Glial cell proliferation in the spinal cord after dorsal rhizotomy or sciatic nerve transection in the adult rat

Proliferation of glial cells is one of the hallmarks of CNS responses to ne ural injury. These responses are likely to play important roles in neuronal survival and functional recovery after central or peripheral injury. The b oundary between the peripheral nervous system (PNS) and CNS in the dorsal r oots, the dorsal root transitional zone (DRTZ), marks a distinct barrier fo r growth by injured dorsal root axons. Regeneration occurs successfully in the PNS environment, but ceases at the PNS-CNS junction. In order to unders tand the role of different glial cells in this process, we analysed the pro liferation pattern of glial cells in central (CNS) and peripheral (PNS) par ts of the dorsal root and the segmental white and grey spinal cord matter a fter dorsal rhizotomy or sciatic nerve transection in adult rats 1-7 days a fter injury. Monoclonal antibody MIB-5 or antibodies to bromodeoxyuridine w ere used to identify proliferating cells. Polyclonal antibodies to laminin were used to distinguish the PNS and CNS compartments of the dorsal root. D orsal root lesion induced glial cell proliferation in the CNS as well as PN S beginning at 1 day, with peaks from 2 to 4 days postoperatively. After sc iatic nerve injury, cell proliferation occurred only in the CNS. was minima l at day, and peaked from 2 to 4 days postoperatively. Double immunostainin g with specific glial cell markers showed that after dorsal root transectio n 60% of the proliferating cells throughout the postoperative period examin ed were microglia, 30% astrocytes and 10% unidentified in the CNS, while in the PNS 40% were Schwann cells, 40% macrophages and 20% unidentified. Afte r sciatic nerve injury virtually all proliferating cells were microglia. Th ese findings indicate that non-neuronal cells in the CNS and PNS are extrem ely sensitive to the initial changes which occur in the degenerating dorsal root axons, and that extensive axonal degeneration is a pre-requisite fur astroglial and Schwann cell, but not microglial cell, proliferation.