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Development (Cambridge, England) Feb 2022The mammalian main olfactory bulb is a crucial processing centre for the sense of smell. The olfactory bulb forms early during development and is functional from birth.... (Review)
Review
The mammalian main olfactory bulb is a crucial processing centre for the sense of smell. The olfactory bulb forms early during development and is functional from birth. However, the olfactory system continues to mature and change throughout life as a target of constitutive adult neurogenesis. Our Review synthesises current knowledge of prenatal, postnatal and adult olfactory bulb development, focusing on the maturation, morphology, functions and interactions of its diverse constituent glutamatergic and GABAergic cell types. We highlight not only the great advances in the understanding of olfactory bulb development made in recent years, but also the gaps in our present knowledge that most urgently require addressing.
Topics: Animals; Axons; Bone Morphogenetic Proteins; Neurogenesis; Olfactory Bulb; Olfactory Receptor Neurons; Signal Transduction; Synapses
PubMed: 35147186
DOI: 10.1242/dev.200210 -
Otolaryngology--head and Neck Surgery :... Jun 2021This study aimed to investigate the differences in olfactory cleft (OC) morphology in coronavirus disease 2019 (COVID-19) anosmia compared to control subjects and...
OBJECTIVE
This study aimed to investigate the differences in olfactory cleft (OC) morphology in coronavirus disease 2019 (COVID-19) anosmia compared to control subjects and postviral anosmia related to infection other than severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
STUDY DESIGN
Prospective.
SETTING
This study comprises 91 cases, including 24 cases with anosmia due to SARS-CoV-2, 38 patients with olfactory dysfunction (OD) due to viral infection other than SARS-CoV-2, and a control group of 29 normosmic cases.
METHODS
All cases had paranasal sinus computed tomography (CT), and cases with OD had magnetic resonance imaging (MRI) dedicated to the olfactory nerve. The OC width and volumes were measured on CT, and T2-weighted signal intensity (SI), olfactory bulb volumes, and olfactory sulcus depths were assessed on MRI.
RESULTS
This study showed 3 major findings: the right and left OC widths were significantly wider in anosmic patients due to SARS-CoV-2 (group 1) or OD due to non-SARS-CoV-2 viral infection (group 2) when compared to healthy controls. OC volumes were significantly higher in group 1 or 2 than in healthy controls, and T2 SI of OC area was higher in groups 1 and 2 than in healthy controls. There was no significant difference in olfactory bulb volumes and olfactory sulcus depths on MRI among groups 1 and 2.
CONCLUSION
In this study, patients with COVID-19 anosmia had higher OC widths and volumes compared to control subjects. In addition, there was higher T2 SI of the olfactory bulb in COVID-19 anosmia compared to control subjects, suggesting underlying inflammatory changes. There was a significant negative correlation between these morphological findings and threshold discrimination identification scores.
LEVEL OF EVIDENCE
Level 4.
Topics: Adult; Anosmia; COVID-19; Case-Control Studies; Female; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Nasal Cavity; Olfactory Bulb; Olfactory Mucosa; Organ Size; Prospective Studies; Tomography, X-Ray Computed
PubMed: 33045908
DOI: 10.1177/0194599820965920 -
Frontiers in Neural Circuits 2022In the mouse olfactory system, odor signals detected in the olfactory epithelium are converted to a topographic map of activated glomeruli in the olfactory bulb. The map... (Review)
Review
In the mouse olfactory system, odor signals detected in the olfactory epithelium are converted to a topographic map of activated glomeruli in the olfactory bulb. The map information is then conveyed by projection neurons, mitral cells and tufted cells, to various areas in the olfactory cortex. An odor map is transmitted to the anterior olfactory nucleus by tufted cells for odor identification and recollection of associated memory for learned decisions. For instinct decisions, odor information is directly transmitted to the valence regions in the amygdala by specific subsets of mitral cells. Transmission of orthonasal odor signals through these two distinct pathways, innate and learned, are closely related with exhalation and inhalation, respectively. Furthermore, the retronasal/interoceptive and orthonasal/exteroceptive signals are differentially processed during the respiratory cycle, suggesting that these signals are processed in separate areas of the olfactory bulb and olfactory cortex. In this review article, the recent progress is summarized for our understanding of the olfactory circuitry and processing of odor signals during respiration.
Topics: Amygdala; Animals; Mice; Odorants; Olfactory Bulb; Olfactory Pathways; Respiration; Smell
PubMed: 35431818
DOI: 10.3389/fncir.2022.861800 -
Human Brain Mapping Jun 2022Brain plasticity is essential for experts to acquire the abilities they need. Sommeliers are olfaction experts who display differences in olfactory regions in the brain...
Brain plasticity is essential for experts to acquire the abilities they need. Sommeliers are olfaction experts who display differences in olfactory regions in the brain that correlate with greater olfactory abilities. While most studies on this topic are cross-sectional, we used a longitudinal design and invited 17 sommelier students at the start and end of their training then to compare them to 17 control students to study the effects of training-related brain plasticity. After a year and a half, 5 sommelier students and 4 control students dropped out, leading to 12 sommelier students versus 13 controls. We used magnetic resonance imaging to measure cortical thickness and olfactory bulb volume, as this structure plays a crucial role in olfactory processing. We used the Sniffin' Sticks test to evaluate olfactory performance. During training, olfactory bulb volume increased in sommelier students while there was no significant change in the control group. We also observed that thickness of right entorhinal cortex increased, and cortical thickness decreased in other cerebral regions. Our olfactory tests did not reveal any significant changes in sommelier students. In conclusion, this is the first longitudinal study to report an increase in olfactory bulb volume in olfaction experts in line with the notion of effects of ecological training-related brain plasticity. The mixed results about cortical thickness might be explained by a "overproduction-pruning" model of brain plasticity, according to which the effects of training-related plasticity are non-linear and simultaneously involve different processes.
Topics: Cross-Sectional Studies; Humans; Longitudinal Studies; Magnetic Resonance Imaging; Olfaction Disorders; Olfactory Bulb; Smell
PubMed: 35218277
DOI: 10.1002/hbm.25809 -
Neuroscience and Biobehavioral Reviews Oct 2022The sense of smell is interrelated with psychosocial functioning. Olfactory disorders often decrease quality of life but treatment options for people with olfactory loss... (Review)
Review
The sense of smell is interrelated with psychosocial functioning. Olfactory disorders often decrease quality of life but treatment options for people with olfactory loss are limited. Additionally, olfactory loss accompanies and precedes psychiatric and neurodegenerative diseases. Regular, systematic exposure to a set of odors, i.e., olfactory training (OT) has been offered for rehabilitation of the sense of smell in clinical practice. As signals from the olfactory bulb are directly projected to the limbic system it has been also debated whether OT might benefit psychological functioning, i.e., mitigate cognitive deterioration or improve emotional processing. In this review we synthesize key findings on OT utility in the clinical practice and highlight the molecular, cellular, and neuroanatomical changes accompanying olfactory recovery in people with smell loss as well as in experimental animal models. We discuss how OT and its modifications have been used in interventions aiming to support cognitive functions and improve well-being. We delineate main methodological challenges in research on OT and suggest areas requiring further scientific attention.
Topics: Animals; Humans; Odorants; Olfaction Disorders; Olfactory Bulb; Quality of Life; Smell
PubMed: 36064146
DOI: 10.1016/j.neubiorev.2022.104853 -
International Forum of Allergy &... Nov 2020
Topics: Humans; Odorants; Olfaction Disorders; Olfactory Bulb; Smell
PubMed: 32776673
DOI: 10.1002/alr.22681 -
FASEB Journal : Official Publication of... Sep 2021Memorizing pheromonal locations is critical for many mammalian species as it involves finding mates and avoiding competitors. In rodents, pheromonal information is...
Memorizing pheromonal locations is critical for many mammalian species as it involves finding mates and avoiding competitors. In rodents, pheromonal information is perceived by the main and accessory olfactory systems. However, the role of somatosensation in context-dependent learning and memorizing of pheromone locations remains unexplored. We addressed this problem by training female mice on a multimodal task to locate pheromones by sampling volatiles emanating from male urine through the orifices of varying dimensions or shapes that are sensed by their vibrissae. In this novel pheromone location assay, female mice' preference toward male urine scent decayed over time when they were permitted to explore pheromones vs neutral stimuli, water. On training them for the associations involving olfactory and whisker systems, it was established that they were able to memorize the location of opposite sex pheromones, when tested 15 days later. This memory was not formed either when the somatosensory inputs through whisker pad were blocked or when the pheromonal cues were replaced with that of same sex. The association between olfactory and somatosensory systems was further confirmed by the enhanced expression of the activity-regulated cytoskeleton protein. Furthermore, the activation of main olfactory bulb circuitry by pheromone volatiles did not cause any modulation in learning and memorizing non-pheromonal volatiles. Our study thus provides the evidence for associations formed between different sensory modalities facilitating the long-term memory formation relevant to social and reproductive behaviors.
Topics: Animals; Discrimination Learning; Female; Male; Memory; Mice; Odorants; Olfactory Bulb; Olfactory Perception; Pheromones; Size Perception; Smell; Vibrissae
PubMed: 34407246
DOI: 10.1096/fj.202100167R -
Scientific Reports Jun 2024Despite its high prevalence, the determinants of smelling impairment in COVID-19 remain not fully understood. In this work, we aimed to examine the association between...
Despite its high prevalence, the determinants of smelling impairment in COVID-19 remain not fully understood. In this work, we aimed to examine the association between olfactory bulb volume and the clinical trajectory of COVID-19-related smelling impairment in a large-scale magnetic resonance imaging (MRI) analysis. Data of non-vaccinated COVID-19 convalescents recruited within the framework of the prospective Hamburg City Health Study COVID Program between March and December 2020 were analyzed. At baseline, 233 participants underwent MRI and neuropsychological testing as well as a structured questionnaire for olfactory function. Between March and April 2022, olfactory function was assessed at follow-up including quantitative olfactometric testing with Sniffin' Sticks. This study included 233 individuals recovered from mainly mild to moderate SARS-CoV-2 infections. Longitudinal assessment demonstrated a declining prevalence of self-reported olfactory dysfunction from 67.1% at acute infection, 21.0% at baseline examination and 17.5% at follow-up. Participants with post-acute self-reported olfactory dysfunction had a significantly lower olfactory bulb volume at baseline than normally smelling individuals. Olfactory bulb volume at baseline predicted olfactometric scores at follow-up. Performance in neuropsychological testing was not significantly associated with the olfactory bulb volume. Our work demonstrates an association of long-term self-reported smelling dysfunction and olfactory bulb integrity in a sample of individuals recovered from mainly mild to moderate COVID-19. Collectively, our results highlight olfactory bulb volume as a surrogate marker that may inform diagnosis and guide rehabilitation strategies in COVID-19.
Topics: Humans; Olfactory Bulb; COVID-19; Male; Female; Middle Aged; Olfaction Disorders; Adult; Magnetic Resonance Imaging; SARS-CoV-2; Aged; Prospective Studies; Neuropsychological Tests; Smell
PubMed: 38862636
DOI: 10.1038/s41598-024-64367-z -
Journal of Investigational Allergology... 2020The first cases of coronavirus 2019 disease (COVID-19) occurred in Wuhan, China, and the disease rapidly become a public health emergency of international proportions.... (Review)
Review
The first cases of coronavirus 2019 disease (COVID-19) occurred in Wuhan, China, and the disease rapidly become a public health emergency of international proportions. COVID-19 can cause mild-to-severe acute respiratory syndrome (SARS) and is caused by the SARS-CoV-2 coronavirus. The clinical manifestations of COVID-19 include fever, dry cough, fatigue, sputum production, shortness of breath, sore throat, and headache. We performed this narrative review to analyze the current literature on postviral olfactory dysfunction related to the SARSCoV- 2 pandemic. Since the initial anecdotal reports from China, increasingly frequent international reports on COVID-19 indicate that 5% to 85% of affected patients lose their sense of smell, thus highlighting the very heterogeneous nature of the literature in this area. Therefore, we advise home isolation measures and/or social distancing, as well as tests to detect SARS-CoV-2 when possible, in patients with sudden and severe loss of smell who cannot be promptly evaluated.
Topics: Betacoronavirus; COVID-19; Coronavirus Infections; Disease Outbreaks; Female; Humans; Male; Olfaction Disorders; Olfactory Bulb; Pandemics; Pneumonia, Viral; SARS-CoV-2; Smell
PubMed: 32406374
DOI: 10.18176/jiaci.0567 -
Molecules and Cells Mar 2020The olfactory bulb (OB) has an extremely higher proportionof interneurons innervating excitatory neurons than otherbrain regions, which is evolutionally conserved across... (Review)
Review
The olfactory bulb (OB) has an extremely higher proportionof interneurons innervating excitatory neurons than otherbrain regions, which is evolutionally conserved across species.Despite the abundance of OB interneurons, little is knownabout the diversification and physiological functions ofOB interneurons compared to cortical interneurons. In thisreview, an overview of the general developmental processof interneurons from the angles of the spatial and temporalspecifications was presented. Then, the distinct featuresshown exclusively in OB interneurons development andmolecular machinery recently identified were discussed.Finally, we proposed an evolutionary meaning for thediversity of OB interneurons.
Topics: Humans; Interneurons; Olfactory Bulb
PubMed: 32208366
DOI: 10.14348/molcells.2020.0033