REPAIR OF THE CENTRAL-NERVOUS-SYSTEM - LESSONS FROM LESIONS IN LEECHES

In contrast to the limited repair observed in the mammalian central ne rvous system (CNS), injured neurons in the leech reliably regenerate s ynapses and restore function with remarkable accuracy at the level of individual neurons. New and recent results reveal important roles for microglial cells and extracellular matrix components, including lamini n, in repair. Tissue culture experiments have permitted isolation of n eurons and manipulation of their environment, providing insights into the influence of substrate, electrical activity, and other cells, incl uding microglia, on axon growth and synapse formation. The results acc ount for distinctive features of successful repair in the adult leech, where axonal sprouting and target selection can be influenced by uneq ual competition between neurons. Differences between the formation of connections during embryonic development and repair in the adult inclu de dissimilarities in the roles of glia and microglia in adults and em bryos, suggesting that axon growth during regeneration in the CNS is n ot simply a recapitulation of processes observed during embryonic deve lopment. It may be possible in the future to improve mammalian CNS reg eneration by recruiting cells whose counterparts in the leech have bee n identified as instrumental in repair. (C) 1995 John Wiley & Sons, In c.