MYELIN FROM PERIPHERAL AND CENTRAL-NERVOUS-SYSTEM IS A NONPERMISSIVE SUBSTRATE FOR RETINAL GANGLION-CELL AXONS

In the CNS of mammals axonal regeneration is limited by inhibitory inf luences of the glial and extracellular environment, Myelin-associated inhibitors of neurite growth as well as some properties of so called ' 'reactive astrocytes'' which make the environment nonpermissive for ax onal growth contribute to the inhibitory nature of the mammalian CNS. In contrast, the PNS is supportive of regeneration and Schwann cell su rfaces and Schwann-cell-derived extracellular matrix provide suitable substrates for regenerating axons in vivo and in vitro. However, as th e results presented here indicate, myelin derived from normal and axot omized sciatic nerves is a nonpermissive substrate for axonal regrowth . Addition of laminin to either CNS or PNS myelin or freezing of the m yelin, however, allows reproducibly axonal growth. Membrane preparatio ns from CNS or PNS tissue on the other hand allow axon outgrowth from retinal explants when adhesive substrates (e.g., polylysin) are availa ble. This suggests that inhibitors of neurite growth are present in my elin from the CNS and PNS. Growth supportive substrates, which are pre sent in large quantities after PNS but not after CNS injury, can overc ome nonpermissive substrate properties. (C) 1995 Academic Press, Inc.