Claim: Dopamine functions as a chemical.

Dopamine -LRB- DA , contracted from 3,4-dihydroxyphenethylamine -RRB- is an organic chemical of the catecholamine and phenethylamine families that plays several important roles in the brain and body . It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA , which is synthesized in the brain and kidneys . Dopamine is also synthesized in plants and most animals .   In the brain , dopamine functions as a neurotransmitter -- a chemical released by neurons -LRB- nerve cells -RRB- 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 . Other brain dopamine pathways are involved in motor control and in controlling the release of various hormones . These pathways and cell groups form a dopamine system which is neuromodulatory .   Outside the central nervous system , dopamine functions primarily as a local chemical messenger . In blood vessels , it inhibits norepinephrine release and acts as a vasodilator -LRB- at normal concentrations -RRB- ; in the kidneys , it increases sodium excretion and urine output ; in the pancreas , it reduces insulin production ; in the digestive system , it reduces gastrointestinal motility and protects intestinal mucosa ; and in the immune system , it reduces the activity of lymphocytes . With the exception of the blood vessels , dopamine in each of these peripheral systems is synthesized locally and exerts its effects near the cells that release it .   Several important diseases of the nervous system are associated with dysfunctions of the dopamine system , and some of the key medications used to treat them work by altering the effects of dopamine . Parkinson 's disease , a degenerative condition causing tremor and motor impairment , is caused by a loss of dopamine-secreting neurons in an area of the midbrain called the substantia nigra . Its metabolic precursor L-DOPA can be manufactured , and in its pure form marketed as Levodopa is the most widely used treatment for the condition . There is evidence that schizophrenia involves altered levels of dopamine activity , and most antipsychotic drugs used to treat this are dopamine antagonists which reduce dopamine activity . Similar dopamine antagonist drugs are also some of the most effective anti-nausea agents . Restless legs syndrome and attention deficit hyperactivity disorder -LRB- ADHD -RRB- are associated with decreased dopamine activity . Dopaminergic stimulants can be addictive in high doses , but some are used at lower doses to treat ADHD . 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 .