Topic of the Month. December, 2001
Serotonin is a neurotransmitter, so before I can talk about serotonin, I first need to talk about neurotransmitters.
Our brains are made of millions of brain cells called neurons. Each neuron has about 10,000 connections with other neurons. Messages travel along these neurons, similar to the way electricity travels down a wire. When the message reaches the end of a neuron, it needs to somehow jump the gap to the next group of cells. The gap between neurons is called a synapse.
At the synapse, the axons on the transmitting neuron release tiny amounts of a neurotranmitter. That bit of neurotransmitter streams out into the gap. The receiving neuron is there, waiting. It has many receptors on it's surface that are analogous to "doors with locks", where only one type of neurotransmitter has the key to open a particular door's lock. When the correct neurotransmitter is released into the gap (and in the right quantity), it unlocks the reciever's "door", which starts a nerve impulse that allows the reciever to receive the message.
Note: There are about 15 different receptors for serotonin.
Once the neurotransmitter has finished its work, it is taken back by the original nerve to be saved for later re-use or is destroyed by monoamine oxidase. The process of taking back is called "re-uptake".
Serotonin (5-hydroxytriptamine) is synthesized from the amino acid tryptophan, and found in the cells of the central nervous system, in blood vessels, but mostly in the intestine (90%). In the central nervous system, serotonin is a key neurotransmitter. In the blood vessels, it is released from platelets when blood vessel walls are damaged. In the intestine, serotonin causes increased gastrointestinal motility and is related to vomiting, secretion and peristalsis.
Discovered 32 years ago, serotonin has been found to be the most diverse physiological substance in the body. Serotonin has numerous functions, including appetite control, sleep, memory and learning, temperature regulation, mood, behavior, cardiovascular function, muscle contraction, endocrine regulation, and depression. The affect of this chemical is amazing, considering that humans have only about one 5 to 10 mg of serotonin in their bodies.
Serotonin is structurally similar to certain hallucinogenic drugs, such as LSD. This leads to speculation about it's role in naturally occurring hallucinogenic mental disorders such as schizophrenia.
In the natural world, serotonin exist in fruits such as pineapples, bananas, plums and nuts. It can also be found in wasp stings and venom. It is believed that in stings and venoms, serotonin may function as an irritant, since intravenous injections of serotonin in man produce pain, gasping, coughing, tingling and prickling, nausea, cramps, and other unpleasant symptoms.
Increasing the levels of serotonin in the body can do all of the following:
Serotonin levels can be altered through consumption of food, vitamins, sunlight or through exercise.
Food
Tryptophan is synthesized into serotonin, so eating adequate amounts of protein is important to serotonin production.
Carbohydrates are also important for serotonin production, since they will trigger the release of insulin into the blood stream. Insulin clears all the amino acids from the blood, except tryptophan. When competing amino acids are out of the way, tryptophan can flood the brain, where it's converted to serotonin. Healthy carbohydrate-rich foods include whole-grain breads and crackers, whole-grain pasta, rice, cereal and fruit.
Chocolate is also known to elevate serotonin levels.
Vitamins
Folic acid, B vitamins and Vitamin C all play a role in serotonin production. Most all of the vitamins are used in some way in neurotransmitter production. Individuals with chronic mental illness tend to have vitamin deficiencies. It's difficult to know if the mental illness is caused by vitamin deficiency or if the poor eating habits of the mentally ill cause the vitamin deficiency (yet another chicken or the egg problem).
Exercise
The most effective way to raise serotonin levels naturally is with vigorous exercise. Studies have shown that serotonin levels are raised with increased activity and the production of serotonin is increased for some days after the activity. Serotonin also plays a part in the "runner's high".
The down side of this increased serotonin production, is that because serotonin causes sleepiness, it also may cause exercise fatigue. To obtain the right balance between the sense of well being and the exercise fatigue, it is advisable to eat carbohydrates before exercise.
In general many chemicals and drugs affect the action of neurotransmitters across the synapse. When an anesthesiologist puts you to sleep they use a chemical that blocks the action of neuro-transmitters at their synapse. The brain grinds to a halt and you lose consciousness.
One of the most widely used drugs that can affect neurotransmitters is caffeine. Caffeine inhibits the enzyme that breaks down the neurotransmitter acetylcholine. This results in increased activity between the nerves in the brain leading to alertness and energy. If the drug is overused it will lead to so much mental activity that it becomes difficult to sleep and difficult to think clearly. It may even lead to hallucinations.
Following are some fairly commonly used drugs that affect serotonin levels.
Selective Serotonin Re-Uptake Inhibitors (SSRI's)
It is widely believed that low serotonin levels lead to depression. Prozac, Zoloft, and Paxil are members of an antidepressant drug family called selective serotonin reuptake inhibitors (SSRI's). SSRIs slow down the process of returning the serotonin from the synapse to to the sending neuron. This means serotonin remains in the vicinity of the receptors for a longer period of time, so it is more likely that enough will build up to set off the impulse in the receiving neuron.
SSRIs allow the body to make the best use of reduced amounts of serotonin. After awhile, natural serotonin levels will rise again, and the SSRI can be reduced and withdrawn.
Triptans
Drugs in the "Triptan" family, such as Immitrex and Maxalt are used to treat migraine headaches.
During a migraine attack, an environmental trigger causes blood vessels to constrict. Serotonin comes on the scene, clotting blood cells and causing more constricting. This constriction limits oxygen to the brain, which causes the body to compensate by dilating the blood vessels in the area to an unusually large size. The area around the expanded blood vessels becomes inflamed, which irritates the nerve endings.
Scientists believe the expansion of blood vessels and the corresponding inflammation cause the throbbing pain in the temple or behind the eye that accompany a migraine. The dramatic changes in serotonin level and reduced blood flow during a migraine may be the cause of not only the head pain, but also the nausea and distorted vision or speech that often accompanies a migraine.
Triptan drugs are serotonin "agonists". A neurotransmitter "agonist" is a drug that mimics a neurotransmitter. The triptan drugs mimic the action of serotonin, and bind to the serotonin receptor sites. This binding causes the blood vessels that have become enlarged from the lack of binding of serotonin to return to their normal size.
Anti-Nausea Drugs
Two serotonin receptor antagonists, ondansetron (Zofran) and granisetron (Kytril), have been marketed to treat nausea associated with radiation and chemotherapy in cancer patients
And that's the end of my serotonin lecture. Stay healthy!