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Neuroscience May 2020Demyelination significantly affects brain function. Several experimental methods, each inducing varying levels of myelin and neuronal damage, have been developed to...
Demyelination significantly affects brain function. Several experimental methods, each inducing varying levels of myelin and neuronal damage, have been developed to understand the process of myelin loss and to find new therapies to promote remyelination. The present work investigates the effect of one such method, lysolecithin administration, on the white matter tracts in the olfactory system. The olfactory forebrain contains two distinct tracts with differing developmental histories, axonal composition, and function: the lateral olfactory tract (LOT), which carries ipsilateral olfactory information from the olfactory bulb to olfactory cortex, and the anterior commissure (AC), which interconnects olfactory regions across hemispheres. The effects of lysolecithin injections were assessed in two ways: (1) the expression of myelin basic protein, a component of compacted myelin sheaths, was quantified using immunohistochemistry and (2) electron microscopy was used to obtain measurements of myelin thickness of individual axons as well as qualitative descriptions of the extent of damage to myelin and surrounding tissue. Data were collected at 7, 14, 21, and 30 days post-injection (dpi). While both the LOT and AC exhibited significant demyelination at 7 dpi and had returned to control levels by 30 dpi, the process differed between the two tracts. Remyelination occurred more rapidly in the LOT: substantial recovery was observed in the LOT by 14 dpi, but not in the AC until 21 dpi. The findings indicate that (a) the LOT and AC are indeed suitable tracts for studying lysolecithin-induced de- and remyelination and (b) experimental demyelination proceeds differently between the two tracts.
Topics: Axons; Demyelinating Diseases; Humans; Myelin Sheath; Olfactory Bulb; Olfactory Pathways; White Matter
PubMed: 32224229
DOI: 10.1016/j.neuroscience.2020.03.026 -
Epileptic Disorders : International... Dec 2016Olfactory auras (phantosmia) are an infrequent phenomenon in complex focal seizures generated in the mesial temporal lobe. It is generally assumed that all such auras... (Review)
Review
Olfactory auras (phantosmia) are an infrequent phenomenon in complex focal seizures generated in the mesial temporal lobe. It is generally assumed that all such auras arise from epileptic foci in the entorhinal cortex, amygdala or rostral insula, all of which have major afferent projections from the olfactory bulb or mainly from its relay, the anterior olfactory nucleus. The histological morphology, synaptic circuitry, and foetal development of the olfactory bulb are unique. The olfactory system is the only special sensory system that does not project to the thalamus because its bulb and tract incorporate an intrinsic thalamic equivalent: axonless granular and periglomerular neurons and the anterior olfactory nucleus. The olfactory bulb exhibits continuous synaptic turnover throughout life. Other brain structures with synaptic plasticity (neocortex, hippocampus, and amygdala) are epileptogenic; synaptically stable structures (brainstem, cerebellum, and basal ganglia) are not epileptogenic. Electrophysiological and neuropathological data of the olfactory bulb in epilepsy are sparse. We propose an alternative hypothesis, first hinted in 1954 by Penfield and Jasper, that some epileptic olfactory auras are primarily generated by the olfactory bulb and secondarily mediated by the amygdala and entorhinal cortex.
Topics: Amygdala; Entorhinal Cortex; Epilepsies, Partial; Hallucinations; Humans; Olfactory Bulb; Olfactory Perception
PubMed: 27818364
DOI: 10.1684/epd.2016.0869 -
Frontiers in Immunology 2022In the vertebrate olfactory tract new neurons are continuously produced throughout life. It is widely believed that neurogenesis contributes to learning and memory and...
In the vertebrate olfactory tract new neurons are continuously produced throughout life. It is widely believed that neurogenesis contributes to learning and memory and can be regulated by immune signaling molecules. Proteins originally identified in the immune system have subsequently been localized to the developing and adult nervous system. Previously, we have shown that olfactory imprinting, a specific type of long-term memory, is correlated with a transcriptional response in the olfactory organs that include up-regulation of genes associated with the immune system. To better understand the immune architecture of the olfactory organs we made use of cell-specific fluorescent reporter lines in dissected, intact adult brains of zebrafish to examine the association of the olfactory sensory neurons with neutrophils and blood-lymphatic vasculature. Surprisingly, the olfactory organs contained the only neutrophil populations observed in the brain; these neutrophils were localized in the neural epithelia and were associated with the extensive blood vasculature of the olfactory organs. Damage to the olfactory epithelia resulted in a rapid increase of neutrophils both within the olfactory organs as well as the central nervous system. Analysis of cell division during and after damage showed an increase in BrdU labeling in the neural epithelia and a subset of the neutrophils. Our results reveal a unique population of neutrophils in the olfactory organs that are associated with both the olfactory epithelia and the lymphatic vasculature suggesting a dual olfactory-immune function for this unique sensory system.
Topics: Animals; Neutrophils; Olfactory Bulb; Olfactory Mucosa; Olfactory Receptor Neurons; Zebrafish
PubMed: 35693773
DOI: 10.3389/fimmu.2022.881702 -
The Journal of Neuroscience : the... Jan 2022The human sense of smell plays an important role in appetite and food intake, detecting environmental threats, social interactions, and memory processing. However,...
The human sense of smell plays an important role in appetite and food intake, detecting environmental threats, social interactions, and memory processing. However, little is known about the neural circuity supporting its function. The olfactory tracts project from the olfactory bulb along the base of the frontal cortex, branching into several striae to meet diverse cortical regions. Historically, using diffusion magnetic resonance imaging (dMRI) to reconstruct the human olfactory tracts has been prevented by susceptibility and motion artifacts. Here, we used a dMRI method with readout segmentation of long variable echo-trains (RESOLVE) to minimize image distortions and characterize the human olfactory tracts We collected high-resolution dMRI data from 25 healthy human participants (12 male and 13 female) and performed probabilistic tractography using constrained spherical deconvolution (CSD). At the individual subject level, we identified the lateral, medial, and intermediate striae with their respective cortical connections to the piriform cortex and amygdala (AMY), olfactory tubercle (OT), and anterior olfactory nucleus (AON). We combined individual results across subjects to create a normalized, probabilistic atlas of the olfactory tracts. We then investigated the relationship between olfactory perceptual scores and measures of white matter integrity, including mean diffusivity (MD). Importantly, we found that olfactory tract MD negatively correlated with odor discrimination performance. In summary, our results provide a detailed characterization of the connectivity of the human olfactory tracts and demonstrate an association between their structural integrity and olfactory perceptual function. This study provides the first detailed description of the cortical connectivity of the three olfactory tract striae in the human brain, using diffusion magnetic resonance imaging (dMRI). Additionally, we show that tract microstructure correlates with performance on an odor discrimination task, suggesting a link between the structural integrity of the olfactory tracts and odor perception. Lastly, we generated a normalized probabilistic atlas of the olfactory tracts that may be used in future research to study its integrity in health and disease.
Topics: Adult; Diffusion Magnetic Resonance Imaging; Female; Humans; Image Processing, Computer-Assisted; Male; Olfactory Bulb; Olfactory Pathways
PubMed: 34759031
DOI: 10.1523/JNEUROSCI.1552-21.2021 -
Trends in Neurosciences Dec 2018Across the animal kingdom, odors are known as potent stimuli that directly steer behavior. In 2007, Hitoshi Sakano and colleagues used the power of mouse genetics to... (Review)
Review
Across the animal kingdom, odors are known as potent stimuli that directly steer behavior. In 2007, Hitoshi Sakano and colleagues used the power of mouse genetics to manipulate the odor map in the olfactory bulb. Elegant behavioral, anatomical, and physiological analyses revealed an apparent dichotomy in how the brain interprets the odor map. Their work paved a way to think of behavioral contingencies as part of early olfactory processing, highlighting innate and learned pathways.
Topics: Animals; Brain Mapping; Olfactory Bulb; Olfactory Pathways
PubMed: 30471665
DOI: 10.1016/j.tins.2018.06.007 -
Progress in Neuro-psychopharmacology &... Oct 2014The olfactory system is involved in sensory functions, emotional regulation and memory formation. Olfactory bulbectomy in rat has been employed as an animal model of... (Review)
Review
The olfactory system is involved in sensory functions, emotional regulation and memory formation. Olfactory bulbectomy in rat has been employed as an animal model of depression for antidepressant discovery studies for many years. Olfaction is impaired in animals suffering from chronic stress, and patients with clinical depression were reported to have decreased olfactory function. It is believed that the neurobiological bases of depression might include dysfunction in the olfactory system. Further, brain stimulation, including nasal based drug delivery could provide novel therapies for management of depression.
Topics: Animals; Depressive Disorder; Disease Models, Animal; Humans; Neurogenesis; Olfactory Bulb; Smell
PubMed: 24879990
DOI: 10.1016/j.pnpbp.2014.05.013 -
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 -
Acta Physiologica (Oxford, England) Jan 2020The most important task of the olfactory system is to generate a precise representation of odour information under different brain and behavioural states. As the first... (Review)
Review
The most important task of the olfactory system is to generate a precise representation of odour information under different brain and behavioural states. As the first processing stage in the olfactory system and a crucial hub, the olfactory bulb plays a key role in the neural representation of odours, encoding odour identity, intensity and timing. Although the neural circuits and coding strategies used by the olfactory bulb for odour representation were initially identified in anaesthetized animals, a large number of recent studies focused on neural representation of odorants in the olfactory bulb in awake behaving animals. In this review, we discuss these recent findings, covering (a) the neural circuits for odour representation both within the olfactory bulb and the functional connections between the olfactory bulb and the higher order processing centres; (b) how related factors such as sniffing affect and shape the representation; (c) how the representation changes under different states; and (d) recent progress on the processing of temporal aspects of odour presentation in awake, behaving rodents. We highlight discussion of the current views and emerging proposals on the neural representation of odorants in the olfactory bulb.
Topics: Animals; Odorants; Olfactory Bulb; Smell
PubMed: 31188539
DOI: 10.1111/apha.13333 -
American Journal of Rhinology & Allergy Jul 2023Olfactory dysfunction has been reported in 47.85% of COVID patients. It can be broadly categorized into conductive or sensorineural olfactory loss. Conductive loss...
BACKGROUND
Olfactory dysfunction has been reported in 47.85% of COVID patients. It can be broadly categorized into conductive or sensorineural olfactory loss. Conductive loss occurs due to impaired nasal air flow, while sensorineural loss implies dysfunction of the olfactory epithelium or central olfactory pathways.
OBJECTIVES
The aim of this study was to analyze the clinical and imaging findings in patients with COVID-related olfactory dysfunction. Additionally, the study aimed to investigate the possible mechanisms of COVID-related olfactory dysfunction.
METHODS
The study included 110 patients with post-COVID-19 olfactory dysfunction, and a control group of 50 COVID-negative subjects with normal olfactory function. Endoscopic nasal examination was performed for all participants with special focus on the olfactory cleft. Smell testing was performed for all participants by using a smell diskettes test. Olfactory pathway magnetic resonance imaging (MRI) was done to assess the condition of the olfactory cleft and the dimensions and volume of the olfactory bulb.
RESULTS
Olfactory dysfunction was not associated with nasal symptoms in 51.8% of patients. MRI showed significantly increased olfactory bulb dimensions and volume competed to controls. Additionally, it revealed olfactory cleft edema in 57.3% of patients. On the other hand, radiological evidence of sinusitis was detected in only 15.5% of patients.
CONCLUSION
The average olfactory bulb volumes were significantly higher in the patients' group compared to the control group, indicating significant edema and swelling in the olfactory bulb in patients with COVID-related olfactory dysfunction. Furthermore, in most patients, no sinonasal symptoms such as nasal congestion or rhinorrhea were reported, and similarly, no radiological evidence of sinusitis was detected. Consequently, the most probable mechanism of COVID-related olfactory dysfunction is sensorineural loss through virus spread and damage to the olfactory epithelium and pathways.
Topics: Humans; Smell; COVID-19; Olfaction Disorders; SARS-CoV-2; Magnetic Resonance Imaging; Sinusitis; Olfactory Bulb
PubMed: 36945746
DOI: 10.1177/19458924231163969 -
Problemy Endokrinologii May 2023The majority of Kallmann patients have anosmia or hyposmia. This is how the disease is diagnosed. Some of them don't have such complaints but olfactory dysfunction is...
BACKGROUND
The majority of Kallmann patients have anosmia or hyposmia. This is how the disease is diagnosed. Some of them don't have such complaints but olfactory dysfunction is diagnosed via olfactometry. Nowadays there is the lack of information about correlation between olfactometry results and subjective complaints. Correlation between olfactory bulbs size and olfactory dysfunction has been little studied.
AIM
To explore olfactory bulb size and olfactory function in patients with congenital isolated hypogonadotropic hypogonadism. To correlate olfactory bulb sizes and smell test scores.
MATERIALS AND METHODS
Single-centre comparative study. 34 patients were included. The main group consisted of 19 patients with hypogonadotropic (15 -with Kallmann syndrome, 4 - with normosmic hypogonadism). Olfactory bulbs MRI were provided to all the patients, olfactory test (Sniffin' Sticks Test) and molecular-genetic studies were provided in all patients with hypogonadism. Control group consisted of 15 patients who were provided with orbits MRI. Olfactory bulbs were evaluated additionally in them.
RESULTS
Normal size of olfactory bulbs were only in 1 patient with hypogonadism. Olfactory bulbs height and width were significantly smaller in patients with hypogonadism in comparison with control group (p<0.01). Height median of right bulb was 1.0 mm [0.2; 1.8] in patients from the main group vs. 3.0 [2.5; 3.2] in controls, width median of right bulb was 1.0 mm [0.2; 1.9] in patients from the main group vs. 2.5 [2.0; 3.0] in controls. Height median of left bulb was 0.8 mm [0.0; 1.2] in patients from the main group vs. 3.0 [2.7; 3.2] in controls, width median of left bulb was 0.8 mm [0.0; 1.2] in patients from the main group vs. 2.5 [2.0; 3.0] in controls. Correlation has been established between left bulb height (r=0.59) and width (r=0.67) and olfactometry results (p<0.05). 4 patients had no anosmia complaints but had olfactory dysfunction according to Sniffin' Sticks Tests.
CONCLUSION
Olfactometry was able to diagnose olfactory dysfunction in 78.5% (i.e. in 15 out of 19 patients with congenital isolated hypogonadotropic hypogonadism. However, anosmia complaints had only 11 out of 19 patients. It is the first results of olfactory bulb sizes in patients with hypogonadotropic hypogonadism in Russia. Uni - or bilateral hypoor aplasia were diagnosed in 94.7% patients with hypogonadism regardless of olfactory dysfunction. Bilateral olfactory bulbs hypoplasia were the most common MRI-finding (36.8%). Unilateral hypoor aplasia was diagnosed in 31.6% patients.
Topics: Humans; Kallmann Syndrome; Olfactory Bulb; Olfaction Disorders; Hypogonadism; Smell; Anosmia
PubMed: 37448273
DOI: 10.14341/probl13216