[1] NP Bechtereva Inst Human Brain, St Petersburg 197376, Russia
[2] Forschungszentrum Julich, Inst Neurosci & Med, INM 5 Nucl Chem, D-52425 Julich, Germany
[3] Univ Clin Cologne, Inst Radiochem & Expt Mol Imaging, D-50937 Cologne, Germany
[4] Max Planck Inst Metab Res, D-50931 Cologne, Germany