Neuroscience

Ischemic stroke is a leading cause of mortality and chronic disability worldwide, underscoring the need for reliable and accurate animal models to study this disease’s pathology, molecular mechanisms of injury, and treatment approaches. As most clinical strokes occur in regions supplied by the middle cerebral artery (MCA), several experimental models have been developed to simulate an MCA occlusion (MCAO), including transcranial MCAO, micro- or macro-sphere embolism, thromboembolisation, photothrombosis, Endothelin-1 injection, and – the most common method for ischemic stroke induction in murine models – intraluminal MCAO. In the intraluminal MCAO model, the external carotid artery (ECA) is permanently ligated, after which a partially-coated monofilament is inserted and advanced proximally to the common carotid artery (CCA) bifurcation, before being introduced into the internal carotid artery (ICA). The coated tip of the monofilament is then advanced to the origin of the MCA and secured for the duration of occlusion. With respect to other MCAO models, this model offers enhanced reproducibility regarding infarct volume and cognitive/functional deficits, and does not require a craniotomy. Here, we provide a detailed protocol for the surgical induction of unilateral transient ischemic stroke in mice, using the intraluminal MCAO model.

Graphic abstract:

Overview of the intraluminal monofilament method for transient middle cerebral artery occlusion (MCAO) in mouse.

Rat transient middle cerebral artery occlusion (tMCAO) model is one of the most commonly used animal models in ischemic stroke studies. In the model, increasing safety and efficacy of therapeutic agent administration, such as stem cells and drugs directly to the ischemic brain using the internal carotid artery (ICA) is essential, because using the common carotid artery (CCA) for injection can close CCA completely and cause many complications after tMCAO surgery. Also, the pterygopalatine artery (PPA) is an arterial branch of the ICA that supplies blood circulation of the external part of the brain and removing the blood circulation of the PPA is required for more complete induction of ischemia to the brain. Herein, we present the insertion of intra-arterial catheter in the ICA via the external carotid artery (ECA) after the PPA in rats subjected to tMCAO surgery.

The photothrombotic model of stroke is commonly used in research as it allows the ischemic infarct to be targeted to specific regions of the cortex with high reproducibility and well-defined infarct borders. Unlike other models of stroke, photothrombosis allows the precise size and location of infarct to be tightly controlled with minimal surgical invasion. Photothrombosis is induced when a circulating photosensitive dye is irradiated in vivo, resulting in focal disruption of the endothelium, activation of platelets and occlusion of the microvasculature (Watson et al., 1985; Dietrich et al., 1987; Carmichael, 2005). The protocols here define how photothrombosis can be specifically targeted to the sensorimotor forelimb cortex of rat with high reproducibility. Detailed methods on rat cortical tissue processing to allow for accurate analysis of stroke volume and stereotactic determination of the precise cortical region of ischemic damage are provided.