Karley Y. Little, MD, and colleagues at the University of Michigan and the VA Ann Arbor studied brain samples from 35 deceased cocaine users and 35 non-users matched for age, sex, race, and cause of death. They found strong evidence that cocaine damages specific brain cells.
These are the cells that produce a brain chemical called dopamine. Dopamine release starts a process that results in pleasurable feelings. Normally, the cells recycle dopamine by sending out transporter molecules to gather it back up. Cocaine blocks these transporters. That lets dopamine build up, increasing the pleasurable feelings. But there's a price to pay. With extended use of the drug, the brain resets the way it responds to dopamine signals. Soon, a person doesn't get nearly as much pleasure from cocaine. But without the drug, the person feels bad. It takes a hit of cocaine just to get back to normal.
When they looked at the cocaine users' brains, the researchers found very few of the transporter molecules. This told them that there likely was damage to the dopamine-making brain cells. They think these changes play a role in the mood disorders and lack of motivation seen in cocaine addicts.
This situation may become permanent, the Little study suggests. Drenching the brain with cocaine damages -- and maybe even kills -- dopamine-making cells.
"This is the clearest evidence we have to date that the specific [brain cells] cocaine interacts with don't like it and are disturbed by the drug's effects," Little says in a news release. "The questions we now face are: Are the cells dormant or damaged? Is the effect reversible or permanent? Is it preventable?"
Harm to dopamine cells may be one reason why long-term cocaine users are at high risk of serious depression. Cocaine addicts who are depressed have a much harder time kicking their habit. Little says he hopes that the study findings will point to new treatments for cocaine addiction.