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Characterisation of Antibodies Specific for Chick Brain Neural Cell Adhesion Molecules Which Cause Amnesia for a Passive Avoidance Task

Abstract: Antisera were prepared against six postsynaptic density glycoprotein fractions (150–180, 62–80, 50, 41, 33, and 28 kDa) that show enhanced fucosylation during memory formation after training day‐old chicks in a one‐trial passive avoidance task. Each antiserum was tested for its possible effect on memory retention. Bilateral intracranial injections of two of the antisera, R‐1 and R‐6, or their IgGs (IgG‐1 and IgG‐6), resulted in amnesia for the passive avoidance task when chicks were tested 24 h later. IgG‐1 and IgG‐6 antibodies were amnestic only when injected 5.5 h after training, and had no effect when injections were made 30 min before training, thus resembling an effect previously observed with polyclonal or monoclonal anti‐N‐CAM antibodies. IgG‐1 and IgG‐6 antibodies were found to be specific for protein epitopes of glycoproteins that contain a high amount of N‐linked mannose and fucose, and a very low amount of polysialic acid and O‐linked galactose. Absorption of IgG‐6 antibodies with neural cell adhesion molecule (N‐CAM) isolated from synaptic plasma membranes derived from day‐old chick brain resulted in loss of amnestic effect. As we have previously shown that long‐term memory for the passive avoidance task requires two waves of glycoprotein synthesis, the first occurring immediately after training and the second 5–8 h later, the present results suggest strongly that isoforms of N‐CAM molecules with a low level of sialic acid are involved specifically in the establishment of an enduring memory for the experience of the passive avoidance task in chicks, possibly by stabilising changes in synaptic connectivity that encode the memory.