A novel mouse model of pediatric cardiac arrest and cardiopulmonary resuscitation reveals age-dependent neuronal sensitivities to ischemic injury

Abstract

Background: Pediatric sudden cardiac arrest (CA) is an unfortunate and devastating condition, often leading to poor neurologic outcomes. However, little experimental data on the pathophysiology of pediatric CA is currently available due to the scarcity of animal models.

New method: We developed a novel experimental model of pediatric cardiac arrest and cardiopulmonary resuscitation (CA/CPR) using postnatal day 20-25 mice. Adult (8-12 weeks) and pediatric (P20-25) mice were subjected to 6min CA/CPR. Hippocampal CA1 and striatal neuronal injury were quantified 3 days after resuscitation by hematoxylin and eosin (H&E) and Fluoro-Jade B staining, respectively.

Results: Pediatric mice exhibited less neuronal injury in both CA1 hippocampal and striatal neurons compared to adult mice. Increasing ischemia time to 8 min CA/CPR resulted in an increase in hippocampal injury in pediatric mice, resulting in similar damage in adult and pediatric brains. In contrast, striatal injury in the pediatric brain following 6 or 8 min CA/CPR remained extremely low. As observed in adult mice, cardiac arrest causes delayed neuronal death in pediatric mice, with hippocampal CA1 neuronal damage maturing at 72 h after insult. Finally, mild therapeutic hypothermia reduced hippocampal CA1 neuronal injury after pediatric CA/CPR.

Comparison with existing method: This is the first report of a cardiac arrest and CPR model of global cerebral ischemia in mice.

Conclusions: Therefore, the mouse pediatric CA/CPR model we developed is unique and will provide an important new tool to the research community for the study of pediatric brain injury.

Keywords: Cardiac arrest; Global cerebral ischemia; Hypothermia; Juvenile; Pediatric.

Figure 1. Adult hippocampal neuronal damage greater than pediatric

Representative photomicrographs of hippocampal CA1 neurons in adult mice following 6 min cardiac arrest (A) and 8 min cardiac arrest (B) and pediatric mice following 6 min cardiac arrest (C) and 8 min cardiac arrest (D) and stained with H & E 3 days later. E) Quantification of ischemic neurons in the CA1 region of the hippocampus 3 days after CA/CPR, indicating significantly less injured neurons in pediatric mice that underwent 6 min cardiac arrest. * P < 0.05

Figure 2. Adult striatal neuronal damage greater than pediatric

Representative fluorescent photomicrographs of striatal neurons in adult mice following 6 min cardiac arrest (A) and 8 min cardiac arrest (B) and pediatric mice following 6 min cardiac arrest (C) and 8 min cardiac arrest (D) and stained with FluoroJade B 3 days later. E) Quantification of ischemic neurons in the striatum 3 days after CA/CPR, indicating significantly less injured neurons in pediatric mice that underwent 6 min cardiac arrest. * P < 0.05

Figure 3. Delayed neuronal death of hippocampal CA1 neurons following 8 min cardiac arrest in pediatric mice

Representative photomicrographs of hippocampal CA1 neurons from 24 hour (A), 3 days (B) and 7 days (C) after resuscitation and stained with H & E. D) Quantification of ischemic neurons in CA1 region of hippocampus at different points after CA/CPR. E) Quantification of density of ischemic and live neurons in the CA1 region of the hippocampus at 3 and 7 days after resuscitation. * P < 0.01 compared with 3 days.

Figure 4. Mild therapeutic hypothermia significantly reduces CA1 neuronal injury in pediatric mice

Representative photomicrophraphs of hippocampal CA1 neurons from pediatric mice exposed to 8 min normothermic cardiac arrest (A) and 8 min cardiac arrest followed by 30 min mild hypothermia (B). C) Quantification of ischemic CA1 neurons 3 days after CA/CPR, indicating significant reduction in neuronal injury in mice treated with post-arrest hypothermia. P < 0.05