tailieunhanh - DEVELOPMENTAL NEUROBIOLOGY - PART 9

Tế bào thần kinh trưởng thành có thể trải qua một chuyển đổi tế bào tự trị từ sản xuất của sợi trục thần kinh sản xuất các tinh thể nhánh cây. Tế bào hạch ở võng mạc (RGCs) trong cơ thể (trống) mở rộng sợi trục thần kinh để phân bố các thần kinh | Regeneration and Repair Chapter 12 343 FIGURE 8. Maturing neurons may undergo a cell autonomous switch from production of axons to production of dendrites. Retinal ganglion cells RGCs in vivo boxes extend axons to innervate targets in the brain during late embryonic stages and extend dendrites during postnatal stages. RGCs placed in tissue culture at embryonic or postnatal stages regenerate processes that are similar to the ones they generate in vivo young neurons re-extend a single axon while older neurons extend multiple short dendrites. Factors that stimulate neurite extension oval can increase the length of the regenerated processes but do alter the axonal vs dendritic nature of the process suggesting that RGCs have undergone a stable cell-intrinsic switch from production of axons to production of dendrites. Contact with cell membranes derived from postnatal amacrine cells is sufficient to switch embryonic RGCs to a postnatal pattern of growth in culture suggesting that amacrine-associated factors may mediate this maturational switch in retina Goldberg et al. 2002 . Figure adapted from Condic 2002 . Changes in Intrinsic Properties of CNS Neurons in Response to Injury Independent of maturational changes in neuronal gene expression the intrinsic state of adult neurons can be a key factor in CNS regeneration. For example adult sensory neurons that have sustained a conditioning peripheral lesion regenerate more readily into the CNS following dorsal root injury Neumann and Woolf 1999 . How such conditioning lesions enhance the ability of neurons to regenerate into the CNS is unknown but it is possible that peripheral injuries indirectly promote expression of genes that are not upregulated in response to CNS injuries Frostick et al. 1998 Terenghi 1999 Kury et al. 2001 . For example activated Schwann cells may supply trophic factors to sensory neurons that are not supplied by activated central glia. Consequently neurons that have been appropriately conditioned may .