubation with leptin attenuated nodose ganglion neuronal excitability, and this effect was reversed by inhibition of SOCS3. Leptin potentiated jejunal afferent nerve responses to CCK in LFF mice but decreased them in HFF mice. Inhibition of SOCS3 restored impaired vagal afferent neuronal excitability and afferent nerve responses to satiety mediators during obesity. Two-pore domain K⁺ channel (K_2P) conductance and nitric oxide (NO) production that we previously demonstrated were elevated during obesity were decreased by inhibitions of SOCS3 or PTP1B.

CONCLUSIONS

This study suggests that obesity impairs vagal afferent sensitivity via SOCS3 and PTP1B, likely as a consequence of obesity-induced hyperleptinemia. The mechanisms underlying leptin resistance appear also to cause a more global impairment of satiety-related vagal afferent responsiveness.

Intestinal microbiota and their metabolic contribution to type 2 diabetes and obesity

Obesity and type 2 diabetes mellitus (T2DM) are common, chronic metabolic disorders with associated significant long-term health problems at global epidemic levels. It is recognised that gut microbiota play a central role in maintaining host homeostasis and through technological advances in both animal and human models it is becoming clear that gut microbiota are heavily involved in key pathophysiological roles in the aetiology and progression of both conditions. This review will focus on current knowledge regarding microbiota interactions with short chain fatty acids, the host inflammatory response, signaling pathways, integrity of the intestinal barrier, the interaction of the gut-brain axis and the subsequent impact on the metabolic health of the host.

Supplementation with Lactiplantibacillus plantarum IMC 510 Modifies Microbiota Composition and Prevents Body Weight Gain Induced by Cafeteria Diet in Rats

Changes in functionality and composition of gut microbiota (GM) have been associated and may contribute to the development and maintenance of obesity and related diseases. The aim of our study was to investigate for the first time the impact of Lactiplantibacillus (L.) plantarum IMC 510 in a rat model of diet-induced obesity, specifically in the cafeteria (CAF) diet. This diet provides a strong motivation to voluntary overeat, due to the palatability and variety of selected energy-dense foods. The oral administration for 84 days of this probiotic strain, added to the CAF diet, decreased food intake and body weight gain. Accordingly, it ameliorated body mass index, liver and white adipose tissue weight, hepatic lipid accumulation, adipocyte size, serum parameters, including glycemia and low-density lipoprotein levels, in CAF fed rats, potentially through leptin control. In this scenario, L. plantarum IMC 510 showed also beneficial effects on GM, limiting the microbial imbalance established by long exposure to CAF diet and preserving the proportion of different bacterial taxa. Further research is necessary to better elucidate the relationship between GM and overweight and then the mechanism of action by which L. plantarum IMC 510 modifies weight. However, these promising results prompt a clear advantage of probiotic supplementation and identify a new potential probiotic as a novel and safe therapeutic approach in obesity prevention and management.

Gut Microbiota: Novel Therapeutic Target of Ginsenosides for the Treatment of Obesity and Its Complications

Obesity, generally characterized by excessive lipid accumulation, is a metabolic threat worldwide due to its rapid growth in global prevalence. Ginsenosides are crucial components derived from natural plants that can confer metabolic benefits for obese patients. Considering the low bioavailability and degradable properties of ginsenosides in vivo, it should be admitted that the mechanism of ginsenosides on anti-obesity contribution is still obscure. Recently, studies have indicated that ginsenoside intervention has beneficial metabolic effects on obesity and its complications because it allows for the correction of gut microbiota dysbiosis and regulates the secretion of related endogenous metabolites. In this review, we summarize the role of gut microbiota in the pathogenetic process of obesity, and explore the mechanism of ginsenosides for ameliorating obesity, which can modulate the composition of gut microbiota by improving the metabolism of intestinal endogenous substances and alleviating the level of inflammation. Ginsenosides are expected to become a promising anti-obesity medical intervention in the foreseeable clinical settings.

Microbiota's Role in Diet-Driven Alterations in Food Intake: Satiety, Energy Balance, and Reward

The gut microbiota plays a key role in modulating host physiology and behavior, particularly feeding behavior and energy homeostasis. There is accumulating evidence demonstrating a role for gut microbiota in the etiology of obesity. In human and rodent studies, obesity and high-energy feeding are most consistently found to be associated with decreased bacterial diversity, changes in main phyla relative abundances and increased presence of pro-inflammatory products. Diet-associated alterations in microbiome composition are linked with weight gain, adiposity, and changes in ingestive behavior. There are multiple pathways through which the microbiome influences food intake. This review discusses these pathways, including peripheral mechanisms such as the regulation of gut satiety peptide release and alterations in leptin and cholecystokinin signaling along the vagus nerve, as well as central mechanisms, such as the modulation of hypothalamic neuroinflammation and alterations in reward signaling. Most research currently focuses on determining the role of the microbiome in the development of obesity and using microbiome manipulation to prevent diet-induced increase in food intake. More studies are necessary to determine whether microbiome manipulation after prolonged energy-dense diet exposure and obesity can reduce intake and promote meaningful weight loss.

Glutaredoxin1 knockout promotes high-fat diet-induced obesity in male mice but not in female ones

This study aims to explore how a high-fat diet and glutaredoxin1 (Glrx1) deficiency affect the development of obesity in male and female mice. A high-fat diet induced great differences in calorie intake and body weight gain between male and female mice; furthermore, the Glrx1 deficiency made male mice more sensitive to a high-fat diet than females. Male mice had higher glucose intolerance, and Glrx1 deficiency aggravated gender differences in glucose intolerance. Glrx1 deficiency aggravated high-fat diet-induced hyperlipidemia. The mRNA levels of HMGCR, Srebf-1c, Srebf-2, CD36, FASN and SCD1 were consistently lower in females than in males. Glrx1 deficiency exacerbated high-fat diet induced liver injury and oxidative stress. Diet but not gender or genotype altered the composition of gut microbiota. These findings provide a new insight into the different susceptibilities to obesity caused by a high-fat diet between males and females.

A review on gut microbiota: a central factor in the pathophysiology of obesity

Obesity and its complications constitute a substantial burden. Considerable published research describes the novel relationships between obesity and gut microbiota communities. It is becoming evident that microbiota behave in a pivotal role in their ability to influence homeostatic mechanisms either to the benefit or detriment of host health, the extent of which is not fully understood. A greater understanding of the contribution of gut microbiota towards host pathophysiology is revealing new therapeutic avenues to tackle the global obesity epidemic. This review focuses on causal relationships and associations with obesity, proposed central mechanisms encouraging the development of obesity and promising prospective methods for microbiota manipulation.

The evolving obesity challenge: targeting the vagus nerve and the inflammatory reflex in the response

Obesity and the metabolic syndrome (MetS), which have reached pandemic proportions significantly increase the risk for type 2 diabetes, cardiovascular disease, and other serious conditions. Recent data with COVID-19 patients indicate that obesity also is a significant risk factor for this novel viral disease and poor outcome of associated critical illness. These findings considerably change the view of obesity as a driver of serious, but slowly-progressing chronic diseases, and emphasize the urgency to explore new therapeutic approaches. Inflammation is a recognized driver of metabolic derangements in obesity and MetS, and a core feature of COVID-19 pathobiology. Recent advances in our understanding of inflammatory regulation have highlighted the role of the nervous system and the vagus nerve-based inflammatory reflex. Current bioelectronic and pharmacological therapeutic explorations centered on the inflammatory reflex offer new approaches for conditions characterized by immune and metabolic dysregulation and for ameliorating the escalating burden of obesity, MetS, and COVID-19.

Physiological Sympathetic Activation Reduces Systemic Inflammation: Role of Baroreflex and Chemoreflex

Baroreflex and chemoreflex act through the autonomic nervous system, which is involved with the neural regulation of inflammation. The present study reports the effects of reflex physiological sympathetic activation in endotoxemic rats using bilateral carotid occlusion (BCO), a physiological approach involving the baroreflex and chemoreflex mechanisms and the influence of the baroreceptors and peripheral chemoreceptors in the cardiovascular and systemic inflammatory responses. After lipopolysaccharide (LPS) administration, the arterial pressure was recorded during 360 min in unanesthetized rats, and serial blood samples were collected to analyze the plasma cytokine levels. BCO elicited the reflex activation of the sympathetic nervous system, providing the following outcomes: (I) increased the power of the low-frequency band in the spectrum of the systolic arterial pressure during the BCO period; (II) reduced the levels of pro-inflammatory cytokines in plasma, including the tumor necrosis factor (TNF) and the interleukin (IL)-1β; (III) increased the plasma levels of anti-inflammatory cytokine IL-10, 90 min after LPS administration. Moreover, selective baroreceptor or chemoreceptor denervation deactivated mechanosensitive and chemical sensors, respectively, and decreased the release of the LPS-induced cytokine but did not alter the BCO modulatory effects. These results show, for the first time, that physiological reflex activation of the sympathetic circuit decreases the inflammatory response in endotoxemic rats and suggest a novel function for the baroreceptors as immunosensors during the systemic inflammation.

The critical role of CCK in the regulation of food intake and diet-induced obesity

In 1973, Gibbs, Young, and Smith showed that exogenous cholecystokinin (CCK) administration reduces food intake in rats. This initial report has led to thousands of studies investigating the physiological role of CCK in regulating feeding behavior. CCK is released from enteroendocrine I cells present along the gastrointestinal (GI) tract. CCK binding to its receptor CCK1R leads to vagal afferent activation providing post-ingestive feedback to the hindbrain. Vagal afferent neurons' (VAN) sensitivity to CCK is modulated by energy status while CCK signaling regulates gene expression of other feeding related signals and receptors expressed by VAN. In addition to its satiation effects, CCK acts all along the GI tract to optimize digestion and nutrient absorption. Diet-induced obesity (DIO) is characterized by reduced sensitivity to CCK and every part of the CCK system is negatively affected by chronic intake of energy-dense foods. EEC have recently been shown to adapt to diet, CCK1R is affected by dietary fats consumption, and the VAN phenotypic flexibility is lost in DIO. Altered endocannabinoid tone, changes in gut microbiota composition, and chronic inflammation are currently being explored as potential mechanisms for diet driven loss in CCK signaling. This review discusses our current understanding of how CCK controls food intake in conditions of leanness and how control is lost in chronic energy excess and obesity, potentially perpetuating excessive intake.

Intact vagal gut-brain signalling prevents hyperphagia and excessive weight gain in response to high-fat high-sugar diet

Aim

The tools that have been used to assess the function of the vagus nerve lack specificity. This could explain discrepancies about the role of vagal gut‐brain signalling in long‐term control of energy balance. Here we use a validated approach to selectively ablate sensory vagal neurones that innervate the gut to determine the role of vagal gut‐brain signalling in the control of food intake, energy expenditure and glucose homoeostasis in response to different diets.

Methods

Rat nodose ganglia were injected bilaterally with either the neurotoxin saporin conjugated to the gastrointestinal hormone cholecystokinin (CCK), or unconjugated saporin as a control. Food intake, body weight, glucose tolerance and energy expenditure were measured in both groups in response to chow or high‐fat high‐sugar (HFHS) diet. Willingness to work for fat or sugar was assessed by progressive ratio for orally administered solutions, while post‐ingestive feedback was tested by measuring food intake after an isocaloric lipid or sucrose pre‐load.

Results

Vagal deafferentation of the gut increases meal number in lean chow‐fed rats. Switching to a HFHS diet exacerbates overeating and body weight gain. The breakpoint for sugar or fat solution did not differ between groups, suggesting that increased palatability may not drive HFHS‐induced hyperphagia. Instead, decreased satiation in response to intra‐gastric infusion of fat, but not sugar, promotes hyperphagia in CCK‐Saporin‐treated rats fed with HFHS diet.

Conclusions

We conclude that intact sensory vagal neurones prevent hyperphagia and exacerbation of weight gain in response to a HFHS diet by promoting lipid‐mediated satiation.

The metabolic impact of small intestinal nutrient sensing

The gastrointestinal tract maintains energy and glucose homeostasis, in part through nutrient-sensing and subsequent signaling to the brain and other tissues. In this review, we highlight the role of small intestinal nutrient-sensing in metabolic homeostasis, and link high-fat feeding, obesity, and diabetes with perturbations in these gut-brain signaling pathways. We identify how lipids, carbohydrates, and proteins, initiate gut peptide release from the enteroendocrine cells through small intestinal sensing pathways, and how these peptides regulate food intake, glucose tolerance, and hepatic glucose production. Lastly, we highlight how the gut microbiota impact small intestinal nutrient-sensing in normal physiology, and in disease, pharmacological and surgical settings. Emerging evidence indicates that the molecular mechanisms of small intestinal nutrient sensing in metabolic homeostasis have physiological and pathological impact as well as therapeutic potential in obesity and diabetes.

The gastrointestinal tract participates in maintaining metabolic homeostasis in part through nutrient-sensing and subsequent gut-brain signalling. Here the authors review the role of small intestinal nutrient-sensing in regulation of energy intake and systemic glucose metabolism, and link high-fat diet, obesity and diabetes with perturbations in these pathways.

Vagally Mediated Gut-Brain Relationships in Appetite Control-Insights from Porcine Studies

Signals arising from the upper part of the gut are essential for the regulation of food intake, particularly satiation. This information is supplied to the brain partly by vagal nervous afferents. The porcine model, because of its sizeable gyrencephalic brain, omnivorous regimen, and comparative anatomy of the proximal part of the gut to that of humans, has provided several important insights relating to the relevance of vagally mediated gut-brain relationships to the regulation of food intake. Furthermore, its large size combined with the capacity to become obese while overeating a western diet makes it a pivotal addition to existing murine models, especially for translational studies relating to obesity. How gastric, proximal intestinal, and portal information relating to meal arrival and transit are encoded by vagal afferents and their further processing by primary and secondary brain projections are reviewed. Their peripheral and central plasticities in the context of obesity are emphasized. We also present recent insights derived from chronic stimulation of the abdominal vagi with specific reference to the modulation of mesolimbic structures and their role in the restoration of insulin sensitivity in the obese miniature pig model.

Variants in Circadian Rhythm Gene Cry1 Interacts with Healthy Dietary Pattern for Serum Leptin Levels: a Cross-sectional Study

Circadian disruption causes obesity and other metabolic disorders. There is no research considering the role of Cryptochromes (Cry) 1 body clock gene and major dietary patterns on serum leptin level and obesity. We aimed to investigate the interaction between Cry1 circadian gene polymorphisms and major dietary patterns on leptin and obesity related measurements. This study was performed on 377 overweight and obese women. Mean age and body mass index (BMI) of study subjects were 36.64 ± 9.02 years and 30.81 ± 3.8 kg/m², respectively. Dietary assessment was done using a validated 147-item food frequency questionnaire. Cry1 rs2287161 were genotyped using polymerase chain reaction-restriction fragment length polymorphism. Generalized linear models were used for interaction analysis. Healthy and unhealthy dietary pattern (HDP and UDP, respectively) were extracted using factor analysis (principal component analysis). Our study revealed a significant higher weight (p = 0.003) and BMI (p = 0.042) in women carrying CC homozygote compared with G allele carriers. Moreover, our findings showed a significant gene-diet interaction between HDP and Cry1 rs2287161 on BMI (p = 0.034) and serum leptin level (p = 0.056) in which, BMI and serum leptin level were lower in subjects with CC genotype than in those with GG genotype while following HDP. This study suggests a significant interaction between Cry1 rs2287161 polymorphisms and HDP on BMI and serum leptin and the lowering effects were apparent among C allele carriers compared to G allele ones. This data highlights the role of dietary pattern in relation of gene and obesity.

TLR4 Signaling Selectively and Directly Promotes CGRP Release from Vagal Afferents in the Mouse

There has been a long-standing debate regarding the role of peripheral afferents in mediating rapid-onset anorexia among other responses elicited by peripheral inflammatory insults. Thus, the current study assessed the sufficiency of peripheral afferents expressing toll-like receptor 4 (TLR4) to the initiation of the anorexia caused by peripheral bacterial lipopolysaccharide (LPS). We generated a Tlr4 null (Tlr4^LoxTB) mouse in which Tlr4 expression is globally disrupted by a loxP-flanked transcription blocking (TB) cassette. This novel mouse model allowed us to restore the endogenous TLR4 expression in specific cell types. Using Zp3-Cre and Na_v1.8-Cre mice, we produced mice that express TLR4 in all cells (Tlr4^LoxTB X Zp3-Cre) and in peripheral afferents (Tlr4^LoxTB X Na_v1.8-Cre), respectively. We validated the Tlr4^LoxTB mice, which were phenotypically identical to previously reported global TLR4 knock-out mice. Contrary to our expectations, the administration of LPS did not cause rapid-onset anorexia in mice with Na_v1.8-restricted TLR4. The later result prompted us to identify Tlr4-expressing vagal afferents using in situ hybridization (ISH). In vivo, we found that Tlr4 mRNA was primarily enriched in vagal Na_v1.8 afferents located in the jugular ganglion that co-expressed calcitonin gene-related peptide (CGRP). In vitro, the application of LPS to cultured Na_v1.8-restricted TLR4 afferents was sufficient to stimulate the release of CGRP. In summary, we demonstrated using a new mouse model that vagally-expressed TLR4 is selectively involved in stimulating the release of CGRP but not in causing anorexia.

Immunity and the carotid body: implications for metabolic diseases

Neuro-immune communication has gained enormous interest in recent years due to increasing knowledge of the way in which the brain coordinates functional alterations in inflammatory and autoimmune responses, and the mechanisms of neuron-immune cell interactions in the context of metabolic diseases such as obesity and type 2 diabetes. In this review, we will explain how this relationship between the nervous and immune system impacts the pro- and anti-inflammatory pathways with specific reference to the hypothalamus-pituitary-adrenal gland axis and the vagal reflex and will explore the possible involvement of the carotid body (CB) in the neural control of inflammation. We will also highlight the mechanisms of vagal anti-inflammatory reflex control of immunity and metabolism, and the consequences of functional disarrangement of this reflex in settlement and development of metabolic diseases, with special attention to obesity and type 2 diabetes. Additionally, the role of CB in the interplay between metabolism and immune responses will be discussed, with specific reference to the different stimuli that promote CB activation and the balance between sympathetic and parasympathetic in this context. In doing so, we clarify the multivarious neuronal reflexes that coordinate tissue-specific responses (gut, pancreas, adipose tissue and liver) critical to metabolic control, and metabolic disease settlement and development. In the final section, we will summarize how electrical modulation of the carotid sinus nerve may be utilized to adjust these reflex responses and thus control inflammation and metabolic diseases, envisioning new therapeutics horizons.

Psychobiology of Appetite and Food Reward in Adults with Type 1 and Type 2 Diabetes: Is there a Role for Exercise?

Hyperglycemia is the defining feature of type 1 diabetes (T1D) and type 2 diabetes (T2D) and results from deficient insulin production, impaired insulin-stimulated glucose uptake or both. It is now well established that hyperglycemia results in profound metabolic complications, but the effect of diabetes and its associated metabolic effects on homeostatic and hedonic appetite control has received less attention. Inappropriate food choices and excess food intake might promote weight gain, further exacerbating the metabolic consequences of T1D and T2D. The need to control blood glucose through diet, physical activity and/or medication as a consequence of impaired insulin secretion and/or sensitivity adds a further level of physiological and behavioural complexity to the processes underlying food choice and appetite control. Alterations in appetite-related processes have been noted in people with T2D, but the effect of T1D on appetite is largely unexplored. Peripheral neuroendocrine signalling appears disrupted in people with T2D, and brain regions involved in the central modulation of appetite might display central insulin resistance. However, it is difficult to isolate the consequences of T2D from those of obesity. Health-care policy advocates the use of physical activity as a means of preventing and treating T2D via the promotion of weight loss and its independent influence on insulin sensitivity. Exercise-induced perturbations to energy balance can elicit biological and behavioural compensation that attenuates weight loss, and diabetes pathophysiology might alter the strength of such compensation. However, the effect of exercise on appetite in people living with diabetes has yet to be fully explored.

A novel role for the pineal gland: Regulating seasonal shifts in the gut microbiota of Siberian hamsters

The gut microbiota plays a significant role in a variety of host behavioral and physiological processes. The mechanisms by which the gut microbiota and the host communicate are not fully resolved but include both humoral and direct neural signals. The composition of the microbiota is affected by internal (host) factors and external (environmental) factors. One such signal is photoperiod, which is represented endogenously by nocturnal pineal melatonin (MEL) secretion. Removal of the MEL signal via pinealectomy abolishes many seasonal responses to photoperiod. In Siberian hamsters (Phodopus sungorus), MEL drives robust seasonal shifts in physiology and behavior, such as immunity, stress, body mass, and aggression. While the profile of the gut microbiota also changes by season, it is unclear whether these changes are driven by pineal signals. We hypothesized that the pineal gland mediates seasonal alterations in the composition of the gut microbiota. To test this, we placed pinealectomized and intact hamsters into long or short photoperiods for 8 weeks, collected weekly fecal samples, and measured weekly food intake, testis volume, and body mass. We determined microbiota composition using 16S rRNA sequencing (Illumina MiSeq). We found significant effects of treatment and time on the abundances of numerous bacterial genera. We also found significant associations between individual OTU abundances and body mass, testis mass, and food intake, respectively. Finally, results indicate a relationship between overall community structure, and body and testis masses. These results firmly establish a role for the pineal gland in mediating seasonal alterations in the gut microbiota. Further, these results identify a novel neuroendocrine pathway by which a host regulates seasonal shifts in gut community composition, and indicates a relationship between seasonal changes in the gut microbiota and seasonal physiological adjustments.

Non-neuronal crosstalk promotes an inflammatory response in nodose ganglia cultures after exposure to byproducts from gram positive, high-fat-diet-associated gut bacteria

Vagal afferent neurons (VAN) projecting to the lamina propria of the digestive tract are the primary source of gut-originating signals to the central nervous system (CNS). VAN cell bodies are found in the nodose ganglia (NG). Responsiveness of VAN to gut-originating signals is altered by feeding status with sensitivity to satiety signals such as cholecystokinin (CCK) increasing in the fed state. Chronic high-fat (HF) feeding results in inflammation at the level of the NG associated with a loss of VAN ability to switch phenotype from the fasted to the fed state. HF feeding also leads to compositional changes in the gut microbiota. HF diet consumption notably drives increased Firmicutes to Bacteroidetes phyla ratio and increased members of the Actinobacteria phylum. Firmicutes and Actinobacteria are largely gram positive (GP). In this study, we aimed to determine if byproducts from GP bacteria can induce an inflammatory response in cultured NG and to characterize the mechanism and cell types involved in the response. NG were collected from male Wistar rats and cultured for a total of 72 hours. At 48-68 hours after plating, cultures were treated with neuronal culture media in which Serinicoccus chungangensis had been grown and removed (SUP), lipoteichoic acid (LTA), or meso-diaminopimelic acid (meso-DAP). Some treatments included the glial inhibitors minocycline (MINO) and/or fluorocitrate (FC). The responses were evaluated using immunocytochemistry, qPCR, and electrochemiluminescence. We found that SUP induced an inflammatory response characterized by increased interleukin (IL)-6 staining and increased expression of genes for IL-6, interferon (IFN)γ, and tumor necrosis factor (TNF)α along with genes associated with cell-to-cell communication such as C-C motif chemokine ligand-2 (CCL2). Inclusion of inhibitors attenuated some responses but failed to completely normalize all indications of response, highlighting the role of immunocompetent cellular crosstalk in regulating the inflammatory response. LTA and meso-DAP produced responses that shared characteristics with SUP but were not identical. Our results support a role for HF associated GP bacterial byproducts' ability to contribute to vagal inflammation and to engage signaling from nonneuronal cells.

Brain-gut-microbiome interactions in obesity and food addiction

Normal eating behaviour is coordinated by the tightly regulated balance between intestinal and extra-intestinal homeostatic and hedonic mechanisms. By contrast, food addiction is a complex, maladaptive eating behaviour that reflects alterations in brain-gut-microbiome (BGM) interactions and a shift of this balance towards hedonic mechanisms. Each component of the BGM axis has been implicated in the development of food addiction, with both brain to gut and gut to brain signalling playing a role. Early-life influences can prime the infant gut microbiome and brain for food addiction, which might be further reinforced by increased antibiotic usage and dietary patterns throughout adulthood. The ubiquitous availability and marketing of inexpensive, highly palatable and calorie-dense food can further shift this balance towards hedonic eating through both central (disruptions in dopaminergic signalling) and intestinal (vagal afferent function, metabolic endotoxaemia, systemic immune activation, changes to gut microbiome and metabolome) mechanisms. In this Review, we propose a systems biology model of BGM interactions, which incorporates published reports on food addiction, and provides novel insights into treatment targets aimed at each level of the BGM axis.

Neural Regulation of Interactions Between Group 2 Innate Lymphoid Cells and Pulmonary Immune Cells

Emerging evidence supports the involvement of nervous system in the regulation of immune responses. Group 2 innate lymphoid cells (ILC2), which function as a crucial bridge between innate and adaptive immunity, are present in large numbers in barrier tissues. Neuropeptides and neurotransmitters have been found to participate in the regulation of ILC2, adding a new dimension to neuroimmunity. However, a comprehensive and detailed overview of the mechanisms of neural regulation of ILC2, associated with previous findings and prospects for future research, is still lacking. In this review, we compile existing information that supports neurons as yet poorly understood regulators of ILC2 in the field of lung innate and adaptive immunity, focusing on neural regulation of the interaction between ILC2 and pulmonary immune cells.

Gut microbiota composition modulates inflammation and structure of the vagal afferent pathway

Vagal afferent neurons (VAN), located in the nodose ganglion (NG) innervate the gut and terminate in the nucleus of solitary tract (NTS) in the brainstem. They are the primary sensory neurons integrating gut-derived signals to regulate meal size. Chronic high-fat diet (HFD) consumption impairs vagally mediated satiety, resulting in overfeeding. There is evidence that HFD consumption leads to alterations in both vagal nerve function and structural integrity. HFD also leads to marked gut microbiota dysbiosis; in rodent models, dysbiosis is sufficient to induce weight gain. In this study, we investigated the effect of microbiota dysbiosis on gut-brain vagal innervation independently of diet. To do so, we recolonized microbiota-depleted rats with gastrointestinal (GI) contents isolated from donor animals fed either a HFD (45 or 60% fat) or a low fat diet (LFD, 13% fat). We used two different depletion models while maintaining the animals on LFD: 1) conventionally raised Fischer and Wistar rats that underwent a depletion paradigm using an antibiotic cocktail and 2) germ free (GF) raised Fischer rats. Following recolonization, receiver animals were designated as ConvLF and ConvHF. Fecal samples were collected throughout these studies and analyzed via 16S Illumina sequencing. In both models, bacteria that were identified as characteristic of HFD were successfully transferred to recipient animals. Three weeks post-colonization, ConvHF rats showed significant increases in ionized calcium-binding adapter molecule-1 (Iba1) positive immune cells in the NG compared to ConvLF animals. Additionally, using isolectin B4 (IB4) staining to identify c-fibers, we found that, compared to ConvLF animals, ConvHF rats displayed decreased innervation at the level of the medial NTS; c-fibers at this level are believed to be primarily of vagal origin. This alteration in vagal structure was associated with a loss in satiety induced by the gut peptide cholecystokinin (CCK). Increased presence of immunocompetent Iba1⁺ cells along the gut-brain axis and alterations in NTS innervation were still evident in ConvHF rats compared to ConvLF animals 12 weeks post-colonization and were associated with increases in food intake and body weight (BW). We conclude from these data that microbiota dysbiosis can alter gut-brain vagal innervation, potentially via recruitment and/or activation of immune cells.

Consumption of a high energy density diet triggers microbiota dysbiosis, hepatic lipidosis, and microglia activation in the nucleus of the solitary tract in rats

Introduction

Obesity is a multifactorial chronic inflammatory disease. Consumption of high energy density (HED) diets is associated with hyperphagia, increased body weight and body fat accumulation, and obesity. Our lab has previously shown that short-term (4 weeks) consumption of a HED diet triggers gut microbiota dysbiosis, gut inflammation, and reorganization of the gut-brain vagal communication.

Objetives

The aim of this study was to investigate the effect of long-term (6 months) consumption of HED diet on body composition, gut microbiome, hepatocellular lipidosis, microglia activation in the nucleus of the solitary tract, and systemic inflammation.

Methods

Male Sprague–Dawley rats were fed a low energy density (LED) diet for 2 weeks and then switched to a HED diet for 26 weeks. Twenty-four-hour food intake, body weight, and body composition were measured twice a week. Blood serum and fecal samples were collected at baseline, 1, 4, 8, and 26 weeks after introduction of the HED diet. Serum samples were used to measure insulin, leptin, and inflammatory cytokines using Enzyme-linked Immunosorbent Assay. Fecal samples were assessed for 16 S rRNA genome sequencing.

Results

HED diet induced microbiota dysbiosis within a week of introducing the diet. In addition, there was significant microglia activation in the intermediate NTS and marked hepatic lipidosis after 4 weeks of HED diet. We further observed changes in the serum cytokine profile after 26 weeks of HED feeding.

Conclusions

These data suggest that microbiota dysbiosis is the first response of the organism to HED diets, followed by increased liver fat accumulation, microglia activation in the brain, and circulating levels of inflammatory markers. To our knowledge, this is the first study to present longitudinal and cross-sectional results on effect of long-term consumption of HED diets on all these parameters in a single cohort of animals.

Sex differences in response to short-term high fat diet in mice

BACKGROUND

Consumption of high-fat diet (HF) leads to hyperphagia and increased body weight in male rodents. Female rodents are relatively resistant to hyperphagia and weight gain in response to HF, in part via effects of estrogen that suppresses food intake and increases energy expenditure. However, sex differences in energy expenditure and activity levels with HF challenge have not been systemically described. We hypothesized that, in response to short-term HF feeding, female mice will have a higher energy expenditure and be more resistant to HF-induced hyperphagia than male mice.

METHODS

Six-week-old male and female C57BL/6 J mice were fed either low fat (LF, 10% fat) or moderate HF (45% fat) for 5 weeks, and energy expenditure, activity and meal pattern measured using comprehensive laboratory animal monitoring system (CLAMS).

RESULTS

After 5 weeks, HF-fed male mice had a significant increase in body weight and fat mass, compared with LF-fed male mice. HF-fed female had a significant increase in body weight compared with LF-fed female mice, but there was no significant difference in fat mass. HF-fed male mice had lower energy expenditure compared to HF-fed female mice, likely due in part to reduced physical activity in the light phase. HF-fed male mice also had increased energy intake in the dark phase compared to LF-fed male mice and a reduced response to exogenous cholecystokinin-induced inhibition of food intake. In contrast, there was no difference in energy intake between LF-fed and HF-fed female mice.

CONCLUSIONS

The data show that female mice are generally protected from short-term HF-induced alterations in energy balance, possibly by maintaining higher energy expenditure and an absence of hyperphagia. However, HF-feeding in male mice induced weight and fat mass gain and hyperphagia. These findings suggest that there is a sex difference in the response to short-term HF-feeding in terms of both energy expenditure and control of food intake.

Targeting Janus Kinases and Signal Transducer and Activator of Transcription 3 to Treat Inflammation, Fibrosis, and Cancer: Rationale, Progress, and Caution

Before it was molecularly cloned in 1994, acute-phase response factor or signal transducer and activator of transcription (STAT)3 was the focus of intense research into understanding the mammalian response to injury, particularly the acute-phase response. Although known to be essential for liver production of acute-phase reactant proteins, many of which augment innate immune responses, molecular cloning of acute-phase response factor or STAT3 and the research this enabled helped establish the central function of Janus kinase (JAK) family members in cytokine signaling and identified a multitude of cytokines and peptide hormones, beyond interleukin-6 and its family members, that activate JAKs and STAT3, as well as numerous new programs that their activation drives. Many, like the acute-phase response, are adaptive, whereas several are maladaptive and lead to chronic inflammation and adverse consequences, such as cachexia, fibrosis, organ dysfunction, and cancer. Molecular cloning of STAT3 also enabled the identification of other noncanonical roles for STAT3 in normal physiology, including its contribution to the function of the electron transport chain and oxidative phosphorylation, its basal and stress-related adaptive functions in mitochondria, its function as a scaffold in inflammation-enhanced platelet activation, and its contributions to endothelial permeability and calcium efflux from endoplasmic reticulum. In this review, we will summarize the molecular and cellular biology of JAK/STAT3 signaling and its functions under basal and stress conditions, which are adaptive, and then review maladaptive JAK/STAT3 signaling in animals and humans that lead to disease, as well as recent attempts to modulate them to treat these diseases. In addition, we will discuss how consideration of the noncanonical and stress-related functions of STAT3 cannot be ignored in efforts to target the canonical functions of STAT3, if the goal is to develop drugs that are not only effective but safe. SIGNIFICANCE STATEMENT: Key biological functions of Janus kinase (JAK)/signal transducer and activator of transcription (STAT)3 signaling can be delineated into two broad categories: those essential for normal cell and organ development and those activated in response to stress that are adaptive. Persistent or dysregulated JAK/STAT3 signaling, however, is maladaptive and contributes to many diseases, including diseases characterized by chronic inflammation and fibrosis, and cancer. A comprehensive understanding of JAK/STAT3 signaling in normal development, and in adaptive and maladaptive responses to stress, is essential for the continued development of safe and effective therapies that target this signaling pathway.

Stress-induced modulation of vagal afferents

Vagally dependent gastric functions, including motility, tone, compliance, and emptying rate, play an important role in the regulation of food intake and satiation. Vagal afferent fibers relay sensory information from the stomach, including meal-related information, centrally and initiate co-ordinated autonomic efferent responses that regulate upper gastrointestinal responses. The purpose of this mini-review is to highlight several recent studies which have uncovered the remarkable degree of neuroplasticity within gastric mechanosensitive vagal afferents and the recent study by Li et al, in this issue of Neurogastroenterology and Motility, who show that the mechanosensitivity of gastric vagal afferents is dysregulated in a murine model of chronic stress. The authors demonstrate that both gastric mucosal and tension afferents are hypersensitive following chronic stress, and responses to mucosal stroking and muscle stretch are enhanced significantly. As gastric distension and volumetric signaling is important in satiety signaling and meal termination, this may provide a mechanistic basis for the gastric hypersensitivity associated with stress-associated clinical problems such as functional dyspepsia.

Recent Advances in the Neurobiology of Altered Motivation Following Bariatric Surgery

PURPOSE OF REVIEW

There is compelling evidence in the clinical population that long-term weight loss secondary to bariatric surgery is mitigated by the reemergence of maladaptive feeding behaviors and in some cases new onset substance abuse.

RECENT FINDINGS

A review of the current literature suggests that physical restructuring of the GI tract during WLS alters secretion of feeding peptides and nutrient-sensing mechanisms that directly target the brain's endogenous reward system, the mesolimbic dopamine system. Post-surgical changes in GI physiology augment activation of the mesolimbic system. In some patients, this process may contribute to a reduced appetite for palatable food whereas in others it may support maladaptive motivated behavior for food and chemical drugs. It is concluded that future studies are required to detail the timing and duration of surgical-induced changes in GI-mesolimbic communication to more fully understand this phenomenon.

The Effect of High Fat High Fructose Diet (Modification of AIN-93M) on Nuclear Factor Kappa Beta Expression in the Liver Tissue of Male Sprague Dawley Rats

Metabolic inflammation (low-grade inflammation) remains an etiopathogenic key factor in the development of metabolic syndrome. Nuclear Factor Kappa Beta (NF-κβ) is a transcription regulator of genes having a role in immunity, the inflammatory response which can be associated with obesity-related pathological conditions like nonalcoholic fatty liver (NAFLD). Various stimuli, such as metabolic stress (hyperglycemia, ROS, fat metabolism) and proinflammatory cytokines (TNF-α, IL-6, IL-1β) could activate NF-κβ. This study was aimed to investigate the underlying molecular mechanisms of NAFLD in rats fed a modified AIN-93M HFHF (High Fat High Fructose) diet. The design of this study was experimental post-test only controlled group design. Thirty male Sprague Dawley rats were distributed into 2 treatment groups by a completely randomized design (CRD) technique. The sacrifice was performed after 17 weeks of treatment. NF-κβ expression was assessed by an immunohistochemical method (IRS score). The results showed there were significant differences in feed intake and energy intake between groups P1 and P2 (p = 0,000, p = 0,000). The average NF-κβ expression in the P2 group was significantly higher (p = 0.000) compared to the control group (P1). The correlation test between dietary intake and NF-κβ expression proved that there was a positive correlation between energy, carbohydrate and fat intake on NF-κβ expression (p = 0.001, 0.000, 0.046). However, there was a negative relationship between protein intake and NF-κβ expression (p = 0.000). This study concluded the modified AIN-93M HFHF diet increased NF-κβ expression in the liver tissue of male Sprague Dawley rats.