Anesthetic protection of neurons injured by hypothermia and rewarming: roles of intracellular Ca2+ and excitotoxicity.
BACKGROUND
Mild hypothermia is neuroprotective after cerebral ischemia but surgery involving profound hypothermia (PH, temperature less than 18°C) is associated with neurologic complications. Rewarming (RW) from PH injures hippocampal neurons by glutamate excitotoxicity, N-methyl-D-aspartate receptors, and intracellular calcium. Because neurons are protected from hypoxia-ischemia by anesthetic agents that inhibit N-methyl-D-aspartic acid receptors, we tested whether anesthetics protect neurons from damage caused by PH/RW.


METHODS
Organotypic cultures of rat hippocampus were used to model PH/RW injury, with hypothermia at 4°C followed by RW to 37°C and assessment of cell death 1 or 24 h later. Cell death and intracellular Ca were assessed with fluorescent dye imaging and histology. Anesthetic agents were present in the culture media during PH and RW or only RW.


RESULTS
Injury to hippocampal CA1, CA3, and dentate neurons after PH and RW involved cell swelling, cell rupture, and adenosine triphosphate (ATP) loss; this injury was similar for 4 through 10 h of PH. Isoflurane (1% and 2%), sevoflurane (3%) and xenon (60%) reduced cell loss but propofol (3 μM) and pentobarbital (100 μM) did not. Isoflurane protection involved reduction in N-methyl-D-aspartate receptor-mediated Ca influx during RW but did not involve γ-amino butyric acid receptors or KATP channels. However, cell death increased over the next day.


CONCLUSIONS
Anesthetic protection of neurons rewarmed from 4°C involves suppression of N-methyl-D-aspartate receptor-mediated Ca overload in neurons undergoing ATP loss and excitotoxicity. Unlike during hypoxia/ischemia, anesthetic agents acting predominantly on γ-aminobutyric acid receptors do not protect against PH/RW. The durability of anesthetic protection against cold injury may be limited.
University of California, San Francisco, CA, USA. bicklerp@anesthesia.ucsf.edu
Philip E
PE
Bickler
Daniel E
DE
Warren
John P
JP
Clark
Pablo
P
Gabatto
Maren
M
Gregersen
Heather
H
Brosnan
D000704:Analysis of Variance; D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D018698:Glutamic Acid / Q000187:drug effects / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D007035:Hypothermia / Q000378:metabolism* / Q000473:pathology; D000860:Hypoxia / Q000473:pathology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D018696:Neuroprotective Agents / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism; D017694:Rewarming
D000777:Anesthetics; D018696:Neuroprotective Agents; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D002118:Calcium