Actin dynamics in dendritic spines: A form of regulated plasticity at excitatory synapses

Dendritic spines form the postsynaptic element at most excitatory synapses in the brain. The spine cytoskeleton consists of actin filaments which, in time-lapse recordings of living neurons expressing actin labeled with green fluorescent protein, can be seen to undergo rapid, dynamic changes. Becaus e actin dynamics are associated with changes in cell shape, these cytoskele tal rearrangements may form a molecular basis for the morphological plastic ity at brain synapses. The rapidity of these dynamic events in dendritic sp ines raises new questions. First, do the changes in actin cytoskeleton that are visible by light microscopy really correspond to changes in spine morp hology, or do they represent changes in the relationship between actin and its many binding partners at postsynaptic sites? Second, how are these chan ges regulated by synaptic transmission? Third, to what extent do these chan ges occur in organized brain tissue? Answers to these questions are now beg inning to emerge. Hippocampus 2000,10:555-560. (C) 2000 Wiley-Liss, Inc.