Damage to the adult CNS often leads to persistent deficits due to the inability of mature axons to regenerate after injury. Mounting evidence suggests that the glial environment of the adult CNS, which includes inhibitory molecules in CNS myelin as well as proteoglycans associated with astroglial scarring, might present a major hurdle for successful axon regeneration. Here, we evaluate the molecular basis of these inhibitory influences and their contributions to the limitation of longdistance axon repair and other types of structural plasticity. Greater insight into glial inhibition is crucial for developing therapies to promote functional recovery after neural injury.The nervous system has the remarkable ability to adapt and respond to various stimuli, ranging from physiological experiences associated with learning and memory, to pathological insults such as traumatic injury, stroke or neurodegenerative diseases. In addition to plasticity at the functional level, nervous system responses might also occur in the form of structural remodelling. In vivo imaging studies have shown that sensory experience can drive the formation and elimination of synapses, and that these changes might underlie the adaptive remodelling of neural circuits 1,2 . Similarly, neural injury is often accompanied by a transient period of anatomical remodel ling in the form of local sprouting at the lesion site 3 . However, although many CNS neurons can survive for years after axotomy, the severed axons ultimately fail to regenerate beyond the lesion site, in contrast to those in the PNS or embryonic nervous system. Recent evidence is beginning to reveal intriguing parallels between some of the molecular mechanisms that affect the different forms of structural plasticity, including both short-range remodelling and long-distance axon regrowth. Therefore, targeting these mechanisms might not only promote the regeneration of damaged nerve fibres, but might also enhance axon sprouting and plasticity after CNS injury. Here, we describe recent progress in under standing the inhibitory components of the adult glial environment, as well as the neuronal receptor complexes and downstream signals that mediate their effects. The limited success in targeting these pathways in vivo will then be evaluated. Finally, we discuss the physiological roles of glial inhibition in the intact nervous system, and their implications for the development of strategies to promote functional recovery after adult CNS injury. The role of extrinsic inhibitionThe regeneration failure in the adult CNS might be partly attributed to the gradual decline in the intrinsic growth ability of neurons as the animal matures. Ramón y Cajal described that, © 2006 Nature Publishing Group Correspondence to Z.H. e-mail: E-mail: zhigang.he@childrens.harvard.edu. Competing interests statementThe authors declare no competing financial interests. DATABASES NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript after injury, the ends of lesioned axons become swollen in...

Inhibitory molecules associated with myelin and the glial scar limit axon regeneration in the adult central nervous system (CNS), but the underlying signaling mechanisms of regeneration inhibition are not fully understood. Here, we show that suppressing the kinase function of the epidermal growth factor receptor (EGFR) blocks the activities of both myelin inhibitors and chondroitin sulfate proteoglycans in inhibiting neurite outgrowth. In addition, regeneration inhibitors trigger the phosphorylation of EGFR in a calcium-dependent manner. Local administration of EGFR inhibitors promotes significant regeneration of injured optic nerve fibers, pointing to a promising therapeutic avenue for enhancing axon regeneration after CNS injury.