Activity in the circular alley does not produce the activity anorexia syndrome in rats

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.

Conditioned taste avoidance induced by forced and voluntary wheel running in rats

Voluntary exercise by rats running in a freely rotating wheel (free wheel) produces conditioned taste avoidance (CTA) of a flavored solution consumed before running [e.g., Lett, B.T., Grant, V.L., 1996. Wheel running induces conditioned taste aversion in rats trained while hungry and thirsty. Physiol. Behav. 59, 699-702]. Forced exercise, swimming or running, also produces CTA in rats [e.g., Masaki, T., Nakajima, S., 2006. Taste aversion induced by forced swimming, voluntary running, forced running, and lithium chloride injection treatments. Physiol. Behav. 88, 411-416]. Energy expenditure may be the critical factor in producing such CTA. If so, forced running in a motorized running wheel should produce CTA equivalent to that produced by a similar amount of voluntary running. In two experiments, we compared forced running in a motorized wheel with voluntary running in a free wheel. Mean distance run over 30 min was equated as closely as possible in the two apparatuses. Both types of exercise produced CTA relative to sedentary, locked-wheel controls. However, voluntary running produced greater CTA than forced running. We consider differences between running in the free and motorized wheels that may account for the differences in strength of CTA.

Behavioral assessment of intermittent wheel running and individual housing in mice in the laboratory

Physical cage enrichment--exercise devices for rodents in the laboratory--often includes running wheels. This study compared responses of mice in enriched physical and social conditions and in standard social conditions to wheel running, individual housing, and open-field test. The study divided into 6 groups, 48 female BALB/c mice group housed in enriched and standard conditions. On alternate days, the study exposed 2 groups to individual running wheel cages. It intermittently separated from their cage mates and housed individually 2 groups with no running wheels; 2 control groups remained in enriched or standard condition cages. There were no significant differences between enriched and standard group housed mice in alternate days' wheel running. Over time, enriched, group housed mice ran less. Both groups responded similarly to individual housing. In open-field test, mice exposed to individual housing without running wheel moved more and faster than wheel running and home cage control mice. They have lower body weights than group housed and wheel running mice. Intermittent withdrawal of individual housing affects the animals more than other commodities. Wheel running normalizes some effects of intermittent separation from the enriched, social home cage.

Relationship between wheel running, feeding, drinking, and body weight in male rats

The amount of wheel running varies widely between rats. Wheel introduction and running also have profound effects on the animal's energy balance. We explored the effects of ad lib wheel access and running levels on feeding, drinking, and body weight in 30 young adult male rats with wheel access and in 30 rats without wheel access. The initial running period (Days 1-8) and a time of stable running [Days 29-32 (DEnd)] were analyzed using both between- and within-group approaches. Initially, wheel access suppressed feeding (by about 25% over the 8 days) but not drinking. There were no significant correlations between the amount of wheel running and the other behaviors. The degree of feeding suppression was also not correlated to the amount of running. When running had stabilized (animal ran from 841 to 13,124 wheel turns per day), food intake was increased by about 0.75 g per 1000 wheel turns. Running at this time correlated positively with feeding and drinking and negatively with body weight and weight gain. In animals without wheel access, feeding and drinking were positively correlated with weight and weight gain, but in animals with wheel access, these correlations were close to zero. Only early running predicted later levels of running but accounted for only 23% of the variance in running. Wheel access has profound but very different immediate and long-term effects on the rats' energy balance.

Wheel access duration in rats: I. Effects on feeding and running

The effects of 0-, 2-, and 24-hr wheel access on the pattern of running, feeding, and weight were explored over 24 days in 3 groups of 8 male rats. Both 2 and 24 hr of wheel access suppressed feeding by about 15% for about 8 days before feeding gradually returned to normal. Weight in these 2 groups was similar and was suppressed for the 24 days. Like the pattern seen with drug self-administration (S. H. Ahmed & G. F. Koob, 1998, 1999), running levels stayed low with short, 2-hr daytime wheel access, but with long, 24-hr access, rats' running escalated over days to chronically high levels. These results may have relevance for the understanding of addiction and anorexia nervosa.

Activity-based anorexia: ambient temperature has been a neglected factor

Activity-based anorexia refers to the self-starvation of rats exposed to experimental conditions that combine restricted access to food with access to an activity wheel. This paper compares previous studies of this phenomenon in relation to the ambient temperatures (AT) that were employed. On this basis, and from some more direct evidence, we argue that AT is an important, but neglected, factor in activity-based anorexia research. More attention to AT is needed in future research, since its neglect threatens the validity of conclusions drawn from those studies. Furthermore, direct examination of the effect of AT on activity-based anorexia will allow a better understanding of the mechanisms underlying this phenomenon and the possible clinical implications for the treatment of human anorexia nervosa.