The HPA Axis

• The term "hypothalamic-pituitary-adrenal axis," or HPA axis, refers to the interactions between the pituitary gland, the adrenal gland and the hypothalamus. These are important limbic system organs that regulate the chemical balance inside the brain and the body.
  
  

What is Cortisol?

• Cortisol is a hormone produced by the adrenal gland. It is secreted at high levels when the body enters "fight or flight" mode. Cortisol therefore is known as a "stress hormone."
  
  

The Effects of Cortisol

• Low levels of cortisol are normal. However, too much cortisol interferes with normal HPA axis processes and damages the brain.
  
  

Cortisol and Depression

• The exact relationship between depression and cortisol is the topic of much current study. However, it is known that patients with major depression often have high levels of cortisol.
  
  

Cause and Effect

• Research in Behavioral Neuroscience showed that mice injected with cortisol developed symptoms of depression. The British Journal of Psychiatry suggests that high levels of cortisol may decrease the function of serotonin and thereby lead to depression. However, more research into the relationship still is required.