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Keywords:

  • brain injury;
  • diffusion tensor imaging;
  • inflammation;
  • manganese-enhanced magnetic resonance imaging;
  • microglia

Abstract

Doxycycline may potentially be a neuroprotective treatment for neonatal hypoxic–ischemic brain injury through its anti-inflammatory effects. The aim of this study was to examine any long-term neuroprotection by doxycycline treatment on cerebral gray and white matter. Hypoxic–ischemic brain injury was induced in 7-day-old rats. Pups were treated with either doxycycline (HI+doxy) or saline (HI+vehicle) by intraperitoneal injection at 1 h after hypoxia–ischemia (HI). At 6 h after HI, MnCl2 was injected intraperitoneally for later manganese-enhanced magnetic resonance imaging (MRI). MRI was performed with diffusion-weighted imaging on day 1 and T1-weighted imaging and diffusion tensor imaging at 7, 21 and 42 days after HI. Animals were killed after MRI on day 42 and histological examinations of the brains were performed. There was a tendency towards lower lesion volumes on diffusion maps among HI+doxy than HI+vehicle rats at 1 day after HI. Volumetric MRI showed increasing differences between groups with time after HI, with less cyst formation and less cerebral tissue loss among HI+doxy than HI+vehicle pups. HI+doxy pups had less manganese enhancement on day 7 after HI, indicating reduced inflammation. HI+doxy pups had higher fractional anisotropy on diffusion tensor imaging in major white matter tracts in the injured hemisphere than HI+vehicle pups, indicating less injury to white matter and better myelination. Histological examinations supported the MRI results. Lesion size on early MRI was highly correlated with final injury measures. In conclusion, a single dose of doxycycline reduced long-term cerebral tissue loss and white matter injury after neonatal HI, with an increasing effect of treatment with time after injury.