In vivo excitotoxicity induced by ouabain, a Na+/K+-ATPase inhibitor.
The susceptibility of immature rat brain to neurotoxicity of N-methyl-D-aspartate (NMDA) has provided a widely used paradigm to study excitotoxicity relevant to acute neurodegenerative diseases such as cerebral ischemia. In this study, excitotoxicity was induced via injection of ouabain (1 mM/0.5 microL), a Na+/K+ -ATPase-inhibitor, into neonatal rat brain and compared with NMDA injection. The aim of the study was to induce excitotoxicity secondary to cellular membrane depolarization, thereby more closely mimicking the pathophysiologic processes of ischemia-induced brain injury where NMDA-receptor overstimulation by glutamate follows, not precedes, membrane depolarization. Na+/K+ -ATPase-inhibition caused an acute, 40% +/- 8% decrease of the apparent diffusion coefficient (ADC) of water, as measured using diffusion-weighted magnetic resonance imaging (MRI), and resulted in infarctlike lesions as measured using T2-weighted MRI and histology up to 2 weeks later. Localized one- and two-dimensional 1H-magnetic resonance spectroscopy (MRS) demonstrated that the early excitotoxic diffusion changes were not accompanied by an overall metabolic disturbance. Furthermore, 31P-MRS demonstrated that energy depletion is not a prerequisite for ADC decrease or excitotoxic cell death. Treatment with the NMDA-antagonist MK-801 (1 mg/kg) attenuated the volume of tissue exhibiting a decreased ADC (P < 0.005), demonstrating that the ouabain-induced injury is indeed excitotoxic in nature. The authors argue that, compared with NMDA-injection, ouabain-induced excitotoxicity elicits more appropriate glutamate-receptor overstimulation and is better suited to detect relevant neuroprotection in that it is more sensitive to attenuation of synaptic glutamate levels.
Veldhuis
Wouter B
WB
Department of Experimental in vivo NMR, Image Sciences Institute, Rudolf Magnus Institute for Neurosciences, University Medical Center, Utrecht, The Netherlands. veldhuis@invivonmr.uu.nl
van der Stelt
Mario
M
Delmas
Florence
F
Gillet
Brigitte
B
Veldink
Gerrit A
GA
Vliegenthart
Johannes F G
JF
Nicolay
Klaas
K
Bär
Peter R
PR
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D001921:Brain / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D038524:Diffusion Magnetic Resonance Imaging; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004734:Energy Metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D009498:Neurotoxins / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D010758:Phosphorus; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D009498:Neurotoxins; D010758:Phosphorus; D010042:Ouabain; D016291:Dizocilpine Maleate; D000254:Sodium-Potassium-Exchanging ATPase