Animals were were anesthetized with sodium pentobarbital injection (i.p., 100 μg/g). As the animals did not have hind paw pinch withdraw reflex, the chest cavity was opened and heparin (0.2ml; 1,000 units/ml) was injected into the left ventricle, followed by transcardial perfusion. Mice were perfused with at least 150 mL 40 °C phosphate-buffered saline (0.1 M PBS, pH = 7.4) at a rate of approximately 40 ml/min, effectively draining the animal of blood via a blunt 18-ga needle inserted to the left ventricle , and blood was drained by cutting the inferior vena cava. The perfusion solution was switched to 150 mL ice cold Zamboni’s fixative (15% picric acid, 2% paraformaldehyde in PBS, pH = 7.4) to fix the tissue. During the entire procedure, extreme care was taken to ensure that no part of the heart or intestine became dry in an effort to minimize autofluorescence during later examination. After the perfusion, the mice heart was removed and post fixed overnight.