Dopamine is in the brain.
Dopamine . In the brain , dopamine functions as a neurotransmitter -- a chemical released by neurons ( nerve cells ) to send signals to other nerve cells . The brain includes several distinct dopamine pathways , one of which plays a major role in reward-motivated behavior . Most types of rewards increase the level of dopamine in the brain , and many addictive drugs increase dopamine neuronal activity . Dopamine itself is available as a manufactured medication for intravenous injection : although it can not reach the brain from the bloodstream , its peripheral effects make it useful in the treatment of heart failure or shock , especially in newborn babies .