[In vivo measurements of astrocyte dynamics]

Evidence for astrocytic participation of neuronal signal processing has cumulated in recent years. In particular, large and long-lasting cytosolic calcium surges in astrocytes, which may result in neurotransmitter release from the astrocytes, have been described in in vivo preparations. While the mechanisms for astrocytic calcium events have been extensively studied in vivo, their existence and functions in the intact brain (i.e. in vivo condition) have just started to be addressed. With the recent progress in genetics and molecular biology, it is now possible to generate gene-manipulated animals that are targeted to assess neuron-glia interaction questions. As we gain molecular tools to study neuron-glia interaction, there is an increasing need to verify in vivo experiments' findings in in vivo experimental preparations. Three physiological methods that can assess contribution of glial cells in vivo are discussed: (1) intracellular recording from a single astrocyte to record the membrane potential fluctuation; (2) multi-channel extracellular recordings to monitor mass activity of neuronal dynamics in gene-manipulated animals; (3) optical imaging using two-photon microscopy to monitor calcium dynamics in astrocytes. Combination of these methods will hopefully lead to a new development in the field of neuron-glia biology.