Exposure of cortical neurons to Aβ-containing medium leads to a reduction of GluR1 intensity at the surface of the dendritic spines. A, Dendrites from neurons treated with wild-type or TgCM for 60 min with or without 3D6 immunodepletion or FK506, and then stained with an antibody to the extracellular N-terminal domain of GluR1 to label surface AMPA receptors, and phalloidin to visualize F-actin. B, Quantification of the effects of oligomeric Aβ on F-actin and surface GluR1 signal intensity (represented as ratios of spines vs shaft). Exposure of neurons to Aβ-containing TgCM reduces the ratios of both phalloidin-stained F-actin and surface GluR1 on the spine to the dendritic shafts, indicating a loss of F-actin and synaptic GluR1 from dendritic spines. This effect is blocked by 3D6 and FK506. Data are presented as mean ± SEM. **p < 0.001; n = total 200 spines in each condition, from three independent experiments.