Author : Jackie Lam
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (11 download)
Book Synopsis The Relationship of Metabotropic Glutamate Receptor Type 5 (MgluR5) Availability with Hypometabolism in Mesial Temporal Lobe Epilepsy by : Jackie Lam
Download or read book The Relationship of Metabotropic Glutamate Receptor Type 5 (MgluR5) Availability with Hypometabolism in Mesial Temporal Lobe Epilepsy written by Jackie Lam and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "[18F]FDG positron emission tomography (PET) imaging in mesial temporal lobe epilepsy (MTLE) patients identifies glucose hypometabolism in the epileptic focus and beyond, including the temporal neocortex. However, the mechanisms underlying this phenomenon are still poorly understood. It is thought disruptions of glutamate cycling, which is coupled to glucose utilization, may be related. Metabotropic glutamate receptor 5 (mGluR5) is a G-protein coupled receptor that shows upregulation in immunohistochemistry studies of hippocampi resected from MTLE patients. However, ex vivo studies are limited as they are conducted in drug-resistant patients needing surgery and convey information only on the seizure focus. [11C]ABP688 is a PET radioligand specific for the allosteric site of mGluR5, allowing for non-invasive in vivo whole brain quantification of mGluR5 availability. In this study, we determined if [11C]ABP688 binding abnormalities are more specific and focal than hypometabolism within the epileptic focus of MTLE patients and whether [11C]ABP688 binding abnormalities can be detected at a higher magnification in different hippocampal subfields as described in a immunohistochemistry study by Kandratavicius et al., 2013. Thirty one unilateral MTLE patients (13 right; 24 female; 40±14 yrs) and 30 healthy controls (12 female; 47±18 yrs) underwent structural magnetic resonance imaging and PET imaging with injection of [11C]ABP688; a subset of 15 patients also underwent [18F]FDG PET. Patients were classified as "normal volume" (NV) or "hippocampal atrophy" (HA) based on their degree of hippocampal volume and asymmetry. We compared partial volume corrected [11C]ABP688 non-displaceable binding potentials (BPND) between patients and controls in regions of interest (ROIs) in mesial temporal structures, temporal neocortex, and hippocampal subfields. For the subset of patients with [18F]FDG data, we performed asymmetry analyses and correlated [11C]ABP688 BPND and [18F]FDG standard uptake value ratios (SUVr) to determine if changes in one are associated with changes in the other. Finally, we compared mGluR5 availability with mGluR5 immunoreactivity (IR) in hippocampal subfields.mGluR5 availability was reduced in the hippocampal head and amygdala of patients compared to controls, with reductions also seen in the temporal neocortex in HA patients only. Patients who were seizure-free following surgery had lower [11C]ABP688 BPND in the ipsilateral hippocampal head and entorhinal cortex than patients who were not seizure-free. [18F]FDG hypometabolism was widespread in ROIs ipsilateral to the focus, while [11C]ABP688 BPND reductions were more prominent and more focal in the hippocampal head. Correlation between [11C]ABP688 BPND and [18F]FDG SUVr in presumably healthy supramarginal gyrus was low, while trends for positive correlations in both ipsilateral and contralateral mesial temporal and cortical regions were found, significant only in contralateral entorhinal cortex and in ipsilateral insula and temporal lobe. [11C]ABP688 PET subfield analyses demonstrated that in vivo reduced mGluR5 availability contrasted to reported ex vivo increased mGluR5 IR. This study is among the first to characterize mGluR5 availability in MTLE patients using [11C]ABP688 PET. [11C]ABP688 BPND reductions in the epileptic focus contrasting to previously reported increased mGluR5 IR in resected tissue suggests that overexpressed mGluR5 in the focus might be internalized or subject to other conditions impacting the binding of the radioligand to the allosteric site. Prominent and focal [11C]ABP688 BPND abnormalities supports mGluR5 imaging as a more specific biomarker for the seizure focus than hypometabolism that may help to predict post-surgical success. Trends for positive association between [18F]FDG SUVr and mGluR5 availability within the MTLE network might further support post-synaptic glutamatergic neurotransmission modulation underlying hypometabolism in MTLE." --