Eating behavior in anorexia nervosa--an excess of both orexigenic and anorexigenic signalling?

Anorexia nervosa (AN) is a disorder characterized by abnormal eating behavior, weight regulation, and disturbances in attitudes and perceptions toward body weight and shape. Although progress has been made in the treatment of AN, a substantial portion of patients have a limited response to treatment. Multiple endocrine and metabolic changes occur after prolonged starvation, conserving energy and protein. A number of the endocrine findings in patients with AN may be secondary to adaptive mechanisms. However, AN differs from simple starvation in that excess of both feeding-stimulatory (orexigenic) and feeding-inhibitory (anorexigenic) signalling is characteristic, producing the "mixed" signal about satiety and desire to feed. This leads to a failure of the adaptive feeding response that is initiated by a decrease in leptin, an adiposity signal from fat tissue, and the resultant increase and decrease of orexigenic and anorexigenic signalling, respectively. The hypothesis of unbalanced shift of feeding-regulatory circuitry places anorexigenic corticotropin-releasing factor and orexigenic neuropeptide Y in the final common neurobiological substrate for AN. Therapeutic intervention using such receptor antagonists may lead to more successful and targeted psychopharmacological treatment.