In the nervous systems of many animals, including vertebrates, isolated axon segments can survive for weeks or even months1-3; they can participate in regeneration4,5 and in some cases receive synapses from regenerating axons6,7. Axon segments in cell culture exhibit limited growth8-10. Although lengths of axon may grow in more intact systems11-14, direct evidence for this has been difficult to obtain, partly because of the difficulty of marking isolated axon segments. We have injected fluorescently labelled synthetic D-peptides15 into identified neurones in the leech central nervous system to mark axon segments. We report here that individual segments can initiate growth at both ends and grow for days, both in organ culture and in vivo. These results support the hypothesis that axon growth is not essentially polar and suggest a novel mechanism by which axon segments may assist nerve regeneration.
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