Abstract
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Purpose: The aim of the present study is to evaluate the mGluR5 expression level in an advanced AD mouse model with an mGlu5 specific PET and to validate change of the protein level by histological immunoassays.
Methods: 10-month-old male 5xFAD transgenic mice and age matched male wild type mice were employed. Here, 5xFAD was used as advanced AD model. After administration of [18F]FPEB to anesthetized mice, dynamic PET scan was performed for 90 min (nanoScan, Mediso Medical Imaging Systems, Budapest, Hungary). PET data were reconstructed by 3D OSEM algorithm with 4 iterations and 6 subsets. For attenuation correction, micro-CT imaging was conducted immediately after PET. After 2 days, MR scans were obtained on Agilent 9.4T scanner (Agilent Technologies, Santa Clara, CA, USA). Volume of interests such as hippocampus, striatum and cerebellum were defined on the study-specific brain template. The decay corrected time-activity curves were acquired form VOI and normalized in units of standardized uptake value (SUV). The distribution volume ratio (DVR) was calculated from non-invasive Logan’s graphical analysis. Binding potential (BPND) was then computed as ‘DVR-1’. Voxel-based parametric mapping was also utilized by Logan’s
Methods: Following the PET scan, animals were anesthetized and intracardially perfused with saline. Brain lysates were derived from the hippocampus and cerebellum then homogenizing tissue. Sample homogenate was purified by differential centrifugation to obtain membrane fractions and then used for immunoblotting.
Results: Brain PET imaging revealed that radioactivities in the hippocampus and the striatum were significantly lower in 5xFAD rats compared to control animals. Binding values were also significantly lowered in 5xFAD mice. This decline was validated by immunoblotting of protein isolates from brain tissues, as the mean band density for 5xFAD mice had a lower mGluR5 intensity than for wild type mice. Conclusion: We conclude that mGluR5 levels in 5xFAD mice were down regulated in the limbic system and this change can be successfully quantified by PET.