Three-dimensional reconstruction of senile plaques in Alzheimer's disease

So far, the three-dimensional approach to senile plaques, one of the principal histopathological hallmarks in Alzheimer's disease besides neurofibrillary tangles, has been scarce. Two main problems in three-dimensional reconstruction of histological specimens are the horizontal distortion during the preparation of serial thin tissue-slides and the need for consecutive vertical readjustment. This is greatly facilitated by the reflection contrast microscope (Leica, Germany) which is a light microscopical instrument causing interference patterns and reflections along interfaces by means of circularly polarized epi-illumination. Using this technique, one can obtain distinct optical sections of a depth of 1.5 microns within specimens up to 30 microns in thickness, thus preserving the integrity of the observed object and rendering a manual alignment superfluous. We applied the reflection contrast microscope (RCM) on thick tissue-slides of the cerebral cortex of a patient suffering from Alzheimer's disease which had been dyed according to Campbell. This is a silver-based staining method detecting beta A4-amyloid, the main component of senile plaques. Under the RCM, these silver-stained extracellular amyloid deposits cause reflections which allow the assessment of their three-dimensional distribution by focusing through the specimen. The optical sections obtained in this way were digitized, and the identified senile plaques reconstructed by the grey-scale image analysis system VIDAS 2.5 (Zeiss/Kontron, Germany).