PROLIFERATIVE ASTROCYTES MAY EXPRESS FIBRONECTIN-LIKE PROTEIN IN THE HIPPOCAMPUS OF EPILEPTIC RATS

Kainic acid treatment, a model of temporal lobe epilepsy, induces in C A3-CA4 fields of hippocampal complex a neuronal degeneration associate d with. glial hypertrophy and proliferation. After treatment with kain ate, fibronectin (an extracellular matrix protein) immunoreactivity in creases in CA3-CA4. Fibronectin antibodies stain proliferative cells ( simultaneously labelled by [H-3]thymidin) of astrocytic type (double-i mmunostained by GFAP antibodies). This result constitutes the first di rect demonstration of astroglial fibronectin expression in vivo. In th e molecular layer of kainate-treated rats there is an axon-terminal de generation of association-fibers. This is associated with a transient hypertrophy of resident astrocytes but not with any glial proliferatio n. Reactive astrocytes do not express (or faintly) fibronectin immunor eactivity in this layer. Since fibronectin is invoked in astroglial pr oliferation in vitro, the present observations suggest that astrocytes contribute in vivo to the astroglial proliferation by an autocrin mec hanism.