Cerebral Oxygenation of the Cortex and Striatum Following Normobaric Hyperoxia and Mild Hypoxia in Rats by EPR Oximetry Using Multi-Probe Implantable Resonators

Abstract

Multi-site electron paramagnetic resonance (EPR) oximetry, using multiprobe implantable resonators, was used to measure the partial pressure of oxygen (pO₂) in the brains of rats following normobaric hyperoxia and mild hypoxia. The cerebral tissue pO₂ was measured simultaneously in the cerebral cortex and striatum in the same rats before, during, and after normobaric hyperoxia and mild hypoxia challenges. The mean baseline tissue pO₂ values were not significantly different between the cortex and striatum.During 30 min of 100%O₂ inhalation, a statistically significant increase in tissue pO₂ of all four sites was observed, however, the tissue pO₂ of the striatum area was significantly higher than in the forelimb area of the cortex. Brain pO₂ significantly decreased from the baseline value during 15 min of 15% O₂ challenge.No differences in the recovery of the cerebral cortex and striatum pO₂ were observed when the rats were allowed to breathe 30% O₂. It appears that EPRoximetry using implantable resonators can provide information on pO₂ under the experimental conditions needed for such a study. The levels of pO₂ that occurred in these experiments are readily resolvable bymulti-siteEPRoximetrywithmulti-probe resonators. In addition, the ability to simultaneouslymeasure the pO₂ in several areas of the brain provides important information that could potentially help differentiate the pO₂ changes that can occur due to global or local mechanisms.