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Drug Testing News
Cocaine Damages the
Brain's Pleasure Cells
Thu Jan 2,11:55 PM ET
THURSDAY, Jan. 2 (HealthScoutNews) -- Cocaine users seek
pleasure, but the more they indulge in the drug, the less
likely they are to feel the pleasure they're seeking.
That's the finding of a new study that shows cocaine damages
brain cells that trigger the feelings of pleasure. The drug
also exerts its most serious effects on those who are
clinically depressed, the researchers found.
This is the first time research shows what happens "in those
humans with the most clinically significant cocaine dependency
problems," says Dr. Karley Little, chief of the Veterans
Affairs Healthcare System in Ann Arbor, Mich., and lead author
of the study in the January issue of the American Journal of
"Ninety-five percent of studies of drug abuse are in animals,"
he adds. "We're showing the change in humans."
The researchers looked at postmortem brain samples of 35 known
cocaine users and 35 non-cocaine users, used as controls. All
were matched for age, sex, race, and cause of death.
All of those known to use cocaine "had cocaine in their system
when they died," although cocaine itself was not the direct
cause of death in most cases, Little says. Many died in car
accidents or of cocaine-related heart disease, and "a fair
number were murdered."
What the brain samples showed is that those who took cocaine
had problems with the amount of dopamine their brains
produced, and how it was released by the brain.
Dopamine is a chemical known to be released to signal
pleasure. "It is essential and coordinates pleasure," Little
says, "but it's not the pure sensation."
Cocaine initially sets in motion changes in brain cells that
disrupt the flow of dopamine. It blocks transporters that
bring dopamine back into cells. This causes dopamine to build
up outside of cells and bind with other receptors, signaling
pleasurable feelings repeatedly. This explains the "high" that
cocaine users crave, Little explains.
However, the continuous use of cocaine led to lower dopamine
levels in the study subjects. Less dopamine was being
produced, and there was less of the protein known as VMAT2,
which lives in the cells and helps prepare dopamine to be
released again. Finally, there was less indication that VMAT
was available for binding.
The cells involved in the functioning of dopamine either fall
asleep or die in those who regularly use cocaine, Little says.
While animal studies have indicated some of these brain
changes, the change in humans is to a much more significant
degree, he notes. "It's an overwhelming change in neurons. The
changes in the VMAT protein are a little unprecedented," he
Another interesting finding is that "we found these changes
correlate with a symptom." Notably, cocaine users known to be
depressed had the most significant changes in their dopamine
levels, Little says.
Seven of the cocaine users they examined had been diagnosed
with depression, and these seven were the ones who showed the
most striking decrease in dopamine being released and increase
in reuptake of the chemical.
"We don't know why the reaction is more severe in the
depressed," Little adds, but he speculates that they may have
a different response to cocaine and "that's why it makes it
harder for these people to stop. Our study is telling us a lot
more about the worse patients."
The researchers next plan to count dopamine neurons to see if
there are actually less of them in the cocaine users, Little
says. He doesn't think the neurons have died off. "It's more
likely they're turned way down. We're not sure if they go back
to normal once a person stops taking cocaine," he adds.
Thomas W. Clark, a research associate at Health and Addictions
Research, Inc., believes this study "helps to show cocaine
addiction is a real physical problem. There are changes in
brain function and structure consequent to cocaine use."
Little says the relevant message of his finding is that
cocaine causes harm.
"It's important to convey to people who might be tempted to
take cocaine that there's a chance they might damage part of
their brain," he says.
For more on cocaine's effect on the brain, visit the National
Institute on Drug Abuse or Emory University.