Washington, Apr 22 : Researchers have made a breakthrough in uncovering the mystery behind why teens get hooked on cocaine more easily than adults by finding that developing brains are more powerfully motivated by drug-related cues.
The study found that adolescent rats given cocaine were more likely than adults to prefer the place where they got it.
Epidemiological studies confirm that of people in various age groups who experiment with drugs, teens are by far the most likely to become addicted as they are driven by drug related cues.
During the study psychologists Heather Brenhouse, PhD, and Susan Andersen, from McLean's Developmental Psychopharmacology Laboratory introduced rats that were 38 or 77 days old which is equivalent to 13 or 20 human years, to an apparatus with one central and two larger side chambers that had different flooring, wall colours and lighting.
The injected the rats with saline solution in the morning fro three days in a row and placed them in one side chamber for an hour.
Four hours later, they injected them with a preference-forming dose of cocaine and placed them in the opposite-side chamber for an hour.
To test the "conditioned place preference" for the chamber where they got cocaine, the rats were let free to explore the entire apparatus in a drug-free state for 30 minutes on the 4th day
Brenhouse and Andersen calculated how long each rat spent in the drug-paired side relative to total time spent on either side. They repeated the procedure every 24 hours until each animal's place preference was extinguished, when the time they spent in the drug-paired chamber was cut in half - suggesting no lingering preference for either side.
Relative to adults, adolescent rats required around 75 percent more trials to extinguish a preference for the place where they were given the drug.
After each rat's last extinction trial, the researchers waited 24 hours, injected a low 5 mg/kg "priming" dose of cocaine, and put it back in the apparatus to test for place preference.
During this test for "reinstatement" of extinguished preferences, adolescent rats showed a significantly greater renewed preference than did adults for the drug-paired chamber. Those that had originally learned on a 10 mg/kg dose of cocaine showed 40 percent greater reinstatement than the few adult rats that showed a place preference at the lower dose.
Brenhouse and Andersen view this as a sign that adolescents form stronger memories for even less potent rewards.
"Adolescent vulnerability to addiction involves robust memories for drug-associated cues that are difficult to extinguish."
They believe that this is because their brains are still developing.
The researchers believe that the new findings may help in developing new treatments for youthful addiction.
The study appears in Behavioral Neuroscience, published by the American Psychological Association.