Major depressive disorder: Causes

Current theories regarding the and causes of can be broadly classified into two categories, Physiological and Sociopsychological:

Physiological

The tendency to develop depression may be inherited: according to the National Institute of Mental Health[22] there is some evidence that depression may run in families. Most experts believe that both biological and play a role.
called neurotransmitters allow to move from the axon of one nerve cell to the soma of another. A shortage of neurotransmitters impairs brain communication.
called neurotransmitters allow to move from the axon of one nerve cell to the soma of another. A shortage of neurotransmitters impairs brain communication.

Neurological

Many modern change levels of certain neurotransmitters, namely serotonin and norepinephrine (). However, the relationship between serotonin, , and depression is typically greatly oversimplified when presented to the public, though this may be due to the lack of scientific knowledge regarding the mechanisms of action.[23] Evidence has shown the involvement of in depression, though the role is not exactly known.[24]

Recent research has suggested that there may be a link between depression and of the .[25] This horseshoe-shaped structure is a center for both mood and memory. Loss of neurons in the is found in depression and correlates with impaired memory and dysthymic mood. The most widely accepted explanation for this is that the drugs increase in the brain which in turn stimulate and therefore increase the total mass of the and would in theory restore mood and memory, therefore assisting in the fight against the .

Another theory regarding the is that it is characterized by an overactive hypothalamic-pituitary-adrenal axis (HPA axis) that resembles the neuro-endocrine response to stress. These HPA axis abnormalities participate in the development of depressive symptoms, and antidepressants serve to regulate HPA axis function.[26]

About one-third of individuals diagnosed with attention-deficit hyperactivity disorder (ADHD), may develop comorbid depression.[27] Dysthymia, a form of chronic, low-level depression, is particularly common in adults with undiagnosed ADHD who have encountered years of frustrating ADHD-related problems with education, employment, and interpersonal relationships.[28]

New evidence shows that individuals with exhibit markedly higher levels of monoamine oxidase A (MAO-A) in the brain compared to people without depression.[29] MAO-A is an enzyme which reacts with and decreases the concentration of monoamines such as serotonin, norepinephrine and dopamine.

Medical conditions

Certain illnesses, including cardiovascular disease,[30] hepatitis, mononucleosis, hypothyroidism, fructose malabsorption,[31] sleep apnea, and organic brain damage caused by degenerative conditions such as Parkinson disease, Multiple Sclerosis or by traumatic blunt force injury may contribute to depression, as may certain prescription drugs such as hormonal contraception methods and steroids. Depression also occurs in patients with chronic pain, such as chronic back pain, much more frequently than in the general population. Fibromyalgia sufferers also experience depression and anxiety.

Sociological

Low self-esteem and self-defeating or distorted thinking are connected with depression. However, it has been proposed that it is the result of depression and not necessarily the cause of it. This is still debated in the scientific community. Although it is not clear which is the cause and which is the effect, it is known that depressed persons who are able to make corrections in their thinking patterns can show improved mood and self-esteem (Cognitive Behavioral Therapy).[32] related to depression include the complex development of one’s personality and how one has learned to cope with external environmental factors, such as stress.[33]

Early experiences

Events such as the death of a parent, issues with biological development, school related problems, abandonment or rejection, neglect, chronic illness, and physical, psychological, or sexual abuse can also increase the likelihood of depression later in life. Post-traumatic stress disorder (PTSD) includes depression as one of its major locomotives symptoms.[34]

Life experiences

Stressful life experiences or circumstances may trigger a depressive episode, such as traumatic experiences such as rape, abortion, or grief over the death of a child, spouse, other family member or friends. A depressive episode may also be triggered by other major changes such as unemployment, divorce, or a loss of religious faith[35]. As well, a depressive episode may arise from ongoing issues, such as financial difficulties or poverty, ongoing major health problems (e.g., eating disorders), addictions (e.g., gambling addiction or drug addiction), sexual difficulties, or work-related stress.

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June 8, 2008 | Filed Under Mental Disorders 

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