Ischemic Brain Damage in Rats following Cardiac Arrest Using a Long-Term Recovery Model

Abstract

A model is described in which transient complete cerebral ischemia is induced in rats by intracardiac injection of potassium chloride. The animals were intubated and mechanically ventilated with a nitrous oxide/oxygen (70:30) mixture. Cardiac arrest was achieved following a brief period of ventricular fibrillation. After 5–6 min, the circulation was restored by cardiopulmonary resuscitation and partial exchange transfusion. Local CBF (LCBF) during ischemia and cardiac resuscitation was studied by injection of [¹⁴C]iodoantipyrine into the right auricle at various periods during cardiac arrest, and was subsequently analyzed by autoradiography. No radioactive tracer could be visualized in any brain structure, demonstrating the absence of CBF during the cardiac standstill. LCBF was also studied at 5 min and 6.5 h after cardiac resuscitation. Five minutes of recirculation showed an increase in blood flow in all brain structures studied, ranging between 130 and 400% of control values. After 6.5 h of recirculation, the CBF was decreased in 13 of 24 brain structures by 20–50%, concomitantly with the depressed rate of glucose utilization found in 15 brain structures. The neocortical, hippocampal, and striatal concentrations of labile phosphates, lactate, pyruvate, phosphocreatine, glucose, and glycogen were measured 5 min after cardiac arrest. Extensive energy failure and elevation of lactate levels were observed and were similar to earlier reported values. One week following recovery from the ischemic insult, the animals were perfusion-fixed with formaldehyde. The brains were embedded in paraffin, sub serially sectioned, and stained with cresyl violet/acid fuchsin. Histopathological changes were assessed by light microscopy as the number of acidophilic or pyknotic neurons. Morphological changes were observed in the hilus of the dentate gyrus, the hippocampal CA₁ and subicular regions, the dorsal and lateral septum, the olfactory tubercle, the primary olfactory cortex, the entorhinal cortex, the amygdaloid nuclei, and the reticular nucleus of the thalamus. The distribution of the morphological changes suggests a transsynaptic mechanism, causing neuronal necrosis primarily in the limbic brain areas.