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Journal of Anatomy Jan 2024Central olfactory pathways (i.e., projection axons of the mitral and tufted cells), and especially olfactory striae, lack common terminology. This is due to their high... (Review)
Review
Central olfactory pathways (i.e., projection axons of the mitral and tufted cells), and especially olfactory striae, lack common terminology. This is due to their high degree of intra- and interindividual variability, which has been studied in detail over the past century by Beccari, Mutel, Klass, Erhart, and more recently, by Duque Parra et al. These variations led to some confusion about their number and anatomical arrangement. Recent advances in fiber tractography have enabled the precise in vivo visualization of human olfactory striae and the study of their projections. However, these studies require their algorithms to be set up according to the presumed anatomy of the analyzed fibers. A more precise definition of the olfactory striae is therefore needed, not only to allow a better analysis of the results but also to ensure the quality of the data obtained. By studying the various published works on the central olfactory pathways from the first systematic description by Soemmerring to the present, I have traced the different discussions on the olfactory tracts and summarized them here. This review adopts a systematic approach by addressing each stria individually and tracing the historical background of what was known about it in the past, compared to the current knowledge. The chronological and organized approach used provides a better understanding of the anatomy of these essential structures of the olfactory system.
Topics: Humans; Olfactory Bulb; Olfactory Pathways; Axons
PubMed: 37712100
DOI: 10.1111/joa.13952 -
Brain Pathology (Zurich, Switzerland) Mar 2022Alzheimer's disease (AD) is the most prevalent form of dementia. Key AD symptoms include memory and cognitive decline; however, comorbid symptoms such as depression and...
Alzheimer's disease (AD) is the most prevalent form of dementia. Key AD symptoms include memory and cognitive decline; however, comorbid symptoms such as depression and sensory-perceptual dysfunction are often reported. Among these, a deterioration of olfactory sensation is observed in approximately 90% of AD patients. However, the precise pathophysiological basis underlying olfactory deficits because of AD remains elusive. The olfactory glomeruli in the olfactory bulb (OB) receive sensory information in the olfactory processing pathway. Maintaining the structural and functional integrity of the olfactory glomerulus is critical to olfactory signalling. Herein, we conducted an in-depth histopathological assessment to reveal detailed structural alterations in the olfactory glomeruli in AD patients. Fresh frozen post-mortem OB specimens obtained from six AD patients and seven healthy age-matched individuals were examined. We used combined immunohistochemistry and stereology to assess the gross morphology and histological alterations, such as those in the expression of Aβ protein, microglia, and neurotransmitters in the OB. Electron microscopy was employed to study the ultrastructural features in the glomeruli. Significant accumulation of Aβ, morphologic damage, altered neurotransmitter levels, and microgliosis in the olfactory glomeruli of AD patients suggests that glomerular damage could affect olfactory function. Moreover, greater neurodegeneration was observed in the ventral olfactory glomeruli of AD patients. The synaptic ultrastructure revealed distorted postsynaptic densities and a decline in presynaptic vesicles in AD specimens. These findings show that the primary olfactory pathway is affected by the pathogenesis of AD, and may provide clues to identifying the mechanism involved in olfactory dysfunction in AD.
Topics: Alzheimer Disease; Autopsy; Humans; Olfactory Bulb; Smell
PubMed: 34704631
DOI: 10.1111/bpa.13033 -
Otolaryngologic Clinics of North America Feb 2020Like sensory maps in other systems, the sense of smell has an organizational structure based on converging projections of olfactory receptor neurons containing unique... (Review)
Review
Like sensory maps in other systems, the sense of smell has an organizational structure based on converging projections of olfactory receptor neurons containing unique odorant receptors onto the olfactory bulb in synaptic aggregations termed glomeruli. This organizational structure provides the potential for electrical stimulation and restoration of smell. Prior animal and human studies support the feasibility of an olfactory stimulation device, encouraging ongoing work in development of olfactory implants.
Topics: Animals; Cranial Nerves; Humans; Implantable Neurostimulators; Olfactory Bulb; Olfactory Receptor Neurons; Smell; Synaptic Transmission
PubMed: 31685237
DOI: 10.1016/j.otc.2019.09.014 -
Folia Morphologica 2022This study aimed to reveal the change in olfactory bulbus volume (OBV) and olfactory sulcus depth (OSD) in healthy Turkish paediatric individuals between 1 month and 18...
BACKGROUND
This study aimed to reveal the change in olfactory bulbus volume (OBV) and olfactory sulcus depth (OSD) in healthy Turkish paediatric individuals between 1 month and 18 years of age with 3 Tesla magnetic resonance imaging (MRI), taking into account different age groups and gender factors.
MATERIALS AND METHODS
In this retrospective study, 190 paediatric individuals who underwent cranial MRI were evaluated. Healthy paediatric cases were divided into four groups as infantile period (first 24 months when cerebral myelinisation was completed), early childhood (2-6 years), childhood (6-12 years) and adolescence (12-18 years). OBV and OSD measurements were performed on coronal T2-weighted brain MRI by 3 Tesla magnetic resonance scan. The mean, right and left OBVs and OSDs were used for evaluation.
RESULTS
The mean age was 9.9 ± 7.5 months for the infantile period, 4.5 ± 1.3 years for early childhood, 9.3 ± 1.7 years for childhood and 15.2 ± 1.7 years for adolescence. Mean, right and left OBV was found to be slightly larger in male children than in female children (p = 0.015, p = 0.033 and p = 0.010, respectively). There was no statistical difference between the genders for mean, right and left OSD (p = 0.559, p = 0.536 and p = 0.598, respectively). Among the age groups, the values of the 3rd and 4th groups in terms of mean, right and left OBV were higher than in the other two groups (p < 0.001). In terms of OSD, mean, right and left values were higher in group 2, 3 and 4 than in group 1 (p < 0.001).
CONCLUSIONS
These data differ by paediatric age group and gender for the development of OBV and OSD. Normal values for the paediatric age group and gender should be calculated to detect olfactory dysfunction.
Topics: Adolescent; Child; Child, Preschool; Female; Humans; Infant; Magnetic Resonance Imaging; Male; Olfaction Disorders; Olfactory Bulb; Prefrontal Cortex; Retrospective Studies
PubMed: 33749801
DOI: 10.5603/FM.a2021.0022 -
Journal of Computer Assisted TomographyWe investigated olfactory bulb (OB) volumes and olfactory sulcus (OS) depths in patients with rheumatoid arthritis (RA).
OBJECTIVES
We investigated olfactory bulb (OB) volumes and olfactory sulcus (OS) depths in patients with rheumatoid arthritis (RA).
METHODS
In this retrospective study, cranial magnetic resonance images of 68 adult patients were included. Group 1 consisted of 34 adult patients with RA. The control group (group 2) consisted of 34 adult patients without RA. In both groups, peripheral odor pathways (OB volumes and OS depths) were measured by magnetic resonance imaging.
RESULTS
Our results showed that the OB volumes of the RA group were significantly lower than those in the control group bilaterally (P < 0.05). In each of the RA and control groups, the OS depth of the right side was found to be significantly higher than those on the left side (P < 0.05). On the left side, OS depth values of RA patients who used biological agents were significantly higher than those RA patients who did not use biological agents (P < 0.05). Correlation tests showed that there were positive correlations between OB volumes and OS depths bilaterally. In older patients with RA, bilateral OS depth values were decreased (P < 0.05).
CONCLUSIONS
Our study has shown that the peripheral olfactory pathways in patients with RA can be affected to a degree that is reflected in anatomical measurements. The use of biological agents contributes to the protection of odor functions to a certain extent. The importance of evaluating the sense of smell in patients with RA clinically and radiologically should be emphasized.
Topics: Adult; Arthritis, Rheumatoid; Female; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Olfactory Bulb; Olfactory Pathways; Prefrontal Cortex; Retrospective Studies
PubMed: 35099148
DOI: 10.1097/RCT.0000000000001250 -
Cell and Tissue Research Jan 2021Evolutionarily, olfaction is one of the oldest senses and pivotal for an individual's health and survival. The olfactory bulb (OB), as the first olfactory relay station... (Review)
Review
Evolutionarily, olfaction is one of the oldest senses and pivotal for an individual's health and survival. The olfactory bulb (OB), as the first olfactory relay station in the brain, is known to heavily process sensory information. To adapt to an animal's needs, OB activity can be influenced by many factors either from within (intrinsic neuromodulation) or outside (extrinsic neuromodulation) the OB which include neurotransmitters, neuromodulators, hormones, and neuropeptides. Extrinsic sources seem to be of special importance as the OB receives massive efferent input from numerous brain centers even outweighing the sensory input from the nose. Here, we review neuromodulatory processes in the rodent OB from such extrinsic sources. We will discuss extrinsic neuromodulation according to points of origin, receptors involved, affected circuits, and changes in behavior. In the end, we give a brief outlook on potential future directions in research on neuromodulation in the OB.
Topics: Animals; Olfactory Bulb; Rodentia
PubMed: 33355709
DOI: 10.1007/s00441-020-03365-9 -
International Journal of Molecular... Apr 2020Endocannabinoid synthesis in the human body is naturally occurring and on-demand. It occurs in response to physiological and environmental stimuli, such as stress,... (Review)
Review
Endocannabinoid synthesis in the human body is naturally occurring and on-demand. It occurs in response to physiological and environmental stimuli, such as stress, anxiety, hunger, other factors negatively disrupting homeostasis, as well as the therapeutic use of the phytocannabinoid cannabidiol and recreational use of exogenous cannabis, which can lead to cannabis use disorder. Together with their specific receptors CB1R and CB2R, endocannabinoids are major components of endocannabinoid-mediated neuromodulation in a rapid and sustained manner. Extensive research on endocannabinoid function and expression includes studies in limbic system structures such as the hippocampus and amygdala. The wide distribution of endocannabinoids, their on-demand synthesis at widely different sites, their co-existence in specific regions of the body, their quantitative differences in tissue type, and different pathological conditions indicate their diverse biological functions that utilize specific and overlapping pathways in multiple organ systems. Here, we review emerging evidence of these pathways with a special emphasis on the role of endocannabinoids in decelerating neurodegenerative pathology through neural networks initiated by cells in the main olfactory bulb.
Topics: Animals; Disease Susceptibility; Endocannabinoids; Humans; Neurodegenerative Diseases; Neuronal Plasticity; Neurons; Olfactory Bulb; Signal Transduction
PubMed: 32325875
DOI: 10.3390/ijms21082850 -
Acta Physiologica (Oxford, England) Oct 2019Leptin is an important peptide hormone that regulates food intake and plays a crucial role in modulating olfactory function. Although a few previous studies have...
AIM
Leptin is an important peptide hormone that regulates food intake and plays a crucial role in modulating olfactory function. Although a few previous studies have investigated the effect of leptin on odor perception and discrimination in rodents, research on the neural basis underlying the behavioral changes is lacking. Here we study how leptin affects behavioral performance during a go/no-go task and how it modulates neural activity of mitral/tufted cells in the olfactory bulb, which plays an important role in odor information processing and representation.
METHODS
A go/no-go odor discrimination task was used in the behavioral test. For in vivo studies, single unit recordings, local field potential recordings and fiber photometry recordings were used. For in vitro studies, we performed patch clamp recordings in the slice of the olfactory bulb.
RESULTS
Behaviorally, leptin affects performance and reaction time in a difficult odor-discrimination task. Leptin decreases the spontaneous firing of single mitral/tufted cells, decreases the odor-evoked beta and high gamma local field potential response, and has bidirectional effects on the odor-evoked responses of single mitral/tufted cells. Leptin also inhibits the population calcium activity in genetically identified mitral/tufted cells and granule cells. Furthermore, in vitro slice recordings reveal that leptin inhibits mitral cell activity through direct modulation of the voltage-sensitive potassium channel.
CONCLUSIONS
The behavioral reduction in odor discrimination observed after leptin administration is likely due to decreased neural activity in mitral/tufted cells, caused by modulation of potassium channels in these cells.
Topics: Action Potentials; Animals; Behavior, Animal; Electrophysiological Phenomena; Ketones; Leptin; Male; Mice; Odorants; Olfactory Bulb; Olfactory Perception; Patch-Clamp Techniques; Pentanols; Smell
PubMed: 31144469
DOI: 10.1111/apha.13319 -
Revista Da Associacao Medica Brasileira... Oct 2021This study aimed to investigate whether the volume and morphology of the olfactory bulb are effective in the occurrence of anosmia in patients after COVID-19 infection.
OBJECTIVE
This study aimed to investigate whether the volume and morphology of the olfactory bulb are effective in the occurrence of anosmia in patients after COVID-19 infection.
METHODS
The olfactory bulbus volume was calculated by examining the brain magnetic resonance imaging of cases with positive (+) COVID-19 polymerase chain reaction test with and without anosmia. Evaluated magnetic resonance imaging images were the scans of patients before they were infected with COVID-19. The olfactory bulbus and olfactory nerve morphology of these patients were examined. The brain magnetic resonance imaging of 59 patients with anosmia and 64 controls without anosmia was evaluated. The olfactory bulb volumes of both groups were calculated. The olfactory bulb morphology and olfactory nerve types were examined and compared between the two groups.
RESULTS
The left and right olfactory bulb volumes were calculated for the anosmia group and control group as 47.8±15/49.3±14.3 and 50.5±9.9/50.9±9.6, respectively. There was no statistically significant difference between the two groups. When the olfactory bulb morphology was compared between the two groups, it was observed that types D and R were dominant in the anosmia group (p<0.05). Concerning olfactory nerve morphology, type N was significantly more common in the control group (p<0.05).
CONCLUSIONS
According to our results, the olfactory bulb volume does not affect the development of anosmia after COVID-19. However, it is striking that the bulb morphology significantly differs between the patients with and without anosmia. It is clear that the evaluation of COVID-19-associated smell disorders requires studies with a larger number of patients and a clinicoradiological approach.
Topics: Anosmia; COVID-19; Humans; Magnetic Resonance Imaging; Olfaction Disorders; Olfactory Bulb; SARS-CoV-2
PubMed: 35018981
DOI: 10.1590/1806-9282.20210678 -
The European Journal of Neuroscience Feb 2022The olfactory system has become an important functional gateway to understand and analyze neuromodulation since olfactory dysfunction and deficits have emerged as... (Review)
Review
The olfactory system has become an important functional gateway to understand and analyze neuromodulation since olfactory dysfunction and deficits have emerged as prodromal and, at other times, as first symptoms of many of neurodegenerative, neuropsychiatric and communication disorders. Considering olfactory dysfunction as outcome of altered, damaged and/or inefficient olfactory processing, in the current review, we analyze how olfactory processing interacts with the endocannabinoid signaling system. In the human body, endocannabinoid synthesis is a natural and on-demand response to a wide range of physiological and environmental stimuli. Our current understanding of the response dynamics of the endocannabinoid system is based in large part on research advances in limbic system areas, such as the hippocampus and the amygdala. Functional interactions of this signaling system with olfactory processing and associated pathways are just emerging but appear to grow rapidly with multidimensional approaches. Recent work analyzing the crystal structure of endocannabinoid receptors bound to their agonists in a signaling complex has opened avenues for developing specific therapeutic drugs that could help with neuroinflammation, neurodegeneration, and alleviation/reduction of pain. We discuss the role of endocannabinoids as signaling molecules in the olfactory system and the relevance of the endocannabinoid system for synaptic plasticity.
Topics: Endocannabinoids; Humans; Neuronal Plasticity; Olfaction Disorders; Olfactory Bulb; Smell
PubMed: 33724578
DOI: 10.1111/ejn.15186