Location of Sialoglycoconjugates Containing the Siaα2–3Gal and Siaα2–6Gal Groups in the Rat Hippocampus and the Effect of Aging on Their Expression

The histochemical distribution of sialoglycoconjugates in the CA1 region in the hippocampus formation of 9-week-old rats and 30-month-old rats was examined using electron microscopy in combination with two lectins, Maackia amurensis lectin, specific for Siaα2–3Gal, and Sambucus sieboldiana agglutinin, specific for Siaα2–6Gal. Each lectin stained the plasma membranes of pyramidal cells, indicating that the Siaα2–3Gal and Siaα2–6Gal groups were expressed on their plasma membranes. These lectins also bound to synapses in the stratum lacunosum moleculare. The staining intensity of the lectins in the synapses in these layers was downregulated in the 30-month-old rats. These results indicated that both the Siaα2–3Gal and Siaα2–6Gal groups are expressed on these synapses and that the expression of these sialyl linkages decreases in the aged brain.