Attention-Deficit/Hyperactivity Disorder (ADHD) is a highly prevalent neuropsychiatric disorder, affecting 3-5% of children and 1-5% of adults. Nearly 60% of adults who are diagnosed with ADHD report that they have been treated with medications, generally psychostimulants. One of the most common stimulants used to treat ADHD is amphetamine. Amphetamine has recently been shown to have the potential to destroy dopamine (DA) axon terminals in the brain of non-human primates (baboons and squirrel monkeys) at plasma concentrations similar to those that develop in ADHD patients. In these studies, amphetamine was given orally according to a schedule of drug administration that simulated the use of amphetamine in ADHD treatment. These preclinical observations, coupled with preliminary results indicating that adult ADHD patients previously treated with amphetamine have decrements  WIN 35,428-labeled binding potential (BP) that are unlikely to be related to acute effects of amphetamine on the DAT, raise concern that amphetamine treatment of adult ADHD may be associated with a risk of brain dopamine neurotoxicity. The purpose of the proposed research is to determine if the use of amphetamine for the treatment of adult ADHD is associated with a risk of brain dopaminergic neurotoxicity. To this end, positron emission tomography (PET) will be used to measure two structural elements of brain DA axon terminals, the DAT and the vesicular monoamine transporter-type 2 (VMAT-2), in adult ADHD patients previously treated with amphetamine. Findings in this group will be compared to those three other groups: 1) Adults with ADHD who have never received pharmacological treatment for ADHD;2) Adults with ADHD who have been treated with methylphenidate, which is known to lack DA neurotoxic potential;and 3) Age- and gender- matched healthy adults never treated with psychostimulants. All subjects will be adults between the ages of 18 and 40 who have been free of CNS-active drugs (including prescribed stimulants) for at least two weeks (approximately 30 half-lives of amphetamine) prior to PET imaging. We hypothesize that adult, drug-free ADHD patients who have been previously treated with amphetamine will have lasting decreases in the DAT and VMAT-2 compared to all three control groups. If our hypothesis is correct, findings will have broad public health implications for the treatment of ADHD. Findings from this research should also shed additional light on the role of brain DA systems in the pathophysiology and symptoms of ADHD.
The overall goal of the present project, entitled: PET Studies of Amphetamine Treatment of Adult ADHD, is to determine if amphetamine treatment of adult ADHD is associated with the risk of brain dopaminergic neurotoxicity. This concern is based on findings in animals (including non-human primates) and pilot data in humans indicating that amphetamine, as used in the treatment of ADHD, has neurotoxic potential toward brain dopamine neurons.