14 DAY TRIAL // Teens may become hooked on cocaine and, once rehabilitated, relapse more rapidly than adults because their developing brains are more sensitive to drug-related cues. At least in the case of rats, this holds true. A new study carried out at McLean Hospital, the largest psychiatric facility at Harvard Medical School, and published in Behavioral Neuroscience found that adolescent rodents which received cocaine were more likely to linger in the same place where they received the drug than adults.
The behavior persisted even after the rats stopped receiving the drug, and it has been noted that a small dose of cocaine triggered that preference again, but only in the case of teen rodents. Epidemiological researches had already showed that in humans, teens are the most vulnerable to drug addiction amongst all age categories.
Psychologists Dr. Heather Brenhouse and Dr. Susan Andersen placed 38 or 77-day-old rats (which is the equivalent of 13 or 20-year-old humans) inside an apparatus with one central and two larger side chambers. The chambers presented different flooring, wall colors and lighting.
In the first 3 days, the rats were injected with saline solution in the morning and left to stay in one side chamber for an hour. 4 hours later, they received a cocaine shot (either 10 or 20 mg per kg of weight, two doses that cause addiction) and placed in the opposite side chamber for another hour. This way the rats associated the withdrawal with the non-drug chamber.
On the 4th day, the rats were let to freely explore the apparatus in a drug-free state for 30 minutes, to see their preference for the chamber where they received the cocaine shot. The researchers assessed how long each rat lingered in the chamber where they received the drug compared to the time spent on other side. This was repeated once each day until the conditioning of each animal was gone. When that moment came, the animals did not show preference for any side. However, the teen rats lost their conditioning in 75% more trials compared to adult animals.
When animals lost their conditioning to the place associated with cocaine, 24 hours later they received a cocaine shot in a dose of 5 mg/kg and were then relocated in the apparatus. Teen rats displayed a much higher renewed preference than adults did. Teen rats that originally received shots of 10 mg/kg dose of cocaine displayed a 40% higher reinstatement than the few adult rats experimenting this.
Individuals that had received shots of 30mg/kg, no matter if teens or adults, experienced a renewed chamber preference to a similar level.
"Adolescent vulnerability to addiction involves robust memories for drug-associated cues that are difficult to extinguish," wrote the authors of the research.
They believe that the more powerful effect of the drug in teens is caused by their still developing frontal cortex. The same team had previously shown that during adolescence, dopamine, a "reward" neurotransmitter whose release is stimulated by cocaine consumption, may reinforce wiring between learning-connected frontal-cortex and reward and addiction brain nuclei.
The forming of new brain wirings slows down in mature brains, and this is why teen brains can store stronger memories associated with rewarding stimuli, like people, places and events connected to drug consumption.
"This heightened salience may require atypical strategies for drug abuse intervention during the adolescent period, such as extended treatment that involves substitution with different rewards, for example, exercise or music," wrote the authors.
"Harnessing their acute ability to learn well and form strong associations with stimuli that predict rewards may be helpful. In addition, it may be important to realize that adolescents might need longer treatment programs," Brenhouse added.