Zonal organization of the mammalian main and accessory olfactory systems

Zonal organization is one of the characteristic features observed in both main and accessory olfactory systems. In the main olfactory system, most of the odorant receptors are classified into four groups according to their zonal expression patterns in the olfactory epithelium. Each group of odorant receptors is expressed by sensory neurons distributed within one of four circumscribed zones. Olfactory sensory neurons in a given zone of the epithelium project their axons to the glomeruli in a corresponding zone of the main olfactory bulb. Glomeruli in the same zone tend to represent similar odorant receptors having similar tuning specificity to odorants. Vomeronasal receptors (or pheromone receptors) are classified into two groups in the accessory olfactory system. Each group of receptors is expressed by vomeronasal sensory neurons in either the apical or basal zone of the vomeronasal epithelium. Sensory neurons in the apical zone project their axons to the rostral zone of the accessory olfactory bulb and form synaptic connections with mitral–tufted cells belonging to the rostral zone. Signals originated from basal zone sensory neurons are sent to mitral–tufted cells in the caudal zone of the accessory olfactory bulb. We discuss functional implications of the zonal organization in both main and accessory olfactory systems.

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Region-specific amyloid-β accumulation in the olfactory system influences olfactory sensory neuronal dysfunction in 5xFAD mice

Alzheimer s Research & Therapy ◽

10.1186/s13195-020-00730-2 ◽

2021 ◽

Vol 13 (1) ◽

Author(s):

Gowoon Son ◽

Seung-Jun Yoo ◽

Shinwoo Kang ◽

Ameer Rasheed ◽

Da Hae Jung ◽

...

Keyword(s):

Olfactory Bulb ◽

Sensory Neurons ◽

Olfactory System ◽

Amyloid Β ◽

Olfactory Sensory Neurons ◽

Basal Cells ◽

Irreversible Damage ◽

5Xfad Mouse ◽

Peripheral Areas ◽

5Xfad Mice

Abstract Background Hyposmia in Alzheimer’s disease (AD) is a typical early symptom according to numerous previous clinical studies. Although amyloid-β (Aβ), which is one of the toxic factors upregulated early in AD, has been identified in many studies, even in the peripheral areas of the olfactory system, the pathology involving olfactory sensory neurons (OSNs) remains poorly understood. Methods Here, we focused on peripheral olfactory sensory neurons (OSNs) and delved deeper into the direct relationship between pathophysiological and behavioral results using odorants. We also confirmed histologically the pathological changes in 3-month-old 5xFAD mouse models, which recapitulates AD pathology. We introduced a numeric scale histologically to compare physiological phenomenon and local tissue lesions regardless of the anatomical plane. Results We observed the odorant group that the 5xFAD mice showed reduced responses to odorants. These also did not physiologically activate OSNs that propagate their axons to the ventral olfactory bulb. Interestingly, the amount of accumulated amyloid-β (Aβ) was high in the OSNs located in the olfactory epithelial ectoturbinate and the ventral olfactory bulb glomeruli. We also observed irreversible damage to the ectoturbinate of the olfactory epithelium by measuring the impaired neuronal turnover ratio from the basal cells to the matured OSNs. Conclusions Our results showed that partial and asymmetrical accumulation of Aβ coincided with physiologically and structurally damaged areas in the peripheral olfactory system, which evoked hyporeactivity to some odorants. Taken together, partial olfactory dysfunction closely associated with peripheral OSN’s loss could be a leading cause of AD-related hyposmia, a characteristic of early AD.

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Retrograde labelling of mitral/tufted cells in the mouse accessory olfactory bulb following local injections of the lipophillic tracer DiI into the vomeronasal amygdala

Brain Research ◽

10.1016/s0006-8993(01)02225-9 ◽

2001 ◽

Vol 896 (1-2) ◽

pp. 198-203 ◽

Cited By ~ 15

Author(s):

Ignacio Salazar ◽

Peter Anthony Brennan

Keyword(s):

Olfactory Bulb ◽

Accessory Olfactory Bulb ◽

Retrograde Labelling ◽

Local Injections ◽

Tufted Cells

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Expression Patterns of Odorant Receptors and Response Properties of Olfactory Sensory Neurons in Aged Mice

Chemical Senses ◽

10.1093/chemse/bjp056 ◽

2009 ◽

Vol 34 (8) ◽

pp. 695-703 ◽

Cited By ~ 30

Author(s):

Anderson C. Lee ◽

Huikai Tian ◽

Xavier Grosmaitre ◽

Minghong Ma

Keyword(s):

Sensory Neurons ◽

Expression Patterns ◽

Odorant Receptors ◽

Olfactory Sensory Neurons ◽

Response Properties ◽

Aged Mice

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Molecular Biology of Vertebrate Olfactory Receptors and Circuits

Oxford Research Encyclopedia of Neuroscience ◽

10.1093/acrefore/9780190264086.013.92 ◽

2021 ◽

Author(s):

Richard P. Tucker ◽

Qizhi Gong

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Olfactory Bulb ◽

Gene Family ◽

Sensory Neuron ◽

Sensory Neurons ◽

Odorant Receptor ◽

Vomeronasal Organ ◽

Odorant Receptors ◽

The Central Nervous System

Animals use their olfactory system for the procurement of food, the detection of danger, and the identification of potential mates. In vertebrates, the olfactory sensory neuron has a single apical dendrite that is exposed to the environment and a single basal axon that projects to the central nervous system (i.e., the olfactory bulb). The first odorant receptors to be discovered belong to an enormous gene family encoding G protein-coupled seven transmembrane domain proteins. Odorant binding to these classical odorant receptors initiates a GTP-dependent signaling cascade that uses cAMP as a second messenger. Subsequently, additional types of odorant receptors using different signaling pathways have been identified. While most olfactory sensory neurons are found in the olfactory sensory neuroepithelium, others are found in specialized olfactory subsystems. In rodents, the vomeronasal organ contains neurons that recognize pheromones, the septal organ recognizes odorant and mechanical stimuli, and the neurons of the Grüneberg ganglion are sensitive to cool temperatures and certain volatile alarm signals. Within the olfactory sensory neuroepithelium, each sensory neuron expresses a single odorant receptor gene out of the large gene family; the axons of sensory neurons expressing the same odorant receptor typically converge onto a pair of glomeruli at the periphery of the olfactory bulb. This results in the transformation of olfactory information into a spatially organized odortopic map in the olfactory bulb. The axons originating from the vomeronasal organ project to the accessory olfactory bulb, whereas the axons from neurons in the Grüneberg ganglion project to 10 specific glomeruli found in the caudal part of the olfactory bulb. Within a glomerulus, the axons originating from olfactory sensory neurons synapse on the dendrites of olfactory bulb neurons, including mitral and tufted cells. Mitral cells and tufted cells in turn project directly to higher brain centers (e.g., the piriform cortex and olfactory tubercle). The integration of olfactory information in the olfactory cortices and elsewhere in the central nervous system informs and directs animal behavior.

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Role of Axonal Odorant Receptors in Olfactory Topography

Neuroscience Insights ◽

10.1177/2633105520923411 ◽

2020 ◽

Vol 15 ◽

pp. 263310552092341

Author(s):

Claudia Lodovichi

Keyword(s):

Olfactory Bulb ◽

Sensory Neurons ◽

Axon Terminal ◽

Internal Representation ◽

Dual Role ◽

Odorant Receptors ◽

Topographic Map ◽

And Function ◽

Guidance Molecule

A unique feature in the organization of the olfactory system is the dual role of the odorant receptors: they detect odors in the nasal epithelium and they play an instructive role in the convergence of olfactory sensory neuron axons in specific loci, ie, glomeruli, in the olfactory bulb. The dual role is corroborated by the expression of the odorant receptors in 2 specific locations of the olfactory sensory neurons: the cilia that protrude in the nostril, where the odorant receptors interact with odors, and the axon terminal, a suitable location for a potential axon guidance molecule. The mechanism of activation and function of the odorant receptors expressed at the axon terminal remained unknown for almost 20 years. A recent study identified the first putative ligand of the axonal odorant receptors, phosphatidylethanolamine-binding protein1, a molecule expressed in the olfactory bulb. The distinctive mechanisms of activation of the odorant receptors expressed at the opposite locations in sensory neurons, by odors, at the cilia, and by molecules expressed in the olfactory bulb, at the axon terminal, explain the dual role of the odorant receptors and link the specificity of odor perception with its internal representation, in the topographic map.

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Odorant Receptors in the Formation of the Olfactory Bulb Circuitry

Physiology ◽

10.1152/physiol.00015.2012 ◽

2012 ◽

Vol 27 (4) ◽

pp. 200-212 ◽

Cited By ~ 14

Author(s):

Claudia Lodovichi ◽

Leonardo Belluscio

Keyword(s):

Olfactory Bulb ◽

Axon Guidance ◽

Sensory Neurons ◽

Odorant Receptors ◽

Olfactory Sensory Neurons ◽

Neural Connectivity ◽

Axon Terminals ◽

Primary Function

In mammals, smell is mediated by odorant receptors expressed by sensory neurons in the nose. These specialized receptors are found both on olfactory sensory neurons' cilia and axon terminals. Although the primary function of ciliary odorant receptors is to detect odorants, their axonal role remains unclear but is thought to involve axon guidance. This review discusses findings that show axonal odorant receptors are indeed functional and capable of modulating neural connectivity.

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Paradoxically sparse chemosensory tuning in broadly-integrating external granule cells in the mouse accessory olfactory bulb

10.1101/703892 ◽

2019 ◽

Author(s):

Xingjian Zhang ◽

Julian P. Meeks

Keyword(s):

Patch Clamp ◽

Olfactory Bulb ◽

Olfactory System ◽

Granule Cells ◽

Ex Vivo ◽

Accessory Olfactory Bulb ◽

Main Olfactory Bulb ◽

Patch Clamp Electrophysiology ◽

Accessory Olfactory System ◽

Critical Circuit

AbstractThe accessory olfactory bulb (AOB) is a critical circuit in the mouse accessory olfactory system (AOS), but AOB processing is poorly understood compared to the main olfactory bulb (MOB). We used 2-photon GCaMP6f Ca2+ imaging in an ex vivo preparation to study the chemosensory tuning of AOB external granule cells (EGCs), an interneuron population hypothesized to broadly integrate from mitral cells (MCs). We measured MC and EGC tuning to natural chemosignal blends and monomolecular ligands, finding that EGC tuning was far sparser than MC tuning. Simultaneous patch-clamp electrophysiology and Ca2+ imaging indicated that this was only partially explained by lower GCaMP6f-to-spiking ratios in EGCs compared to MCs. Ex vivo patch-clamp recordings revealed that EGC subthreshold responsivity was broad, but monomolecular ligand responses were insufficient to elicit spiking. These results indicate that EGC spiking is selectively engaged by chemosensory blends, suggesting different roles for EGCs than analogous interneurons in the MOB.

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An update on anatomy and function of the teleost olfactory system

PeerJ ◽

10.7717/peerj.7808 ◽

2019 ◽

Vol 7 ◽

pp. e7808 ◽

Cited By ~ 5

Author(s):

Jesús Olivares ◽

Oliver Schmachtenberg

Keyword(s):

Olfactory System ◽

Olfactory Receptor Neurons ◽

Odorant Receptors ◽

Odor Coding ◽

Animal Group ◽

Different Types ◽

Olfactory Systems ◽

Receptor Neurons ◽

Olfactory Organs ◽

And Function

About half of all extant vertebrates are teleost fishes. Although our knowledge about anatomy and function of their olfactory systems still lags behind that of mammals, recent advances in cellular and molecular biology have provided us with a wealth of novel information about the sense of smell in this important animal group. Its paired olfactory organs contain up to five types of olfactory receptor neurons expressing OR, TAAR, VR1- and VR2-class odorant receptors associated with individual transduction machineries. The different types of receptor neurons are preferentially tuned towards particular classes of odorants, that are associated with specific behaviors, such as feeding, mating or migration. We discuss the connections of the receptor neurons in the olfactory bulb, the differences in bulbar circuitry compared to mammals, and the characteristics of second order projections to telencephalic olfactory areas, considering the everted ontogeny of the teleost telencephalon. The review concludes with a brief overview of current theories about odor coding and the prominent neural oscillations observed in the teleost olfactory system.

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