The Biology of Depression: Brain Changes and Depression Symptoms
Depression is a complex medical condition associated with physical and emotional symptoms. People with depression usually suffer from changes in mood and loss of interest in daily activities. In addition, they may also experience fatigue or changes in sleep patterns.
Depression is caused and influenced by a variety of factors. Though traumatic events or difficult life conditions can contribute to depression, biochemical brain changes also affect depression symptoms. Understanding the biology of depression can help you make informed decisions about depression treatment.
Function of Neurotransmitters in Depression
Neurotransmitters are chemicals that convey messages between neurons. One neuron releases a certain type of neurotransmitter, which travels across a small space known as the synaptic gap to receptors in another neuron. When the neurotransmitter binds to the receptor, it causes a chemical reaction in the neuron, ultimately resulting in changes in emotions, behavior and other bodily functions.
Types of neurotransmitters include the following:
- Dopamine helps regulate mood
- Norepinephrine regulates emotions, sleep and learning
- Serotonin affects mood, sleep, appetite and pain.
Changes in neurotransmitter concentrations in depression can lead to changes in the body functions controlled by these chemicals. The connection between depression and chemicals in the brain is not fully understood. However, because an imbalance of neurotransmitters is thought to contribute to depression symptoms, antidepressants that alter neurotransmitter function are a common course of treatment.
Depression, Brain Changes and Antidepressants
Antidepressants work to change the amount of specific neurotransmitters in the brain. The goal is to prolong the activity of neurotransmitters by preventing their reuptake or breakdown. Though all antidepressants ultimately affect neurotransmitter activity, they do this in a variety of ways. Reuptake inhibitors limit the reabsorption of neurotransmitters into the brain, boosting mood and relieving depression symptoms. Types of reuptake inhibitors are the following:
- Norepinephrine and dopamine reuptake inhibitors (NDRIs) reduce both dopamine and norepinephrine reuptake into brain cells.
- Selective serotonin reuptake inhibitors (SSRIs) inhibit reuptake of serotonin.
- Serotonin and norepinephrine reuptake inhibitors (SNRIs) reduce norepinephrine and serotonin reuptake.
- Tricyclics inhibit reuptake of serotonin, norepinephrine, and, to a lesser extent, dopamine.
Another type of antidepressant is a monoamine oxidase inhibitor (MAOI). These antidepressants prevent the enzyme monoamine oxidase from breaking down neurotransmitters before they bind to receptors.
The Hypothalamus, Depression and Chemicals
The hypothalamus is a brain structure that is part of the limbic system that regulates emotions, mood and memory. The hypothalamus regulates stress responses and sleep. It is also part of a system known as the hypothalamic-pituitary-adrenal (HPA) axis, a component of the endocrine system.
The endocrine system regulates hormone secretion in the body. Individuals with depression are more likely to have HPA axis dysfunction; overactivity of this system in depression causes the hypothalamus to increase production of corticotrophin-releasing factor (CRF). This increases hormone secretion, sometimes causing changes in:
- Appetite
- Mood
- Sleep.
Resources
Barden, N. (2004). Implication of the hypothalamic-pituitary-adrenal axis in the pathophysiology of depression. Journal of Psychiatry and Neuroscience, 29(3): 185-193.
Mayo Clinic Staff. (n.d.). Monoamine oxidase inhibitors (MAOIs). Retrieved May 10, 2010, from Mayo Clinic website: www.mayoclinic.com/health/maois/mh00072.
Mayo Clinic Staff. (n.d.). Tricyclic antidepressants (TCAs). Retrieved May 10, 2010, from Mayo Clinic website: www.mayoclinic.com/health/antidepressants/mh00071.
McGill University Staff. (n.d.). The brain from top to bottom: Synapses. Retrieved May 10, 2010, from McGill University website: thebrain.mcgill.ca/flash/i/i_01/i_01_m/i_01_m_ana/i_01_m_ana.html.
U.S. News and World Report Staff. (n.d.). Depression channel. Retrieved May 10, 2010, from U.S. News and World Report website: usnews.healthline.com/usnewschannel/depression.
Chudler, E. (n.d.). Neurotransmitters and neuroactive peptides. Retrieved May 10, 2010, from University of Washington website: faculty.washington.edu/chudler/chnt1.html.