409 - A novel neonatal rat model of global cerebral ischemia model reveals post-ischemic deficits in hippocampal long-term potentiation.

Poster Number: 409
Publication Number: 409.237

ANDRA L. DINGMAN, University of Colorado Anschutz Medical Campus, Aurora, CO, United States; Erika Tiemeier, Anesthesiology Department at Anschutz, Denver, CO, United States; Jose J. Vigil, University of Colorado School of Medicine, Denver, CO, United States; Crystal Minjarez, University of Colorado Anschutz Medical Campus, Denver, CO, United States; Nidia Quillinan, University of Colorado, Anschutz Medical Campus, Aurora, CO, United States; Robert M. Dietz, University of Colorado School of Medicine, Aurora, CO, United States

Background:
Neonatal global cerebral ischemia (GCI) often leads to poor neurologic outcomes, including learning and memory deficits. Previous neonatal ischemia models have not modeled GCI and reperfusion that occurs in human neonates leading to hypoxic ischemic encephalopathy. Using a novel murine model of neonatal cardiac arrest (CA), we investigate the mechanism of ischemia-induced cognitive deficits and recovery. Long-term potentiation (LTP) is a well-accepted cellular model of learning and memory and has been extensively studied following ischemia in the hippocampus. 

Objective: We hypothesize that our novel GCI model will result in LTP impairment at delayed time points following CA.

Design/Methods:
Post-natal day 10 male rats were subjected to 14-min CA and cardiopulmonary resuscitation (CA/CPR). Mice were intubated and jugular access was obtained prior to injection of potassium chloride (0.5ml of 0.5M solution) to induce asystole. The ventilator is off during asystole. Following 14 minutes of asystole, CPR was performed with chest compressions and epinephrine with return of spontaneous resuscitation within 3 minutes. Temperature is maintained at 37oC throughout the experiment. Blood gas measurements were performed by collecting left ventricular whole blood samples 30 minutes after CA/CPR and analyzed immediately using an iStat machine. The cognitive outcome of memory function was measured using LTP. LTP was measured in acute hippocampal slices following a theta-burst stimulation (TBS, 40 pulses 100Hz). Increase in field excitatory post-synaptic potential (fEPSP) slope 60 min after TBS was analyzed as a measurement of LTP. Results reported as mean±SD.

Results:
In total 10/14 rats survived CA/CPR. Blood gas analysis 30 min after CA/CPR revealed pH 6.7±0.14 compared to 7.3±0.05 in sham rats (n=3, p=0.02). In addition, lactate was increased 30 min following GCI (10.3±1.4 mmol/L vs 2.4±0.4 mmol/L in sham, n=3, p=0.03), as was troponin (GCI: 8.1±2.3 ng/ml vs Sham 1.2±0.4 ng/ml, n=3, p=0.04). To assess cognitive function, hippocampal LTP was assessed 14 days following GCI. In sham mice, LTP was 179±45% (n=5) of baseline (set to 100%) 14 days following surgery. In contrast, LTP was impaired 14 days after GCI (106±20%, n=5, p=0.01 compared to sham mice).
Conclusion(s):
This is the first report of a CA/CPR model in a neonatal rodent. We show that this model results in profound acidosis and systemic organ injury following CA/CPR which leads to cognitive dysfunction.  This neonatal GCI model is unique and will provide an important new tool to the research community for the study of neonatal GCI.