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European Archives of... Mar 2022To evaluate the success of olfactory training in patients with olfactory loss and olfactory bulb (OB) atrophy detected on magnetic resonance imaging (MRI) and other...
PURPOSE
To evaluate the success of olfactory training in patients with olfactory loss and olfactory bulb (OB) atrophy detected on magnetic resonance imaging (MRI) and other characteristics.
METHODS
This study included 48 patients with olfactory loss who underwent a nasal endoscopic examination and MRI before olfactory training. The Korean Version of the Sniffin' Sticks Test was performed before and after training. The olfactory training success was defined as an improvement of more than 6 points in the Threshold-Discrimination-Identification (TDI) score. Patient characteristics and OB atrophy pre-training were compared between successful and unsuccessful groups.
RESULTS
The etiology of olfactory loss included respiratory viral infection in 30 (62.5%), trauma in 10 (20.8%), and idiopathic loss in 8 (16.7%) patients. Twenty-three (47.9%) of 48 patients exhibited successful olfactory training. Etiology, age, gender, and symptom duration were not different between unsuccessful and successful groups. Pre-training discrimination, identification, and TDI scores were significantly different between unsuccessful and successful groups (P < 0.05). Success rate of patients with bilateral OB atrophy was significantly lower than that of patients with unilateral OB atrophy and normal morphology (P = 0.006). OB height was significantly lower in the unsuccessful group than in the successful group (P < 0.05). Bilateral OB atrophy was an independent risk factor for failure of olfactory training according to the multivariate analysis.
CONCLUSION
Olfactory loss patients with bilateral OB atrophy may not be able to improve olfactory function after olfactory training.
Topics: Atrophy; Humans; Magnetic Resonance Imaging; Olfaction Disorders; Olfactory Bulb; Smell
PubMed: 34091728
DOI: 10.1007/s00405-021-06917-z -
Frontiers in Neural Circuits 2020Generation of neuronal diversity is a biological strategy widely used in the brain to process complex information. The olfactory bulb is the first relay station of... (Review)
Review
Generation of neuronal diversity is a biological strategy widely used in the brain to process complex information. The olfactory bulb is the first relay station of olfactory information in the vertebrate central nervous system. In the olfactory bulb, axons of the olfactory sensory neurons form synapses with dendrites of projection neurons that transmit the olfactory information to the olfactory cortex. Historically, the olfactory bulb projection neurons have been classified into two populations, mitral cells and tufted cells. The somata of these cells are distinctly segregated within the layers of the olfactory bulb; the mitral cells are located in the mitral cell layer while the tufted cells are found in the external plexiform layer. Although mitral and tufted cells share many morphological, biophysical, and molecular characteristics, they differ in soma size, projection patterns of their dendrites and axons, and odor responses. In addition, tufted cells are further subclassified based on the relative depth of their somata location in the external plexiform layer. Evidence suggests that different types of tufted cells have distinct cellular properties and play different roles in olfactory information processing. Therefore, mitral and different types of tufted cells are considered as starting points for parallel pathways of olfactory information processing in the brain. Moreover, recent studies suggest that mitral cells also consist of heterogeneous subpopulations with different cellular properties despite the fact that the mitral cell layer is a single-cell layer. In this review, we first compare the morphology of projection neurons in the olfactory bulb of different vertebrate species. Next, we explore the similarities and differences among subpopulations of projection neurons in the rodent olfactory bulb. We also discuss the timing of neurogenesis as a factor for the generation of projection neuron heterogeneity in the olfactory bulb. Knowledge about the subpopulations of olfactory bulb projection neurons will contribute to a better understanding of the complex olfactory information processing in higher brain regions.
Topics: Animals; Dendrites; Humans; Interneurons; Neurons; Olfactory Bulb; Olfactory Pathways; Olfactory Receptor Neurons; Synapses
PubMed: 32982699
DOI: 10.3389/fncir.2020.561822 -
Cell and Tissue Research Jan 2021Whether an odorant is perceived as pleasant or unpleasant (hedonic value) governs a range of crucial behaviors: foraging, escaping danger, and social interaction.... (Review)
Review
Whether an odorant is perceived as pleasant or unpleasant (hedonic value) governs a range of crucial behaviors: foraging, escaping danger, and social interaction. Despite its importance in olfactory perception, little is known regarding how odor hedonics is represented and encoded in the brain. Here, we review recent findings describing how odorant hedonic value is represented in the first olfaction processing center, the olfactory bulb. We discuss how olfactory bulb circuits might contribute to the coding of innate and learned odorant hedonics in addition to the odorant's physicochemical properties.
Topics: Animals; Odorants; Olfactory Bulb; Vertebrates
PubMed: 33515292
DOI: 10.1007/s00441-020-03372-w -
Cell and Tissue Research Jan 2021The necklace glomeruli are a loosely defined group of glomeruli encircling the caudal main olfactory bulb in rodents. Initially defined by the expression of various... (Review)
Review
The necklace glomeruli are a loosely defined group of glomeruli encircling the caudal main olfactory bulb in rodents. Initially defined by the expression of various immunohistochemical markers, they are now better understood in the context of the specialized chemosensory neurons of the main olfactory epithelium and Grueneberg ganglion that innervate them. It has become clear that the necklace region of the rodent main olfactory bulb is composed of multiple distinct groups of glomeruli, defined at least in part by their afferent inputs. In this review, we will explore the necklace glomeruli and the chemosensory neurons that innervate them.
Topics: Animals; Olfactory Bulb; Olfactory Pathways; Rodentia
PubMed: 33404845
DOI: 10.1007/s00441-020-03388-2 -
Ageing Research Reviews Jun 2024Parkinson's disease (PD) is a prevalent neurodegenerative disorder that affects 7-10 million individuals worldwide. A common early symptom of PD is olfactory dysfunction... (Review)
Review
Parkinson's disease (PD) is a prevalent neurodegenerative disorder that affects 7-10 million individuals worldwide. A common early symptom of PD is olfactory dysfunction (OD), and more than 90% of PD patients suffer from OD. Recent studies have highlighted a high incidence of OD in patients with SARS-CoV-2 infection. This review investigates the potential convergence of OD in PD and COVID-19, particularly focusing on the mechanisms by which neuroinflammation contributes to OD and neurological events. Starting from our fundamental understanding of the olfactory bulb, we summarize the clinical features of OD and pathological features of the olfactory bulb from clinical cases and autopsy reports in PD patients. We then examine SARS-CoV-2-induced olfactory bulb neuropathology and OD and emphasize the SARS-CoV-2-induced neuroinflammatory cascades potentially leading to PD manifestations. By activating microglia and astrocytes, as well as facilitating the aggregation of α-synuclein, SARS-CoV-2 could contribute to the onset or exacerbation of PD. We also discuss the possible contributions of NF-κB, the NLRP3 inflammasome, and the JAK/STAT, p38 MAPK, TLR4, IL-6/JAK2/STAT3 and cGAS-STING signaling pathways. Although olfactory dysfunction in patients with COVID-19 may be reversible, it is challenging to restore OD in patients with PD. With the emergence of new SARS-CoV-2 variants and the recurrence of infections, we call for continued attention to the intersection between PD and SARS-CoV-2 infection, especially from the perspective of OD.
Topics: Humans; COVID-19; Parkinson Disease; Neuroinflammatory Diseases; Olfaction Disorders; SARS-CoV-2; Olfactory Bulb
PubMed: 38580172
DOI: 10.1016/j.arr.2024.102288 -
Journal of Parkinson's Disease 2022MRI is a valuable method to assist in the diagnostic work-up of Parkinson's disease (PD). The olfactory tract (OT) has been proposed as a potential MRI biomarker for...
BACKGROUND
MRI is a valuable method to assist in the diagnostic work-up of Parkinson's disease (PD). The olfactory tract (OT) has been proposed as a potential MRI biomarker for distinguishing PD patients from healthy controls.
OBJECTIVE
This study aims to further investigate whether diffusion measures of the OT differ between early stage PD patients and healthy controls.
METHODS
Twenty hyposmic/anosmic PD patients, 65 normosmic PD patients, and 36 normosmic healthy controls were evaluated and a 7T diffusion weighted image scan was acquired. Manual seed regions of interest were drawn in the OT region. Tractography of the OT was performed using a deterministic streamlines algorithm. Diffusion measures (fractional anisotropy and mean- radial- and axial diffusivity) of the generated streamlines were compared between groups.
RESULTS
Diffusion measures did not differ between PD patients compared to healthy controls and between hyposmic/anosmic PD patients, normosmic PD patients, and normosmic healthy controls. A positive correlation was found between age and mean- and axial diffusivity within the hyposmic/anosmic PD subgroup, but not in the normosmic groups. A positive correlation was found between MDS-UPDRSIII scores and fractional anisotropy.
CONCLUSION
This study showed that fiber tracking of the OT was feasible in both early stage PD and healthy controls using 7T diffusion weighted imaging data. However, 7T MRI diffusion measures of the OT are not useful as an early clinical biomarker for PD. Future work is needed to clarify the role of other OT measurements as a biomarker for PD and its different subgroups.
Topics: Anisotropy; Diffusion Magnetic Resonance Imaging; Diffusion Tensor Imaging; Humans; Magnetic Resonance Imaging; Olfactory Bulb; Parkinson Disease
PubMed: 36093714
DOI: 10.3233/JPD-223349 -
Chemical Senses Jan 2023Odors guide food seeking, and food intake modulates olfactory function. This interaction is mediated by appetite-regulating hormones like ghrelin, insulin, and leptin,...
Odors guide food seeking, and food intake modulates olfactory function. This interaction is mediated by appetite-regulating hormones like ghrelin, insulin, and leptin, which alter activity in the rodent olfactory bulb, but their effects on downstream olfactory cortices have not yet been established in humans. The olfactory tract connects the olfactory bulb to the cortex through 3 main striae, terminating in the piriform cortex (PirC), amygdala (AMY), olfactory tubercule (OT), and anterior olfactory nucleus (AON). Here, we test the hypothesis that appetite-regulating hormones modulate olfactory processing in the endpoints of the olfactory tract and the hypothalamus. We collected odor-evoked functional magnetic resonance imaging (fMRI) responses and plasma levels of ghrelin, insulin, and leptin from human subjects (n = 25) after a standardized meal. We found that a hormonal composite measure, capturing variance relating positively to insulin and negatively to ghrelin, correlated inversely with odor intensity ratings and fMRI responses to odorized vs. clean air in the hypothalamus, OT, and AON. No significant correlations were found with activity in PirC or AMY, the endpoints of the lateral stria. Exploratory whole-brain analyses revealed significant correlations near the diagonal band of Broca and parahippocampal gyrus. These results demonstrate that high (low) blood plasma concentrations of insulin (ghrelin) decrease perceived odor intensity and odor-evoked activity in the cortical targets of the medial and intermediate striae of the olfactory tract, as well as the hypothalamus. These findings expand our understanding of the cortical mechanisms by which metabolic hormones in humans modulate olfactory processing after a meal.
Topics: Humans; Odorants; Leptin; Ghrelin; Appetite; Olfactory Bulb; Olfactory Cortex; Hypothalamus; Piriform Cortex; Perception; Insulins; Olfactory Perception
PubMed: 37796827
DOI: 10.1093/chemse/bjad039 -
The Journal of Comparative Neurology Aug 2018Both the lateral olfactory tract (LOT) and anterior limb of the anterior commissure (AC) carry olfactory information. The LOT forms the projection from the olfactory...
Both the lateral olfactory tract (LOT) and anterior limb of the anterior commissure (AC) carry olfactory information. The LOT forms the projection from the olfactory bulb to the ipsilateral olfactory cortices, while the AC carries odor information across the midline to the contralateral olfactory cortex and bulb. The LOT and AC differ on a number of dimensions, including early development and functional onset. The present work, examining their myelination in mice, reveals additional important differences. For example, the LOT initiates myelination 3-4 days earlier than the AC, evidenced by both an earlier increase in myelin basic protein staining seen with immunohistochemistry and an earlier appearance of myelinated fibers using electron microscopy. While both exhibit a period of rapid myelination, it occurs 4-5 days earlier in the LOT than the AC. The tracts also respond differently to early sensory restriction. Unilateral naris occlusion from the day after birth to postnatal day 30 had no consistent effects on the AC but resulted in significantly thinner myelin sheaths relative to axon caliber in the LOT. Finally, the two tracts differ structurally (the LOT contains larger, more densely packed axons with significantly thicker myelin sheaths resulting in a conduction velocity that is more than twice as fast as the AC). The findings indicate that these two large, accessible tracts provide an important means for studying brain maturation due to basic differences in both the timing of their maturation and general organization.
Topics: Animals; Axons; Female; Immunohistochemistry; Male; Mice; Mice, Inbred C57BL; Myelin Basic Protein; Myelin Sheath; Nasal Cavity; Neural Conduction; Olfactory Bulb; Oligodendroglia; Sensory Deprivation; White Matter
PubMed: 29665005
DOI: 10.1002/cne.24452 -
Neuroradiology Feb 2021Impaired olfactory function is one of the main features of Parkinson's disease. However, how peripheral olfactory structures are involved remains unclear. Using...
PURPOSE
Impaired olfactory function is one of the main features of Parkinson's disease. However, how peripheral olfactory structures are involved remains unclear. Using diffusion tensor imaging fiber tracking, we investigated for MRI microstructural changes in the parkinsonian peripheral olfactory system and particularly the olfactory tract, in order to seek a better understanding of the structural alternations underlying hyposmia in Parkinson's disease.
METHODS
All patients were assessed utilizing by the Italian Olfactory Identification Test for olfactory function and the Unified Parkinson's Disease Rating Scale-III part as well as Hoehn and Yahr rating scale for motor disability. Imaging was performed on a 3 T Clinical MR scanner. MRI data pre-processing was carried out by DTIPrep, diffusion tensor imaging reconstruction, and fiber tracking using Diffusion Toolkit and tractography analysis by TrackVis. The following parameters were used for groupwise comparison: fractional anisotropy, mean diffusivity, radial diffusivity, axial diffusivity, and tract volume.
RESULTS
Overall 23 patients with Parkinson's disease (mean age 63.6 ± 9.3 years, UPDRS-III 24.5 ± 12.3, H&Y 1.9 ± 0.5) and 18 controls (mean age 56.3 ± 13.7 years) were recruited. All patients had been diagnosed hyposmic. Diffusion tensor imaging analysis of the olfactory tract showed significant fractional anisotropy, and tract volume decreases for the Parkinson's disease group compared with controls (P < 0.05). Fractional anisotropy and age, in the control group, were significant for multiple correlations (r = - 0.36, P < 0.05, Spearman's rank correlation).
CONCLUSIONS
Fiber tracking diffusion tensor imaging analysis of olfactory tract was feasible, and it could be helpful for characterizing hyposmia in Parkinson's disease.
Topics: Aged; Anisotropy; Diffusion Tensor Imaging; Disabled Persons; Humans; Middle Aged; Motor Disorders; Olfactory Bulb; Parkinson Disease
PubMed: 32918150
DOI: 10.1007/s00234-020-02551-4 -
Communications Biology Sep 2022The olfactory nerve map describes the topographical neural connections between the olfactory epithelium in the nasal cavity and the olfactory bulb. Previous studies have...
The olfactory nerve map describes the topographical neural connections between the olfactory epithelium in the nasal cavity and the olfactory bulb. Previous studies have constructed the olfactory nerve maps of rodents using histological analyses or transgenic animal models to investigate olfactory nerve pathways. However, the human olfactory nerve map remains unknown. Here, we demonstrate that high-field magnetic resonance imaging and diffusion tensor tractography can be used to visualize olfactory sensory neurons while maintaining their three-dimensional structures. This technique allowed us to evaluate the olfactory sensory neuron projections from the nasal cavities to the olfactory bulbs and visualize the olfactory nerve maps of humans, marmosets and mice. The olfactory nerve maps revealed that the dorsal-ventral and medial-lateral axes were preserved between the olfactory epithelium and olfactory bulb in all three species. Further development of this technique might allow it to be used clinically to facilitate the diagnosis of olfactory dysfunction.
Topics: Animals; Humans; Magnetic Resonance Imaging; Mice; Olfactory Bulb; Olfactory Mucosa; Olfactory Nerve; Olfactory Pathways
PubMed: 36068329
DOI: 10.1038/s42003-022-03794-y