NCAM IMMUNOREACTIVITY ON MOSSY FIBERS AND REACTIVE ASTROCYTES IN THE HIPPOCAMPUS OF EPILEPTIC RATS

Sprouting and synaptogenesis of mossy fibers develop in adult hippocam pus after epilepsy. In control conditions, mossy fibers constitute the main afferent pathway to the Ammon's horn, where they mainly innervat e CA3 pyramidal cells, but after treatment with the convulsant agent, kainate, mossy fibers also innervate granule cell dendrites generating recurrent excitatory circuits which may contribute to the maintenance of the epileptic condition. In the present study we show an enhanced immunoreactivity to neural cell adhesion molecules (NCAMs), a family o f membrane glycoproteins involved in axonal growth. NCAM immunoreactiv ity is enriched on cytoplasmic membranes of axon shafts that are likel y to be mossy fiber collaterals. NCAM immunoreactivity was also observ ed on the cytoplasmic membranes of reactive astrocytes, at the axon-gl ial contacts. Our results therefore suggest that there is an interacti on of newly developed mossy fibers with other fibers and glial cells. This interaction may be mediated by NCAMs. Taking into account the tro phic properties of NCAMs we suggest that they regulate the sprouting, growing and synaptogenesis of mossy fibers in epileptic conditions.