Schematic timeline of the ten day protocol for rHI studies showing the assignment of animals from twin pairs to the four experimental conditions.

<p>Animals recovered from surgery for 3 days before the initial exposure to hypoxemia with or without concurrent ischemia (black arrowheads indicate the timing of ischemia). The first gray shaded bar indicates that all groups sustained a 30-minute period of maternal hypoxemia at this time. Note that the twin control for the early HI group and the late HI twin of the rHI group did not sustain ischemia at this time. Thereafter, the early HI group and their twin controls survived for 7 days (i.e., 10 days after surgery). The rHI cases were exposed to a second episode of HI six days after the first HI episode. The corresponding twins for the rHI group were the late HI animals. The rHI group and the late HI cases were both exposed to an insult that involved maternal hypoxemia (gray shaded bar) and ischemia (arrowheads) at 24-hours before brain collection (i.e., 7 days after the initial insult and 10 days after surgery). Hence, the animals in all four groups survived for 10 days after surgery.