Proliferative astrocytes may express fibronectin-like protein in the hippocampus of epileptic rats

Kainic acid treatment, a model of temporal lobe epilepsy, induces in CA3-CA4 fields of hippocampal complex a neuronal degeneration associated with glial hypertrophy and proliferation. After treatment with kainate, fibronectin (an extracellular matrix protein) immunoreactivity increases in CA3-CA4. Fibronectin antibodies stain proliferative cells (simultaneously labelled by [3H]thymidin) of astrocytic type (double-immunostained by GFAP antibodies). This result constitutes the first direct demonstration of astroglial fibronectin expression in vivo. In the molecular layer of kainate-treated rats there is an axon-terminal degeneration of association-fibers. This is associated with a transient hypertrophy of resident astrocytes but not with any glial proliferation. Reactive astrocytes do not express (or faintly) fibronectin immunoreactivity in this layer. Since fibronectin is involved in astroglial proliferation in vitro, the present observations suggest that astrocytes contribute in vivo to the astroglial proliferation by an autocrin mechanism.