Assistant Professor University of Colorado School of Medicine University of Colorado Denver School of Medicine Aurora, Colorado, United States
Background: Hypoxic ischemic encephalopathy (HIE) due to perinatal global cerebral ischemia (GCI) leads to significant morbidity and mortality. Current GCI models do not fully mimic the global nature of HIE, and the effect of oxygen levels during resuscitation on long-term outcomes remains underexplored. We have developed a neonatal rat model of global cerebral ischemia to test the hypothesis that 21% oxygen resuscitation yields better synaptic function than 100% oxygen. Objective: Develop a new rodent model of HIE for improved translational outcomes. Design/Methods: Global cerebral ischemia was induced using cardiac arrest in intubated post-natal day 10 rats via intravenous 0.5M potassium chloride. Following 12-min of asystole, cardiopulmonary resuscitation (CPR) was performed with chest compressions and intravenous epinephrine. Resuscitation was performed using 21% or 100% oxygen. Whole blood samples from the left ventricle of rats in the 100% oxygen group and analyzed them 30 minutes after reperfusion. Neuronal injury was assessed 3 days after GCI by Fluorojade staining. To evaluate hippocampal CA1 synaptic plasticity, we stimulated the Schaffer Collateral pathway and assessed long-term potentiation (LTP) 14 days post-GCI through extracellular recordings. We measured the increase in field excitatory post-synaptic potential (fEPSP) slope 60 minutes after a theta-burst stimulation. Results are presented as mean±SD. Results: Blood gas analysis 30 minutes post-GCI showed a pH of 6.7±0.14, compared to 7.3±0.05 in sham rats (n=3, p=0.02). Lactate levels increased 30 minutes after GCI (10.3±1.4 mmol/L vs. 2.4±0.4 mmol/L in sham, n=3, p=0.03), as did troponin (GCI: 8.1±2.3 ng/ml vs. Sham 1.2±0.4 ng/ml, n=3, p=0.04). Fluorojade staining revealed neuronal cell death in the hippocampus and striatum at 3 days post-GCI. To assess cognitive function, we evaluated hippocampal LTP 14 days post-GCI. In the 100% oxygen resuscitation group, LTP was 186±38% compared to the sham group (n=7), set at 100%. LTP was impaired 14 days post-GCI (106±21%, n=5, p=0.01). In the 21% oxygen resuscitation group, LTP in the sham group was 156±37% (n=4) versus 161±21% (n=4) post-GCI. LTP in the 21% oxygen GCI group was improved compared to the 100% group (p=0.04).
Conclusion(s): These findings illustrate neuronal cell death and hippocampal dysfunction following neonatal GCI. This innovative model enables the comparison of long-term functional outcomes resulting from resuscitation with varying FiO2 levels. Subsequent studies will expand upon these findings by assessing cognitive and affective outcomes during the juvenile developmental stage.
