In Vivo 2-Photon Imaging of Fine Structure in the Rodent Brain

The recent application of 2-photon microscopy to biological specimens has allowed investigators to examine individual synapses within live animals. The gain in resolution over conventional in vivo imaging techniques has been several orders of magnitude. We outline steps for the preparation and maintenance of animals for 2-photon microscopy of fine brain structure. We discuss the in vivo resolution of the method and the ability to image blood flow and synaptic structure in vivo. Applications of in vivo 2-photon microscopy include the study of synapse turnover in adult animals under normal conditions and during pathology such as stroke. In the case of stroke, 2-photon imaging has revealed marked swelling of dendrites and loss of spines within minutes of ischemic onset. Surprisingly, restoration of blood flow during reperfusion was associated with a return of relatively normal structure. Over longer time scales, 2-photon imaging revealed elevated rates of synaptogenesis within peri-infarct tissues recovering from stroke. These results provide an example of how high-resolution in vivo microscopy can be used to provide insight into both the acute pathology and recovery from stroke damage.