title: In vivo quantification of dopamine transporters in mice with unilateral 6-OHDA lesions using [11C]methylphenidate and PET.
abstract: Quantification of the binding of [11C]methylphenidate to the dopamine transporter (DAT) using positron emission tomography (PET) is often used to evaluate the integrity of dopaminergic neurons in the striatal regions of the brain. Over the past decade, many genetically engineered mouse models of human disease have been developed and have become particularly useful for the study of disease onset and progression over time. Quantitative imaging of small structures such as the mouse brain is especially challenging. Thus, the aims of this study were (1) to evaluate the accuracy of quantifying DAT binding using in vivo PET and (2) to examine the impact of different methodologies.
  
  
  METHODS
  Eight mice were scanned with [11C]methylphenidate under true or transient equilibrium conditions using a bolus and constant infusion protocol or a bolus injection protocol to evaluate the accuracy of the Logan graphical approach for [11C]methylphenidate imaging in mice. Displacement with unlabeled methylphenidate (0.1, 3 and 10 mg/kg) was used to verify specific binding. In a second experiment, 30 mice were lesioned by injection of 6-hydroxydopamine (6-OHDA) at doses of 0, 2 or 4 μg (n=10) into the right striatum to assess the dose-dependent correlation between the PET signal and dopaminergic degeneration. In addition, we performed test-retest experiments and used ex vivo autoradiography (AR) to validate the effect of partial volume on the accuracy of the [11C]methylphenidate PET quantification in the mouse striatum.
  
  
  RESULTS
  The binding potentials (BPND) calculated from the Logan graphical analysis under transient equilibrium conditions (1.03±0.1) were in excellent agreement with those calculated at true equilibrium (1.07±0.1). Displacement of specific binding with 0.1, 3 and 10mg/kg methylphenidate resulted in 38%, 77% and 81% transporter occupancy in the striatum. Intra-striatal injections of 6-OHDA caused a dose-dependent decrease in the specific binding of [11C]methylphenidate to the DAT in the striatum. The BPND was reduced by 49% and 61% after injection with 2 and 4 μg of 6-OHDA, respectively. The test-retest reproducibility was 6% in the healthy striatum and 27% in the lesioned striatum. In addition, only a small (15%) difference was found between the [11C]methylphenidate DVR-1 values determined by PET and AR on the healthy side, and no differences were observed on the lesioned side.
  
  
  CONCLUSIONS
  The present work demonstrates for the first time that [11C]methylphenidate PET is useful for the quantification of striatal dopamine transporters at the dopaminergic nerve terminals in the mouse striatum; therefore, this marker may be used as a biomarker in genetically engineered mouse models of neurodegenerative disorders. However, only changes resulting in greater than 10% differences in BPND values can reliably be detected in vivo.
authors.affiliation: Department of Preclinical Imaging and Radiopharmacy, Laboratory for Preclinical Imaging and Imaging Technology of the Werner Siemens-Foundation, Eberhard-Karls University of Tübingen, Germany. kristina.fischer@med.uni-tuebingen.de
authors.forename: Kristina
authors.initials: K
authors.lastname: Fischer
authors.forename: Vesna
authors.initials: V
authors.lastname: Sossi
authors.forename: Andreas
authors.initials: A
authors.lastname: von Ameln-Mayerhofer
authors.forename: Gerald
authors.initials: G
authors.lastname: Reischl
authors.forename: Bernd J
authors.initials: BJ
authors.lastname: Pichler
mesh_terms: D000465:Algorithms; D000818:Animals; D001345:Autoradiography; D002531:Cerebellum / Q000000981:diagnostic imaging; D003342:Corpus Striatum / Q000000981:diagnostic imaging; D015259:Dopamine Agents; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007839:Functional Laterality; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008774:Methylphenidate; D051379:Mice; D008810:Mice, Inbred C57BL; D016627:Oxidopamine / Q000633:toxicity*; D049268:Positron-Emission Tomography / Q000379:methods*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012984:Software
chemical_list: D015259:Dopamine Agents; D050483:Dopamine Plasma Membrane Transport Proteins; D008774:Methylphenidate; D016627:Oxidopamine