Due to a lack of consistency in the literature regarding the methodology of plaque counting, it was necessary to establish a reproducible method for counting plaques. This would allow the quantitative neuropathology to be integrated into the longitudinal study and correlated with various aspects of Alzheimer's disease such as neuropsychology, neuro-imaging and neuropharmacology. The volume of the brain and the cranial cavity volume (CCV) were determined in cases of senile dementia of the Alzheimer type (SDAT) and age matched controls. This was to provide correction factors for the plaque counts and also to determine whether or not there was any atrophy of the brain in SDAT. The volume of each individual lobe and the amount of cortex, white matter and the size of the ventricles were also measured. There was some loss of tissue in the normal aged brain, but even more in SDAT. There was loss of cerebral cortex in the left temporal, frontal, parietal and occipital lobes, whereas in the right hemisphere only the cortex of the parietal lobe showed any atrophy. When comparing the size of the ventricles it was found that even though the ventricles of the SDAT group were generally larger than the controls, the difference was not statistically significant. Plaque counts were undertaken on both frozen and paraffin sections and 7 different staining techniques employed to establish which method was the most suitable for demonstrating senile plaques. The highest plaque counts were obtained on the frozen sections stained by the King's amyloid and the von Braunmuhl silver impregnation techniques. The King's amyloid technique was more reproducible with less variation in staining. It also gave the highest plaque counts in all but a few cases and was therefore employed throughout this study for the quantitative plaque counts. The quantitative plaque counts were corrected for the effects of fixation and atrophy of the brain. Once it had been established that the King's amyloid was the staining technique which would be employed, the reproducibility of the method of counting plaques had to be evaluated. The number of plaques per mm2 were counted manually using an image analyser at 1, 3 and 6 reference points in each region of the brain being examined and the standard deviation (SD) of the difference in the day to day variability examined. The smaller the SD number, the more reproducible the plaque counts, and the greater the SD number, the less reproducible the plaque counts. By increasing the number of reference points from 1 to 6 in each brain region, the day to day error in the reproducibility of plaque counts was halved in the superficial layers and quartered in the deep layers. The day to day error in the mean plaque count was +/-0.7 plaques/mm2 (+ 3.9% of the day 1 count). It was therefore decided that counting plaques at 6 reference points was sufficiently accurate and reproducible for the purpose of this study. When examining both the number and the area of plaques it was found that there was a significant increase in the number and the area of plaques in the SDAT group compared to the age matched controls. In fact in 4 control cases there were no plaques at all and in the other 2 there were very few. This suggested that SDAT was not simply a continuation of normal ageing. Since in the controls the vast majority of the plaque counts was zero, the various asymmetric studies on plaque counts were confined to the SDAT cases. When examining the literature on choline acetyl transferase activity (ChAT) and mental test scores (MTS), it appeared that when a mean plaque count of 10-12 was reached that the ChAT activity and MTS had fallen to approximately 50% of normal. Based on these well established data sets it was decided that a 5 plaque change represented a biologically significant difference. Since a 5 plaque change between 1-6 and 45-50 plaques is a percentage change of between 500% and 10% respectively, it was decided that a second criterion was required. Since ChAT activity was substantially reduced at lower plaque counts (below about 12 plaques) and that a mean plaque count of 12 can segregate dements from non-dements, a 5 plaque change below 12 will give an approximate percentage change of between 40%-500%. Therefore, in this study asymmetric plaque counts would have to fulfil both criteria of a 5 plaque change as well as a minimum of a 40% difference before the counts would be called asymmetric
