The early reactions of non-neuronal cells to brain injury.

One of the great goals in neuroscience research has been to improve the recovery of the mammalian central nervous system after damage. Considerable effort has gone into learning about changes that occur in the brain after injury, and the extent to which these changes are protective or injurious in themselves. This review deals with the responses of non-neuronal cells in the central nervous system that occur from the first seconds to hours after brain injury. This is a very large topic, and it has been necessary to select only some aspects for consideration. Emphasis is placed on three cell populations: astrocytes, brain macrophages, and endothelial cells. For each cell type, we can distinguish responses related to properties existing before the lesion, and responses reflecting the expression of new properties. Where possible, interactions between these cell types are discussed, but the complex and important interactions with the immune system are mentioned only briefly. Different classes of injury are associated with different arrays of cellular responses; the injury of ischemic stroke is discussed in sufficient detail to emphasize the complexity and interactions of cellular responses. Only some of the cellular responses to injury have obvious benefits, and others may fail to support or may inhibit recovery.