Examples of this behavioral hierarchy appear in every vertebrate group ( Gilliam and Fraser, 1987 Abrahams and Sutterlin, 1999 Carrascal and Polo, 1999 Lilliendahl, 2000 Whitham and Mathis, 2000 Ziemba et al., 2000). In the acute phase of this response, behaviors that are necessary for dealing with an imminent threat (avoidance, escape) emerge whereas feeding behavior is temporarily suspended. Often overlooked in this approach is the fact that the neuronal and endocrine mechanisms involved in human eating disorders are evolutionarily ancient and have been conserved as part of a process for rapidly redirecting behavior in response to a threat.

To date, most research into this phenomenon has focused on the deleterious effects of stress on appetite in mammals, with an emphasis on understanding the physiological basis of stress-related eating disorders such as anorexia nervosa. Nonetheless, in every organism in which it has been studied, severe psychological or physical stress reduces appetite and food intake. The effects of stress on feeding are complex and depend upon a multitude of factors, not the least of which are the type, intensity, and duration of the stressor.

Most of us are reminded on a routine basis that stress affects appetite and food intake. By modulating visuomotor processing these neuropeptides may help animals make appropriate behavioral decisions during stress. Thus, changes in neuroendocrine status during stress may dramatically influence the efficacy with which visual stimuli release feeding behavior. The effects of these neuropeptides are rapid, occurring within 30 min after administration. Melanocortins also reduce prey-oriented turning movements and, in addition, facilitate the acquisition of habituation to a moving prey item. Stress rapidly reduces visually guided prey-catching behavior in toads, an effect that can be mimicked by administration of CRH, while corticosterone and isoproterenol are without effect. Although there is evidence that CRH and the melanocortins influence hypothalamic circuitry controlling food intake, these peptides may have a more primitive role in modulating visuomotor pathways involved in the recognition and acquisition of food. The effects of melanocortins on food intake have not been as extensively studied, but available evidence suggests that the anorexic role of neuronal melanocortins has been conserved. The effects of CRH on food intake are evolutionarily ancient, as this peptide inhibits feeding in fishes, birds, and mammals. Data from mammals suggest an important role for hypothalamic neuropeptides, in particular the melanocortins and corticotropin-releasing hormone (CRH)-like peptides, in mediating stress-induced inhibition of feeding. Stress inhibits feeding behavior in all vertebrates.

Endorphin lowry