Glutamate-mediated injury in focal cerebral ischemia: the excitotoxin hypothesis revised.
Neuronal injury following focal cerebral ischemia is widely attributed to the excitotoxic effects of glutamate. However, critical analysis of published data on glutamate toxicity in vitro and the comparison of these data with in vivo release of glutamate and the therapeutic effect of glutamate antagonists raises doubts about a neurotoxic mechanism. An alternative explanation for glutamate-mediated injury is hypoxia due to peri-infarct spreading depression-like depolarizations. These depolarizations are triggered in the core of the ischemic infarct and spread at irregular intervals into the peri-infarct surrounding. In ischemically uncompromised tissue, the metabolic workload associated with spreading depression is coupled to an increase in blood flow and oxygen supply, assuring maintenance of oxidative respiration. In the penumbra region of focal ischemia, the hemodynamic constraints of collateral blood circulation prevail the adequate adjustment of oxygen delivery, leading to transient episodes of relative tissue hypoxia. The hypoxic episodes cause a suppression of protein synthesis, a gradual deterioration of energy metabolism and a progression of irreversibly damaged tissue into the penumbra zone. The generation of peri-infarct spreading depressions and the associated metabolic workload can be suppressed by NMDA and non-NMDA antagonists. As a result, the penumbral inhibition of protein synthesis and the progressing energy failure is also prevented, and the volume of ischemic infarct decreases. Interventions to improve ischemic resistance should therefore aim at improving the oxygen supply or reducing the metabolic workload in the penumbra region.
Hossmann
K A
KA
Department of Experimental Neurology, Max-Planck-Institute for Neurological Research, Colgne, Germany.
D000818:Animals; D002545:Brain Ischemia / Q000150:complications / Q000188:drug therapy / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers; D015220:Calcium Channels / Q000502:physiology; D002560:Cerebrovascular Circulation; D013181:Cortical Spreading Depression; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates / Q000378:metabolism* / Q000633:toxicity; D018698:Glutamic Acid; D006801:Humans; D002534:Hypoxia, Brain / Q000209:etiology / Q000517:prevention & control; D051379:Mice; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D009498:Neurotoxins / Q000633:toxicity*; D010101:Oxygen Consumption; D011817:Rabbits; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D009419:Nerve Tissue Proteins; D009498:Neurotoxins; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D002118:Calcium