Misrouted olfactory fibres and ectopic olfactory glomeruli in normal humans and in Parkinson and Alzheimer patients

Abstract

The presence and distribution of misrouted (MR) olfactory projection fibres were studied in the olfactory bulbs of control human brains and in the brains of people who had suffered from Parkinson's and Alzheimer's disease. It appeared that MR fibres, that is, fibres that terminate deep into the glomerular layer, are a common phenomenon in the bulbs of aged people. In all but one of the bulbs studied, MR fibres are present. The amount of MR fibres is not related to age. With a few exceptions, the MR fibres are restricted to the external plexiform layer (EPL). Only in Parkinson bulbs the MR fibres occasionally form glomerulus-like structures. These pseudo glomeruli are located in the EPL. It is concluded that MR olfactory projection fibres are a normal phenomenon in the human olfactory bulb. In nonhuman mammalians, MR fibres have only been observed in foetal and neonatal olfactory bulbs. Possibly, the age-related loss of mitral cells, which are the natural synaptic targets for the olfactory projection fibres, may play a role in the aberrant behaviour of the MR olfactory receptor cell axons. The ectopic glomerulus-like structures in Parkinson bulbs share some characteristics with normal rat glomeruli that are not observed in normal human olfactory glomeruli. This may refer to possible changes in the genetic content of olfactory structures in Parkinson patients.

Smell Identification in Japanese Parkinson's Disease Patients: Using the Odor Stick identification Test for Japanese Subjects

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Association of Olfactory Bulb Volume and Olfactory Sulcus Depth with Olfactory Function in Patients with Parkinson Disease

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Biopsies of olfactory epithelium in patients with Parkinson's disease

“…As a matter of fact, hyposmia or anosmia develop as preclinical signs in PD patients. 3,4 This deficit has also been related to structural and/or functional changes at the level of the olfactory bulb, e.g., including misrouted axonal terminals of olfactory receptor neurons that form glomerulus-like structures 3 or signs of neuroinflammation and microgliosis.…”