Chronic depression (also called “clinical depression” or “severe depression”) is a complex condition affected by a combination of biological changes in brain function, genetic predispositions and environmental factors. Chronic depression and biology are connected on the level of neurotransmitters in the brain.
Neurotransmitter Function in Chronic Depression
The biology of your brain affects mood, and, therefore, depression. Researchers have found that chronic depression is influenced by changes in the function and levels of neurotransmitters in the brain.
Neurotransmitters are brain chemicals that affect mood and behavior. They travel from one neuron across a space called the “synaptic cleft,” and bind to a receptor, facilitating message transmission in the brain. Neurotransmitters that influence the appearance of depression symptoms include:
- Dopamine: Mood, including desire to seek pleasure
- Norepinephrine: Sleep and emotion
- Serotonin: Sleep, appetite and mood.
When these neurotransmitters donÃ•t bind to receptors properly, they can cause disturbances in the physical and mental processes they control. For example, decreased norepinephrine levels can cause depressive episodes. Neurotransmitters can also affect one another; for example, reduced serotonin levels can cause a drop in norepinephrine.
Use of Antidepressants for Chronic Depression
Several treatments are available for chronic depression, many of which alter the biological processes that cause symptoms. Antidepressant drugs help to normalize neurotransmitter function. They work by increasing the concentration of neurotransmitters in the synaptic cleft, helping them bind to receptors. Improvement of neurotransmitter function improves depression symptoms, including disturbances of mood, sleep and appetite. Types of antidepressants include:
- Monoamine oxidase inhibitors (MAOIs)
- Norepinephrine and dopamine reuptake inhibitors (NDRIs)
- Selective-serotonin reuptake inhibitors (SSRIs)
- Serotonin and norepinephrine reuptake inhibitors (SNRIs)
- Tricyclic antidepressants (TCAs).
Chronic depression is often more severe than episodic depression, and can be harder to treat. This is particularly true of “double depression,” a condition in which a person with underlying mild depression (dysthymia) also experiences intermittent episodes of major depression. However, antidepressants are often effective treatments for chronic depression. Some research suggests that adding psychotherapy to the treatment regimen can be effective as well. Efficacy varies on a case-by-case basis, depending on symptom severity.
The Hypothalamic-Pituitary-Adrenal (HPA) Axis
Researchers have found that the hypothalamic-pituitary-adrenal (HPA) axis, a group of brain structures involved in the endocrine system, may be involved in some types of depression. A hyperactive HPA system results in increased secretion of cortisol, a hormone involved in the stress response. The HPA axis helps modulate the bodyÃ•s physiological stress response. Abnormal HPA axis function has been found in some patients with depression. However, its role in chronic depression remains poorly understood, and further research is needed to determine the role it plays in long-term depression symptoms.
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