Role of spontaneous physical activity in prediction of susceptibility to activity based anorexia in male and female rats

Long-lasting BDNF signaling alterations in the amygdala of adolescent female rats exposed to the activity-based anorexia model

Introduction: Anorexia nervosa (AN) is a severe psychiatric disorder characterized by a pathological fear of gaining weight, excessive physical exercise, and emotional instability. Since the amygdala is a key region for emotion processing and BDNF has been shown to play a critical role in this process, we hypothesized that alteration in the amygdalar BDNF system might underline vulnerability traits typical of AN patients. Methods: To this end, adolescent female rats have been exposed to the Activity-Based Anorexia (ABA) protocol, characterized by the combination of caloric restriction and intense physical exercise. Results: The induction of the anorexic phenotype caused hyperactivity and body weight loss in ABA animals. These changes were paralleled by amygdalar hyperactivation, as measured by the up-regulation of cfos mRNA levels. In the acute phase of the pathology, we observed reduced Bdnf exon IX, exon IV, and exon VI gene expression, while mBDNF protein levels were enhanced, an increase that was, instead, uncoupled from its downstream signaling as the phosphorylation of TrkB, Akt, and S6 in ABA rats were reduced. Despite the body weight recovery observed 7 days later, the BDNF-mediated signaling was still downregulated at this time point. Discussion: Our findings indicate that the BDNF system is downregulated in the amygdala of adolescent female rats under these experimental conditions, which mimic the anorexic phenotype in humans, pointing to such dysregulation as a potential contributor to the altered emotional processing observed in AN patients. In addition, since the modulation of BDNF levels is observed in other psychiatric conditions, the persistent AN-induced changes of the BDNF system in the amygdala might contribute to explaining the onset of comorbid psychiatric disorders that persist in patients even beyond recovery from AN.

Rethinking the Approach to Preclinical Models of Anorexia Nervosa

PURPOSE OF REVIEW

The goal of this review is to describe how emerging technological developments in pre-clinical animal research can be harnessed to accelerate research in anorexia nervosa (AN).

RECENT FINDINGS

The activity-based anorexia (ABA) paradigm, the best characterized animal model of AN, combines restricted feeding, excessive exercise, and weight loss. A growing body of evidence supports the idea that pathophysiological weight loss in this model is due to cognitive inflexibility, a clinical feature of AN. Targeted manipulations that recapitulate brain changes reported in AN - hyperdopaminergia or hyperactivity of cortical inputs to the nucleus accumbens - exacerbate weight loss in the ABA paradigm, providing the first evidence of causality. The power of preclinical research lies in the ability to assess the consequences of targeted manipulations of neuronal circuits that have been implicated in clinical research. Additional paradigms are needed to capture other features of AN that are not seen in ABA.

Is the Activity-Based Anorexia Model a Reliable Method of Presenting Peripheral Clinical Features of Anorexia Nervosa?

Anorexia nervosa (AN) causes the highest number of deaths among all psychiatric disorders. Reduction in food intake and hyperactivity/increased anxiety observed in AN are also the core features of the activity-based anorexia animal model (ABA). Our aim was to assess how the acute ABA protocol mimics common AN complications, including gonadal and cardiovascular dysfunctions, depending on gender, age, and initial body weight, to form a comprehensive description of ABA as a reliable research tool. Wheel running, body weight, and food intake of adolescent female and male rats were monitored. Electrocardiography, heart rate variability, systolic blood pressure, and magnetic resonance imaging (MRI) measurements were performed. Immediately after euthanasia, tissue fragments and blood were collected for further analysis. Uterine weight was 2 times lower in ABA female rats, and ovarian tissue exhibited a reduced number of antral follicles and decreased expression of estrogen and progesterone receptors. Cardiovascular measurements revealed autonomic decompensation with prolongation of QRS complex and QT interval. The ABA model is a reliable research tool for presenting the breakdown of adaptation mechanisms observed in severe AN. Cardiac and hormonal features of ABA with underlying altered neuroendocrine pathways create a valid phenotype of a human disease.

Animal Models for Anorexia Nervosa-A Systematic Review

Anorexia nervosa is an eating disorder characterized by intense fear of gaining weight and a distorted body image which usually leads to low caloric intake and hyperactivity. The underlying mechanism and pathogenesis of anorexia nervosa is still poorly understood. In order to learn more about the underlying pathophysiology of anorexia nervosa and to find further possible treatment options, several animal models mimicking anorexia nervosa have been developed. The aim of this review is to systematically search different databases and provide an overview of existing animal models and to discuss the current knowledge gained from animal models of anorexia nervosa. For the systematic data search, the Pubmed—Medline database, Embase database, and Web of Science database were searched. After removal of duplicates and the systematic process of selection, 108 original research papers were included in this systematic review. One hundred and six studies were performed with rodents and 2 on monkeys. Eighteen different animal models for anorexia nervosa were used in these studies. Parameters assessed in many studies were body weight, food intake, physical activity, cessation of the estrous cycle in female animals, behavioral changes, metabolic and hormonal alterations. The most commonly used animal model (75 of the studies) is the activity-based anorexia model in which typically young rodents are exposed to time-reduced access to food (a certain number of hours a day) with unrestricted access to a running wheel. Of the genetic animal models, one that is of particular interest is the anx/anx mice model. Animal models have so far contributed many findings to the understanding of mechanisms of hunger and satiety, physical activity and cognition in an underweight state and other mechanisms relevant for anorexia nervosa in humans.

The Utility of Animal Models for Studying the Metabo-Psychiatric Origins of Anorexia Nervosa

Anorexia nervosa (AN) is a severe eating disorder that primarily affects young women and girls, and is characterized by abnormal restrictive feeding and a dangerously low body-mass index. AN has one of the highest mortality rates of any psychiatric disorder, and no approved pharmacological treatments exist. Current psychological and behavioral treatments are largely ineffective, and relapse is common. Relatively little basic research has examined biological mechanisms that underlie AN compared to other major neuropsychiatric disorders. A recent large-scale genome-wide association study (GWAS) revealed that the genetic architecture of AN has strong metabolic as well as psychiatric origins, suggesting that AN should be reconceptualized as a metabo-psychiatric disorder. Therefore, identifying the metabo-psychiatric mechanisms that contribute to AN may be essential for developing effective treatments. This review focuses on animal models for studying the metabo-psychiatric mechanisms that may contribute to AN, with a focus on the activity-based anorexia (ABA) paradigm. We also highlight recent work using modern circuit-dissecting neuroscience techniques to uncover metabolic mechanisms that regulate ABA, and encourage further work to ultimately identify novel treatment strategies for AN.

Activity Based Anorexia as an Animal Model for Anorexia Nervosa-A Systematic Review

Anorexia nervosa (AN) is a severe eating disorder affecting around 1 per 100 persons. However, the knowledge about its underlying pathophysiology is limited. To address the need for a better understanding of AN, an animal model was established early on in the late 1960's: the activity-based anorexia (ABA) model in which rats have access to a running wheel combined with restricted food access leading to self-starving/body weight loss and hyperactivity. Both symptoms, separately or combined, can also be found in patients with AN. The aim of this systematic review was to compile the current knowledge about this animal model as well as to address gaps in knowledge. Using the data bases of PubMed, Embase and Web of science 102 publications were identified meeting the search criteria. Here, we show that the ABA model mimics core features of human AN and has been characterized with regards to brain alterations, hormonal changes as well as adaptations of the immune system. Moreover, pharmacological interventions in ABA animals and new developments, such as a chronic adaptation of the ABA model, will be highlighted. The chronic model might be well suited to display AN characteristics but should be further characterized. Lastly, limitations of the model will be discussed.

Assessing Activity-based Anorexia in Mice

Rodents develop activity-based anorexia (ABA) when exposed to a restricted feeding schedule and allowed free access to a running wheel. These conditions lead to a life-threatening reduction in body weight. However, rodents exposed to only one of these conditions ultimately adapt to re-establish normal body weight. Although increased running coupled with reduction in voluntary food intake appear paradoxical under ABA conditions, ABA behavior is observed across numerous mammalian species. The ABA paradigm provides an animal model for anorexia nervosa (AN), an eating disorder with severe dysregulation of appetite-behavior. Subjects are singly housed with free access to a running wheel. Each day, the subject is offered food for a limited amount of time. During the course of the experiment, a subject's body weight decreases from high activity and low caloric intake. The duration of the study varies based on how long food is offered daily, the type of food offered, the strain of mouse, if drugs are being tested, and environmental factors. A lack of effective pharmacological treatments for AN patients, their low quality of life, high cost of treatment, and their high mortality rate indicate the urgency to further research AN. We provide a basic outline for performing ABA experiments with mice, offering a method to investigate AN-like behavior in order to develop novel therapies. This protocol is optimized for use in Balb/cJ mice, but can easily be manipulated for other strains, providing great flexibility in working with different questions, especially related to genetic factors of ABA.

Spontaneous Physical Activity Defends Against Obesity

PURPOSE OF REVIEW

Spontaneous physical activity (SPA) is a physical activity not motivated by a rewarding goal, such as that associated with food-seeking or wheel-running behavior. SPA is often thought of as only "fidgeting," but that is a mischaracterization, since fidgety behavior can be linked to stereotypies in neurodegenerative disease and other movement disorders. Instead, SPA should be thought of as all physical activity behavior that emanates from an unconscious drive for movement.

RECENT FINDINGS

An example of this may be restless behavior, which can include fidgeting and gesticulating, frequent sit-to-stand movement, and more time spent standing and moving. All physical activity burns calories, and as such, SPA could be manipulated as a means to burn calories, and defend against weight gain and reduce excess adiposity. In this review, we discuss human and animal literature on the use of SPA in reducing weight gain, the neuromodulators that could be targeted to this end, and future directions in this field.

Continuous Aerobic Training in Individualized Intensity Avoids Spontaneous Physical Activity Decline and Improves MCT1 Expression in Oxidative Muscle of Swimming Rats

Although aerobic training has been shown to affect the lactate transport of skeletal muscle, there is no information concerning the effect of continuous aerobic training on spontaneous physical activity (SPA). Because every movement in daily life (i.e., SPA) is generated by skeletal muscle, we think that it is possible that an improvement of SPA could affect the physiological properties of muscle with regard to lactate transport. The aim of this study was to evaluate the effect of 12 weeks of continuous aerobic training in individualized intensity on SPA of rats and their gene expressions of monocarboxylate transporters (MCT) 1 and 4 in soleus (oxidative) and white gastrocnemius (glycolytic) muscles. We also analyzed the effect of continuous aerobic training on aerobic and anaerobic parameters using the lactate minimum test (LMT). Sixty-day-old rats were randomly divided into three groups: a baseline group in which rats were evaluated prior to initiation of the study; a control group (Co) in which rats were kept without any treatment during 12 weeks; and a chronic exercise group (Tr) in which rats swam for 40 min/day, 5 days/week at 80% of anaerobic threshold during 12 weeks. After the experimental period, SPA of rats was measured using a gravimetric method. Rats had their expression of MCTs determined by RT-PCR analysis. In essence, aerobic training is effective in maintaining SPA, but did not prevent the decline of aerobic capacity and anaerobic performance, leading us to propose that the decline of SPA is not fully attributed to a deterioration of physical properties. Changes in SPA were concomitant with changes in MCT1 expression in the soleus muscle of trained rats, suggestive of an additional adaptive response toward increased lactate clearance. This result is in line with our observation showing a better equilibrium on lactate production-remotion during the continuous exercise (LMT). We propose an approach to combat the decline of SPA of rats in their home cages. This new finding is worth for scientists who work with animal models to study the protective effects of exercise.

Sex-dependent effects of developmental exposure to bisphenol A and ethinyl estradiol on metabolic parameters and voluntary physical activity

Endocrine disrupting chemicals (EDC) have received considerable attention as potential obesogens. Past studies examining obesogenic potential of one widespread EDC, bisphenol A (BPA), have generally focused on metabolic and adipose tissue effects. However, physical inactivity has been proposed to be a leading cause of obesity. A paucity of studies has considered whether EDC, including BPA, affects this behavior. To test whether early exposure to BPA and ethinyl estradiol (EE, estrogen present in birth control pills) results in metabolic and such behavioral disruptions, California mice developmentally exposed to BPA and EE were tested as adults for energy expenditure (indirect calorimetry), body composition (echoMRI) and physical activity (measured by beam breaks and voluntary wheel running). Serum glucose and metabolic hormones were measured. No differences in body weight or food consumption were detected. BPA-exposed females exhibited greater variation in weight than females in control and EE groups. During the dark and light cycles, BPA females exhibited a higher average respiratory quotient than control females, indicative of metabolizing carbohydrates rather than fats. Various assessments of voluntary physical activity in the home cage confirmed that during the dark cycle, BPA and EE-exposed females were significantly less active in this setting than control females. Similar effects were not observed in BPA or EE-exposed males. No significant differences were detected in serum glucose, insulin, adiponectin and leptin concentrations. Results suggest that females developmentally exposed to BPA exhibit decreased motivation to engage in voluntary physical activity and altered metabolism of carbohydrates v. fats, which could have important health implications.