This review summarises some of the major findings derived from
studies using the model of a glia-depleted environment developed and
characterised in this laboratory. Glial depletion is achieved by
exposure of the immature rodent spinal cord to x-radiation which
markedly reduces both astrocyte and oligodendrocyte populations and
severely impairs myelination. This glia-depleted, hypomyelinated state
presents a unique opportunity to examine aspects of spinal cord
maturation in the absence of a normal glial population. An associated
sequela within 2–3 wk following irradiation is the appearance of
Schwann cells in the dorsal portion of the spinal cord. Characteristics
of these intraspinal Schwann cells, their patterns of myelination or
ensheathment, and their interrelations with the few remaining central
glia have been examined. A later sequela is the development of Schwann
cells in the ventral aspect of the spinal cord where they occur
predominantly in the grey matter. Characteristics of these ventrally
situated intraspinal Schwann cells are compared with those of Schwann
cells located dorsally. Recently, injury responses have been defined in
the glia-depleted spinal cord subsequent to the lesioning of dorsal
spinal nerve roots. In otherwise normal animals, dorsal nerve root
injury induces an astrocytic reaction within the spinal segments with
which the root(s) is/are associated. Lesioning of the 4th lumbar
dorsal root on the right side in irradiated or nonirradiated animals
results in markedly different glial responses with little astrocytic
scarring in the irradiated animals. Tracing studies reveal that these
lesioned dorsal root axons regrow rather robustly into the spinal cord
in irradiated but not in nonirradiated animals. To examine role(s) of
glial cells in preventing this axonal regrowth, glial cells are now
being added back to this glia-depleted environment through
transplantation of cultured glia into the irradiated area. Transplanted
astrocytes establish barrier-like arrangements within the irradiated
cords and prevent axonal regrowth into the cord. Studies using other
types of glial cultures (oligodendrocyte or mixed) are
ongoing.