Belmont--December 2003, Harvard Medical School affiliate McLean Hospital--McLean Hospital researchers have demonstrated that early exposure to Ritalin could reduce sensitivity to cocaine reward, a potentially beneficial effect, but could also increase depressive-like symptoms in adult rats.  The study, led by McLean Hospital's William Carlezon, PhD, and Susan Andersen, PhD, found that adult rats given Ritalin as juveniles behaved differently than their placebo-treated counterparts in a host of tests that reflect mood and attention.  Published in the Dec.15 issue of Biological Psychiatry, the study follows up previous work by the researchers showing that young rats given Ritalin were less likely to find cocaine pleasurable as adults.

     For the new study, Carlezon and Andersen raised two sets of rats: one was given Ritalin during the rat equivalent of pre-adolescence, while the other was given saline.  At adulthood, all of the rats were examined in a model of "learned helplessness," which tested how quickly they gave up on behavioral tasks under stress. 

     "Rats exposed to Ritalin as juveniles showed large increases in learned-helplessness behavior during adulthood, suggesting a tendency toward depression," said Carlezon, director of McLean Hospital's Behavioral Genetics Laboratory.  "These rats also showed abnormally high levels of activity in familiar environments, which might reflect basic alterations in the way rats pay attention to their surroundings."

     Carlezon and Andersen do not believe the effects they see in their rats are specific to Ritalin.  Rather, they believe they are observing a general effect of how stimulant drugs, many of which act by increasing the activity of a neurochemical called dopamine, affect the way that neuronal connections become cemented into place during development.  They also report that early studies indicate that juvenile exposure to cocaine instead of Ritalin produces the same pattern of results.