Dopamine is a neurotransmitter—one of the chemicals that allow nerves to “talk” to each other. It’s in the family of biogenic amines, which includes serotonin, acetylcholine, adrenalin, and noradrenalin.
Dopamine (DA) causes or prevents several abnormal brain functions, but not because it takes different actions. It always does the same thing: it is released from one nerve ending and moves a microscopic distance to specific receptors or docks on an adjacent nerve. Problems arise not when DA does different things, but when there is more or less than enough to get a normal response.
Conditions Affected By Dopamine
Schizophrenia. Generally believed to be a genetic abnormality, it usually becomes apparent between age 20 and 30. It’s characterized by “positive” characteristic (e.g., hallucinations), and “negative” characteristics (e.g., apathy, social withdrawal). The positive characteristics often receive the most attention as they can be the most disruptive. Positive characteristics are attributed to too much DA in one brain area, the mesolimbic pathway. Neuroleptic drugs (Haldol, Risperdal, Seroquel, others) retard or block the effects of DA, and help control positive characteristics.
Interestingly, negative characteristics are felt to be the result of too little DA in another area, the prefrontal cortex. This apparent contradiction (schizophrenia: is it too much or too little dopamine?) can be explained by recalling that there are several DA systems in the brain, and they can work independently.
Parkinson’s Disease. Characterized by inability to make smooth muscle movements, Parkinson’s Disease is caused by insufficient DA in the basal ganglia, the brain region that controls fine muscle movement. People with Parkinson’s Disease sometimes also have negative characteristics similar to those in schizophrenia, due presumably to low DA in the prefrontal cortex.
Pleasure Seeking and Addiction. There is no doubt that DA is involved in pleasure seeking. It’s not clear, though, if DA causes the reward (the pleasure feeling) or causes the reward-seeking behavior. The issue is, does DA lead to wanting, or to liking? Those who believe DA causes wanting suggest DA’s primary effect is to increase motivation, or craving. Cueing seems to increase DA. Thus, alcoholics who associate drinking with a certain location, such as a tavern, will have increased DA when in a tavern, which causes craving for alcohol. Other factors that increase DA are sex, food, and drugs such as cocaine and amphetamine.
Learning and Dementia. The brain’s frontal lobes regulate the flow of information related to memory and problem solving. Low DA contributes to attention deficit disorder, according to some experts. In several dementias, there is degeneration of DA producing cells in the frontal lobe, contributing to difficulty in learning, showing up as short term memory loss.
Outside the Brain. DA participates in prolactin control. Prolactin is involved in development of mammary glands and is necessary for milk production. It also is involved in maternal and sexual behavior. Most but not all neuroleptic (antipsychotic) medications elevate prolactin levels. This can lead to decreased libido, hypogonadism, and reduced muscle mass.
There are DA receptors in blood vessels that cause vasodilatation, while artificially high DA, such as used in treatment, causes vasoconstriction.
Some Sources
Dopamine and Glutamate in Psychiatric Disorders. Werner J. Schmidt, Maarten E. A.. Humana Press 2005
About Prolactin
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