What is dopamine?
Dopamine is a monoamine neurotransmitter that carries signals between nerve cells in the brain. In other areas of the body however, it has more functions that go beyond its role as a neurotransmitter, like in the regulation of hormones and blood pressure. Some of the functions of this important neurotransmitter include:
- Pleasure and reward modulation
- Motor control
- Growth hormone regulation
- Prolactin regulation
- Sex drive regulation
- Decision making
- Mood control
- Blood pressure modulation
- Attention, memory, and learning
- General health and lifespan
There are also many somewhat unknown facets of dopamine, and the neurotransmitter may even be linked to attention, concentration, and learning. This is particularly likely given that dysfunction of the dopamine receptors is thought to be the main cause of attention deficit disorder. ADD is treated with drugs like Ritalin and amphetamines that boost the effect of dopamine. These medications are able to boost attention and assist the learning process.
Scientists haven't unlocked the full role of dopamine in conditions like ADD yet, but the distinctions are becoming clearer every day. What we do know about dysfunctions of the system tells us that having too little dopamine, or dysfunctional receptors in certain areas of the brain leads to conditions like Parkinson's disease and ADD.
Having too much dopamine on the other hand, or receptors that are overly sensitive to dopamine, seems to contribute to schizophrenia somehow, which is why dopamine antagonists (Anti-psychotics), are used to treat schizophrenia. A similar effect can be seen in drug users who take a high dosage of amphetamines or related drug; psychosis results. This psychosis is temporary in this case, but not for those with a predisposition to schizophrenia. As such, having the proper levels of dopamine in every area of the brain is important for the mind and body to function properly.
Dopamine and depression
The link between dopamine and depression follows along the same vein as that of the other illnesses that are thought to be produced by dopamine level dysfunction. Dopamine mediates the reward system and motivation, and if these systems are 'out of whack', you will find it hard to find pleasure in the usual activities that once gave you pleasure.
This is one of the hallmark symptoms of depression. People who are depressed are often unable to experience pleasure from activities they used to enjoy, and they lack motivation to go out and achieve their goals. Most of the time, this is simply the result of trauma that has been experienced, rather than dopamine dysfunction. For some people though, dopamine levels may be producing the symptoms of their depression.
The lack of pleasure and motivation that comes from low dopamine levels is not a new discovery and this same effect can often be seen in drug addiction. Drugs like opiates, amphetamines, and cocaine, which produce a surge of dopamine, allow intense pleasure to be felt during intoxication. Once addiction sets in however, the dopamine receptors are down-regulated by this excessive stimulation and it becomes harder for people with a drug addiction to find joy in everyday life as a result.
This same mechanism could be at play in depression, or at least, dopamine reuptake inhibitors could certainly present a unique way to treat the lack of motivation and pleasure that depression entails. Such treatment should only be used after conservative measures have failed, and preferably on a temporary basis to help speed up therapy and get the sufferer to start enjoying life again.
How can dopamine treat depression?
True 'chemical imbalances' are very rare—much rarer than the media would have you believe. Your body maintains a strict balance of all receptors, at all times. This is called homeostasis, and is also the reason why withdrawals occur to medications, followed by a gradual return to normal.
For this reason, a 'chemical imbalance', where the brain isn't producing enough dopamine, serotonin, or epinephrine is almost impossible because the receptors can become more sensitive to even tiny amounts of a substrate if necessary. This definition of depression is propagated by the media and needs to be thrown away. The majority of people with depression do not have a neurotransmitter imbalance. Antidepressant drugs treat the symptoms simply because they make people feel good, not because the chemical was lacking.
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Dopamine can be targeted as a treatment for depression for either of these cases, but the method of treatment will vary depending on whether there is a problem with the receptors or the depression is purely psychological. Those with a receptor dysfunction may benefit from dopamine reuptake inhibitors taken constantly. This form of treatment would be aimed at correcting the levels of the stimulation that the receptors receive.
People without such genetic conditions would be more suited towards temporary modulation of dopamine however. In this case, dopamine would be targeted as a temporary way to boost motivation and pleasure, helping to expedite therapy by getting the person back into the world. This would be most effective when these symptoms are the main hardship faced in that person's recovery from depression.
Whilst dopamine and depression are linked, there is more research that needs to occur before treatments involving the neurotransmitter become more widespread and common place. Chances are that in the future, we'll have a better picture of the role of dopamine in depression, as well as how to use it as a way to treat the symptoms of depression and boost the effects of therapy.