title: Hypoxia-tolerant neonatal CA1 neurons: relationship of survival to evoked glutamate release and glutamate receptor-mediated calcium changes in hippocampal slices.
abstract: Neurons in the neonatal mammalian brain survive greater degrees of hypoxic stress than those in the mature brain. To investigate how developmental changes in glutamate receptor-mediated neurotoxicity contribute to this difference, we measured hypoxia-evoked glutamate release, glutamate receptor contribution to hypoxia-evoked intracellular calcium changes, and survival of hypoxia-/ischemia-sensitive CA1 neurons in rat hippocampus. Glutamate release was measured by a fluorescence assay, calcium changes in CA1 neurons with fura-2, and cell viability using Nissl and fluorescence staining with calcein-AM/ethidium homodimer, all in 300-micron thick hippocampal slices from 3-30 post-natal day (PND) rats. Glutamate released from PND 3-7 slices during hypoxia (PO2 = 5 mmHg) was only one third that of PND 18-22 slices. In PND 3-7 slices, survival of CA1 neurons after 5 min of hypoxia and 6 h of recovery was significantly greater than in PND 18-22 slices (viability indices 0.60 and 0.28, respectively, (p < 0.05). Five min of anoxia significantly altered Nissl staining pattern and morphology of CA1 neurons in PND 18-22 but not PND 3-7 slices. Hypoxia (PO2 = 5 mm Hg) caused three to five times greater increases in [Ca2+]i in PND 18-22 slices than in PND 3-7 slices (p < 0.001). During re-oxygenation, [Ca2+]i returned to baseline in PND 3-7 slices, but remained elevated in PND 18-22 slices. Glutamate receptor-mediated calcium changes in CA1 during hypoxia were 33% and 62% of the total calcium change in PND 3-7 and PND 18-22 CA1, respectively. We conclude that survival of CA1 neurons in PND 3-7 slices following hypoxic stress is associated with smaller increases and enhanced recovery of [Ca2+]i, less accumulation of glutamate, and less glutamate receptor-mediated calcium influx than in PND 18-22 slices.
authors.affiliation: Department of Anesthesia, University of California, San Francisco 94143-0542, USA. phil_bickler@quickmail.ucsf.edu
authors.forename: P E
authors.initials: PE
authors.lastname: Bickler
authors.forename: B M
authors.initials: BM
authors.lastname: Hansen
mesh_terms: D000375:Aging / Q000378:metabolism / Q000473:pathology; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology*; D002470:Cell Survival / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D016202:N-Methylaspartate; D002118:Calcium