Reconstruction of the glial environment of a photochemically induced lesion in the rat spinal cord by transplantation of mixed glial cells.

It is becoming increasingly apparent that the astrocytic environment is critical to the normal development and functioning of the CNS, and that acute injury to the spinal cord causes destruction of glial cells in addition to neurones and axons. The aims of this study were to assess the viability of reconstructing the astrocytic environment of a cystic spinal cord lesion by transplantation of glial cells and to examine the effect of the transplanted cells on meningeal cell invasion and revascularisation of the lesion and on axonal regeneration. Neonatal rat and kitten mixed glial cells and the CG-4 rat O-2A progenitor cell line were transplanted into a lesion produced in the dorsal funiculus of the rat spinal cord by photochemical infarction. The animals were killed 4 weeks after injury, their cords examined with light and electron microscopy and compared with control animals that were injected with medium alone. Transplantation of all three preparations resulted in increased numbers of astrocytes in the area of Wallerian degeneration cranial to the lesion and within the cyst. Mixed glial cell cultures prepared from neonatal rat forebrain contained cells with in vitro characteristics of type-1 astrocytes, and produced dense clusters of astrocytes that were surrounded by meningeal cells, resulting in a fragmented environment in the cyst. In contrast, glial cell cultures prepared from kitten forebrain and the CG-4 cell line produced cells that filled the cyst with a loose network of fine processes and reduced meningeal cell infiltration of the lesion. The CG-4 cell line significantly increased the density of blood vessels in the centre of the lesion and the number of spared axons present dorsal to the lesion, but none of the preparations significantly increased the number of axons regenerating at the caudal end of the lesion. We conclude that O-2A progenitor-derived astrocytes are more suitable for reconstruction of the glial environment of a cystic lesion in the rat spinal cord than 'type-1 like' astrocytes and would therefore be the cell of choice to engineer to produce factors that promote axonal regeneration.