GLIOSIS AND AXONAL SPROUTING IN THE HIPPOCAMPUS OF EPILEPTIC RATS AREASSOCIATED WITH AN INCREASE OF TENASCIN-C IMMUNOREACTIVITY

Temporal lobe epilepsy is associated with neuronal death, gliosis and sprouting of messy fibres in the hippocampus of human and rats. In the present study we show that immunoreactivity for tenascin-C (an extrac ellular matrix glycoprotein) increases in the hippocampus of epileptic rats. However, this increase was only observed in the cases displayin g neuronal cell loss and glial reaction (i.e. after kainate treatment but not after kindling). Tenascin-C increase was particularly striking at Ammon's horn, where the antibody labelled both reactive astrocytes (confirmed by double-labelling experiments) and axonal plasma membran es. In the molecular layer tenascin-C immunoreactivity remained unchan ged in both kindled or kainate treated rats. It is interesting that in creased tenascin-C immunoreactivity was observed within zones in which axonal regeneration did not occur (the CA3 area in kainate-treated an imals) whereas zones in which reactive synaptogenesis occurred (such a s the CA3 area of kindled rats or the molecular layer of both kindled and kainate-treated rats) were devoid of tenascin-C immunoreactivity. We infer from these results that tenascin-C impedes the terminal sprou ting of messy fibres in CA3 of kainate-treated rats.