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Hirata T. Olfactory information processing viewed through mitral and tufted cell-specific channels. Front Neural Circuits 2024; 18:1382626. [PMID: 38523698 PMCID: PMC10957668 DOI: 10.3389/fncir.2024.1382626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2024] [Accepted: 02/29/2024] [Indexed: 03/26/2024] Open
Abstract
Parallel processing is a fundamental strategy of sensory coding. Through this processing, unique and distinct features of sensations are computed and projected to the central targets. This review proposes that mitral and tufted cells, which are the second-order projection neurons in the olfactory bulb, contribute to parallel processing within the olfactory system. Based on anatomical and functional evidence, I discuss potential features that could be conveyed through the unique channel formed by these neurons.
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Affiliation(s)
- Tatsumi Hirata
- Brain Function Laboratory, National Institute of Genetics, SOKENDAI, Mishima, Japan
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Jones S, Zylberberg J, Schoppa N. Cellular and Synaptic Mechanisms That Differentiate Mitral Cells and Superficial Tufted Cells Into Parallel Output Channels in the Olfactory Bulb. Front Cell Neurosci 2020; 14:614377. [PMID: 33414707 PMCID: PMC7782477 DOI: 10.3389/fncel.2020.614377] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 11/24/2020] [Indexed: 11/29/2022] Open
Abstract
A common feature of the primary processing structures of sensory systems is the presence of parallel output “channels” that convey different information about a stimulus. In the mammalian olfactory bulb, this is reflected in the mitral cells (MCs) and tufted cells (TCs) that have differing sensitivities to odors, with TCs being more sensitive than MCs. In this study, we examined potential mechanisms underlying the different responses of MCs vs. TCs. For TCs, we focused on superficial TCs (sTCs), which are a population of output TCs that reside in the superficial-most portion of the external plexiform layer, along with external tufted cells (eTCs), which are glutamatergic interneurons in the glomerular layer. Using whole-cell patch-clamp recordings in mouse bulb slices, we first measured excitatory currents in MCs, sTCs, and eTCs following olfactory sensory neuron (OSN) stimulation, separating the responses into a fast, monosynaptic component reflecting direct inputs from OSNs and a prolonged component partially reflecting eTC-mediated feedforward excitation. Responses were measured to a wide range of OSN stimulation intensities, simulating the different levels of OSN activity that would be expected to be produced by varying odor concentrations in vivo. Over a range of stimulation intensities, we found that the monosynaptic current varied significantly between the cell types, in the order of eTC > sTC > MC. The prolonged component was smaller in sTCs vs. both MCs and eTCs. sTCs also had much higher whole-cell input resistances than MCs, reflecting their smaller size and greater membrane resistivity. To evaluate how these different electrophysiological aspects contributed to spiking of the output MCs and sTCs, we used computational modeling. By exchanging the different cell properties in our modeled MCs and sTCs, we could evaluate each property's contribution to spiking differences between these cell types. This analysis suggested that the higher sensitivity of spiking in sTCs vs. MCs reflected both their larger monosynaptic OSN signal as well as their higher input resistance, while their smaller prolonged currents had a modest opposing effect. Taken together, our results indicate that both synaptic and intrinsic cellular features contribute to the production of parallel output channels in the olfactory bulb.
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Affiliation(s)
- Shelly Jones
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Joel Zylberberg
- Department of Physics and Center for Vision Research, York University, Toronto, ON, Canada
| | - Nathan Schoppa
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
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Abstract
Generation of neuronal diversity is a biological strategy widely used in the brain to process complex information. The olfactory bulb is the first relay station of olfactory information in the vertebrate central nervous system. In the olfactory bulb, axons of the olfactory sensory neurons form synapses with dendrites of projection neurons that transmit the olfactory information to the olfactory cortex. Historically, the olfactory bulb projection neurons have been classified into two populations, mitral cells and tufted cells. The somata of these cells are distinctly segregated within the layers of the olfactory bulb; the mitral cells are located in the mitral cell layer while the tufted cells are found in the external plexiform layer. Although mitral and tufted cells share many morphological, biophysical, and molecular characteristics, they differ in soma size, projection patterns of their dendrites and axons, and odor responses. In addition, tufted cells are further subclassified based on the relative depth of their somata location in the external plexiform layer. Evidence suggests that different types of tufted cells have distinct cellular properties and play different roles in olfactory information processing. Therefore, mitral and different types of tufted cells are considered as starting points for parallel pathways of olfactory information processing in the brain. Moreover, recent studies suggest that mitral cells also consist of heterogeneous subpopulations with different cellular properties despite the fact that the mitral cell layer is a single-cell layer. In this review, we first compare the morphology of projection neurons in the olfactory bulb of different vertebrate species. Next, we explore the similarities and differences among subpopulations of projection neurons in the rodent olfactory bulb. We also discuss the timing of neurogenesis as a factor for the generation of projection neuron heterogeneity in the olfactory bulb. Knowledge about the subpopulations of olfactory bulb projection neurons will contribute to a better understanding of the complex olfactory information processing in higher brain regions.
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Affiliation(s)
- Fumiaki Imamura
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA, United States
| | - Ayako Ito
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA, United States
| | - Brandon J LaFever
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA, United States
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Hirata T, Shioi G, Abe T, Kiyonari H, Kato S, Kobayashi K, Mori K, Kawasaki T. A Novel Birthdate-Labeling Method Reveals Segregated Parallel Projections of Mitral and External Tufted Cells in the Main Olfactory System. eNeuro 2019; 6:ENEURO.0234-19.2019. [PMID: 31672846 PMCID: PMC6868177 DOI: 10.1523/eneuro.0234-19.2019] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 10/16/2019] [Accepted: 10/19/2019] [Indexed: 01/09/2023] Open
Abstract
A fundamental strategy in sensory coding is parallel processing, whereby unique, distinct features of sensation are computed and projected to the central target in the form of submodal maps. It remains unclear, however, whether such parallel processing strategy is employed in the main olfactory system, which codes the complex hierarchical odor and behavioral scenes. A potential scheme is that distinct subsets of projection neurons in the olfactory bulb (OB) form parallel projections to the targets. Taking advantage of the observation that the distinct projection neurons develop at different times, we developed a Cre-loxP-based method that allows for birthdate-specific labeling of cell bodies and their axon projections in mice. This birthdate tag analysis revealed that the mitral cells (MCs) born in an early developmental stage and the external tufted cells (TCs) born a few days later form segregated parallel projections. Specifically, the latter subset converges the axons onto only two small specific targets, one of which, located at the anterolateral edge of the olfactory tubercle (OT), excludes widespread MC projections. This target is made up of neurons that express dopamine D1 but not D2 receptor and corresponds to the most anterolateral isolation of the CAP compartments (aiCAP) that were defined previously. This finding of segregated projections suggests that olfactory sensing does indeed involve parallel processing of functionally distinct submodalities. Importantly, the birthdate tag method used here may pave the way for deciphering the functional meaning of these individual projection pathways in the future.
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Affiliation(s)
- Tatsumi Hirata
- Brain Function Laboratory, National Institute of Genetics
- Graduate University for Advanced Studies, SOKENDAI, Mishima 411-8540, Japan
| | - Go Shioi
- Laboratory for Genetic Engineering, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
| | - Takaya Abe
- Laboratory for Genetic Engineering, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
- Laboratory for Animal Resource Development, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
| | - Hiroshi Kiyonari
- Laboratory for Genetic Engineering, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
- Laboratory for Animal Resource Development, RIKEN Center for Biosystems Dynamics Research, Kobe 650-0047, Japan
| | - Shigeki Kato
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Kazuto Kobayashi
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Kensaku Mori
- Department of Physiology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-0033, Japan
| | - Takahiko Kawasaki
- Brain Function Laboratory, National Institute of Genetics
- Graduate University for Advanced Studies, SOKENDAI, Mishima 411-8540, Japan
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Sánchez-Guardado L, Lois C. Lineage does not regulate the sensory synaptic input of projection neurons in the mouse olfactory bulb. eLife 2019; 8:46675. [PMID: 31453803 PMCID: PMC6744224 DOI: 10.7554/elife.46675] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Accepted: 08/26/2019] [Indexed: 12/14/2022] Open
Abstract
Lineage regulates the synaptic connections between neurons in some regions of the invertebrate nervous system. In mammals, recent experiments suggest that cell lineage determines the connectivity of pyramidal neurons in the neocortex, but the functional relevance of this phenomenon and whether it occurs in other neuronal types remains controversial. We investigated whether lineage plays a role in the connectivity of mitral and tufted cells, the projection neurons in the mouse olfactory bulb. We used transgenic mice to sparsely label neuronal progenitors and observed that clonally related neurons receive synaptic input from olfactory sensory neurons expressing different olfactory receptors. These results indicate that lineage does not determine the connectivity between olfactory sensory neurons and olfactory bulb projection neurons.
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Affiliation(s)
- Luis Sánchez-Guardado
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States
| | - Carlos Lois
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States
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Short SM, Wachowiak M. Temporal Dynamics of Inhalation-Linked Activity across Defined Subpopulations of Mouse Olfactory Bulb Neurons Imaged In Vivo. eNeuro 2019; 6:ENEURO. [PMID: 31209151 DOI: 10.1523/ENEURO.0189-19.2019] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Accepted: 05/23/2019] [Indexed: 11/21/2022] Open
Abstract
In mammalian olfaction, inhalation drives the temporal patterning of neural activity that underlies early olfactory processing. It remains poorly understood how the neural circuits that process incoming olfactory information are engaged in the context of inhalation-linked dynamics. Here, we used artificial inhalation and two-photon calcium imaging to compare the dynamics of activity evoked by odorant inhalation across major cell types of the mouse olfactory bulb (OB). We expressed GCaMP6f or jRGECO1a in mitral and tufted cell (MTC) subpopulations, olfactory sensory neurons (OSNs), and two major juxtaglomerular interneuron classes and imaged responses to a single inhalation of odorant. Activity in all cell types was strongly linked to inhalation, and all cell types showed some variance in the latency, rise times, and durations of their inhalation-linked response. Juxtaglomerular interneuron dynamics closely matched that of sensory inputs, while MTCs showed the highest diversity in responses, with a range of latencies and durations that could not be accounted for by heterogeneity in sensory input dynamics. Diversity was apparent even among “sister” tufted cells innervating the same glomerulus. Surprisingly, inhalation-linked responses of MTCs were highly overlapping and could not be distinguished on the basis of their inhalation-linked dynamics, with the exception of a subpopulation of superficial tufted cells expressing cholecystokinin (CCK). Our results are consistent with a model in which diversity in inhalation-linked patterning of OB output arises first at the level of sensory input and is enhanced by feedforward inhibition from juxtaglomerular interneurons which differentially impact different subpopulations of OB output neurons.
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Cheetham CEJ, Grier BD, Belluscio L. Bulk regional viral injection in neonatal mice enables structural and functional interrogation of defined neuronal populations throughout targeted brain areas. Front Neural Circuits 2015; 9:72. [PMID: 26594154 PMCID: PMC4633521 DOI: 10.3389/fncir.2015.00072] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 10/23/2015] [Indexed: 11/15/2022] Open
Abstract
The ability to label and manipulate specific cell types is central to understanding the structure and function of neuronal circuits. Here, we have developed a simple, affordable strategy for labeling of genetically defined populations of neurons throughout a targeted brain region: Bulk Regional Viral Injection (BReVI). Our strategy involves a large volume adeno-associated virus (AAV) injection in the targeted brain region of neonatal Cre driver mice. Using the mouse olfactory bulb (OB) as a model system, we tested the ability of BReVI to broadly and selectively label tufted cells, one of the two principal neuron populations of the OB, in CCK-IRES-Cre mice. BReVI resulted in labeling of neurons throughout the injected OB, with no spatial bias toward the injection site and no evidence of damage. The specificity of BReVI labeling was strikingly similar to that seen previously using immunohistochemical staining for cholecystokinin (CCK), an established tufted cell marker. Hence, the CCK-IRES-Cre line in combination with BReVI can provide an important tool for targeting and manipulation of OB tufted cells. We also found robust Cre-dependent reporter expression within three days of BReVI, which enabled us to assess developmental changes in the number and laminar distribution of OB tufted cells during the first three postnatal weeks. Furthermore, we demonstrate that BReVI permits structural and functional imaging in vivo, and can be combined with transgenic strategies to facilitate multi-color labeling of neuronal circuit components. BReVI is broadly applicable to different Cre driver lines and can be used to regionally manipulate genetically defined populations of neurons in any accessible brain region.
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Affiliation(s)
- Claire E. J. Cheetham
- National Institute of Neurological Disorders and StrokeBethesda, MD, USA
- Department of Biological Sciences, Carnegie Mellon UniversityPittsburgh, PA, USA
| | - Bryce D. Grier
- National Institute of Neurological Disorders and StrokeBethesda, MD, USA
| | - Leonardo Belluscio
- National Institute of Neurological Disorders and StrokeBethesda, MD, USA
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Zak JD, Whitesell JD, Schoppa NE. Metabotropic glutamate receptors promote disinhibition of olfactory bulb glomeruli that scales with input strength. J Neurophysiol 2014; 113:1907-20. [PMID: 25552635 DOI: 10.1152/jn.00222.2014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Increasing evidence indicates that the neural circuitry within glomeruli of the olfactory bulb plays a major role in affecting information flow between olfactory sensory neurons (OSNs) and output mitral cells (MCs). Glutamatergic external tufted (ET) cells, located at glomeruli, can act as intermediary cells in excitation between OSNs and MCs, whereas activation of MCs by OSNs is, in turn, suppressed by inhibitory synapses onto ET cells. In this study, we used patch-clamp recordings in rat olfactory bulb slices to examine the function of metabotropic glutamate receptors (mGluRs) in altering these glomerular signaling mechanisms. We found that activation of group II mGluRs profoundly reduced inhibition onto ET cells evoked by OSN stimulation. The mGluRs that mediated disinhibition were located on presynaptic GABAergic periglomerular cells and appeared to be activated by glutamate transients derived from dendrites in glomeruli. In terms of glomerular output, the mGluR-mediated reduction in GABA release led to a robust increase in the number of action potentials evoked by OSN stimulation in both ET cells and MCs. Importantly, however, the enhanced excitation was specific to when a glomerulus was strongly activated by OSN inputs. By being selective for strong vs. weak glomerular activation, mGluR-mediated disinhibition provides a mechanism to enhance the contrast in odor signals that activate OSN inputs into a single glomerulus at varying intensities.
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Affiliation(s)
- Joseph D Zak
- Neuroscience Program, University of Colorado, Anschutz Medical Campus, Aurora, Colorado; and
| | - Jennifer D Whitesell
- Neuroscience Program, University of Colorado, Anschutz Medical Campus, Aurora, Colorado; and
| | - Nathan E Schoppa
- Neuroscience Program, University of Colorado, Anschutz Medical Campus, Aurora, Colorado; and Department of Physiology and Biophysics, University of Colorado, Anschutz Medical Campus, Aurora, Colorado
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Cauthron JL, Stripling JS. Long-term plasticity in the regulation of olfactory bulb activity by centrifugal fibers from piriform cortex. J Neurosci 2014; 34:9677-87. [PMID: 25031407 PMCID: PMC4099545 DOI: 10.1523/jneurosci.1314-14.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 06/05/2014] [Accepted: 06/10/2014] [Indexed: 11/21/2022] Open
Abstract
Olfactory bulb granule cells are activated synaptically via two main pathways. Mitral/tufted (M/T) cells form dendrodendritic synapses on granule cells that can be activated by antidromic stimulation of the lateral olfactory tract (LOT). Centrifugal fibers originating from the association fiber (AF) system in piriform cortex (PC) make axodendritic synapses on granule cells within the granule cell layer (GCL) that can be activated by orthodromic stimulation of AF axons in the PC. We explored functional plasticity in the AF pathway by recording extracellularly from individual M/T cells and presumed granule cells in male Long-Evans rats under urethane anesthesia while testing their response to LOT and AF stimulation. Presumed granule cells driven synaptically by LOT stimulation (type L cells) were concentrated in the superficial half of the GCL and were activated at short latencies, whereas those driven synaptically by AF stimulation (type A cells) were concentrated in the deep half of the GCL and were activated at longer latencies. Type A cells were readily detected only in animals in which the AF input to the GCL had been previously potentiated by repeated high-frequency stimulation. An additional bout of high-frequency stimulation administered under urethane caused an immediate increase in the number of action potentials evoked in type A cells by AF test stimulation and a concomitant increase in inhibition of M/T cells. These results underscore the importance of the role played in olfactory processing by PC regulation of OB activity and document the long-lasting potentiation of that regulation by repeated high-frequency AF activation.
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Affiliation(s)
- Joy L Cauthron
- Department of Psychological Science, University of Arkansas, Fayetteville, Arkansas 72701
| | - Jeffrey S Stripling
- Department of Psychological Science, University of Arkansas, Fayetteville, Arkansas 72701
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Zhan X, Yin P, Heinbockel T. The basal forebrain modulates spontaneous activity of principal cells in the main olfactory bulb of anesthetized mice. Front Neural Circuits 2013; 7:148. [PMID: 24065892 PMCID: PMC3778317 DOI: 10.3389/fncir.2013.00148] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2012] [Accepted: 09/03/2013] [Indexed: 11/24/2022] Open
Abstract
Spontaneous activity is an important characteristic of the principal cells in the main olfactory bulb (MOB) for encoding odor information, which is modulated by the basal forebrain. Cholinergic activation has been reported to inhibit all major neuron types in the MOB. In this study, the effect of diagonal band (NDB) stimulation on mitral/tufted (M/T) cell spontaneous activity was examined in anesthetized mice. NDB stimulation increased spontaneous activity in 66 MOB neurons which lasted for 2–35 s before returning to the baseline level. The majority of the effected units showed a decrease of interspike intervals (ISI) at a range of 8–25 ms. Fifty-two percent of NDB stimulation responsive units showed intrinsic rhythmical bursting, which was enhanced temporarily by NDB stimulation, whereas the remaining non-rhythmic units were capable of synchronized bursting. The effect was attenuated by scopolamine in 21 of 27 units tested. Only four NDB units were inhibited by NDB stimulation, an inhibition that lasted less than 10 s. The NDB stimulation responsive neurons appeared to be M/T cells. Our findings demonstrate an NDB excitation effect on M/T neurons that mostly requires muscarinic receptor activation, and is likely due to non-selectivity of electrical stimulation. This suggests that cholinergic and a diverse group of non-cholinergic neurons in the basal forebrain co-ordinately modulate the dynamics of M/T cell spontaneous activity, which is fundamental for odor representation and attentional perception.
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Affiliation(s)
- Xiping Zhan
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine Baltimore, MD 20059, USA.
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Nagayama S, Enerva A, Fletcher ML, Masurkar AV, Igarashi KM, Mori K, Chen WR. Differential axonal projection of mitral and tufted cells in the mouse main olfactory system. Front Neural Circuits 2010; 4. [PMID: 20941380 PMCID: PMC2952457 DOI: 10.3389/fncir.2010.00120] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Accepted: 09/13/2010] [Indexed: 12/04/2022] Open
Abstract
In the past decade, much has been elucidated regarding the functional organization of the axonal connection of olfactory sensory neurons to olfactory bulb (OB) glomeruli. However, the manner in which projection neurons of the OB process odorant input and send this information to higher brain centers remains unclear. Here, we report long-range, large-scale tracing of the axonal projection patterns of OB neurons using two-photon microscopy. Tracer injection into a single glomerulus demonstrated widely distributed mitral/tufted cell axonal projections on the lateroventral surface of the mouse brain, including the anterior/posterior piriform cortex (PC) and olfactory tubercle (OT). We noted two distinct groups of labeled axons: PC-orienting axons and OT-orienting axons. Each group occupied distinct parts of the lateral olfactory tract. PC-orienting axons projected axon collaterals to a wide area of the PC but only a few collaterals to the OT. OT-orienting axons densely projected axon collaterals primarily to the anterolateral OT (alOT). Different colored dye injections into the superficial and deep portions of the OB external plexiform layer revealed that the PC-orienting axon populations originated in presumed mitral cells and the OT-orienting axons in presumed tufted cells. These data suggest that although mitral and tufted cells receive similar odor signals from a shared glomerulus, they process the odor information in different ways and send their output to different higher brain centers via the PC and alOT.
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Affiliation(s)
- Shin Nagayama
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston Houston, TX, USA
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