Activity of the Hypothalamic-Pituitary-Adrenal Axis is Elevated in Rats with Activity-Based Anorexia

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Abstract
Activity-based anorexia is characterized by suppressed food intake and excessive physical activity. These behaviors are typical of persons with anorexia nervosa. Activity of the hypothalamic-pituitary-adrenal axis is known to be elevated in anorexia nervosa. We investigated the status of this axis in activity-based anorexia. Meal fed-control (MFC) and meal fed-wheel running (MFWR) rats were given access to food for 90 min daily; MFWR animals were allowed access to an activity wheel the remainder of the day. The experiment terminated when MFWR animals reached 75% of pre-experimental body weight (males 3.9 ± 0.3 d; females 4.2 ± 0.2 d). Male and female MFWR rats consumed less food than MFC animals, while maintaining a high level of wheel running. Corticosterone concentrations were significantly elevated in MFWR animals. Corticotropin-releasing hormone mRNA concentrations in the paraventricular nucleus were not different. Relative adrenal gland weights were greater and thymus gland weights were lower in MFWR animals. Changes in food intake could not be explained by differences in insulin, glucose, β-hydroxybutyrate or norepinephrine concentrations. Our results suggest increased activity of the hypothalamic-pituitary-adrenal axis in activity-based anorexia.