NEURONAL REGENERATION AND THE GLIAL BARRIER

The dogma of abortive axonal regrowth set by Cajal (1914) is now broke n since the demonstration by Aguayo (1982) that severed axons can regr ow in an appropriate environment. Over the last decade, the impediment s to such a regrowth in the central nervous system of higher vertebrat es have been identified or, at least, some of them. On the one hand, t he inhibitory molecules synthesized and secreted by oligodendrocytes h ave been counteracted by appropriate antibodies (Schnell & Schwab, 199 0), which have permitted some regrowth of severed cortico-spinal axons in the rat spinal cord. On the other hand, the reduction by a pharmac ological treatment of hypertrophy and hyperplasia of astrocytes has pe rmitted some regrowth of monoaminergic axons in an hemisected cord (Gi menez y Ribotta et al. 1995). Finally, the identification of a subcate gory of astrocytes, the tanycytes of the basal hypothalamus, as a perm issive substrate for axonal regeneration opens a new avenue for future research.