Neurons, Nose, and Neurodegenerative Diseases: Olfactory Function and Cognitive Impairment

Abstract

Olfactory capacity declines with aging, but increasing evidence shows that smell dysfunction is one of the early signs of prodromal neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. The study of olfactory ability and its role in neurodegenerative diseases arouses much interest in the scientific community. In neurology, olfactory impairment is a potential early marker for the onset of neurodegenerative diseases, but the underlying mechanism is poorly understood. The loss of smell is considered a clinical sign of early-stage disease and a marker of the disease’s progression and cognitive impairment. Highlighting the importance of biological bases of smell and molecular pathways could be fundamental to improve neuroprotective and therapeutic strategies. We focused on the review articles and meta-analyses on olfactory and cognitive impairment. We depicted the neurobiology of olfaction and the most common olfactory tests in neurodegenerative diseases. In addition, we underlined the close relationship between the olfactory and cognitive deficit due to nasal neuroepithelium, which is a direct extension of the CNS in communication with the external environment. Neurons, Nose, and Neurodegenerative diseases highlights the role of olfactory dysfunction as a clinical marker for early stages of neurodegenerative diseases when it is associated with molecular, clinical, and neuropathological correlations.

Advances in the study of cholinergic circuits in the central nervous system

“…Furthermore, it has bidirectional projections to the prefrontal cortex's anterior/ventral regions (PL/IL) in the medial prefrontal cortex (mPFC), which are associated with olfactory dysfunction in neurodegenerative diseases such as PD and AD. 44 The NBM projects to most sensory cortex regions, including frontal sensorimotor, parietal, temporal, cingulate gyrus, and visual cortex, 69 with a wider range of targets in the sensorimotor cortex, but without a specific pattern. Therefore, the correlation of the Meynert basal ganglion-cortical cholinergic circuit with neurodegenerative diseases is of great significance.…”

“…demonstrated that the HDB/VDB region is primarily associated with the primary sensory cortex and exhibits specific projections to the primary somatosensory (S1), auditory (A1), and visual (V1) cortical regions based on the distribution of its neck and tail neurons. Furthermore, it has bidirectional projections to the prefrontal cortex's anterior/ventral regions (PL/IL) in the medial prefrontal cortex (mPFC), which are associated with olfactory dysfunction in neurodegenerative diseases such as PD and AD 44 . The NBM projects to most sensory cortex regions, including frontal sensorimotor, parietal, temporal, cingulate gyrus, and visual cortex, 69 with a wider range of targets in the sensorimotor cortex, but without a specific pattern.…”

Proteoform Analysis of the Human Olfactory System: A Window into Neurodegenerative Diseases

“…The human olfactory system is responsible for the detection, transmission, and identification of odorous stimuli [ 1 ]. To encode the odors, the olfactory pathways are connected by several circuits, comprising approximately 400 peripheral olfactory receptors, about 10 7 olfactory sensory neurons (OSNs), and central structures, where olfactory information is recognized and stored [ 2 ].…”

Odor Reproduction Technology Using a Small Set of Odor Components

“…Reprinted from I. Fatuzzo et al [10] a set of primary odors, it is challenging to reproduce the odor we sense [15]. Moreover, it would be impractical to utilize the primary odors with the same number as human olfactory receptors since it is roughly 400.…”