Distribution and Expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid(AMPA) Receptor Subunits in Moderate Hypoxic Newborn Piglet Brain

Kim, Na Yeon; Kim, Woo Taek

Abstract

PURPOSE: The mechanism of hypoxic damage is mainly intracellular influx of calcium ions through the glutamate ionotropic receptor(NMDA, AMPA/kainate). This study was performed to determine alterations in distribution and expression of AMPA receptor subunits after 1-hour of moderate hypoxia in the newborn piglet brain, in a state of mild to moderate perinatal hypoxic-ischemic encephalopathy.
METHODS
Ten newborn piglets were mechanically ventilated with a mixture of 21% oxygen and 79% nitrous oxide at PaO2 over 80mmHg for 30min. Thereafter, control group(n=5) was ventilated with 21% oxygen for 1-hour, and hypoxic group(n=5) was ventilated with 6% oxygen at PaO2 below 25mmHg for 1-hour. Concentrations of protein, adenosine triphosphate(ATP) and phosphocreatine were determined. The proteins were immunostained with anti-rat glutamate receptor 1(GluR1), anti-rat GluR2/3 and anti-rat GluR4 antibody.
RESULTS
Hypoxia(PaO2 20+/-1mmHg) and acidosis(pH 7.06+/-0.09) developed significantly in the hypoxic group compared to the control group(PaO2 104+/-4mmHg, pH 7.44+/-0.03, respectively, P<0.01). Concentrations of ATP(2.84+/-1.28micromol/kg brain, P<0.05) and phosphocreatine(0.78+/-1.07micromol/kg brain, P<0.001) were significantly reduced compared to the control group(5.04+/-0.25micromol/kg brain, 4.03+/-0.31micromol/kg brain, respectively). The protein contents of GluR1 and GluR2/3 subunits were ordered; hippocampus > cerebral cortex, thalamus, basal ganglia, hypothalamus > white matter, cerebellum, and the protein contents of GluR4 subunits were observed in the cerebellum only. The distribution of GluR1, GluR2/3, and GluR4 subunits between the hypoxic group and control group were similar.
CONCLUSION
GluR1 and GluR2/3 subunits were highly distributed in the hippocampus and cere bral cortex, and GluR4 subunits in the cerebellum. These regions may be the most vulnerable to excitotoxic injury. In addition, AMPA receptor subunits did not change after 1-hour of moderate hypoxia.