The olfactory bulb in Alzheimer's disease

This report describes the laminar distribution of acetylcholinesterase-posi tive structures in the human olfactory bulb of control and Alzheimer's dise ase brain samples. Light microscopic histochemistry revealed the enzyme-pos itive neurons and nerve fibres. No acetylcholinesterase staining was presen t in the olfactory nerve layer, the glomerular layer or the external granul e cell layer. A few enzyme-positive (cholinergic) nerve fibres were detecte d in the external plexiform layer and the white matter. A large number of c holinergic axons were present in the internal plexiform layer and the inter nal granule cell layer. Acetylcholinesterase-positive nerve fibres and cell s were present in the mitral/tufted cell layer and the anterior olfactory n ucleus. In Alzheimer's disease brain samples, a weak and patchy acetylcholi nesterase staining appeared in the internal plexiform layer and the interna l granule cell layer. In the anterior olfactory nucleus, enzyme-positive ne urofibrillary tangles and senile plaques were found. The neuropathological changes were studied with silver impregnation techniques and immunohistoche mistry revealed a diffuse amyloid staining in the olfactory nerve layer and in the external plexiform layer, and large numbers of senile plaques in th e glomerular layer and the anterior olfactory nucleus. The presence of amyl oid positivity in the olfactory nerve layer and in a number of glomeruli su ggests that no correlation exists between the cholinergic structures and th e neuropathologic alterations in the human olfactory bulb in Alzheimer's di sease.