Serotonin and the Link to Mood Disorders

Serotonin is a monoamine neurotransmitter that assists in the regulation of mood, sleep, muscle contractions, appetite, etc. Below is a diagram of brain that shows the different serotonin pathways.
In the past couple of years, studies have shown there to be a link between serotonin deficiency and depression.
The following excerpt is taken from the article, Serotonin: From Bliss to Despair by Joseph M. Carver, Ph.D.

"Perhaps the best way to think of Serotonin is again with an automobile example. Most automobiles in the United States are made to cruise at 70 miles per hour, perfect for interstate highways and that summer vacation. If we place that same automobile on a racetrack and drive day-after-day at 130 mph, two things would happen. Parts would fail and we would run the engine so hot as to evaporate or burnout the oil. Serotonin is the brain’s “oil”.

Like a normal automobile on a race track, when we find ourselves living in a high stress situation for a prolonged period of time, we use more Serotonin than is normally replaced. Imagine a list of your pressures, responsibilities, difficulties and environmental issues (difficult job, bad marriage, poor housing, rough neighborhood, etc.). Prolonged exposure to such a high level of stress gradually lowers our Serotonin level. As we continue to “hang on” we develop symptoms of a severe stress-produced depression.

An automobile can be one, two or three quarts low in oil. Using the automobile as an example, imagine that brain Serotonin can have similar stages, being low (one quart low), moderately low (two quarts low), and severely low (three quarts low). The less Serotonin available in the brain, the more severe our depression and related symptoms.

When Serotonin is low, we experience problems with concentration and attention. We become scatterbrained and poorly organized. Routine responsibilities now seem overwhelming. It takes longer to do things because of poor planning. We lose our car keys and put odd things in the refrigerator. We call people and forget why we called or go to the grocery and forget what we needed. We tell people the same thing two or three times.

As stress continues and our Serotonin level continues to drop, we become more depressed. At this point, moderately low or “two quarts” low, major changes occur in those bodily functions regulated by Serotonin. When Serotonin is moderately low, we have the following symptoms and behaviors:

· Chronic fatigue. Despite sleeping extra hours and naps, we remain tired. There is a sense of being “worn out”

· Sleep disturbance, typically we can’t go to sleep at night as our mind/thought is racing. Patients describe this as “My mind won’t shut up!” Early-morning awakening is also common, typically at 4:00 am, at which point returning to sleep is difficult, again due to the racing thoughts.

· Appetite disturbance is present, usually in two types. We experience a loss of appetite and subsequent weight loss or a craving for sweets and carbohydrates when the brain is trying to make more Serotonin.

· Total loss of sexual interest is present. In fact, there is loss of interest in everything, including those activities and interests that have been enjoyed in the past.

· Social withdrawal is common – not answering the phone, rarely leaving the house/apartment, we stop calling friends and family, and we withdraw from social events.

· Emotional sadness and frequent crying spells are common.

· Self-esteem and self-confidence are low.

· Body sensations, due to Serotonin’s role as a body regulator, include hot flushes and temperature changes, headaches, and stomach distress.

· Loss of personality – a sense that our sense of humor has left and our personality has changed.

· We begin to take everything very personally. Comments, glances, and situations are viewed personally and negatively. If someone speaks to you, it irritates you. If they don’t speak, you become angry and feel ignored.

· Your family will have the sense that you have “faded away”. You talk less, smile less, and sit for hours without noticing anyone.

· Your behavior becomes odd. Family members may find you sitting in the dark in the kitchen at 4:00 am.

Individuals can live many years moderately depressed. They develop compensations for the sleep and other symptoms, using sleeping medication or alcohol to get some sleep. While chronically unhappy and pessimistic, they explain their situation with “It’s just my life!” They may not fully recognize the depressive component."