ANN ARBOR, Mich., Jan. 1 (UPI) -- Cocaine appears to damage and perhaps destroy the brain cells associated with the "high" it produces, researchers reported Wednesday.

"For a long time we have known that cocaine causes a pleasure response immediately after it is taken because it increases dopamine levels in the brain," Dr. Karley Little, associate professor of psychiatry at the University of Michigan School of Medicine, told United Press International. "But now we see that the specific neurons interacting with cocaine are disturbed, damaged and maybe destroyed in the drug-use process."

Dopamine is the brain chemical responsible for causing feelings of pleasure. Along with inducing a cocaine high, its release contributes to pleasurable feelings associated with ordinary human activities such as eating, working and sexual relations.

The researchers examined brain samples removed during autopsies of 35 known cocaine abusers and 35 non-drug users chosen for similar age, sex, race or cause of death. They used three standard molecular measurements to evaluate the condition of dopamine brain cells. They found levels for all three standards were significantly lower for cocaine users than for the control subjects. The levels were lowest among cocaine users who had been diagnosed with depression.

"About a third of cocaine users feel markedly depressed, listless, anxious, and uncomfortable when they stop using cocaine, and this persists in a sizeable number," Little said.

Little, who also is chief of the VAHS Affective Neuropharmacology Laboratory in Ann Arbor, said, "We know that people who have those symptoms are likely to become more dependent on the drug and find it harder to quit. So, cocaine is most addicting to those individuals who experience not only pleasure from its use, but are also punished by its withdrawal. Our results provide a very good biochemical basis for cocaine withdrawal symptoms."

The research results appear in the January issue of the American Journal of Psychiatry. They are the latest from brain tissue research begun in 1993 comparing samples from cocaine abusers and control subjects.

"This is a pioneering study," Cindy Miner, chief of science policy at the National Institute of Drug Abuse, told UPI. It raises the possibility that cocaine use causes damage to the brain, which is an unexpected result following prior animal studies that seemed to suggest otherwise. It isn't possible to say yet whether the cellular damage observed by these researchers is temporary or permanent, but at the very least it is a 'first' and intriguing finding that sets a direction for further research."

Little added: "What we need to do now is to count the dopamine neurons and axons in our remaining samples, which is a big undertaking. If we find they are not decreased then it will mean we are dealing with a down-regulation process, a reduction in cellular activity in response to cocaine use. If the numbers are diminished then were are dealing with unprecedented neuronal loss. If the change is permanent it's a serious problem, and if it is reversible then we must find out the mechanism by which it can be reversed."

The research was funded by the National Institute on Drug Abuse of the National Institutes of Health in Bethesda, Md., and by a Veterans Administration Merit Award.