Dopamine is produced in several areas of the brain, and its presence activates five different types of receptors in nerve cells. It affects behavior, recognition, voluntary movement, motivation, reward, sleep, mood, the ability to concentrate and learning. For example, it is believed that dopamine production is responsible for the conditioned response first demonstrated in Pavlov's dogs. As a hormone released by the hypothalamus, it suppresses the production of the hormones associated with lactation produced by the pituitary gland.
Dopamine's main benefit as a treatment for brachycardia and low blood pressure is that the molecules are too large to breach the blood-brain barrier and as such a dose of dopamine will not effect the central nervous system. There are three different dosing levels:
- Renal - a low dose to dilate blood vessels, allowing better blood flow to the heart and kidneys.
- Intermediate - to treat shock or heart failure.
- Pressor - a high dose that causes constriction of the blood vessels, to increase blood pressure. Hoewever, doses this high can cause kidney failure as a side effect
Dopamine's effect as a precursor molecule to adrenaline was discovered as early as 1958. However, it was not until much later that it's role as a neurotransmitter was understood.
A lack of naturally produced dopamine will often result in Parkinson's disease. Unfortunately, dopamine cannot be used to treat Parkinson's because of its inability to breach the blood-brain barrier and reach the central nervous system where it can be used. Instead, L-Dopa, a precursor molecule to dopamine may give some relief as it can breach the blood-brain barrier and be converted to dopamine in many patients. Lack of dopamine in the brain can also result in memory problems, inability to pay attention, and difficulty with problem solving. It is thought to play a role in attention-deficit disorder. Low dopamine levels are also thought to have a role in anhedonia, social anxiety,
Dopamine also plays a role in the sensation of pleasure. Sex and good food naturally cause the release of dopamine, and in some people aggression can also release dopamine. It is theorized that certain drugs such as cocaine, nicotine and amphetamines prevent dopamine from binding to transmitters, increasing the period of time dopamine has its pleasurable effects. Dopamine may also play a role in addiction to these drugs.