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Stimulants increase motor activity in normal adults by blocking the dopamine transporter (DAT), thereby increasing synaptic dopamine. Paradoxically, stimulants decrease activity and enhance attention in children with attention deficit hyperactivity disorder (ADHD). To study this paradox, Duke University researchers developed mice that lack the dopamine transporter and have features that mimic the symptoms of children with ADHD. A striking behavioral feature of these mice is persistent hyperactivity that is exacerbated in novel environments. This study demonstrates that stimulants exhibit a paradoxical calming effect in mice lacking the dopamine transporter and suggests that serotonin may also play a role.
Researchers compared DAT knock-out m…