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Dopamine and norepinephrine are neurotransmitters that are related and often affected in depression. Dopamine creates norepinephrine, and pharmaceutical companies have developed drugs that target both receptors. However, too much of these neurotransmitters can cause negative effects.
Dopamine and norepinephrine are, along with serotonin, related because they are three very important neurotransmitters that are the major constituents of the monoamine group of neurotransmitters. All three are listed as potentially affected when illnesses such as depression occur and where levels of any of the three may be lower than normal. It may seem that each neurotransmitter is produced by itself, but in fact these substances have a special relationship with each other.
As scientists continue to learn more about dopamine and norepinephrine, one thing is pretty clear. In the absence of dopamine, norepinephrine is unlikely to be produced. Dopamine specifically creates norepinephrine with the use of other chemicals such as beta-hydroxylase. Low dopamine levels tend to suggest low norepinephrine levels, and the absence or near-absence of these chemicals in concert could cause very severe depression or anxiety.
With this in mind, pharmaceutical companies have worked hard to develop new types of antidepressants that target norepinephrine and dopamine receptors. One of them is the successful Wellbutrin® or Zyban® (bupropion), which is called an NDRI, or norepinephrine dopamine reuptake inhibitor. For some people this NDRI has tamed depression well and Zyban® has been used as a smoking cessation aid.
Given the relationship between dopamine and norepinephrine, other people have argued for a dopamine reuptake inhibitor strictly since it could cater to norepinephrine production as well. There are actually quite a few. The best known is the popular attention deficit disorder (ADD) drug Ritalin® (methylphenidate). Some people with depression respond exclusively to a dopamine reuptake inhibitor, but others seem to respond more to an NDRI or other drugs that either stimulate or inhibit the reuptake of serotonin.
When in good quantities, norepinephrine and dopamine can act on the mind in a positive way. Norepinephrine can help regulate stress, help people experience pleasure, keep people alert, and aid in learning and normal emotional development. Dopamine also helps people feel pleasure, focus, think more clearly, maintain an even mood, remember things, and learn new behaviors. Together the two can interfere with the rewards caused by dangerous substances such as cocaine or nicotine, which explains why Zyban® has been marketed as a smoking cessation aid, although it is not entirely successful.
There can be too much of a good thing, and having too much of these two neurotransmitters can be disastrous. If dopamine increases in supply, it could stimulate more norepinephrine production, and this could cause tremors, anxiety, mania, paranoia, or other extremely undesirable characteristics. The balance has to be right, or else dopamine and norepinephrine can wreak havoc on the brain and body. Nowhere is this better demonstrated than when people with bipolar disorder are treated with an NDRI; most of them progress rapidly to manic states.
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