Development Of Activity-based Anorexia Research Articles

Socialization, and its modulation by sex, on the development and recovery of activity-based anorexia in rats

The activity-based anorexia (ABA) animal model has been used in the laboratory to study the role of excessive physical activity in the manifestation of anorexia nervosa (AN) in humans. Factors of social context are crucial in human health and the emergence of many psychological disorders, which have also been observed in studies using different mammal species that, like human beings, set their lives in groups. In the present study, the animals’ social condition was manipulated to observe the effect of socialization in ABA development, and the possible different influence of the variable sex on the phenomenon. Eighty Wistar Han rats were distributed into four male and four female groups with 10 subjects each, manipulating social conditions (group housing or social isolation) and physical activity (access or not to a running wheel). Throughout the procedure, all groups had food restricted to 1 h/day during the light period. Furthermore, ABA experimental groups with access to the running wheel had two periods of access to the wheel of 2 h each, one before and the other after the food period. In this experiment, socialized rats were less vulnerable to weight loss during the procedure, although there were no differences between the ABA groups. Moreover, social enrichment was shown to be an enabling variable of the animals’ recovery after their withdrawal from the procedure, with this effect being more pronounced in females. The results in this study suggest the need to further in the analysis of the role of socialization in the development of ABA.

In pursuit of biomarkers for predicting susceptibility to activity-based anorexia in adolescent female rats.

ObjectiveIdentifying risk factors that contribute to the development of anorexia nervosa (AN) is critical for the implementation of early intervention strategies. Anxiety, obsessive–compulsive behavior, and immune dysfunction may be involved in the development of AN; however, their direct influence on susceptibility to the condition remains unclear. Here, we used the activity‐based anorexia (ABA) model to examine whether activity, anxiety‐like behavior, compulsive behavior, and circulating immune markers predict the subsequent development of pathological weight loss.MethodFemale Sprague–Dawley rats (n = 44) underwent behavioral testing before exposure to ABA conditions after which they were separated into susceptible and resistant subpopulations. Blood was sampled before behavioral testing and after recovery from ABA to screen for proinflammatory cytokines.ResultsRats that were vulnerable to pathological weight loss differed significantly from resistant rats on all key ABA parameters. While the primary measures of anxiety‐like or compulsive behavior were not shown to predict vulnerability to ABA, increased locomotion and anxiety‐like behavior were both associated with the extent of weight loss in susceptible but not resistant animals. Moreover, the change in expression of proinflammatory markers IL‐4 and IL‐6 evoked by ABA was associated with discrete vulnerability factors. Intriguingly, behavior related to risk assessment was shown to predict vulnerability to ABA.DiscussionWe did not find undisputable behavioral or immune predictors of susceptibility to pathological weight loss in the ABA rat model. Future research should examine the role of cognition in the development of ABA, dysfunction of which may represent an endophenotype linking anorectic, anxiety‐like and compulsive behavior.Public SignificanceAnorexia nervosa (AN) has among the highest mortality rates of all psychiatric disorders and treatment options remain limited in their efficacy. Understanding what types of risk factors contribute to the development of AN is essential for implementing early intervention strategies. This study describes how some of the most common psychological features of AN could be used to predict susceptibility to pathological weight loss in a well‐established animal model.

β-endorphin differentially contributes to food anticipatory activity in male and female mice undergoing activity-based anorexia.

Anorexia nervosa (AN) has a lifetime prevalence of up to 4% and a high mortality rate (~5–10%), yet little is known regarding the etiology of this disease. In an attempt to fill the gaps in knowledge, activity‐based anorexia (ABA) in rodents has been a widely used model as it mimics several key features of AN including severely restricted food intake and excessive exercise. Using this model, a role for the hypothalamic proopiomelanocortin (POMC) system has been implicated in the development of ABA as Pomc mRNA is elevated in female rats undergoing the ABA paradigm. Since the Pomc gene product α‐MSH potently inhibits food intake, it could be that elevated α‐MSH might promote ABA. However, the α‐MSH receptor antagonist SHU9119 does not protect against the development of ABA. Interestingly, it has also been shown that female mice lacking the mu opioid receptor (MOR), the primary receptor activated by the Pomc‐gene‐derived opioid β‐endorphin, display blunted food anticipatory behavior (FAA), a key feature of ABA. Thus, we hypothesized that the elevation in Pomc mRNA observed during ABA may lead to increased β‐endorphin concentrations and MOR activation to promote ABA. Further, given the known sex differences in AN and ABA, we hypothesized that MORs may contribute differentially in male and female mice. Using wild‐type and MOR knockout mice of both sexes, a MOR antagonist and careful analysis of food anticipatory behavior and β‐endorphin levels, we found 1) increased Pomc mRNA levels in both female and male mice that underwent ABA, 2) increased β‐endorphin in female mice that underwent ABA, and 3) blunted FAA in both sexes in response to MOR genetic deletion yet blunted FAA only in males in response to MOR antagonism. The results presented provide support for both hypotheses and suggest that it may be the β‐endorphin resulting from increased Pomc transcription that supports the development of some features of ABA.

Activity-based anorexia activates CRF immunoreactive neurons in female rats

Activity-based anorexia (ABA) is a well-established animal model mimicking the eating disorder anorexia nervosa (AN). Since the pathophysiology of AN is yet poorly understood and specific drug treatments are lacking so far, animal models might be useful to further understand this disease. ABA consists of time-restricted access to food for 1.5 h/day and the possibility to exercise in a running wheel for 24 h/day. This combination leads to robust body weight loss as observed in AN. Here, we investigated the activation of brain corticotropin-releasing factor (CRF) neurons, a transmitter involved in the response to stress, emotional processes and also food intake. After development of ABA, rat brains were processed for c-Fos and CRF double immunohistochemistry. ABA increased the number of c-Fos/CRF double labeled neurons in the paraventricular nucleus (PVN) and the dorsomedial hypothalamic nucleus (DMH) compared to the ad libitum (AL, ad libitum fed, no running wheel) and activity (AC, ad libitum fed, running wheel, p < 0.05) but not to the restricted feeding (RF, food for 1.5 h/day, no running wheel, p > 0.05) group. Also the number of CRF neurons was increased in the DMH of ABA rats compared to AL and AC (p < 0.05). In the Edinger-Westphal nucleus (EW) the number of c-Fos positive neurons was increased in ABA and RF compared to AC (p < 0.05), while the number of double labeled neurons was not different (p > 0.05). Taken together, brain CRF activated under conditions of ABA might play a role in the development and maintenance of this animal model and possibly also in human AN.

Activity-based anorexia activates nesfatin-1 immunoreactive neurons in distinct brain nuclei of female rats

Activity-based anorexia (ABA) is an established animal model for the eating disorder anorexia nervosa (AN). The pathophysiology of AN and the involvement of food intake-regulatory peptides is still poorly understood. Nesfatin-1, an anorexigenic peptide also involved in the mediation of stress, anxiety and depression might be a likely candidate involved in the pathogenesis of AN. Therefore, activation of nesfatin-1 immunoreactive (ir) brain nuclei was investigated under conditions of ABA. Female Sprague-Dawley rats were used and divided into four groups (n=6/group): activity-based anorexia (ABA), restricted feeding (RF), activity (AC) and ad libitum fed (AL). After the 21-day experimental period and development of ABA, brains were processed for c-Fos/nesfatin-1 double labeling immunohistochemistry. ABA increased the number of nesfatin-1 immunopositive neurons in the paraventricular nucleus, arcuate nucleus, dorsomedial hypothalamic nucleus, locus coeruleus and in the rostral part of the nucleus of the solitary tract compared to AL and AC groups (p<0.05) but not to RF rats (p>0.05). Moreover, we observed significantly more c-Fos and nesfatin-1 ir double-labeled cells in ABA rats compared to RF, AL and AC in the supraoptic nucleus (p<0.05) and compared to AL and AC in the paraventricular nucleus, arcuate nucleus, dorsomedial hypothalamic nucleus, dorsal raphe nucleus and the rostral raphe pallidus (p<0.05). Since nesfatin-1 plays a role in the inhibition of food intake and the response to stress, we hypothesize that the observed changes of brain nesfatin-1 might play a role in the pathophysiology and symptomatology under conditions of ABA and potentially also in patients with AN.

Exploring Body Weight, Voluntary Activity, and Intrinsic Value in Rats

Modeling activity-based anorexia, food-deprived rats consistently show that activity increases as weight decreases. This effect was explored in 8 food-deprived, Sprague-Dawley rats as potentially mediated by intrinsic value of activity. Running-wheel activity rates were recorded for free-fed weight, reduction to 90% of free-fed weight, and to 80% of free-fed weight. As expected, activity increased as weight decreased. Further, significant differences appeared in the trends of individual run rates when compared across all trials. These individual trends were expressed as varied rates of running, with extreme high and low run rates prevalent. The rewarding nature of exercise itself might serve to predict these trends in individual rats and reveal potential indicators for the development of activity-based anorexia.

The Cannabinoid Receptor Agonist THC Attenuates Weight Loss in a Rodent Model of Activity-Based Anorexia

Anorexia nervosa (AN) is characterized by anhedonia whereby patients experience little pleasure or reward in many aspects of their lives. Reward pathways and the endocannabionid system have been implicated in the mediation of food intake. The potential to exploit these systems to reverse weight loss is investigated in a rodent model of activity-based anorexia (ABA). The effect of subchronic (6 days) Δ(9)-tetrahydrocannabinol (THC) treatment (0.1, 0.5, or 2.0 mg/kg/day) was assessed on chow and high-fat diet (HFD) intake, body weight, running wheel activity (RWA) as well as thermogenesis in brown adipose tissue (BAT) and lipid metabolism in white adipose tissue (WAT). Limited time availability of food and continuous access to running wheels led to anorexia and significantly reduced body weight. THC treatment (0.5 and 2.0 mg/kg/day) transiently stimulated chow intake with a moderate effect on RWA. THC (2.0 mg/kg/day) significantly reduced body weight loss and shifted markers of thermogenesis in BAT and lipid metabolism in WAT in directions consistent with reduced energy expenditure and lipolysis. THC (2.0 mg/kg/day) combined with HFD, produced a transient increase in food intake, reduction in RWA, attenuation of body weight loss, and changes in markers of thermogensis in BAT and lipolysis in the WAT. These changes were significantly greater than those seen in vehicle (HFD), vehicle (chow), and THC (chow)-treated animals. These data show for the first time the effectiveness of the endocannabinoid system in attenuating the weight loss associated with the development of ABA via a mechanism involving reduced energy expenditure.

The effects of food presentation at regular or irregular times on the development of activity-based anorexia in rats

Activity-based anorexia occurs when food availability is restricted to 1h of the day and a wheel is freely available to the rest of the time. Under such conditions rats run excessively and stop eating even during periods in which food is available. A defining characteristic of the excessive activity is that there is a peak of running in the anticipation of food availability. The present study was designed to test whether the occurrence of the food period at different times of the light phase of the light-dark cycle (from 08:00 to 20:00h) could impede or postpone the normal development of activity anorexia. We compared the effect of presenting the food at a fixed time of the light period with presenting it on a variable schedule. Far from impeding or postponing the development of activity-based anorexia, presenting food at irregular times resulted in a pronounced body-weight loss, a low food intake and an increase in locomotor activity. Animals ran excessively, with a peak at the start of the dark period, and again when lights were turned on in the experimental room (running in the anticipation of food). Both fixed and variable schedules of food availability resulted in the development of activity-based anorexia in rats.

Activity‐based anorexia during adolescence does not promote binge eating during adulthood in female rats

Given the frequency of transition from anorexia nervosa to bulimia nervosa, this study investigated whether a history of activity-based anorexia (ABA) during adolescence would promote binge eating during adulthood in female rats. Adolescent rats were given 1-h unlimited access to chow and ad libitum access to a running wheel until body weight reached <80%, indicating the development of ABA. During adulthood, all groups were given 21 days of access to a palatable food for 2 h/day and ad libitum access to chow. During adolescence, rats in the ABA paradigm developed increased wheel running and decreased food intake, reaching <80% of body weight after 3 days. However, there were no significant differences between groups in the amount of binge food consumed during adulthood. A brief episode of ABA during adolescence did not lead to increased binge eating later in life. Longer-term models are needed to determine whether a propensity toward binge eating may result from more sustained ABA during adolescence.

Neurobiological parameters and anorexia nervosa: Findings from animal studies

Although anorexia nervosa (AN) was already described in the 19th century, its etiology remains unclear. Animal models may help to advance our knowledge on AN. The rat activity-based anorexia (ABA) model, which consists of scheduled feeding along with running wheel access (RWA), mimics the starvation and physical hyperactivity of AN patients. Following introduction of a feeding schedule (1–2 h/d), rats further reduce food intake, become hyperactive, and lose body weight. The aim of this translational work was to identify neurobiological parameters associated with the development of ABA. Circulating metabolic fuels and hormones, hypothalamic gene expression, and behavioural responses to icv leptin infusion were investigated in ABA rats and appropriate controls. Rats showed marked, but expected, changes in circulating metabolic fuels (e.g. glucose, β-hydroxybutyrate) and hormones (e.g. leptin, insulin) during development of ABA. Hypothalamic POMC and CART mRNA levels were decreased in ABA rats, whereas AgRP and NPY mRNA levels were increased. Expression of second-order neuropeptides, e.g. CRH, prepro-orexin, was not changed. Chronic icv infusion of leptin, acting upstream of POMC/CART and NPY/AgRP neurons, decreased food intake as well as RWA in ABA rats, discordant to earlier results of melanocortin (ant)agonist infusions. These results warrant further research on the role of the (extra)hypothalamic leptin pathway in the development of ABA. Meanwhile the relevance of these preclinical data is investigated in clinical studies by studying the relation between plasma leptin levels and physical activity in AN patients.

AgRP (83–132) and SHU9119 differently affect activity-based anorexia

Activity-based anorexia (ABA) mimics starvation and hyperactivity of anorexia nervosa patients in rats. Activation of the melanocortin (MC) system leads to hypophagia and increased energy expenditure in ad libitum fed rats. Therefore, activation of the MC system might underlie the development and propagation of ABA. Pro-opiomelanocortin (POMC) gene expression is normally decreased during negative energy balance. Strikingly, we found a transient up-regulation of POMC mRNA levels in the arcuate nucleus during the development of ABA, indicating a hyperactive MC system. However, wheel running and food intake were not influenced by treating ABA rats with the competitive antagonist SHU9119. This suggests that agonism of MC receptors by endogenous α-melanocyte-stimulating hormone (α-MSH) levels does not underlie ABA. Instead, treatment with the inverse agonist AgRP (83–132) did ameliorate signs of ABA. This implies that modulation of constitutive MC receptor activity rather than antagonizing putative α-MSH release contributes to the development and propagation of ABA.

Hypothalamic neuropeptide expression following chronic food restriction in sedentary and wheel-running rats

When rats are given access to a running-wheel in combination with food restriction, they will become hyperactive and decrease their food intake, a paradoxical phenomenon known as activity-based anorexia (ABA). Little is known about the regulation of the hypothalamic neuropeptides that are involved in the regulation of food intake and energy balance during the development of ABA. Therefore, rats were killed during the development of ABA, before they entered a state of severe starvation. Neuropeptide mRNA expression levels were analysed using quantitative real-time PCR on punches of separate hypothalamic nuclei. As is expected in a state of negative energy balance, expression levels of agouti-related protein (AgRP) and neuropeptide Y (NPY) were increased 5-fold in the arcuate nucleus (ARC) of food-restricted running ABA rats vs 2-fold in sedentary food-restricted controls. The co-regulated expression of AgRP and NPY strongly correlated with relative body weight and white adipose tissue mass. Arcuate expression of pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) was reduced 2-fold in the ABA group. In second-order neurons of the lateral hypothalamic area (LHA), melanin-concentrating hormone (MCH) mRNA expression was upregulated 2-fold in food-restricted running rats, but not in food-restricted sedentary controls. Prepro-orexin, CART and corticotropin-releasing hormone expression levels in the LHA and the paraventricular nucleus (PVN) were unchanged in both food-restricted groups. From this study it was concluded that during the development of ABA, neuropeptides in first-order neurons in the ARC and MCH in the LHA are regulated in an adequate response to negative energy balance, whereas expression levels of the other studied neuropeptides in secondary neurons of the LHA and PVN are unchanged and are probably regulated by factors other than energy status alone.

Animal Behavior and Internal Drives

Animal Behavior and Internal Drives