Astrocyte, the star avatar: redefined.

Until recently, the neuroscience community held the belief that glial cells such as astrocytes and oligodendrocytes functioned solely as "support" cells of the brain. In this role, glial cells simply provide physical support and housekeeping functions for the more important cells of the brain, the neurons. However, this view has changed radically in recent years with the discovery of previously unrecognized and surprising functions for this underappreciated cell type. In the past decade or so, emerging evidence has provided new insights into novel glial cell activities such as control of synapse formation and function, communication,cerebrovascular tone regulation, immune regulation and adult neurogenesis. Such advances in knowledge have effectively elevated the role of the astrocyte to one that is more important than previously realized. This review summarizes the past and present knowledge of glial cell functions that has evolved over the years, and has resulted in a new appreciation of astrocytes and their value in studying the neurobiology of human brain cells and their functions. In this review, we highlight recent advances in the role of glial cells in physiology, pathophysiology and, most importantly, in adult neurogenesis and "stemness", with special emphasis on astrocytes.