Serotonin -- The Mood Molecule

Serotonin is a hormone that acts as a neurotransmitter.  Manufactured by
the body, it is found along with its receptor sites in the brain, blood
platelets, and lining of the digestive tract.  It is also a precursor to a
hormone called melatonin, which plays multiple life-giving roles in the
body, including regulating biological rhythms.  Neurotransmitters send
message (electrical impulses) from one nerve cell to another.  Serotonin is
believed to be more than simply a messenger, because it affects a wide
range of mental and physical responses in the body and plays a significant
role in activities such as temperature regulation, hunger sensations,
sexual behavior, and sleep patterns.  Serotonin deficiencies can give rise
to a wide range of illnesses, depending on what part of the brain is affected.

Serotonin is known as the "mood molecule" because it modulates raw
information and gives it its emotional tone.  James Stockard, a
Northwestern University psychiatrist, stated, "A person's mood is like a
symphony, and serotonin is like the conductor's baton."  For example,
serotonin levels in the brain determine whether we will perceive a glass of
water as being half-empty or half-full.  Other neurotransmitters may give
the message that we are full, but serotonin levels determine if we feel
satisfied.  Low serotonin levels in the brain are linked to clinical
depression, suicidal tendencies, anxiety disorders, obsessive-compulsive
behaviors (such as overeating), bulimia, schizophrenia, sleep problems,
migraine headaches, autism, drug and alcohol addictions, Alzheimer's
disease, and patterns of violent behavior.  The conditions listed above may
miraculously disappear or improve significantly when serotonin levels are
raised.