Clinical neuropsychopharmacology S69 Breier A, 2003, Efficacy of olanzapine and olanzapine- fluoxetine combination in the treatment of bipolar I depression. Arch Gen Psychiatry 60, 1079–1088. P.3.08 Effects of methylphenidate on 18-F fallypride binding in patients with ADHD and healthy controls N. del Campo 1 ° , Y. Hong 2 , D. Izquierdo 2 , J. van der Aart 1 , S.R. Chamberlain 1 , J. Dowson 1 , T.D. Fryer 2 , T.W. Robbins 3 , B.J. Sahakian 1 , U. Muller 1 . 1 University of Cambridge, Dept of Psychiatry, Cambridge, United Kingdom; 2 Addenbrooke’s Hospital, Wolfson Brain Imaging Centre, Cambridge, United Kingdom; 3 University of Cambridge, Behaviour and Clinical Neuroscience Institute, Cambridge, United Kingdom Purpose of study: Attention-deficit hyperactivity disorder (ADHD) is a debilitating disorder characterised by prob- lems with inattention, impulsivity, and/or hyperactivity. Dysfunction of the fronto-striatal dopamine system has been heavily implicated in the neurobiology of the disor- der [1]. Neuropsychological deficits on tests of prefrontal cognitive functioning, namely sustained attention, motor inhibition, working memory and planning, have been shown in studies of children and adults with the disorder. Symptoms and neurocognitive deficits in ADHD are ame- liorated by drugs acting on the dopaminergic system, no- tably the psychostimulant methylphenidate. Radio-ligand positron emission tomography represents a fruitful tool for elucidating relationships between neurotransmitter abnor- malities and cognitive deficits; and for exploring pharma- cological treatment mechanisms. The aims of the study were to investigate methylphenidate-induced changes in D2/D3 receptor availability in adults with ADHD and healthy controls, and to examine relationships with performance on tests of prefrontal cognitive functioning. Methods: N = 16 adults with ADHD and N = 16 healthy controls were entered into the study after providing written informed consent. Groups were matched for age, education, and IQ (National Adult Reading Test). Effects of a single dose (0.5 mg/kg) of methylphenidate were assessed by means of [18F] fallypride positron emission tomography (PET) in a within-subjects double- blind placebo controlled design. Neuropsychological tests of sustained attention, working memory, and impulse control were administered. Striatal regions of interest were defined on coregistered MR images. Region of interest tracer concentrations were partial volume corrected with the Rousset algorithm [2] and the resultant time- activity curves were corrected for radioactive decay. Binding potentials were determined through fitting with a simplified reference tissue model. Effects of methylphenidate on binding potentials and cognition were evaluated using repeated-measures ANOVA (significance set at p < 0.05; drug condition as within-subject factor; clinical group as between-subject factor). Results: In the interim analysis (N = 6 patients, N=6 controls) methylphenidate significantly reduced binding potentials bilaterally in the caudate and putamen (all p < 0.05, both pre- and post-commissural). These effects were similar in patients and controls and there was no evidence for significant drug treatment by group interactions (all p > 0.40). Beneficial effects of methylphenidate on cognitive performance were identified, including speeding of response latencies on a test of sustained attention (p < 0.05). Conclusion: Despite worldwide increasing prescrip- tions and popularity of methylphenidate there is incom- plete understanding of the neurobiological mechanisms behind symptoms of ADHD and psychostimulant- induced improvement. These preliminary data indicate that methylphenidate increases free striatal dopamine levels similarly in healthy volunteers and in adults with ADHD. Ongoing analysis is exploring the effects of methylphenidate on [18F] binding potential in the striatum in the complete sample and relationships between dopamine receptor binding and (i) cognitive deficits identified in ADHD patients; and (ii) beneficial cognitive effects of methylphenidate. Voxel-wise maps will be produced to explore binding potential in extra-striatal regions. It is hoped that such research will ultimately contribute to improved treatment algorithms for ADHD and related disorders. Reference(s) [1] Chamberlain SR, Robbins TW, Sahakian BJ, 2007, The neurobiology of attention-deficit/hyperactivity disorder. Biol Psychiatry 61(12), 1317−9. [2] Rousset OG, Ma Y, Evans AC, 1998, Correction for partial volume effects in PET: principle and validation. J Nucl Med 39(5), 904−11. P.3.09 The predictive value of neurocognitive decision-making for heavy alcohol use in a longitudinal, prospective study A. Goudriaan 1 ° , E.R. Grekin 2 , K.J. Sher 2 . 1 Academic Medical Center University of Amsterdam, Department of Psychiatry, Amsterdam, The Netherlands; 2 University of Missouri, Department of Clinical Psychology, Columbia, USA Background: There is a lack of predictive studies, investigating the real life predictive value of instruments