Spine dynamics and synapse remodeling during LTP and memory processes.

While changes in the efficacy of synaptic transmission are believed to represent the physiological bases of learning mechanisms, other recent studies have started to highlight the possibility that a structural reorganization of synaptic networks could also be involved. Morphological changes of the shape or size of dendritic spines or of the organization of postsynaptic densities have been described in several studies, as well as the growth and formation following stimulation of new protrusions. Confocal in vivo imaging experiments have further revealed that dendritic spines undergo a continuous turnover and replacement process that may vary as a function of development, but can be markedly enhanced by sensory activation or following brain damage. The implications of these new aspects of plasticity for learning and memory mechanisms are discussed.

WITHDRAWN: Role of NCAM in Spine Dynamics and Synaptogenesis.

Increasing evidence indicates that adhesion molecules are critically involved in the regulation of mechanisms of synaptic plasticity including synapse formation, but also synaptic remodeling associated to changes in synaptic strength. Among these, the Neural Cell Adhesion Molecule (NCAM) and its polysialylated form PSA-NCAM are important candidates. Here we review recent results that point to a possible role of these two molecules in regulating the structural properties of excitatory synapses and namely the composition and stability of the postsynaptic density, thereby accounting for their contribution to mechanisms of synaptogenesis and activity-dependent synaptic plasticity.