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The dopamine transporter is a type of protein that actively transports the neurotransmitter dopamine within nerve synapses. When dopamine is moved from a synapse into a neuron, it is the dopamine transporter that is mostly responsible for performing this function. By doing this, it effectively terminates the dopamine signal being communicated to the neuron. Because of this, malfunctions of the dopamine transporter are blamed for contributing to several psychological disorders, including clinical depression, alcoholism, and bipolar disorder.
As is the case with all proteins, there is a certain specific place in the human genome which contains the code for the dopamine transporter protein. It is located on the fifth chromosome, and can sometimes be subject to a condition called genetic polymorphism. This causes more transporter proteins to be created than would normally be healthy. Too much of the protein could result in the premature clearing of dopamine from synapses, and this would constitute a genetic predisposition to disorders like those described above.
Dopamine is one of the principal neurotransmitters in the brain, and is especially crucial to feelings such as motivation and reward. Attention and learning are also influenced by it, as are movement, moods, and sleep. It is easy to see how even a minor imbalance in the dopamine transporter can have significant repercussions in a person's life. As a person ages, less dopamine is produced in the body's cells. As the dopamine levels decrease, the levels of transporters also decrease proportionally, to compensate for this difference.
Several types of drugs can work to block the transporter by keeping it from functioning as it normally would. Cocaine and amphetamines fall into this category, as do some medications used as anti-depressants, such as bupropion hydrochloride. All of these drugs reduce the rate at which dopamine is removed from the synapse, leaving it there to transmit signals again and again. The pleasurable feelings that all these drugs bring is most likely a direct result of the way they act on neurotransmitters.
Certain disorders related to dopamine result not from the overactivity of dopamine transporter, but from a lack of dopamine itself. When administered as a medication, dopamine affects the sympathetic nervous system in ways such as raising the heart rate, but in this form it cannot enter the brain through the blood-brain barrier. For this reason, other drugs which affect the transporter, or which supply dopamine in other ways, must be given to treat conditions which are related to a deficiency of dopamine rather than a surplus of transporter.