Effects of baclofen on operant performance for food pellets and vegetable shortening after a history of binge-type behavior in non-food deprived rats

Behavioural and physiological effects of binge eating: A systematic review and meta-analysis of animal models

Binge eating is defined as eating abnormally large amounts in a brief period of time. Many animal studies have examined the behavioural and physiological effects of binge eating of high-fat, high-sugar foods to model the consequences of human binge eating. The present systematic review of 199 rodent studies sought to identify the behavioural and physiological consequences of binge eating and determine whether changes were specific to binge eating or to general effects of exposure to a palatable diet. A meta-analysis of 18 rodent studies revealed that binge eating produces greater anxiety-like behaviour on the Elevated Plus-Maze with a small effect size and significant funnel plot asymmetry, suggesting that the true effect size is overestimated. A history of binge-like access generally increases progressive ratio breakpoint for the binged food, without altering 'liking' as measured by lick microstructure, suggesting that dissociable effects on 'wanting' but not 'liking' accompany binge eating behaviour and contribute to its persistence. Binge eating appears to enhance compulsive food-seeking behaviour and prevent stress-induced reductions in intake but does not appear to alter depression-like behaviour or locomotor activity. Notably, binge eating may produce comparable metabolic impairments to those observed after extended continuous exposure to a palatable diet despite no overall effects on body weight outcomes in most studies.

GABAB Receptor: Structure, Biological Functions, and Therapy for Diseases

Gamma-aminobutyric acid (GABA) B receptors (GABABRs) that acts slowly and maintains the inhibitory tone are versatile regulators in the complex nervous behaviors and their involvement in various neuropsychiatric disorders, such as anxiety, epilepsy, pain, drug addiction, and Alzheimer's disease. Additional study advances have implied the crucial roles of GABABRs in regulating feeding-related behaviors, yet their therapeutic potential in addressing the neuropsychiatric disorders, binge eating, and feeding-related disorders remains underutilized. This general review summarized the physiological structure and functions of GABABR, explored the regulation in various psychiatric disorders, feeding behaviors, binge eating, and metabolism disorders, and fully discussed the potential of targeting GABABRs and its regulator-binding sites for the treatment of different psychiatric disorders, binge eating and even obesity. While agonists that directly bind to GABABR1 have some negative side effects, positive allosteric modulators (PAMs) that bind to GABABR2 demonstrate excellent therapeutic efficacy and tolerability and have better safety and therapeutic indexes. Moreover, phosphorylation sites of downstream GABABRs regulators may be novel therapeutic targets for psychiatric disorders, binge eating, and obesity. Further studies, clinical trials in particular, will be essential for confirming the therapeutic value of PAMs and other agents targeting the GABABR pathways in a clinical setting.

Effects of Highly Palatable Diet on motivation for food and resistance to punishment in rats: Role of sex and age of exposure

Exposure to highly palatable food is believed to induce behavioral and neurobiological changes that may produce addiction-like behavior and increase the risks of obesity and overweight. Studies in rodents have led to conflicting results suggesting that several factors such as sex and age of exposure contribute to the development of maladaptive behaviors towards food. In addition, it is not clear whether effects of exposure to highly palatable diets (HPD) persist after their discontinuation, which would indicate long-term risks to develop addiction-like behavior. In this study, we investigated the persistent effects of an intermittent 8-week exposure to HPD in male and female rats as a function of age of exposure (adult and adolescent). We found that intermittent exposure to HPD did not alter body weight, but it affected consumption of standard food during the time of exposure in all groups. In addition, in adults, HPD produced a decrease in the initial baseline responding in FR1 schedules, an effect that persisted for 4 weeks in males but not in female rats. However, we found that exposure to HPD did not affect resistance to punishment measured by progressive shock strength break points or motivation for food as measured by progressive-ratio break points regardless of sex or age of exposure. Altogether, these results do not provide support for the hypothesis that intermittent exposure to HPD produce persistent increases in the vulnerability to develop addiction-like behaviors towards palatable food.

Systematic Review of Binge Eating Rodent Models for Developing Novel or Repurposing Existing Pharmacotherapies

Recent advances in developing and screening candidate pharmacotherapies for psychiatric disorders have depended on rodent models. Eating disorders are a set of psychiatric disorders that have traditionally relied on behavioral therapies for effective long-term treatment. However, the clinical use of Lisdexamfatamine for binge eating disorder (BED) has furthered the notion of using pharmacotherapies for treating binge eating pathologies. While there are several binge eating rodent models, there is not a consensus on how to define pharmacological effectiveness within these models. Our purpose is to provide an overview of the potential pharmacotherapies or compounds tested in established rodent models of binge eating behavior. These findings will help provide guidance for determining pharmacological effectiveness for potential novel or repurposed pharmacotherapies.

Prefrontal Cortical Control of Activity in Nucleus Accumbens Core Is Weakened by High-Fat Diet and Prevented by Co-Treatment with N-Acetylcysteine: Implications for the Development of Obesity

A loss of neuroplastic control on nucleus accumbens (NAc) neuronal activity exerted by the medial prefrontal cortex (mPFC) through long-term depression (LTD) is involved in triggering drug-seeking behavior and relapse on several substances of abuse due to impaired glutamate homeostasis in tripartite synapses of the nucleus accumbens (NAc) core. To test whether this maladaptive neuroplastic mechanism underlies the addiction-like behavior induced in young mice by a high-fat diet (HFD), we utilized 28-days-old male mice fed HFD ad-libitum over 2 weeks, followed by 5 days of HFD abstinence. Control groups were fed a regular diet. HFD fed mice showed increased ΔFosB levels in the NAc core region, whereas LTD triggered from the mPFC became suppressed. Interestingly, LTD suppression was prevented by an i.p. injection of 100 mg/kg N-acetylcysteine 2.5 h before inducing LTD from the mPFC. In addition, excessive weight gain due to HFD feeding was diminished by adding 2mg/mL N-acetylcysteine in drinking water. Those results show a loss of neuroplastic mPFC control over NAc core activity induced by HFD consumption in young subjects. In conclusion, ad libitum consumption of HFD can lead to neuroplastic changes an addiction-like behavior that can be prevented by N-acetylcysteine, helping to decrease the rate of excessive weight gain.

A review of sex differences in the mechanisms and drivers of overeating

Disordered eating is often associated with marked psychological and emotional distress, and severe adverse impact on quality of life. Several factors can influence eating behavior and drive food consumption in excess of energy requirements for homeostasis. It is well established that stress and negative affect contribute to the aetiology of eating disorders and weight gain, and there is substantial evidence suggesting sex differences in sub-clinical and clinical types of overeating. This review will examine how negative affect and stress shape eating behaviors, and how the relationship between the physiological, endocrine, and neural responses to stress and eating behaviors differs between men and women. We will examine several drivers of overeating and explore possible mechanisms underlying sex differences in eating behavior.

Binge eating behavior and incentive motivation with a cafeteria diet

Binge-like eating behavior (BLE) has been characterized as an eating disorder in which subjects have an enhanced intake of food, mainly fats. However, intake of fats and carbohydrates may have differential effects on motivation. Previously it was shown that BLE produces an increase in operant responding for vegetable shortening, but others were unable to replicate the finding using sucrose as the reinforcer. Our aim was to determine if BLE behavior induced with a cafeteria-like diet (CaLD) with several options with fat content would produce an increment in performance. Male Wistar rats were trained under an exponential progressive ratio schedule of sucrose reinforcement; thereafter, the limited access model was used to induce BLE using CaLD options. Finally, subjects were tested for increments in break points (BPs) in the progressive ratio schedule. Rats with intermittent access to CaLD options showed a clear BLE with an escalation in their intake; however they showed compensatory decrements of chow intake that rendered a similar body weight gain to a continuous access group. Although we were unable to observe an increase in BPs after BLE we were able to observe a protection against the decrements of BP previously observed with sugar. Different mechanisms for processing high fat and high carbohydrate reinforcers are variables worth exploring to gain a better understanding of BLE behavior in rodent models.

Dissociation between binge eating behavior and incentive motivation

Binge-like eating behavior (BLE) has been characterized as an eating disorder in which subjects have an enhanced intake of food, mainly fats. However, intake of fats and carbohydrates may have differential effects on motivation. Previously it was shown that BLE produces an increase in operant responding for vegetable shortening. Our aim was to determine if BLE behavior induced with a sucrose solution would produce an increment in performance for sucrose reinforcers. Male Wistar rats were trained under an exponential progressive ratio schedule of sucrose reinforcement; thereafter, the limited access model was used to induce BLE. Finally, subjects were tested for increments in break points (BPs) in the progressive ratio schedule. We were unable to observe an increase in BPs after BLE. No increments in BPs were observed when a distinctive flavor (vanilla-flavored sucrose) was correlated with BLE induction and reinforcement, or when different types of ratio progression in the operant schedules were employed. However, rats adjusted their BPs according to reinforcer concentration after BLE induction, demonstrating that valuation (cost/benefit decision) of reinforcers was intact. Extent of training, alterations of reward processing after extended exposure to sucrose, and different mechanisms for processing high fat and high carbohydrate reinforcers are variables worth exploring to gain a better understanding of BLE behavior in rodent models.

Neuroendocrine response to GABA-B receptor agonism in alcohol-dependent individuals: Results from a combined outpatient and human laboratory experiment

Gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the nervous system, plays an important role in biobehavioral processes that regulate alcohol seeking, food intake, and stress response. The metabotropic GABA-B receptor has been investigated as a potential therapeutic target for alcohol use disorder, by using orthosteric agonists (e.g., baclofen) and positive allosteric modulators. Whether and how pharmacological manipulation of the GABA-B receptor, in combination with alcohol intake, may affect feeding- and stress-related neuroendocrine pathways remains unknown. In the present randomized, double-blind, placebo-controlled study, thirty-four alcohol-dependent individuals received baclofen (30 mg/day) or placebo in a naturalistic outpatient setting for one week, and then performed a controlled laboratory experiment which included alcohol cue-reactivity, fixed-dose priming, and self-administration procedures. Blood samples were collected, and the following neuroendocrine markers were measured: ghrelin, leptin, amylin, glucagon-like peptide-1 (GLP-1), insulin, prolactin, thyroid-stimulating hormone, growth hormone, cortisol, and adrenocorticotropic hormone (ACTH). During the outpatient phase, baclofen significantly increased blood concentrations of acyl-ghrelin (p = 0.01), leptin (p = 0.01), amylin (p = 0.004), and GLP-1 (p = 0.02). Significant drug × time-point interaction effects for amylin (p = 0.001) and insulin (p = 0.03), and trend-level interaction effects for GLP-1 (p = 0.06) and ACTH (p = 0.10) were found during the laboratory experiment. Baclofen, compared to placebo, had no effect on alcohol drinking in this study (p's ≥ 0.05). Together with previous studies, these findings shed light on the role of the GABAergic system and GABA-B receptors in the shared neurobiology of alcohol-, feeding-, and stress-related behaviors.

A behavioral and pharmacological characterization of palatable diet alternation in mice

Obesity and eating disorders are widespread in Western societies. Both the increased availability of highly palatable foods and dieting are major risk factors contributing to the epidemic of disorders of feeding. The purpose of this study was to characterize an animal model of maladaptive feeding induced by intermittent access to a palatable diet alternation in mice. In this study, mice were either continuously provided with standard chow food (Chow/Chow), or provided with standard chow for 2days and a high-sucrose, palatable food for 1day (Chow/Palatable). Following stability of intake within the cycling paradigm, we then investigated the effects of several pharmacological treatments on excessive eating of palatable food: naltrexone, an opioid receptor antagonist, SR141716A, a cannabinoid-1 receptor antagonist/inverse agonist, and BD-1063, a sigma-1 receptor antagonist. Over successive cycles, Chow/Palatable mice showed an escalation of palatable food intake within the first hour of renewed access to palatable diet and displayed hypophagia upon its removal. Naltrexone, SR141716A, and BD-1063 all reduced overconsumption of palatable food during this first hour. Here we provide evidence of strong face and convergent validity in a palatable diet alternation model in mice, confirming multiple shared underlying mechanisms of pathological eating across species, and thus making it a useful therapeutic development tool.

Can We Selectively Reduce Appetite for Energy-Dense Foods? An Overview of Pharmacological Strategies for Modification of Food Preference Behavior

Excessive intake of food, especially palatable and energy-dense carbohydrates and fats, is largely responsible for the growing incidence of obesity worldwide. Although there are a number of candidate antiobesity drugs, only a few of them have been proven able to inhibit appetite for palatable foods without the concurrent reduction in regular food consumption. In this review, we discuss the interrelationships between homeostatic and hedonic food intake control mechanisms in promoting overeating with palatable foods and assess the potential usefulness of systemically administered pharmaceuticals that impinge on the endogenous cannabinoid, opioid, aminergic, cholinergic, and peptidergic systems in the modification of food preference behavior. Also, certain dietary supplements with the potency to reduce specifically palatable food intake are presented. Based on human and animal studies, we indicate the most promising therapies and agents that influence the effectiveness of appetite-modifying drugs. It should be stressed, however, that most of the data included in our review come from preclinical studies; therefore, further investigations aimed at confirming the effectiveness and safety of the aforementioned medications in the treatment of obese humans are necessary.

Development of bingeing in rats altered by a small operant requirement

Previous studies have shown that providing an optional food for a brief period of time to non-food deprived rats on an intermittent basis in the home cage engenders significantly more intake (binge-type behavior) than when the optional food is provided for a brief period on a daily basis. Experiment 1 examined the effects of placing a small operant response requirement on access to an optional food (vegetable shortening) on the establishment of binge-type behavior. Experiment 2 examined the effects of different schedules of reinforcement, a period of abstinence from shortening, and 24h of food deprivation on established binge-type behavior. In Experiment 1 the group of rats with 30-min access to shortening on an intermittent basis in their home cages (IC) consumed significantly more shortening than the group with 30-min daily access in the home cage (DC). The group with 30-min intermittent access in an operant chamber (IO group) earned significantly more reinforcers than the group with 30-min daily access in an operant chamber (DO). In Experiment 2, the IO group earned significantly more reinforcers than the DO group regardless of the response cost, the period of shortening abstinence, and overnight food deprivation. These results demonstrate that while intermittent access generates binge-type eating, the size of the binge (intake) can be altered by different contingency arrangements.

Role of relaxin-3/RXFP3 system in stress-induced binge-like eating in female rats

Binge eating is frequently stimulated by stress. The neuropeptide relaxin-3 (RLN3) and its native receptor RXFP3 are implicated in stress and appetitive behaviors. We investigated the dynamics of the central RLN3/RXFP3 system in a newly established model of stress-induced binge eating. Female Sprague-Dawley rats were subjected to unpredictable intermittent 1-h access to 10% sucrose. When sucrose intake stabilized, rats were assessed for consistency of higher or lower sucrose intake in response to three unpredictable episodes of foot-shock stress; and assigned as binge-like eating prone (BEP) or binge-like eating resistant (BER). BEP rats displayed elevated consumption of sucrose under non-stressful conditions (30% > BER) and an additional marked increase in sucrose intake (60% > BER) in response to stress. Conversely, sucrose intake in BER rats was unaltered by stress. Chow intake was similar in both phenotypes on 'non-stress' days, but was significantly reduced by stress in BER, but not BEP, rats. After stress, BEP, but not BER, rats displayed a significant increase in RLN3 mRNA levels in the nucleus incertus. In addition, in response to stress, BEP, but not BER, rats had increased RXFP3 mRNA levels in the paraventricular and supraoptic nuclei of the hypothalamus. Intracerebroventricular administration of a selective RXFP3 antagonist, R3(B1-22)R, blocked the stress-induced increase in sucrose intake in BEP rats and had no effect on sucrose intake in BER rats. These results provide important evidence for a role of the central RLN3/RXFP3 system in the regulation of stress-induced binge eating in rats, and have therapeutic implications for eating disorders.

Preference for high-fat diet is developed by young Swiss CD1 mice after short-term feeding and is prevented by NMDA receptor antagonists

Obesity is a worldwide epidemic that is increasing at an alarming rate. One of its causes is the increased availability and consumption of diets rich in fat. In the present study, we investigated the effects of short-term consumption of a high fat diet (HFD) on dietary preferences in Swiss CD1 mice and its relation in time to specific metabolic effects. Mice that were weaned 21days postpartum and fed a chow diet for one week were afterward subjected to a diet preference test for 5days, exposed to both a regular diet (RD) and HFD. We found that mice did not show any preferences. In a second experiment, two groups of mice that were weaned 21days postpartum and subjected to a chow diet for one week were fed either RD or HFD for 18days, and a diet preference test was performed for 5days. After this short-term consumption of HFD, mice preferred HFD, while mice subjected to RD did not show any preference. Importantly, no differences in blood glucose levels were found between the groups prior to and after the experiments. The results support our hypothesis that the preference for HFD is not a spontaneous behavior in CD1 mice, but it can be observed after short-term consumption; additionally, this preference develops before metabolic effects appear. Finally, this preference for HFD could not be observed when the mice were i.p. injected daily with low doses of the NMDA receptor antagonists, ketamine, ifenprodil or MK-801 during the HFD feeding period. These data suggest that acquisition of dietary preference for HFD is a NMDA receptor-dependent learning process.

Nutritional controls of food reward

The propensity to select and consume palatable nutrients is strongly influenced by the rewarding effects of food. Neural processes integrating reward, emotional states and decision-making can supersede satiety signals to promote excessive caloric intake and weight gain. While nutritional habits are influenced by reward-based neural mechanisms, nutrition and its impact on energy metabolism, in turn, plays an important role in the control of food reward. Feeding modulates the release of metabolic hormones that have an important influence on central controls of appetite. Nutrients themselves are also an essential source of energy fuel, while serving as key metabolites and acting as signalling molecules in the neural pathways that control feeding and food reward. Along these lines, this review discusses the impact of nutritionally regulated hormones and select macronutrients on the behavioural and neural processes underlying the rewarding effects of food.

Environments predicting intermittent shortening access reduce operant performance but not home cage binge size in rats

When non-food-deprived rats are given brief access to vegetable shortening (a semi-solid fat used in baked products) on an intermittent basis (Monday, Wednesday, Friday), they consume significantly more and emit more operant responses for shortening than a separate group of rats given brief access to shortening every day. Since both groups are traditionally housed in the same room, it is possible that the environmental cues associated with placing shortening in the cages (e.g., investigator in room, cages opening and closing, etc.) provide predictable cues to the daily group, but unpredictable cues to the intermittent group. The present study examined the effects of providing predictable environmental cues to an isolated intermittent group in order to examine the independent contributions of intermittency and predictability on intake and operant performance. Two groups of rats were housed in the same room, with one group provided 30-min intermittent (INT) access and the second group provided 30-min daily access (D) to shortening. A third group (ISO) of rats was housed in a room by themselves in which all environmental cues associated with intermittent shortening availability were highly predictable. After five weeks of home cage shortening access, all rats were then exposed to several different operant schedules of reinforcement. The INT and ISO groups consumed significantly more shortening in the home cage than the D group. In contrast, the INT group earned significantly more reinforcers than both the ISO and D groups under all but one of the reinforcement schedules, while ISO and D did not differ. These data indicate that intermittent access will generate binge-type eating in the home cage independent of cue predictability. However, predictable cues in the home cage reduce operant responding independent of intermittent access.

Baclofen-induced reductions in optional food intake depend upon food composition

Baclofen reduces intake of some foods but stimulates intake or has no effect on others. The reasons for these differences are not known. The present study examined effects of baclofen when composition, energy density, preference, presentation and intake of optional foods varied. Semi-solid fat emulsions and sucrose products were presented for brief periods to non-food-deprived rats. In Experiment 1, fat and sucrose composition were varied while controlling energy density. In Experiment 2A, schedule of access and the number of optional foods were varied. In Experiment 2B, the biopolymer (thickener) was examined. Baclofen reduced intake of fat and/or sugar options with different energy densities (1.28-9kcal/g), when presented daily or intermittently, and when intakes were relatively high or low. However, the efficacy of baclofen was affected by the biopolymer used to thicken the options: baclofen had no effect when options were thickened with one biopolymer (3173), but reduced intake when options were thickened with another biopolymer (515). Baclofen failed to reduce intake of a concentrated sugar option (64% sucrose), regardless of biopolymer. Based upon these results, caution is urged when interpreting results obtained with products using different thickening agents. Systematic research is needed when designing products used in rat models of food intake.

Baclofen administration alters fear extinction and GABAergic protein levels

The investigation of GABAergic systems in learning and extinction has principally focused on ionotropic GABA(A) receptors. Less well characterized is the metabotropic GABA(B) receptor, which when activated, induces a more sustained inhibitory effect and has been implicated in regulating oscillatory activity. Few studies have been carried out utilizing GABA(B) ligands in learning, and investigations of GABA(B) in extinction have primarily focused on interactions with drugs of abuse. The current study examined changes in GABA(B) receptor function using the GABA(B) agonist baclofen (2 mg/mL) or the GABA(B) antagonist phaclofen (0.3 mg/mL) on trace cued and contextual fear conditioning and extinction. The compounds were either administered during training and throughout extinction in Experiment 1, or starting 24 h after training and throughout extinction in Experiment 2. All drugs were administered 1 mL/kg via intraperitoneal injection. These studies demonstrated that the administration of baclofen during training and extinction trials impaired animals' ability to extinguish the fear association to the CS, whereas the animals that were administered baclofen starting 24 h after training (Experiment 2) did display some extinction. Further, contextual fear extinction was impaired by baclofen in both experiments. Tissue analyses suggest the cued fear extinction deficit may be related to changes in the GABA(B2) receptor subunit in the amygdala. The data in the present investigation demonstrate that GABA(B) receptors play an important role in trace cued and contextual fear extinction, and may function differently than GABA(A) receptors in learning, memory, and extinction.

Towards an animal model of food addiction

The dramatically increasing prevalence of obesity, associated with potentially life-threatening health problems, including cardiovascular diseases and type II diabetes, poses an enormous public health problem. It has been proposed that the obesity epidemic can be explained by the concept of 'food addiction'. In this review we focus on possible similarities between binge eating disorder (BED), which is highly prevalent in the obese population, and drug addiction. Indeed, both behavioral and neural similarities between addiction and BED have been demonstrated. Behavioral similarities are reflected in the overlap in DSM-IV criteria for drug addiction with the (suggested) criteria for BED and by food addiction-like behavior in animals after prolonged intermittent access to palatable food. Neural similarities include the overlap in brain regions involved in food and drug craving. Decreased dopamine D2 receptor availability in the striatum has been found in animal models of binge eating, after cocaine self-administration in animals as well as in drug addiction and obesity in humans. To further explore the neurobiological basis of food addiction, it is essential to have an animal model to test the addictive potential of palatable food. A recently developed animal model for drug addiction involves three behavioral characteristics that are based on the DSM-IV criteria: i) extremely high motivation to obtain the drug, ii) difficulty in limiting drug seeking even in periods of explicit non-availability, iii) continuation of drug-seeking despite negative consequences. Indeed, it has been shown that a subgroup of rats, after prolonged cocaine self-administration, scores positive on these three criteria. If food possesses addictive properties, then food-addicted rats should also meet these criteria while searching for and consuming food. In this review we discuss evidence from literature regarding food addiction-like behavior. We also suggest future experiments that could further contribute to our understanding of behavioral and neural commonalities and differences between obesity and drug addiction.

Neurobiology of consummatory behavior: mechanisms underlying overeating and drug use

Consummatory behavior is driven by both caloric and emotional need, and a wide variety of animal models have been useful in research on the systems that drive consumption of food and drugs. Models have included selective breeding for a specific trait, manipulation of gene expression, forced or voluntary exposure to a substance, and identification of biomarkers that predict which animals are prone to overconsuming specific substances. This research has elucidated numerous brain areas and neurochemicals that drive consummatory behavior. Although energy homeostasis is primarily mediated by the hypothalamus, reinforcement is more strongly mediated by nuclei outside the hypothalamus, in mesocorticolimbic regions. Orexigenic neurochemicals that control food intake can provide a general signal for promoting caloric intake or a more specific signal for stimulating consumption of a particular macronutrient, fat, carbohydrate, or protein. The neurochemicals involved in controlling fat ingestion--galanin, enkephalin, orexin, melanin-concentrating hormone, and the endocannabinoids--show positive feedback with this macronutrient, as these peptides both increase fat intake and are further stimulated by its intake. This positive association offers some explanation for why foods high in fat are so often overconsumed. Consumption of ethanol, a drug of abuse that also contains calories, is similarly driven by the neurochemical systems involved in fat intake, according to evidence that closely relates fat and ethanol consumption. Further understanding of the systems involved in consummatory behavior will enable the development of effective therapies for the treatment of both overeating and drug abuse.

A history of bingeing on fat enhances cocaine seeking and taking

Binge eating and substance dependence are disorders characterized by a loss of control over consummatory behaviors. Given the common characteristics of these two types of disorders, it is not surprising that the comorbidity between eating disorders and substance abuse disorders is high (20-40%; Conason et al., 2006). It is unknown, however, whether loss of control in one disorder predisposes an individual to loss of control in the other. The present study, therefore, used a rodent model to test whether a history of binge eating would augment subsequent responding for cocaine. Using the limited access protocol described by Corwin et al. (1998), 45 adult male Sprague-Dawley rats were maintained on one of four dietary protocols for a period of six weeks: chow only (Chow; n = 9), continuous access to an optional source of dietary fat (Ad Lib; n = 12), 1-h access to an optional source of dietary fat daily (Daily; n = 12), or 1-h access to an optional source of dietary fat on Monday, Wednesday, and Friday (MWF; n = 12). All four groups also had unrestricted access to a nutritionally complete diet of chow and water. Fat-bingeing behaviors developed in the MWF rats, the group with the most restricted access to the optional fat. Thereafter, cocaine-seeking and -taking behaviors were assessed in all rats using a self-administration protocol modified from that described by Deroche-Gamonet et al. (2004), which focused on the motivation for and preoccupation with obtaining and consuming drug (assessed using a progressive ratio [PR] schedule of reinforcement) and persistence in responding for drug during periods of signaled drug non-availability (SNA). Rats with the MWF history tended to take more cocaine late in fixed ratio (FR) training, they persisted in their efforts to obtain cocaine in the face of signaled non-availability, worked harder for cocaine on a PR schedule of reinforcement, and exhibited more goal-directed behavior toward the cocaine-associated operandum. These results demonstrate a link between binge-type intake of fat and the development of drug-seeking and -taking behaviors, suggesting that a history of fat bingeing may predispose individuals to exhibit more robust "addiction-like" behaviors toward a substance of abuse. Thus, it appears that conditions promoting excessive behavior toward one substance (e.g., a palatable fatty food) beget excessive behavior toward another (e.g., cocaine).

Natural rewards, neuroplasticity, and non-drug addictions

There is a high degree of overlap between brain regions involved in processing natural rewards and drugs of abuse. "Non-drug" or "behavioral" addictions have become increasingly documented in the clinic, and pathologies include compulsive activities such as shopping, eating, exercising, sexual behavior, and gambling. Like drug addiction, non-drug addictions manifest in symptoms including craving, impaired control over the behavior, tolerance, withdrawal, and high rates of relapse. These alterations in behavior suggest that plasticity may be occurring in brain regions associated with drug addiction. In this review, I summarize data demonstrating that exposure to non-drug rewards can alter neural plasticity in regions of the brain that are affected by drugs of abuse. Research suggests that there are several similarities between neuroplasticity induced by natural and drug rewards and that, depending on the reward, repeated exposure to natural rewards might induce neuroplasticity that either promotes or counteracts addictive behavior.

Rats that binge eat fat-rich food do not show somatic signs or anxiety associated with opiate-like withdrawal: implications for nutrient-specific food addiction behaviors

Previous studies suggest that binge eating sugar leads to behavioral and neurochemical changes similar to those seen with drug addiction, including signs of opiate-like withdrawal. Studies are emerging that show multiple neurochemical and behavioral indices of addiction when animals overeat a fat-rich diet. The goal of the present study was to utilize liquid and solid diets high in sugar and fat content to determine whether opiate-like withdrawal is seen after binge consumption of these diets in Sprague-Dawley rats. Control groups were given ad libitum access to the sweet-fat food or standard chow. All rats were then given a battery of tests to measure signs of opiate-like withdrawal, which included somatic signs of distress, elevated plus-maze anxiety, and locomotor hypoactivity. Neither naloxone-precipitated (3 mg/kg) nor deprivation-induced withdrawal was observed in rats that were maintained on a nutritionally complete pelleted sweet-fat diet or a sweet, high-fat diet supplemented with standard rodent chow. Naloxone-precipitated withdrawal was also not seen in rats fed a liquid sweet-fat food. Further, body weight reduction to 85%, which is known to potentiate the reinforcing effects of substances of abuse, did not affect naloxone-precipitated signs of opiate-like withdrawal. Thus, unlike previous findings reported regarding rats with binge access to a sucrose solution, rats that binge eat sweet-fat combinations do not show signs of opiate-like withdrawal under the conditions tested. These data support the idea that excessive consumption of different nutrients can induce behaviors associated with addiction in different ways, and that the behaviors that could characterize "food addiction" may be subtyped based on the nutritional composition of the food consumed.

Feeding and reward: perspectives from three rat models of binge eating

Research has focused on understanding how overeating can affect brain reward mechanisms and subsequent behaviors, both preclinically and in clinical research settings. This work is partly driven by the need to uncover the etiology and possible treatments for the ongoing obesity epidemic. However, overeating, or non-homeostatic feeding behavior, can occur independent of obesity. Isolating the variable of overeating from the consequence of increased body weight is of great utility, as it is well known that increased body weight or obesity can impart its own deleterious effects on physiology, neural processes, and behavior. In this review, we present data from three selected animal models of normal-weight non-homeostatic feeding behavior that have been significantly influenced by Bart Hoebel's 40+-yr career studying motivation, feeding, reinforcement, and the neural mechanisms that participate in the regulation of these processes. First, a model of sugar bingeing is described (Avena/Hoebel), in which animals with repeated, intermittent access to a sugar solution develop behaviors and brain changes that are similar to the effects of some drugs of abuse, serving as the first animal model of food addiction. Second, another model is described (Boggiano) in which a history of dieting and stress can perpetuate further binge eating of palatable and non-palatable food. In addition, a model (Boggiano) is described that allows animals to be classified as having a binge-prone vs. binge-resistant behavioral profile. Lastly, a limited access model is described (Corwin) in which non-food deprived rats with sporadic limited access to a high-fat food develop binge-type behaviors. These models are considered within the context of their effects on brain reward systems, including dopamine, the opioids, cholinergic systems, serotonin, and GABA. Collectively, the data derived from the use of these models clearly show that behavioral and neuronal consequences of bingeing on a palatable food, even when at a normal body weight, are different from those that result from simply consuming the palatable food in a non-binge manner. These findings may be important in understanding how overeating can influence behavior and brain chemistry.

Effect of 2-hydroxyestradiol on binge intake in rats

One conundrum of binge eating is that women are more likely to suffer from binge-related disorders, even though estradiol decreases food intake. 2-hydroxyestradiol (2OHE2), an estrogen metabolite, may account for the contradiction, due to possible interference with DA signaling. We hypothesized that 2OHE2 would enhance bingeing in a rodent model. Two cohorts (1 male, 1 female) of 34 non-food-deprived rats were separated into daily control (D) (received an optional source of dietary fat for 20 min every day) or bingeing (INT) groups (received fat intermittently, i.e. 20 min on Mon, Weds, Fri). During the 5-week binge induction period, shortening intakes escalated significantly faster in females than in males, such that males consumed significantly less fat/kg body mass than did females after 5 weeks. This result is consistent with the idea that biological differences contribute to sex differences in bingeing. Rats were then injected with 2OHE2 (1.0, 3.0, and 10.0 μg/kg intraperitoneally), vehicle, or 2-methoxyestradiol (2ME2) immediately prior to fat access. Fat intake was significantly stimulated by 2OHE2 only in the INT rats (p<0.03). Furthermore, this effect seemed to be more subtle in females than in males. Thus, 2OHE2 appears to exacerbate binge size. These data suggest a novel biological mechanism for sex differences in the risk of eating disorders.

Reinforcing efficacy of fat, as assessed by progressive ratio responding, depends upon availability not amount consumed

Intermittent limited access to an optional source of dietary fat can induce binge-type behavior in rats. However, the ability of such access to alter the reinforcing efficacy of fat has not been clearly demonstrated. In this study, performance under progressive ratio one (PR1) and three (PR3) schedules of shortening (fat) reinforcement was assessed in non-food deprived rats (n=15/group). One group of rats had intermittent access to a dietary fat option (INT, 1-hour shortening access in the home cage each Monday, Wednesday, and Friday), whereas the other group had daily access to the fat option (D, 1-hour shortening access daily). Chow and water were continuously available. After five weeks, the INT group consumed more shortening during the 1-hour access period than did the D group. Rats were then trained to lever press for a solid shortening reinforcer (0.1 gm). INT rats earned significantly more reinforcers than did D rats under PR1, but not under PR3. Subgroups of INT and D rats (n=7 each) were matched on the amount of shortening consumed in the home cage during week five of the protocol and the PR data were reanalyzed. The INT subgroup earned significantly more reinforcers than the D subgroup did under PR1, but not PR3. These results demonstrate that: (1) intermittent access to shortening in the home cage, but not the amount consumed during the access period (i.e. bingeing), increases the reinforcing efficacy of solid shortening; and (2) the type of PR schedule is critical in delineating differences between the groups.

Food addiction: true or false?

PURPOSE OF REVIEW

Food addiction has been implicated as a putative causal factor in chronic overeating, binge eating, and obesity. The concept of food addiction has been controversial historically due to definitional and conceptual difficulties and to a lack of rigorous scientific data.

RECENT FINDINGS

Support for the food addiction hypothesis comes from alterations in neurochemistry (dopamine, endogenous opioids), neuroanatomy (limbic system), and self-medication behaviors. Foods identified as having potential addictive properties include sweets, carbohydrates, fats, sweet/fat combinations, and possibly processed and/or high salt foods. Eating topography has been identified as a necessary factor in neural pathway changes that promote addiction-like properties in response to some foods. A recently developed food addiction scale shows promise in identifying food addiction.

SUMMARY

Recent findings have strengthened the case for food addiction. These findings may serve to validate the perception of food addiction in patients and inform psychoeducational, cognitive-behavioral, and/or pharmacological treatment for chronic food cravings, compulsive overeating, and binge eating that may represent a phenotype of obesity. Screening for food addiction has the potential to identify people with eating difficulties that seriously compromise weight management efforts. Future research should include a focus on human food addiction research; evaluating the impact of treatment on underlying neurochemistry; and prevention or reversal of food addiction in humans.

Shared brain vulnerabilities open the way for nonsubstance addictions: carving addiction at a new joint?

For more than half a century, since the beginning of formal diagnostics, our psychiatric nosology has compartmentalized the compulsive pursuit of substance (e.g., alcohol, cocaine, heroin, nicotine) from nonsubstance (e.g., gambling, food, sex) rewards. Emerging brain, behavioral, and genetic findings challenge this diagnostic boundary, pointing to shared vulnerabilities underlying the pathological pursuit of substance and nonsubstance rewards. Working groups for the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-V), are thus considering whether the nosologic boundaries of addiction should be redrawn to include nonsubstance disorders, such as gambling. This review discusses how neurobiological data from problem gambling, obesity, and "normal" states of attachment (romantic infatuation, sexual attraction, maternal bonds) may help us in the task of carving addictions "at a new joint." Diagnostic recarving may have a positive effect on addiction research, stimulating discovery of "crossover" pharmacotherapies with benefit for both substance and nonsubstance addictions.

Behavioral effects of withdrawal from sweetened vegetable shortening in rats

This study tested the hypothesis that withdrawal from intermittent access to a sweet fat mixture would lead to an exaggerated motivation and craving for palatable food. Male Long-Evans rats were divided into three weight-matched groups based on access to sweetened vegetable shortening (SVS). Groups received 1-hour SVS access everyday (7D group), 1-hour SVS access intermittently, 3 days/week (3D group), or no SVS access (Naïve group). By the second week 3D rats began to display a disordered eating pattern. After 28 days on this feeding schedule SVS was withdrawn and anxiety was measured in an elevated plus maze. Motivation was assessed through operant performance for 10% sucrose on a progressive ratio schedule and craving was examined with a reinstatement test for lever pressing following extinction. Initial measures of anxiety and motivation found no differences among groups. However, when food was deprived overnight, there was a greater increase in lever pressing in the 3D group compared to 7D and Naïve rats. Thus a history of intermittent SVS access enhanced the reinforcing value of sucrose, but only under deprivation conditions. Interestingly, reinstatement of responding for sucrose was present only in the Naïve group. These findings suggest that a history of disordered eating may result in augmented motivation for palatable foods during a state of negative energy balance.

Appetite and reward

The tendency to engage in or maintain feeding behaviour is potently influenced by the rewarding properties of food. Affective and goal-directed behavioural responses for food have been assessed in response to various physiological, pharmacological and genetic manipulations to provide much insight into the neural mechanisms regulating motivation for food. In addition, several lines of evidence tie the actions of metabolic signals, neuropeptides and neurotransmitters to the modulation of the reward-relevant circuitry including midbrain dopamine neurons and corticolimbic nuclei that encode emotional and cognitive aspects of feeding. Along these lines, this review pulls together research describing the peripheral and central signalling molecules that modulate the rewarding effects of food and the underlying neural pathways.

The plausibility of sugar addiction and its role in obesity and eating disorders

BACKGROUND & AIMS

To consider the hypothesis that addiction to food, or more specifically sucrose, plays a role in obesity and eating disorders.

METHODS

By considering the relevant literature a series of predictions were examined, derived from the hypothesis that addiction to sucrose consumption can develop. Fasting should increase food cravings, predominantly for sweet items; cravings should occur after an overnight fast; the obese should find sweetness particularly attractive; a high-sugar consumption should predispose to obesity. More specifically predictions based on the hypothesis that addiction to sugar is central to bingeing disorders were developed. Dieting should predate the development of bingeing; dietary style rather than psychological, social and economic factors should be predispose to eating disorders; sweet items should be preferentially consumed while bingeing; opioid antagonists should cause withdrawal symptoms; bingeing should develop at a younger age when there is a greater preference for sweetness.

RESULTS

The above predications have in common that on no occasion was the behaviour predicted by an animal model of sucrose addiction supported by human studies.

CONCLUSION

There is no support from the human literature for the hypothesis that sucrose may be physically addictive or that addiction to sugar plays a role in eating disorders.

Baclofen, raclopride, and naltrexone differentially affect intake of fat and sucrose under limited access conditions

Gamma-aminobutyric acid (GABA), dopamine, and opioids are implicated in impulse control, addiction and binge eating. Recent evidence suggests that sucrose alters the effects of GABAergic, dopaminergic, and opioid receptor ligands on consumption of a fatty food in a rat limited-access binge protocol. This study determined the independent effects of fat and sucrose on the efficacy of these ligands under limited-access conditions. Nonfood-deprived male Sprague-Dawley rats had 1 h access to fat (vegetable shortening) or sucrose (3.2, 10, or 32% w/v). Half had intermittent access (Monday, Wednesday, Friday) and half had daily access. Effects of baclofen (GABAB agonist), SCH 23390 (D1 antagonist), raclopride (D2 antagonist), and naltrexone (opioid antagonist) were assessed. Baclofen and naltrexone reduced fat intake regardless of the access schedule. Baclofen had no effect on sucrose intake; naltrexone reduced sucrose intake at higher doses than were required to reduce fat intake. Raclopride stimulated fat intake in intermittent-access rats and had no effect in daily-access rats; raclopride reduced sucrose intake in all groups. SCH 23390 reduced intake in a nonspecific manner. The results indicate the involvement of GABAB receptors in fat but not sucrose intake, and of D2 receptor dysfunction in rats with a history of bingeing on fat.

Baclofen suppresses binge eating of pure fat but not a sugar-rich or sweet-fat diet

Baclofen is a γ-aminobutyric acid-B agonist that is known to reduce the intake of some drugs of abuse. Binge eating of sugar or fat has been shown to have behavioral and neurochemical similarities to drug abuse, and may be special cases suggestive of natural addiction. To determine whether a treatment for drug abuse would have an effect on binge eating, and if so, which type of food intake might be affected, this study compared the effects of baclofen on binge eating sucrose, fat, and a sweet-fat combination. Rats were maintained for 21 days on a schedule of 12-h daily access to (i) a 10% sucrose solution, (ii) vegetable fat, or (iii) a commercially available sweet-fat chow. A fourth group had only 2-h daily access to vegetable fat. All four experimental groups, plus a control group, had ad libitum access to water and standard rodent chow. Food intake was then measured after intraperitoneal administration of baclofen (0, 0.6, 1.0, or 1.8 mg/kg). Results showed that although there was no effect of drug on standard chow intake of rats in any group, baclofen stimulated binge eating of sweet-fat food, suppressed binge eating of pure fat (vegetable shortening) in the group with 2-h access, and had no effect on sucrose binges. These results support earlier findings of a suppressive effect of baclofen on binge eating of fat and introduce a new finding that the drug differentially affects binge eating of sucrose and a sugar-fat combination.

Baclofen, raclopride, and naltrexone differentially affect intake of fat/sucrose mixtures under limited access conditions

This study assessed the effects of the opioid antagonist naltrexone, the dopamine 2-like (D2) antagonist raclopride, and the GABA(B) agonist baclofen on consumption of fat/sucrose mixtures (FSM) using a limited access protocol. Sixty male Sprague-Dawley rats were grouped according to two schedules of access (Daily [D] or Intermittent [I]) to an optional FSM. Each FSM was created by whipping 3.2% (L), 10% (M), or 32% (H) powdered sugar into 100% vegetable shortening in a w/w manner (n=10 per group). One-hour intakes of the IL and IM groups were significantly greater than intakes of the respective DL and DM groups, thus fulfilling our operational definition of binge-type eating in these groups. Baclofen reduced intakes of the L and M mixtures regardless of access schedule, but failed to reduce intake of the H mixture. Naltrexone reduced intake in all groups, but potency was greater in IL rats than in DL rats. Furthermore, potency was attenuated in Intermittent rats, but enhanced in Daily rats, at higher sucrose concentrations. Raclopride reduced intake in the DL and stimulated intake in the IL groups, reduced intake in both M groups, and was without effect in both H groups. These results indicate that fat/sucrose mixtures containing relatively low concentrations of sucrose allow distinctions to be made between: 1) intakes stimulated by different access schedules and 2) opioid and dopaminergic modulation of those intakes. These results also suggest that brief bouts of food consumption involving fatty, sugar-rich foods may prove to be particularly resistant to pharmacological intervention.

Sugar and fat bingeing have notable differences in addictive-like behavior

Ingestion of different nutrients, such as fats and sugars, normally produces different effects on physiology, the brain, and behavior. However, they do share certain neural pathways for reinforcement of behavior, including the mesolimbic dopamine (DA) system. When these nutrients are consumed in the form of binges, this can release excessive DA, which causes compensatory changes that are comparable to the effects of drugs of abuse. In this article, we review data obtained with animal models of fat and sugar bingeing. The concept of "food addiction" is described and reviewed from both clinical and laboratory animal perspectives. Behavioral manifestations of addictive-like behavior and concomitant alterations in DA and opioid systems are compared for sugar and fat bingeing. Finally, in relation to eating disorders and obesity, we discuss how fat may be the macronutrient that results in excess body weight, and sweet taste in the absence of fat may be largely responsible for producing addictive-like behaviors that include a withdrawal syndrome.

Symposium overview--Food addiction: fact or fiction?

Food addiction is a pervasive, yet controversial, topic that has gained recent attention in both lay media and the scientific literature. The goal of this series of articles is to use a combination of preclinical and clinical data to determine whether foods, like drugs of abuse, can be addictive, the conditions under which the addiction develops, and the underlying neurophysiological substrates. Operational definitions of addiction that have been used in the treatment of human disorders and to guide research in both humans and animals are presented, and an overview of the symposium articles is provided. We propose that specific foods, especially those that are rich in fat and/or sugar, are capable of promoting "addiction"-like behavior and neuronal change under certain conditions. That is, these foods, although highly palatable, are not addictive per se but become so following a restriction/binge pattern of consumption. Such consummatory patterns have been associated with increased risk for comorbid conditions such as obesity, early weight gain, depression, anxiety, and substance abuse as well as with relapse and treatment challenges. The topic of food addiction bears study, therefore, to develop fresh approaches to clinical intervention and to advance our understanding of basic mechanisms involved in loss of control.

Access conditions affect binge-type shortening consumption in rats

When non-food-deprived rats are given intermittent access to certain substances, consumption of those substances is greater than when more frequent access is provided. The present study examined the effects of three different shortening access conditions on subsequent shortening intake in rats. Each of the three different shortening conditions lasted five weeks and was followed by a five-week period in which shortening access was limited by time (1 h of availability) on either an Intermittent (Monday, Wednesday, Friday) or Daily schedule of access. In Part 1, limiting the quantity of shortening provided during the 1-h period of availability attenuated subsequent 1-h shortening intake in the Intermittent access group, but had no statistically significant effect in the Daily access group. In Part 2, unrestricted availability of shortening (24 h/day-7 days/week) attenuated subsequent 1-h shortening intake in all groups. In Part 3, shortening non-availability for five weeks enhanced subsequent 1-h shortening intake in all groups. It was also shown that rats under an Intermittent, but not a Daily, schedule of access consumed as much shortening during a 1-h period of availability, as was consumed in 24 h when shortening availability was unrestricted. These results demonstrate that while intermittent access is necessary and sufficient to stimulate binge-type eating in rats, the behavioral history can modulate binge size.

Use of an operant task to estimate food reinforcement in adult humans with and without BED

OBJECTIVE

The purpose of this study was to demonstrate the utility of food-reinforced operant task performance in modeling binge-eating disorder (BED). We hypothesized that food reinforcement after a caloric preload would be related to BED status, but not hunger.

METHODS AND PROCEDURES

We investigated the association between reports of hunger, binge tendency, and food reinforcement in a sample of 18 women (12 non-BED, 7 lean, 5 obese, and 6 obese BED). Participants completed two sessions of operant task performance after consuming 600 ml of flavored water or 600 ml of a 1 kcal/ml liquid meal.

RESULTS

Under the water condition, food reinforcement did not differ between the non-BED and BED groups, and was positively correlated with hunger ratings across all participants (r = 0.55, P = 0.023). Under the liquid meal condition, food reinforcement was significantly decreased compared with the water condition in the non-BED group (t = -2.6, P = 0.026). There was also a significant difference between the non-BED and BED groups in the fed condition (41 +/- 40, 117 +/- 60, F = 10.3, P = 0.005, non-BED vs. BED, respectively, mean +/- s.d.). The correlation between food reinforcement and hunger remained significant only in the non-BED group (r = 0.69, P = 0.011).

DISCUSSION

Our results support the hypothesis that food reinforcement measured after a caloric preload is related to BED status but not hunger in those subjects with BED. The data also suggest that operant task performance can be useful in modeling BED criteria such as "eating when not physically hungry."

Intermittent access to preferred food reduces the reinforcing efficacy of chow in rats

Intermittent, extended access to preferred diets increases their intake. However, the effects of such access on the acceptance and reinforcing efficacy of otherwise satisfying alternatives is less known. To investigate the role of nonnutritional contributions to the hypophagia that follows removal of preferred food, male Wistar rats were fed a chow diet (Chow A/I), preferred to their regular chow (Chow), which was equally consumed under 1-choice conditions to an even more preferred chocolate-flavored, sucrose-rich diet (Preferred). Rats then learned to obtain Chow A/I pellets under a progressive ratio schedule of reinforcement and were assigned to two matched groups. Each week, one group (n = 15) was diet-cycled, receiving Chow A/I for 5 days followed by the Preferred diet for 2 days. Controls received Chow A/I daily (n = 14). Progressive ratio sessions were performed daily during the 5 days that all subjects received Chow A/I in the home cage. Across 5 wk, diet-cycled rats progressively ate less of the otherwise palatable Chow A/I diet. Hypophagia was not due to greater prior intake or weight gain, motor impairment, or facilitated satiation and was associated with changes in progressive ratio performance that suggested a reduced reinforcing efficacy of the Chow A/I diet in diet-cycled animals. By week 4, diet-cycled animals began to overeat the preferred diet, especially during the first 6 h of renewed access, resembling a deprivation effect. The results suggest that intermittent access to highly preferred food, as practiced by many restrained eaters, may progressively decrease the acceptability of less palatable foods, and may promote relapse to more rewarding alternatives.

Binge-type behavior in rats consuming trans-fat-free shortening

Studies from this and another laboratory involving an animal model of binge-type behavior have used vegetable shortening containing trans-fats. Due to reformulations by vegetable shortening manufacturers to remove trans-fats from their products, only trans-fat-free shortenings are now available. The goal of the present study was to assess binge-type behavior in rats with trans-fat and trans-free vegetable shortening. Trans-fat-free shortening was provided to three different groups of non-food-deprived male Sprague Dawley rats on different schedules of access: continuous access (24 h/day-7 days/week), daily access (1 h every day), and intermittent access (1 h on Mondays, Wednesdays, Fridays). Trans-fat shortening was provided to a fourth group on the intermittent access schedule. A fifth group had no shortening access (chow only). Both intermittent groups (trans-fat-free and trans-fat) consumed significantly more shortening during the 1-h period of availability than did the daily group, and there was no difference in shortening intakes between the intermittent groups. These results are identical to previous reports of binge-type behavior in rats using this model. Thus, binge-type behavior in the present behavioral model depends upon the schedule of access, not the presence of trans-fats in the shortening.

Baclofen, raclopride, and naltrexone differentially reduce solid fat emulsion intake under limited access conditions

Previous work in rats has demonstrated that an Intermittent (Monday, Wednesday, Friday) schedule of access promotes binge-type consumption of 100% vegetable shortening during a 1-h period of availability. The present study used novel shortening-derived stable solid emulsions of various fat concentrations. These emulsions were the consistency of pudding and did not demonstrate oil and water phase separation previously reported with oil-based liquid emulsions. Male Sprague-Dawley rats were grouped according to schedule of access (Daily or Intermittent) to one of three concentrations (18%, 32%, 56%) of solid fat emulsion. There were no significant Intermittent vs. Daily differences in amount consumed, due to high intakes in all groups. This indicated the acceptability of the emulsions. Baclofen (GABA(B) agonist) and raclopride (D2-like antagonist) both significantly reduced emulsion intake in all Daily groups, but only in the 56% fat Intermittent group. Naltrexone (opioid antagonist), in contrast, significantly reduced 32% and 56% fat emulsion intake in the Intermittent, as well as the Daily groups. These results indicate that the fat intake-reducing effects of GABA(B) activation and D(2) blockade depend upon fat concentration and schedule of fat access, while the fat intake-reducing effects of opioid blockade depend upon fat concentration but not schedule of access.

Baclofen for binge eating: an open-label trial

OBJECTIVE

Baclofen is a GABA-B agonist that may be useful in the treatment of substance use disorders, and also reduces 'binge-like' eating in rodents. We hypothesized that baclofen might be effective in reducing binge eating episodes in binge eating disorder (BED) and bulimia nervosa (BN).

METHOD

Seven women with BED (n = 4) or BN (n = 3) took baclofen (60 mg/day) for 10 weeks.

RESULTS

Six out of seven patients completed the full 10-week trial. Five out of seven participants (3 BED; 2 BN) demonstrated 50% or greater reduction of frequency of binge eating from beginning to end of the study. Three out of seven participants (2 BED; 1 BN) were free of binge eating at study end. Four out of seven participants elected to continue baclofen at study end. Baclofen was well tolerated by the participants.

CONCLUSION

In this open-label trial, baclofen was associated with decreased binge eating frequency in patients with BED and BN.

Liquid sucrose bingeing in rats depends on the access schedule, concentration and delivery system

Previous studies have reported binge-type consumption of solid vegetable shortening in non-food deprived rats maintained on schedules of limited shortening access. The current study determined if limited access would promote binge-type consumption of sucrose solutions. Adult male rats (6 groups, n = 10 each) were provided with one of three different sucrose concentrations (3.2%, 10%, 32% w/v) for 2 h either everyday (Daily) or Monday, Wednesday, and Friday (Intermittent). A 'binge' during the 2-h access periods was operationally defined as Intermittent intakes significantly greater than Daily intakes. Sucrose initially was provided in a 100 ml glass tube equipped with a stainless-steel drinking spout. Under these conditions, there were no differences in sucrose intake between Daily and Intermittent groups at any of the concentrations. In contrast, when sucrose was provided in a modified 60 ml plastic syringe with the same drinking spout, intakes of the Intermittent groups consuming 3.2% and 10% sucrose were greater than those of the respective Daily groups, indicating that binge-type consumption of sucrose occurred. These results demonstrate that brief, intermittent access to low and moderate concentrations of sucrose can promote binge-type behavior, and the characteristics of the drinking apparatus can affect sucrose intake.

Peripherally administered baclofen reduced food intake and body weight indb/dbas well as diet-induced obese mice

Peripheral administration of baclofen significantly reduced food intake and body weight increase in both diabetic (db/db) and diet-induced obese mice for 5 weeks, whereas it had no significant effects on energy balance in their lean control mice. Despite the decreased body weight, neuropeptide Y expression in the arcuate nucleus was significantly decreased, whereas pro-opiomelanocortin expression was significantly increased by baclofen treatment. These data demonstrate that the inhibitory effects of baclofen on body weight in the obese mice were mediated via the arcuate nucleus at least partially, and suggest that GABA(B) agonists could be a new therapeutic reagent for obesity.