Dopamine DAa contraction of 3,4- d ihydr o xy p henethyl amine is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemicalL-DOPAwhich 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 nerve cells to send signals to other nerve cells. Neurotransmitters are synthesized in specific regions of the brain, but affect many regions systemically.
The brain includes several distinct dopamine pathwaysone of which plays a major role in the motivational component of reward-motivated behavior. The anticipation of most types of rewards increases the level of dopamine in the brain, [4] and many addictive drugs increase dopamine release or block its reuptake into neurons following release.
These pathways and cell groups form a dopamine system which is neuromodulatory. In popular culture and media, dopamine is often portrayed as the main chemical of pleasure, but the current opinion in pharmacology is that dopamine instead confers motivational salience ; [6] [7] [8] in other words, dopamine signals the perceived motivational prominence i.
Outside the central nervous system, dopamine functions primarily as a local paracrine messenger. In blood vessels, it inhibits norepinephrine release and acts as a vasodilator at normal concentrations ; 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 diseasea 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. 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.
Restless legs syndrome and attention deficit hyperactivity disorder ADHD are associated with decreased dopamine activity. Dopamine itself is available as a manufactured medication for intravenous injection : although it cannot reach the brain from the bloodstreamits peripheral effects make it useful in the treatment of heart failure or shockespecially in newborn babies.
A dopamine molecule consists of a catechol structure a benzene ring with two hydroxyl side groups with one amine group attached via an Hälsa och välmående chain. Like most amines, dopamine is an organic base. Dopamine is synthesized in a restricted set of cell types, mainly neurons and cells in the medulla of the adrenal glands.
The direct precursor of dopamine, L -DOPAcan be synthesized indirectly from the essential amino acid phenylalanine or directly from the non-essential amino acid tyrosine. Although dopamine is also found in many types of food, it is incapable of crossing the blood—brain barrier that surrounds and protects the brain.
L -Phenylalanine is converted into L -tyrosine by the enzyme phenylalanine hydroxylasewith molecular oxygen O 2 and tetrahydrobiopterin as cofactors. Dopamine itself is used as precursor in the synthesis of the neurotransmitters norepinephrine and epinephrine.
Some of the cofactors also require their own synthesis. In clinical research on schizophrenia, measurements of homovanillic acid in plasma have been used to estimate levels of dopamine activity in the brain.