What Is Serotonin in the Brain?

Serotonin is a neurotransmitter, or chemical passed by one neuron to another neuron in the brain. The job of a neurotransmitter is to pass information from the central nervous system to other cells in the body. Serotonin is commonly known as a "mood neurotransmitter" and is responsible, when not in sufficient quantity, for depression. However, serotonin has been linked to several other moods, such as mania and aggression.

History

Serotonin was isolated in 1948 by Maurice Rapport, Arda Greene and Irvine Page of the Cleveland Clinic. The team originally thought it was a vasoconstrictor, or substance that causes narrowing of blood vessels. However, as scientists continued to study the chemical structure and its effects in the brain, serotonin was reclassified as a neurotransmitter.

How it Works

Serotonin, like any other neurotransmitter, is passed down the vesicle to the presynaptic terminal where a chemical process occurs, allowing that synapse to release the neurotransmitter. On the other end, receptors sit on the next synapse to receive those neurotransmitters, where the process will repeat until it is passed on to the rest of the body.
When a neurotransmitter is not received by the next synapse, it will go through the reuptake process, meaning it is carried back to the synapse of origin.

Serotonin and Depression

It is when too much or too little serotonin is received by the next synapse that problems occur.
Low levels of serotonin have been linked to depression, aggression and poor impulse control. While scientists are still trying to figure out all the roles serotonin plays, it is clear that it does not affect all people the same way.
Serotonin is believed to carry messages of positive effect, which when too few reach the opposite synapse, will be inhibited. Many symptoms of depression are linked to low serotonin levels such as sleeplessness, hopelessness and psychomotor agitation (involuntary movements in the body).
When a patient is prescribed an anti-depressant, they are usually known as MAOI's (Monoamine oxidase inhibitors) or SSRI's (Selectiv Serotonin Reuptake Inhibitors). Unlike MAOI's, SSRI's pinpoint only serotonin. What a SSRI does is block the reuptake process, allowing more serotonin to enter the receptor sites of the opposite synapse.
Common SSRI's include Celexa (citalopram), Lexapro (escitalopram), Zoloft (sertraline) and Paxil (paroxetine).

Serotonin and Aggression

Low levels of serotonin are also linked to aggression and poor impulse control. Several comparisons between violent criminals and their brain chemistry reflect low serotonin levels. It is important to consider that increased levels of aggression may be linked more toward poor impulse control.
As a result, scientists are not certain whether low serotonin is a cause of aggression or only correlated through poor impulse control, which is a major contributor to violence.

Serotonin and Street Drugs

Several street, or illegal, drugs can either impede or enhance the level of serotonin in a person's brain.
Amphetamines can increase the concentration of serotonin in certain parts of the brain, generating heightened mood.
Cocaine, while impacting the neurotransmitter dopamine at a higher rate, may also prevent the reuptake of serotonin, producing a temporary feeling of happiness and increased energy.
LSD actually shares the chemical structure of serotonin, stimulating receptors and increasing the quantity in certain areas of the brain.