Higher meal disengagement and meal presentation are uniquely related to psychological distress and lower quality of life in undergraduate students

Objective: Picky eating, which occurs in emerging adulthood and is associated with psychological distress and quality of life, has historically been conceptualized as unidimensional despite research suggesting it is a multifaceted construct. Participants: An undergraduate sample (N = 509; Mage = 19.96). Methods: A cross-sectional survey assessed picky eating facets (food variety, meal disengagement, meal presentation, and taste aversion), disordered eating, anxiety, depression, stress, obsessive compulsive disorder (OCD), and social phobia symptoms, and quality of life. Results: Meal disengagement was uniquely related to higher anxiety, depression, stress, and social phobia symptoms and lower quality of life, whereas meal presentation was uniquely related to higher anxiety, stress, and OCD symptoms, beyond covariates and disordered eating. Food variety and taste aversion were not uniquely related to outcomes. Conclusions: Considering picky eating multidimensionally may yield important insights beyond the broader construct in terms of its relationship with psychological well-being in undergraduates.

Food avoidance learning based on swimming in laboratory mice (Mus musculus)

Although it is now well documented that laboratory rats learn to avoid the flavored substance consumed immediately before running in activity wheels or swimming in water buckets, research on this activity-based flavor avoidance learning in other species is limited. Recently, running-based flavor avoidance learning has been demonstrated in laboratory mice by employing a method of resistance-to-habituation of neophobic reaction to novel food; mice that repeatedly experience running after encountering a novel food have a prolonged tendency to reject that food compared to control mice without paired running. The present article reports a series of attempts to obtain evidence of flavor avoidance learning based on swimming rather than running using this resistance-to-habituation method. Swimming-based flavor avoidance was clearly demonstrated in a differential conditioning paradigm; however, its demonstration in a simple conditioning paradigm requires a post-training choice test of the target food and another type of food. These results are likely due to the short swimming time (20min) and the formation of weak flavor aversion.

Intranasal Administration of Rotenone Reduces GABAergic Inhibition in the Mouse Insular Cortex Leading to Impairment of LTD and Conditioned Taste Aversion Memory

The pesticide rotenone inhibits mitochondrial complex I and is thought to cause neurological disorders such as Parkinson’s disease and cognitive disorders. However, little is known about the effects of rotenone on conditioned taste aversion memory. In the present study, we investigated whether intranasal administration of rotenone affects conditioned taste aversion memory in mice. We also examined how the intranasal administration of rotenone modulates synaptic transmission and plasticity in layer V pyramidal neurons of the mouse insular cortex that is critical for conditioned taste aversion memory. We found that the intranasal administration of rotenone impaired conditioned taste aversion memory to bitter taste. Regarding its cellular mechanisms, long-term depression (LTD) but not long-term potentiation (LTP) was impaired in rotenone-treated mice. Furthermore, spontaneous inhibitory synaptic currents and tonic GABA currents were decreased in layer V pyramidal neurons of rotenone-treated mice compared to the control mice. The impaired LTD observed in pyramidal neurons of rotenone-treated mice was restored by a GABA_A receptor agonist muscimol. These results suggest that intranasal administration of rotenone decreases GABAergic synaptic transmission in layer V pyramidal neurons of the mouse insular cortex, the result of which leads to impairment of LTD and conditioned taste aversion memory.

Distinct and Overlapping Patterns of Acute Ethanol-Induced C-Fos Activation in Two Inbred Replicate Lines of Mice Selected for Drinking to High Blood Ethanol Concentrations

The inbred high drinking in the dark (iHDID1 and iHDID2) strains are two replicate lines bred from the parent HS/Npt (HS) line for achieving binge levels of blood ethanol concentration (≥80 mg/dL BEC) in a four-hour period. In this work, we sought to evaluate differences in baseline and ethanol-induced c-Fos activation between the HS, iHDID1, and iHDID2 genetic lines in brain regions known to process the aversive properties of ethanol. Methods: Male and female HS, iHDID1, and iHDID2 mice underwent an IP saline 2 3 g/kg ethanol injection. Brain sections were then stained for c-Fos expression in the basolateral/central amygdala (BLA/CeA), bed nucleus of the stria terminals (BNST), A2, locus coeruleus (LC), parabrachial nucleus (PBN), lateral/medial habenula (LHb/MHb), paraventricular nucleus of the thalamus (PVT), periaqueductal gray (PAG), Edinger–Westphal nuclei (EW), and rostromedial tegmental nucleus (RMTg). Results: The iHDID1 and iHDID2 lines showed similar and distinct patterns of regional c-Fos; however, in no region did the two both significantly differ from the HS line together. Conclusions: Our findings lend further support to the hypothesis the iHDID1 and the iHDID2 lines arrive at a similar behavior phenotype through divergent genetic mechanisms.

Sex Differences in Cue Competition Effects With a Conditioned Taste Aversion Preparation

This study aimed to test whether male and female rats might show differences in cue competition effects in a conditioned taste aversion (CTA) model. Experiment 1 tested for sex differences in overshadowing. After conditioning of a flavored compound AB or only one simple flavor A (being A and B a solution of sugar 10% and salt 1%, counterbalanced), consumption of the A solution at test was larger in the former than in the latter case only in males. Thus, the usual effect of overshadowing was observed in males but not in females. Experiment 2 examined sex differences in blocking with the same stimuli used in Experiment 1. After conditioning of AB, the consumption of B was larger for the animals that previously received a single conditioning trial with A than for those that received unpaired presentations of A and the illness. As observed in Experiment 1, the typical blocking effect appeared only in males but not in females. The present findings thus support the hypothesis that sex dimorphism might be expressed in classical conditioning, or at least, in cue competition effects such as overshadowing and blocking with a taste aversion model.

Genetic Relationships Between Ethanol-Induced Conditioned Place Aversion and Other Ethanol Phenotypes in 15 Inbred Mouse Strains

The genetic relationships between different behaviors used to index the aversive effects of ethanol are unknown. To address this issue, ethanol-induced conditioned place aversion (CPA) was tested in a genetically diverse panel of 15 inbred mouse strains. Mice were exposed to an unbiased place conditioning procedure using ethanol doses of 0, 2, or 4 g/kg; all injections were given immediately after 5-min exposure to distinctive tactile cues. There were dose-dependent effects of ethanol on CPA and on the change in pre-injection activity rates between the first and last conditioning trials. Most strains (80%) developed CPA, demonstrating the generalizability of this behavior. Moreover, genotype had significant effects on CPA magnitude and locomotor activity rates. Strain means from this study and previously published studies were then used to examine genetic correlations. These analyses showed significant genetic correlations between CPA and ethanol intake/preference, conditioned taste aversion, and drug withdrawal (but not blood ethanol concentration or conditioned place preference), supporting the idea of commonality in the genes underlying CPA and each of these behaviors. The overall pattern of findings is consistent with previous data suggesting that genetic differences in sensitivity to ethanol's aversive effects play a role in determining strain differences in ethanol drinking. The broader implication is that individuals who are more sensitive to the aversive effects of ethanol may be protected from developing the excessive drinking behaviors characteristic of alcohol use disorders.

Pre-exposure Schedule Effects on Generalization of Taste Aversion and Palatability for Thirsty and Not Thirsty Rats

The study reported four experiments aiming to test the effects of the pre-exposure schedule and water deprivation on the generalization of a conditioned taste aversion in rats, with a particular focus on testing whether or not the concurrent schedule might enhance generalization. In two experiments, non-water-deprived rats received concurrent, intermixed, or blocked exposure to a sweet-acid solution and a salty-acid solution before conditioning of one of these compounds and testing of both flavors. During pre-exposure, the rats consumed a greater amount of the sweet-acid solution than the salty-acid solution (Experiments 1 and 2), consumption of the former increasing during pre-exposure while consumption of the latter decreased (Experiment 1). Furthermore, consumption of the salty-acid solution was lower during concurrent than intermixed or blocked pre-exposure (Experiment 1 and 2) while consumption of the sweet-acid solution was greater during intermixed than concurrent or blocked pre-exposure (Experiment 1). It is discussed whether the pre-exposure schedule might modify stimulus perception beyond the mere enhancement of stimulus differentiation, by, for instance, affecting the palatability of gustatory stimuli. Evidence for enhanced generalization after concurrent pre-exposure was not found for either deprived (Experiments 1, 2, and 3) or non-deprived rats (Experiments 3 and 4), with deprivation leading to a general increase in consumption of both the conditioned and test flavors. This then raised the question of whether or not concurrent pre-exposure to flavors always increases generalization between them. The present study highlights the importance of this issue for various accounts of perceptual learning.

How Does Food Taste in Anorexia and Bulimia Nervosa? A Protocol for a Quasi-Experimental, Cross-Sectional Design to Investigate Taste Aversion or Increased Hedonic Valence of Food in Eating Disorders

Background: Despite on-going efforts to better understand dysregulated eating, the olfactory-gustatory deficits and food preferences in eating disorders (ED), and the mechanisms underlying the perception of and responses to food properties in anorexia nervosa (AN) and bulimia nervosa (BN) remain largely unknown; both during the course of the illness and compared to healthy populations. It is, therefore, necessary to systematically investigate the gustatory perception and hedonics of taste in patients with AN and BN. To this end, we will examine whether aversions to the taste of high-calorie food is related to the suppression of energy intake in restricting-type AN, and whether an increased hedonic valence of sweet, caloric-dense foods may be part of the mechanisms triggering binge-eating episodes in BN. In addition, the role of cognitions influencing these mechanisms will be examined.

Method: In study 1, four mixtures of sweet-fat stimuli will be presented in a sensory two-alternative forced-choice test involving signal detection analysis. In study 2, a full-scale taste reactivity test will be carried out, including psychophysiological and behavioral measures to assess subtle and covert hedonic changes. We will compare the responses of currently-ill AN and BN patients to those who have recovered from AN and BN, and also to those of healthy normal-weight and underweight individuals without any eating disorder pathology.

Discussion: If taste response profiles are differentially linked to ED types, then future studies should investigate whether taste responsiveness represents a useful diagnostic measure in the prevention, assessment and treatment of EDs. The expected results on cognitive mechanisms in the top-down processes of food hedonics will complement current models and contribute to the refinement of interventions to change cognitive aspects of taste aversions, to establish functional food preferences and to better manage food cravings associated with binge-eating episodes. No trial registration was required for this protocol, which was approved by the Swiss ethics committee (CER-VD, n° 2016-02150) and the Ethics Review Panel of the University of Luxembourg.

Ecological immunization: in situ training of free-ranging predatory lizards reduces their vulnerability to invasive toxic prey

In Australia, large native predators are fatally poisoned when they ingest invasive cane toads (Rhinella marina). As a result, the spread of cane toads has caused catastrophic population declines in these predators. Immediately prior to the arrival of toads at a floodplain in the Kimberley region, we induced conditioned taste aversion in free-ranging varanid lizards (Varanus panoptes), by offering them small cane toads. By the end of the 18-month study, only one of 31 untrained lizards had survived longer than 110 days, compared to more than half (nine of 16) of trained lizards; the maximum known survival of a trained lizard in the presence of toads was 482 days. In situ aversion training (releasing small toads in advance of the main invasion front) offers a logistically simple and feasible way to buffer the impact of invasive toads on apex predators.

The Perceptual Characteristics of Sodium Chloride to Sodium-Depleted Rats

Three experiments assessed potential changes in the rat's perception of sodium chloride (NaCl) during a state of sodium appetite. In Experiment 1, sodium-sufficient rats licking a range of NaCl concentrations (0.028-0.89M) in 15s trials showed an inverted U-shaped concentration response function peaking at 0.281M. Depleted rats (furosemide) showed an identical function, merely elevated, suggesting altered qualitative or hedonic perception but no change in perceived intensity. In Experiment 2, sodium-depleted rats were tested with NaCl, sodium gluconate, and potassium chloride (KCl; 0.028-0.89M) similar to Experiment 1. KCl was licked at the same rate as water except for a slight elevation at 0.158; sodium gluconate and NaCl were treated similarly, but rats showed more licking for hypertonic sodium gluconate than hypertonic NaCl. Sodium-depleted rats were also tested with NaCl mixed in amiloride (10-300 μM). Amiloride reduced licking but did not alter the shape of the concentration-response function. Collectively, these results suggest that transduction of sodium by epithelial sodium channels (which are blocked by amiloride and are more dominant in sodium gluconate than NaCl transduction) is crucial for the perception of sodium during physiological sodium depletion. In Experiment 3, sodium-deplete rats were tested with NaCl as in Experiment 1 but after taste aversion conditioning to 0.3M NaCl or sucrose. Rats conditioned to avoid NaCl but not sucrose failed to express a sodium appetite, strongly suggesting that NaCl does not undergo a change in taste quality during sodium appetite-rats show no confusion between sucrose and NaCl in this paradigm.

Bitter tastant responses in the amoeba Dictyostelium correlate with rat and human taste assays

Treatment compliance is reduced when pharmaceutical compounds have a bitter taste and this is particularly marked for paediatric medications. Identification of bitter taste liability during drug discovery utilises the rat in vivo brief access taste aversion (BATA) test which apart from animal use is time consuming with limited throughput. We investigated the suitability of using a simple, non-animal model, the amoeba Dictyostelium discoideum to investigate taste-related responses and particularly identification of compounds with a bitter taste liability. The effect of taste-related compounds on Dictyostelium behaviour following acute exposure (15 minutes) was monitored. Dictyostelium did not respond to salty, sour, umami or sweet tasting compounds, however, cells rapidly responded to bitter tastants. Using time-lapse photography and computer-generated quantification to monitor changes in cell membrane movement, we developed an assay to assess the response of Dictyostelium to a wide range of structurally diverse known bitter compounds and blinded compounds. Dictyostelium showed varying responses to the bitter tastants, with IC50 values providing a rank order of potency. Comparison of Dictyostelium IC50 values to those observed in response to a similar range of compounds in the rat in vivo brief access taste aversion test showed a significant (p = 0.0172) positive correlation between the two models, and additionally a similar response to that provided by a human sensory panel assessment test. These experiments demonstrate that Dictyostelium may provide a suitable model for early prediction of bitterness for novel tastants and drugs. Interestingly, a response to bitter tastants appears conserved from single-celled amoebae to humans.

Gustatory learning and processing in the Drosophila mushroom bodies

The Drosophila mushroom bodies are critical association areas whose role in olfactory associative learning has been well characterized. Recent behavioral studies using a taste association paradigm revealed that gustatory conditioning also requires the mushroom bodies (Masek and Scott, 2010; Keene and Masek, 2012). Here, we examine the representations of tastes and the neural sites for taste associations in the mushroom bodies. Using molecular genetic approaches to target different neuronal populations, we find that the gamma lobes of the mushroom bodies and a subset of dopaminergic input neurons are required for taste associative learning. Monitoring responses to taste compounds in the mushroom body calyx with calcium imaging reveals sparse, taste-specific and organ-specific activation in the Kenyon cell dendrites of the main calyx and the dorsal accessory calyx. Our work provides insight into gustatory representations in the mushroom bodies, revealing the essential role of gustatory inputs not only as rewards and punishments but also as adaptive cues.

Correlation Between Activation of the Prelimbic Cortex, Basolateral Amygdala, and Agranular Insular Cortex During Taste Memory Formation

Conditioned taste aversion (CTA) is a well-established learning paradigm, whereby animals associate tastes with subsequent visceral illness. The prelimbic cortex (PL) has been shown to be involved in the association of events separated by time. However, the nature of PL activity and its functional network in the whole brain during CTA learning remain unknown. Here, using awake functional magnetic resonance imaging and fiber tracking, we analyzed functional brain connectivity during the association of tastes and visceral illness. The blood oxygen level-dependent (BOLD) signal significantly increased in the PL after tastant and lithium chloride (LiCl) infusions. The BOLD signal in the PL significantly correlated with those in the amygdala and agranular insular cortex (IC), which we found were also structurally connected to the PL by fiber tracking. To precisely examine these data, we then performed double immunofluorescence with a neuronal activity marker (c-Fos) and an inhibitory neuron marker (GAD67) combined with a fluorescent retrograde tracer in the PL. During CTA learning, we found an increase in the activity of excitatory neurons in the basolateral amygdala (BLA) or agranular IC that project to the PL. Taken together, these findings clearly identify a role of synchronized PL, agranular IC, and BLA activity in CTA learning.

Delineation of vagal emetic pathways: intragastric copper sulfate-induced emesis and viral tract tracing in musk shrews

Signals from the vestibular system, area postrema, and forebrain elicit nausea and vomiting, but gastrointestinal (GI) vagal afferent input arguably plays the most prominent role in defense against food poisoning. It is difficult to determine the contribution of GI vagal afferent input on emesis because various agents (e.g., chemotherapy) often act on multiple sensory pathways. Intragastric copper sulfate (CuSO4) potentially provides a specific vagal emetic stimulus, but its actions are not well defined in musk shrews (Suncus murinus), a primary small animal model used to study emesis. The aims of the current study were 1) to investigate the effects of subdiaphragmatic vagotomy on CuSO4-induced emesis and 2) to conduct preliminary transneuronal tracing of the GI-brain pathways in musk shrews. Vagotomy failed to inhibit the number of emetic episodes produced by optimal emetic doses of CuSO4 (60 and 120 mg/kg ig), but the effects of lower doses were dependent on an intact vagus (20 and 40 mg/kg). Vagotomy also failed to affect emesis produced by motion (1 Hz, 10 min) or nicotine administration (5 mg/kg sc). Anterograde transport of the H129 strain of herpes simplex virus-1 from the ventral stomach wall identified the following brain regions as receiving inputs from vagal afferents: the nucleus of the solitary tract, area postrema, and lateral parabrachial nucleus. These data indicate that the contribution of vagal pathways to intragastric CuSO4-induced emesis is dose dependent in musk shrews. Furthermore, the current neural tracing data suggest brain stem anatomical circuits that are activated by GI signaling in the musk shrew.

Egr-1 induction provides a genetic response to food aversion in zebrafish

As soon as zebrafish larvae start eating, they exhibit a marked aversion for bitter and acidic substances, as revealed by a consumption assay, in which fluorescent Tetrahymena serve as a feeding basis, to which various stimuli can be added. Bitter and acidic substances elicited an increase in mRNA accumulation of the immediate-early response gene egr-1, as revealed by in situ hybridization. Conversely, chemostimulants that did not induce aversion did not induce egr-1 response. Maximum labeling was observed in cells located in the oropharyngeal cavity and on the gill rakers. Gustatory areas of the brain were also labeled. Interestingly, when bitter tastants were repeatedly associated with food reward, zebrafish juveniles learned to ingest food in the presence of the bitter compound. After habituation, the acquisition of acceptance for bitterness was accompanied by a loss of egr-1 labeling. Altogether, our data indicate that egr-1 participates specifically in food aversion. The existence of reward-coupled changes in taste sensitivity in humans suggests that our results are relevant to situations in humans.

Repeated cycles of chronic intermittent ethanol exposure leads to the development of tolerance to aversive effects of ethanol in C57BL/6J mice

BACKGROUND

Repeated cycles of chronic intermittent ethanol (CIE) exposure lead to increased voluntary ethanol (EtOH) intake in C57BL/6J mice. This study evaluates the development of tolerance to EtOH's aversive effects in CIE exposure.

METHODS

Adult male C57BL/6J mice were trained to drink 15% EtOH (vs. water) in a limited access procedure and then exposed to CIE (EtOH mice) or air (control [CTL] mice) for 5 cycles alternating with weekly access to EtOH drinking. Following the 4th CIE cycle, the aversive effects of EtOH were evaluated using a conditioned taste aversion (CTA) paradigm with 1% saccharin as the conditioned stimulus. Several doses of EtOH (0, 1, 2, and 3 g/kg) and LiCl (0.4 M, 0.02 ml/g) served as unconditioned stimuli. Finally, mice underwent a 5th CIE cycle to measure blood and brain concentrations following a 2 g/kg EtOH dose.

RESULTS

CIE exposure increased EtOH drinking in EtOH mice while drinking in CTL mice remained stable. The lowest EtOH dose (1 g/kg) did not induce CTA in either group, but the highest dose (3 g/kg) produced CTA in both groups (49% reduction for CTL vs. 25% reduction for EtOH) although the group differences were not statistically significant. However, the 2 g/kg EtOH dose induced a significant aversion in CTL mice (27% reduction) but not in EtOH mice (20% increase), indicating tolerance to EtOH's aversive effects. LiCl caused a similar aversion in CTL and EtOH mice (50% reduction). Finally, blood and brain ethanol concentrations were not different between CTL and EtOH mice following a 2 g/kg EtOH dose.

CONCLUSIONS

The data indicate that CIE exposure produces tolerance to the aversive effects of 2 g/kg EtOH. This effect does not appear to be related to a learning deficit or altered EtOH pharmacokinetics. These data support the notion that tolerance to EtOH's aversive effects may contribute to excessive EtOH drinking in EtOH-dependent mice.

Differential pattern of cAMP response element-binding protein activation in the rat brain after conditioned aversion as a function of the associative process engaged: taste versus context association

Ample data indicate that cAMP-response element-binding protein (CREB) is essential for the formation of long-term memory in various species and learning systems. This implies that activated CREB could delineate neuronal circuits that subserve items in memory, while leaving open the possibility that the specifics of CREB activation itself contribute to the specificity of the internal representation encoded by the relevant circuit. We describe here the differential activation of CREB in the rat brain as a function of two related yet distinct forms of aversive conditioning: conditioned taste aversion (CTA) and conditioned context aversion (CCA). We found that CTA induces strong CREB activation in the insular cortex (IC) and the lateral septum (LS), but not in the parietal cortex (PC) and the medial septum (MS). In contrast, CCA results in strong activation in the PC and MS, but not in the IC and LS. These findings are congruent with a model that links differential pattern of activity within the LS and the MS with the acquisition of elemental versus contextual conditioning and, more generally, with the notion that CREB activation delineates learning-dependent circuits as a function of the type of cognitive process engaged.

Increased histone acetyltransferase and lysine acetyltransferase activity and biphasic activation of the ERK/RSK cascade in insular cortex during novel taste learning

Changes in gene expression are thought to be involved in neuronal plasticity associated with learning and memory. Although acetylation of lysine residues on histones by histone acetyltransferases (HAT) is an obligatory component of transcription, HAT activity has been largely ignored in studies of the nervous system. We developed a new model for studying novel taste learning using novel solid food presentation to nondeprived animals. Using this behavioral paradigm, we investigated short- and long-term regulation of lysine acetyltransferase activity and the ERK/mitogen-activated protein kinase (MAPK)/RSK cascade in insular cortex, a CNS region known to be crucial for the formation of novel taste memories. We observed that novel taste learning elicited biphasic (acute and long-lasting) activation of two distinct lysine acetyltransferase activities along with the ERK/MAPK cascade in insular cortex. In vitro studies revealed that the ERK cascade could regulate the lysine acetylation of a 42 kDa lysine acetyltransferase substrate, suggesting a causal relationship between ERK activation and lysine acetyltransferase activity in insular cortex. Overall, our studies reveal an unanticipated long-lasting activation of insular cortex signal transduction cascades in novel taste learning. Furthermore, our studies suggest the hypothesis that acute and long-term ERK activation and lysine-histone acetyltransferase activation may play a role in regulating gene expression in single-trial learning and long-term memory formation.

A novel selective melanocortin-4 receptor agonist reduces food intake in rats and mice without producing aversive consequences

Studies using nonselective agonists and antagonists of melanocortin-3 receptor (MC3R) and MC4R point to the importance of the CNS melanocortin system in the control of food intake. We describe here a novel compound that is highly selective as an agonist at the MC4 receptor but has minimal activity at the MC3 receptor. When administered centrally to rats, this selective agonist increased Fos-like immunoreactivity in the paraventricular nucleus, central nucleus of the amygdala, nucleus of the solitary tract, and area postrema, a pattern of neuronal activation that is similar to that induced by a nonselective MC3/4R agonist. Additionally, it suppresses food intake when administered centrally to rats or peripherally to db/db mice that lack functional leptin receptors via a mechanism that is not accompanied by illness or other nonspecific effects. Conversely, a related compound that is a selective MC4R antagonist potently increased food intake when administered centrally in rats. These results support the hypothesis that the brain MC4R is intimately involved in the control of food intake and body weight and provide evidence that selective activation of MC4R causes anorexia that is not secondary to aversive effects.