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Anesthesiology ; 131(5): 1077-1091, 2019 11.
Article in English | MEDLINE | ID: mdl-31436548

ABSTRACT

BACKGROUND: Early postnatal exposure to general anesthetics may interfere with brain development. We tested the hypothesis that isoflurane causes a lasting disruption in myelin development via actions on the mammalian target of rapamycin pathway. METHODS: Mice were exposed to 1.5% isoflurane for 4 h at postnatal day 7. The mammalian target of rapamycin inhibitor, rapamycin, or the promyelination drug, clemastine, were administered on days 21 to 35. Mice underwent Y-maze and novel object position recognition tests (n = 12 per group) on days 56 to 62 or were euthanized for either immunohistochemistry (n = 8 per group) or Western blotting (n = 8 per group) at day 35 or were euthanized for electron microscopy at day 63. RESULTS: Isoflurane exposure increased the percentage of phospho-S6-positive oligodendrocytes in fimbria of hippocampus from 22 ± 7% to 51 ± 6% (P < 0.0001). In Y-maze testing, isoflurane-exposed mice did not discriminate normally between old and novel arms, spending equal time in both (50 ± 5% old:50 ± 5% novel; P = 0.999), indicating impaired spatial learning. Treatment with clemastine restored discrimination, as evidenced by increased time spent in the novel arm (43 ± 6% old:57 ± 6% novel; P < 0.001), and rapamycin had a similar effect (44 ± 8% old:56 ± 8% novel; P < 0.001). Electron microscopy shows a reduction in myelin thickness as measured by an increase in g-ratio from 0.76 ± 0.06 for controls to 0.79 ± 0.06 for the isoflurane group (P < 0.001). Isoflurane exposure followed by rapamycin treatment resulted in a g-ratio (0.75 ± 0.05) that did not differ significantly from the control value (P = 0.426). Immunohistochemistry and Western blotting show that isoflurane acts on oligodendrocyte precursor cells to inhibit both proliferation and differentiation. DNA methylation and expression of a DNA methyl transferase 1 are reduced in oligodendrocyte precursor cells after isoflurane treatment. Effects of isoflurane on oligodendrocyte precursor cells were abolished by treatment with rapamycin. CONCLUSIONS: Early postnatal exposure to isoflurane in mice causes lasting disruptions of oligodendrocyte development in the hippocampus via actions on the mammalian target of rapamycin pathway.


Subject(s)
Anesthetics, Inhalation/adverse effects , Hippocampus/drug effects , Isoflurane/adverse effects , Myelin Sheath/drug effects , Neurogenesis/drug effects , Oligodendroglia/drug effects , Age Factors , Anesthetics, Inhalation/administration & dosage , Animals , Animals, Newborn , Female , Hippocampus/cytology , Hippocampus/physiology , Isoflurane/administration & dosage , Male , Mice , Mice, Inbred C57BL , Myelin Sheath/physiology , Neurogenesis/physiology , Oligodendroglia/physiology , Spatial Behavior/drug effects , Spatial Behavior/physiology
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