2.2 Germinal matrix hemorrhage (GMH) model

The general procedure for inducing GMH in unsexed P7 rats using collagenase infusion was performed as previously described (Lekic et al., 2015). In brief, pups were anesthetized with isoflurane (3.0% induction, 1.0–1.5% maintenance) on a stereotaxic frame. The skin was incised on the longitudinal plane to expose the bregma. A burr hole (1mm) was drilled on the skull (1.6mm lateral, 1.5mm anterior to the bregma), and a 27-gauge needle was inserted (2.7mm deep from the dura) for collagenase (0.3 unites of clostridial collagenase VII-S, Sigma-Aldrich, MO) infusion (3μL/3min) using a 10μL Hamilton syringe (Hamilton Co, Reno, NV, USA) guided by a microinfusion pump (Harvard Apparatus, Holliston, MA). The core temperature was maintained at 37°C. After infusion, the needle was left in place for additional 10 minutes to prevent possible leakage and then was withdrawn at rate of 0.5mm/min. After infusion, the pups were then placed back to the dams until sacrifice.