Growth of adult rat retinal ganglion cell neurites on astrocytes

Abstract

Astrocytes, as well as Schwann cells (SC), can provide suitable substrata for embryonic neurites during development, but their abilities to support adult regenerating neurites have not been directly compared. The aim of the present study was to determine the ability of astrocytes to promote adult rat retinal ganglion cell (RGC) regeneration in vitro and to compare this to previously determined growth on the surface of Schwann cells. We prepared Type I astrocytes (Raff et al: J. Neurosci. 3:1289–1300, 1983) from perinatal rats. These were subcultured and maintained in either a serum‐free medium for at least 2 weeks (stellate astrocytes with little immunoreactivity for laminin) or in serum containing medium for 7 to 10 days (flat and polygonal astrocytes with immunoreactivity for laminin). Stellate astrocytes might therefore represent mature astrocytes in vivo (Ard and Bunge: J. Neurosci. 8:2844–2858, 1988), while flat astrocytes might resemble immature brain astrocytes (Liesi et al: J. Cell Biol. 96:920–924, 1983). Adult RGC survival and axonal regrowth on these glia populations was compared to that observed on different SC populations, as previously reported (Baehr and Bunge: Exp. Neurol. 106:27–40, 1989). Both astrocyte populations (either flat or stellate astrocytes) did not enhance RGC survival. Stellate astrocytes were less effective in supporting RGC axon regeneration than flat astrocytes. When these date were compared to RGC survival and axon growth on SC (Baehr and Bunge: Exp. Neurol. 106:27–40, 1989) only “ctivated” mature SC populations were superior to astrocytes in enhancing RGC survival and neurite regrowth. These results suggest 1) that astrocytes and “immature” SC are similar in their ability to support RGC survival; 2) “activated” mature SC populations are significantly better than astrocytes and “immature” SC in enhancing RGC survival and neurite growth; 3) stellate (“mature”) astrocytes, although permissive for regrowing axons, are not a favorable substrate for regenerating adult RGC neurites, nor do they effectively support RGC survival.