Serotonin (noun)

1. A chemical messenger that is found in the body and helps to regulate mood, appetite, sleep, and other functions.
2. A neurotransmitter that is primarily found in the gut, platelets, and the central nervous system.

Origin:

From the french sérotonine, coined in 1948 by the french biochemist maurice harold gray and his colleagues from the greek σῆρος (sēros, "serum") + tonos ("tone"), because it was first identified in blood serum.

Examples:

1. Serotonin levels are known to affect mood and behavior.
2. An imbalance in serotonin levels is thought to play a role in depression.
3. The drug works by increasing serotonin levels in the brain.
4. Serotonin is believed to play a role in regulating anxiety and aggression.
5. The serotonin receptor is an important target for the treatment of mood disorders.