Neural responses to oral administration of erythritol vs. sucrose and sucralose explain differences in subjective liking ratings.

INTRODUCTION: High sugar intake is associated with many chronic diseases. However, non-caloric sweeteners (NCSs) might fail to successfully replace sucrose due to the mismatch between their rewarding sweet taste and lack of caloric content. The natural NCS erythritol has been proposed as a sugar substitute due to its satiating properties despite being non-caloric. We aimed to compare brain responses to erythritol vs. sucrose and the artificial NCS sucralose in a priori taste, homeostatic, and reward brain regions of interest (ROIs). METHODS: We performed a within-subject, single-blind, counterbalanced fMRI study in 30 healthy men (mean ± SEM age:24.3 ± 0.8 years, BMI:22.3 ± 0.3 kg/m2). Before scanning, we individually matched the concentrations of both NCSs to the perceived sweetness intensity of a 10% sucrose solution. During scanning, participants received 1 mL sips of the individually titrated equisweet solutions of sucrose, erythritol, and sucralose, as well as water. After each sip, they rated subjective sweetness liking. RESULTS: Liking ratings were significantly higher for sucrose and sucralose vs. erythritol (both pHolm = 0.0037); water ratings were neutral. General Linear Model (GLM) analyses of brain blood oxygen level-depended (BOLD) responses at qFDR<0.05 showed no differences between any of the sweeteners in a priori ROIs, but distinct differences were found between the individual sweeteners and water. These results were confirmed by Bayesian GLM and machine learning-based models. However, several brain response patterns mediating the differences in liking ratings between the sweeteners were found in whole-brain multivariate mediation analyses. Both subjective and neural responses showed large inter-subject variability. CONCLUSION: We found lower liking ratings in response to oral administration of erythritol vs. sucrose and sucralose, but no differences in neural responses between any of the sweeteners in a priori ROIs. However, differences in liking ratings between erythritol vs. sucrose or sucralose are mediated by multiple whole-brain response patterns.

Acquisition and expression of fat conditioned flavor preferences following dopamine D1, opioid and NMDA receptor antagonism in C57BL/6 mice.

Objectives: Inbred mouse strains differ in the pharmacology mediating sugar and fat intake and conditioned flavor preferences (CFP). C57BL/6, BALB/c and SWR inbred mice are differentially sensitive to dopamine (DA) D1, opioid and muscarinic receptor antagonism of sucrose, saccharin or fat intake, and to DA, opioid, muscarinic and N-methyl-D-aspartate (NMDA) receptor antagonism of acquisition of sucrose-CFP. DA D1, opioid and NMDA receptor antagonists differentially alter fat (Intralipid)-CFP in BALB/c and SWR mice. The present study examined whether naltrexone, SCH23390 or MK-801 altered acquisition and expression of Intralipid-CFP in C57BL/6 mice.Methods: In acquisition, groups of male food-restricted C57BL/6 mice received vehicle, naltrexone (1, 5 mg/kg), SCH23390 (50, 200 nmol/kg) or MK-801 (100, 200 µg/kg) before 10 training sessions in which mice alternately consumed two novel-flavored 5% (CS+) and 0.5% (CS-) Intralipid solutions. Six two-bottle CS choice tests followed with both flavors mixed in 0.5% Intralipid without injections. In expression, C57BL/6 mice underwent the 10 training sessions without injections followed by two-bottle CS choice tests 30 min following vehicle, naltrexone (1, 5 mg/kg), SCH23390 (200, 800 nmol/kg) or MK-801 (100, 200 µg/kg).Results: Fat-CFP acquisition in C57BL/6 mice was significantly though marginally reduced following naltrexone, SCH23390 and MK-801. Fat-CFP expression was similarly reduced by naltrexone, SCH23390 and MK-801 in C57BL/6 mice. Discussion: C57BL/6 mice were more sensitive to DA D1, opioid and NMDA antagonists in the expression of fat-CFP relative to sugar-CFP, but were less sensitive to DA D1 and NMDA antagonists in the acquisition of fat-CFP relative to sugar-CFP.

Optogenetic Stimulation of Type I GAD65+ Cells in Taste Buds Activates Gustatory Neurons and Drives Appetitive Licking Behavior in Sodium-Depleted Mice.

Mammalian taste buds are comprised of specialized neuroepithelial cells that act as sensors for molecules that provide nutrition (e.g., carbohydrates, amino acids, and salts) and those that are potentially harmful (e.g., certain plant compounds and strong acids). Type II and III taste bud cells (TBCs) detect molecules described by humans as "sweet," "bitter," "umami," and "sour." TBCs that detect metallic ions, described by humans as "salty," are undefined. Historically, type I glial-like TBCs have been thought to play a supportive role in the taste bud, but little research has been done to explore their role in taste transduction. Some evidence implies that type I cells may detect sodium (Na+) via an amiloride-sensitive mechanism, suggesting they play a role in Na+ taste transduction. We used an optogenetic approach to study type I TBCs by driving the expression of the light-sensitive channelrhodopsin-2 (ChR2) in type I GAD65+ TBCs of male and female mice. Optogenetic stimulation of GAD65+ TBCs increased chorda tympani nerve activity and activated gustatory neurons in the rostral nucleus tractus solitarius. "N neurons," whose NaCl responses were blocked by the amiloride analog benzamil, responded robustly to light stimulation of GAD65+ TBCs on the anterior tongue. Two-bottle preference tests were conducted under Na+-replete and Na+-deplete conditions to assess the behavioral impact of optogenetic stimulation of GAD65+ TBCs. Under Na+-deplete conditions GAD65-ChR2-EYFP mice displayed a robust preference for H2O illuminated with 470 nm light versus nonilluminated H2O, suggesting that type I glial-like TBCs are sufficient for driving a behavior that resembles Na+ appetite.SIGNIFICANCE STATEMENT This is the first investigation on the role of type I GAD65+ taste bud cells (TBCs) in taste-mediated physiology and behavior via optogenetics. It details the first definitive evidence that selective optogenetic stimulation of glial-like GAD65+ TBCs evokes neural activity and modulates behavior. Optogenetic stimulation of GAD65+ TBCs on the anterior tongue had the strongest effect on gustatory neurons that responded best to NaCl stimulation through a benzamil-sensitive mechanism. Na+-depleted mice showed robust preferences to "light taste" (H2O illuminated with 470 nm light vs nonilluminated H2O), suggesting that the activation of GAD65+ cells may generate a salt-taste sensation in the brain. Together, our results shed new light on the role of GAD65+ TBCs in gustatory transduction and taste-mediated behavior.

Effects of Dopamine D1-Like Receptor Ligands on Food-Cocaine Choice in Socially Housed Male Cynomolgus Monkeys.

Although dopamine plays a prominent role in mediating cocaine's abuse-related effects, the specific roles of dopamine receptor subtypes are not fully understood. Whereas the effects of drugs acting at dopamine D2-like receptors (D2Rs) have been characterized, less is known about dopamine D1-like receptors (D1Rs). The present experiments examined the effects of drugs with varying intrinsic efficacy at D1R on the relative reinforcing strength of cocaine in male cynomolgus monkeys. Use of socially housed monkeys permitted the assessment of whether social status influenced the behavioral effects of D1R-acting drugs. The high-efficacy D1R agonist SKF 81297, low-efficacy D1R agonist SKF 38393, and D1R antagonist SCH 23390 were administered acutely to monkeys self-administering cocaine under a food-cocaine choice procedure in which a cocaine-choice dose-effect curve was determined daily. To assess selectivity of behavioral effects on cocaine choice, effects of doses that did not disrupt responding (indicated by a ≥35% decrease in total reinforcers delivered) were analyzed. Neither SKF 81297 nor SCH 23390 affected cocaine choice in dominant or subordinate monkeys. However, the low-efficacy agonist SKF 38393 selectively decreased cocaine choice; this effect was larger and only reached statistical significance in subordinate monkeys. Increasing the time between D1-acting drug administration and the cocaine choice session did not affect these results. The results indicate that, like D2R-acting drugs, the behavioral effects of D1R-acting drugs on cocaine choice can vary according to intrinsic efficacy and social status. Moreover, they demonstrate that D1R-acting drugs affect behavior under a narrower range of conditions than D2R-acting drugs. SIGNIFICANCE STATEMENT: Cocaine use disorder represents an insidious public health concern with no Food and Drug Administration-approved medications. Although dopamine receptors have been strongly implicated in mediating the abuse-related effects of cocaine, the roles of dopamine receptor subtypes are incompletely understood. The present study in nonhuman primates found that cocaine choice was decreased only by a low-efficacy D1R agonist, and that this effect depended on the social status of the monkey.

Diet Protein Content and Individual Phenotype Affect Food Intake and Protein Appetence in Rats.

BACKGROUND: A low-protein diet can induce compensatory intake of excess energy. This must be better evaluated to anticipate the obesogenic risk that may result from the dietary recommendations for reducing animal protein consumption. OBJECTIVES: We aimed to further characterize the behavioral and physiological responses to a reduction in dietary protein and to identify the determinants of protein appetite. METHODS: Thirty-two male Wistar rats [4 wk old, (mean ± SEM) 135 ± 32 g body weight] were fed a low-protein (LP; 6% energy value) or normal-protein (NP; 20%) diet for 8 wk. Food intake and body mass were measured during the entire intervention. During self-selection sessions after 4 wk of experimental diets, we evaluated rat food preference between LP, NP, or high-protein (HP; 55%) pellets. At the end of the experiment, we assessed their hedonic response [ultrasonic vocalizations (USVs)] and c-Fos neuronal activation in the olfactory tubercle and nucleus accumbens (NAcc) associated with an LP or HP meal. RESULTS: Rats fed an LP diet had greater food intake (24%), body weight (5%), and visceral adiposity (30%) than NP rats. All LP rats and half of the NP rats showed a nearly exclusive preference for HP pellets during self-selection sessions, whereas the other half of the NP rats showed no preference. This suggests that the appetite for proteins is driven not only by a low protein status but also by individual traits in NP rats. LP or HP meal induced similar USV emission and similar neuronal activation in the NAcc in feed-deprived LP and NP rats, showing no specific response linked to protein appetite. CONCLUSIONS: Protein appetite in rats is driven by low protein status or individual preferences in rats receiving adequate protein amounts. This must be considered and further analyzed, in the context of current recommendations for protein intake reduction.

ALTERTASTE: improving food pleasure and intake of oncology patients receiving chemotherapy.

ALTERTASTE is a prospective study to evaluate changes in taste/flavor perception and food preferences in patients treated with adjuvant or neoadjuvant chemotherapy for breast or colorectal cancer. The study adopts a longitudinal approach. Taste and odor responsiveness, food preferences and habits, emotions elicited by foods, and quality of life will be measured at six-time points: before chemotherapy (T0), after two cycles (T1, after around 1 month), after four cycles (T2, after around 2 months), after six cycles (T3, after around 4 months), at the end of chemotherapy (T4, after around 6 months) and 3 months after the conclusion of the therapy (T5). In addition, patients will be characterized for oral responsiveness and their psychological traits and attitudes toward food. The ALTERTASTE trial is expected to improve the understanding of the impact of chemotherapy on taste and smell and the repercussions of these alterations on food behaviors. Furthermore, the trial aims to develop an easy and reliable procedure to test smell, taste and food behavior alterations to allow a routine measure with patients. Clinical trial registration: NCT04495387 (ClinicalTrials.gov).

Lay abstract Malnutrition (under- or over-nutrition) is highly prevalent in cancer patients receiving chemotherapy and is an important predictor of morbidity, mortality, treatment response and toxicity. Alterations in taste and smell are frequently reported as side effects of chemotherapy and may contribute strongly to malnutrition through an impact on eating behaviors and to a worse quality of life. ALTERTASTE is a prospective longitudinal study to evaluate changes in taste/flavor perception and food preferences in patients treated with chemotherapy for breast, colon or rectal cancer. Taste and odor responsiveness, food preferences and habits, emotions elicited by foods, and quality of life will be measured at six-time points: before chemotherapy (T0), after two cycles (T1, after around 1 month), after four cycles (T2, after around 2 months), after six cycles (T3, after around 4 months), at the end of chemotherapy (T4, after around 6 months) and 3 months after the conclusion of the therapy (T5). In addition, patients will be characterized for oral responsiveness and psychological traits and attitudes toward food. The ALTERTASTE trial is expected to improve the understanding of the impact of chemotherapy on taste and smell and the repercussions of these alterations on food behaviors.

Bees prefer foods containing neonicotinoid pesticides.

The impact of neonicotinoid insecticides on insect pollinators is highly controversial. Sublethal concentrations alter the behaviour of social bees and reduce survival of entire colonies. However, critics argue that the reported negative effects only arise from neonicotinoid concentrations that are greater than those found in the nectar and pollen of pesticide-treated plants. Furthermore, it has been suggested that bees could choose to forage on other available flowers and hence avoid or dilute exposure. Here, using a two-choice feeding assay, we show that the honeybee, Apis mellifera, and the buff-tailed bumblebee, Bombus terrestris, do not avoid nectar-relevant concentrations of three of the most commonly used neonicotinoids, imidacloprid (IMD), thiamethoxam (TMX), and clothianidin (CLO), in food. Moreover, bees of both species prefer to eat more of sucrose solutions laced with IMD or TMX than sucrose alone. Stimulation with IMD, TMX and CLO neither elicited spiking responses from gustatory neurons in the bees' mouthparts, nor inhibited the responses of sucrose-sensitive neurons. Our data indicate that bees cannot taste neonicotinoids and are not repelled by them. Instead, bees preferred solutions containing IMD or TMX, even though the consumption of these pesticides caused them to eat less food overall. This work shows that bees cannot control their exposure to neonicotinoids in food and implies that treating flowering crops with IMD and TMX presents a sizeable hazard to foraging bees.

Dose Frequency Optimization of the Dual Amylin and Calcitonin Receptor Agonist KBP-088: Long-Lasting Improvement in Food Preference and Body Weight Loss.

Dual amylin and calcitonin receptor agonists (DACRAs) are novel candidates for treatment of type 2 diabetes and obesity because of their beneficial effects on body weight, blood glucose, insulin sensitivity, and food preference, at least short-term. DACRAs activate the receptors for a prolonged time period, resulting in metabolic effects superior to those of amylin. Because of the prolonged receptor activation, different dosing intervals and, hence, less frequent receptor activation might change the efficacy of DACRA treatment in terms of weight loss and food preference. In this study, we compared daily dosing to dosing every other day with the aim of understanding the optimal balance between efficacy and tolerability. Obese and lean male Sprague-Dawley rats were treated with the DACRA KBP-088, applying two different dosing intervals (1.5 nmol/kg once daily and 3 nmol/kg every other day) to assess the effect on body weight, food intake, glucose tolerance, and food preference when given the choice between chow (13% fat) and a high-fat diet (60% fat). Treatment with KBP-088 induced significant weight loss, reduction in adiposity, improvement in glucose control, and altered food preference toward food that is less calorie-dense. KBP-088 dosed every other day (3 nmol/kg) was superior to KBP-088 once daily (1.5 nmol/kg) in terms of weight loss and improvement of food preference. The beneficial effects were evident in both lean and obese rats. Hence, dosing KBP-088 every other day positively affects overall efficacy on metabolic parameters regardless of the lean/obese state, suggesting that less-frequent dosing with KBP-088 could be feasible. SIGNIFICANCE STATEMENT: Here, we show that food preference can be altered chronically toward choices that are less calorie-dense by pharmacological treatment. Further, pharmacological dosing regimens affect the efficacy differently, as dosing every other day improved body weight loss and alterations in food preference compared with daily dosing. This suggest that alterations of the dosing regimens could be feasible in the treatment of obesity.

Cannabinoid Modulation of Food-Cocaine Choice in Male Rhesus Monkeys.

Marijuana and other cannabinoid compounds are widely used by cocaine users. Preclinical animal studies suggest that these compounds can increase the reinforcing effects of cocaine under some schedules of cocaine self-administration and reinstatement, but not in all cases. To date, no studies have used a food-cocaine concurrent choice procedure, which allows for assessment of drug effects on response allocation, not just changes in cocaine self-administration. The goal of the present study was to examine the effects of compounds differing in their efficacy at the cannabinoid receptor (CBR) on cocaine self-administration using a food-drug choice procedure in monkeys. Four adult male rhesus monkeys were trained to self-administer cocaine in the context of an alternative food (1.0-g banana-flavored pellets) reinforcer, such that complete cocaine dose-response curves (0, 0.003-0.1 mg/kg per injection) were determined each session. Monkeys were tested acutely with the CBR full agonist CP 55,940 (0.001-0.01 mg/kg); the CBR partial agonist Δ9-tetrahydrocannabinol (THC; 0.03-0.3 mg/kg), which is also the primary active ingredient in marijuana and the CBR antagonist rimonabant (0.3-3.0 mg/kg). Cocaine choice increased in a dose-dependent manner. Acute treatment with CP 55,940 decreased cocaine choice, whereas THC and rimonabant enhanced the reinforcing effects of cocaine. Chronic (7-day) treatment with CP 55,940 resulted in tolerance to the decreases in cocaine choice. These findings with Δ9-THC provide support for a potential mechanism for co-abuse of marijuana and cocaine. Additional research with chronic treatment with full CBR agonists on attenuating the reinforcing strength of cocaine is warranted. SIGNIFICANCE STATEMENT: Co-abuse of tetrahydrocannabinol and cocaine is a significant public health problem. The use of animal models allows for the determination of how cannabinoid receptor stimulation or blockade influences the reinforcing strength of cocaine.

Inefficient weapon-the role of plant secondary metabolites in cotton defence against the boll weevil.

MAIN CONCLUSION: Cotton genotypes displayed similar volatile organic compound (VOC) profiles, but major differences in terpenoid aldehyde (TA) content. The differences in VOC production were minor among genotypes, but these differences are crucial for boll weevil attraction. Weevils did not display any preference in feeding behaviour towards cotton genotypes, suggesting physiological adaptation to cope with cotton chemical defence mechanisms. Plant cultivar selection for resistance to herbivore pests is an effective, environmentally safe and inexpensive method to implement in integrated pest management programmes. In this study, we evaluated seven cotton genotypes with respect to the production of volatile organic compounds (VOCs) and non-volatile compounds [terpenoid aldehydes (TAs)], and the attraction and feeding preference of adult boll weevils. Chemical analyses of VOCs from BRS-293, BRS-Rubi, CNPA TB-15, CNPA TB-85, CNPA TB-90, Delta Opal, and Empire Glandless showed that there were few qualitative and quantitative differences across the range of genotypes. In contrast, major differences in TA content were observed, with CNPA TB-15 and CNPA TB-85 producing higher levels of TAs compared to the other genotypes. Our results showed that boll weevil attraction to cotton genotypes varied, suggesting that the ratios and quantities of emitted cotton VOCs are important for host location. However, boll weevil feeding behaviour was neither positively nor negatively influenced by the terpenoid content (non-volatile compounds) of cotton genotypes. The results in this study suggest that boll weevils have adapted physiologically to cope with cotton chemical defence mechanisms.

Role of glucocorticoid signaling in exercise-associated changes in high-fat diet preference in rats.

The simultaneous introduction of wheel running (WR) and diet choice (high-carbohydrate chow vs. high-fat diet) results in sex-specific diet choice patterns in rats. WR induces a high-fat (HF) diet avoidance, and such avoidance persists in the majority of males, but not females, throughout a 2-wk period. Exercise is a physiological stressor that activates the hypothalamic-pituitary-adrenal (HPA) axis and stimulates glucocorticoid (GC) release, which can alter dietary preferences. Here, we examined the role of the HPA axis and GC signaling in mediating exercise-induced changes in diet preference and the associated neurobiological adaptations that may underlie sex differences in diet choice patterns. Experiment 1 revealed that adrenalectomy did not significantly alter the initiation and persistence of running-induced HF diet avoidance in male rats. Experiment 2 showed that acute WR resulted in greater neural activation than chronic WR in the medial prefrontal (mPFC) and insular cortices (IC) in male rats. Experiment 3 revealed sex differences in the molecular adaptation to exercise and diet preference. First, exercise increased gene expression of fkbp5 in the mPFC, IC, and hippocampus of WR females but had limited influence in males. Second, male and female WR rats that reversed or maintained HF diet avoidance showed distinct sex- and HF diet preference-dependent expression profiles of genes involved in cortical GC signaling (e.g., nr3c1, nr3c2, and src1). Taken together, our results suggest sex differences in region-specific neural adaptations may underlie sex differences in diet preference and the health benefits from exercise.

The Angiotensin Type 1 Receptor Antagonist Losartan Prevents Ovariectomy-Induced Cognitive Dysfunction and Anxiety-Like Behavior in Long Evans Rats.

Women who have bilateral oophorectomies prior to the age of natural menopause are at increased risk of developing mild cognitive decline, dementia, anxiety, and depressive type disorders. Clinical and animal studies indicate angiotensin type 1 receptor (AT1R) blockers (ARBs) have blood pressure (BP)-independent neuroprotective effects. To investigate the potential use of ARBs in normotensive women at increased risk of developing neurocognitive problems, we studied a rat model of bilateral oophorectomy. Long Evans rats were sham-operated (Sham) or ovariectomized (Ovx) at 3 months of age and immediately treated continuously with vehicle (Veh) or the ARB losartan (Los) for the duration of the experiment. In contrast to many hypertensive rat models, ovariectomy did not increase mean arterial pressure (MAP) in these normotensive rats. Ovariectomized rats spent less time in the open arms of the elevated plus maze (EPM) [(% total time): Veh, 34.1 ± 5.1 vs. Ovx, 18.7 ± 4.4; p < 0.05] and in the center of the open field (OF) [(s): Veh, 11.1 ± 1.7 vs. Ovx, 6.64 ± 1.1; p < 0.05]. They also had worse performance in the novel object recognition (NOR) test as evidenced by a reduction in the recognition index [Veh, 0.62 ± 0.04 vs. Ovx, 0.45 ± 0.03; p < 0.05]. These adverse effects of ovariectomy were prevented by Los. Losartan also reduced plasma corticosterone in Ovx rats compared to Veh treatment [(ng/mL): Ovx-Veh, 238 ± 20 vs. Ovx-Los, 119 ± 42; p < 0.05]. Ovariectomy increased AT1R mRNA expression in the CA3 region of the hippocampus (Hc) [(copies x 106/µg RNA): Sham-Veh, 7.15 ± 0.87 vs. Ovx-Veh, 9.86 ± 1.7; p < 0.05]. These findings suggest the neuroprotective effects of this ARB in normotensive Ovx rats involve reduction of plasma corticosterone and blockade of increased AT1R activity in the hippocampus. These data suggest ARBs have therapeutic potential for normotensive women at increased risk of developing cognitive and behavioral dysfunction due to bilateral oophorectomy prior to the natural age of menopause.

Effects of caloric or non-caloric sweetener long-term consumption on taste preferences and new aversive learning.

Food palatability and caloric content are crucial factors in guiding diet choice and amount consumed; as a result, sweet caloric tastes are associated with a positive hedonic value. Recent evidence in rodents indicates that consumption of artificial (non-caloric) sweeteners, in which sweet taste is dissociated from normal caloric consequences, could induce changes in energy and body weight regulation, suggesting that sweeteners not only modify intake and appetitive behavior, but could also change taste-learning processes. Particularly, there are different properties in some artificial sweeteners, like saccharin, that might differ from sugar in the reward responses that, after long-term consumption, could also be associated with the inability to learn new negative consequences related to the same taste. Thus, the main goal of this study was to determine, in adult rats, the effects of long-term consumption (14 days) of sugar or saccharin, on taste preference, on new aversive learning, i.e. latent inhibition (LI) of conditioned taste aversion (CTA), and appetitive taste re-learning after aversive taste associations. The results showed that 14 days' exposure to sugar, but not to saccharin, induced a significant increment in the LI of CTA and that taste preference is rapidly recovered during the next 3 days (e.g. CTA extinctions), indicating that long-term sugar consumption significantly accelerates aversive memory extinction during appetitive re-learning of a specific sweet taste; furthermore, high familiarization to sugar, but not to saccharin, promotes appetitive learning for the same taste. Overall, the results indicate that long-term consumption of sugar, but not saccharin, produces changes in appetitive re-learning and suggests that long-term sugar consumption could trigger escalating consumption due to the inability to learn new negative consequences associated with the same taste.

Acquisition and expression of sucrose conditioned flavor preferences following dopamine D1, opioid and NMDA receptor antagonism in C57BL/6 mice.

The study of inbred mouse strains is a useful animal model to assess differences in ingestive behavior responses, including conditioned flavor preferences (CFP). C57BL/6, BALB/c and SWR inbred mice display differential sensitivity to dopamine (DA) D1, opioid and muscarinic cholinergic receptor antagonism of sucrose or saccharin intake as well as to muscarinic cholinergic antagonism of acquisition (learning) of sucrose-CFP. Given that DA D1, opioid and N-methyl-D-aspartate (NMDA) receptor antagonists differentially alter sucrose-CFP in BALB/c and SWR inbred mice, the present study examined whether systemic administration of naltrexone, SCH23390 or MK-801 altered acquisition and expression of sucrose-CFP in C57BL/6 mice. In acquisition experiments, male food-restricted C57BL/6 mice were treated with vehicle, naltrexone (1, 5 mg/kg), SCH23390 (50, 200 nmol/kg) or MK-801 (100, 200 µg/kg) 30 min prior to each of ten daily sessions in which they alternately consumed a flavored (CS+, e.g. cherry) 16% sucrose solution and a differently-flavored (CS-, e.g. grape) 0.05% saccharin solution followed by six two-bottle CS choice tests mixed in 0.2% saccharin without injections. SCH23390 and MK-801, but not naltrexone eliminated sucrose-CFP acquisition in food-restricted C57BL/6 mice. In expression experiments, food-restricted C57BL/6 mice underwent the ten training sessions without injections followed by two-bottle CS choice tests 30 min following vehicle, naltrexone (1, 5 mg/kg), SCH23390 (200, 800 nmol/kg) or MK-801 (100, 200 µg/kg). SCH23390 more effectively reduced the magnitude of sucrose-CFP expression than naltrexone or MK-801 in food-restricted C57BL/6 mice. Thus, dopamine D1 and NMDA receptor signaling is essential for learning of sucrose-CFP in C57BL/6 mice.

Leptin promotes the fat preference associated with low-temperature acclimation in mice.

Although fluctuations in energy metabolism are known to influence intake as well as nutrient selection, there are no definitive reports on how food preferences change with changes in habitat temperature. We investigated the effects of habitat temperature on appetite and food preference and elucidated the underlying mechanism by conducting a feeding experiment and a leptin administration test on mice reared at low temperatures. Our results showed that the increased food intake and HFD preference observed in the 10°C group were induced by decrease in plasma leptin concentration. Then, a leptin administration experiment was conducted to clarify the relationship between leptin and food preference with low-temperature acclimation. The control group reared in 10°C significantly preferred the HFD, but the leptin-administered group did not. These results show that the peripheral system appetite-regulating hormone leptin not only acts to suppress appetite but also might inhibit preference for lipids in low-temperature acclimation.

Individual differences in the perception of orthonasal irritation induced by food.

Oral responsiveness to the burning/spicy sensation affects food behaviors and diet; therefore, it is reasonable to hypothesize that the variation in nasal responsiveness to irritant foods may play a role in modulating food behaviors. This study explored the variation among individuals in orthonasal irritation induced by smelling food ingredients containing irritant compounds: mustard oil (2.0, 10.0, and 100.0% v/v mustard oil in corn oil; irritant compound: allyl isothiocyanate); vinegar (3.5, 42.3, and 98.6% v/v vinegar in water; irritant compound: acetic acid); and wasabi (0.1, 0.2, and 0.4% w/w wasabi powder in water; irritant compound: allyl isothiocyanate). Sixty-eight subjects (40% males; 19-87 years) smelled the nine samples and rated their perceived intensity of odor, irritation and liking. Wide individual variation in the perception of irritation and odor intensity was found, especially at the highest concentrations. Young individuals were the most sensitive to all stimuli. No significant differences were found between males and females. Fifty-seven percent of subjects were "HYPO" and 43 percent "HYPER" responsive to irritation, respectively. Perceived irritation was positively correlated with odor intensity and tended to be negatively correlated with liking, especially in familiar stimuli. The results suggest that the variation in nasal responsiveness to irritant foods may contribute to influencing food acceptance and therefore, to modulating food behaviors.

Preference for and sensitivity to flavanol mean degree of polymerization in model wines is correlated with body composition.

Bitterness and astringency (dryness) are characteristic sensory attributes of flavanol-rich foods. The degree of polymerization (DP) of flavanols influences their bitter and astringent sensations. Smaller DP compounds can enter the papillae on the tongue, eliciting a bitter response. Larger DP compounds are sterically inhibited from entering papillae and instead interact with oral proteins, cause precipitation, and elicit astringent sensations. Previous research has indicated that bitterness preference is related to health status, density of fungiform papillae on the tongue, and sensitivity to bitter compounds such as 6-n-propyl-thiouracil (PROP). The purpose of this study was to examine trends in liking, bitterness intensity, and astringency intensity of wine-like products with flavanols of different DP using a consumer sensory panel. Participants (n = 102) were segmented by phenotypes: body fat percentage (BF%), body mass index (BMI), PROP sensitivity, and stated bitter food preference. Differences in wine liking, perceived bitterness intensity, and astringency intensity were observed between three model wine samples of varying flavanol mean degrees of polymerization (mDP, i.e. the average size (polymer length) of flavanol compounds in a mixture). Specifically, with increased mDP, overall liking and bitterness liking decreased, with concurrent increased perception of bitterness and astringency intensity. Greater differences between phenotypes were observed when participants were segmented by BF% and BMI classification, than when segmented by PROP sensitivity classification. Reduced ability to detect differences in bitterness and astringency were noted in participants of higher weight status. Overall, these data suggest that weight status in adults is a greater predictor of liking of flavanol-rich foods than bitterness sensitivity (as determined by PROP classification), and that reduced perception of bitterness and astringency associated with weight gain may impact selection and preference for these foods.

Chronic exposure to liquid sucrose and dry sucrose diet have differential effects on peripheral taste responses in female rats.

Sugar-sweetened beverages are the major source of added calories in the Western diet and their prevalence is associated with obesity and metabolic disruption. Despite the critical role of the taste system in determining food selection and consumption, the effects of chronic sucrose consumption on the peripheral taste system in mammals have received limited attention. We offered female Sprague Dawley rats free access to water and one of three diets for up to 40 days: (1) sucrose-free chow or "NS" diet; (2) a high-sucrose dry diet or "HS"; or (3) 30% sucrose solution and the NS diet, designated "LiqS" diet. Sucrose consumption by LiqS rats gradually increased and by day 14 was equal to that of HS rats. Food intake decreased in LiqS rats, but their energy intake remained higher than for NS or HS rats. There was no significant difference in weight gain of the groups during the study. Recordings from the chorda tympani nerve (CT), which innervates taste buds on the anterior tongue, revealed decreased responses to 1 M sucrose in both LiqS and HS rats and to acesulfame K and salt tastants in LiqS rats after 40 days on diet. Umami, bitter, and acid response magnitudes were unchanged in both groups. These results demonstrate that chronic sucrose exposure inhibits taste responses to higher concentrations of sweet stimuli. More surprisingly, CT responses to NaCl and 0.5M NaAc were significantly reduced in rats on the LiqS diet. Thus, the physical form of the diet influences taste responsiveness to salt and sweet taste function. These data suggest that taste buds are previously unappreciated targets of chronic sucrose consumption.

Involvement of mTOR-related signaling in antidepressant effects of Sophoraflavanone G on chronically stressed mice.

SophoraflavanoneG (SG), an important prenylated flavonoid isolated from Sophoraalopecuroides.L, is effective for many illnesses. The present study was designed to investigate whether the compound could reverse depressive-like symptoms and investigate its possible mechanisms. Chronic Unpredictable Mild Stress (CUMS) mice were treated with fluoxetine and SG. The immobility time in forced swimming test (FST) and tail suspension test (TST) were recorded. The levels of pro-inflammatory cytokines and neurotransmitters in the hippocampus were evaluated. Furthermore, the protein expressions of PI3K, AKT, mTOR, p70S6K, BDNF, and Trkb in hippocampus were detected. Rapamycin, the selective mTOR inhibitor, was used to estimate the potential mechanism. As a result, after 7 days of SG treatment, the immobility time in FST and TST was declined obviously. The levels of IL-6, IL-1ß, and TNF-α in the hippocampus were significantly reduced, and the quantity of 5-HT and NE was raised considerably in SG-treated group compared with the CUMS-exposed group. Additionally, SG could up-regulate the expressions of PI3K, AKT, mTOR, 70S6K, BDNF, and Trkb. The blockade of mammalian target of rapamycin signaling blunted the antidepressant effect and reversed the up-regulation of BDNF expression caused by SG. These findings suggested that SG treatment alleviated depressive-like symptoms via mTOR-mediated BDNF/Trkb signaling.

Dopamine drives binge-like consumption of a palatable food in experimental Parkinsonism.

BACKGROUND: Prolonged dopaminergic replacement therapy in PD results in pulsatile dopamine receptors stimulation in both dorsal and ventral striatum causing wearing off, motor fluctuations, and nonmotor side effects such as behavioral addictions. Among impulse control disorders, binge eating can be easily modeled in laboratory animals. OBJECTIVES: We hypothesize that manipulation of dopamine levels in a 6-hydroxydopamine-lesioned rats, as a model of PD characterized by a different extent of dopamine denervation between dorsal and ventral striatum, would influence both synaptic plasticity of the nucleus accumbens and binge-like eating behavior. METHODS: Food preference, food intake, and weight gain were monitored in sham-operated and unilaterally lesioned rats, subjected to a modified version of Corwin's limited access protocol, modelling binge eating disorder. Electrophysiological properties and long-term potentiation of GABAergic spiny projection neurons of the nucleus accumbens core were studied through ex vivo intracellular and patch-clamp recordings from corticostriatal slices of naïve and l-dopa-treated rats. RESULTS: Sham-operated animals with intact nucleus accumbens core plasticity reliably developed food-addiction-like behavior when exposed to intermittent access to a highly palatable food. In contrast, parkinsonian rats were unresponsive to such restriction regimens, and also plasticity was lost in ventral spiny neurons. Chronic l-dopa reestablished long-term potentiation and compulsive eating, but with a different temporal dynamic that follows that of drug administration. CONCLUSIONS: Our data indicate that endogenous and exogenous dopamine drive binge-like consumption of a palatable food in healthy and parkinsonian rats with distinct temporal dynamics, providing new insights into the complexity of l-dopa effects on the mesolimbic dopaminergic system. © 2019 International Parkinson and Movement Disorder Society.