Dopamine is a neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In the human brain|brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors — Dopamine D1 receptor|D1, Dopamine D2 receptor|D2, Dopamine D3 receptor|D3, Dopamine D4 receptor|D4, and Dopamine D5 receptor|D5, and their variants. Dopamine is produced in several areas of the brain, including the substantia nigra and the ventral tegmental area.[1] Dopamine is also a neurohormone released by the hypothalamus. Its main function as a hormone is to inhibit the release of prolactin from the anterior lobe of the pituitary.
Dopamine can be supplied as a medication that acts on the sympathetic nervous system|sympathetic nervous system, producing effects such as increased heart rate and blood pressure. However, because dopamine cannot cross the blood-brain barrier, dopamine given as a drug does not directly affect the central nervous system. To increase the amount of dopamine in the brains of patients with diseases such as Parkinson's disease and dopa-responsive dystonia, L-DOPA (levodopa), which is the precursor of dopamine, can be given because it can cross the blood-brain barrier.