In a recently developed rodent model for cauda equina/ conus medullaris forms of spinal cord injury, a lumbosacral ventral root avulsion (VRA) injury results in a progressive death of both autonomic and motor neurons (Hoang et al., JCN, 2003). An acute implantation of avulsed lumbosacral ventral roots into the spinal cord protects many of the axotomized neurons against cell death and promotes axonal regeneration by spinal cord neurons into the implanted graft (Hoang et al., SfN Abstract 76.15, 2003). The potential beneficial or detrimental role provided by the glial and microglial responses after a spinal cord injury remains controversial and their response patterns in this injury and repair model are unknown. Here, we investigate the glial and microglial reactions in the rat conus medullaris to a lumbosacral VRA with and without subsequent implantation into the spinal cord. Control rats and rats with an L5-S2 VRA, with and without root implantation, are studied. Rats of the experimental series are studied...