Cryo-injury Induced Heart Regeneration in the Axolotl and Echocardiography and Unbiased Quantitative Histology to Evaluate Regenerative Progression

The urodele amphibians, salamanders and newts, represent the phylogenetic group closest to mammals capable of performing complete myocardial regeneration following ventricular resection. The resection model has generated a basic knowledge of the processes involved in cardiac repair. However, the model does not relate well to clinical situations in which tissue damage, apoptosis, necrosis, fibrosis, and hypertrophy are all key detrimental consequences of ischemia-induced myocardial infarctions rather than tissue removal. On the other hand, cryoinjury-induced myocardial infarction resembles ischemia-induced myocardial infarction more closely. Here we provide a detailed description of the cryoinjury procedure in the axolotl (Ambystoma mexicanum), which provides a tool for investigating basic mechanisms in cardiac repair in a tetrapod model. Additionally, we provide quantitative methods for estimating infarction size non-invasively in vivo with echocardiography and for measuring infarction size precisely with unbiased quantitative histology ex vivo.