What is dopamine, what is its role in the brain? Why do researchers think dopamine is involved in causing psychosis?

Professor Robin Murray: Dopamine is a neurotransmitter, so it helps take the messages from one nerve cell to another nerve cell.

If something exciting happens to you, then you release dopamine, but also if something bad happens, something unexpected, you would release dopamine.

For example, if you were watching television, I think it is on a Saturday night, and the Lottery results were on, and each week you watch the Lottery, and each week you find you’ve wasted your money, you don’t release any dopamine.

But the Saturday night when your number comes up, you see that’s my number – whoof!, you release dopamine from your striatum because you’re excited by this, you rush to find your number, ‘is it really my number, did I get it right?’ So dopamine is involved in making things significant. That number, which most other Saturday nights is trivial, suddenly becomes important to you. And we know that when things are important, dopamine is released.

Now the problem with schizophrenia is that people are releasing too much dopamine all the time, so that things that should be of no significance become important to them.

So for example, if you were to ask me how many red cars did I see on the way to work today, I have no idea. But if I am releasing too much dopamine, maybe I think red means danger, I notice all these red cars, why are all these red cars seeming to be all about? Are there more than usual? Is it possible that a company which employs people in red cars is following me? So you read too much significance into events. That you notice somebody is talking to their neighbour, they glance at you in a strange way, well probably they are just noticing you passing by, but you read too much into that and say, ‘why are they looking at me in that way? Why are they talking to their friend? Are they talking about me? Do they know something about me? Can they read my thoughts?’ And so you begin to put too much importance, or significance, or salience into events either happening out in society, or even things happening in your head.

So this is why dopamine, we think, is the final common pathway of psychosis. Just like in heart disease, the clot in the artery is the final common pathway which brings on the heart attack. So excess dopamine is the final common pathway through which one brings on the hallucinations and the delusions.

If you take drugs like amphetamines, speed or cocaine, these drugs we know increase dopamine, and we know if you take a lot of these then you can go psychotic. So too much dopamine makes you psychotic.

The other thing that made us concentrate on dopamine was that all the drugs that made people with psychosis better, or schizophrenia better, are dopamine blockers. So drugs like the old-fashioned drugs like chlorpromazine or haloperidol, or the more modern drugs like risperidone and aripiprazole, all of them have in common the fact that they block dopamine.

Too much dopamine is more likely to make you psychotic. Too little dopamine is likely to improve or perhaps abolish delusions and hallucinations.

We think that some of the genes, which we inherit, may give us a pre-disposition to having this dopamine-ergic abnormality. But also, we suspect that the other risk factors for schizophrenia may also contribute, so, for example, we know that hypoxia at birth, birth complications, prematurity, a range of what we would collectively call obstetric complications, they increase the risk of schizophrenia. We can’t prove it but we suspect this may be through an effect on the dopamine system.