Biological research concerning the development of mood disorders suggests that

Biological research concerning the development of mood disorders suggest that genetics and brain chemistry have a big impact on mood disorders. This is due to findings showing that serotonin may be key neurotransmitter in depression and that motor tension also has an impact on anxiety

Biological research concerning the development of mood disorders suggests that depressed people have high levels of cortisol, which can affect the hippocampus and amygdala.

Explanation:

Cortisol is a hormone that is produced in the adrenal gland and serves to increase the level of blood sugar. People with depression tend to have reduced levels of serotonin in the brain and elevated levels of cortisol in the bloodstream( cortisol is related to stress).

The limbic system is a complex set of structures that are located on both sides of the thalamus, just below the brain. It includes the hypothalamus, hippocampus, amygdala and other nearby areas. And he is primarily responsible for our emotional life.