Glial reactions in a rodent cauda equina injury and repair model

In the adult rat, an avulsion injury of lumbosacral ventral roots results in a progressive and pronounced loss of the axotomized motoneurons. A subsequent acute implantation of an avulsed ventral root into the spinal cord has neuroprotective effects. However, it has not been known whether a surgical implantation of an avulsed ventral root into the spinal cord for neural repair purposes affects intramedullary glial and microglial reactions. Here, adult female Sprague-Dawley rats underwent a unilateral L5-S2 ventral root avulsion injury with or without acute implantation of the L6 ventral root into the spinal cord. At 4 weeks postoperatively, immunohistochemistry using primary antibodies to GFAP (astrocytes), Ox-42 (microglia), and ED-1 (macrophages) was performed at the L6 spinal cord segment, and quantified using densitometry. Our results show that a lumbosacral ventral root avulsion injury induces an activation of astrocytes, microglia, and macrophages in the ventral horn. Interestingly, an acute implantation of an avulsed root into the white matter does not significantly affect the activation of glial cells or macrophages in the ventral horn. We speculate that neuroprotective and axonal growth promoting benefits of the combined glial and microglial/ macrophage responses may outweigh their potential negative effects, as previous studies have shown that implantation of avulsed roots is a successful strategy in promoting reinnervation of peripheral targets.