-
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 -
Neural Plasticity 2015The olfactory system provides a great opportunity to explore the mechanisms that underlie the formation and function of neural circuits because of the simplicity of its... (Review)
Review
The olfactory system provides a great opportunity to explore the mechanisms that underlie the formation and function of neural circuits because of the simplicity of its structure. Olfactory sensory neurons (OSNs) located in the peripheral olfactory epithelium (OE) take part in the initial formation and function of glomeruli in the olfactory bulb (OB) inside the central nervous system. Glomeruli are key in the process of transduction of olfactory information, as they constitute a map in the OB that sorts the different types of odorant inputs. This odorant categorization allows proper olfactory perception, and it is achieved through the anatomical organization and function of the different glomerular circuits. Once formed, glomeruli keep the capacity to undergo diverse plasticity processes, which is unique among the different neural circuits of the central nervous system. In this context, through the expression and function of the odorant receptors (ORs), OSNs perform two of the most important roles in the olfactory system: transducing odorant information to the nervous system and initiating the development of the glomerular map to organize olfactory information. This review addresses essential information that has emerged in recent years about the molecular basis of these processes.
Topics: Animals; Humans; Neuronal Plasticity; Olfactory Bulb; Olfactory Receptor Neurons; Receptors, Odorant; Smell
PubMed: 25688305
DOI: 10.1155/2015/975367 -
Chemical Senses Jul 2019Cross-modal sensory communication is an innate biological process that refers to the combination and/or interpretation of different types of sensory input in the brain.... (Review)
Review
Cross-modal sensory communication is an innate biological process that refers to the combination and/or interpretation of different types of sensory input in the brain. Often, this process conjugates with neural modulation, by which the neural signals that convey sensory information are adjusted, such as intensity, frequency, complexity, and/or novelty. Although the anatomic pathways involved in cross-modal sensory integration have been previously described, the course of development and the physiological roles of multisensory signaling integration in brain functions remain to be elucidated. In this article, I review some of the recent findings in sensory integration from research using the zebrafish models. In zebrafish, cross-modal sensory integration occurs between the olfactory and visual systems. It is mediated by the olfacto-retinal centrifugal (ORC) pathway, which originates from the terminalis nerve (TN) in the olfactory bulb and terminates in the neural retina. In the retina, the TNs synapse with the inner nuclear layer dopaminergic interplexiform cells (DA-IPCs). Through the ORC pathway, stimulation of the olfactory neurons alters the cellular activity of TNs and DA-IPCs, which in turn modulates retinal neural function and increases behavioral visual sensitivity.
Topics: Animals; Neurons; Olfactory Bulb; Retina; Smell; Zebrafish
PubMed: 31066902
DOI: 10.1093/chemse/bjz022 -
Journal of Neurophysiology Oct 2017Synaptic inhibition critically influences sensory processing throughout the mammalian brain, including the main olfactory bulb (MOB), the first station of sensory... (Review)
Review
Synaptic inhibition critically influences sensory processing throughout the mammalian brain, including the main olfactory bulb (MOB), the first station of sensory processing in the olfactory system. Decades of research across numerous laboratories have established a central role for granule cells (GCs), the most abundant GABAergic interneuron type in the MOB, in the precise regulation of principal mitral and tufted cell (M/TC) firing rates and synchrony through lateral and recurrent inhibitory mechanisms. In addition to GCs, however, the MOB contains a vast diversity of other GABAergic interneuron types, and recent findings suggest that, while fewer in number, these oft-ignored interneurons are just as important as GCs in shaping odor-evoked M/TC activity. Here I challenge the prevailing centrality of GCs. In this review, I first outline the specific properties of each GABAergic interneuron type in the rodent MOB, with particular emphasis placed on direct interneuron recordings and cell type-selective manipulations. On the basis of these properties, I then critically reevaluate the contribution of GCs vs. other interneuron types to the regulation of odor-evoked M/TC firing rates and synchrony via lateral, recurrent, and other inhibitory mechanisms. This analysis yields a novel model in which multiple interneuron types with distinct abundances, connectivity patterns, and physiologies complement one another to regulate M/TC activity and sensory processing.
Topics: Animals; GABAergic Neurons; Interneurons; Mammals; Olfactory Bulb
PubMed: 28724776
DOI: 10.1152/jn.00109.2017 -
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 -
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 -
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 -
Cold Spring Harbor Perspectives in... Jul 2015Adult neurogenesis appears very well conserved among mammals. It was, however, not until recently that quantitative data on the extent of this process became available... (Review)
Review
Adult neurogenesis appears very well conserved among mammals. It was, however, not until recently that quantitative data on the extent of this process became available in humans, largely because of methodological challenges to study this process in man. There is substantial hippocampal neurogenesis in adult humans, but humans appear unique among mammals in that there is no detectable olfactory bulb neurogenesis but continuous addition of new neurons in the striatum.
Topics: Adult; Cell Differentiation; Cellular Senescence; Corpus Striatum; Hippocampus; Humans; Neurogenesis; Neurons; Olfactory Bulb; Time Factors
PubMed: 26134318
DOI: 10.1101/cshperspect.a018994 -
The International Journal of... Sep 2017Evidence for olfactory dysfunction in schizophrenia has been firmly established. However, in the typical understanding of schizophrenia, olfaction is not recognized to...
BACKGROUND
Evidence for olfactory dysfunction in schizophrenia has been firmly established. However, in the typical understanding of schizophrenia, olfaction is not recognized to contribute to or interact with the illness. Despite the solid presence of olfactory dysfunction in schizophrenia, its relation to the rest of the illness remains largely unclear. Here, we aimed to examine functional connectivity of the olfactory bulb, olfactory tract, and piriform cortices and isolate the network that would account for the altered olfaction in schizophrenia.
METHODS
We examined the functional connectivity of these specific olfactory regions in order to isolate other brain regions associated with olfactory processing in schizophrenia. Using the resting state functional MRI data from the Center for Biomedical Research Excellence in Brain Function and Mental Illness, we compared 84 patients of schizophrenia and 90 individuals without schizophrenia.
RESULTS
The schizophrenia group showed disconnectivity between the anterior piriform cortex and the nucleus accumbens, between the posterior piriform cortex and the middle frontal gyrus, and between the olfactory tract and the visual cortices.
CONCLUSIONS
The current results suggest functional disconnectivity of olfactory regions in schizophrenia, which may account for olfactory dysfunction and disrupted integration with other sensory modalities in schizophrenia.
Topics: Adult; Brain Mapping; Case-Control Studies; Female; Frontal Lobe; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Male; Middle Aged; Olfaction Disorders; Olfactory Bulb; Olfactory Pathways; Oxygen; Rest; Schizophrenia; Young Adult
PubMed: 28582529
DOI: 10.1093/ijnp/pyx045 -
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