The Ups And Downs Of Dopamine

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It's a North Carolina summer morning. Sunlight warms the farmer's market air, lapping gently against your skin. The color and aroma of fresh fruits and vegetables distract your senses, when you are beckoned by a sample of candy-red strawberries. Gloriously sweet juices transport you to childhood, when you sat in the backyard tree-swing, gleefully eating ripe strawberries from your Mama's garden.

You buy a box, and by the time you arrive home, the strawberries are gone. What makes you eat one strawberry after the other? Why does it feel like stopping, if you wanted to stop, would be impossible?

The human body, engineered over billions of years by evolutionary experiments in adaptation, owes its survival as a species to the experiences of pleasure, which is enacted by brain chemistry.

Dopamine is actually the basis for natural responses to pleasurable events. So, for example, if you get an A on a test, or you eat a piece of chocolate cake, your dopamine levels will go up, and that causes the feeling of pleasure, and also causes you to want to repeat the behavior. It increases your motivation to seek those rewards. And that is very important in evolution, to drive individuals to make their circumstances better.

That's Dr. Sarah Jones, Professor in the Department of Physiology and Pharmacology, Wake Forest School of Medicine.

Ironically, it's this pleasure that also drives us towards destructive behavior, such as binge eating or drug use.

The changes that cocaine produces in the brain are biochemical and physiological changes that massively alter the way the dopamine system functions. There's no conscious control over how the brain is responding in a biochemical way.

In fact, illegal drugs work by stimulating the dopamine systems, though most often indirectly.

Dr. Jones is the co-author of a recent paper published in the Journal of Neuroscience which looks at potential causes of cocaine's highly addictive nature. She notes that cocaine is different because it works directly on the dopamine systems.

Cocaine has hijacked this natural reward pathway, and so you can't tell someone to stop engaging that system. That's impossible.

Our research has led us to focus on the dopamine transport in our brain.

And the dopamine transmitters responsible for clearing dopamine out, cocaine comes along and inhibits the dopamine transporter and causes sort of a burst of dopamine, which is where the pleasure comes from.

Cocaine has another diabolical aspect that makes it so dangerous, and this is the subject of Dr. Jones's research.

We have discovered that the transporter becomes tolerant so you have to take more cocaine to get the same effects, or high, or rush that you did the first time that you took it. Even after a long period of abstinence one of the primary reasons for relapse being so terrible is that the brain goes back to being adapted to the high doses of cocaine.

We think it's completely irreversible. And that person will be primed to respond in this addicted state to pre-exposure to the drug for the rest of their lives. That sounds like there's no hope, but actually there is hope. There are actually drugs on the horizon that have the potential to reverse this tolerance and get people back to more normal dopamine states. It's possible that we can stop this relapse cycle.

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