Nicotine during rat youth primes brain for harder drugs.

The addictive ingredient in those cigarettes in the schoolyard could prep the brain for reliance on illicit drugs, say researchers working with adolescent rats.

Previous studies have suggested that teenagers who smoke cigarettes are more likely to progress to drugs such as marijuana or cocaine than are teens who never smoke. However, researchers haven't directly tested whether cigarettes themselves might be responsible for this effect.

To investigate, Susan McQuown of the University of California, Irvine and her colleagues gave some 1-month-old rats multiple low-dose nicotine injections over 4 days. The amount of nicotine was the rat equivalent of a person smoking 4 cigarettes a day. Other rats received injections of saline.

The researchers then placed each animal in a box with several holes, one of which delivered a dose of cocaine when the rat poked its nose inside.

McQuown and her team discovered dramarie differences in how quickly the two groups picked up the cocaine habit. Within the first day in the box, half the rats that received nicotine were frequently self-administering cocaine. In contrast, only 20 percent of the animals that received saline took up the drug immediately.

Trying an identical experiment with sugar pellets instead of cocaine, the researchers saw no difference between the nicotine and saline groups. In a separate experiment with adult rats, animals that received nicotine were no more likely to take up cocaine than were adult rats that received saline.

These results suggest that nicotine "might change the wiring of the brain during adolescence, heightening the response to other addictive drugs, says McQuown. She and her colleagues plan to test whether the effects of receiving nicotine in youth persist into adulthood.--C.B.