AXONAL LOSS FROM THE OLFACTORY TRACTS IN ALZHEIMERS-DISEASE

Senile dementia of the Alzheimer type has been shown to be associated with impaired olfactory function early in the course of the disease. N europathology in the olfactory system is also a feature of Alzheimer's disease (AD) and it has been suggested that the disease may be caused by a pathogen entering the brain via olfactory pathways. To investiga te this hypothesis, the effect of AD on the olfactory tract was invest igated. There was a 40% decrease in the cross-sectional area of the ol factory tract and a 52% loss of myelinated axons from the tract in AD. These results, together with those of previous studies suggest that p eripheral regions of the olfactory system, i.e., the olfactory bulb an d primary sensory olfactory neurons are less affected by the pathology of AD than more central parts, i.e., cortical regions, the anterior o lfactory nuclei, and olfactory tract. This less severe pathology at th e periphery argues against a pathogen entering the brain via the perip heral olfactory apparatus and suggests a central pathogenesis which sp reads centrifugally along olfactory pathways.