Abstract
Imaging of type 1 metabotropic glutamate receptor (mGluR1) has recently become possible using positron emission tomography (PET). To date, little evidence exists on the role of mGluR1 in the pathophysiology of Alzheimer's disease (AD). We aimed to examine mGluR1 availability in patients with AD. Ten patients with AD (78.9 ± 5.9 years) and 12 age-matched volunteers (74.6 ± 2.6 years) underwent PET using an mGluR1 radiotracer. All patients were anti-dementia drug-naive. Volumes-of-interest were placed on the anterior and posterior lobes and vermis in the cerebellum and frontal, parietal, and temporal cortices. The binding potential (BPND) was calculated to estimate mGluR1 availability, and partial volume correction was applied to the BPND values. Mini Mental State Examination (MMSE) scores were also obtained (22.0 ± 4.8). No significant difference was observed in BPND between the AD and control groups in the anterior lobe (p = .30), posterior lobe (p = .95), vermis (p = .96), frontal cortex (p = .61), parietal cortex (p = .59), or temporal cortex (p = .27). No significant correlation was observed between BPND and MMSE scores in the anterior lobe (p = .59), posterior lobe (p = .35), vermis (p = .92), frontal cortex (p = .78), parietal cortex (p = .83), or temporal cortex (p = .82). In conclusions, this study suggests that mGluR1 availability is unchanged in the relatively early stage of AD. However, because regional mGluR1 availability may change with the progression of AD, further longitudinal follow-up is necessary.
Highlights
Imaging of type 1 metabotropic glutamate receptor in living human brains became possible in the early 2010s using positron emission tomography (PET) (Toyohara et al, 2013a; Toyohara et al, 2013b)
No significant difference was observed between the Alzheimer's disease (AD) and control groups in the whole cerebellum (p = .91), anterior lobe (p = .30), posterior lobe (p = .95), vermis (p = .96), frontal cortex (p = .61), parietal cortex (p = .59), or temporal cortex (p = .27)
The objectives of this study were to assess whether mGluR1 availability differs between the AD and control groups and whether mGluR1 availability and Mini Mental State Examination (MMSE) scores are correlated in patients with AD
Summary
Imaging of type 1 metabotropic glutamate receptor (mGluR1) in living human brains became possible in the early 2010s using positron emission tomography (PET) (Toyohara et al, 2013a; Toyohara et al, 2013b). In concordance with the existing knowledge that mGluR1 is predominantly expressed on the dendrites of Purkinje cells facing the synaptic terminals of parallel and climbing fibers (Ferraguti et al, 2008), the first PET imaging of mGluR1 in human volunteers showed that its availability is higher in the cerebellar cortex than the cerebral cortex (Toyohara et al, 2013a; Toyohara et al, 2013b) These findings suggest that alterations in cerebellar mGluR1 expression are closely linked to the pathophysiology of Purkinje cells.
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