Role of microglia in postinjury repair and regeneration of the CNS

The functional roles of microglial cells and brain macrophages are currently under intense scientific scrutiny because these cells are known to be critical elements in the central nervous system's response to injury. Of particular interest are the interactions between microglia and injured neurons, since experimental data suggest that microglia and brain macrophages can have neurotrophic, as well as neurotoxic, effects. In this review, we summarize some of the key observations that have given rise to neurotrophic and neurotoxic theories on microglial cell function. At the same time, we also stress our own experiments involving microglial cell transplants into the injured spinal cord-which strongly support the idea that posttraumatic microgliosis and macrophage formation are critical for postinjury tissue repair, neuron regeneration, and associated neuritic outgrowth.