Until recently, the conventional methods to investigate structure of synaptic and dendritic morphology have been Golgi staining, immunostaining of synaptic proteins, imaging by fluorescent markers such as GFP labeling, or by ultrastructure. These techniques, however, infer, but do not directly assay, number of synapses and underestimate the number of dendritic spines (Friedland et al., 2006; Pilati et al., 2008). To provide convincing evidence that APP is required for the maintenance of dendritic structure, synapse formation, and synaptic function, we re-examined the effect of APP on synaptic plasticity and dendritic and spine morphology in an APP KO mouse line using 3-dimensional reconstruction of individual neurons and spines to analyze accurately alterations in dendritic and spine structure in vivo. We also conducted in vitro studies in neurons from APP KO mice to assess whether spine density differences were accompanied by alterations in synaptic plasticity or basal synaptic transmission.
