artery and forwarded until the tip occludes the origin of the middle cerebral artery, resulting in a cessation of blood flow and subsequent brain infarction in its area of supply. If the suture is removed after a certain interval, reperfusion is achieved (transient MCAO); if the filament is left in place the procedure is suitable as model of permanent MCAO, too. The most common modification is based on Longa (1989) who described filament introduction via the external carotid artery, allowing closure of the access point with preserved blood supply via the common and internal carotid artery to the brain after the removal of the filament. Known pitfalls of this method are insufficient occlusion, subarachnoid hemorrhage , hyperthermia , and necrosis of the ipsilateral extracranial tissue . Filament MCAO is not applicable to all rat strains . Permanent transcranial middle cerebral artery occlusion In this animal model of ischemic stroke the middle cerebral artery (MCA) is surgically dissected and subsequently permanently occluded, e.g. by electrocautery or ligation. Occlusion can be performed on the proximal or distal part of the MCA. In the latter, ischemic damage is restricted to the cerebral cortex. MCAO can be combined with temporal or permanent common carotid artery occlusion. These models require a small craniotomy. Transient transcranial middle cerebral artery occlusion The technique of modeling ischemic stroke by transient transcranial MCAO is similar to that of permanent transcranial MCAO, with the MCA being reperfused after a defined period of focal cerebral ischemia . Like permanent MCAO, craniotomy is required and common carotid artery (CCA) occlusion can be combined. Occluding one MCA and both CCAs is referred to as the three vessel occlusion model of focal cerebral ischemia. Cerebrocortical photothrombosis Photothrombotic models of ischemic stroke use local intravascular photocoagulation of circumscribed cortical areas. After intravenous injection of photosensitive dyes like rose-bengal, the brain is irradiated through the skull via a small hole or a thinned cranial window, leading to photochemical occlusion of the irradiated vessels with secondary tissue ischemia . This approach was initially proposed by Rosenblum and El-Sabban in 1977, and improved by Watson in 1985 in the rat brain. This method has also been adapted for use in mice. See also animal models of stroke References References Ischemia Ischemic stroke Stroke