The 1990s have witnessed a remarkable upsurge in research on neurochemical pathways in the central nervous system (CNS) that contribute to the regulation of food intake and body weight homeostasis. These investigations have been driven in part by increasing recognition that obesity, anorexia nervosa and bulimia nervosa represent major public health concerns. Moreover, advances in molecular neurobiology have accelerated the identification of new peptides, proteins and their receptors in the hypothalamus and other brain regions critical to the regulation of ingestive behaviour. This chapter begins with a clinical overview of anorexia nervosa and bulimia nervosa, including brief summaries of diagnostic criteria and therapeutic considerations. Subsequent sections highlight promising areas of research on the clinical neurobiology of these disorders. Findings to date suggest that alterations in regulatory systems involving serotonin, cholecystokinin (CCK) and leptin may contribute to the initial onset or perpetuation of eating disorder symptoms.
Symptom patterns and diagnostic criteria
Descriptions of anorexia nervosa as a disorder of unexplained weight loss first appeared in the medical literature more than a century ago. The central psychological symptom of the disorder is ‘refusal to maintain body weight at or above a minimally normal weight for age and height’ (Table 54.1) (American Psychiatric Association, 2000). Patients demonstrate a persistent preoccupation with body shape and weight, with an underlying pervasive fear of becoming fat. Clinical observations and laboratory studies have shown that patients with anorexia nervosa do not suffer from loss of appetite, however (Sunday & Halmi, 1996). The characteristic amenorrhea appearing in postmenarcheal women is generally thought to be a consequence of malnutrition, although in some cases the loss of menstrual cycles can precede the onset of significant weight loss.
In most survey data, the prevalence of anorexia nervosa is approximately 0.5% among adolescent girls and young women. The typical age of onset is 18 years, and the prevalence in boys and young men is estimated to be 10% of that in females (Lucas et al., 1991; Whitaker et al., 1990). Episodes of recurrent dieting typically precede the onset of an eating disorder, and psychological and cultural factors contributing to increased preoccupation with body weight and appearance are thought to play a role in the etiology of anorexia nervosa. Behavioural risk factors include perfectionism and negative self-esteem (Fairburn et al., 1999).