A reproducible experimental model of focal cerebral ischemia in the cat

In the past experimental methods used for producing focal cerebral ischemia have had considerable difficulty with regard to reproducibility of the size of the infarcted region. In this study we have developed an experimental model which enables us to consistently produce focal regions of cerebral ischemia (resulting in infarction) which vary little in size in a number of animals. Thirty-seven cats (3–4 kg b. wt.) anesthetized with chlorolose and urethane were used. Physiologic monitoring and adjustments maintained arterial food values as follows: pCO₂ 27–35 Torr, pO₂ 100–150 Torr, pH ± 7.4, glucose 200 mg%, hematocrit > 25. The left middle cerebral artery was exposed via a transorbital approach and occluded for 1–2 h with and without left and/or both carotid artery occlusion. Sixteen hours following the ischemic episode, the animals were sacrificed and sections of fresh brain tissue were processed for vital staining using 1% tetrazolium solution. With this method normal brain areas appear dark red, ischemic regions (without infarction) appear gray and irreversibly infarcted areas appear pinkish-white. The volumetric dimensions of the lesioned area were measured using a planimeter. The same tissue was also evaluated histologically by means of standard histopathologic techniques on paraffin-embedded material. Infarcted areas as delineated macroscopically by the tetrazolium correlated well with the light microscopic findings. Ten animals subjected to a 2-h occlusion of the left middle cerebral artery (LMCA) and both carotid arteries resulted in a reproducible infarct which was 3.2 ± 0.7 ml in volume. This represents 13.3 ± 2.9 % of the total volume of both cerebral hemispheres (above the level of the inferior colliculus). This experimental procedure was used to yield reproducible regions of focal cerebral ischemia in a subsequent study involving the use of flourocarbon emulsion to reverse the ischemic process and prevent permanent neurological damage with infarction. Neurological manifestations of permanent cerebral ischemia were assessed using a clinical scale developed in this model.