RAPID ACTIN-BASED PLASTICITY IN DENDRITIC SPINES

Dendritic spines have been proposed as primary sites of synaptic plast icity in the brain. Consistent with this hypothesis, spines contain hi gh concentrations of actin, suggesting that they might be motile. To i nvestigate this possibility, we made video recordings from hippocampal neurons expressing actin tagged with green fluorescent protein (GFP-a ctin). This reagent incorporates into actin-containing structures and allows the visualization of actin dynamics in living neurons. In matur e neurons, recordings of GFP fluorescence revealed large actin-depende nt changes in dendritic spine shape, similar to those inferred from pr evious studies using fixed tissues. Visible changes occured within sec onds, suggesting that anatomical plasticity at synapses can be extreme ly rapid. As well as providing a molecular basis for structural plasti city, the presence of motile actin in dendritic spines implicates the postsynaptic element as a primary site of this phenomenon.