Prey consumption does not restore hydration state but mitigates the energetic costs of water deprivation in an insectivorous lizard.

To cope with limited availability of drinking water in their environment, terrestrial animals have developed numerous behavioral and physiological strategies including maintaining an optimal hydration state through dietary water intake. Recent studies performed in snakes, which are generalist carnivorous reptiles, suggest that the benefits of dietary water intake are negated by hydric costs of digestion. Most lizards are generalist insectivores that can shift their prey types, but firm experimental demonstration of dietary water intake is currently missing in these organisms. Here, we performed an experimental study in the common lizard Zootoca vivipara, a keystone mesopredator from temperate climates exhibiting a great diversity of prey in its mesic habitats, in order to investigate the effects of food consumption and prey type on physiological responses to water deprivation. Our results indicate that common lizards cannot improve their hydration state through prey consumption, irrespective of prey type, suggesting that they are primarily dependent upon drinking water. Yet, high-quality prey consumption reduced the energetic costs of water deprivation, potentially helping lizards to conserve a better body condition during periods of limited water availability. These findings have important implications for understanding the physiological responses of ectotherms to water stress, and highlight the complex interactions between hydration status, energy metabolism and feeding behavior in insectivorous lizards.

Regulation of feeding and energy homeostasis by clock-mediated Gart in Drosophila.

Feeding behavior is essential for growth and survival of animals; however, relatively little is known about its intrinsic mechanisms. Here, we demonstrate that Gart is expressed in the glia, fat body, and gut and positively regulates feeding behavior via cooperation and coordination. Gart in the gut is crucial for maintaining endogenous feeding rhythms and food intake, while Gart in the glia and fat body regulates energy homeostasis between synthesis and metabolism. These roles of Gart further impact Drosophila lifespan. Importantly, Gart expression is directly regulated by the CLOCK/CYCLE heterodimer via canonical E-box, in which the CLOCKs (CLKs) in the glia, fat body, and gut positively regulate Gart of peripheral tissues, while the core CLK in brain negatively controls Gart of peripheral tissues. This study provides insight into the complex and subtle regulatory mechanisms of feeding and lifespan extension in animals.

Manduca sexta caterpillars parasitized by the wasp Cotesia congregata stop chewing despite an intact motor system.

The parasitic wasp Cotesia congregata suppresses feeding in its host, the caterpillar Manduca sexta, during specific periods of wasp development. We examined both feeding behaviour and the neurophysiology of the mandibular closer muscle in parasitized and unparasitized control M. sexta to determine how the wasp may accomplish this. To test whether the wasps activated a pre-existing host mechanism for feeding cessation, we examined the microstructure of feeding behaviour in caterpillars that stopped feeding due to illness-induced anorexia or an impending moult. These microstructures were compared with that shown by parasitized caterpillars. While there were overall differences between parasitized and unparasitized caterpillars, the groups showed similar progression in feeding microstructure as feeding ended, suggesting a common pattern for terminating a meal. Parasitized caterpillars also consumed less leaf area in 100 bites than control caterpillars at around the same time their feeding microstructure changed. The decline in food consumption was accompanied by fewer spikes per burst and shorter burst durations in chewing muscle electromyograms. Similar extracellular results were obtained from the motorneuron of the mandibular closer muscle. However, chewing was dramatically re-activated in non-feeding parasitized caterpillars if the connectives posterior to the suboesophageal ganglion were severed. The same result was observed in unparasitized caterpillars given the same treatment. Our results suggest that the reduced feeding in parasitized caterpillars is not due to damage to the central pattern generator (CPG) for chewing, motor nerves or chewing muscles, but is more likely to be due to a suppression of chewing CPG activity by ascending or descending inputs.

Xiphoid nucleus of the midline thalamus controls cold-induced food seeking.

Maintaining body temperature is calorically expensive for endothermic animals1. Mammals eat more in the cold to compensate for energy expenditure2, but the neural mechanism underlying this coupling is not well understood. Through behavioural and metabolic analyses, we found that mice dynamically switch between energy-conservation and food-seeking states in the cold, the latter of which are primarily driven by energy expenditure rather than the sensation of cold. To identify the neural mechanisms underlying cold-induced food seeking, we used whole-brain c-Fos mapping and found that the xiphoid (Xi), a small nucleus in the midline thalamus, was selectively activated by prolonged cold associated with elevated energy expenditure but not with acute cold exposure. In vivo calcium imaging showed that Xi activity correlates with food-seeking episodes under cold conditions. Using activity-dependent viral strategies, we found that optogenetic and chemogenetic stimulation of cold-activated Xi neurons selectively recapitulated food seeking under cold conditions whereas their inhibition suppressed it. Mechanistically, Xi encodes a context-dependent valence switch that promotes food-seeking behaviours under cold but not warm conditions. Furthermore, these behaviours are mediated by a Xi-to-nucleus accumbens projection. Our results establish Xi as a key region in the control of cold-induced feeding, which is an important mechanism in the maintenance of energy homeostasis in endothermic animals.

Contextualizing the Neural Vulnerabilities Model of Obesity.

In recent years, investigators have focused on neural vulnerability factors that increase the risk of unhealthy weight gain, which has provided a useful organizing structure for obesity neuroscience research. However, this framework, and much of the research it has informed, has given limited attention to contextual factors that may interact with key vulnerabilities to impact eating behaviors and weight gain. To fill this gap, we propose a Contextualized Neural Vulnerabilities Model of Obesity, extending the existing theory to more intentionally incorporate contextual factors that are hypothesized to interact with neural vulnerabilities in shaping eating behaviors and weight trajectories. We begin by providing an overview of the Neural Vulnerabilities Model of Obesity, and briefly review supporting evidence. Next, we suggest opportunities to add contextual considerations to the model, including incorporating environmental and developmental context, emphasizing how contextual factors may interact with neural vulnerabilities to impact eating and weight. We then synthesize earlier models and new extensions to describe a Contextualized Neural Vulnerabilities Model of Obesity with three interacting components-food reward sensitivity, top-down regulation, and environmental factors-all within a developmental framework that highlights adolescence as a key period. Finally, we propose critical research questions arising from the framework, as well as opportunities to inform novel interventions.

Behavioural susceptibility theory: the role of appetite in genetic susceptibility to obesity in early life.

Excess weight gained during the early years and, in particular, rapid weight gain in the first 2 years of life, are a major risk factors for adult obesity. The growing consensus is that childhood obesity develops from a complex interaction between genetic susceptibility and exposure to an 'obesogenic' environment. Behavioural susceptibility theory (BST) was developed to explain the nature of this gene-environment interaction, and why the 'obesogenic' environment does not affect all children equally. It hypothesizes that inherited variation in appetite, which is present from birth, determines why some infants and children overeat, and others do not, in response to environmental opportunity. That is, those who inherit genetic variants promoting an avid appetite are vulnerable to overeating and developing obesity, while those who are genetically predisposed to have a smaller appetite and lower interest in food are protected from obesity-or even at risk of being underweight. We review the breadth of research to-date that has contributed to the evidence base for BST, focusing on early life, and discuss implications and future directions for research and theory. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

Zebrafish larvae use stimulus intensity and contrast to estimate distance to prey.

The ability to determine the distance to objects is an important feature of most visual systems, but little is known about the neuronal mechanisms for distance estimation. Larval zebrafish execute different visual behaviors depending on distance; at medium distances, they converge their eyes and approach, but when the prey is close enough, they execute a strike and suck the prey into their mouths. To study distance estimation, we developed a head-fixed strike assay. We found that we could evoke strike behavior in head-fixed larvae and quantify head movements to classify the behavior as a strike. Strikes were dependent on distance to prey, allowing us to use them to study distance estimation. Light intensity is rapidly attenuated as it travels through water, so we hypothesized that larvae could use intensity as a distance cue. We found that increasing stimulus intensity could cause larvae to strike at prey that would normally be out of range, and decreasing the intensity could lower the strike rate even for very proximal stimuli. In addition, stimulus contrast is a key parameter, and this could allow larvae to estimate distance over the range of natural illumination. Finally, we presented prey in the binocular vs. monocular visual field and found that monocular prey did evoke strikes, although the binocular input produced more. These results suggest that strike behavior is optimally evoked by bright UV dots in the binocular zone with minimal UV background light and provide a foundation to study the neuronal mechanisms of distance estimation.

Ontogenetic changes in bite force and gape in tufted capuchins.

Bite force and gape are two important performance metrics of the feeding system, and these metrics are inversely related for a given muscle size because of fundamental constraints in sarcomere length-tension relationships. How these competing performance metrics change in developing primates is largely unknown. Here, we quantified in vivo bite forces and gapes across ontogeny and examined these data in relation to body mass and cranial measurements in captive tufted capuchins, Sapajus spp. Bite force and gape were also compared across geometric and mechanical properties of mechanically challenging foods to investigate relationships between bite force, gape and food accessibility (defined here as the ability to breach shelled nuts). Bite forces at a range of gapes and feeding behavioral data were collected from a cross-sectional ontogenetic series of 20 captive and semi-wild tufted capuchins at the Núcleo de Procriação de Macacos-Prego Research Center in Araçatuba, Brazil. These data were paired with body mass, photogrammetric measures of jaw length and facial width, and food geometric and material properties. Tufted capuchins with larger body masses had absolutely higher in vivo bite forces and gapes, and animals with wider faces had absolutely higher bite forces. Bite forces and gapes were significantly smaller in juveniles compared with subadults and adults. These are the first primate data to empirically demonstrate the gapes at which maximum active bite force is generated and to demonstrate relationships to food accessibility. These data advance our understanding of how primates meet the changing performance demands of the feeding system during development.

Patients' Pre and Post-Bariatric Surgery Experience of Dieting Behaviours: Implications for Early Intervention.

PURPOSE: Bariatric surgery works, in part, by surgically changing signals of hunger and satiety to achieve weight loss. Not all patients experience optimal outcomes. One potential explanation is that post-surgery dieting may subvert the ability to identify physiological cues of hunger and fullness. Dieting behaviours (e.g. restriction/cognitive restraint) are correlated with disordered eating, and disordered eating implicated in poor outcomes. This study examines the experience of dieting after bariatric surgery. METHOD: Seventeen adult participants who had undertaken bariatric surgery and residing in Australia participated in semi-structured interviews. Surgeries occurred in 2021 (n = 8), 2020 (n = 4), 2019 (n = 2), and one participant each had surgery in 2014, 2009, and 2004. Thematic analysis elicited themes related to post-operative dieting. RESULTS: All participants reported chronic pre-surgery dieting. Lifestyle change was the overarching post-surgical theme comprising (i) flexibility (e.g. allowing food, intuitive eating), and (ii) control, comprising surgery control (e.g. set portions, surgery instilled control) and dieting control (e.g. discipline, restriction/restraint). Descriptions of lifestyle change often mirrored pre-surgery descriptions of dieting. CONCLUSION: Post-surgery lifestyle change appears to encompass a tension between flexible/adaptive approaches to eating and the need to maintain control. Control may emerge as practices that mirror pre-surgery dieting with the potential to interfere with adaptive eating behaviours or promote disordered eating. Dieting behaviours may be a precursor to the development of disordered eating. Health care practitioners should regularly assess dieting behaviour post-surgery to enable early intervention where warranted. Future research should consider how post-surgery re-emerging dieting may be identified and measured to aid in intervention.

Central Regulation of Eating Behaviors in Humans: Evidence from Functional Neuroimaging Studies.

Neuroimaging has great potential to provide insight into the neural response to food stimuli. Remarkable advances have been made in understanding the neural activity underlying food perception, not only in normal eating but also in obesity, eating disorders, and disorders of gut-brain interaction in recent decades. In addition to the abnormal brain function in patients with eating disorders compared to healthy controls, new therapies, such as neurofeedback and neurostimulation techniques, have been developed that target the malfunctioning brain regions in patients with eating disorders based on the results of neuroimaging studies. In this review, we present an overview of early and more recent research on the central processing and regulation of eating behavior in healthy and patient populations. In order to better understand the relationship between the gut and the brain as well as the neural mechanisms underlying abnormal ingestive behaviors, we also provide suggestions for future directions to enhance our current methods used in food-related neuroimaging studies.

Behavioral dissection of hunger states in Drosophila.

Hunger is a motivational drive that promotes feeding, and it can be generated by the physiological need to consume nutrients as well as the hedonic properties of food. Brain circuits and mechanisms that regulate feeding have been described, but which of these contribute to the generation of motive forces that drive feeding is unclear. Here, we describe our first efforts at behaviorally and neuronally distinguishing hedonic from homeostatic hunger states in Drosophila melanogaster and propose that this system can be used as a model to dissect the molecular mechanisms that underlie feeding motivation. We visually identify and quantify behaviors exhibited by hungry flies and find that increased feeding duration is a behavioral signature of hedonic feeding motivation. Using a genetically encoded marker of neuronal activity, we find that the mushroom body (MB) lobes are activated by hedonic food environments, and we use optogenetic inhibition to implicate a dopaminergic neuron cluster (protocerebral anterior medial [PAM]) to α'/ß' MB circuit in hedonic feeding motivation. The identification of discrete hunger states in flies and the development of behavioral assays to measure them offers a framework to begin dissecting the molecular and circuit mechanisms that generate motivational states in the brain.

Characterizing the Protein Isoforms of foraging (for), the PKGI Ortholog in Drosophila melanogaster.

The foraging (for) gene of Drosophila melanogaster encodes a cGMP-dependent protein kinase (PKG), which is a major effector of the cGMP signaling pathway involved in the regulation of behaviour and metabolic traits. Despite being well studied at the transcript level, little is known about the for gene at the protein level. Here, we provide a detailed characterization of the for gene protein (FOR) products and present new tools for their study, including five isoform-specific antibodies and a transgenic strain that carries an HA-labelled for allele (forBAC::HA). Our results showed that multiple FOR isoforms were expressed in the larval and adult stages of D. melanogaster and that the majority of whole-body FOR expression arises from three (P1, P1α, and P3) of eight putative protein isoforms. We found that FOR expression differed between the larval and adult stages and between the dissected larval organs we analyzed, which included the central nervous system (CNS), fat body, carcass, and intestine. Moreover, we showed that the FOR expression differed between two allelic variants of the for gene, namely, fors (sitter) and forR (rover), that are known to differ in many food-related traits. Together, our in vivo identification of FOR isoforms and the existence of temporal, spatial, and genetic differences in their expression lay the groundwork for determining their functional significance.

Prefrontal cortex melanocortin 4 receptors (MC4R) mediate food intake behavior in male mice.

BACKGROUND: Melanocortin 4 receptor (MC4R) activity in the hypothalamus is crucial for regulation of metabolism and food intake. The peptide ligands for the MC4R are associated with feeding, energy expenditure, and also with complex behaviors that orchestrate energy intake and expenditure, but the downstream neuroanatomical and neurochemical targets associated with these behaviors are elusive. In addition to strong expression in the hypothalamus, the MC4R is highly expressed in the medial prefrontal cortex, a region involved in executive function and decision-making. METHODS: Using viral techniques in genetically modified male mice combined with molecular techniques, we identify and define the effects on feeding behavior of a novel population of MC4R expressing neurons in the infralimbic (IL) region of the cortex. RESULTS: Here, we describe a novel population of MC4R-expressing neurons in the IL of the mouse prefrontal cortex that are glutamatergic, receive input from melanocortinergic neurons, and project to multiple regions that coordinate appetitive responses to food-related stimuli. The neurons are stimulated by application of MC4R-specific peptidergic agonist, THIQ. Deletion of MC4R from the IL neurons causes increased food intake and body weight gain and impaired executive function in simple food-related behavior tasks. CONCLUSION: Together, these data suggest that MC4R neurons of the IL play a critical role in the regulation of food intake in male mice.

Intraspecific variation in feeding and locomotor kinematics during prey capture in redbreast sunfish (Lepomis auritus).

Biomechanics research often revolves around understanding traits impacting suction feeding performance in fishes, using freshwater ray-finned sunfishes (Family Centrarchidae) as models. However, simultaneous feeding and locomotion kinematics during prey capture are not recorded for many species and there is less information on how these kinematics vary within a species and within individuals. To (1) add to existing data on the prey capture kinematics of centrarchids, (2) assess variation in a species both within and across individuals, and (3) compare morphology and prey capture kinematics of well-sampled centrarchids, we filmed five redbreast sunfish (Lepomis auritus) at 500 fps-1 approaching and striking non-evasive prey. Redbreast approach prey at ~30 cm s-1 and use approximately 70% of their maximum gape size. Traits related to feeding are more repeatable than traits related to locomotion. However, the Accuracy Index (AI) was consistent across individuals (AI = 0.76 ± 0.07). Functionally, redbreast sunfish are more similar to bluegill sunfish but morphologically they fall in the intermediate morphospace alongside green sunfish when compared with other centrarchids. These data show that whole organism outcomes (AI) are similar despite variation present both within and across individuals and demonstrate the importance of considering both interspecific and intraspecific differences in the functional diversity of ecologically and evolutionarily important behaviors such as prey capture.

Boldness predicts plasticity in flight responses to winds.

Behavioural plasticity can allow populations to adjust to environmental change when genetic evolution is too slow to keep pace. However, its constraints are not well understood. Personality is known to shape individual behaviour, but its relationship to behavioural plasticity is unclear. We studied the relationship between boldness and behavioural plasticity in response to wind conditions in wandering albatrosses (Diomedea exulans). We fitted multivariate hidden Markov models to an 11-year GPS dataset collected from 294 birds to examine whether the probability of transitioning between behavioural states (rest, prey search and travel) varied in response to wind, boldness and their interaction. We found that movement decisions varied with boldness, with bolder birds showing preferences for travel, and shyer birds showing preferences for search. For females, these effects depended on wind speed. In strong winds, which are optimal for movement, females increased time spent in travel, while in weaker winds, shyer individuals showed a slight preference for search, while bolder individuals maintained preference for travel. Our findings suggest that individual variation in behavioural plasticity may limit the capacity of bolder females to adjust to variable conditions and highlight the important role of behavioural plasticity in population responses to climate change.

Weight Gain in Early Infancy Impacts Appetite Regulation in the First Year of Life. A Prospective Study of Infants Living in Cyprus.

BACKGROUND: Eating behavior is associated with weight gain in infancy and childhood. Few studies found a bidirectional association between weight gain and eating behavior development in childhood, but there is little data on the association in early infancy, a period critical for the programming of obesity risk. OBJECTIVE: We investigated the bidirectional association between appetite traits and weight gain during the first year of life. METHODS: Participants were part of a cohort of 432 infants born in Cyprus. Appetite traits were measured using the Baby Eating Behavior Questionnaire or the Child Eating Behavior Questionnaire at age 2 to 4 wk, 6 mo, and 12 mo. Weight and length were collected at birth, 4 wk, 6 mo, and 12 mo. Multivariable linear regression was used to analyze associations between appetite traits at 2 to 4 wk and 6 mo and weight for age z-score change (WFAZC) between 4 wk and 6 mo and 6 and 12 mo. Associations were also analyzed in the opposite direction, between WFAZC from birth to 4 wk, 4 wk to 6 mo, and 6 mo to 12 mo and appetite traits at 4 wk, 6 mo, and 12 mo. RESULTS: Satiety responsiveness (SR) at 2 to 4 wk was associated with lower WFAZC from 4 wk to 6 mo (ß: -0.17; 95% CI: -0.30, -0.04) and SR at age 6 mo was associated with lower WFAZC from 6 to 12 mo (ß: -0.09; 95% CI: -0.17, -0.02). WFAZC from 4 wk to 6 mo was associated with higher enjoyment of food at 12 mo (ß: 0.11; 95% CI: 0.01, 0.20), higher food responsiveness at 12 mo (ß: 0.17; 95% CI: 0.04, 0.30), and lower SR at both 6 mo (ß: -0.11; 95% CI: -0.21, -0.01) and 12 mo (ß: -0.14; 95% CI: -0.24, -0.03). CONCLUSIONS: We found a bidirectional association between weight gain and appetite traits in infancy, suggesting that the effect of postnatal weight gain on obesity development is partly mediated by programming of appetite traits.

The gut-brain axis mediates bacterial driven modulation of reward signaling.

OBJECTIVE: Our goal is to investigate if microbiota composition modulates reward signaling and assess the role of the vagus in mediating microbiota to brain communication. METHODS: Male germ-free Fisher rats were colonized with gastrointestinal contents from chow (low fat (LF) ConvLF) or HF (ConvHF) fed rats. RESULTS: Following colonization, ConvHF rats consumed significantly more food than ConvLF animals. ConvHF rats displayed lower feeding-induced extracellular DOPAC levels (a metabolite of dopamine) in the Nucleus Accumbens (NAc) as well as reduced motivation for HF foods compared to ConvLF rats. Dopamine receptor 2 (DDR2) expression levels in the NAc were also significantly lower in ConvHF animals. Similar deficits were observed in conventionally raised HF fed rats, showing that diet-driven alteration in reward can be initiated via microbiota. Selective gut to brain deafferentation restored DOPAC levels, DRD2 expression, and motivational drive in ConvHF rats. CONCLUSIONS: We concluded from these data that a HF-type microbiota is sufficient to alter appetitive feeding behavior and that bacteria to reward communication is mediated by the vagus nerve.

Food induced distractibility in restrictive anorexia nervosa: Different motor patterns for different foods as revealed by a mouse tracker evaluation.

An altered automatic processing of food stimuli may contribute to the maintenance of calorie restriction in patients with restrictive Anorexia Nervosa (AN-R). The present study aimed to assess whether task-irrelevant food distractors elicited a different interference effect in the motor actions of patients with AN-R compared to healthy controls (HC). 40 patients with acute AN-R and 40 HC performed an irrelevant distractor task in which they were required to perform a reaching movement from a starting point to a green dot, while an irrelevant distractor (a high-calorie food, low-calorie food, or neutral object) was presented in the middle of the screen. Mouse trajectories and response times (RT) were recorded. The analyses conducted on the kinematic variables revealed that while the trajectories of HC veered similarly toward the three categories of stimuli, AN-R patients showed an increased deviation toward low-calorie foods and a reduced deviation toward high-calorie foods compared to neutral objects. No significant results emerged as regards RT. The pattern of responses observed in patients with AN-R (deviation increased toward low-calorie and reduced toward high-calorie) is consistent with their eating habits and may thus represent an implicit mechanism sustaining calorie restriction in patients with AN-R.

The influence of stress on the neural underpinnings of disinhibited eating: a systematic review and future directions for research.

Disinhibited eating involves overconsumption and loss of control over food intake, and underpins many health conditions, including obesity and binge-eating related disorders. Stress has been implicated in the development and maintenance of disinhibited eating behaviours, but the mechanisms underlying this relationship are unclear. In this systematic review, we examined how the impact of stress on the neurobiological substrates of food-related reward sensitivity, interoception and cognitive control explains its role in disinhibited eating behaviours. We synthesised the findings of functional magnetic resonance imaging studies including acute and/or chronic stress exposures in participants with disinhibited eating. A systematic search of existing literature conducted in alignment with the PRISMA guidelines identified seven studies investigating neural impacts of stress in people with disinhibited eating. Five studies used food-cue reactivity tasks, one study used a social evaluation task, and one used an instrumental learning task to probe reward, interoception and control circuitry. Acute stress was associated with deactivation of regions in the prefrontal cortex implicated in cognitive control and the hippocampus. However, there were mixed findings regarding differences in reward-related circuitry. In the study using a social task, acute stress associated with deactivation of prefrontal cognitive control regions in response to negative social evaluation. In contrast, chronic stress was associated with both deactivation of reward and prefrontal regions when viewing palatable food-cues. Given the small number of identified publications and notable heterogeneity in study designs, we propose several recommendations to strengthen future research in this emerging field.

Impact of Nighttime Food Consumption and Feasibility of Fasting during Night Work: A Narrative Review.

Shift work has been associated with an increased risk of developing chronic non-communicable diseases, such as obesity. The reduction in overnight fasting and its physiological consequences seem to affect the metabolic health of shift workers, but little has been discussed regarding the feasibility and implications of maintaining a night-long fast during work. This narrative review aims to discuss the impact of eating behavior on the reduction of overnight fasting in shift workers, as well as possible nutritional strategies involving fasting that have been tested for shift workers, to contribute to the establishment of nutritional guidelines for them. We used various databases and search engines to retrieve relevant articles, reviews, and investigations. Despite the potential benefits of overnight fasting for other groups, few studies have investigated this approach in the context of shift work. Generally, it seems to be a feasible and metabolically beneficial strategy for shift workers. However, it is essential to investigate the potential risks and benefits of reducing the fasting time for shift workers, considering social, hedonic, and stress-related factors. Furthermore, randomized clinical trials are necessary to establish safe and feasible strategies for shift workers to practice different fasting windows.