The pattern of binding of horseradish peroxidase conjugated lectins (Concanavalin A, fucose binding protein, Ricinus communis agglutinin) was examined in the rat hippocampal formation both prior to and following a lesion of the entorhinal cortex. In normal animals, Concanavalin A binding sites were concentrated around the granular and pyramidal cell bodies. Receptors were less concentrated in the stratum radiatum, stratum oriens and the dentate molecular layer. Receptors of fucose binding protein were concentrated in the granular and pyramidal cells, the boundary between the first and second quarters of the molecular layer and at the hippocampal fissure. Ricinus communis agglutinin binding sites were highest in the first 1 4 of the molecular layer and lowest in the stratum lacunosum-moleculare. Three days after an entorhinal lesion, the binding of Concanavalin A and fucose binding protein in the molecular layer was increased and while Ricinus communis agglutinin binding was unchanged. At thirty days post-lesion there was an increase in the binding of Concanavalin A and fucose binding protein in the molecular layer and stratum lacunosum-moleculare, whereas Ricinus communis agglutinin binding sites increased only in the molecular layer. The extensive alterations of lectin receptors that occur simultaneously with reactive synaptogenesis may indicate that membrane-bound glycoconjugates have an important role in this process.
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