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Background: Eating behaviors are determined by a complex interplay between behavioral and physiologic signaling occurring before, during, and after eating.Objectives: The aim was to explore how selected behavioral and physiologic variables separately and grouped together predicted intake of 8 different foods.Methods: One hundred adults with normal weight performed a food preference task combined with biometric measurements (the Steno Biometric Food Preference Task) in the fasting state. The task measured food reward as well as biometric (eye tracking, electrodermal activity, and facial expressions) responses to images of foods varying in fat content and taste. Energy intake from an ad libitum buffet of the same 8 foods as assessed in the preference task was subsequently assessed. A mixed-effects random forest approach was applied to explore how individual and combined measures of food reward and biometric responses predicted energy intake of the 8 single foods. The performance of the different prediction models was compared with the predictions from a linear model including only an intercept (naïve model) using bootstrap cross-validation.Results: Participants had a median [IQR] intake of 369 kJ [126-472 kJ] per food. Combined or separate measures of food reward or biometric responses did not predict energy intake better than the naïve model.Conclusions: We did not find that the reward or biometric responses to food cues assessed in a clinical setting were useful in predicting energy intake of single foods. However, this study provides a framework in the field of behavioral nutrition for applying machine learning with a focus on individual predictions. This is necessary on the road toward personalized nutrition and provides great potential for handling complex data with multiple variables.This trial was registered at clinicaltrials.gov as NCT03986619. [ABSTRACT FROM AUTHOR]

Leptin reduces the motivation to obtain food by modulating activity of the mesolimbic dopamine (DA) system upon presentation of cues that predict a food reward. Although leptin directly reduces the activity of ventral tegmental area (VTA) DA neurons, the majority of leptin receptor (LepR)-expressing DA neurons do not project to the nucleus accumbens, the projection implicated in driving food reward seeking. Therefore, the precise locus of leptin action to modulate motivation for a food reward is unresolved. We used transgenic mice expressing Cre recombinase under the control of the LepR promoter, anatomical tracing, optogenetics-assisted patch-clamp electrophysiology, in vivo optogenetics with fiber photometric calcium measurements, and chemogenetics to unravel how leptin-targeted neurocircuitry inhibits food reward seeking. A large number of DA neurons projecting to the nucleus accumbens are innervated by local VTA LepR-expressing GABA (gamma-aminobutyric acid) neurons. Leptin enhances the activity of these GABA neurons and thereby inhibits nucleus accumbens–projecting DA neurons. In addition, we find that lateral hypothalamic LepR-expressing neurons projecting to the VTA are inhibited by leptin and that these neurons modulate DA neurons indirectly via inhibition of VTA GABA neurons. In accordance with such a disinhibitory function, optogenetically stimulating lateral hypothalamic LepR projections to the VTA potently activates DA neurons in vivo. Moreover, we found that chemogenetic activation of lateral hypothalamic LepR neurons increases the motivation to obtain a food reward only when mice are in a positive energy balance. We identify neurocircuitry through which leptin targets multiple inputs to the DA system to reduce food reward seeking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tongue length of H. itama is 2.30 ± 0.05 mm and can be extended to 3.39 ± 0.03 mm. • Averrhoa carambola produced the highest sugar nectar concentration (43.36 ± 2.55%). • Antigonon leptopus produced 34.40 ± 2.11% of nectar sugar concentration. • Both flowers have short tube length. It is compatible with the bee tongue length. • High sugar nectar and short tube length attract the bee to forage on both flowers. Heterotrigona itama is a stingless bee species from Meliponini tribe. The bee collects nectar, pollen and resin to produce honey, bee bread, and propolis. The bee is also known to visit and collect nectar from various types of flowers but there are limited studies on why this species of bee prefers to visit certain types of flowers. This study was conducted to identify the nectar concentration in selected flowers favoured by H. itama and the relationship between the bee and the morphology of the flowers. Nectar was obtained from different species of flowers and the concentrations were measured using a digital refractometer. The tube length of each flower species and the tongue length of the bees were also measured. The results revealed that flowers preferred by H. itama have high nectar concentrations. The tube lengths of the preferred flowers were between 2.0 and 4.0 mm, which is compatible with the tongue length of the bee. This study revealed that both nectar concentration and flower morphology are important factors for the bees in choosing their food sources. The results from this study will benefit the beekeepers in the identification of flowers that should be planted in their farms to improve stingless bee beekeeping activities. Understanding the relationship between the bees and their flower preferences could also help us to understand the importance of conserving both the bee colonies and the various species of flowering plants to ensure the sustainability of flora and fauna in the ecosystem. [ABSTRACT FROM AUTHOR]

Background Reward sensitivity has been proposed as a potential mediator of outcomes for bariatric surgery. Objectives We aimed to determine whether gustatory and psychometric measures of reward-related feeding are predictors of bariatric-induced weight loss. Methods A multicenter longitudinal cohort study was conducted in patients scheduled for bariatric surgery (surgical group), assessed at baseline and 2 follow-up assessments. Predictions of % weight loss from baseline (%WL) according to baseline gustatory measures, including intensity and pleasantness ratings of sweet and other tastants, and psychometric measures of reward-related feeding behavior, including hedonic hunger scores, were assessed with multivariable linear regression. Exploratory analyses were conducted to test for associations between %WL and changes in gustatory and psychophysical measures, as well as for comparisons with data from patients on the surgery waiting list (control group). Results We included 212 patients, of whom 96 in the surgical group and 50 in the control group were prospectively assessed. The groups were similar at baseline and, as expected, bariatric surgery resulted in higher %WL (BTreatment-Time  = 2.4; 95% CI: 2.1–2.8; P   < 0.0001). While variation in gustatory measures did not differ between groups, in the surgery group baseline sweet intensity predicted %WL at the primary endpoint (11 to 18 months postoperatively; β = 0.2; B = 0.2, 95% CI: 0.02 to 0.3; P   = 0.02), as did hedonic hunger scores (β = −0.2; B = −2.0, 95% CI: −3.8 to −0.3; P   = 0.02). Furthermore, at this endpoint, postsurgical reduction of sweet taste intensity and acceptance of sweet foods were associated with %WL (β = −0.3; B = −3.5, 95% CI: −5.8 to −1.3; P   = 0.003, and β = −0.2; B = −4.7, 95% CI: −8.5 to −0.8; P   = 0.02, respectively). The use of sweet intensity as a predictor of weight change was confirmed in another bariatric cohort. Conclusions Sweet intensity ratings and hedonic hunger scores predict %WL after surgery. The variability of sweet intensity ratings is also associated with %WL, further suggesting they may reflect physiological processes that are variably modulated by bariatric surgery, influencing clinical outcomes. [ABSTRACT FROM AUTHOR]

• Diet containing stearic acid increases food reward-related behaviors compared with oleic acid diet. • Diet containing stearic acid influences the mesolimbic dopamine system compared with oleic acid diet. • Diet containing stearic acid decreased leptin levels in the serum compared with oleic acid diet. • Diet containing stearic acid decreased leptin signaling in the VTA compared with oleic acid diet. Obesity is currently a worldwide phenomenon. The consumption of calorie-rich foods is responsible for most obesity cases, but not all humans exposed to high-calorie diets develop obesity. According to recent studies, exposure to fat-rich diets may be the actual cause of obesity. Dietary long-chain fatty acids affect brain function and are linked to food intake and motivation-related behaviors. Recently, many studies have shown that different types of fatty acids play different roles in animals. In our study, the effects of stearic acid (a saturated fatty acid) and oleic acid (a monounsaturated fatty acid) in diets on hedonic feeding behaviors were investigated, and changes of feeding-related protein levels in the brain were detected to explore the possible mechanism underlying the effects of these fatty acids. As a result, mice fed a diet containing stearic acid, compared to a diet containing oleic acid, exhibited increased food intake, hedonic eating, and an operant response to sucrose and locomotor activity. Furthermore, stearic acid corresponded to a higher level of leptin in serum than oleic acid. In addition, the stearic acid treated group had lower protein levels of p-JAK2 and p-STAT3 in the VTA and a higher dopamine concentration in the NAc than the oleic acid-treated group. Meanwhile, the protein level of TH in the NAc was higher and the protein level of the DA transporter in the VTA was lower in the stearic acid-fed group than in the oleic acid-fed group. In conclusion, these findings indicated that a diet containing stearic acid can increase hedonic feeding behavior and affect mesolimbic dopamine system signals in mice. Moreover, the lowering of serum leptin and leptin signaling in the VTA may contribute to this effect. [ABSTRACT FROM AUTHOR]

Background and Aim: Exercise timing has been suggested to affect appetite and energy intake (EI). The aim of this study was to examine the impact of exercising immediately before or after a meal on EI, appetite sensations and food reward (FR) in adolescents with obesity.Methods and Results: Seventeen adolescents with obesity completed 3 experimental sessions (randomized controlled trial): rest + lunch (CON); exercise + lunch (EX-MEAL); lunch + exercise (MEAL-EX). The exercise consisted of cycling 30 min at 65%V̇O2peak. Outcomes included ad libitum EI (weighed lunch and dinner), FR (Leeds Food Preference Questionnaire at pre- and post-combination of exercise/rest and lunch, and pre-dinner) and appetite sensations (visual analogue scales). EI was not different between conditions. Compared with CON, relative EI at lunch was lower in EX-MEAL and MEAL-EX (p ≤ 0.05) and daily only in MEAL-EX (p < 0.01). Postprandial fullness was higher in EX-MEAL compared to CON. Compared with CON, both EX-MEAL and MEAL-EX attenuated the increase in wanting for sweet food and reduced explicit liking for fat.Conclusions: These preliminary results suggest that exercising immediately before or after a meal produce few differences in appetite and have small beneficial effects on overall energy balance in adolescents with obesity, as well as on FR.Clinical Trials: NCT03967782. [ABSTRACT FROM AUTHOR]

Associative learning is often studied using food reward as the unconditioned stimulus (US). With warm-blooded species, to get the subject more motivated the solution has been to feed less, making the subject hungrier. Here we show the opposite with zebrafish. We randomly assigned zebrafish to two groups: a once-a-day-fed and a five-times-a-day-fed group, with the same amount of food fed per occasion for fish of both groups, a feeding regimen that lasted for three months. Subsequently, we trained fish by pairing food (US) with a red cue card (the conditioned stimulus, CS), which were placed together in one arm of a plus-maze across eight training sessions. We also ran unpaired training, in which the CS and US were presented in different arms. We found the previously once-a-day-fed zebrafish to consume less food throughout habituation and training sessions compared to the previously five-times-a-day-fed ones. Furthermore, five-times-a-day-fed fish in the paired group swam significantly closer to the CS during a post-training probe trial compared to the five-times-a-day-fed unpaired fish, a paired training effect that was absent in once-a-day-fed fish. Groups did not differ in health or general activity. In sum, elevated chronic feeding improved food consumption and enhanced learning and memory performance without affecting activity levels in adult zebrafish. • Food is an excellent rewarding stimulus with which previously neutral stimuli may be paired. • In most species, hungry subjects learn better in food rewarded tasks than well-fed ones. • In zebrafish, we found the opposite: chronically increased feeding led to increased motivation to eat. • Chronically increased feeding led to better learning/memory performance. [ABSTRACT FROM AUTHOR]

• The Leeds Food Preference Questionnaire was adapted to the German Population. • The LFPQ-G provides a valid tool to assess liking and wanting in the German Population. • The LFPQ-G is sensitive to changes in satiety from pre to post meal. • The LFPQ-G identifies changes in taste preference following a test meal. • The LFPQ-G associates with trait eating behavior. The computerized Leeds Food Preference Questionnaire measures liking and wanting for food images as separable components of food reward. We aimed to validate a German version of this instrument (LFPQ-G). LFPQ-G-development included a standardized production of culturally adapted food images representing four food categories varying in fat (high vs. low) and taste (sweet vs. savory). The LFPQ-G was validated in 59 mostly female (69.5 %), on average normal weight participants with a median BMI of 23.2 kg/m2 [21.3 kg/m2; 26.3 kg/m2], aged between 21 and 65 years, who completed the LFPQ-G in a fasted state and after a test meal. Repeated measure ANOVA assessed changes in LFPQ-G outcome measures from a fasted to a fed state. The Three Factor Eating Questionnaire (TFEQ) was applied to assess associations between LFPQ-G outcome measures and individual differences in eating behavior. Explicit liking and wanting for food in general decreased from pre to post meal (p < 0.001). Significant two-way-interactions revealed greater explicit liking and wanting and implicit wanting for savory over sweet foods in the fasted condition, while opposite in the fed state (p < 0.001). Implicit wanting and explicit wanting and liking were greater for low- than for high-fat foods (p < 0.001). Outcome measures of the new LFPQ-G are sensitive to changes in satiety and identify changes in taste preference following a test meal as described in previous studies, indicating valid assessment of different aspects of food reward. [ABSTRACT FROM AUTHOR]

Pharmacotherapies targeting motivational aspects of feeding and palatable food reward, while sparing mood and cognitive function, represent an alluring approach to reverse obesity and maintain weight loss in an obesogenic environment. A novel glucagon-like peptide-1/dexamethasone (GLP-1/Dexa) conjugate, developed to selectively activate glucocorticoid receptors in GLP-1 receptor-expressing cells was shown to decrease food intake and lower body weight in obese mice. Here, we investigate if this novel drug candidate modulates the rewarding properties of food and if it affects behavioral indices of mood and memory. C57Bl6 mice treated with the GLP-1/Dexa conjugate, GLP-1 or vehicle lever-pressed for high-fat, high sugar (HFHS) food rewards in an operant task. Alterations in food-motivated behavior were also assessed following a HFHS diet withdrawal manipulation (switch to chow). The effects of repeated GLP-1/Dexa conjugate, GLP-1 or vehicle on free-feeding intake, body weight, anxiodepressive behaviors (elevated-plus maze, open field test & forced swim test), memory (novel object recognition) and mRNA expression of reward-relevant markers in the nucleus accumbens were also evaluated in mice fed a HFHS diet for 12 weeks. Mice treated with a GLP-1 analogue displayed a transient (4 h) reduction in their motivation to lever press for HFHS reward, whereas treatment with equimolar doses of GLP-1/Dexa delivered a superior and sustained (20 h) suppression of food-motivated behavior. GLP-1/Dexa also inhibited food reward following withdrawal from the HFHS diet. These benefits coincided with related transcriptional changes of dopaminergic markers in the nucleus accumbens. Importantly, repeated GLP-1/Dexa treatment during a HFHS diet caused weight loss without affecting anxiodepressive behavior and memory. Via its actions to blunt the rewarding effects of palatable food without affecting mood and recognition memory, GLP-1-directed targeting of dexamethasone may serve as a promising and safe anti-obesity strategy. • GLP-1/Dexamethasone (GLP-1/Dexa) is a new pre-clinical anti-obesity drug candidate. • GLP-1/Dexa suppresses food-motivated behaviors in mice. • GLP-1/Dexa induces changes in reward-relevant markers in the nucleus accumbens. • GLP-1/Dexa has no adverse effect on anxio-depressive behavior and recognition memory. [ABSTRACT FROM AUTHOR]

• Distraction by a food reward influenced horses' startle response to a novel object. • Horses distracted by a food reward were not completely "blind" to a visual stimulus. • The food reward decreased corridor passage duration induced by focused expectation. • Horses' reaction to the novel object was not affected by visual lateralization. Inattentional Blindness (IB) is a phenomenon which has been widely researched in humans. If attention is highly focused, humans may become blind to other environmental cues. To further understand the perception of horses, we applied the well-tested experimental design of human IB studies to the first study of this kind in horses. Since the use of cognitive tasks in human IB-studies ensures that the subject's attention is focused in a certain direction, we wanted to show if a food reward is strong enough to induce IB in the horse while confronted with a novel object. Therefore, we tested 24 horses, divided in an experimental (n = 12) and a control group (n = 12). The horses had to walk through the same corridor (10 m) for 12 consecutive trials. In the experimental group, animals were trained to focus on a food reward presented at the end of the corridor. Their duration to pass the run decreased significantly, indicating that an expectation focused on the feed was induced. In the test trials 11 and 12, a startle stimulus was presented to both groups. The response to the novel object was scored from 1 (no reaction) to 5 (flight reaction). We found a significant difference between the groups in the second test run with the experimental group showing lower reactions to the novel object (p = 0.018). The horses in the experimental group where not completely "blind" to the object, but the food reward clearly influenced their reaction. The results of the study suggest that while the occurrence of IB in horses has yet to be proven, a suitable distractor can lower horses' startle response to a novel object. By further investigation into IB, new insight into the perception of horses can emerge and improve the understanding between horses and their handlers. [ABSTRACT FROM AUTHOR]

Food rewards are commonly used as positive reinforcement in rodent behavioral experiments. Bioserv dustless precision pellets and Noyes formula P precision pellets are both used for this purpose in behavioral experiments in multiple laboratories, as they are nutritionally consistent with standard laboratory diets. Because of the nutritional value, they are superior to other positive food rewards such as chocolate. Whether male Wistar rats prefer either of these pellets was tested with a T-maze choice test, because Noyes formula P precision pellets could no longer easily be purchased in Europe. Rats did not show preference for either Bioserv dustless precision pellets or Noyes formula P precision pellets. Concluding, both pellet types can be used reliably as positive reinforcement in behavioral experiments. We advise against repeating of experiments replacing one of these pellet types with the other, to reduce the number of experimental animals needed. [ABSTRACT FROM AUTHOR]

Abstract Food intake is tightly regulated by homeostatic and reward mechanisms and the adequate function of both is necessary for the proper maintenance of energy balance. Ghrelin impacts on these two levels to induce feeding. In this review, we present the actions of ghrelin in food reward, including their dependence on other relevant modulators implicated in the motivational aspects of feeding, including dopamine, opioid peptides, and endocannabinoids. We also describe the interaction between brain areas involved in homeostatic regulation of feeding and the reward system, with a special emphasis on the role of arcuate nucleus melanocortins and lateral hypothalamus orexins in ghrelin function. Finally, we briefly discuss the actions of ghrelin in food reward in obesity. We propose that new insights into the mechanism of action of ghrelin in the rewarding and motivational control of food intake will help to understand food-related disorders including obesity and anorexia. Highlights • Ghrelin can be aversive by itself but reinforces food reward. • The DA mesolimbic system is the mediator of the actions of ghrelin on food reward. • Ghrelin interacts also with opioid peptides and endocannabinoids. • Obesity induces resistance to ghrelin actions in tests measuring food reward. [ABSTRACT FROM AUTHOR]

Background The endocannabinoid system (ECS) is considered a key player in the neurophysiology of food reward. Animal studies suggest that the ECS stimulates the sensory perception of food, thereby increasing its incentive-motivational and/or hedonic properties and driving consumption, possibly via interactions with metabolic hormones. However, it remains unclear to what extent this can be extrapolated to humans. Objective We aimed to investigate the effect of oral Δ9-tetrahydrocannabinol (THC) on subjective and metabolic hormone responses to visual food stimuli and food intake. Methods Seventeen healthy subjects participated in a single-blinded, placebo-controlled, 2 × 2 crossover trial. In each of the 4 visits, subjective "liking" and "wanting" ratings of high- and low-calorie food images were acquired after oral THC or placebo administration. The effect on food intake was quantified in 2 ways: via ad libitum oral intake (half of the visits) and intragastric infusion (other half) of chocolate milkshake. Appetite-related sensations and metabolic hormones were measured at set time points throughout each visit. Results THC increased "liking" (P  = 0.031) and "wanting" ratings (P  = 0.0096) of the high-calorie, but not the low-calorie images, compared with placebo. Participants consumed significantly more milkshake after THC than after placebo during oral intake (P  = 0.0005), but not intragastric infusion, of milkshake. Prospective food consumption ratings during the food image paradigm were higher after THC than after placebo (P  = 0.0039). THC also increased plasma motilin (P  = 0.0021) and decreased octanoylated ghrelin (P  = 0.023) concentrations before milkshake consumption (i.e. in both oral intake and intragastric infusion test sessions), whereas glucagon-like peptide 1 responses to milkshake intake were attenuated by THC during both oral (P  = 0.0002) and intragastric (P  = 0.0055) administration. Conclusions These findings suggest that the ECS drives food intake by interfering with anticipatory, cephalic phase, and metabolic hormone responses. This trial was registered at clinicaltrials.gov as NCT02310347. [ABSTRACT FROM AUTHOR]

Abstract The Leeds Food Preference Questionnaire (LFPQ) assesses, among other components, food preference (FP) using a procedure that requires both time and concentration. Its use may therefore be difficult in a complex protocol. In this article, we assessed the suitability of two shorter versions: 1) the LFPQ-S 2 , using two instead of four foods per group, and 2) the food preference questionnaire (FPQ–S 16), using the 16 same foods as the LFPQ, displayed simultaneously, that have to be ranked in order of preference. We assessed the reliability of these short versions using correlations and interchangeability (Bland and Altman) analyses. Sixty-nine healthy French adults completed the original LFPQ using foods adapted to the French context, and then the FPQ-S 16 procedure before (hungry state) and after (satiated state) a classic lunch. Finally, they had to select the two foods that best depict the characteristics of each group. The two foods receiving the most votes were used to calculate FP scores with the LFPQ-S 2 procedure. The FP scores were no different between the three questionnaires and were modified similarly by lunch intake. The FP scores also highly correlated between the two short versions and the LFPQ (mean r = 0.83 and 0.88 in the hungry state and r = 0.86 and 0.87 in the satiated state for LFPQ-S 2 and FPQ–S 16 , respectively). Finally, the FPQ-S 16 was considered to be a better surrogate of the LFPQ than the LFPQ-S 2. Scores of specific categories (groups of foods categorized by one property; e.g. high-fat foods) showed modest-to-good agreement, whereas scores of combined categories (groups of foods categorized by combined properties, e.g. high-fat and sweet foods) showed poor-to-modest agreement. Overall, the two short versions of the LFPQ could replace it to assess FP in a protocol in which time is limited. The FPQ-S 16 appears to be a better solution than the LFPQ-S 2 , based on interchangeability analyses. Highlights • The Leeds Food Preference Questionnaire (LFPQ) can be shortened to decrease the response burden. • A food preference questionnaire (FPQ-S 16) was proposed based on a buffet procedure. • The FPQ-S 16 appears to be a good surrogate for the LFPQ to assess food. [ABSTRACT FROM AUTHOR]

Background: Obesity and type 2 diabetes have been linked to alterations in food reward processing, which may be linked to insulin resistance. Objectives: In this clinical study, we investigated the respective contribution of insulin resistance, anthropometric measurements, and behavioral factors to brain reward activation in response to visual stimuli. Design: Food reward–related brain reward activation was assessed with functional magnetic resonance imaging in 39 overweight or obese individuals with impaired fasting glucose, impaired glucose tolerance, or both [22 women, 17 men; mean ± SD insulin sensitivity index (ISI): 2.7 ± 1.3; body mass index (BMI; kg/m²): 32.3 ± 3.7; body fat percentage: 40.5% ± 7.9%; fasting glucose: 6.3 ± 0.6 mmol/L]. Food and nonfood images were shown in a randomized block design. Brain activation (food compared with nonfood images) was correlated with anthropometric and behavioral variables. Behavioral variables included eating behavior [Three-Factor Eating Questionnaire (TFEQ)] and habitual physical activity (Baecke). Glucose and insulin concentrations, determined during an oral-glucose challenge, were used to assess the homeostatic model assessment for insulin resistance (HOMA-IR) and Matsuda ISI. Results: Food compared with nonfood brain activation was positively associated with HOMA-IR in the nucleus accumbens, right and left insula, and right cingulate gyrus (P < 0.005, corrected for multiple comparisons). TFEQ factor 2 was positively related to food compared with nonfood brain activation in the supramarginal gyrus (P < 0.005, corrected for multiple comparisons). Habitual physical activity during leisure time was negatively associated with food compared with nonfood brain activation in multiple regions associated with the attention and reward network (P < 0.005, corrected for multiple comparisons). Conclusions: Individuals with increased insulin resistance and emotional eating or disinhibition showed higher brain reactivity to food cues, which may imply changes in food preference and hyperphagia. Individuals with higher habitual physical activity showed less food reward–related brain activation. [ABSTRACT FROM AUTHOR]

Abstract The emission of 50 kHz ultrasonic vocalizations (USVs) by rats is thought to represent a measurable expression of the individuals underlying emotional state. These calls are also posited as fulfilling important communicative functions among conspecifics. In addition to social situations, 50 kHz USVs are recorded in a variety of reward-related contexts including sugary foods and drink, consumable ethanol, and drugs of abuse. The current study sought to directly compare several of these behavioural contexts in their capability to induce and modulate 50 kHz USV emission in adult male rats. Using two social conditions (exposure of naïve rat to a naturally cycling female and reuniting with a same-sex cage partner) and two non-social conditions (access to consumables as Fruit Loops or 2% ethanol v/v), we analyzed USVs recorded in 6 stimulus-presentation sessions. Only the female-exposure condition was found to increase 50 kHz call rate significantly over baseline, and this induction sensitized across 4 standard recording sessions. The use of a same-sex cage-mate and the two consumable food rewards did not elicit higher than baseline 50 kHz calling. None of the behavioural contexts altered the acoustic parameters (peak frequency, duration, and bandwidth) of emitted 50 kHz calls. In counter-balanced recording sessions, calling across all groups was significantly reduced by pre-treatment with the dopamine antagonist haloperidol compared with vehicle. Non-social conditions appeared to induce a greater proportion of flat calls at the expense of non-trill FM calls, while the reverse was seen for social conditions. However, the type of food reward and the type of social context mattered for proportion of flat and trill calls respectively. When compared with a control, access to sugary food but not ethanol induced a greater proportion of flat calls, and the female but not the cage-mate stimulus induced a greater proportion of trill calls. Highlights • 50 kHz USVs recorded in multiple sessions in response to distinct behavioural contexts. • Analysis reveals no differences in acoustic features of calls in these contexts. • 50 kHz USVs to both social and non-social contexts depended on dopamine signaling. • Consumable food-rewards appear to preferentially increase proportion of flat calls. • Social contexts appear to preferentially increase FM calls, with female inducing trills. [ABSTRACT FROM AUTHOR]

Understanding the neurobiological controls of feeding behavior is critical in light of the growing obesity pandemic, a phenomenon largely based on excessive caloric consumption. Feeding behavior and its underlying biological substrates are frequently divided in the literature into two separate categories: [1] homeostatic processes involving energy intake based on caloric and other metabolic deficits, and [2] non-homeostatic processes that involve feeding driven by environmental and cognitive factors. The present review summarizes both historic and recent research examining the homeostatic regulation of feeding with specific emphasis on hypothalamic and hindbrain circuitry that monitor and regulate various metabolic signals. Regarding non-homeostatic controls, we highlight higher-order brain structures that integrate feeding-relevant external, interoceptive, and cognitive factors, including sensory cortical processing, learned associations in the hippocampus, and reward-based processing in the nucleus accumbens and interconnected mesolimbic circuitry. Finally, the current review focuses on recent evidence that challenges the traditional view that distinct neural systems regulate homeostatic vs. non-homeostatic controls of feeding behavior. Specifically, we highlight several feeding-related endocrine systems that act on both lower- and higher-order substrates, present evidence for the modulation of learned and cognitive feeding-relevant behaviors by lower-order brain regions, and highlight data showing that apparent homeostatic-based feeding behavior is modulated by higher-order brain regions. Our concluding perspective is that the classic dissociation between homeostatic and non-homeostatic constructs in relation to feeding behavior is limited with regards to understanding the complex integrated neurobiological systems that control energy balance. [ABSTRACT FROM AUTHOR]

We developed a smart phone application to measure participants' food-reward perceptions and eating behavior in their naturalistic environment. Intensity ratings (0 - not at all to 10 - very strongly) of perceived anticipation of food (wanting) and food enjoyment at endpoint of intake (liking) were recorded as they occurred over a period of 14 days. Moreover, food craving trait, implicit and explicit attitude towards healthy food, and body composition were assessed. 53 participants provided complete data. Participants were classified by percentage of body fat; 33 participants with lower body fat (L-group) and 20 with higher body fat (H-group; ≥25% body fat for males and ≥32% for females). L-group participants reported 6.34 (2.00) food wanting events per day, whereas H-group participants recorded significantly fewer food wanting events (5.07 (1.42)); both groups resisted about the same percentage of wanting events (L-group: 29.2 (15.5)%; H-group 27.3 (12.8)%). Perceived intensity ratings were significantly different within the L-group in the order liking (7.65 (0.81)) > un-resisted wanting (leading to eating) (7.00 (1.01)) > resisted wanting (not leading to eating) (6.02 (1.72)) but not in the H-group. Liking scores (L-group: 7.65 (0.81); H-group: 7.14 (1.04)) were significantly higher in L-group than in H-group after controlling for age. Our results show that individuals with higher percentage of body fat show less food enjoyment after intake and reveal no differentiation in intensity ratings of perceived anticipatory and consummatory food reward. These results are consistent with a hypothesized reward deficiency among individuals with higher percentage of body fat. [ABSTRACT FROM AUTHOR]

Objective The incidence of depression is significantly compounded by obesity. Obesity arising from excessive intake of high-fat food provokes anxiodepressive behavior and elicits molecular adaptations in the nucleus accumbens (NAc), a region well-implicated in the hedonic deficits associated with depression and in the control of food-motivated behavior. To determine the etiology of diet-induced depression, we studied the impact of different dietary lipids on anxiodepressive behavior and metabolic and immune outcomes and the contribution of NAc immune activity. Methods Adult C57Bl/6 mice were subjected to isocaloric high-fat/high-sucrose diets (HFD), enriched in either saturated or monounsaturated fat, or a control low-fat diet (LFD). Metabolic responses, anxiodepressive behavior, and plasma and NAc inflammatory markers were assessed after 12 weeks. In separate experiments, an adenoviral construct inhibiting IKKβ, an upstream component of the nuclear factor kappa-b (NFkB) pathway, was a priori injected into the NAc. Results Both HFDs resulted in obesity and hyperleptinemia; however, the saturated HFD uniquely triggered anxiety-like behavior, behavioral despair, hyperinsulinemia, glucose intolerance, peripheral inflammation, and multiple pro-inflammatory signs in the NAc, including reactive gliosis, increased expression of cytokines, antigen-presenting markers and NFкB transcriptional activity. Selective NAc IKKβ inhibition reversed the upregulated expression of inflammatory markers, prevented anxiodepressive behavior and blunted compulsive sucrose-seeking in mice fed the saturated HFD. Conclusions Metabolic inflammation and NFкB-mediated neuroinflammatory responses in the NAc contribute to the expression of anxiodepressive behavior and heightened food cravings caused by a diet high in saturated fat and sugar. [ABSTRACT FROM AUTHOR]

• The LFPQ-fr proposes a culturally adapted tool to evaluate food reward in French populations. • The LFPQ-fr is a reproducible and reliable methods to approach liking and wanting for food. • The LFPQ-fr is reliable in identifying the effect of a meal on French individuals food reward. There is a growing global interest in the evaluation of food reward, necessitating the adaptation of culturally appropriate instruments for use in empirical studies. This work presents the development and validation of a culturally adapted French version of the Leeds Food Preference Questionnaire (LFPQ-fr). The LFPQ-fr was developed and validated in healthy-weight adults using the following systematic approach: i) selection and validation of appropriate food pictures; ii) linguistic translation of liking and wanting constructs in the target population (n = 430; 81% female; 42.2 ± 12.7 years); iii) validation of the sensitivity and reliability of the task performed in a fasted state and in response to a standardized test meal (n = 50; 50% female; 30.0 ± 8.4 years). During the first and second phases, the nutritional and perceptual validation of culturally appropriate food pictures and pertinent reward constructs, respectively, was demonstrated in a healthy-weight French sample. Findings from the third phase indicated that all food reward components were sensitive to the test meal and showed moderate to high agreement in both fasted (Lin's CCC =0.72–0.94) and fed (Lin's CCC = 0.53–0.80) appetitive states between visit 1 (V1) and visit (V2). Except for explicit liking fat bias, all primary outcomes were statistically consistent in fasted and fed states between V1 and V2. Changes in fat and taste biases in response to a standardized meal for all primary outcomes were also consistent between V1 and V2 except for explicit liking fat bias (Lin's CCC = 0.49- 0.72). The LFPQ-fr developed and tested in this study is a reproducible and reliable method to assess food reward in both the fasted and fed states in a healthy-weight French population. [ABSTRACT FROM AUTHOR]

Background Social reward plays a critical role in the development of beneficial social relationships, and disorders of the mechanisms controlling social reward are involved in the etiology of many psychiatric diseases. New method We present a novel operant social preference task to quantify social reward in rodents using an apparatus with three chambers separated by one-way vertical-swing doors. The experimental animal is placed in the larger chamber while the two smaller chambers either remain empty or contain a stimulus animal or other potential reward stimulus. Adding weights to the door can alter effort required for rewards. Results Hamsters (Mesocricetus auratus) entered the chamber containing a stimulus hamster significantly more frequently than an empty chamber. When the reinforcing effects of social interactions were compared to food reward under progressive cost requirements, the reinforcing effects of social interaction and sunflower seeds were similar. Progressively increasing the door weight decreased number of entries, but increased time spent attempting to open the doors. Comparison with existing methods The quantification of the rewarding properties of social interactions has almost exclusively used the conditioned place preference (CPP) paradigm. Although robust and reliable, CPP includes a memory component, because it relies on the association of place with the social interaction while the operant task presented here does not. Conclusions This task allows for detailed and direct assessment of social and non-social rewards that may serve as effective behavioral reinforcers in this operant conditioning model, and it can be used to investigate the neural mechanisms regulating motivation. [ABSTRACT FROM AUTHOR]

The female bias in eating disorder prevalence is the largest in all of psychiatry. Binge eating on palatable food (PF) is a core, maladaptive symptom that cuts across all major types of eating disorders and can be studied via animal models. Using an individual differences rat model of binge eating that identifies binge eating prone (BEP) and binge eating resistant (BER) phenotypes, we previously showed that, compared with males, females consume more PF and are more likely to be classified as BEP. One potential explanation for this sex difference is that PF is inherently more rewarding to females, leading to higher rates of binge eating. Here we tested the hypothesis that females have more robust behavioral and neural responses to PF reward than males. Adult male ( N = 18) and female ( N = 17) Sprague-Dawley rats were exposed to the Conditioned Place Preference paradigm using PF as the unconditioned stimulus. Select males ( N = 9) and females ( N = 9) were video-recorded during three of the PF-paired conditioning sessions to score feeding behavior. Following CPP, 13 male and 12 female rats were exposed to PF just prior to sacrifice to induce expression of the neural activation marker Fos, and Fos expression was quantified in mesocorticolimbic, hypothalamic, and amygdalar circuits. In the CPP paradigm, females displayed a more robust shift in preference for the chamber paired with PF compared with males, and behavioral analyses revealed that average duration of individual feeding bouts during pairing sessions was longer in females than in males. Fos expression was significantly higher in females vs. males in select regions of the mesocorticolimbic reward circuit, with no sex differences in hypothalamic or amygdalar regions. These results provide initial evidence that PF may be more rewarding to females than to males, possibly due to heightened responsiveness of neural substrates that mediate the hedonic and motivational responses to PF, which in part, may underlie sex differences in binge eating proneness. [ABSTRACT FROM AUTHOR]

Although attentional biases towards food cues may play a critical role in food choices and eating behaviours, it remains largely unexplored which specific food attribute governs visual attentional deployment. The allocation of visual attention might be modulated by anticipatory postingestive consequences, from taste sensations derived from eating itself, or both. Therefore, in order to obtain a comprehensive understanding of the attentional mechanisms involved in the processing of food-related cues, we recorded the eye movements to five categories of well-standardised pictures: neutral non-food, high-calorie, good taste, distaste and dangerous food. In particular, forty-four healthy adults of both sexes were assessed with an antisaccade paradigm (which requires the generation of a voluntary saccade and the suppression of a reflex one) and a free viewing paradigm (which implies the free visual exploration of two images). The results showed that observers directed their initial fixations more often and faster on items with high survival relevance such as nutrient and possible dangers; although an increase in antisaccade error rates was only detected for high-calorie items. We also found longer prosaccade fixation duration and initial fixation duration bias score related to maintained attention towards high-calorie, good taste and danger categories; while shorter reaction times to correct an incorrect prosaccade related to less difficulties in inhibiting distasteful images. Altogether, these findings suggest that visual attention is differentially modulated by both the accepted and rejected food attributes, but also that normal-weight, non-eating disordered individuals exhibit enhanced approach to food's postingestive effects and avoidance of distasteful items (such as bitter vegetables or pungent products). [ABSTRACT FROM AUTHOR]

In the present study we investigated whether stimulation of muscarinic acetylcholine (mACh) receptors in the ventral tegmental area (VTA) plays a role in the acquisition of food-based conditioned approach learning. Rats were exposed to 3 (in Experiment 1) or 7 (in Experiment 2) conditioning sessions in which 30, randomly presented light (CS) presentations were paired with delivery of food pellets (US), followed by one session with no light or food and finally one CS-only test session with only light stimulus presentations. Bilateral microinjections of scopolamine (a mACh receptor antagonist) were made either prior to each conditioning session (Experiment 1; to test effects on acquisition) or prior to the CS-only test (Experiment 2; to test effects on performance of the learned response). Scopolamine produced a dose-related significant reduction in the acquisition of conditioned approach but had no effect on its performance. These results suggest that mACh receptor stimulation in the VTA plays a necessary role in the acquisition of reward-related learning. [ABSTRACT FROM AUTHOR]

Here we sought to define behavioural traits linked to anxiety, reward, and exploration in different strains of rats commonly used in obesity research. We hypothesized that genetic variance may contribute not only to their metabolic phenotype (that is well documented) but also to the expression of these behavioural traits. Rat strains that differ in their susceptibility to develop an obese phenotype (Sprague-Dawley, Obese Prone, Obese Resistant, and Zucker rats) were exposed to a number of behavioural tests starting at the age of 8 weeks. We found a similar phenotype in the obesity susceptible models, Obese Prone and Zucker rats, with a lower locomotor activity, exploratory activity, and higher level of anxiety-like behaviour in comparison to the leaner Obese Resistant strain. We did not find evidence that rat strains with a genetic predisposition to obesity differed in their ability to experience reward from chocolate (in a condition place preference task). However, Zucker rats show higher motivated behaviour for sucrose compared to Obese Resistant rats when the effort required to obtain palatable food is relatively low. Together our data demonstrate that rat strains that differ in their genetic predisposition to develop obesity also differ in their performance in behavioural tests linked to anxiety, exploration, and reward and that these differences are independent of body weight. We conclude that genetic variations which determine body weight and the aforementioned behaviours co-exist but that future studies are required to identify whether (and which) common genes are involved. [ABSTRACT FROM AUTHOR]

While previous studies have demonstrated direct and generalized reciprocity in female Norway rats [26], the present study determined if unrelated male laboratory rats respond on behalf of a partner in an iterated sequential game. Pairs of rats worked for food reward in an operant chamber, where participants alternated as Donor and Responder in successive trials. In each trial, the Donor chose between variable and constant reward levers, where the constant reward lever delivered 1 pellet, and the variable reward lever triggered insertion of Responder lever(s); the Donor received 2 pellets when the Responder made any response. In forced-choice constant (FC) trials, the Responder also received 1 pellet for responding on the constant reward lever. In forced-choice variable (FV) trials, the Responder received no pellets for responding on the variable reward lever. In free-choice (FR) trials, the Responder chose between constant (1 pellet) and variable reward levers (0 pellets). With their cagemate, rats earned 61.4 ± 2.0 pellets (64.0 ± 2.1% of 96 possible pellets). As Donor in FC trials, rats preferred the variable reward lever, and the Responder responded frequently. In FV trials, Donor preference for the variable reward lever declined as Responder lever responses decreased. In FR trials, rats alternated responding on variable and constant reward levers as Donor and Responder, respectively. When paired with a new partner, there was no effect on Donor responses, but responses by the Responder decreased in the FV block. Similar effects were observed when paired with a maximally-cooperative stooge. Importantly, rats did not adjust their behavior as Donor to receive more pellets. Results suggest that unrelated male rats will work on behalf of a partner, and that their behavior is sensitive to familiarity, and to cooperative responses by their partner. [ABSTRACT FROM AUTHOR]

The rodent tasks with food rewards are useful methods to evaluate memory functions, including hole-board and corridor tests. The AMBITUS system (a square corridor with several food rewards), as a combination of these tests, was developed for the investigation of a variety of parameters associated with exploration and cognitive performance in rodents. Experiments were performed to characterize these behaviors in healthy rats and a new “schizophrenia-like” rat substrain with impaired learning ability to reveal the reliability in tests related to these functions. A square corridor was constructed with equally spaced sites along each wall (4 inside and 4 outside) resulting in 16 side-boxes for food rewards. Photocells at each box recorded the visits into the side-boxes (as exploratory activity), while the eating parameters were obtained from video records. The animals were exposed to two types of tasks repeatedly in two series: all (16) or only the inside (8) boxes (Task 1 or Task 2, respectively) were baited. Most of the rats acquired Task 1, and their performance improved by repetition, but the new substrain showed decreased exploration and learning capacity. The introduction of Task 2 caused prompt preference of the baited inner side-boxes, and gradually improved working and reference memory during the trials. The manual and automated scoring of the visits into the side-boxes showed significant ( r = 0.97) correlation. The results proved that healthy animals could perform the simple tasks in the square corridor after a few repetitions. The semi-automated AMBITUS system might be appropriate to detect cognitive flexibility after different manipulations, and it provides immediate, online assessment of exploratory behavior of a large number of animals within a short period of time, and it reduces the possibility of experimenter bias. [ABSTRACT FROM AUTHOR]

• Self-reported hunger and desire to eat something tasty did not change after tDCS. • Energy and macronutrient intake were not altered after tDCS. • Mood states did not change after tDCS. • a-tDCS over the left DPFC showed a trend towards to decrease implicit wanting for low-fat savory food. • future studies with feed participants, multisession stimulations, and other montages may be tested in an attempt to alleviate mood and appetite disturbances that occur in luteal phase of the menstrual cycle. This study investigated the acute effect of anodal transcranial direct current stimulation (a-tDCS) over the left dorsolateral prefrontal cortex (DLPFC) on appetite, energy intake, food preferences, and mood states in the luteal and follicular phases of the menstrual cycle in women presenting premenstrual syndrome. Sixteen women (26.5 ± 5.2 years; 1.63 ± 0.1 m; 64.2 ± 12.8 kg; body mass index 24.0 ± 5.0 kg/m2; body fat 27.6 ± 7.5%) with the eumenorrheic menstrual cycle were submitted to a-tDCS and sham-tDCS conditions over their follicular and luteal phases. At pre - and post-tDCS, hunger and desire to eat something tasty, (analogic visual scale), the profile of mood states (POMS), and the psychological components of food preferences (Leeds Food Preference Questionnaire-BR) were assessed. Participants recorded their food intake for the rest of the day using a diary log. There was a trend towards main effect of condition for decreased implicit wanting for low-fat savory food after a-tDCS but not sham-tDCS regardless of menstrual cycle phase (p = 0.062). There was no effect for self-reported hunger, desire to eat, energy and macronutrient intake, and on other components of food preferences (explicit liking and wanting for low- and high-fat savory and sweet foods, implicit wanting for low- and high-fat sweet and high-fat savory food); as well as for mood states. Although no significant effects of a-tDCS were found, the present investigation provides relevant perspectives for future studies. [ABSTRACT FROM AUTHOR]

• Food reward is a contributing factor to eating disorders and obesity. • Meal-induced changes in fNIRS activation were associated with food reward (LFPQ-CH) • fNIRS combined with LFPQ-CH predicted food intake and eating behaviour traits. • LFPQ-CH with fNIRS are valid complementary tools for food reward in Chinese adults. Adverse neurobehavioral responses to food could be one of the contributing factors to obesity in China, which is a major public health issue. There is a need for methodologies to better understand the cognitive processes and neural mechanisms underlying eating behaviors. This study investigated neurobehavioral markers of food preference and reward in pre- and post-meal states, and their association with eating behaviors in young Chinese adults. Chinese adults (N = 80: 39 male) completed the Leeds Food Preference Questionnaire (LFPQ-CH), and a Functional Near-Infrared Spectroscopy (fNIRS) Visual Food Cues Paradigm before and after an ad libitum test meal. The Dutch Eating Behavior Questionnaire (DEBQ) and VAS appetite scores were used to measure appetitive traits and states. Results showed that categorisation of foods along dimensions of sweetness and fat content were valid for the general population in China. Changes in food preferences and increased dorsolateral prefrontal cortex (DLPFC) activation to high-fat savoury (HFSA) food were shown following a test meal. LFPQ-CH and fNIRS variables were able to predict unique variance in ad libitum food intake and DEBQ traits. The current results support the use of LFPQ-CH with fNIRS as valid and complementary tools for the neurobehavioral evaluation of food reward and preference. This methodological approach is sensitive to changes in appetitive state; can differentiate along the spectrum of eating behaviour traits and is predictive of food intake. [ABSTRACT FROM AUTHOR]

• We measured autonomic outflow and efferent metabolism before and after consumption. • We manipulated the location of nVNS stimulation in the outer ear. • The different locations were earlobe, cymba conchae, tragus, cymba conchae+tragus. • nVNS in cymba conchae decreases pre -consumption heart-rate variability. • nVNS in other locations decreases post -consumption heart-rate variability. Vagus nerve signals from the gut to brain carry information about nutrients and drive food reward. Such signals are disrupted by consuming large amounts of high-calorie foods, necessitating greater food intake to elicit a similar neural response. Non‐invasive vagus nerve stimulation (nVNS) via a branch innervating the ear is a candidate treatment for obesity in humans. There is disagreement on the optimal location of nVNS in the ear for experimental and clinical studies. There are also no studies comparing nVNS in hungry and post-prandial states. We aimed to compare ear position(s) for nVNS and explore the effects of nVNS during hungry and post-prandial states on proxies for autonomic outflow (heart-rate variability) and efferent metabolism (gastric wave frequency and resting energy expenditure). In a within-subject design, 14 participants (10 women, on average 29.4 +/- 6.7 years old) received nVNS in four different locations (cymba conchae, tragus, earlobe, or tragus AND cymba conchae) on separate days. In each session, participants were asked to consume a palatable chocolate flavored milk. With electrography on the abdomen and indirect calorimetry in a canopy, we measured electro-cardiogram, electro-gastrogram and resting energy expenditure for 15 min before and at least 35 min after consumption of the palatable drink. We also collected ratings of the palatable drink and internal and other states. Pre-drink consumption (in a hungry state) we observed no differences in the effect of location of acute nVNS on resting energy expenditure and gastric wave measures. However, nVNS in cymba conchae decreases heart-rate variability (relative to sham) and ratings of how much participants want to consume the drink (relative to tragus AND cymba conchae and a trend relative to sham). After drink consumption and with continued nVNS, gastric wave frequency is unchanged, and resting energy expenditure increases regardless of stimulation location. Heart-rate variability decreases in all locations, except cymba conchae. We also observe a trend for an increase in gastric wave amplitude in late post-drink consumption time-points in cymba conchae. We observe no support for the combined stimulation of tragus AND cymba conchae being more effective than either of the individual locations. These results suggest that nVNS in the cymba conchae in a hungry state has a similar acute effect on vagal tone as food consumption: to decrease heart rate variability. This effect then negates the usual postprandial effects of a decrease in heart rate variability as seen in the other nVNS locations. These preliminary observations suggest that nVNS in cymba conchae may act primarily on vagal afferent autonomic (and only modestly on metabolic output) in a similar way as food consumption does. [ABSTRACT FROM AUTHOR]

The Leeds Food Preference Questionnaire (LFPQ), a computer-based task for measuring reward responses (liking/wanting) and preferences for images of food, is a widely used tool. However, no cultural adaptation studies to date have addressed its validity and repeatability in a test–retest design. The present study aimed to develop a Japanese version of the LFPQ (LFPQ-J); examine its outcomes under fasted and fed states; and test its reproducability after one week. An online survey containing foods that were either low-fat sweet, high-fat sweet, low-fat savoury or high-fat savoury was first conducted among a sample of 200 Japanese adults (100 men and 100 women) to develop and validate a culturally appropriate food image database. Sixty participants (30 men and 30 women) then participated in two identical trials where they completed the LFPQ-J under fasted and fed states (immediately after a standardised meal), at least one week apart. The absolute difference within the participants in scores for explicit liking, explicit wanting, implicit wanting and relative preference between the trials was analysed using Bland-Altman plots and Pearson's or Spearman's correlation coefficients. In the fasted state for each food category, 91.1 to 96.4 % of the data were plotted within the 95% limits of agreement and intra-personal correlation were 0.58–0.81. In the fed state for each food category, 91.1 to 98.2 % of the data were plotted within the 95% limits of agreement and intra-personal correlation were 0.40–0.83. The present study demonstrates that the LFPQ-J is a sensitive and reproducible instrument for the evaluation of liking and wanting for food varying in fat content and sweet taste in Japanese adults. [ABSTRACT FROM AUTHOR]

The obesity epidemic continues unabated and currently available pharmacological treatments are not sufficiently effective. Combining gut/brain peptide, GLP-1, with estrogen into a conjugate may represent a novel, safe and potent, strategy to treat diabesity. Here we demonstrate that the central administration of GLP-1-estrogen conjugate reduced food reward, food intake, and body weight in rats. In order to determine the brain location of the interaction of GLP-1 with estrogen, we avail of single-photon emission computed tomography imaging of regional cerebral blood flow and pinpoint a brain site unexplored for its role in feeding and reward, the supramammillary nucleus (SUM) as a potential target of the conjugated GLP-1-estrogen. We confirm that conjugated GLP-1 and estrogen directly target the SUM with site-specific microinjections. Additional microinjections of GLP-1-estrogen into classic energy balance controlling nuclei, the lateral hypothalamus (LH) and the nucleus of the solitary tract (NTS) revealed that the metabolic benefits resulting from GLP-1-estrogen injections are mediated through the LH and to some extent by the NTS. In contrast, no additional benefit of the conjugate was noted on food reward when the compound was microinjected into the LH or the NTS, identifying the SUM as the only neural substrate identified here to underlie the reward reducing benefits of GLP-1 and estrogen conjugate. Collectively we discover a surprising neural substrate underlying food intake and reward effects of GLP-1 and estrogen and uncover a new brain area capable of regulating energy balance and reward. [ABSTRACT FROM AUTHOR]

The idea that food intake is motivated by (or in anticipation of) ‘hunger’ arising from energy depletion is apparent in both public and scientific discourse on eating behaviour. In contrast, our thesis is that eating is largely unrelated to short-term energy depletion. Energy requirements meal-to-meal are trivial compared with total body energy stores, and energy supply to the body's tissues is maintained if a meal or even several meals are missed. Complex and exquisite metabolic machinery ensures that this happens, but metabolic regulation is only loosely coupled with the control of energy intake. Instead, food intake needs to be controlled because the limited capacity of the gut means that processing a meal presents a significant physiological challenge and potentially hinders other activities. We illustrate the relationship between energy (food) intake and energy expenditure with a simple analogy in which: (1) water in a bathtub represents body energy content, (2) water in a saucepan represents food in the gut, and (3) the bathtub is filled via the saucepan. Furthermore, (4) it takes hours to process and pass the full energy (macronutrient) content of the saucepan to the bathtub, and (5) both the saucepan and bathtub resist filling, representing negative feedbacks on appetite (desire to eat). This model is consistent with the observations that appetite is reduced acutely by energy intake (a meal added to the limited capacity of the saucepan/gut), but not increased by an acute increase in energy expenditure (energy removed from the large store of energy in the bathtub/body). The existence of relatively very weak but chronic negative feedback on appetite proportional to body fatness is supported by observations on the dynamics of energy intake and weight gain in rat dietary obesity. (We use the term ‘appetite’ here because ‘hunger’ implies energy depletion.) In our model, appetite is motivated by the accessibility of food and the anticipated and experienced pleasure of eating it. The latter, which is similar to food reward, is determined primarily by the state of emptiness of the gut and food liking related to the food's sensory qualities and macronutrient value and the individual's dietary history. Importantly, energy density adds value because energy dense foods are less satiating kJ for kJ and satiation limits further intake. That is, energy dense foods promote energy intake by virtue (1) of being more attractive and (2) having low satiating capacity kJ for kJ, and (1) is partly a consequence of (2). Energy storage is adapted to feast and famine and that includes unevenness over time of the costs of obtaining and ingesting food compared with engaging in other activities. However, in very low-cost food environments with energy dense foods readily available, risk of obesity is high. This risk can be and is mitigated by dietary restraint, which in its simplest form could mean missing the occasional meal. Another strategy we discuss is the energy dilution achieved by replacing some sugar in the diet with low-calorie sweeteners. Perhaps as or more significant, though, is that belief in short-term energy balancing (the energy depletion model) may undermine attempts to eat less. Therefore, correcting narratives of eating to be consistent with biological reality could also assist with weight control. [ABSTRACT FROM AUTHOR]

Background: Evidence from experimental studies has demonstrated that higher than normal iron concentrations can lead to pancreatic β cell dysfunction and impaired glucose metabolism. Studies on body iron stores in early pregnancy and subsequent gestational diabetes mellitus (GDM) risk are sparse.Objective: Our objective was to determine whether biomarkers of body iron stores measured in early pregnancy are associated with GDM risk.Methods: A case-control study of 350 GDM cases and 349 non-GDM controls was conducted in participants from the Danish National Birth Cohort. Blood was collected at a mean ± SD gestational age of 9.4 ± 3.2 wk. Plasma biomarkers of iron stores, including ferritin and soluble transferrin receptor (sTfR), were measured. Logistic regression was used to estimate the OR of GDM associated with quintiles of plasma biomarkers of body iron stores, controlling for maternal age, family history of diabetes, exercise in pregnancy, parity, and prepregnancy body mass index (BMI).Results: Cases were older (mean ± SD age: 32.2 ± 4.3 compared with 29.9 ± 4.2 y) and had a higher BMI (in kg/m(2); mean ± SD: 28.7 ± 6.0 compared with 24.1 ± 4.6) than controls. Plasma concentrations of both ferritin and sTfR in early pregnancy were significantly higher in GDM cases than in controls [means ± SDs: 80.6 ± 56.0 compared with 71.8 ± 50.1 μg/L (P = 0.03) and 1.5 ± 0.7 compared with 1.4 ± 0.6 mg/L (P = 0.002) for ferritin and sTfR, respectively]. Ferritin was positively and significantly associated with GDM risk even after adjustment for major risk factors of GDM, including prepregnancy BMI. ORs across increasing quintiles of ferritin were 1.00 (reference), 1.25 (95% CI: 0.70, 2.22), 1.89 (95% CI: 1.06, 3.37), 0.82 (95% CI: 0.46, 1.48), and 2.34 (95% CI: 1.30, 4.21) (P-linear trend = 0.02).Conclusion: These findings suggest that plasma ferritin measured in early pregnancy is significantly and positively associated with GDM risk. [ABSTRACT FROM AUTHOR]

Background: The Power of Food Scale (PFS) seeks to identify individuals who experience high appetitive drive in response to food cues, which is a construct termed "hedonic hunger."Objective: The purpose of this study was to assess cross-sectional correlates and predictive power of PFS scores to probe the construct of hedonic hunger.Methods: Separate data from 3 studies (study 1, n = 44; study 2, n = 398; study 3, n = 100) were used to evaluate the construct of hedonic hunger. We examined the correlations between the PFS and neural responsivity during intake and anticipated intake of palatable foods, behavioral food reinforcement, perceptual hedonic ratings of food images, and change in body mass index (BMI) and binge eating over time.Results: Hedonic hunger was strongly related to bilateral brain response in regions implicated in oral somatosensory processing during cue-elicited anticipation of food intake (study 1; right postcentral gyrus: r = 0.67, P < 0.001; left postcentral gyrus: r = 0.64, P < 0.001), and was correlated with behavioral food reinforcement (study 2; r = 0.31, P = 0.03) and perceptual hedonic ratings (study 3; r = 0.24, P = 0.02). Hedonic hunger was not associated with baseline BMI (studies 1-3: P = 0.14, 0.21, and 0.37, respectively) or change in BMI over the 2-y follow-up (studies 1 and 2: P = 0.14 and 0.37, respectively) but was significantly correlated with baseline binge eating in 2 samples (study 1: r = 0.58, P = 0.001; study 2: r = 0.31, P = 0.02; and study 3: P = 0.02).Conclusions: Hedonic hunger was not predictive of weight regulation. However, individuals who report high hedonic hunger are likely to show increased neural and perceptual responses to cues of palatable foods, increased motivation to consume such foods, and a greater likelihood of current binge eating. [ABSTRACT FROM AUTHOR]

There is a well-established literature linking obesity to altered dopamine signaling and brain response to food-related stimuli. Neuroimaging studies frequently report enhanced responses in dopaminergic regions during food anticipation and decreased responses during reward receipt. This has been interpreted as reflecting anticipatory “reward surfeit”, and consummatory “reward deficiency”. In particular, attenuated response in the dorsal striatum to primary food rewards is proposed to reflect anhedonia, which leads to overeating in an attempt to compensate for the reward deficit. In this paper, we propose an alternative view. We consider brain response to food-related stimuli in a reinforcement-learning framework, which can be employed to separate the contributions of reward sensitivity and reward-related learning that are typically entangled in the brain response to reward. Consequently, we posit that decreased striatal responses to milkshake receipt reflect reduced reward-related learning rather than reward deficiency or anhedonia because reduced reward sensitivity would translate uniformly into reduced anticipatory and consummatory responses to reward. By re-conceptualizing reward deficiency as a shift in learning about subjective value of rewards, we attempt to reconcile neuroimaging findings with the putative role of dopamine in effort, energy expenditure and exploration and suggest that attenuated brain responses to energy dense foods reflect the “fuel”, not the fun entailed by the reward. [ABSTRACT FROM AUTHOR]

Desire, purchase, and consumption of fast-moving consumer goods often follow actual motivational states instead of habitual preferences. This has led to an increasing interest within health sciences to investigate the causes for irrational eating behaviours among consumers, particularly with the use of indirect measurements. However, literature results on the relationship between dynamic, motivational concepts (e.g., approach or avoidance tendencies) and evaluative concepts (e.g., positive or negative associations) remain inconclusive, possibly due to the use of different experimental manipulations and methodologies to operationalize these. Our aim with this study is to contribute to this line of research by developing a novel methodology that is based on structurally identical indirect measurement procedures. We measured explicit desire (motivation) and liking (evaluation) of two different foods (sandwich and sweets) on visual analogue scales, as well as implicit approach–avoidance tendencies and implicit positive–negative associations with two variants of the recoding-free Implicit Association Tests (IAT-RFs). At first, all participants ( N = 108) unwrapped, smelled, and explicitly judged the two foods, then all watched a video clip (during which half of the participants were allowed to eat the sandwich but not the sweets), and finally they all performed the two indirect measurements. Thus, desire for the foods was experimentally manipulated between participants. We hypothesized that a valid measure should show an interaction of food category (manipulated within participants) and desire fulfilment. Hence, explicit desire and implicit approach motivation should be higher for participants that were not allowed to consume the sandwich and fulfil their desire, compared to the group that was able to eat the sandwich during the experiment. Results confirm our hypothesis. The motivational IAT-RF correctly assessed approach tendencies towards the sandwich in the group that did not eat, and approach tendencies towards the sweets in the group that just ate a sandwich. In contrast, the evaluative IAT-RF measure did not reflect a clear “preference” towards any of the two popular products in both groups. This research provides a potentially relevant methodology for consumer studies’ by offering a chance to differentiate between implicit motivational and evaluative concepts within consumer behaviour. [ABSTRACT FROM AUTHOR]

Animals learn to prefer and increase consumption of flavors paired with postingestive nutrient sensing. Analogous effects have been difficult to observe in human studies. One possibility is experience with the modern, processed diet impairs learning. Food processing manipulates flavor, texture, sweetness, and nutrition, obscuring ordinary correspondences between sensory cues and postingestive consequences. Over time, a diet of these processed ‘junk’ foods may impair flavor-nutrient learning. This ‘flavor-confusion’ hypothesis was tested by providing rats long-term exposure to cafeteria diets of unusual breadth (2 or 3 foods per day, 96 different foods over 3 months, plus ad libitum chow). One group was fed processed foods (PF) with added sugars/fats and manipulated flavors, to mimic the sensory-nutrient properties of the modern processed diet. Another group was fed only ‘natural’ foods (NF) meaning minimally-processed foods without manipulated flavors or added sugars/fats (e.g., fresh fruits, vegetables, whole grains) ostensibly preserving the ordinary correspondence between flavors and nutrition. A CON group was fed chow only. In subsequent tests of flavor-nutrient learning, PF and NF rats consistently acquired strong preferences for novel nutrient-paired flavors and PF rats exhibited enhanced learned acceptance, contradicting the ‘flavor-confusion’ hypothesis. An unexpected finding was PF and NF diets both caused lasting reduction in ad lib sweet solution intake. Groups did not differ in reinforcing value of sugar in a progressive ratio task. In lick microstructure analysis the NF group paradoxically showed increased sucrose palatability relative to PF and CON, suggesting the diets have different effects on sweet taste evaluation. [ABSTRACT FROM AUTHOR]

Background: Millions of Americans attempt to lose weight each year, and it is unclear whether the modality of acute, tightly controlled energy depletions can differently affect appetite parameters and olfaction. Objective: The objectives were to examine how the modality of an acute 3-d isocaloric 25% energy depletion by dieting alone or by aerobic exercise alone differently affects appetite and appetite-related hormones, ad libitum feeding, food reward (snack points), and olfaction. Design: Ten male participants with a mean ± SD age of 23.7 ± 5.1 y and an initial mean ± SD body weight of 83.2 ± 11.5 kg participated in this randomized crossover design. Baseline measurement [day 1 of the control condition (CON1)] was performed and repeated 3 d later [day 4 of the control condition (CON4)], after which randomization was applied to the order of the 2 experimental conditions: 25% daily needs energy deficits induced by diet only (DIET) and by exercise only (EX) and tested before [day 1 of DIET (DIET1) and day 1 of EX (EX1)] and after 3 d [day 4 of DIET (DIET4) and day 4 of EX (EX4)] of the intervention. Body weight, leptin and ghrelin concentrations, relative-reinforcing value of food, and olfaction were measured at days 1 and 4. Body composition (dual-energy X-ray absorptiometry), ad libitum energy intake (EI; buffet), and pal-atability (visual analog scale) were measured only at day 4. Results: Relative to CON4, EI (P = 0.001), payability (P = 0.01), and odor threshold (P = 0.05) were higher at DIET4; relative to CON4, palatability (P = 0.03) was higher at EX4. Compared with EX4, EI was higher for DIET4 (P = 0.006). Relative to CON4, snack points earned were higher at DIET4 (P = 0.03) and EX4 (P = 0.001); more snack points were earned at EX4 relative to DIET4 (P = 0.001). Conclusions: Compared with the control condition, DIET represented a greater acute challenge to appetite regulation than EX, as demonstrated by greater appetite and ad libitum EI. This study confirms that compared with depletions by exercise alone, acute caloric restriction results in rapid changes in appetite that result in compensatory eating, which may initially dissuade potential success in weight-loss efforts. [ABSTRACT FROM AUTHOR]

Dogs' responsiveness to instructions of the handler is known to be influenced by several factors. In this study we examined whether reward-handler dissociation has an effect on the obedience performance of family dogs with basic training history. We looked at situations involving human-dog interactions under controlled laboratory settings by measuring dogs' obedience performance to two known commands ('sit' and 'down') in several different conditions. For two different groups of dogs, we manipulated the source of the food reward: it was provided either by the handler or by a remote controlled food dispenser device during a practising period, when the handler stood in the dog's close vicinity (0.5 m). In three different test conditions the position of the handler was manipulated: he/she stood further away (3 m) from the dog either beside a screen, hid behind the screen or was outside of the room. No food reward was provided during the test trials, which were interrupted by so called reminder sessions, where dog-handler dyads practiced both commands in close vicinity to each other and food reward was also involved. We found that the performance of dogs that experienced receiving food reward from the handler was significantly poorer during the test conditions, i.e. in contexts with increased distance between them and the handler(including handler out of sight), as compared to their performance during the reminder sessions in the handlers' close vicinity. Experience with receiving food reward form the dispenser device lessened the difference in dogs' obedience between the test conditions and reminder sessions, and moreover, it also revealed a more prompt response to the 'sit' than to the 'down' commands. Thus our results show that reward-handler dissociation seems to affect dogs' obedience performance in the investigated conditions. [ABSTRACT FROM AUTHOR]

Dietary glucose is a robust elicitor of central reward responses and ingestion, but the key peripheral sensors triggering these orexigenic mechanisms are not entirely known. The objective of this study was to determine whether glucokinase, a phosphorylating enzyme with known glucosensory roles, is also expressed in taste bud cells and contributes to the immediate hedonic appeal of glucose-containing substances. Glucokinase (GCK) gene transcripts were localized in murine taste bud cells with RNAScope®, and GCK mRNA was found to be upregulated in the circumvallate taste papillae in response to fasting and after a period of dietary access to added simple sugars in mice, as determined with real time-qPCR. Pharmacological activation of glucokinase with Compound A increased primary taste nerve and licking responses for glucose but did not impact responsivity to fructose in naïve mice. Virogenetic silencing of glucokinase in the major taste fields attenuated glucose-stimulated licking, especially in mice that also lacked sweet receptors, but did not disrupt consummatory behaviors for fructose or the low-calorie sweetener, sucralose in sugar naïve mice. Knockdown of lingual glucokinase weakened the acquired preference for glucose over fructose in sugar-experienced mice in brief access taste tests. Collectively, our data establish that glucokinase contributes to glucose appetition at the very first site of nutrient detection, in the oral cavity. The findings expand our understanding of orosensory inputs underlying nutrition, metabolism, and food reward. • Glucokinase is expressed in the taste bud cells. • Gustatory glucokinase is upregulated by energy deficit and regular consumption of simple sugars. • Gustatory glucokinase is required for normal glucose taste detection and contributes to the hedonic appeal of this nutrient. [ABSTRACT FROM AUTHOR]

Through flavor–nutrient conditioning rats learn to prefer and increase their intake of flavors paired with rewarding, postingestive nutritional consequences. Since obesity is linked to altered experience of food reward and to perturbations of nutrient sensing, we investigated flavor–nutrient learning in rats made obese using a high fat/high carbohydrate (HFHC) choice model of diet-induced obesity (ad libitum lard and maltodextrin solution plus standard rodent chow). Forty rats were maintained on HFHC to induce substantial weight gain, and 20 were maintained on chow only (CON). Among HFHC rats, individual differences in propensity to weight gain were studied by comparing those with the highest proportional weight gain (obesity prone, OP) to those with the lowest (obesity resistant, OR). Sensitivity to postingestive food reward was tested in a flavor–nutrient conditioning protocol. To measure initial, within-meal stimulation of flavor acceptance by post-oral nutrient sensing, first, in sessions 1–3, baseline licking was measured while rats consumed grape- or cherry-flavored saccharin accompanied by intragastric (IG) water infusion. Then, in the next three test sessions they received the opposite flavor paired with 5 ml of IG 12% glucose. Finally, after additional sessions alternating between the two flavor-infusion contingencies, preference was measured in a two-bottle choice between the flavors without IG infusions. HFHC-OP rats showed stronger initial enhancement of intake in the first glucose infusion sessions than CON or HFHC-OR rats. OP rats also most strongly preferred the glucose-paired flavor in the two-bottle choice. These differences between OP versus OR and CON rats suggest that obesity is linked to responsiveness to postoral nutrient reward, consistent with the view that flavor–nutrient learning perpetuates overeating in obesity. [ABSTRACT FROM AUTHOR]

Binge eating is a behavior observed in a variety of human eating disorders. A d libitum fed rodents daily and time-limited exposed to a high-fat diet (HFD) display robust binge eating events that gradually escalate over the initial accesses. Intake escalation is proposed to be part of the transition from a controlled to a compulsive or loss of control behavior. Here, we used a combination of behavioral and neuroanatomical studies in mice daily and time-limited exposed to HFD to determine the neuronal brain targets that are activated – as indicated by the marker of cellular activation c-Fos – under these circumstances. Also, we used pharmacologically or genetically manipulated mice to study the role of orexin or ghrelin signaling, respectively, in the modulation of this behavior. We found that four daily and time-limited accesses to HFD induce: (i) a robust hyperphagia with an escalating profile, (ii) an activation of different sub-populations of the ventral tegmental area dopamine neurons and accumbens neurons that is, in general, more pronounced than the activation observed after a single HFD consumption event, and (iii) an activation of the hypothalamic orexin neurons, although orexin signaling blockage fails to affect escalation of HFD intake. In addition, we found that ghrelin receptor-deficient mice fail to both escalate the HFD consumption over the successive days of exposure and fully induce activation of the mesolimbic pathway in response to HFD consumption. Current data suggest that the escalation in high fat intake during repeated accesses differentially engages dopamine neurons of the ventral tegmental area and requires ghrelin signaling. [ABSTRACT FROM AUTHOR]

Anabolic–androgenic steroid (AAS) abuse is implicated in maladaptive behaviors such as increased aggression and risk taking. Impaired judgment due to changes in the mesocorticolimbic dopamine system may contribute to these behavioral changes. While AAS are known to influence dopamine function in mesocorticolimbic circuitry, the effects on decision making are unknown. This was the focus of the present study. Adolescent male Long-Evans rats were treated chronically with high-dose testosterone (7.5 mg/kg) or vehicle (13% cyclodextrin in water), and tested for cost/benefit decision making in two discounting paradigms. Rats chose between a small reward (1 sugar pellet) and a large discounted reward (3 or 4 pellets). Probability discounting (PD) measures sensitivity to reward uncertainty by decreasing the probability (100, 75, 50, 25, 0%) of receiving the large reward in successive blocks of each daily session. Effort discounting (ED) measures sensitivity to a work cost by increasing the lever presses required to earn the large reward (1, 2, 5, 10, 15 presses). In PD, testosterone-treated rats selected the large/uncertain reward significantly less than vehicle-treated controls. However, during ED, testosterone-treated rats selected the large/high effort reward significantly more than controls. These studies show that testosterone has divergent effects on different aspects of decision making. Specifically, testosterone increases aversion to uncertainty but decreases sensitivity to the output of effort for reward. These results have implications for understanding maladaptive behavioral changes in human AAS users. [ABSTRACT FROM AUTHOR]

Anabolic–androgenic steroid (AAS) abuse is prevalent not only among elite athletes, but is increasingly common in high school and collegiate sports. AAS are implicated in maladaptive behaviors such as increased aggression and risk taking, which may result from impaired cognition. Because they affect dopamine function in prefrontal cortical (PFC)-striatal circuitry, AAS may disrupt PFC-dependent processes such as behavioral flexibility. This was the focus of the present study. Adolescent male Long-Evans rats were treated chronically with high-dose testosterone (7.5 mg/kg in water with 13% cyclodextrin) or vehicle sc, and tested for set-shifting and reversal-learning. For set-shifting, rats were trained on a visual cue task (VCT), then were shifted to a direction cue task (DCT), or vice-versa. For reversal learning, rats were first trained on VCT and were then required to press the opposite lever. 2-cue set-shifting introduced a novel paradigm in which rats shifted from a 1-Light Visual Task (1LVT) to a tone cue task (TCT). Testosterone-treated rats were significantly impaired on the set-shift from DCT to VCT compared to vehicle-treated controls (trials to criterion: vehicle 240.9±29.9, testosterone 388.3±59.3, p <0.05). However, on the set-shift from VCT to DCT, testosterone did not affect performance. During reversal-learning, testosterone significantly increased trials to criterion (vehicle: 495.9±91.8 trials, testosterone: 793.7±96.7 trials, p <0.05). In 2-cue set-shifting, testosterone diminished performance and the difference showed borderline significance (vehicle: 443.2±84.4 trials, testosterone: 800.4±178.2 trials, p =0.09). Our results show that testosterone impairs behavioral flexibility and have implications for understanding cognitive and behavioral changes in human AAS users. [ABSTRACT FROM AUTHOR]

Anticipatory behaviours may serve a useful tool in studying positive emotional states in animals. This study aimed to investigate if lambs express anticipatory behaviours for opportunities to play or a food reward and if these behaviours would differ depending on the anticipated event. Forty-two male lambs were allocated into three treatment groups (control, play, food). Play and food lambs were conditioned to anticipate play or food in a holding pen for three minutes prior to accessing a reward arena containing toy objects or concentrate, respectively. Control lambs returned to their home pen following three minutes in the holding pen. Compared to the control lambs, both play and food lambs differed in several behaviours frequencies and durations, e.g. by an increased frequency of behavioural transitions and duration of walking. Following these observations, food lambs received the toy objects when entering the reward arena. The subsequent session in the holding pen resulted in a decrease in number of behavioural transitions, time spent walking and an increase in time standing still. In conclusion, anticipating a positive event resulted in differences in behaviour compared to a control group, and these behaviours are affected when the anticipated event does not fit with the lambs’ expectations. [ABSTRACT FROM AUTHOR]

Melanin-concentrating hormone [MCH] is a neuropeptide that modulates several behaviors, such as feeding and reward. Because the hedonic and rewarding features of a food also influence feeding behavior, the nucleus accumbens [Acb] has been highlighted as a key area integrating these roles. Functional data confirm that MCH acts on a subdivision of the Acb; however, considering the importance of finding anatomical and neurochemical data that correlate the previously demonstrated function of MCH, we delineated this investigation based on the following points: (1) Is there a pattern of innervation by MCH fibers regarding the subregions within the Acb? (2) Specifically, which hypothalamic nuclei synthesize MCH and innervate the Acb? (3) Finally, what are the neurochemical identities of the accumbal neurons innervated by MCH inputs? We examined the MCH immunoreactivity [MCH-ir] in the Acb in rat brains using the peroxidase technique. Additionally, after injecting retrograde neuronal tracer [Fluoro-Gold® – FG®] into subdivisions of the Acb [shell or core], we mapped single- or double-labeled cells. Moreover, using a double immunoperoxidase protocol, we investigated the MCH-ir fibers for gamma-aminobutyric acid [GABA]-ir and choline acetyltransferase [ChAT]-ir cells in the shell subdivision of the Acb [AcbSh]. We found that the MCH-ir fibers preferentially innervate the medial AcbSh, particularly the septal pole. This innervation originated from the incerto-hypothalamic area [IHy], internuclear area, lateral hypothalamic area, perifornical area, periventricular nucleus and posterior hypothalamus. Moreover, the IHy has the highest relationship between double/single retrogradely labeled cells [ n = 5.33 ± 0.66/16 ± 0.93, i.e. 33.33%] in the whole hypothalamus. Furthermore, our data suggest that MCH-ir fibers are in apposition to GABAergic and cholinergic cells in the AcbSh. Therefore, we provide anatomical support to the ongoing functional studies investigating the relation among the hypothalamus, MCH transmission into the Acb and the involvement of known neuronal phenotypes within the AcbSh. [ABSTRACT FROM AUTHOR]

Mesolimbic dopamine plays a critical role in food-related reward processing and learning. The literature focuses primarily on the nucleus accumbens as the key dopaminergic target in which enhanced dopamine signaling is associated with reward. Here, we demonstrate a novel neurobiological mechanism by which dopamine transmission in the amygdala regulates food intake and reward. We show that food intake was associated with increased dopamine turnover in the amygdala. Next, we assess the impact of direct intra-amygdala D1 and D2 receptor activation on food intake and sucrose-driven progressive ratio operant conditioning in rats. Amygdala D2 receptor activation reduced food intake and operant behavior for sucrose, whereas D2 receptor blockade increased food intake but surprisingly reduced operant behavior. In contrast, D1 receptor stimulation or blockade did not alter feeding or operant conditioning for food. The glucagon-like peptide 1 (GLP-1) system, a target for type 2 diabetes treatment, in addition to regulating glucose homeostasis, also reduces food intake. We found that central GLP-1R receptor activation is associated with elevated dopamine turnover in the amygdala, and that part of the anorexic effect of GLP-1 is mediated by D2 receptor signaling in the amygdala. Our findings indicate that amygdala dopamine signaling is activated by both food intake and the anorexic brain-gut peptide GLP-1 and that amygdala D2 receptor activation is necessary and sufficient to change feeding behavior. Collectively these studies indicate a novel mechanism by which the dopamine system affects feeding-oriented behavior at the level of the amygdala. [ABSTRACT FROM AUTHOR]

Mounting evidence suggests that gustation is important for the orosensory detection of dietary fats, and might contribute to preferences that humans, rodents, and possibly other mammals exhibit for fat-rich foods. In contrast to sweet, sour, salty, bitter, and umami, fat is not widely recognized as a primary taste quality. Recent investigations, however, provide a wealth of information that is helping to elucidate the specific molecular, cellular, and neural mechanisms required for fat detection in mammals. The latest evidence supporting a fat taste will be explored in this review, with a particular focus on recent studies that suggest a surprising role for gut-brain endocannabinoid signaling in controlling intake and preference for fats based on their proposed taste properties. [ABSTRACT FROM AUTHOR]

Central nervous system control of food intake involves detecting, integrating and responding to diverse internal and external signals. For maintenance of energy homeostasis, the brain uses long-term signals of metabolic status and short-term signals related to the nutrient content of individual meals. Feeding is also clearly influenced by hedonic, reward-related factors: palatability, motivation, and learned associations and cues that predict the availability of food. Different neural circuits have been proposed to mediate these homeostatic and hedonic aspects of eating. This review describes research on neural pathways that appear to be involved in both, integrating gastrointestinal satiation signaling with food reward. First, the glucagon-like peptide 1 projections from the nucleus of the solitary tract to the nucleus accumbens and ventral tegmental area are discussed as a mechanism through which meal-related gut signals may influence palatability, motivation for food, and meal size. Second, the orexin projection from lateral hypothalamus to the nucleus of the solitary tract and area postrema is discussed as a mechanism through which cues that predict rewarding food may act to increase motivation for food and also to suppress satiation. Additional potential integrative sites and pathways are also briefly discussed. Based on these findings, it is suggested that the brain circuitry involved in energy homeostasis and the circuitry mediating food reward are, in fact, overlapping and far less distinct than previously considered. [ABSTRACT FROM AUTHOR]