Abstract
Background
Therapeutic hypothermia is partially protective for neonatal hypoxic–ischemic encephalopathy (HIE). Damage to the white matter tracts is highly associated with adverse outcomes after HIE, but the effectiveness and optimal duration of hypothermia to attenuate axonal injury are unclear.
Methods
Near-term fetal sheep were randomized to sham control or cerebral ischemia for 30 min with normothermia or cerebral hypothermia from 3 to either 48 or 72 h. Sheep were killed after 7 days. SMI-312-labeled axons and myelin basic protein were quantified in the intragyral white matter of the first and second parasagittal gyri.
Results
Ischemia was associated with reduced axonal and myelin area fraction (p < 0.05); loss of axonal and myelin linearity (p < 0.05); and thin, sparse axons, with spheroids, compared to dense, linear morphology in sham controls and associated with induction of microglia in an amoeboid morphology. Both ischemia–48 h hypothermia and ischemia–72 h hypothermia improved axonal area fraction and linearity (p < 0.05), although abnormal morphological features were seen in a subset. Microglial induction was partially suppressed by ischemia–48 h hypothermia, with a ramified morphology.
Conclusions
These data suggest that therapeutic hypothermia can alleviate post-ischemic axonopathy, in part by suppressing secondary inflammation.
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Acknowledgements
This study was funded by The Health Research Council of New Zealand (grant numbers: 16/003, 17/601) and the Marsden Fund (grant number: 17-UOA232). J.O.D. holds a Sir Charles Hercus Fellowship from the Health Research Council of New Zealand (16/003). K.Q.Z. was supported by a University of Auckland Doctoral Scholarship.
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K.Q.Z., L.B., A.J.G., and J.O.D. conceptualized and designed the study. J.O.D. undertook experiments. K.Q.Z., V.D., C.A.L., J.L.A., and Y.H. developed linearity analysis. K.Q.Z., V.D., and J.M.D. contributed to immunohistochemistry and microscopy. K.Q.Z. conducted data analysis, preparation of figures, and drafted the manuscript. All authors approved the final version of the manuscript.
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Zhou, K.Q., Draghi, V., Lear, C.A. et al. Protection of axonal integrity with 48 or 72 h of cerebral hypothermia in near-term fetal sheep. Pediatr Res 88, 48–56 (2020). https://doi.org/10.1038/s41390-019-0475-8
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DOI: https://doi.org/10.1038/s41390-019-0475-8
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