DIFFERENCES IN THE PATTERN OF HIPPOCAMPAL NEURONAL LOSS IN NORMAL AGING AND ALZHEIMERS-DISEASE

The distinction between the neurodegenerative changes that accompany n ormal ageing and those that characterise Alzheimer's disease is not cl ear. The resolution of this issue has important implications for the d esign of therapeutic and investigative strategies. To this end we have used modern stereological techniques to compare the regional pattern of neuronal cell loss in the hippocampus related to normal ageing to t hat associated with Alzheimer's disease. The loss related to normal ag eing was evaluated from estimates of the total number of neurons in ea ch of the major hippocampal subdivisions of 45 normal ageing subjects who ranged in age from 13 to 101 years. The Alzheimer's disease relate d losses were evaluated from similar data obtained from 7 cases of Alz heimer's disease and 14 age matched controls. Qualitative differences were observed in the regional patterns of neuronal loss related to nor mal ageing and Alzheimer's disease. The most distinctive Alzheimer's d isease related neuron loss was seen in the CA1 region of the hippocamp us. In the normal ageing group there was almost no neuron loss in this region (final neuron count in the CA1 region: 4.40 x 10(6) neurons fo r the Alzheimer's disease group vs 14.08 x 10(6) neurons in the normal ageing group). It is concluded that the neurodegenerative processes a ssociated with normal ageing and with Alzheimer's disease are qualitat ively different and that Alzheimer's disease is not accelerated by age ing but is a distinct pathological process.