threedimensional structures of canine senile plaques in this study the threedimensional structures of two types of canine senile plaques sp diffuse plaques dp and mature plaques mp were compared using a confocal laser scanning microscope the threedimensional observation revealed that canine dp were uneven nebulalike assemblies of amyloidbeta abeta while mp were comparatively uniform assemblies of membranelike or fibrous abeta materials with some differences among subtypes primitive classic and compact we also noticed the presence of areas with lowdensity abeta deposition inside dp and mp indicating degradation of abeta double staining for abeta and other sp constituents was also conducted amyloid precursor protein app was mainly deposited as rough granules around abeta assemblies in dp and both inside and around abeta assemblies in mp the patten of ubiquitin deposition was quite similar to that of app glial fibrillary acidic proteinpositive astroglial projections were found around and inside abeta assemblies in both types of sp but were more prominent in mp than dp dp were often invaded by neurofilamentpositive neuronal processes neurites while no such neurites were observed inside mp dystrophic neurites were however frequently detected around mp these results clearly showed that canine dp and mp have completely different threedimensional structures consistent with different processes of dp and mp formation