Training in chicks alters PSA-N-CAM distribution in forebrain cell membranes

The intermediate and medial hyperstriatum ventrale (IMHV) in the chick is involved in memory formation following one-trial passive avoidance training. Possible links between neural cell adhesion molecule (N-CAM) distribution and memory consolidation were examined in an immunoelectron microscope study of IMHV 6 h after training. An antibody against alpha 2,8 polysialic acid (PSA), characteristic for embryonic N-CAM, and one against the protein backbones of N-CAM were labelled (post-embedding), separately, with 15 nm immunogold, and binding to their epitopes was analysed using the statistics of point processes. No difference in labelling levels between control and trained chicks, for either antibodies, was found, both groups of birds showing that cell membrane regions are 10-30 times more enriched in N-CAM isoforms, and have a two-fold greater proportion of PSA-N-CAM, than tissue as a whole. However, 375-400 nm regular arrays of labelled PSA-N-CAM were revealed statistically in cell membranes of control, but not trained, chicks, which may be related to the possible involvement of such membrane PSA domains in memory-related neuroplasticity.