The Molecule of More

PROGRESS

Excessive dopamine activity isn’t the only problem in bipolar mania,

but it plays an important role. As noted, it’s not caused by a highly

active DRD4 receptor allele. Instead, scientists believe that it’s caused by

a problem with something called the dopamine transporter (Figure 5).

Figure 5

The dopamine transporter is like a vacuum cleaner. Its job is to limit
the amount of time dopamine spends stimulating the cells around it.
When a  dopamine-producing cell  fires, it  releases its  store of dopamine, 
which then binds to receptors on other brain cells. Then, to bring the
interaction to an end, the dopamine transporter sucks the dopamine
back into the cell where it came from so the process can start all over
again. The transporter is sometimes called a reuptake pump because it
pumps the dopamine back into the cell.
What happens when the transporter doesn’t function normally? We
can answer this question by looking at the behavior of people who abuse
cocaine. Cocaine blocks the dopamine transporter like a sock shoved
into  a  vacuum cleaner nozzle. The blockage allows the  dopamine to 
interact with its receptor over and over again. When that happens,
people experience increased energy, goal-directed activity, and sexual
drive. They have elevated self-esteem, euphoria, and racing thoughts
that jump from one topic to another. Cocaine intoxication is so similar
to mania that doctors have trouble telling them apart.