PERSPECTIVES ON AXONAL REGENERATION IN THE MAMMALIAN CNS

In the CNS of mammals, axonal regeneration is limited by inhibitory in fluences 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 non-permissive for a xonal growth, contribute to the inhibitory nature of the mammalian CNS . Furthermore, mechanisms for effective removal or neutralization of i nhibitory components of cell debris are lacking in the mature mammalia n CNS. However, in a permissive environment, mammalian CNS axons are a ble to regrow, to recognize target areas and to re-establish functiona l synapses with target neurones. Moreover, recent observations suggest that guiding molecules, like those required for axon guidance in the developing CNS, become expressed after lesions. Regenerating CNS axons seem to be able to recognize such guidance cues. Thus, even regenerat ing CNS axons of mammals might ultimately succeed in re-establishing t opographically ordered functional synapses in their target regions.