Gastrointestinal mechanisms of satiation for food

Manipulation of feeding patterns in high fat diet fed rats improves microbiota composition dynamics, inflammation and gut-brain signaling

Chronic consumption of high fat (HF) diets has been shown to increase meal size and meal frequency in rodents, resulting in overeating. Reducing meal frequency and establishing periods of fasting, independently of caloric intake, may improve obesity-associated metabolic disorders. Additionally, diet-driven changes in microbiota composition have been shown to play a critical role in the development and maintenance of metabolic disorders. In this study, we used a pair-feeding paradigm to reduce meal frequency and snacking episodes while maintaining overall intake and body weight in HF fed rats. We hypothesized that manipulation of feeding patterns would improve microbiota composition and metabolic outcomes. Male Wistar rats were placed in three groups consuming either a HF, low fat diet (LF, matched for sugar), or pair-fed HF diet for 7 weeks (n = 11-12/group). Pair-fed animals received the same amount of food consumed by the HF fed group once daily before dark onset (HF-PF). Rats underwent oral glucose tolerance and gut peptide cholecystokinin sensitivity tests. Bacterial DNA was extracted from the feces collected during both dark and light cycles and sequenced via Illumina MiSeq sequencing of the 16S V4 region. Our pair-feeding paradigm reduced meal numbers, especially small meals in the inactive phase, without changing total caloric intake. This shift in feeding patterns reduced relative abundances of obesity-associated bacteria and maintained circadian fluctuations in microbial abundances. These changes were associated with improved gastrointestinal (GI) function, reduced inflammation, and improved glucose tolerance and gut to brain signaling. We concluded from these data that targeting snacking may help improve metabolic outcomes, independently of energy content of the diet and hyperphagia.

Brain Perception of Different Oils on Appetite Regulation: An Anorectic Gene Expression Pattern in the Hypothalamus Dependent on the Vagus Nerve

(1) Background: We examined the effect of the acute administration of olive oil (EVOO), linseed oil (GLO), soybean oil (SO), and palm oil (PO) on gastric motility and appetite in rats. (2) Methods: We assessed food intake, gastric retention (GR), and gene expression in all groups. (3) Results: Both EVOO and GLO were found to enhance the rate of stomach retention, leading to a decrease in hunger. On the other hand, the reduction in food intake caused by SO was accompanied by delayed effects on stomach retention. PO caused an alteration in the mRNA expression of NPY, POMC, and CART. Although PO increased stomach retention after 180 min, it did not affect food intake. It was subsequently verified that the absence of an autonomic reaction did not nullify the influence of EVOO in reducing food consumption. Moreover, in the absence of parasympathetic responses, animals that received PO exhibited a significant decrease in food consumption, probably mediated by lower NPY expression. (4) Conclusions: This study discovered that different oils induce various effects on parameters related to food consumption. Specifically, EVOO reduces food consumption primarily through its impact on the gastrointestinal tract, making it a recommended adjunct for weight loss. Conversely, the intake of PO limits food consumption in the absence of an autonomic reaction, but it is not advised due to its contribution to the development of cardiometabolic disorders.

Transfer with microbiota from lean donors prevents excessive weight gain and restores gut-brain vagal signaling in obese rats maintained on a high fat diet

Background

The collection of microorganisms, mainly bacteria, which live in the gastrointestinal (GI) tract are collectible known as the gut microbiota. GI bacteria play an active role in regulation of the host's immune system and metabolism, as well as certain pathophysiological processes. Diet is the main factor modulating GI microbiota composition and recent studies have shown that high fat (HF) diets induce detrimental changes, known as dysbiosis, in the GI bacterial makeup. HF diet induced microbiota 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 restoring normal microbiota in obesity can improve 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 Sprague-Dawley rats were maintained on regular chow, or 45% HF diet for nine weeks followed by three weeks of microbiota depletion using an antibiotic cocktail. The animals were then divided into four groups (n=10 each): LF - control group on regular chow, LF-LF - chow fed animals that received antibiotics and microbiota from chow fed animals, HF-LF - HF fed animals that received microbiota from chow fed animals, and HF-HF - HF fed animals that received microbiota from HF fed animals. Animals were gavaged with donor microbiota for three consecutive days on week one and once a week thereafter for three more weeks. HF-LF animals received inulin as a prebiotic to aid the establishment of the lean microbiome.

Results

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. We did not observe significant changes in the density of vagal afferents terminating in the brainstem among the groups, however, HF-LF animals displayed an increase in postprandial activation of both primary sensory neurons innervating the GI tract and brainstem secondary neurons.

Conclusions

We concluded from these data that normalizing microbiota composition in obese rats improves gut-brain communication and restores normal feeding patterns which was associated with a reduction in weight gain.

An economon model of drug addiction

The term "economon" (i:'ka.nə.muhn; plural: economa) is introduced here to describe an economic unit composed of two participants engaged in mutually reinforcing operant behavior. Economa are basic building blocks of transactional behavior that aggregate in social networks called economies. In a drug-addiction economon, operant behavior by one participant (the "supplier") provides an addictive drug as a reinforcer to the second participant (a "Person with Substance Use Disorder; PwSUD"). Reciprocal operant behavior by the PwSUD usually provides money as a reinforcer to the supplier. After defining the features of the drug-addiction economon, this article discusses its implications for (1) prevalence and virulence of drug addiction, (2) opportunities for drug-addiction research in general, (3) the "brain-disease model of addiction" in particular, and (4) factors that mitigate harm or promote risk of drug addiction. The economon model is intended to provide a novel perspective on the uniquely human disorder of drug addiction.

Interactive Effect of Dietary Heat-Killed Lactobacillus Plantarum L-137 and Berberine Supplementation on Intestinal Mucosa and Microbiota of Juvenile Black Sea Bream (Acanthopagrus Schlegelii)

To compare the synergistic impact of dietary heat-killed Lactobacillus plantarum and berberine supplementation on intestinal health of juvenile black sea bream, the test fish (5.67 ± 0.05 g) were fed three diets: a basal control diet designated as Con; basal diet supplemented with 400 mg/kg L. plantarum, labelled LP; and basal diet supplemented with 400 mg/kg L. plantarum + 50 mg/k berberine, labelled LPBB. After 56 days of feeding, the control fish had significantly lower intestinal villus height (VH), villus surface area (VSA), and muscularis mucosae (MS) thickness than the rest of the groups (P < 0.05). The LPBB fish had significantly higher VH than the control fish, and wider MS and VSA than the rest of the groups (P < 0.05). Occludin was significantly upregulated in the LPBB fish, and heat shock protein 90 was upregulated in the control fish (P < 0.05). The abundance of Proteobacteria family was significantly higher in the intestinal microbiome of the control and LP fish, the LPBB fish had higher abundance of Cyanobacteria and Spirochaetes, and the LP group had higher Bacteroidetes abundance (P < 0.05). Potentially beneficial Delftia and Brevinema were the significantly abundant genera in the LP and LPBB fish, respectively; potentially pathogenic Elizabethkingia was abundant in the LP fish; and the control fish had higher abundance of potentially pathogenic Burkholderia-Caballeronia-Paraburkholderia (P < 0.05). According to these results, there is possible synergy between L. plantarum and berberine as dietary supplements in fostering healthy intestine for black sea bream than L. plantarum alone.

Meta-Analysis and Systematic Review of Resting-State High-Frequency Heart Rate Variability in Binge-Eating Disorder

Abstract. Binge-eating disorder (BED) is associated with a greater risk for cardiac problems and co-occurring health conditions. Resting-state measures of high-frequency heart rate variability (HF-HRV), which is a physiological proxy of self-regulatory neural functioning, may aid understanding of health risks. We systematically reviewed and meta-analyzed the literature on HF-HRV in individuals with BED and without BED. Six studies were reviewed in the qualitative synthesis, and five studies assessing HRV in individuals with BED ( n = 153) and without BED ( n = 124) were included in the meta-analysis. A non-significant effect size (Hedges’ g = .08, SE = 0.36, 95% CI [−0.62, 0.78]; z = 0.23, p = .82) was found, suggesting no difference in HF-HRV between groups. Age, BMI, and BMI-matched control status were not significant covariates. Synthesizing the five studies with available data, we found no difference in resting-state HF-HRV between individuals with and without BED. There was high heterogeneity in the sample, suggesting potential moderators. We discuss potential mechanisms, methodological and demographic confounds, and future directions for study.

Neural signalling of gut mechanosensation in ingestive and digestive processes

Eating and drinking generate sequential mechanosensory signals along the digestive tract. These signals are communicated to the brain for the timely initiation and regulation of diverse ingestive and digestive processes - ranging from appetite control and tactile perception to gut motility, digestive fluid secretion and defecation - that are vital for the proper intake, breakdown and absorption of nutrients and water. Gut mechanosensation has been investigated for over a century as a common pillar of energy, fluid and gastrointestinal homeostasis, and recent discoveries of specific mechanoreceptors, contributing ion channels and the well-defined circuits underlying gut mechanosensation signalling and function have further expanded our understanding of ingestive and digestive processes at the molecular and cellular levels. In this Review, we discuss our current understanding of the generation of mechanosensory signals from the digestive periphery, the neural afferent pathways that relay these signals to the brain and the neural circuit mechanisms that control ingestive and digestive processes, focusing on the four major digestive tract parts: the oral and pharyngeal cavities, oesophagus, stomach and intestines. We also discuss the clinical implications of gut mechanosensation in ingestive and digestive disorders.

The importance of estradiol for body weight regulation in women

Obesity in women of reproductive age has a number of adverse metabolic effects, including Type II Diabetes (T2D), dyslipidemia, and cardiovascular disease. It is associated with increased menstrual irregularity, ovulatory dysfunction, development of insulin resistance and infertility. In women, estradiol is not only critical for reproductive function, but they also control food intake and energy expenditure. Food intake is known to change during the menstrual cycle in humans. This change in food intake is largely mediated by estradiol, which acts directly upon anorexigenic and orexigenic neurons, largely in the hypothalamus. Estradiol also acts indirectly with peripheral mediators such as glucagon like peptide-1 (GLP-1). Like estradiol, GLP-1 acts on receptors at the hypothalamus. This review describes the physiological and pathophysiological mechanisms governing the actions of estradiol during the menstrual cycle on food intake and energy expenditure and how estradiol acts with other weight-controlling molecules such as GLP-1. GLP-1 analogs have proven to be effective both to manage obesity and T2D in women. This review also highlights the relationship between steroid hormones and women's mental health. It explains how a decline or imbalance in estradiol levels affects insulin sensitivity in the brain. This can cause cerebral insulin resistance, which contributes to the development of conditions such as Parkinson's or Alzheimer's disease. The proper use of both estradiol and GLP-1 analogs can help to manage obesity and preserve an optimal mental health in women by reducing the mechanisms that trigger neurodegenerative disorders.

Female sweet-likers have enhanced cross-modal interoceptive abilities

There are well known phenotypic differences in sweet-liking across individuals, but it remains unknown whether these are related to broader underlying differences in interoceptive abilities (abilities to sense the internal state of the body). Here, healthy women (N = 64) classified as sweet likers (SLs) or sweet dislikers (SDs) completed a bimodal interoception protocol. A heartbeat tracking and a heartbeat discrimination task determined cardiac interoception; both were accompanied by confidence ratings. A water load task, where participants consumed water to satiation and then to maximum fullness was used to assess gastric interoceptive abilities. Motivational state, psychometric characteristics and eating behaviour were also assessed. SLs performed significantly better than SDs on both heartbeat tasks, independently of impulsivity, anxiety, depression, and alexithymia. No differences in metacognitive awareness and subjective interoceptive measures were found. With gastric interoception, SLs were more sensitive to stomach distention, and they ingested less water than SDs to reach satiety when accounting for stomach capacity. SLs also scored higher on mindful and intuitive eating scales and on emotional eating particularly in response to negative stimuli; emotional overeating was fully mediated via interoceptive performance. Overall, our data suggest the SL phenotype may reflect enhanced responsiveness to internal cues more broadly.

Interplay between grain digestion and fibre in relation to gastro-small-intestinal passage rate and feed intake in pigs

PURPOSE

The combined effects of grain digestibility and dietary fibre on digesta passage rate and satiety in humans are poorly understood. Satiety can be increased through gastric distention, reduced gastric emptying rate and when partially digested nutrients reach the terminal ileum to stimulate peptide release through the ileal/colonic brakes to slow the rate of digesta passage. This study determined the effects of grain digestibility and insoluble fibre on mean retention time (MRT) of digesta from mouth-to-ileum, feed intake (FI), starch digestion to the terminal ileum and faecal short chain fatty acids (SCFA) in a pig model.

METHOD

Twelve grain-based [milled sorghum (MS), steam-flaked-sorghum, milled wheat, and steam-flaked-wheat (SFW)] diets with different intrinsic rates of starch digestion, assessed by apparent amylase diffusion coefficient (ADC), and fibre from oat hulls (OH) at 0, 5 and 20% of the diet were fed to ileal-cannulated pigs.

RESULT

MRT was affected by grain-type/processing (P < 0.05) and fibre amount (P < 0.05). An approximate tenfold increase in ADC showed a limited decline in MRT (P = 0.18). OH at 20% increased MRT (P < 0.05) and reduced FI (P < 0.05). Ileal digestibility of starch increased and faecal SCFA concentration decreased with ADC; values for MS being lower (P < 0.001) and higher (P < 0.05), respectively, than for SFW.

CONCLUSIONS

Lower ileal digestibility of starch, higher faecal SCFA concentration and longer MRT of MS than SFW, suggest the ileal/colonic brakes may be operating. FI appeared to decrease with increasing MRT. MRT increased and intake decreased with grain-based foods/feeds that have low starch digestibility and substantial amounts of insoluble fibre.

A hindbrain dopaminergic neural circuit prevents weight gain by reinforcing food satiation

The neural circuitry mechanism that underlies dopaminergic (DA) control of innate feeding behavior is largely uncharacterized. Here, we identified a subpopulation of DA neurons situated in the caudal ventral tegmental area (cVTA) directly innervating DRD1-expressing neurons within the lateral parabrachial nucleus (LPBN). This neural circuit potently suppresses food intake via enhanced satiation response. Notably, this cohort of DAcVTA neurons is activated immediately before the cessation of each feeding bout. Acute inhibition of these DA neurons before bout termination substantially suppresses satiety and prolongs the consummatory feeding. Activation of postsynaptic DRD1LPBN neurons inhibits feeding, whereas genetic deletion of Drd1 within the LPBN causes robust increase in food intake and subsequent weight gain. Furthermore, the DRD1LPBN signaling manifests the central mechanism in methylphenidate-induced hypophagia. In conclusion, our study illuminates a hindbrain DAergic circuit that controls feeding through dynamic regulation in satiety response and meal structure.

Effects of Oro-Sensory Exposure on Satiation and Underlying Neurophysiological Mechanisms-What Do We Know So Far?

The mouth is the first part of the gastrointestinal tract. During mastication sensory signals from the mouth, so-called oro-sensory exposure, elicit physiological signals that affect satiation and food intake. It has been established that a longer duration of oro-sensory exposure leads to earlier satiation. In addition, foods with more intense sweet or salty taste induce earlier satiation compared to foods that are equally palatable, but with lower taste intensity. Oro-sensory exposure to food affects satiation by direct signaling via the brainstem to higher cortical regions involved in taste and reward, including the nucleus accumbens and the insula. There is little evidence that oro-sensory exposure affects satiation indirectly through either hormone responses or gastric signals. Critical brain areas for satiation, such as the brainstem, should be studied more intensively to better understand the neurophysiological mechanisms underlying the process of satiation. Furthermore, it is essential to increase the understanding of how of highly automated eating behaviors, such as oral processing and eating rate, are formed during early childhood. A better understanding of the aforementioned mechanisms provides fundamental insight in relation to strategies to prevent overconsumption and the development of obesity in future generations.

Effect of Obesity on the Expression of Nutrient Receptors and Satiety Hormones in the Human Colon

Background: Receptors located on enteroendocrine cells (EECs) of the colon can detect nutrients in the lumen. These receptors regulate appetite through a variety of mechanisms, including hormonal and neuronal signals. We assessed the effect of obesity on the expression of these G-protein coupled receptors (GPCRs) and hormones at both mRNA and protein level. Methods: qPCR and immunohistochemistry were used to examine colonic tissue from cohorts of patients from the Netherlands (proximal and sigmoid tissue) and the United Kingdom (tissue from across the colon) and patients were grouped by body mass index (BMI) value (BMI < 25 and BMI ≥ 25). Results: The mRNA expression of the hormones/signaling molecules serotonin, glucagon, peptide YY (PYY), CCK and somatostatin were not significantly different between BMI groups. GPR40 mRNA expression was significantly increased in sigmoid colon samples in the BMI ≥ 25 group, but not proximal colon. GPR41, GPR109a, GPR43, GPR120, GPRC6A, and CaSR mRNA expression were unaltered between low and high BMI. At the protein level, serotonin and PYY containing cell numbers were similar in high and low BMI groups. Enterochromaffin cells (EC) showed high degree of co-expression with amino acid sensing receptor, CaSR while co-expression with PYY containing L-cells was limited, regardless of BMI. Conclusions: While expression of medium/long chain fatty acid receptor GPR40 was increased in the sigmoid colon of the high BMI group, expression of other nutrient sensing GPCRs, and expression profiles of EECs involved in peripheral mechanisms of appetite regulation were unchanged. Collectively, these data suggest that in human colonic tissue, EEC and nutrient-sensing receptor expression profiles are not affected despite changes to BMI.

The Satiation Framework: Exploring processes that contribute to satiation

Satiation has been described as a process that leads to the termination of eating and controls meal size. However, studies have shown that the termination of eating can be influenced by multiple behavioral and biological processes over the course of a meal as well as those related to the context in which the meal is consumed. To expand understanding of how individuals experience satiation during a meal, we recently developed the Reasons Individuals Stop Eating Questionnaire (RISE-Q). The development of the RISE-Q revealed five distinct factors reported to contribute to meal termination: Planned Amount, Self-Consciousness, Decreased Food Appeal, Physical Satisfaction, and Decreased Priority of Eating. Thus, we define satiation as a series of dynamic processes that emerge over the course of a meal to promote meal termination. We suggest that each of the factors identified by the RISE-Q represents a distinct process, and illustrate the contribution of each process to meal termination in the Satiation Framework. Within this framework the prominence of each process as a reason to stop eating likely depends on meal context in addition to individual variability. Therefore, we discuss contexts in which different processes may be salient as determinants of meal termination. Expanding the definition of satiation to include several dynamic processes as illustrated in the Satiation Framework will help to stimulate investigation and understanding of the complex nature of meal termination.

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.

Vagotomy increases alcohol intake in female rats in diet dependent manner: Implications for increased alcohol use disorder after roux-en-y gastric bypass surgery

A variety of weight loss surgeries have been developed to fight the obesity epidemic, with Roux-en-Y gastric bypass (RYGB) being one of the most effective and popular procedures. However, the underlying mechanisms behind its efficacy are still not well understood. Furthermore, growing clinical evidence suggests that RYGB may result in increased risk for development of alcohol use disorder (AUD). The vagus nerve is a potentially critical contributor to increased risk of AUD following RYGB due to the potential for significant damage to the vagus during surgery, which has been confirmed in rodent studies. Studies aiming at the mechanisms underlying development of alcohol or substance use disorders following the surgery have exclusively used male rats, despite the majority of RYGB patients being female. Thus, the current study had two objectives: 1) to investigate the effect of RYGB on ethanol (EtOH) intake in female rats using a protocol previously established in male rats, and 2) to test the effect of vagal damage and high fat diet (HFD) on EtOH intake in female rats. In the first study, 22 female rats were maintained on HFD for four weeks and then split into two surgical groups, RYGB (n = 10) and Sham (n = 12). All rats then underwent a two-bottle choice test of increasing EtOH concentrations: 2%, 4%, 6%, 8%. Rats were then forced to abstain from EtOH for two weeks, after which access to 8% EtOH was reinstated. The RYGB female rats significantly increased their intake for low concentrations of EtOH (2% and 4%) and during the reinstatement period for 8%. These results mirror those seen in male rats, and thus, confirms RYGB in female rats as an equally viable model to males. In the second study, 40 female rats were separated into four groups: HFD/Sham, HFD/Vagotomy, normal diet (ND)/Sham, and ND/Vagotomy. All rats then were subjected to the same two-bottle choice test protocol as in the previous study. Rats in the vagotomy condition had significantly greater preference for 2% and 4% EtOH compared with Sham-operated controls. EtOH intake, either in ml or adjusted for body weight, was greater in rats maintained on ND compared with rats maintained on HFD. These data suggest that vagal damage may, at least in part, contribute to increased preference for EtOH. Furthermore, this increase in EtOH preference is counter to the blunting effect of HFD. In conclusion, the data presented here suggest a role for vagal damage in risk of AUD after weight loss surgery.

Gastrointestinal Distension by Pectin-Containing Carbonated Solution Suppresses Food Intake and Enhances Glucose Tolerance via GLP-1 Secretion and Vagal Afferent Activation

Diet-induced gastrointestinal distension is known to evoke satiation and suppress postprandial hyperglycemia; however, the underlying mechanisms remain poorly understood. This study explored how gastrointestinal distension regulates energy homeostasis by using inflating stomach formulation (ISF), the carbonated solution containing pectin that forms stable gel bubbles under acidic condition in the stomach. Here we show that, in mice, oral administration of ISF induced distension of stomach and proximal intestine temporarily, stimulated intestinal glucagon-like peptide-1 (GLP-1) secretion, and activated vagal afferents and brainstem. ISF suppressed food intake and improved glucose tolerance via enhancing insulin sensitivity. The anorexigenic effect was partially inhibited, and the beneficial glycemic effect was blunted by pharmacological GLP-1 receptor blockade and chemical denervation of capsaicin-sensitive sensory nerves. In HFD-fed obese mice showing arrhythmic feeding and obesity, subchronic ISF treatment at the light period (LP) onset for 10 days attenuated LP hyperphagia and visceral fat accumulation. These results demonstrate that gastrointestinal distension by ISF stimulates GLP-1 secretion and the vagal afferent signaling to the brain, thereby regulating feeding behavior and glucose tolerance. Furthermore, subchronic ISF treatment ameliorates HFD-induced visceral obesity. We propose the diet that induces gastrointestinal distension as a novel treatment of hyperphagic obesity and diabetes.

Greater gastric interoception is associated with more positive body image: Evidence from adults in Malaysia and the United Kingdom

Gastric interoception refers to the processing of sensory stimuli originating in the gut. Previous research has found that gastric interoception (measured using a water load task) is associated with drive for thinness in young Western women. However, associations with broader facets of body image and in diverse national groups have not been previously investigated. To address these issues, we asked samples of adults in the United Kingdom (UK; N = 91, women n = 54) and Malaysia (N = 100, women n = 50) to complete a 2-stage water load task (WLT) and measures of positive body image (i.e., body appreciation, functionality appreciation). The results indicated that a greater change in the intensity of self-reported WLT-related sensations was associated with significantly higher body appreciation and functionality appreciation after accounting for gender identity, body mass index, and national group. Behavioural performance on the WLT was significantly associated with body appreciation and functionality appreciation for the Malaysian sample, but not the UK adults, after accounting for gender identity and body mass index. These findings extend previous research by demonstrating that there are significant associations between facets of gastric interoception and previously unexplored facets of body image in both Western and non-Western settings.

The homeostatic dynamics of feeding behaviour identify novel mechanisms of anorectic agents

Better understanding of feeding behaviour will be vital in reducing obesity and metabolic syndrome, but we lack a standard model that captures the complexity of feeding behaviour. We construct an accurate stochastic model of rodent feeding at the bout level in order to perform quantitative behavioural analysis. Analysing the different effects on feeding behaviour of peptide YY3-36 (PYY3-36), lithium chloride, glucagon-like peptide 1 (GLP-1), and leptin shows the precise behavioural changes caused by each anorectic agent. Our analysis demonstrates that the changes in feeding behaviour evoked by the anorectic agents investigated do not mimic the behaviour of well-fed animals and that the intermeal interval is influenced by fullness. We show how robust homeostatic control of feeding thwarts attempts to reduce food intake and how this might be overcome. In silico experiments suggest that introducing a minimum intermeal interval or modulating upper gut emptying can be as effective as anorectic drug administration.

Review: Effects of fibre, grain starch digestion rate and the ileal brake on voluntary feed intake in pigs

Grains rich in starch constitute the primary source of energy for both pigs and humans, but there is incomplete understanding of physiological mechanisms that determine the extent of digestion of grain starch in monogastric animals including pigs and humans. Slow digestion of starch to produce glucose in the small intestine (SI) leads to undigested starch escaping to the large intestine where it is fermented to produce short-chain fatty acids. Glucose generated from starch provides more energy than short-chain fatty acids for normal metabolism and growth in monogastrics. While incomplete digestion of starch leads to underutilised feed in pigs and economic losses, it is desirable in human nutrition to maintain consistent body weight in adults. Undigested nutrients reaching the ileum may trigger the ileal brake, and fermentation of undigested nutrients or fibre in the large intestine triggers the colonic brake. These intestinal brakes reduce the passage rate in an attempt to maximise nutrient utilisation, and lead to increased satiety that may reduce feed intake. The three physiological mechanisms that control grain digestion and feed intake are: (1) gastric emptying rate; (2) interplay of grain digestion and passage rate in the SI controlling the activation of the ileal brake; and (3) fermentation of undigested nutrients or fibre in the large intestine activating the colonic brake. Fibre plays an important role in influencing these mechanisms and the extent of their effects. In this review, an account of the physiological mechanisms controlling the passage rate, feed intake and enzymatic digestion of grains is presented: (1) to evaluate the merits of recently developed methods of grain/starch digestion for application purposes; and (2) to identify opportunities for future research to advance our understanding of how the combination of controlled grain digestion and fibre content can be manipulated to physiologically influence satiety and food intake.

Hindbrain glucoregulatory mechanisms: Critical role of catecholamine neurons in the ventrolateral medulla

Glucose is the required metabolic substrate for the brain. Yet the brain stores very little glucose. Therefore, the brain continuously monitors glucose availability to detect hypoglycemia and to mobilize system-wide responses to protect and restore euglycemia. Catecholamine (CA) neurons in the hindbrain are critical elements of the brain's glucoregulatory mechanisms. They project widely throughout the brain and spinal cord, innervating sites controlling behavioral, endocrine and visceral responses. Hence, CA neurons are capable of triggering a rapid, coordinated and multifaceted response to glucose challenge. This article reviews experimental data that has begun to elucidate the importance of CA neurons for glucoregulation, the functions of specific CA subpopulations in the ventrolateral medulla, and the extended circuitry through which they engage other levels of the nervous system to accomplish their essential glucoregulatory task. Hopefully, this review also suggests the vast amount of work yet to be done in this area and the justification for engaging in that effort.

Correlation between the motility of the proximal antrum and the high-frequency power of heart rate variability in freely moving rats

BACKGROUND

Cardiac vagal tone can be monitored non-invasively via electrocardiogram measurements of the high-frequency power spectrum of heart rate variability (HF-HRV). Vagal inputs to the upper GI tract are cumbersome to measure non-invasively. Although cardiac and GI vagal outputs arise from distinct brainstem nuclei, the nucleus ambiguus, and the dorsal motor nucleus of the vagus, respectively, we aim to test the hypotheses that in freely moving rats HF-HRV power is correlated to proximal antral motility and can be altered by high levels of circulating estrogen and vagal-selective treatments known to affect antral motility.

METHODS

Male and female Sprague-Dawley rats were implanted with a miniaturized strain gauge on the proximal gastric antrum and ECG electrodes to collect simultaneous antral motility and electrocardiogram. After recovery, male rats underwent baseline recordings before and after administration of saline (N = 8), cholecystokinin (CCK; N = 7), ghrelin (N = 6), or food (N = 6). Female rats (N = 6) underwent twice-daily recordings to determine baseline correlations during estrous cycle stages.

KEY RESULTS

There was a significant positive correlation between HF-HRV and proximal antral motility at baseline in males and females with low, but not high, estrogen levels. In male rats, the significant positive correlation was maintained following CCK, but not ghrelin or food administration.

CONCLUSIONS AND INFERENCES

Our data suggest that in rodents, HF-HRV positively correlates to proximal antral motility at baseline conditions in males and low-estrogen females or following interventions, such as CCK, known to affect vagal tone. This correlation is not observed when antral motility is influenced by more complex events.

The Influence of the Gut Microbiome on Host Metabolism Through the Regulation of Gut Hormone Release

The microbial community of the gut conveys significant benefits to host physiology. A clear relationship has now been established between gut bacteria and host metabolism in which microbial-mediated gut hormone release plays an important role. Within the gut lumen, bacteria produce a number of metabolites and contain structural components that act as signaling molecules to a number of cell types within the mucosa. Enteroendocrine cells within the mucosal lining of the gut synthesize and secrete a number of hormones including CCK, PYY, GLP-1, GIP, and 5-HT, which have regulatory roles in key metabolic processes such as insulin sensitivity, glucose tolerance, fat storage, and appetite. Release of these hormones can be influenced by the presence of bacteria and their metabolites within the gut and as such, microbial-mediated gut hormone release is an important component of microbial regulation of host metabolism. Dietary or pharmacological interventions which alter the gut microbiome therefore pose as potential therapeutics for the treatment of human metabolic disorders. This review aims to describe the complex interaction between intestinal microbiota and their metabolites and gut enteroendocrine cells, and highlight how the gut microbiome can influence host metabolism through the regulation of gut hormone release.

PYY(3-36) and exendin-4 reduce food intake and activate neuronal circuits in a synergistic manner in mice

Peptide YY(3-36) ((PYY(3-36)) and glucagon like peptide 1 (GLP-1) in combination reduce food intake and body weight in an additive or synergistic manner in animal models and in humans. Nevertheless, the mechanisms behind are not completely understood. The present study aims to investigate the effect of combining PYY(3-36) and the GLP-1 receptor agonist exendin-4 (Ex4) by examining acute food intake and global neuronal activation as measured by c-fos in C57BL/6 J mice. An additive reduction in food intake was found 1.5 h after s.c dosing with the combination of PYY(3-36) (200 μg/kg) and Ex4 (2.5 μg/kg). This was associated with a synergistic enhancement of c-fos reactivity in central amygdalar nucleus (CeA), rostral part of the mediobasal arcuate nucleus (ARH), supratrigeminal nucleus (SUT), lateral parabrachial nucleus (PB), area postrema (AP) and nucleus tractus solitarius (NTS) compared to vehicle, PYY(3-36) and Ex4 individually dosed mice. The regions activated by Ex4 individually and PYY(3-36) and Ex4 in combination resembled each other, but the combination group had a significantly stronger c-fos response. Twenty-five brain areas were activated by PYY(3-36) and Ex4 in combination compared to vehicle versus nine brain areas by Ex4 individually. No significant increase in c-fos reactivity was found by PYY(3-36) compared to vehicle dosed mice. The neuronal activation of ARH and the AP/NTS to PB to CeA pathway is important for appetite regulation while SUT has not previously been reported in the regulation of energy balance. As PYY(3-36) and Ex4 act on different neurons leading to recruitment of different signalling pathways within and to the brain, an interaction of these pathways may contribute to their additive/synergistic action. Thus, PYY(3-36) boosts the effect of Ex4 possibly by inducing less inhibition of neuronal activity leading to an enhanced neuronal activity induced by Ex4.

The Dose Makes the Poison: Sugar and Obesity in the United States - a Review

Two-thirds of the US population is either overweight or obese. Obesity is one of the major drivers of preventable diseases and health care costs. In the US, current estimates for these costs range from $147 to $210 billion per year. Obesity is a multifactorial disease: genetics, lifestyle choices, metabolism, and diet. Low-fat diets have been suggested as the key to weight management. However, over the past 30 years, the calories from fat in people's diets have gone down, but obesity rates keep climbing. Evidence suggests that diets high in added sugar promote the development of obesity. However, the impact of sugar consumption on weight gain and body fat accumulation remains a controversial topic. Therefore, the aim of this review is to provide basic framework information about the prevalence of obesity and sugar consumption in the US over the last five decades. We also review the process by which sugar is converted to fat and stored in the human body. The relationship between sugar consumption and obesity was analyzed using United States Department of Agriculture (USDA) Sugar and Sweetener Outlook data, and obesity prevalence was analyzed using data from the Centers for Disease Control and Prevention (CDC). The analysis revealed a reduction in sugar consumption concurrent with a slowing down of the annual rate of increase of obesity. However, although the data show that the sugar consumption trend is going in the right direction (declining), the US population still consumes more than 300% of the recommended daily amount of added sugar.

The Influence of the Gut Microbiome on Host Metabolism Through the Regulation of Gut Hormone Release

The microbial community of the gut conveys significant benefits to host physiology. A clear relationship has now been established between gut bacteria and host metabolism in which microbial-mediated gut hormone release plays an important role. Within the gut lumen, bacteria produce a number of metabolites and contain structural components that act as signaling molecules to a number of cell types within the mucosa. Enteroendocrine cells within the mucosal lining of the gut synthesize and secrete a number of hormones including CCK, PYY, GLP-1, GIP, and 5-HT, which have regulatory roles in key metabolic processes such as insulin sensitivity, glucose tolerance, fat storage, and appetite. Release of these hormones can be influenced by the presence of bacteria and their metabolites within the gut and as such, microbial-mediated gut hormone release is an important component of microbial regulation of host metabolism. Dietary or pharmacological interventions which alter the gut microbiome therefore pose as potential therapeutics for the treatment of human metabolic disorders. This review aims to describe the complex interaction between intestinal microbiota and their metabolites and gut enteroendocrine cells, and highlight how the gut microbiome can influence host metabolism through the regulation of gut hormone release.

Gastric Emptying and Dynamic In Vitro Digestion of Drinkable Yogurts: Effect of Viscosity and Composition

Gastric emptying of food is mainly driven by the caloric concentration, the rheological properties of the chyme, and the physical state (liquid/solid) of food once in the stomach. The present work investigated: (1) The effect of the composition and the viscosity of drinkable yogurts on gastric emptying in pigs, and (2) the behavior of yogurts during dynamic in vitro digestion. Three isocaloric liquid yogurts were manufactured: Two enriched in protein and fiber showing either a low (LV) or high (HV) viscosity, one control enriched in sugar and starch (CT). They were labelled with 99mTc-sulfur colloid and given to pigs (n = 11) to determine gastric emptying pattern by gamma scintigraphy. Then dynamic in vitro digestion of the yogurts was done using the parameters of gastric emptying determined in vivo. Gastric emptying half-times were significantly longer for LV than CT, whereas HV exhibited an intermediate behavior. In vitro gastric digestion showed a quick hydrolysis of caseins, whereas whey proteins were more resistant in the stomach particularly for LV and HV. During the intestinal phase, both whey proteins and caseins were almost fully hydrolyzed. Viscosity was shown to affect the behavior of yogurt in the small intestine.

RYGB increases the satiating effect of intrajejunal lipid infusions in female rats

We used a novel rat model to investigate the physiological bases of early satiation after Roux-en-Y gastric bypass surgery (RYGB). Female rats were subjected to RYGB or sham surgery. Chronic infusion catheters were placed in the Roux limb of RYGB rats and the corresponding anatomical locus of the jejuna of sham-RYGB rats. Rats were also ovariectomized and chronically treated with either estradiol (E2; 2 μg each 4th day SC) or the oil vehicle. Testing was begun 10-12 wk after surgery. Intrajejunal lipid infusions (10 min, 4.4 mL, 8.8 kcal) were performed just before test meals of a low-energy artificially sweetened gel diet (0.1 kcal/g) that RYGB rats ingest avidly. Intrajejunal lipid infusions reduced test-meal size more in RYGB rats than sham-operated rats, indicating that, at least after prolonged adaptation to surgery, the satiating actions of lipids acting intra- or post-jejunally are increased by RYGB and that accelerated meal appearance in the intestines after RYGB is not necessary for this effect. The satiating effects of intrajejunal lipid infusions were similar in E2-and oil-treated rats, suggesting that the effect was not dependent on an activational effect of estrogens. In a second experiment, pretreatment with the cholecystokinin A-receptor antagonist devazepide reduced the satiating effect of intrajejunal lipid infusions in E2-treated RYGB rats. Although these data are preliminary due to the smaller numbers of rats than in the first experiment, they suggest that cholecystokinin-mediated jejunal satiation contributes to early satiation after RYGB in ovariectomized rats with peri-ovulatory levels of estradiol. The results of these experiments may be relevant to understanding RYGB outcome in pre- and postmenopausal women.

The Parabrachial Nucleus: CGRP Neurons Function as a General Alarm

The parabrachial nucleus (PBN), which is located in the pons and is dissected by one of the major cerebellar output tracks, is known to relay sensory information (visceral malaise, taste, temperature, pain, itch) to forebrain structures including the thalamus, hypothalamus, and extended amygdala. The availability of mouse lines expressing Cre recombinase selectively in subsets of PBN neurons and viruses for Cre-dependent gene expression is beginning to reveal the connectivity and functions of PBN component neurons. This review focuses on PBN neurons expressing calcitonin gene-related peptide (CGRPPBN) that play a major role in regulating appetite and transmitting real or potential threat signals to the extended amygdala. The functions of other specific PBN neuronal populations are also discussed. This review aims to encourage investigation of the numerous unanswered questions that are becoming accessible.

Signalling from the periphery to the brain that regulates energy homeostasis

The CNS regulates body weight; however, we still lack a clear understanding of what drives decisions about when, how much and what to eat. A vast array of peripheral signals provides information to the CNS regarding fluctuations in energy status. The CNS then integrates this information to influence acute feeding behaviour and long-term energy homeostasis. Previous paradigms have delegated the control of long-term energy homeostasis to the hypothalamus and short-term changes in feeding behaviour to the hindbrain. However, recent studies have identified target hindbrain neurocircuitry that integrates the orchestration of individual bouts of ingestion with the long-term regulation of energy balance.

Encoding of danger by parabrachial CGRP neurons

Animals must respond to various threats to survive. Neurons that express calcitonin gene-related peptide (CGRP) in the parabrachial nucleus (PBN) relay sensory signals that contribute to satiation and pain-induced fear behavior, but it is unknown how they encode these distinct processes. By recording calcium transients in vivo from individual CGRP^PBN neurons, we reveal that most neurons are activated by noxious cutaneous (shock, heat, itch) and visceral stimuli (lipopolysaccharide). These same neurons are inhibited during feeding, but become activated during satiation, consistent with evidence that CGRP^PBN neurons prevent overeating. CGRP^PBN neurons are also activated during consumption of novel food or by an auditory cue that was previously paired with electrical foot shocks. Correspondingly, silencing CGRP^PBN neurons attenuates expression of food neophobia and conditioned fear responses. Therefore, in addition to transducing primary sensory danger signals, CGRP^PBN neurons promote affective-behavioral states that limit harm in response to potential threats.

Subdiaphragmatic Vagotomy With Pyloroplasty Ameliorates the Obesity Caused by Genetic Deletion of the Melanocortin 4 Receptor in the Mouse

Background/Objectives: We tested the hypothesis that abolishing vagal nerve activity will reverse the obesity phenotype of melanocortin 4 receptor knockout mice (Mc4r^−/−).

Subjects/Methods: In two separate studies, we examined the efficacy of bilateral subdiaphragmatic vagotomy (SDV) with pyloroplasty in the prevention and treatment of obesity in Mc4r^−/− mice.

Results: In the first study, SDV prevented >20% increase in body weight (BW) associated with this genotype. This was correlated with a transient reduction in overall food intake (FI) in the preventative arm of the study. Initially, SDV mice had reduced weekly FI; however, FI normalized to that of controls and baseline FI within the 8-week study period. In the second study, the severe obesity that is characteristic of the adult Mc4r^−/− genotype was significantly improved by SDV with a magnitude of 30% loss in excess BW over a 4-week period. Consistent with the first preventative study, within the treatment arm, SDV mice also demonstrated a transient reduction in FI relative to control and baseline levels that normalized over subsequent weeks. In addition to the accompanying loss in weight, mice subjected to SDV showed a decrease in respiratory exchange ratio (RER), and an increase in locomotor activity (LA). Analysis of the white fat-pad deposits of these mice showed that they were significantly less than the control groups.

Conclusions: Altogether, our data demonstrates that SDV both prevents gain in BW and causes weight loss in severely obese Mc4r^−/− mice. Moreover, it suggests that an important aspect of weight reduction for this type of monogenic obesity involves loss of signaling in vagal motor neurons.

Influence of Cholecystokinin-8 on Compound Nerve Action Potentials from Ventral Gastric Vagus in Rats

OBJECTIVE

Vagus Nerve Stimulation (VNS) has shown great promise as a potential therapy for a number of conditions, such as epilepsy, depression and for Neurometabolic Therapies, especially for treating obesity. The objective of this study was to characterize the left ventral subdiaphragmatic gastric trunk of vagus nerve (SubDiaGVN) and to analyze the influence of intravenous injection of gut hormone cholecystokinin octapeptide (CCK-8) on compound nerve action potential (CNAP) observed on the same branch, with the aim of understanding the impact of hormones on VNS and incorporating the methods and results into closed loop implant design.

METHODS

The cervical region of the left vagus nerve (CerVN) of male Wistar rats was stimulated with electric current and the elicited CNAPs were recorded on the SubDiaGVN under four different conditions: Control (no injection), Saline, CCK1 (100[Formula: see text]pmol/kg) and CCK2 (1000[Formula: see text]pmol/kg) injections.

RESULTS

We identified the presence of A[Formula: see text], B, C1, C2, C3 and C4 fibers with their respective velocity ranges. Intravenous administration of CCK in vivo results in selective, statistically significant reduction of CNAP components originating from A and B fibers, but with no discernible effect on the C fibers in [Formula: see text] animals. The affected CNAP components exhibit statistically significant ([Formula: see text] and [Formula: see text]) higher normalized stimulation thresholds.

CONCLUSION

This approach of characterizing the vagus nerve can be used in closed loop systems to determine when to initiate VNS and also to tune the stimulation dose, which is patient-specific and changes over time.

Comparison between male and female rats in a model of self-administration of a chocolate-flavored beverage: Behavioral and neurochemical studies

The existence of sex differences was studied in a rat model of operant self-administration of a chocolate-flavored beverage (CFB), which possesses strong reinforcing properties and is avidly consumed by rats. Whether these differences occurred concomitantly to changes in extracellular dopamine in the dialysate obtained from the nucleus accumbens, was assessed by intracerebral microdialysis. Male, ovariectomized and intact female rats showed similar self-administration profiles, with minor differences in both acquisition and maintenance phases. Intact females self-administered larger amounts of CFB, when expressed per body weight, than males and ovariectomized females, in spite of similar values of lever-responding, latency to the first lever-response and consumption efficiency (a measure of rat's licking effectiveness) in males, ovariectomized and intact females and no difference in breakpoint value and number of lever-responses emerged when males, ovariectomized and intact females were exposed to a progressive ratio schedule of reinforcement. Intracerebral microdialysis revealed a slight but significant increase in dopamine activity in the shell of the nucleus accumbens of male rats when compared to intact female rats during CFB self-administration. The above differences may be caused by the hormonal (mainly estradiol) fluctuations that occur during the estrus cycle in intact females. Accordingly, in intact females CFB self-administration and dopamine activity were found to fluctuate across the estrus cycle, with lower parameters of CFB self-administration and lower dopamine activity in the Proestrus and Estrus phases vs. the Metestrus and Diestrus phases of the cycle.

Central and peripheral control of food intake

The maintenance of the body weight at a stable level is a major determinant in keeping the higher animals and mammals survive. Th e body weight depends on the balance between the energy intake and energy expenditure. Increased food intake over the energy expenditure of prolonged time period results in an obesity. Th e obesity has become an important worldwide health problem, even at low levels. The obesity has an evil effect on the health and is associated with a shorter life expectancy. A complex of central and peripheral physiological signals is involved in the control of the food intake. Centrally, the food intake is controlled by the hypothalamus, the brainstem, and endocannabinoids and peripherally by the satiety and adiposity signals. Comprehension of the signals that control food intake and energy balance may open a new therapeutic approaches directed against the obesity and its associated complications, as is the insulin resistance and others. In conclusion, the present review summarizes the current knowledge about the complex system of the peripheral and central regulatory mechanisms of food intake and their potential therapeutic implications in the treatment of obesity.

Medical devices for the treatment of obesity

Obesity is a major public health concern that leads to numerous metabolic, mechanical and psychological complications. Although lifestyle interventions are the cornerstone of obesity management, subsequent physiological neurohormonal adaptations limit weight loss, strongly favour weight regain and counteract sustained weight loss. A range of effective therapies are therefore needed to manage this chronic relapsing disease. Bariatric surgery delivers substantial, durable weight loss but limited access to care, perceived high risks and costs restrict uptake. Medical devices are uniquely positioned to bridge the gap between more conservative lifestyle intervention and weight-loss pharmacotherapy and more disruptive bariatric surgery. In this Review, we examine the range of gastrointestinal medical devices that are available in clinical practice to treat obesity, as well as those that are in advanced stages of development. We focus on the mechanisms of action as well as the efficacy and safety profiles of these devices. Many of these devices are placed endoscopically, which provides gastroenterologists with exciting opportunities for treatment.

Scientific familial lessons in ingestive behavior research: 2016 Alan N. Epstein research award

While energy balance is under the control of the central nervous system (CNS), a major source of neural regulation for the behavioral, physiological and endocrine processes governing energy balance originates in the periphery. Indeed, the organs of the gastrointestinal (GI) tract, supporting organs of the peritoneal cavity and adipose tissue are the source of numerous neurotransmitter and neuroendocrine signals released from non-neuronal peripheral tissue that signal in a paracrine and endocrine fashion to regulate the physiological and behavioral processes that affect energy balance. Given the ever increasing appreciation that chronic hyperphagia of highly-palatable/rewarding food is a major contributing factor to the obesity epidemic, it is not surprising that the field has increased research efforts focusing on understanding what role peripherally-derived neuroendocrine signals play in modulating food reward and motivated behaviors. Research throughout my career has focused on understanding gut-to-brain communication of relevance to energy balance control. Through very fortuitous opportunities and amazing collaborations, my research program has also expanded widely to include analyses of multiple GI-, pancreatic- and adipose tissue-derived anorectic signals involved in food intake and energy balance control, as well as analyses of higher-order determinants of food reward, nausea, aversion and maladaptive motivated behaviors. I am honored to be the recipient of the 2016 Alan N. Epstein Research Award from the Society for the Study of Ingestive Behavior, and express much appreciation for the amazing collaborations I have had with my mentors, colleagues and trainees.

Energy-dense diet triggers changes in gut microbiota, reorganization of gut‑brain vagal communication and increases body fat accumulation

Obesity is associated with consumption of energy-dense diets and development of systemic inflammation. Gut microbiota play a role in energy harvest and inflammation and can influence the change from lean to obese phenotypes. The nucleus of the solitary tract (NTS) is a brain target for gastrointestinal signals modulating satiety and alterations in gut-brain vagal pathway may promote overeating and obesity. Therefore, we tested the hypothesis that high-fat diet‑induced changes in gut microbiota alter vagal gut-brain communication associated with increased body fat accumulation. Sprague-Dawley rats consumed a low energy‑dense rodent diet (LFD; 3.1 kcal/g) or high energy‑dense diet (HFD, 5.24 kcal/g). Minocycline was used to manipulate gut microbiota composition. 16S Sequencing was used to determine microbiota composition. Immunofluorescence against IB4 and Iba1 was used to determine NTS reorganization and microglia activation. Nodose ganglia from LFD rats were isolated and co-cultured with different bacteria strains to determine neurotoxicity. HFD altered gut microbiota with increases in Firmicutes/Bacteriodetes ratio and in pro-inflammatory Proteobacteria proliferation. HFD triggered reorganization of vagal afferents and microglia activation in the NTS, associated with weight gain. Minocycline-treated HFD rats exhibited microbiota profile comparable to LFD animals. Minocycline suppressed HFD‑induced reorganization of vagal afferents and microglia activation in the NTS, and reduced body fat accumulation. Proteobacteria isolated from cecum of HFD rats were toxic to vagal afferent neurons in culture. Our findings show that diet‑induced shift in gut microbiome may disrupt vagal gut‑brain communication resulting in microglia activation and increased body fat accumulation.

Effects of dietary fibers with high water-binding capacity and swelling capacity on gastrointestinal functions, food intake and body weight in male rats

Objective: The aim of this study was to investigate the effects of supplementation of dietary soluble fibers with high water-binding capacity (WBC) and swelling capacity (SC) on gastrointestinal tract mass, physicochemical properties of digesta, gastrointestinal mean retention time (MRT), body weight, and food intake in male rats. Methods: Thirty-two male Sprague-Dawley rats were randomized to four equal groups and fed the control diet or diet containing 2% konjac flour (KF), pregelatinized waxy maize starch plus guar gum (PWMS+GG), andPWMS plus xanthan gum (PWMS+XG) for three weeks. Results: WBC and SC of diets followed the order of PWMS+GG > KF > PWMS + XG > control. PWMS+GG and KF groups had a lower average daily food intake than the control group, but all the groups showed no difference in final body weightand the weight gain rate. The high WBC and SC of the PWMS+GG and KF groupsled to an increase of WBC and SC in the stomach digesta, and a gain of the cecal digesta weight, due to increased cecal moisture content. Conclusion: The inclusion of the novel fiber, PWMS+GG, in the diet of male rats appears to facilitate the modulation of WBC and SC of stomach digesta and the reduction of food intake.

Estradiol is a critical regulator of food-reward behavior

Food intake is reduced by estrogenic hormones, levels of which vary throughout life and fluctuate throughout the ovarian cycle in females. However, estrogens have also been shown to increase reward derived from drugs of abuse, where motivational properties of drugs and progression to addiction are potentiated by estrogens. Whether reward derived from food, and specifically motivational properties of food, are altered by estrogens remains unknown. Here we investigated the effect of the estrous cycle on food reward behavior and show estrous cycle dictated variability in food motivation, measured by progressive ratio operant conditioning, in female rats. Reward behavior was lowest on days associated with high estrogen signaling. We therefore also examined the actions of subcutaneously administered β-estradiol on food reward and found that β-estradiol reduced food reward behavior. The ventral tegmental area (VTA) is a crucial node of the neurocircuitry underlying motivated behavior and estrogen receptors are expressed in this nucleus. Thus, we examined whether the effects of estrogens on reward were exerted directly at the level of the VTA. Intra-VTA microinjection of β-estradiol led to a significant reduction in food-motivated behavior. Interestingly, this effect was not accompanied by a reduction in chow intake or body weight, nor did it alter locomotor activity. Importantly, removal of the ovaries produced a potent and lasting elevation in food reward and food-seeking behavior, suggesting that ovarian sex steroids are critical for maintenance of normal food reward behavior. These data reveal a novel role for estrogens in the control of food reward behavior.​.

Satiety and memory enhancing effects of a high-protein meal depend on the source of protein

OBJECTIVE

High- protein diets have become increasingly popular with various touted benefits. However, the extent to which protein quantity and source affects cognitive functioning through altering postprandial amino acid profiles has not been investigated. Further, whether all protein sources are similarly anorexigenic is uncertain. The objective of this study was to determine the influence of protein level and source on Barnes maze performance, satiety and plasma amino acid levels in male Sprague-Dawley rats.

METHODS

Rats were entrained to a meal-feeding schedule consisting of a 30 minutes meal, equivalent to 20% of average daily intake, one hour into the dark phase then ad libitum access to food for 5 h. On test days, rats received one of three isocaloric diets as their first meal, hereafter referred to as Egg White (EW), Wheat Gluten (WG), or Basal, and then were measured for cognitive performance, feeding behavior, or plasma amino acid levels via jugular catheter. Percentage energy from protein was 35% for both EW and WG and 20% for Basal with equal amounts provided by EW and WG proteins.

RESULTS

Rats provided EW performed similarly to Basal on the Barnes maze, whereas WG performed worse. EW increased satiety, whereas WG reduced satiety relative to Basal. Both EW and WG increased postprandial concentrations of large neutral and branched chain amino acids relative to Basal, but in EW, concentrations were slower to peak, and peaked to a higher level than WG.

DISCUSSION

Results demonstrate the importance of protein source for cognition and satiety enhancing effects of a high-protein meal.

Reassessing wanting and liking in the study of mesolimbic influence on food intake

Humans and animals such as rats and mice tend to overconsume calorie-dense foods, a phenomenon that likely contributes to obesity. One often-advanced explanation for why we preferentially consume sweet and fatty foods is that they are more "rewarding" than low-calorie foods. "Reward" has been subdivided into three interdependent psychological processes: hedonia (liking a food), reinforcement (formation of associations among stimuli, actions, and/or the food), and motivation (wanting the food). Research into these processes has focused on the mesolimbic system, which comprises both dopamine neurons in the ventral tegmental area and neurons in their major projection target, the nucleus accumbens. The mesolimbic system and closely connected structures are commonly referred to as the brain's "reward circuit." Implicit in this title is the assumption that "rewarding" experiences are generally the result of activity in this circuit. In this review, I argue that food intake and the preference for calorie-dense foods can be explained without reference to subjective emotions. Furthermore, the contribution of mesolimbic dopamine to food intake and preference may not be a general one of promoting or coordinating behaviors that result in the most reward or caloric intake but may instead be limited to the facilitation of a specific form of neural computation that results in conditioned approach behavior. Studies on the neural mechanisms of caloric intake regulation must address how sensory information about calorie intake affects not just the mesolimbic system but also many other forms of computation that govern other types of food-seeking and food-oriented behaviors.

Astrocytes Regulate GLP-1 Receptor-Mediated Effects on Energy Balance

Astrocytes are well established modulators of extracellular glutamate, but their direct influence on energy balance-relevant behaviors is largely understudied. As the anorectic effects of glucagon-like peptide-1 receptor (GLP-1R) agonists are partly mediated by central modulation of glutamatergic signaling, we tested the hypothesis that astrocytic GLP-1R signaling regulates energy balance in rats. Central or peripheral administration of a fluorophore-labeled GLP-1R agonist, exendin-4, localizes within astrocytes and neurons in the nucleus tractus solitarius (NTS), a hindbrain nucleus critical for energy balance control. This effect is mediated by GLP-1R, as the uptake of systemically administered fluorophore-tagged exendin-4 was blocked by central pretreatment with the competitive GLP-1R antagonist exendin-(9-39). Ex vivo analyses show prolonged exendin-4-induced activation (live cell calcium signaling) of NTS astrocytes and neurons; these effects are also attenuated by exendin-(9-39), indicating mediation by the GLP-1R. In vitro analyses show that the application of GLP-1R agonists increases cAMP levels in astrocytes. Immunohistochemical analyses reveal that endogenous GLP-1 axons form close synaptic apposition with NTS astrocytes. Finally, pharmacological inhibition of NTS astrocytes attenuates the anorectic and body weight-suppressive effects of intra-NTS GLP-1R activation. Collectively, data demonstrate a role for NTS astrocytic GLP-1R signaling in energy balance control.

SIGNIFICANCE STATEMENT

Glucagon-like peptide-1 receptor (GLP-1R) agonists reduce food intake and are approved by the Food and Drug Administration for the treatment of obesity, but the cellular mechanisms underlying the anorectic effects of GLP-1 require further investigation. Astrocytes represent a major cellular population in the CNS that regulates neurotransmission, yet the role of astrocytes in mediating energy balance is largely unstudied. The current data provide novel evidence that astrocytes within the NTS are relevant for energy balance control by GLP-1 signaling. Here, we report that GLP-1R agonists activate and internalize within NTS astrocytes, while behavioral data suggest the pharmacological relevance of NTS astrocytic GLP-1R activation for food intake and body weight. These findings support a previously unknown role for CNS astrocytes in energy balance control by GLP-1 signaling.