How Antidepressants Work in the Brain

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  • 0:01 Depression
  • 0:50 How the Brain Works
  • 1:58 How Antidepressants Work
  • 3:50 SSRIs & SNRIs
  • 5:15 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Depression leads to feelings of sadness. It's thought that the mood disorder is influenced by lower than normal concentrations of certain neurotransmitters within the brain. Learn how antidepressants increase these feel-good neurotransmitters.

Depression

Depression is a disorder characterized by feelings of hopelessness, sadness and a lack of interest in life. Despite the fact that this mood disorder is common in places like the United States, the definitive cause is not well understood.

This lack of understanding may stem from the fact that depression can have multiple contributing factors, including a genetic propensity toward the disorder, hormonal imbalance and emotional upset. Regardless of the factors that lead a person to feel depressed, the medical community agrees that an underlying alteration in the brain's chemistry plays a role. In this lesson, we will explore how the brain is affected by depression and how antidepressants work to prevent and treat depression.

How the Brain Works

From the outside, the human brain looks like an unimpressive mass of bumpy tissue. However, inside, there's a lot of chemical activity happening among countless nerve cells, or neurons. The balance of chemicals being exchanged between these neurons directs your thoughts, affects your mood and influences your emotions. Specific chemicals, known as neurotransmitters, act as chemical messengers that allow neurons to communicate with each other.

When one nerve wants to send a message to another nerve, the first nerve releases neurotransmitters into a gap that separates the two nerves. Some of these neurotransmitters get transferred to the second nerve, and any remaining neurotransmitters get reabsorbed back into the first nerve. Certain neurotransmitters, such as serotonin, norepinephrine and dopamine, have the ability to affect your mood, emotions and overall feeling of well-being. These chemicals are naturally produced in the brain but may be available in lower quantities in a person with depression. It's these neurotransmitters that are affected by antidepressants.

How Antidepressants Work

Generally, antidepressants work by increasing the concentration of certain neurotransmitters within the brain, which, in turn, improves mood. While there are different types of antidepressants, each one works to manipulate one or more of the brain's neurotransmitters.

For example, tricyclic antidepressants, or TCAs, are a type of antidepressant that work by increasing the concentration of norepinephrine and serotonin. The drug is able to do this because it blocks the reabsorption of the neurotransmitters back into the first communicating neuron. It's as if the TCAs lock the door behind the neurotransmitters once they leave the first neuron.

Since the neurotransmitters cannot go back to the first neuron, they stay in the gap between the nerve cells, therefore increasing the concentration within the gap. The higher concentration of neurotransmitters in the space is thought to push more of the chemical messengers toward the second neuron, which strengthens the communication.

TCAs, along with monoamine oxidase inhibitor antidepressants, or MAOIs, are older families, or types, of antidepressants. MAOIs do not block reabsorption; instead they inhibit the breakdown of the neurotransmitters by stopping the action of an enzyme called monoamine oxidase. Because the neurotransmitters are not broken down, their concentrations are increased within the brain.

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