Evaluation of Altered Glutamatergic Activity in a Piglet Model of Hypoxic-Ischemic Brain Damage Using 1H-MRS

Abstract

Background and Objective. The excitotoxicity of glutamate (Glu) is a major risk factor for neonatal hypoxic-ischemic brain damage (HIBD). The role of excitatory amino acid transporter 2 (EAAT2) and the α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionic acid receptor (AMPAR) subunit GluR2 in mediating the Glu excitotoxicity has always been the hotspot. This study was aimed at investigating the early changes of glutamate metabolism in the basal ganglia following hypoxia-ischemia (HI) in a neonatal piglet model using 1H-MRS. Methods. Twenty-five newborn piglets were selected and then randomly assigned to the control group (n=5) and the model group (n=20) subjected to HI. HI was induced by blocking bilateral carotid blood flow under simultaneous inhalation of a 6% oxygen mixture. 1H-MRS data were acquired from the basal ganglia at the following time points after HI: 6, 12, 24, and 72 h. Changes in protein levels of EAAT2 and GluR2 were determined by immunohistochemical analysis. Correlations among metabolite concentrations, metabolite ratios, and the protein levels of EAAT2 and GluR2 were investigated. Results. The Glu level sharply increased after HI, reached a transient low level of depletion that approached the normal level in the control group, and subsequently increased again. Negative correlations were found between concentrations of Glu and EAAT2 protein levels (Rs=−0.662, P<0.001) and between the Glu/creatine (Cr) ratio and EAAT2 protein level (Rs=−0.664, P<0.001). Moreover, changes in GluR2 protein level were significantly and negatively correlated with those in Glu level (the absolute Glu concentration, Rs=−0.797, P<0.001; Glu/Cr, Rs=−0.567, P=0.003). Conclusions. Changes in Glu level measured by 1H-MRS were inversely correlated with those in EAAT2 and GluR2 protein levels following HI, and the results demonstrated that 1H-MRS can reflect the early changes of glutamatergic activity in vivo.