Sequential training in separate paradigms impairs second task consolidation and learning-associated modulations of hippocampal NCAM polysialylation

As transient and time-dependent modulations of neural cell adhesion molecul e polysialylation (NCAM PSA) are associated with morphofunctional change an d required for the consolidation of spatial and nonspatial forms of learnin g, we determined the demands imposed on this system by sequential training in the Morris water maze followed by the passive avoidance paradigm. Animal s trained in this manner had recall of the water maze but not the passive a voidance response as judged by their escape and avoidance latencies, respec tively. Activation of NCAM PSA on dentate neurons at the 12-h post-training time suggested information processing; however, this was significantly les s than that predicted for coincident acquisition of both tasks. When sequen tial training was separated by an interparadigm period of 2 h, an enduring NCAM PSA activation was observed which was indistinguishable from the sum o f the expected activations for each individual task. These observations sug gest that the NCAM PSA response may become saturated when alternate tasks a re presented without an intervening period. (C) 1999 Academic Press.