This is a fluorescence image of two dendrites from hippocampal neurons growing in cell culture. One of the cells is expressing actin tagged with green fluorescent protein (GFP-actin), which giving the green staining in dendritic spines where actin is highly concentrated (see Kaech et al, 1997). The culture was fixed and counterstained with an antibody (red fluorescence) against MAP2, a microtubule-associated protein which is selectively associated with microtubules in dendrites and shows the shafts of dendrites.