The olfactory bulb (OB) is an emerging neuroendocrine centre regulating appetite, metabolism, and behaviours such as those linked to anxiety, motivation and spatial navigation. These processes are likely mediated by one or more of the many hormone receptors found in the OB. For instance, recent studies show that selective OB deletion of the receptor for ghrelin and LEAP2 (GHSR; growth hormone secretagogue receptor) increases anxiety-like behaviour and impacts peripheral glucose and energy homeostasis. As GHSR function has been linked to motivated behaviours and spatial navigation, we decided to investigate whether OB-selective GHSR (OBGHSR) deletion affects motivation, using an operant progressive ratio schedule, and/or spatial navigation, using a Y maze and radial arm maze. In contrast to wild-type mice, our study shows that OBGHSR deletion increased motivated sucrose seeking after a short fast, but not in ad libitum fed mice, and had a mild effect to delay extinction learning. In both Y-maze and radial arm maze studies for spatial navigation, OBGHSR deletion reduced spatial exploration in terms of distance moved and arm entries. However, the proportion of correct and incorrect arm entries relative to the total number of entries was not affected in either the Y-maze or the radial arm maze, suggesting that spatial memory was not affected. Our study demonstrates that intact OBGHSRs in male mice normally restrain motivated sucrose seeking in a metabolic state-dependent manner and optimise spatial navigation by increasing exploration, without affecting spatial memory.

Fiber photometry is a neuroscience technique that can continuously monitor in vivo fluorescence to assess population neural activity or neuropeptide/transmitter release in freely behaving animals. Despite the widespread adoption of this technique, methods to statistically analyze data in an unbiased, objective, and easily adopted manner are lacking. Various pipelines for data analysis exist, but they are often system specific, are only for preprocessing data, and/or lack usability. Current post hoc statistical approaches involve inadvertently biased user-defined time-binned averages or area under the curve analysis. To date, no post hoc user-friendly tool with few assumptions for a standardized unbiased analysis exists, yet such a tool would improve reproducibility and statistical reliability for all users. Hence, we have developed a user-friendly post hoc statistical analysis package in Python that is easily downloaded and applied to data from any fiber photometry system. This Fiber Photometry Post Hoc Analysis (FiPhoPHA) package incorporates a variety of tools, a downsampler, bootstrapped confidence intervals (CIs) for analyzing peri-event signals between groups and compared with baseline, and permutation tests for comparing peri-event signals across comparison periods. We also include the ability to quickly and efficiently sort the data into mean time bins, if desired. This provides an open-source, user-friendly Python package for unbiased and standardized post hoc statistical analysis to improve reproducibility using data from any fiber photometry system.

Approximately 50-80 % of cancer patients suffer from cachexia, a metabolic syndrome involving inflammation, appetite loss, and muscle and fat wasting. Another common co-morbidity of cancer patients is cognitive impairment, and clinical evidence suggests the incidence of cachexia is linked to more severe cognitive symptoms. Given the difficulty of studying changes in cognitive function in human cancer patients, we set out to examine key aspects of cognitive performance in a mouse model of pancreatic cancer (pancreatic ductal adenocarcinoma; PDAC) cachexia, using an in-cage operant device (Feeding Experimental Device version 3; FED3) and a reversal learning task. Performance on the operant reversal task was compared to two control groups without cancer: ad libitum fed, sham injected with phosphate buffered saline (PBS), calorie restricted (CR) to 90-95 % of original body weight to control for reduced food intake and weight loss in cachexia mice. Our PDAC model recapitulated features of cachexia, including anorexia, weight loss, muscle wastage and inflammation. CR mice performed significantly better on the reversal task than both PDAC and PBS mice, achieving significantly more reversals and greater pellet retrieval. There was no difference between PBS and PDAC groups. These results suggest that the weight and appetite loss that occurs during cancer is processed by the brain differently to weight loss that occurs as a result of calorie restriction, with PDAC mice not experiencing an increase in motivational drive for food in line with their falling body weight. To mimic the malaise experienced by the PDAC group, we dosed CR mice with LiCl. Low dose (150 mM) LiCl did not affect responding, however, high dose (300 mM) LiCl significantly reduced both number of active pokes and pellet retrieval. This indicates a sickness-induced devaluation of reward, a factor that may impact poor performance of this task in the PDAC group. We additionally examined exploratory and anxiety-like behaviour in PBS and PDAC groups using a battery of maze-based tests. We saw no significant differences in performance between groups in the elevated plus maze, open field or light/dark box, suggesting no elevations in baseline anxiety-like symptoms in this cachexia model. These results occurred in the face of significantly elevated levels of the pro-cachexia factors GDF15, Activin A and Activin B, indicating that elevated levels of these TGF-β family peptides are not sufficient to produce behavioural changes in these tests. Our results provide evidence for a specific impact of sickness state on cognitive flexibility during pancreatic cancer.

Diets that are high in fat cause overeating and weight gain in multiple species of animals, suggesting that high dietary fat is sufficient to cause obesity. However, high-fat diets are typically provided freely to animals in obesity experiments, so it remains unclear whether high-fat diets would still cause obesity if these diets required more effort to obtain. We hypothesized that unrestricted access to high-fat diets is important for these diets to induce overeating and that requiring mice to perform small amounts of work to obtain a high-fat diet would reduce calorie intake and associated weight gain. To test this hypothesis, we developed a novel home-cage-based feeding device that provided the high-fat diet in two conditions: either freely or after mice poked their noses into a port one time-a simple action that is easy for them to do. Consistent with our hypothesis, requiring mice to nose-poke reduced high-fat diet intake and nearly completely prevented weight gain. Requiring mice to nose-poke also reduced low-fat grain-based pellet intake, confirming that this is a general mechanism governing food choice and not something specific to a high-fat diet. We conclude that unrestricted access to food promotes overeating and that requiring a simple action such as a nose-poke can reduce overeating and weight gain in mice. Our results may have implications for why overeating and obesity are common in modern food environments, which are often characterized by easy access to low-cost unhealthy foods.

Hunger increases the motivation for calorie consumption, often at the expense of low-taste appeal. However, the neural mechanisms integrating calorie-sensing with increased motivation for calorie consumption remain unknown. Agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus sense hunger, and the ingestion of caloric solutions promotes dopamine release in the absence of sweet taste perception. Therefore, we hypothesised that metabolic-sensing of hunger by AgRP neurons would be essential to promote dopamine release in the nucleus accumbens in response to caloric, but not non-caloric solutions. Moreover, we examined whether metabolic sensing in AgRP neurons affected taste preference for bitter solutions under conditions of energy need. Here we show that impaired metabolic sensing in AgRP neurons attenuated nucleus accumbens dopamine release in response to sucrose, but not saccharin, consumption. Furthermore, metabolic sensing in AgRP neurons was essential to distinguish nucleus accumbens dopamine response to sucrose consumption when compared with saccharin. Under conditions of hunger, metabolic sensing in AgRP neurons increased the preference for sucrose solutions laced with the bitter tastant, quinine, to ensure calorie consumption, whereas mice with impaired metabolic sensing in AgRP neurons maintained a strong aversion to sucrose/quinine solutions despite ongoing hunger. In conclusion, we demonstrate normal metabolic sensing in AgRP neurons drives the preference for calorie consumption, primarily when needed, by engaging dopamine release in the nucleus accumbens.

The resurgence of interest in psychedelics as treatments for psychiatric disorders necessitates a better understanding of potential sex differences in response to these substances. Sex as a biological variable (SABV) has been historically neglected in medical research, posing limits to our understanding of treatment efficacy. Human studies have provided insights into the efficacy of psychedelics across various diagnoses and aspects of cognition, yet sex-specific effects remain unclear, making it difficult to draw strong conclusions about sex-dependent differences in response to psychedelic treatments. Compounding this further, animal studies used to understand biological mechanisms of psychedelics predominantly use one sex and present mixed neurobiological and behavioral outcomes. Studies that do include both sexes often do not investigate sex differences further, which may hinder the translation of findings to the clinic. In reviewing sex differences in responses to psychedelics, we will highlight the direct interaction between estrogen (the most extensively studied steroid hormone) and the serotonin system (central to the mechanism of action of psychedelics), and the potential that estrogen-serotonin interactions may influence the efficacy of psychedelics in female participants. Estrogen influences serotonin neurotransmission by affecting its synthesis and release, as well as modulating the sensitivity and responsiveness of serotonin receptor subtypes in the brain. This could potentially influence the efficacy of psychedelics in females by modifying their therapeutic efficacy across menstrual cycles and developmental stages. Investigating this interaction in the context of psychedelic research could aid in the advancement of therapeutic outcomes, especially for conditions with sex-specific prevalence.

OBJECTIVE:Although the metabolic state of an organism affects olfactory function, the precise mechanisms and their impact on behavior and metabolism remain unknown. Here, we assess whether ghrelin receptors (GHSRs) in the olfactory bulb (OB) increase olfactory function and influence foraging behaviors and metabolism. METHODS:We performed a detailed behavioural and metabolic analysis in mice lacking GHSRs in the OB (OBGHSR deletion). We also analsyed OB scRNA-seq and spatial transcriptomic datasets to assess GHSR+ cells in the main and accessory olfactory bulbs, as well as the anterior olfactory nucleus. RESULTS:OBGHSR deletion affected olfactory discrimination and habituation to both food and non-food odors. Anxiety-like and depression-like behaviors were significantly greater after OBGHSR deletion, whereas exploratory behavior was reduced, with the greatest effect under fasted conditions. OBGHSR deletion impacted feeding behavior as evidenced by altered bout number and duration, as well as buried food-seeking. OBGHSR deletion increased body weight and fat mass, spared fat utilisation on a chow diet and impaired glucose metabolism indicating metabolic dysfunction. Cross referenced analysis of OB scRNA-seq and spatial transcriptomic datasets revealed GHSR+ glutamate neurons in the main and accessory olfactory bulbs, as well as the anterior olfactory nucleus. Ablation of glutamate neurons in the OB reduced ghrelin-induced food finding and phenocopied results seen after OBGHSR deletion. CONCLUSIONS:OBGHSRs help to maintain olfactory function, particularly during hunger, and facilitate behavioral adaptations that optimise food-seeking in anxiogenic environments, priming metabolic pathways in preparation for food consumption.

The melanocortin system is fundamental to neural control of energy balance and long-term weight regulation. Recent evidence shows that melanocortins also act at peripheral tissues to regulate metabolism, independent of the brain or the sympathetic nervous system (SNS). One such target is skeletal muscle, which contributes to energy expenditure through changes in adaptive thermogenesis. We aimed to determine 1) whether direct femoral infusion of alpha-melanocyte-stimulating hormone (alpha MSH) could increase muscle heat production independent of SNS activation and 2) if alpha MSH-induced skeletal muscle heat production was associated with altered mitochondrial function. Dataloggers were implanted into one hind leg of ovariectomized ewes and set to record vastus lateralis temperature every 15 minutes. A cannula was inserted into one femoral artery for infusion of either alpha MSH (0.1 mu g/h) or saline. Femoral infusion of alpha MSH increased (P < .0001) skeletal muscle heat production, without effect on food intake. State 4 respiration increased (P < .05) and the respiratory control ratio decreased (P < .05) in mitochondria isolated from alpha MSH-treated animals. In addition, femoral infusion of alpha MSH reduced plasma glucose concentration in the femoral, but not the jugular vein; there was no effect of alpha MSH treatment on nonesterified fatty acid concentrations. These data suggest that alpha MSH can act locally to increase glucose uptake. We further show that blockade of the alpha- and beta-adrenergic limbs of the SNS with either phentolamine or propranolol infusion had no effect on alpha MSH-induced skeletal muscle heat production. Overall, we show that alpha MSH acts directly at skeletal muscle to promote glucose uptake and increase energy expenditure via mitochondrial thermogenesis.

Reward-seeking involves the engagement and computation of multiple physiological and motivational parameters. The lateral hypothalamus (LH) is a necessary node in the circuits that control food-seeking and motivation. One group of cells that plays an important yet incompletely understood role in these processes are the orexin/hypocretin (OX/HT) neurons. OX/HT cells are located exclusively within the LH and are implicated in feeding, arousal, and reward-seeking behavior. Importantly, the role of OX/HT neurons in consummatory versus reward-seeking actions is not fully defined, nor are the circuits that control the activity of these neurons under different behavioral states. Here we show that OX/HT neurons respond in real time to food presentation and that this response is modulated by differences in metabolic state. We observed increased OX/HT neuron activity on approach to food, but this activity trended towards pre-approach levels by the start of the consummatory phase. Next, we studied ventrostriatopallidal (VSP) inputs to the OX/HT neurons. Using optogenetics and cell type-specific electrophysiology, we found that ventral pallidum inputs onto OX/HT neurons exert strong inhibitory (and weak excitatory) effects whereas the lateral nucleus accumbens shell provides weaker direct inhibitory connections with OX/HT neurons. These findings reveal that the activity of OX/HT neurons is strongly modulated by metabolic and hedonic state. Further, OX/HT neurons is primarily associated with food approach and that the effect of VSP-terminal output is to suppress OX/HT activity.

Neuroscientists have long believed that hunger increases activity in agouti-related peptide (AgRP) neurons to regulate feeding-related behaviors and metabolism, but a new study shows that the story is much more complicated. Sayar-Atasoy and colleagues show that the time of day uncouples activity in AgRP neurons from hunger and demonstrate how daily feeding patterns influence future AgRP neuron activity.

The insular cortex is a multifunctional and richly connected region of the cerebral cortex, critical in the neural integration of external stimuli and internal signals. Well-served for this role by a large network of afferent and efferent connections, the mouse insula can be simplified into an anterior, medial and posterior portion. Here we focus on the medial subregion, a once over-looked area that has gained recent attention for its involvement in an array of behaviours. Although the connections of medial insular cortex neurons have been previously identified, their precise glutamatergic phenotype remains undefined (typically defined by the presence of the subtype of vesicular glutamate transporters). Hence, we combined Cre knock-in mouse lines and adeno-associated viral tracing to distinguish between the expression of the two major vesicular glutamate transporters, type 1 (vGlut1) and 2 (vGlut2), in the subregion’s neuronal inputs and outputs. Our results determined that the medial insula has extensive glutamatergic efferents expressing both vGlut1 and vGlut2 throughout the neuraxis. In contrast, a more conservative number of glutamatergic inputs were observed, with exclusively vGlut2+ projections received from hypothalamic and thalamic regions. Taken together, we demonstrate that vGlut1- and vGlut2-expressing networks of this insular subdivision have distinct connectivity patterns, including a greater abundance of vGlut1+ fibres innervating hypothalamic regions and the extended amygdala. These findings provide insight into the distinct chemo-architecture of this region, which may facilitate further investigation into the role of the medial insula in complex behaviour.

Objective: An environmental context, which reliably predicts food availability, can increase the appetitive food drive within the same environment context. However, hunger is required for the development of such a context-induced feeding (CIF) response, suggesting the neural circuits sensitive to hunger link an internal energy state with a particular environment context. Since Agouti related peptide (AgRP) neurons are activated by energy deficit, we hypothesised that AgRP neurons are both necessary and sufficient to drive CIF. Methods: To examine the role of AgRP neurons in the CIF process, we used fibre photometry with GCaMP7f, chemogenetic activation of AgRP neurons, as well as optogenetic control of AgRP neurons to facilitate acute temporal control not permitted with chemogenetics. Results: A CIF response at test was only observed when mice were fasted during context training and AgRP population activity at test showed an attenuated inhibitory response to food, suggesting increased food-seeking and/or decreased satiety signalling drives the increased feeding response at test. Intriguingly, chemogenetic activation of AgRP neurons during context training did not increase CIF, suggesting precise temporal firing properties may be required. Indeed, termination of AgRP neuronal photostimulation during context training (ON-OFF in context), in the presence or absence of food, increased CIF. Moreover, photoinhibition of AgRP neurons during context training in fasted mice was sufficient to drive a subsequent CIF in the absence of food. Conclusions: Our results suggest that AgRP neurons regulate the acquisition of CIF when the acute inhibition of AgRP activity is temporally matched to context exposure. These results establish acute AgRP inhibition as a salient neural event underscoring the effect of hunger on associative learning.

By modeling neural network dynamics related to homeostatic state and BMI, we identified a novel pathway projecting from the medial prefrontal cortex (mPFC) to the lateral hypothalamus (LH) in humans. We then assessed the physiological role and dissected the function of this mPFC-LH circuit in mice. In vivo recordings of population calcium activity revealed that this glutamatergic mPFC-LH pathway is activated in response to acute stressors and inhibited during food consumption, suggesting a role in stress-related control over food intake. Consistent with this role, inhibition of this circuit increased feeding and sucrose seeking during mild stressors, but not under non-stressful conditions. Finally, chemogenetic or optogenetic activation of the mPFC-LH pathway is sufficient to suppress food intake and sucrose-seeking in mice. These studies identify a glutamatergic mPFC-LH as a novel stress-sensitive anorexigenic neural pathway involved in the cortical control of food intake.

It is well-established that stress and negative affect trigger eating disorder symptoms and that the brains of men and women respond to stress in different ways. Indeed, women suffer disproportionately from emotional or stress-related eating, as well as associated eating disorders such as binge eating disorder. Nevertheless, our understanding of the precise neural circuits driving this maladaptive eating behavior, particularly in women, remains limited. We recently established a clinically relevant model of 'emotional' stress-induced binge eating whereby only female mice display binge eating in response to an acute "emotional" stressor. Here, we combined neuroanatomic, transgenic, immunohistochemical and pathway-specific chemogenetic approaches to investigate whole brain functional architecture associated with stress-induced binge eating in females, focusing on the role of Vglut2 projections from the paraventricular thalamus (PVTVglut2+) to the medial insular cortex in this behavior. Whole brain activation mapping and hierarchical clustering of Euclidean distances revealed distinct patterns of coactivation unique to stress-induced binge eating. At a pathway-specific level, PVTVglut2+ cells projecting to the medial insular cortex were specifically activated in response to stress-induced binge eating. Subsequent chemogenetic inhibition of this pathway suppressed stress-induced binge eating. We have identified a distinct PVTVglut2+ to insular cortex projection as a key driver of "emotional" stress-induced binge eating in female mice, highlighting a novel circuit underpinning this sex-specific behavior.

AIMS:To examine association of liver-expressed antimicrobial peptide 2 (LEAP2), an endogenous ghrelin antagonist with anorexiant effects, to key cardiometabolic risk factors in people with overweight and obesity. METHODS:In this cross-sectional study, we sought to identify associations between LEAP2 levels and cardiometabolic risk factors, including body composition (dual X-ray absorptiometry), insulin and glucose metabolism (oral and intravenous glucose tolerance tests and hyperinsulinaemic-euglycaemic clamps), plasma lipids and inflammation markers (ELISA and multiplex assays). RESULTS:In 65 participants with overweight or obesity (63.1% male, mean age 31.3 ± 8.5 years), LEAP2 levels were associated with total body fat, but not with body mass index or waist-hip ratio in both univariable and age- and sex-adjusted models (P < 0.05). Higher LEAP2 level was also positively associated with higher insulin secretion in univariable (P = 0.047) and multivariable models adjusted for age, sex and body fat (P = 0.03), but not with fasting glucose levels (P ≥ 0.05). Higher LEAP2 levels were associated insulin resistance (P = 0.07) after adjustment for age and sex, but the association disappeared after an additional adjustment for body fat (P = 0.2). There was an inverse association between LEAP2 levels and nuclear factor kappa-B (NFκB) activity in the peripheral blood mononuclear cells in age-, sex- and body fat-adjusted models (P = 0.04). There were no associations with cardiovascular risk factors (lipids, blood pressure) or other inflammation markers. CONCLUSIONS:These results provide important insights into the association between LEAP2 and cardiometabolic health in a high-risk population of individuals with overweight and obesity. This is a first report of an association between LEAP2 and insulin secretion, insulin sensitivity and NFκB activity. LEAP2 may represent an important potential therapeutic target to promote insulin secretion in people with type 2 diabetes and obesity.

Anorexia nervosa has among the highest mortality rates of any psychiatric disorder and is characterized by cognitive inflexibility that persists after weight recovery and contributes to the chronic nature of the condition. What remains unknown is whether cognitive inflexibility predisposes individuals to anorexia nervosa, a question that is difficult to address in human studies. Our previous work using the most well-established animal model of anorexia nervosa, known as activity-based anorexia (ABA) identified a neurobiological link between cognitive inflexibility and susceptibility to pathological weight loss in female rats. However, testing flexible learning prior to exposure to ABA in the same animals has been thus far impossible due to the length of training required and the necessity of daily handling, which can itself influence the development of ABA. Here, we describe experiments that validate and optimize the first fully-automated and experimenter-free touchscreen cognitive testing system for rats and use this novel system to examine the reciprocal links between reversal learning (an assay of cognitive flexibility) and weight loss in the ABA model. First, we show substantially reduced testing time and increased throughput compared to conventional touchscreen testing methods because animals engage in test sessions at their own direction and can complete multiple sessions per day without experimenter involvement. We also show that, contrary to expectations, cognitive inflexibility measured by this reversal learning task does not predispose rats to pathological weight loss in ABA. Instead, rats that were predisposed to weight loss in ABA were more quickly able to learn this reversal task prior to ABA exposure. Intriguingly, we show reciprocal links between ABA exposure and cognitive flexibility, with ABA-exposed (but weight-recovered) rats performing much worse than ABA naïve rats on the reversal learning task, an impairment that did not occur to the same extent in rats exposed to food restriction conditions alone. On the other hand, animals that had been trained on reversal learning were better able to resist weight loss upon subsequent exposure to the ABA model. We also uncovered some stable behavioral differences between ABA susceptible versus resistant rats during touchscreen test sessions using machine learning tools that highlight possible predictors of anorectic phenotypes. These findings shed new light on the relationship between cognitive inflexibility and pathological weight loss and provide targets for future studies using the ABA model to investigate potential novel pharmacotherapies for anorexia nervosa.

An environment can have a powerful influence over appetite and feeding behaviour. For example, an environmental context, which reliably predicts food, will increase the appetitive food drive to the same environment context. Interestingly, mice are required to be hungry to develop such a context-induced feeding (CIF) response, suggesting the neural circuits sensitive to hunger play an important role to associate an internal energy state with a particular environment context. Hunger-sensing Agouti related peptide (AgRP) neurons are activated by circulating signals of energy deficit and reset to a silenced state by gut feedback mechanisms following food consumption. We hypothesised that AgRP neurons are both necessary and sufficient to drive CIF in the absence of hunger. While fasting increased CIF, chemogenetic inhibition of AgRP neurons during context acquisition prevented this effect. Intriguingly, chemogenetic activation of AgRP neurons during context acquisition did not increase CIF, suggesting precise temporal firing properties may be required. Indeed, photostimulation of AgRP neurons, only during context exposure (ON-OFF in context), increased CIF. Moreover, AgRP photostimulation prior to context exposure, coupled with the termination of photostimulation in the context in the absence of food consumption, was sufficient to drive a subsequent CIF. Our results suggest that AgRP neurons regulate the acquisition of CIF when the temporal firing properties are matched to context exposure. These results further highlight that acute AgRP inhibition is a salient neural event underscoring the effect of hunger on associative learning.

ABSTRACT Modifying the relative proportions of macronutrients in an animal’s diet has noteworthy effects on its reproduction, lifelong health, and lifespan. Because of this, a wide range of animals carefully regulate their nutrient intake toward species and stage-specific targets. However, when animals are unable to reach their nutrient target from their existing food resources, they will compromise between overconsuming one nutrient and under-consuming the deficit nutrient. In this study, we used capillary feeding (CAFE) assays to understand the rules of compromise of adult fruit flies ( Drosophila melanogaster ) of different sex, mating status, and age when constrained to single diets. We found that young male and female D. melanogaster compromised by consuming more food on diets with low protein to carbohydrate (P:C) ratios compared to diets with high P:C ratios. Further, young male and female flies varied their carbohydrate intake significantly more than their protein intake, and female flies varied their carbohydrate intake significantly more than males. To test for effects of mating status on nutrient intake, we compared food intake of young mated and virgin females. We found that both virgin and mated females compromised by consuming more food on the low P:C diet compared to high P:C diets; however, mated females consumed more food than virgin females. As flies aged, they decreased their overall food intake and showed more modest alterations in their food intake across varying P:C diets. Further, mated females ceased to compromise for the protein deficit at a younger age than males. These findings provide new understanding about differences in protein leveraging behaviour across sexes, and how these behaviours change with age. Highlights Young fruit flies exhibit protein leveraging behaviour, varying their carbohydrate consumption more than protein Young mated female flies vary their carbohydrate consumption significantly more than young males Both virgin and mated female flies balance their nutrient intake similarly As flies age, their ability to protein leverage declines, and this occurs faster in female flies

OBJECTIVE:The sensory detection of food and food cues suppresses Agouti related peptide (AgRP) neuronal activity prior to consumption with greatest suppression occurring in response to highly caloric food or interoceptive energy need. However, the interoceptive mechanisms priming an appropriate AgRP neural response to external sensory information of food availability remain unexplored. Since hunger increases plasma ghrelin, we hypothesized that ghrelin receptor (GHSR) signalling on AgRP neurons is a key interoceptive mechanism integrating energy need with external sensory cues predicting caloric availability. METHODS:We used in vivo photometry to measure the effects of ghrelin administration or fasting on AgRP neural activity with GCaMP6s and dopamine release in the nucleus accumbens with GRAB-DA in mice lacking ghrelin receptors in AgRP neurons. RESULTS:The deletion of GHSR on AgRP neurons prevented ghrelin-induced food intake, motivation and AgRP activity. The presentation of food (peanut butter pellet) or a wooden dowel suppressed AgRP activity in fasted WT but not mice lacking GHSRs in AgRP neurons. Similarly, peanut butter and a wooden dowel increased dopamine release in the nucleus accumbens after ip ghrelin injection in WT but not mice lacking GHSRs in AgRP neurons. No difference in dopamine release was observed in fasted mice. Finally, ip ghrelin administration did not directly increase dopamine neural activity in the ventral tegmental area. CONCLUSIONS:Our results suggest that AgRP GHSRs integrate an interoceptive state of energy need with external sensory information to produce an optimal change in AgRP neural activity. Thus, ghrelin signalling on AgRP neurons is more than just a feedback signal to increase AgRP activity during hunger.

Hunger and satiety states drive eating behaviours via changes in brain function. The hypothalamus is a central component of the brain networks that regulate food intake. Animal research parsed the roles of the lateral hypothalamus (LH) and the medial hypothalamus (MH) in hunger and satiety respectively. Here, we examined how hunger and satiety change information flow between human LH and MH brain networks, and how these interactions are influenced by body mass index. Forty participants (15 overweight/obese) underwent two resting-state functional MRI scans: after overnight fasting (fasted state) and following a standardised meal (sated state). The direction and valence (excitatory/inhibitory influence) of information flow between the MH and LH was modelled using spectral dynamic causal modelling. Our results revealed two core networks interacting across homeostatic state and weight status: subcortical bidirectional connections between the LH, MH and the substantia nigra pars compacta (prSN), and cortical top-down inhibition from frontoparietal and temporal areas. During fasting relative to satiety, we found higher inhibition between the LH and prSN, whereas the prSN received greater top-down inhibition from across the cortex. Individuals with higher BMI showed that these network dynamics occur irrespective of fasted or satiety states. Our findings reveal fasting affects brain dynamics over a distributed hypothalamic-midbrain-cortical network. This network is less sensitive to state-related fluctuations among people with obesity.