Metabolic action of N-methyl-D-aspartate in newborn rat brain ex vivo: 31p magnetic resonance spectroscopy

Abstract

N-methyl-D-aspartate (NMDA) is an agonist used to identify neuronal receptive sites for dicarboxylic amino acid neurotransmitters; NMDA receptors are implicated in neuronal damage of ischemic or hypoglycemic origin in newborns although involved mechanisms remain to be identified. In the present study, 31P magnetic resonance spectroscopy with fast (6/min) data acquisition was used in newborn rat brain slices to measure changes of intracellular phosphocreatine and nucleotide triphosphate levels following extracellular NMDA applications. The rapid exhaustion of phosphocreatine stores in 50% of the total population of brain cells was induced in all cases by application of NMDA (30-45 s, 25-100 mM). It was not reproduced by other excitatory agents: potassium ions (24.6 mM, 4 min), isobutylxanthine (1mM), muscarine (10 mM), serotonin (0.1 mM) or substance P (10 microM). Such an effect of NMDA was not modified after tetrodotoxin (1 microM) and was reduced by extracellular 2-amino-5-phosphonovalerate (50 microM) or magnesium ions (2.2 mM). However it did develop during NMDA-induce neuronal excitations and was reversible within 10-30 min. This action of NMDA was followed by an irreversible decrease of phosphorus metabolites if mitochondrial creatine kinase and adenosine triphosphatase were decoupled by atractyloside (50 microM). Experiments revealed a link between selective NMDA action at neuronal plasma membranes, neurotoxicity and energy production by mitochondria.