THE OLFACTORY-BULB IN ALZHEIMER-DISEASE - A MORPHOLOGIC STUDY OF NEURON LOSS, TANGLES, AND SENILE PLAQUES IN RELATION TO OLFACTION

Complete pairs of olfactory bulbs of six Alzheimer disease (AD) patien ts and of six age- and sex-matched controls were morphologically inves tigated using a random systematic sampling procedure. The total number of cells and the number of mitral cells were the same for controls an d patients, but the volume of the bulb and the number of neurons in th e anterior olfactory nucleus (AON) were decreased in AD patients. The loss of AON neurons was limited to the younger AD patients and was ver y severe (75%). Neurofibrillary tangles (NFT) and senile plaques (SP) were found in controls, but they were more frequent in AD, especially in the younger cases. A new finding was the occurrence of very large n umbers of so-called diffuse or ''very primitive plaques'' with the met henamine-silver stain (MS-SP). NFT and SP were limited to the AON but MS-SP also occurred in other parts of the bulb. The data are discussed in relation to olfaction, and it was concluded that odor identificati on is processed in central rather than in peripheral olfactory structu res.