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Cocaine trips brain appetite suppressor.

While the munchies triggered by smoking marijuana provide a rich vein of humor for comedians, the appetite suppression brought about by cocaine abuse is no laughing matter. People addicted to the drug can become dangerously thin.

Investigators have now found that cocaine-charged rat brains overproduce a small protein, or peptide, that seems to regulate food intake. This chemical may also play a role in other symptoms of cocaine use, such as frenzied motor activity.

A few years ago, Pastor R. Couceyro. now at the Yerkes Regional Primate Research Center in Atlanta, and his colleagues went looking for genes in the rat brain that become more active after cocaine or amphetamine use. "We were on a fishing expedition," says Couceyro.

The investigators reeled in one gene whose activity increases dramatically. The gene encodes a peptide, about 120 amino acids long, that they named Cocaine and Amphetamine Regulated Transcript, or CART. The researchers believe that cells cut CART into several pieces and that each has its own function in the brain.

CART's presence in vesicles at the tips of nerve cells suggests that the cells secrete the peptide to communicate with each other, says Couceyro.

Injecting specific fragments of CART into the brains of rats decreases the animals' appetites and increases their locomotor activity, Couceyro. Yerkes' Philip D. Lambert, and their coworkers reported at this week's Society for Neuroscience meeting in New Orleans. "This is the same thing that cocaine does," says Couceyro.

Since injections of even inert substances into the brain can induce behavioral changes such as loss of appetite, the investigators sought further proof that CART has a direct role in controlling food intake. They injected into rat brains blood serum containing CART-binding antibodies, which should block the peptide's function, explains Couceyro. "The antibody causes the animals to eat significantly more."

The investigators have also found that parts of the hypothalamus make CART. Couceyro notes that these same brain regions have been implicated in control of feeding behavior.

The peptide is synthesized elsewhere in the brain, which may help explain cocaine's addictive properties and other physiological effects. A fuller understanding of CART's role might ultimately suggest new ways to treat eating disorders as well as cocaine addiction, suggests Couceyro.
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Title Annotation:researchers identify Cocaine and Amphetamine Regulated Transcript
Author:Travis, John
Publication:Science News
Article Type:Brief Article
Date:Nov 1, 1997
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