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Abstract
.Animal models of stroke are used extensively to study the mechanisms involved in the acute and chronic phases of recovery following stroke. A translatable animal model that closely mimics the mechanisms of a human stroke is essential in understanding recovery processes as well as developing therapies that improve functional outcomes. We describe a photothrombosis stroke model that is capable of targeting a single distal pial branch of the middle cerebral artery with minimal damage to the surrounding parenchyma in awake head-fixed mice. Mice are implanted with chronic cranial windows above one hemisphere of the brain that allow optical access to study recovery mechanisms for over a month following occlusion. Additionally, we study the effect of laser spot size used for occlusion and demonstrate that a spot size with small axial and lateral resolution has the advantage of minimizing unwanted photodamage while still monitoring macroscopic changes to cerebral blood flow during photothrombosis. We show that temporally guiding illumination using real-time feedback of blood flow dynamics also minimized unwanted photodamage to the vascular network. Finally, through quantifiable behavior deficits and chronic imaging we show that this model can be used to study recovery mechanisms or the effects of therapeutics longitudinally.
Highlights
Stroke is the leading cause of long-term disability and the second leading cause of death worldwide.[1]
The most commonly used animal model of ischemic stroke is occlusion of the middle cerebral artery (MCA), which is usually induced by direct mechanical blocking of blood flow via a suture inserted through the carotid artery.[10,11]
Downloaded From: https://www.spiedigitallibrary.org/journals/Neurophotonics on 10 Nov 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use we show that after nonoptimized photothrombosis there is a significant decline in capillary density immediately surrounding the targeted pial artery compared to before stroke
Summary
Stroke is the leading cause of long-term disability and the second leading cause of death worldwide.[1]. A recent study has shown the ability to perform MCA occlusion in a semiawake setting, the animal preparation is acute and does not allow longitudinal monitoring of stroke progression.[15] Other currently used models of ischemic stroke are through ferric chloride– induced vascular thrombosis,[16] endothelin-1–induced vasoconstriction,[17] or thrombin injection.[18] these models suffer from the drawbacks of using anesthetics, being acute preparations, and requiring invasive surgery without recovery to induce stroke Another common model of ischemic stroke is photothrombosis, which induces ischemic stroke by photoactivation of a photosensitive dye.[19] Illumination of the injected dye with a specific wavelength of light triggers a clotting cascade and leads to thrombosis. As shown through laser speckle contrast imaging (LSCI) and behavioral evaluation, this method leads to the formation of a reliable stroke with a functional deficit, which can be monitored chronically to study recovery mechanisms following stroke or to test the effects of potential therapeutics on the recovery process
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