New insights into the brain – Monitoring glial cells in the intact neocortex

In addition to neurons the brain contains several types of glial cells. While neurons are responsible for fast signal transmission and processing, the functional roles of glial cells have largely remained elusive, in part because methods to investigate these cells in the intact brain were lacking. The development of novel staining methods and in vivo application of two-photon fluorescence microscopy has now enabled to visualize glial cells with high spatial and temporal resolution in the intact neocortex and to study their behavior. Using this combined approach, wave-like oscillations of the intracellular calcium concentration were resolved in the network of astrocytes. These waves might be involved in long-range signaling in the neocortex. In addition, microglial cells, the defense cells of the brain, were found to be not at rest in the healthy brain; they continually survey the surrounding parenchyma with their motile processes showing an astonishingly high level of structural plasticity that far exceeds what is known from other cell types. Moreover, microglial cells took immediate protective actions upon rupture of a blood vessel by targeting and shielding the injured site with their processes. These new results highlight the importance of glial cells as fundamental elements of the brain, both under normal physiological conditions as well as following brain damage such as for example caused by a stroke.