CHRONIC COCAINE USE IMPAIRS 'PLEASURE CIRCUITS' - STUDY

Dow Jones Newswires

NEW YORK -- Chronic cocaine use harms brain circuits that help produce the
sense of pleasure, which may help explain why cocaine addicts have a higher
rate of depression, a study suggests.

It's not clear whether cocaine kills brain cells or merely impairs them, or
whether the effect is reversible, said study author Dr. Karley Little. But
it's bad news for cocaine addicts in any case, he said.

"I personally wouldn't want to lose 10% or 20% of my reward-pleasure center
neurons, or have them just deranged or not working right," said Little, of
the Ann Arbor, Michigan, Veterans Affairs Medical Center and the University
of Michigan.

He and colleagues studied brain samples taken during autopsies from
long-term, heavy cocaine users. Their results were reported in the January
issue of the American Journal of Psychiatry.

Little said the research didn't reveal whether the brain impairment
resulted from years of use or just recent use before death.

Stephen Kish, head of the human brain laboratory at the Center for
Addiction and Mental Health in Toronto, said researchers have "always
considered cocaine to be a dangerous drug " because of its potential for
addiction and harm to the heart.

"We now have to add to the list (of risks) a damaging effect of cocaine on
the brain, which was something we never expected before," Kish said.

The research provides "a piece of the puzzle" in explaining why cocaine
users run a higher risk of depression, said Dr. Deborah Mash, a
neuroscientist at the University of Miami School of Medicine.

It remains unclear whether cocaine causes depression or whether people
start using the drug because they are depressed. But in either case, Mash
said, the study suggests brain changes could "light the fuse" for
depression in a cocaine user who is prone to it.

The study also suggests that the brain changes could cause the depression
commonly seen during cocaine withdrawal, Mash said.

In the study, Little and colleagues studied brain autopsy specimens from an
area called the striatum in 35 cocaine users and 35 non-users of similar
age and sex.

They measured levels of a protein called VMAT2, which is found in brain
cells that signal each other with a chemical called dopamine. Dopamine
neurons form circuits that are critical for the brain to feel pleasure.

The study found that cocaine users' VMAT2 levels were lower on average.
That could mean dopamine neurons had been damaged or killed - an effect not
observed in animal studies - or that they were making less VMAT2, which
suggests they also were making less dopamine, Little said.

A person with impaired or missing dopamine neurons could have difficulty
feeling pleasure and might become depressed, said Little, who added that
researchers will now compare the number of dopamine neurons in the autopsy
specimens.

The study found hints that VMAT2 levels were lower in cocaine users with
severe depression than in other users, but statistical analysis suggested
this could be a coincidence. Little said the link is strengthened when
other data are taken into account.