Dopamine

Dopamine is a chemical produced by the human body that acts as a neurotransmitter in the brain. Its chemical formula is (C₆H₃(OH)₂-CH₂-CH₂-NH₂) and its chemical name is 4-(2-aminoethyl)benzene-1,2-diol. Dopamine is abbreviated as DA. The brain contains five types of receptors to which dopamine binds (D1, D2, D3, D4 and D5).

Reward, Prediction and Motivation

Dopamine plays an important role in brain reward systems in the nucleus accumbens, reward prediction and error in the Ventral tegmental area, and appears to be involved in various levels of behavioral motivation.

Actions and substances that increase the amount of DA that is released in the nucleus accumbens increase the hedonistic responses of the animal. While dopamine antagonist (blockers) in the nucleus accumbens decrease these hedonistic responses. Manipulations of dopamine in the ventral tegmental area and the substantia nigra do not alter the hedonistic response but decrease or increase the motivation to perform behaviors. It is believed that dopamine acting in these regions actually signals predictions of future reward and errors in predicted reward and actual reward. Because of its role in both direct hedonistic assessment and its predictive ability dopamine is theorized to be the central neurotransmitter mediated reinforcement learning.

Dopamine is released by natural behaviors such as eating and sexual activity, and also by drugs such as cocaine and amphetamine.

Link to Mental Illness

Dopamine has also been linked to mental illness, particularly schizophrenia, which is characterized by psychotic episodes. Studies have shown that drugs which block D2 receptors (preventing dopamine from binding to them) reduce psychotic symptoms, and drugs which increase dopamine relase (e.g., cocaine) can lead to psychotic episodes. Most medications used in psychiatry to treat schizophrenia and other psychotic disorders work by inhibiting dopaminergic activity.

Therapeutic Uses

Dopamine is used to increase cardiac output and blood pressure. Levodopa (or L-DOPA), which is a dopamine precursor, is often used to treat Parkinsons' disease.