Neuropathology 2006; 26, 501–507 doi:10.1111/j.1440-1789.2006.00718.x © 2006 Japanese Society of Neuropathology Original Article Differential expression of glycans in the hippocampus of rats trained on an inhibitory learning paradigm Alejandra Hidalgo, 1 Valeria Burgos, 1 Haydée Viola, 2 Jorge Medina 2 and Pablo Argibay 1 1 Institute of Basic Sciences and Experimental Medicine, Italian Hospital of Buenos Aires, and 2 Institute of Cellular Biology and Neurosciences Eduardo de Robertis, Faculty of Medicine, University of Buenos Aires, Buenos Aires, Argentina The glycan chains of glycoconjugates play important roles in cell–cell and cell–matrix interactions. In the CNS, pre- vious studies on learning and memory suggest the impor- tance of oligosaccharides attached to glycoconjugates in the modulation of synaptic connections. We studied the hip- pocampal glycan distribution of rats subject to an inhibitory avoidance task. The expression of glycans was examined by lectin-histochemistry using Vicia villosa lectin (VVL) for terminal a/b N-acetylgalactosamine (a/b GalNAc); Galanthus nivalus lectin (GNL) for terminal mannose a-1,3 (Man a-1,3); Peanut agglutinin (PNA) for galactose b-1,3N- acetylgalactosamine (Gal b-1,3 GalNAc); Erythrina crista- galli lectin (ECL) for galactose b-1,4 N-acetylglucosamine (Gal b-1,4 GlcNAc); Sambucus nigra lectin (SNA) for sialic acid a-2.6 galactose (SA a-2,6 Gal); Maackia amurensis lec- tin II (MAL II) for sialic acid a-2,3 (SA a-2,3); Wheat germ agglutinin (WGA) for terminal N-acetylglucosamine with/ without sialic acid (GlcNAc wo SA); succynilated WGA (sWGA) for terminal N-acetylglucosamine without sialic acid (terminal GlcNAc without SA); Griffonia simplicifolia lectin II (GSL II) for terminal a/b N-acetylglucosamine (a/ b GlcNAc terminal); and Lotus tetragonolobus lectin (LTL) a–fucose. Two groups of 10 animals were ex- amined: non-trained (Control) and Trained rats. ECL, sWGA and GSL II were negative for both groups in all the hippocampal subfields studied. For both groups, VVL was negative in CA4 and granular cells of the Dentate Gyrus (DG) and LTL was negative in the CA4 subfield. Expres- sion of a/b GalNAc, a-fucose and GlcNAc in other hip- pocampal subfields was positive, with no differences between groups. However, expression of Man a-1,3 was sig- nificantly higher in the CA1, CA2, CA3, and CA4 subfields in the Trained group. On the other hand, expression of Gal b-1,3 GalNAc was significantly low in CA4 and DG in the Trained group. In conclusion, the results here presented in- dicate that the exposure of rats to an associative behavioral paradigm related to declarative memory, involves some reg- ulatory mechanism/s for the differential patterns of glycan expression. Key words: hippocampus, learning, lectins, memory, oligosaccharides. INTRODUCTION Carbohydrates, as part of proteins and lipids, are distributed throughout plant and animal tissues, as well as in bacteria and virus capsules. Unlike proteins and nucleic acids, the diversity of carbohydrate structures is enormous. The highly branched oligosaccharide tree involves different types of residues and linkages: their syntheses do not depend only on a template. A concerted temporal and spatial action of gly- cosyltransferases is also involved. 1 Much research in the glycobiology area has suggested the involvement or mod- ulatory roles of oligosaccharides attached to cell surface gly- coproteins, glycolipids and proteoglycans in cell–cell and cell–matrix interactions in an array of conditions in the ner- vous system: altered GlcNAc expression in cells of astro- cytoma and ependynoma origin, 2 different lectin staining in a schizophrenic and Alzheimer’s disease brain, 3 and normal cell surface carbohydrates distribution. 4,5 The hippocampus has an important role in the declara- tive memory capacity in animals and humans. 6 It is impor- tantly involved in spatial learning, 7–9 and is a structure with continued neurogenesis in the adult brain. 10,11 Glycan mod- ifications in hippocampal neural plasticity are well docu- mented in rodents: changes in the sialoglycoprotein hippocampal content have been reported in the rat brain Correspondence: Pablo Argibay, MD, PhD, Potosí 4240 8th floor, C1199ACL, Buenos Aires, Argentina. Email: pablo.argibay@ hospitalitaliano.org.ar Received 7 December 2005; revised and accepted 10 February 2006. Blackwell Publishing AsiaMelbourne, AustraliaNEUNeuropathology0919-65442006 Blackwell Publishing Asia Pty LtdDecember 2006266501507Original Article A lectin-histochemistry study of memoryA Hidalgo et al.