RELATIONSHIP BETWEEN INJURY-INDUCED ASTROGLIOSIS, LAMININ EXPRESSION AND AXONAL SPROUTING IN THE ADULT-RAT BRAIN

Lesion-induced regenerative sprouting of CNS axons is accompanied by s tructural and metabolic changes of astrocytes. In order to evaluate th e effects of these astrocytic changes on axonal regeneration, we inves tigated the spatio-temporal relationship of gliosis, laminin expressio n and axonal sprouting in the postcommissural fornix of the adult rat. Using immunocytochemical methods we observed (1) a perilesional area with a transient lack of astrocytes and axons, (2) the reappearance of reactive astrocytes followed by the ingrowth of sprouting fibres and finally an increase in laminin-immunoreactivity, (3) the absence of le sion-induced laminin-expression in reactive astrocytes and (4) the for mation and long-lasting (at least 28 months) persistence of a dense pl exus of laminin-immunopositive blood vessels at the site of transectio n and in the proximal and distal stumps. These data indicate that astr ogliosis is permeable for regrowing axons and that injury-induced axon al sprouting in the transected postcommissural fornix may be mediated by laminin-independent mechanisms.