Question:

Would you please discuss serotonin and the role that it plays in the body? How is it linked to depression?

Answer:

Neurons (nerve cells) in the brain and the rest of the nervous system use chemical messengers called neurotransmitters to communicate with each other. These chemicals are released at the end of one nerve cell when a nerve impulse arrives there; they move across the gap between one nerve cell and the next - called a synapse - and change the membrane of the second nerve cell in such a way that it becomes either less or more likely to fire.

Serotonin is one of dozens of neurotransmitters and is found in body tissues including the brain, blood, and the mucous membranes lining the stomach and digestive tract. It is formed from tryptophan, an amino acid (an essential building block of protein) that is found in food.

In the past decade, research studies of serotonin have found that it plays an essential role in the regulation of sleep, appetite, temperature, blood vessel tone, secretion of certain hormones and in the perception of pain, thereby affecting a wide range of conditions, such as migraine headaches, depression and sleep disturbances.

It is the role that serotonin plays in depression that perhaps is of most interest to scientists, who conclude that people with depression have "imbalances" in the brain's neurotransmitters; low levels of serotonin and another neurotransmitter norepinephrine are believed to play a critical role.

In 1988, with the introduction of fluoxetine (Prozac), a new generation of antidepressant medication hit the U.S. market. Known as selective serotonin-reuptake inhibitors (SSRIs), these drugs enhance the activity of serotonin by prolonging the amount of time it is available in the brain. Other SSRIs that have been approved by the Food and Drug Administration for treatment of depression are sertraline (Zoloft), paroxetine (Paxil) and citalopram (Celexa).

Many U.S. psychiatrists favor the newer SSRIs as "first-line" medications for the treatment of depression. Unlike older medications for depression, they are easier to use, have fewer side-effects, and are less likely to be abused. The increased serotonin levels that result from taking SSRIs, however, can produce negative side effects in some people, including nausea, diarrhea, headache, tremor, daytime sedation, sexual dysfunction, nervousness and insomnia.

In addition to serotonin's role in depression, research shows that increased levels of serotonin reduces appetite. Scientists are seeking to develop drugs that could help selected overweight individuals control their appetite and lose weight.

Research also suggests that serotonin has a significant effect on the size of the blood vessels that cause migraine headaches. Current research is seeking to develop migraine drugs that can bind to the particular serotonin receptor that controls the constriction of blood vessels.

For the treatment of sleep-related disorders, increased levels of serotonin have been shown to induce a relaxed feeling, sleepiness and decreased alertness.