Dopamine is a naturally occurring chemical in the body that functions as a neurotransmitter and neurohormone. It primarily affects movement control, emotions and the pleasure and reward centers of the brain. It activates five dopamine receptors, D1 through D5, which are found throughout the brain and body. The receptors are classified into either the D1-like receptor family or the D2-like receptor family, based upon morphological, pharmaceutical and functional properties.
The dopamine receptor D1 (Drd1) is a member of the D1-like receptor family and is the most abundant dopamine receptor in the central nervous system. The receptor is found in the cortex, striatum and limbic system of the brain and the cardiovascular system. When dopamine binds D1 receptors, it regulates the growth and development of neurons in the brain and plays a role in behavioral responses. It also modulates the actions of dopamine receptor D2.
Dopamine receptor D2 (Drd2) is a member of the D2-like receptor family. It can be found in a variety of locations in the brain with the highest concentration in the basal ganglia. The basal ganglia is comprised of a group of structures and functions in motor control and learning. Mutations in the D2 receptor have been implicated in the movement disorder myoclonus dystonia and schizophrenia, according to the National Center for Biotechnology Information. Together with dopamine receptor D1, it is involved in the reinforcing effects of drug abuse, according to an article in Physiological Reviews.
A member of the D2-like receptor family, dopamine receptor D3 (Drd3) is maximally expressed in two regions of the limbic system called the islands of Calleja and nucleus accumbens. These two regions are involved in the reinforcing effects of pleasurable activities and many types of emotions such as laughter and addiction. According to the NCBI, mutations in this receptor are connected to increases in susceptibility to hereditary essential tremor 1, a type of movement disorder.
Another member of the D2-like receptor family is dopamine receptor D4 (Drd4). This receptor is a target of medications indicated for the treatment of schizophrenia and Parkinson's disease, conditions in which dopamine dysregulation is implicated as a cause. The receptor has been shown to be involved in exploratory behavior and motor coordination. According to NCBI, mutations in Drd4 are connected to attention deficit hyperactivity disorder and autonomic nervous system dysfunction.
Dopamine receptor D5 (Drd5) is the second member of the D1-like receptor family. The receptors are located primarily in the limbic system of the brain. The limbic system is a region in the brain containing structures such as the hippocampus and amygdala. The region plays a role in a variety of functions such as emotion and behavior, long-term memory and smell. According to the NCBI, the D5 receptors have a much higher affinity for dopamine as compared with the D1 receptors, meaning they more easily bind to dopamine neurotransmitters.