Binge Eating in Female Rats Induced by Yo-Yo Dieting and Stress. In: Avena NM, editor. Animal Models of Eating Disorders. Totowa: Humana Press; 2013. pp. 27-49. [DOI: 10.1007/978-1-62703-104-2_3]

Repeated binge-like eating episodes in female rats alter adenosine A2A and dopamine D2 receptor genes regulation in the brain reward system

OBJECTIVE

Binge-eating disorder is an eating disorder characterized by recurrent binge-eating episodes, during which individuals consume excessive amounts of highly palatable food (HPF) in a short time. This study investigates the intricate relationship between repeated binge-eating episode and the transcriptional regulation of two key genes, adenosine A2A receptor (A2AAR) and dopamine D2 receptor (D2R), in selected brain regions of rats.

METHOD

Binge-like eating behavior on HPF was induced through the combination of food restrictions and frustration stress (15 min exposure to HPF without access to it) in female rats, compared to control rats subjected to only restriction or only stress or none of these two conditions. After chronic binge-eating episodes, nucleic acids were extracted from different brain regions, and gene expression levels were assessed through real-time quantitative PCR. The methylation pattern on genes' promoters was investigated using pyrosequencing.

RESULTS

The analysis revealed A2AAR upregulation in the amygdala and in the ventral tegmental area (VTA), and D2R downregulation in the nucleus accumbens in binge-eating rats. Concurrently, site-specific DNA methylation alterations at gene promoters were identified in the VTA for A2AAR and in the amygdala and caudate putamen for D2R.

DISCUSSION

The alterations on A2AAR and D2R genes regulation highlight the significance of epigenetic mechanisms in the etiology of binge-eating behavior, and underscore the potential for targeted therapeutic interventions, to prevent the development of this maladaptive feeding behavior. These findings provide valuable insights for future research in the field of eating disorders.

PUBLIC SIGNIFICANCE

Using an animal model with face, construct, and predictive validity, in which cycles of food restriction and frustration stress evoke binge-eating behavior, we highlight the significance of epigenetic mechanisms on adenosine A2A receptor (A2AAR) and dopamine D2 receptor (D2R) genes regulation. They could represent new potential targets for the pharmacological management of eating disorders characterized by this maladaptive feeding behavior.

Stress hyper-reactivity increases vulnerability to developing binge-type eating and associated anxiety-like behavior; comparison between Wistar-Kyoto and Sprague-Dawley rats

Introduction

Binge eating disorder (BED) is a widespread eating disorder that primarily affects women worldwide, and it is characterized by the presence of binge eating episodes and the absence of any compensatory behavior to prevent weight gain. BED presents elevated comorbidity with other psychiatric disorders, such as anxiety, and it has been suggested that stress sensibility could be a vulnerability factor for the development of BED and the associated anxiety comorbidity. In this study, we aim to investigate whether the Wistar-Kyoto rat strain (WKY), which has a stress hyper-reactive phenotype, could develop both binge-type eating and anxiety-like behaviors simultaneously. We also aim to compare its vulnerability to developing both behaviors with the Sprague Dawley rat strain (SD), a rat strain commonly used in binge-eating models.

Methods

WKY and SD rats were subjected to the model of intermittent access to palatable food (sucrose solution 30% or shortening) without calorie restriction or stress exposure. We evaluated and compared the development of binge-type eating behavior, anxiety-like behavior, and serum corticosterone variation as an index of the stress response in both rat strains.

Results

WKY rats presented a higher percentage of binge-type eaters and required less time to develop binge-type eating behavior than SD rats. The WKY eating pattern emulated a binge-eating episode regardless of the palatable food. Although the development of sucrose binge-type eating was similar between strains, WKY developed more easily the shortening binge-type eating than SD and was more susceptible to developing anxiety-like behavior. Additionally, sucrose binge eating seems to differentially affect both strains' hypothalamic-pituitary-adrenal (HPA) axis response to stress since it facilitated its response in SD and blunted it in WKY.

Discussion

Our results show that high-stress sensitive phenotype is a common vulnerability factor for the development of binge-type eating and anxiety-like behavior. Regardless of the macronutrient composition of the palatable food, WKY is susceptible to developing a binge-type eating behavior and is more susceptible than SD to developing anxiety-like behavior simultaneously. In conclusion, results showed that a hyper-reactive stress phenotype predisposes the development of binge-type eating behavior and anxiety-like behavior in the absence of calorie restriction and stress exposure.

Targeting orexin receptors: Recent advances in the development of subtype selective or dual ligands for the treatment of neuropsychiatric disorders

Orexin-A and orexin-B, also named hypocretin-1 and hypocretin-2, are two hypothalamic neuropeptides highly conserved across mammalian species. Their effects are mediated by two distinct G protein-coupled receptors, namely orexin receptor type 1 (OX1-R) and type 2 (OX2-R), which share 64% amino acid identity. Given the wide expression of OX-Rs in different central nervous system and peripheral areas and the several pathophysiological functions in which they are involved, including sleep-wake cycle regulation (mainly mediated by OX2-R), emotion, panic-like behaviors, anxiety/stress, food intake, and energy homeostasis (mainly mediated by OX1-R), both subtypes represent targets of interest for many structure-activity relationship (SAR) campaigns carried out by pharmaceutical companies and academies. However, before 2017 the research was predominantly directed towards dual-orexin ligands, and limited chemotypes were investigated. Analytical characterizations, including resolved structures for both OX1-R and OX2-R in complex with agonists and antagonists, have improved the understanding of the molecular basis of receptor recognition and are assets for medicinal chemists in the design of subtype-selective ligands. This review is focused on the medicinal chemistry aspects of small molecules acting as dual or subtype selective OX1-R/OX2-R agonists and antagonists belonging to different chemotypes and developed in the last years, including radiolabeled OX-R ligands for molecular imaging. Moreover, the pharmacological effects of the most studied ligands in different neuropsychiatric diseases, such as sleep, mood, substance use, and eating disorders, as well as pain, have been discussed. Poly-pharmacology applications and multitarget ligands have also been considered.

Serum metabolic signature of binge-like palatable food consumption in female rats by nuclear magnetic resonance spectroscopy

Maladaptive eating behavior is a growing public health problem and compulsively eating excessive food in a short time, or binge eating, is a key symptom of many eating disorders. In order to investigate the binge-like eating behavior in female rats, induced by intermittent food restrictions/refeeding and frustration stress, we analyzed for the first time the metabolic profile obtained from serum of rats, through nuclear magnetic resonance (NMR) spectroscopy. In this experimental protocol, rats were exposed to chow food restricting/refeeding and frustration stress manipulation. This stress procedure consists of 15 min exposure to the odor and sight of a familiar chocolate paste, without access to it, just before offering the palatable food. In this model, a "binge-eating episode" was considered the significantly higher palatable food consumption within 2 h in restricted and stressed rats (R + S) than in the other three experimental groups: rats with no food restriction and no stress (NR + NS), only stressed rats (NR + S) or only restricted rats (R + NS). Serum samples from these four different rat groups were collected. The statistical analysis of the ¹ H NMR spectral profiles of the four sets of samples pointed to O- and N-acetyl glycoproteins as the main biomarkers for the discrimination of restriction effects. Other metabolites, such as threonine, glycine, glutamine, acetate, pyruvate and lactate, showed trends that may be useful to understand metabolic pathways involved in eating disorders. This study suggested that NMR-based metabolomics is a suitable approach to detect biomarkers related to binge-eating behavior.

Novel Highly Potent and Selective Sigma1 Receptor Antagonists Effectively Block the Binge Eating Episode in Female Rats

In this paper, the benzo-cracking approach was applied to the potent sigma1 (σ₁) receptor antagonist 1 to afford the less conformationally constrained 1,3-dioxane derivatives 2 and 3. To evaluate the effect of the increase in the distance between the two hydrophobic structural elements that flank the basic function, the cis and trans diastereomers of 4 and 5 were also prepared and studied. Compounds 2 and 3 showed affinity values at the σ₁ receptor significantly higher than that of the lead compound 1. In particular, 3 displayed unprecedented selectivity over the σ₂ receptor, the phencyclidine site of the NMDA receptor, and opioid receptor subtypes, as well as over the dopamine transporter. Docking results supported the structure–activity relationship studies. Due to its interesting biological profile, derivative 3, selected for an in vivo study in a validated preclinical model of binge eating, was able to counteract the overeating of palatable food only in binging rats, without affecting palatable food intake in the control group and anxiety-like and depression-related behaviors in female rats. This result strengthened the involvement of the σ₁ receptor in the compulsive-like eating behavior and supported the σ₁ receptor as a promising target for the management of eating disorders.

Oleoylethanolamide decreases frustration stress-induced binge-like eating in female rats: a novel potential treatment for binge eating disorder

Binge eating disorder (BED) is the most frequent eating disorder, for which current pharmacotherapies show poor response rates and safety concerns, thus highlighting the need for novel treatment options. The lipid-derived messenger oleoylethanolamide (OEA) acts as a satiety signal inhibiting food intake through the involvement of central noradrenergic and oxytocinergic neurons. We investigated the anti-binge effects of OEA in a rat model of binge-like eating, in which, after cycles of intermittent food restrictions/refeeding and palatable food consumptions, female rats show a binge-like intake of palatable food, following a 15-min exposure to their sight and smell ("frustration stress"). Systemically administered OEA dose-dependently (2.5, 5, and 10 mg kg^-1) prevented binge-like eating. This behavioral effect was associated with a decreased activation (measured by mapping the expression of c-fos, an early gene widely used as a marker of cellular activation) of brain areas responding to stress (such as the nucleus accumbens and amygdala) and to a stimulation of areas involved in the control of food intake, such as the VTA and the PVN. These effects were paralleled, also, to the modulation of monoamine transmission in key brain areas involved in both homeostatic and hedonic control of eating. In particular, a decreased dopaminergic response to stress was observed by measuring dopamine extracellular concentrations in microdialysates from the nucleus accumbens shell, whereas an increased serotonergic and noradrenergic tone was detected in tissue homogenates of selected brain areas. Finally, a decrease in corticotropin-releasing factor (CRF) mRNA levels was induced by OEA in the central amygdala, while an increase in oxytocin mRNA levels was induced in the PVN. The restoration of a normal oxytocin receptor density in the striatum paralleled the oxytocinergic stimulation produced by OEA. In conclusion, we provide evidence suggesting that OEA might represent a novel potential pharmacological target for the treatment of binge-like eating behavior.

Regulation of adenosine A2A receptor gene expression in a model of binge eating in the amygdaloid complex of female rats

BACKGROUND

Pharmacological treatment approaches for eating disorders, such as binge eating disorder and bulimia nervosa, are currently limited.

METHODS AND AIMS

Using a well-characterized animal model of binge eating, we investigated the epigenetic regulation of the A_2A Adenosine Receptor (A_2AAR) and dopaminergic D2 receptor (D2R) genes.

RESULTS

Gene expression analysis revealed a selective increase of both receptor mRNAs in the amygdaloid complex of stressed and restricted rats, which exhibited binge-like eating, when compared to non-stressed and non-restricted rats. Consistently, pyrosequencing analysis revealed a significant reduction of the percentage of DNA methylation but only at the A_2AAR promoter region in rats showing binge-like behaviour compared to the control animals. Focusing thus on A_2AAR agonist (VT 7) administration (which inhibited the episode of binge systemically at 0.1 mg/kg or intra-central amygdala (CeA) injection at 900 ng/side) induced a significant increase of A_2AAR mRNA levels in restricted and stressed rats when compared to the control group. In addition, we observed a significant decrease in A_2AAR mRNA levels in rats treated with the A_2AAR antagonist (ANR 94) at 1 mg/kg. Consistent changes in the DNA methylation status of the A_2AAR promoter were found in restricted and stressed rats after administration of VT 7 or ANR 94.

CONCLUSION

We confirm the role of A_2AAR in binge eating behaviours, and we underline the importance of epigenetic regulation of the A_2AAR gene, possibly due to a compensatory mechanism to counteract the effect of binge eating. We suggest that A_2AAR activation, inducing receptor gene up-regulation, could be relevant to reduction of food consumption.

Transcriptional regulation of the endocannabinoid system in a rat model of binge-eating behavior reveals a selective modulation of the hypothalamic fatty acid amide hydrolase gene

OBJECTIVE

Binge-eating episodes are recurrent and are defining features of several eating disorders. Thus binge-eating episodes might influence eating disorder development of which exact underlying mechanisms are still largely unknown.

METHODS

Here we focused on the transcriptional regulation of the endocannabinoid system, a potent regulator of feeding behavior, in relevant rat brain regions, using a rat model in which a history of intermittent food restriction and a frustration stress induce binge-like palatable food consumption.

RESULTS

We observed a selective down-regulation of fatty acid amide hydrolase (faah) gene expression in the hypothalamus of rats showing the binge-eating behavior with a consistent reduction in histone 3 acetylation at lysine 4 of the gene promoter. No relevant changes were detected for any other endocannabinoid system components in any brain regions under study, as well as for the other epigenetic mechanisms investigated (DNA methylation and histone 3 lysine 27 methylation) at the faah gene promoter.

DISCUSSION

Our findings suggest that faah transcriptional regulation is a potential biomarker of binge-eating episodes, with a relevant role in the homeostatic regulation of food intake.

N/OFQ-NOP System in Food Intake

While lifestyle modifications should be the first-line actions in preventing and treating obesity and eating disorders, pharmacotherapy also provides a necessary tool for the management of these diseases.However, given the limitations of current anti-obesity drugs, innovative treatments that improve efficacy and safety are needed.Since the discovery that the activation of the Nociceptin/Orphanin (N/OFQ) FQ peptide (NOP) receptor by N/OFQ induces an increase of food intake in laboratory animals, and the finding that this effect can be blocked by NOP antagonists, many NOP agonists and antagonists have been synthesized and tested in vitro and in vivo for their potential regulation of feeding behavior. Promising results seem to suggest that the N/OFQergic system may be a potential therapeutic target for the neural control of feeding behavior and related pathologies, especially in binge-like eating behavior.

Hypothalamic CRF1 receptor mechanisms are not sufficient to account for binge-like palatable food consumption in female rats

OBJECTIVE

The present study evaluated the effect of systemic injection of the CRF1 receptor antagonist R121919, the corticosterone synthesis inhibitor metyrapone and central amygdala (CeA) injections of the nonselective CRF antagonist D-Phe-CRF_(12-41) in rats in which binge eating was evoked by stress and cycles of food restriction.

METHOD

Female rats were subjected or not to repeated cycles of regular chow food restriction/ad libitum feeding during which they were also given limited access (2 h) to palatable food. On the test day, rats were either exposed or not to the sight of the palatable food for 15 min without allowing access, before assessing food consumption.

RESULTS

Systemic injections of R121919, but not of the metyrapone, blocked binge-like eating behavior. Restricted and stressed rats showed up-regulation of crh1 receptor mRNA signal in the bed nucleus of the stria terminalis and CeA but not in basolateral amygdala (BLA) or in the paraventricular nucleus. Injection D-Phe-CRF_(12-41) in CeA but not in the BLA-blocked binge-like eating behavior.

DISCUSSION

These findings demonstrate that extra-hypothalamic CRF1 receptors, rather than those involved in endocrine functions, are involved in binge eating and the crucial role of CRF receptors in CeA. CRF1 receptor antagonism may represent a novel pharmacological treatment for binge-related eating disorders.

Estrogenic suppression of binge-like eating elicited by cyclic food restriction and frustrative-nonreward stress in female rats

Because binge eating and emotional eating vary through the menstrual cycle in human females, we investigated cyclic changes in binge-like eating in female rats and their control by estrogens. Binge-like eating was elicited by three cycles of 4 days of food restriction and 4 days of free feeding followed by a single frustrative nonreward-stress episode (15 min visual and olfactory exposure to a familiar palatable food) immediately before presentation of the palatable food. Intact rats showed binge-like eating during the diestrous and proestrous phases of the ovarian cycle, but not during the estrous (periovulatory) phase. Ovariectomized (OVX) rats not treated with estradiol (E2) displayed binge-like eating, whereas E2-treated OVX rats did not. The procedure did not increase signs of anxiety in an open-field test. OVX rats not treated with E2 that were subjected to food restriction and sacrificed immediately after frustrative nonreward had increased numbers of cells expressing phosphorylated extracellular signal-regulated kinases (ERK) in the central nucleus of the amygdala (CeA), paraventricular nucleus of hypothalamus (PVN), and dorsal and ventral bed nuclei of the stria terminalis (BNST) compared with nonrestricted or E2-treated rats. These data suggest that this female rat model is appropriate for mechanistic studies of some aspects of menstrual-cycle effects on emotional and binge eating in human females, that anxiety is not a sufficient cause of binge-like eating, and that the PVN, CeA, and BNST may contribute to information processing underlying binge-like eating.