A ROLE FOR THE NEURAL CELL-ADHESION MOLECULE IN A LATE, CONSOLIDATINGPHASE OF GLYCOPROTEIN-SYNTHESIS 6 HOURS FOLLOWING PASSIVE-AVOIDANCE TRAINING OF THE YOUNG CHICK

We have investigated the effect of intracranial injections of the amne stic anti-metabolite, 2-deoxygalactose, and antibodies to the neural c ell adhesion molecule on retention of a one-trial passive avoidance ta sk in chicks. Groups of chicks received bilateral intracranial injecti ons of 10 mumol/hemisphere 2-deoxygalactose or 10 mul/hemisphere anti- neural cell adhesion molecule and were tested 24 h following training. 2-Deoxygalactose injections were amnestic when administered at a prev iously established time (30 min pre-training). Here we show that the a gent is also amnestic when injected within a second time window occurr ing specifically 6-8 h after training. Administration of 2-deoxygalact ose between 2 and 6 h or after 8 h post-training was without effect on retention tested 24 h following training. Anti-neural cell adhesion m olecule injections were amnestic only when performed at a time which c oincided with the second phase of 2-deoxygalactose susceptibility. Fur ther experiments demonstrated that the neural cell adhesion molecule i s one of the molecules into which 2-deoxygalactose is incorporated. Ad ditionally, we investigated the extent of diffusion of 2-deoxygalactos e and anti-neural cell adhesion molecule following their injection, wi th respect to their residence in forebrain loci known to be involved i n the memory for passive avoidance. We interpret these data as indicat ing that two waves of glycoprotein synthesis are necessary for the est ablishment of long-term memory for the experience of passive avoidance training. The evidence is discussed in the context of earlier results indicating that the two waves involve different glycoprotein species and, possibly, different forebrain regions. We speculate that the late phase of glycoprotein synthesis coincides with, and is required for, modulation of cell-cell adhesion processes, reflecting the selection a nd stabilization of synapses which maintain an enduring representation of long-term memory.