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Science (New York, N.Y.) May 2017It is commonly believed that humans have a poor sense of smell compared to other mammalian species. However, this idea derives not from empirical studies of human... (Review)
Review
It is commonly believed that humans have a poor sense of smell compared to other mammalian species. However, this idea derives not from empirical studies of human olfaction but from a famous 19th-century anatomist's hypothesis that the evolution of human free will required a reduction in the proportional size of the brain's olfactory bulb. The human olfactory bulb is actually quite large in absolute terms and contains a similar number of neurons to that of other mammals. Moreover, humans have excellent olfactory abilities. We can detect and discriminate an extraordinary range of odors, we are more sensitive than rodents and dogs for some odors, we are capable of tracking odor trails, and our behavioral and affective states are influenced by our sense of smell.
Topics: Animals; Humans; Mammals; Neurons; Olfactory Bulb; Olfactory Perception; Smell
PubMed: 28495701
DOI: 10.1126/science.aam7263 -
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 -
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 -
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 -
Acta Neuropathologica Communications May 2024The majority of patients with Parkinson disease (PD) experience a loss in their sense of smell and accumulate insoluble α-synuclein aggregates in their olfactory bulbs...
The majority of patients with Parkinson disease (PD) experience a loss in their sense of smell and accumulate insoluble α-synuclein aggregates in their olfactory bulbs (OB). Subjects affected by a SARS-CoV-2-linked illness (COVID-19) also frequently experience hyposmia. We previously postulated that microglial activation as well as α-synuclein and tau misprocessing can occur during host responses following microbial encounters. Using semiquantitative measurements of immunohistochemical signals, we examined OB and olfactory tract specimens collected serially at autopsies between 2020 and 2023. Deceased subjects comprised 50 adults, which included COVID19 + patients (n = 22), individuals with Lewy body disease (e.g., PD; dementia with Lewy bodies (n = 6)), Alzheimer disease (AD; n = 3), and other neurodegenerative disorders (e.g., progressive supranuclear palsy (n = 2); multisystem atrophy (n = 1)). Further, we included neurologically healthy controls (n = 9), and added subjects with an inflammation-rich brain disorder as neurological controls (NCO; n = 7). When probing for microglial and histiocytic reactivity in the anterior olfactory nuclei (AON) by anti-CD68 immunostaining, scores were consistently elevated in NCO and AD cases. In contrast, microglial signals on average were not significantly altered in COVID19 + patients relative to healthy controls, although anti-CD68 reactivity in their OB and tracts declined with progression in age. Mild-to-moderate increases in phospho-α-synuclein and phospho-tau signals were detected in the AON of tauopathy- and synucleinopathy-afflicted brains, respectively, consistent with mixed pathology, as described by others. Lastly, when both sides were available for comparison in our case series, we saw no asymmetry in the degree of pathology of the left versus right OB and tracts. We concluded from our autopsy series that after a fatal course of COVID-19, microscopic changes in the rostral, intracranial portion of the olfactory circuitry -when present- reflected neurodegenerative processes seen elsewhere in the brain. In general, microglial reactivity correlated best with the degree of Alzheimer's-linked tauopathy and declined with progression of age in COVID19 + patients.
Topics: Humans; COVID-19; Olfactory Bulb; Aged; Male; Female; Aged, 80 and over; Middle Aged; Microglia; alpha-Synuclein; tau Proteins; SARS-CoV-2; Neurodegenerative Diseases
PubMed: 38698465
DOI: 10.1186/s40478-024-01761-8 -
Neurologia Medico-chirurgica Apr 2004A 30-year-old man presented with a 2-year history of intermittent headache. No neurological deficit was detected. Computed tomography (CT) and magnetic resonance imaging... (Review)
Review
A 30-year-old man presented with a 2-year history of intermittent headache. No neurological deficit was detected. Computed tomography (CT) and magnetic resonance imaging showed a tumor with a diameter of 2.5 cm in the left anterior skull base associated with bone scalloping on three-dimensional CT. Angiography showed a hypovascular tumor. Craniotomy demonstrated a tumor in the region of the left olfactory groove attached to the anterior part of the cribriform plate. The histological diagnosis was schwannoma. Schwannoma arising from near the olfactory groove is rare, with only 13 other cases reported. The precise origin of these tumors is not well understood, but the tumor in this case probably arose from the fila olfactoria, because the olfactory bulb was involved in the tumor, whereas the olfactory tract remained intact.
Topics: Adult; Carotid Arteries; Cerebral Angiography; Diagnosis, Differential; Humans; Imaging, Three-Dimensional; Magnetic Resonance Imaging; Male; Neurilemmoma; Olfactory Bulb; Skull Base; Tomography, X-Ray Computed
PubMed: 15185758
DOI: 10.2176/nmc.44.191 -
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 -
Pediatric Radiology Sep 2019We describe association of olfactory bulb and olfactory tract abnormalities in a child with acrocallosal syndrome caused by kinesin family membrane 7 (KIF7) mutation in...
We describe association of olfactory bulb and olfactory tract abnormalities in a child with acrocallosal syndrome caused by kinesin family membrane 7 (KIF7) mutation in sonic hedgehog pathway. The child also had fontanellar bone in the anterior fontanelle, short sagittal suture, sagittal synostosis, hippocampal malrotation and Joubert malformation. Fontanellar bone has been described in GLI3 mutation and mutant mice models but has not been reported in KIF7 mutation. We briefly review the role of sonic hedgehog pathway and its components KIF7 and GLI3 in forebrain and olfactory system development and also describe olfactory system abnormality in a child with GLI3 mutation.
Topics: Abnormalities, Multiple; Acrocallosal Syndrome; Acrocephalosyndactylia; Brain; Child, Preschool; Female; Humans; Infant; Magnetic Resonance Imaging; Olfactory Bulb; Tomography, X-Ray Computed
PubMed: 31399769
DOI: 10.1007/s00247-019-04480-8 -
International Journal of Molecular... Apr 2019The olfactory system, composed of the olfactory organs and the olfactory bulb, allows organisms to interact with their environment and through the detection of odor... (Review)
Review
The olfactory system, composed of the olfactory organs and the olfactory bulb, allows organisms to interact with their environment and through the detection of odor signals. Olfaction mediates behaviors pivotal for survival, such as feeding, mating, social behavior, and danger assessment. The olfactory organs are directly exposed to the milieu, and thus are particularly vulnerable to damage by environmental pollutants and toxicants, such as heavy metals, pesticides, and surfactants, among others. Given the widespread occurrence of olfactory toxicants, there is a pressing need to understand the effects of these harmful compounds on olfactory function. Zebrafish () is a valuable model for studying human physiology, disease, and toxicity. Additionally, the anatomical components of the zebrafish olfactory system are similar to those of other vertebrates, and they present a remarkable degree of regeneration and neuroplasticity, making it an ideal model for the study of regeneration, reorganization and repair mechanisms following olfactory toxicant exposure. In this review, we focus on (1) the anatomical, morphological, and functional organization of the olfactory system of zebrafish; (2) the adverse effects of olfactory toxicants and injury to the olfactory organ; and (3) remodeling and repair neuroplasticity mechanisms following injury and degeneration by olfactory toxicant exposure.
Topics: Animals; Disease Models, Animal; Neuronal Plasticity; Neurotoxicity Syndromes; Odorants; Olfactory Bulb; Zebrafish
PubMed: 30986990
DOI: 10.3390/ijms20071639 -
Trends in Neurosciences Jan 2011In mammals, new neurons are recruited into restricted brain areas throughout life. Adult-born neurons produced in the subventricular zone of the lateral ventricle... (Review)
Review
In mammals, new neurons are recruited into restricted brain areas throughout life. Adult-born neurons produced in the subventricular zone of the lateral ventricle migrate rostrally towards the olfactory bulb. Although thousands of neurons reach this central structure every day, the functional impact of their integration into mature circuits remains a matter of debate. Recent investigations have revealed no striking sensory deficits per se when adult bulbar neurogenesis is challenged. However, some cognitive functions, such as perceptual learning and olfactory memory, are clearly impaired. In this review we highlight the role of network activity in shaping ongoing neurogenesis and, in turn, how the integration of adult-born neurons refines pre-existing network function, and consequently olfactory behavior.
Topics: Animals; Learning; Nerve Net; Neurogenesis; Neurons; Odorants; Olfactory Bulb; Smell
PubMed: 20980064
DOI: 10.1016/j.tins.2010.09.006