Two-Photon Imaging of Neuronal Structural Plasticity in Mice during and after Ischemia

To gain insight into the dendritic structural changes that occur within minutes of ischemia, as well as circuit-level plasticity that occurs over days to weeks, it is necessary to devise stroke models for anesthetized transgenic mice that are compatible with in vivo imaging methods. In particular, we are interested in examining events during the first few minutes of ischemia that are associated with a wave of ischemic depolarization. Given the short latency to ischemic depolarization (∼2 min), we have found it necessary to develop ischemia models that can be initiated while the animal is within the two-photon microscope for in vivo imaging. We describe both a global ischemia model and a targeted photothrombotic ischemia model in green fluorescent protein- and yellow fluorescent protein-expressing transgenic mice in which in vivo imaging of dendritic structure can be performed. The advantage of the global model is the speed with which ischemia can be induced and reversed, whereas the focal model lacks precise temporal control but can be targeted to a select region.