[Visualization of synapse-glia dynamics].

Increasing evidence indicates the importance of neuron-astrocyte interaction in synaptic function. However, structural evidence is scarce compared to abundant information from electrophysiological studies. Meticulous studies using serial electron microscopic technique in hippocampal CAI and cerebellum provided the earliest knowledge about three-dimensional close relationship between synapses and glial processes. Nevertheless, morphological observation of synapse-glia interaction in live tissues is important to support the idea of astrocytic effects on synaptic transmission. Recently several methods enabled live imaging of astrocytes as well as dendritic spines in acute slices and tissues cultures. The techniques to visualize live astrocytes in brain tissues include transgenic mice (GFAP promoter-GFP), sulforhodamine 101 (SR101) application to the surface of neocortex in vivo, ballistic labeling with EGFP plasmid and recombinant viruses (Semliki Forest virus A7 or adenovirus expressing EGFP). Live astrocytes in brain tissues showed higher motility than neuronal structures in the vicinity of dendrites. Astrocytes extend or retract their numerous fine processes and change their volume or shape in a complex manner. Simultaneous observation of filopodia/spines and astrocytes revealed that filopodia/spines often contact with astrocytic processes and that they showed coordinated morphological dynamics in adult and developmental stage, suggesting possible functions of synapse-astrocyte contacts. Indeed, the local regulation of filopodial stabilization and maturation into spines by astrocytic contacts was reported. In the next step any astrocytic structural changes around mature synapses correlated with plastic change of synaptic efficacy, such as long-term potentiation, should be investigated. Structural relationship between axon terminals and astrocytic processes should also be revealed. Furthermore, in vivo time-lapse imaging of synapseastrocyte pairs will soon be accomplished, as techniques of in vivo two-photon imaging showed remarkable progress recently.