3-DIMENSIONAL RECONSTRUCTION OF SENILE PLAQUES IN ALZHEIMERS-DISEASE

So far, the three-dimensional approach to senile plaques, one of the p rincipal histopathological hallmarks in Alzheimer's disease besides ne urofibrillary tangles, has been scarce. Two main problems in three-dim ensional reconstruction of histological specimens are the horizontal d istortion during the preparation of serial thin tissue-slides and the need for consecutive Vertical readjustment. This is greatly facilitate d by the reflection contrast microscope (Leica, Germany) which is a li ght microscopical instrument causing interference patterns and reflect ions along interfaces by means of circularly polarized epi-illuminatio n. Using this technique, one can obtain distinct optical sections of a depth of 1.5 mu m within specimens up to 30 mu m in thickness, thus p reserving 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 suffer ing from Alzheimer's disease which had been dyed according to Campbell . This is a silver-based staining method detecting beta A4-amyloid, th e main component of senile plaques. Under the RCM, these silver-staine d extracellular amyloid deposits cause reflections which allow the ass essment of their three-dimensional distribution by focusing through th e specimen. The optical sections obtained in this way were digitized, and the identified senile plaques reconstructed by the grey-scale imag e analysis system VIDAS 2.5 (Zeiss/Kontron, Germany).