NMDA receptor-mediated differential laminar susceptibility to the intracellular Ca2+ accumulation induced by oxygen-glucose deprivation in rat neocortical slices.
Slices of somatosensory cortex taken from immature rats on postnatal day (P)7-14 were labeled with fura-2. Intracellular Ca2+ concentration ([Ca2+]i) was monitored in identified pyramidal cells as the ratio of fluorescence intensities (RF340/F380) during oxygen-glucose deprivation. The RF340/F380 ([Ca2+]i) of individual pyramidal cells was monitored in each of the cortical layers II-VI simultaneously. Neurons in all neocortical layers exhibited significant increases in [Ca2+]i that varied with the duration of oxygen-glucose deprivation. Individual neurons responded to oxygen-glucose deprivation with abrupt increases in [Ca2+]i after various latencies. The ceiling level of the [Ca2+]i increase differed from cell to cell. Neurons in layer II/III showed significantly greater increases in [Ca2+]i than those in layers IV, V, or VI. Kynurenic acid, a nonselective glutamate receptor antagonist, and bicuculline, a selective gamma-aminobutyric acid (GABA)A receptor antagonist, suppressed the intracellular Ca2+ accumulation induced by oxygen-glucose deprivation in all neocortical layers examined. After kynurenic acid, but not after bicuculline, there was no longer a differential [Ca2+]i increases in layer II/III. Both 2-amino-5-phosphonopentanoic acid (AP5), a selective N-methyl-D-aspartate (NMDA) receptor antagonist, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, strongly suppressed the intracellular Ca2+ accumulation induced by oxygen-glucose deprivation in all layers. The laminar difference in terms of the [Ca2+]i increases was abolished by AP5, but not by CNQX. These results indicate that layer II/III cells are the most prone to oxygen-glucose deprivation-induced intracellular Ca2+ accumulation, and that this is primarily mediated by NMDA receptors. Thus, layer II/III neurons would be more likely to suffer cellular Ca2+ overload and excitotoxicity during ischemia than layer IV-VI cells. Such a differential laminar vulnerability might play an important role in determining the pathological characteristics of the immature cortex and its sequelae later in life.
Fukuda
A
A
Department of Physiology, Nagoya City University Medical School, Nagoya, Aichi 467, Japan.
Muramatsu
K
K
Okabe
A
A
Shimano
Y
Y
Hida
H
H
Fujimoto
I
I
Nishino
H
H
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D016257:Fura-2; D058787:GABA-A Receptor Antagonists; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D007736:Kynurenic Acid / Q000494:pharmacology; D019579:Neocortex / Q000187:drug effects / Q000502:physiology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D013003:Somatosensory Cortex / Q000187:drug effects / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D007736:Kynurenic Acid; D005947:Glucose; D002118:Calcium; D016257:Fura-2; D001640:Bicuculline