Anoxic depolarization mediates acute damage independent of glutamate in neocortical brain slices.
An important but poorly understood event associated with ischemia is anoxic depolarization (AD), a sudden and profound depolarization of neurons and glia in cortical and subcortical gray matter. Leao first measured the AD as a wave of electrical silence moving across the cerebral cortex in 1947 and noted its similarity to spreading depression (SD). SD is harmless when coursing through normoxic cortical tissue as during migraine aura. However for 3-4 h following focal ischemia, the additional metabolic stress arising from recurring SD in the penumbra expands the ischemic core, so SD blockade is potentially beneficial therapeutically. In the present study, we measured intrinsic optical signals (IOSs) to monitor anoxic depolarization in submerged rat neocortical slices during O2/glucose deprivation (OGD). After approximately 6 min of OGD, the AD was imaged as a focal increase in light transmittance which then propagated across neocortical gray at approximately 2 mm/min. Although the slice was globally stressed, the AD always initiated focally, sometimes at multiple sites. Its propagation was coincident with a transient negative shift in the extracellular potential, the electrical signature of AD. Acute damage to neocortex (measured as a delayed decrease in LT and as a loss of the evoked field potential) followed only where the AD had propagated, so it is the combined metabolic demands of AD and OGD that acutely damages all layers of the neocortex. Glutamate receptor antagonists (2 mM kynurenate or 25 microM AP-5/10 microM CNQX) did not block AD initiation, slow its propagation or prevent post-AD damage. This study shows that acute ischemic damage is greatly exacerberated by AD during metabolic stress and that glutamate receptor antagonists are not protective. Using this slice model, therapeutically tolerable drugs that block the AD and SD can be investigated.
Department of Anatomy and Cell Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
C R
CR
Jarvis
T R
TR
Anderson
R D
RD
Andrew
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D002545:Brain Ischemia / Q000473:pathology / Q000503:physiopathology*; D013181:Cortical Spreading Depression; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D018698:Glutamic Acid / Q000172:deficiency*; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology; D007736:Kynurenic Acid / Q000494:pharmacology; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D019579:Neocortex / Q000187:drug effects* / Q000473:pathology / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000187:drug effects / Q000502:physiology
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D018698:Glutamic Acid; D016202:N-Methylaspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D007736:Kynurenic Acid