TRANSIENT EXPRESSION OF GLIAL-FIBRILLARY ACIDIC PROTEIN (GFAP) IN THE EPENDYMA OF THE REGENERATING SPINAL-CORD IN ADULT NEWTS

In the homeotherms the presence of glial-fibrillary acidic protein (GFAP) and that of neurofilaments (NF) are used as specific molecular markers associated with intermediate filaments (IF) of the glial and neuronal elements respectively. On this basis a comparison was made between trends in the immunohistochemical response to these markers of the ependyma of a both a normal and a regenerating spinal cord in Triturus carnifex (Urodele Amphibian) adults, whose high spinal cord regenerative capacity is due to the ependymal epithelium cells. Under normal conditions, the ependymal cells are vimentine positive and negative for GFAP and the IF, respectively, while GFAP and NF positivity is found in the grey and white matter. During regeneration, by about day 10, vimentine positivity begins to decrease in the ependymal epithelium of the caudal stump and GFAP positive elements appear (subsequently, this was observed also in the ependymal epithelium of the cephalic stump). High GFAP positivity is found also in the newly formed apical ampullae. From day 20 to after day 30 these patterns develop both in the stumps and in the regenerating spinal cord. NF positivity is always restricted to the grey matter alone and to the axonal processes of the white matter. At about day 60, by which time the regenerative processes may be considered as having terminated and the spinal cord has virtually regained its original structure, the immunohistochemical features typical of the rest state are restored in the ependymal epithelium. As well as confirming that ependymal cells in Urodele Amphibians play a key role in the regeneration of neuronal and glial elements of the regenerated spinal cord, this evidence indicates that the differentiation of the astroglial cells already occurs at the ependymal level and also earlier than neuronal differentiation. In the lower Vertebrates, such as the Urodeles it may be postulated that these data are related to the high regenerative power of the ependyma, which is inversely proportional to the degree of ependymal specialization.