Study of the Hypothalmic-Pituitary-Adrenal (HPA) Axis and Its Role in Major Depression

Major depression represents a major public health problem worldwide and in the U.S. Fifteen percent of the U.S. population has depression at some point in life (40 million individuals). The condition is more common in women, occurring at a female to male ratio of 5:2. Presently, 6-8% of all outpatients in primary care meet the diagnostic criteria for major depression. Fifteen percent of untreated patients with depression will commit suicide. Most of the people committing suicide are depressed. Researchers believe that by the year 2020 suicide will be the 10th most common cause of death in the U.S. In addition to mortality due to suicide, depression is also associated with other severe health conditions. Areas of the brain (hippocampus) begin to deteriorate, heart disease, and decreased bone mineral density (osteoporosis) are all associated with major depression. Researchers have believed for years that hormones controlled by the hypothalmus, pituitary gland, and adrenal gland (commonly referred to as the HPA axis or system) are in some way associated with psychiatric illnesses like depression. According to previous studies, researchers have theorized that increased activity of the HPA axis is associated with depressed patients with typical melancholic features. Melancholia refers to the feelings of anhedonia (absence of pleasure from activites that would normally be thought of as pleasurable), insomnia (inability to sleep), guilt, and psychomotor changes. On the other hand a decrease in activity of the HPA axis may be associated with the atypical features of depression. This study has already developed and refined studies that have improved the understanding of the HPA axis in healthy humans and depressed patients. Researchers have already identified and plan to continue identifying distinct subtypes of depressive disorders based on the activity of the HPA axis.