THE OLFACTORY BULB IN ALZHEIMER'S DISEASE

This report describes the laminar distribution of acetylcholinesterase-positive structures in the human olfactory bulb of control and Alzheimer’s disease brain samples. Light microscopic histochemistry revealed the enzyme-positive neurons and nerve fibres. No acetylcholinesterase staining was present in the olfactory nerve layer, the glomerular layer or the external granule cell layer. A few enzyme-positive (cholinergic) nerve fibres were detected in the external plexiform layer and the white matter. A large number of cholinergic axons were present in the internal plexiform layer and the internal granule cell layer. Acetylcholinesterase-positive nerve fibres and cells were present in the mitral/tufted cell layer and the anterior olfactory nucleus. In Alzheimer’s disease brain samples, a weak and patchy acetylcholinesterase staining appeared in the internal plexiform layer and the internal granule cell layer. In the anterior olfactory nucleus, enzyme-positive neurofibrillary tangles and senile plaques were found. The neuropathological changes were studied with silver impregnation techniques and immunohistochemistry revealed a diffuse amyloid staining in the olfactory nerve layer and in the external plexiform layer, and large numbers of senile plaques in the glomerular layer and the anterior olfactory nucleus. The presence of amyloid positivity in the olfactory nerve layer and in a number of glomeruli suggests that no correlation exists between the cholinergic structures and the neuropathologic alterations in the human olfactory bulb in Alzheimer’s disease.