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Sakelaris B, Riecke H. Adult Neurogenesis Reconciles Flexibility and Stability of Olfactory Perceptual Memory. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.03.583153. [PMID: 38737721 PMCID: PMC11087939 DOI: 10.1101/2024.03.03.583153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/14/2024]
Abstract
In brain regions featuring ongoing plasticity, the task of quickly encoding new information without overwriting old memories presents a significant challenge. In the rodent olfactory bulb, which is renowned for substantial structural plasticity driven by adult neurogenesis and persistent turnover of dendritic spines, we show that such plasticity is vital to overcoming this flexibility-stability dilemma. To do so, we develop a computational model for structural plasticity in the olfactory bulb and show that the maturation of adult-born neurons facilitates the abilities to learn quickly and forget slowly. Particularly important to achieve this goal are the transient enhancement of the plasticity, excitability, and susceptibility to apoptosis that characterizes young neurons. The model captures many experimental observations and makes a number of testable predictions. Overall, it identifies memory consolidation as an important role of adult neurogenesis in olfaction and exemplifies how the brain can maintain stable memories despite ongoing extensive plasticity.
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Affiliation(s)
- Bennet Sakelaris
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, Illinois, United States of America
| | - Hermann Riecke
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, Illinois, United States of America
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2
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Bao S, Romero JM, Belfort BD, Arenkiel BR. Signaling mechanisms underlying activity-dependent integration of adult-born neurons in the mouse olfactory bulb. Genesis 2024; 62:e23595. [PMID: 38553878 PMCID: PMC10987073 DOI: 10.1002/dvg.23595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Revised: 03/18/2024] [Accepted: 03/19/2024] [Indexed: 04/02/2024]
Abstract
Adult neurogenesis has fascinated the field of neuroscience for decades given the prospects of harnessing mechanisms that facilitate the rewiring and/or replacement of adult brain tissue. The subgranular zone of the hippocampus and the subventricular zone of the lateral ventricle are the two main areas in the brain that exhibit ongoing neurogenesis. Of these, adult-born neurons within the olfactory bulb have proven to be a powerful model for studying circuit plasticity, providing a broad and accessible avenue into neuron development, migration, and continued circuit integration within adult brain tissue. This review focuses on some of the recognized molecular and signaling mechanisms underlying activity-dependent adult-born neuron development. Notably, olfactory activity and behavioral states contribute to adult-born neuron plasticity through sensory and centrifugal inputs, in which calcium-dependent transcriptional programs, local translation, and neuropeptide signaling play important roles. This review also highlights areas of needed continued investigation to better understand the remarkable phenomenon of adult-born neuron integration.
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Affiliation(s)
- Suyang Bao
- Development, Disease Models, and Therapeutics Graduate Program, Baylor College of Medicine, Houston, Texas 77030, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, Texas 77030, USA
| | - Juan M. Romero
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, Texas 77030, USA
- Medical Scientist Training Program, Baylor College of Medicine, Houston, Texas 77030, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Benjamin D.W. Belfort
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, Texas 77030, USA
- Medical Scientist Training Program, Baylor College of Medicine, Houston, Texas 77030, USA
- Genetics and Genomics Graduate Program, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Benjamin R. Arenkiel
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, Texas 77030, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA
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3
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Zhong H, Xing C, Zhou M, Jia Z, Liu S, Zhu S, Li B, Yang H, Ma H, Wang L, Zhu R, Qu Z, Ning G. Alternating current stimulation promotes neurite outgrowth and plasticity in neurons through activation of the PI3K/AKT signaling pathway. Acta Biochim Biophys Sin (Shanghai) 2023; 55:1718-1729. [PMID: 37814815 PMCID: PMC10679878 DOI: 10.3724/abbs.2023238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 04/04/2023] [Indexed: 10/11/2023] Open
Abstract
As a commonly used physical intervention, electrical stimulation (ES) has been demonstrated to be effective in the treatment of central nervous system disorders. Currently, researchers are studying the effects of electrical stimulation on individual neurons and neural networks, which are dependent on factors such as stimulation intensity, duration, location, and neuronal properties. However, the exact mechanism of action of electrical stimulation remains unclear. In some cases, repeated or prolonged electrical stimulation can lead to changes in the morphology or function of the neuron. In this study, immunofluorescence staining and Sholl analysis are used to assess changes in the neurite number and axon length to determine the optimal pattern and stimulation parameters of ES for neurons. Neuronal death and plasticity are detected by TUNEL staining and microelectrode array assays, respectively. mRNA sequencing and bioinformatics analysis are applied to predict the key targets of the action of ES on neurons, and the identified targets are validated by western blot analysis and qRT-PCR. The effects of alternating current stimulation (ACS) on neurons are more significant than those of direct current stimulation (DCS), and the optimal parameters are 3 μA and 20 min. ACS stimulation significantly increases the number of neurites, the length of axons and the spontaneous electrical activity of neurons, significantly elevates the expression of growth-associated protein-43 (GAP-43) without significant changes in the expression of neurotrophic factors. Furthermore, application of PI3K/AKT-specific inhibitors significantly abolishes the beneficial effects of ACS on neurons, confirming that the PI3K/AKT pathway is an important potential signaling pathway in the action of ACS.
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Affiliation(s)
- Hao Zhong
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Cong Xing
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Mi Zhou
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Zeyu Jia
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Song Liu
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Shibo Zhu
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Bo Li
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Hongjiang Yang
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Hongpeng Ma
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Liyue Wang
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
| | - Rusen Zhu
- Department of Spine SurgeryTianjin Union Medical CenterTianjin300121China
| | - Zhigang Qu
- College of Electronic Information and AutomationAdvanced Structural Integrity International Joint Research CenterTianjin University of Science and TechnologyTianjin300222China
| | - Guangzhi Ning
- International Science and Technology Cooperation Base of Spinal Cord InjuryTianjin Key Laboratory of Spine and Spinal Cord InjuryDepartment of OrthopedicsTianjin Medical University General HospitalTianjin300052China
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4
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Coppola DM, Reisert J. The Role of the Stimulus in Olfactory Plasticity. Brain Sci 2023; 13:1553. [PMID: 38002512 PMCID: PMC10669894 DOI: 10.3390/brainsci13111553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 11/02/2023] [Accepted: 11/02/2023] [Indexed: 11/26/2023] Open
Abstract
Plasticity, the term we use to describe the ability of a nervous system to change with experience, is the evolutionary adaptation that freed animal behavior from the confines of genetic determinism. This capacity, which increases with brain complexity, is nowhere more evident than in vertebrates, especially mammals. Though the scientific study of brain plasticity dates back at least to the mid-19th century, the last several decades have seen unprecedented advances in the field afforded by new technologies. Olfaction is one system that has garnered particular attention in this realm because it is the only sensory modality with a lifelong supply of new neurons, from two niches no less! Here, we review some of the classical and contemporary literature dealing with the role of the stimulus or lack thereof in olfactory plasticity. We have restricted our comments to studies in mammals that have used dual tools of the field: stimulus deprivation and stimulus enrichment. The former manipulation has been implemented most frequently by unilateral naris occlusion and, thus, we have limited our comments to research using this technique. The work reviewed on deprivation provides substantial evidence of activity-dependent processes in both developing and adult mammals at multiple levels of the system from olfactory sensory neurons through to olfactory cortical areas. However, more recent evidence on the effects of deprivation also establishes several compensatory processes with mechanisms at every level of the system, whose function seems to be the restoration of information flow in the face of an impoverished signal. The results of sensory enrichment are more tentative, not least because of the actual manipulation: What odor or odors? At what concentrations? On what schedule? All of these have frequently not been sufficiently rationalized or characterized. Perhaps it is not surprising, then, that discrepant results are common in sensory enrichment studies. Despite this problem, evidence has accumulated that even passively encountered odors can "teach" olfactory cortical areas to better detect, discriminate, and more efficiently encode them for future encounters. We discuss these and other less-established roles for the stimulus in olfactory plasticity, culminating in our recommended "aspirations" for the field going forward.
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Affiliation(s)
- David M. Coppola
- Biology Department, Randolph-Macon College, Ashland, VA 23005, USA
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Li K, Figarella K, Su X, Kovalchuk Y, Gorzolka J, Neher JJ, Mojtahedi N, Casadei N, Hedrich UBS, Garaschuk O. Endogenous but not sensory-driven activity controls migration, morphogenesis and survival of adult-born juxtaglomerular neurons in the mouse olfactory bulb. Cell Mol Life Sci 2023; 80:98. [PMID: 36932186 PMCID: PMC10023654 DOI: 10.1007/s00018-023-04753-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 02/06/2023] [Accepted: 03/07/2023] [Indexed: 03/19/2023]
Abstract
The development and survival of adult-born neurons are believed to be driven by sensory signaling. Here, in vivo analyses of motility, morphology and Ca2+ signaling, as well as transcriptome analyses of adult-born juxtaglomerular cells with reduced endogenous excitability (via cell-specific overexpression of either Kv1.2 or Kir2.1 K+ channels), revealed a pronounced impairment of migration, morphogenesis, survival, and functional integration of these cells into the mouse olfactory bulb, accompanied by a reduction in cytosolic Ca2+ fluctuations, phosphorylation of CREB and pCREB-mediated gene expression. Moreover, K+ channel overexpression strongly downregulated genes involved in neuronal migration, differentiation, and morphogenesis and upregulated apoptosis-related genes, thus locking adult-born cells in an immature and vulnerable state. Surprisingly, cells deprived of sensory-driven activity developed normally. Together, the data reveal signaling pathways connecting the endogenous intermittent neuronal activity/Ca2+ fluctuations as well as enhanced Kv1.2/Kir2.1 K+ channel function to migration, maturation, and survival of adult-born neurons.
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Affiliation(s)
- Kaizhen Li
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany
- Department of Physiology, University of Bern, Bern, Switzerland
| | - Katherine Figarella
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany
| | - Xin Su
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany
| | - Yury Kovalchuk
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany
| | - Jessika Gorzolka
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany
| | - Jonas J Neher
- German Center for Neurodegenerative Diseases (DZNE), Tübingen, Germany
- Department of Cellular Neurology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
| | - Nima Mojtahedi
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany
| | - Nicolas Casadei
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany
- NGS Competence Center Tübingen, Tübingen, Germany
| | - Ulrike B S Hedrich
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
| | - Olga Garaschuk
- Department of Neurophysiology, Institute of Physiology, University of Tübingen, Tübingen, Germany.
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6
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Fitzwater E, Coppola DM. Olfactory Deprivation and Enrichment: An Identity of Opposites? Chem Senses 2020; 46:5939855. [PMID: 33103187 DOI: 10.1093/chemse/bjaa071] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effects of deprivation and enrichment on the electroolfactogram of mice were studied through the paradigms of unilateral naris occlusion and odor induction, respectively. Deprivation was shown to cause an increase in electroolfactogram amplitudes after 7 days. We also show that unilateral naris occlusion is not detrimental to the gross anatomical appearance or electroolfactogram of either the ipsilateral or contralateral olfactory epithelium even after year-long survival periods, consistent with our previous assumptions. Turning to induction, the increase in olfactory responses after a period of odor enrichment, could not be shown in CD-1 outbred mice for any odorant tried. However, consistent with classical studies, it was evident in C57BL/6J inbred mice, which are initially insensitive to isovaleric acid. As is the case for deprivation, enriching C57BL/6J mice with isovaleric acid causes an increase in their electroolfactogram response to this odorant over time. In several experiments on C57BL/6J mice, the odorant specificity, onset timing, recovery timing, and magnitude of the induction effect were studied. Considered together, the current findings and previous work from the laboratory support the counterintuitive conclusion that both compensatory plasticity in response to deprivation and induction in response to odor enrichment are caused by the same underlying homeostatic mechanism, the purpose of which is to preserve sensory information flow no matter the odorant milieu. This hypothesis, the detailed evidence supporting it, and speculations concerning human odor induction are discussed.
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Affiliation(s)
- Emily Fitzwater
- Department of Biology, Randolph-Macon College, Ashland, VA, USA
| | - David M Coppola
- Department of Biology, Randolph-Macon College, Ashland, VA, USA
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McDole B, Berger R, Guthrie K. Genetic Increases in Olfactory Bulb BDNF Do Not Enhance Survival of Adult-Born Granule Cells. Chem Senses 2020; 45:3-13. [PMID: 31562506 PMCID: PMC6923167 DOI: 10.1093/chemse/bjz058] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Adult-born neurons produced in the dentate gyrus subgranular zone (SGZ) develop as excitatory hippocampal granule cells (GCs), while those from the subventricular zone (SVZ) migrate to the olfactory bulb (OB), where most develop as GABAergic olfactory GCs. Both types of neurons express TrkB as they mature. Normally ~50% of new olfactory GCs survive, but survival declines if sensory drive is reduced. Increases in endogenous brain-derived neurotrophic factor (BDNF) in hippocampus, particularly with wheel running, enhance dentate GC survival. Whether survival of new olfactory GCs is impacted by augmenting BDNF in the OB, where they mature and integrate, is not known. Here, we determined if increasing OB BDNF expression enhances survival of new GCs, and if it counters their loss under conditions of reduced sensory activity. Neurogenesis was assessed under normal conditions, and following unilateral naris occlusion, in mice overexpressing BDNF in the granule cell layer (GCL). OB BDNF levels were significantly higher in transgenic mice compared to controls, and this was maintained following sensory deprivation. Bromodeoxyuridine (BrdU) cell birth dating showed that at 12-14 days post-BrdU, numbers of new GCs did not differ between genotypes, indicating normal recruitment to the OB. At later intervals, transgenic and control mice showed levels of GC loss in deprived and nondeprived animals that were indistinguishable, as was the incidence of apoptotic cells in the GCL. These results demonstrate that, in contrast to new dentate GCs, elevations in endogenous BDNF do not enhance survival of adult-born olfactory GCs.
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Affiliation(s)
- Brittnee McDole
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, USA
| | - Rachel Berger
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, USA
| | - Kathleen Guthrie
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, USA
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Reshef R, Kudryavitskaya E, Shani-Narkiss H, Isaacson B, Rimmerman N, Mizrahi A, Yirmiya R. The role of microglia and their CX3CR1 signaling in adult neurogenesis in the olfactory bulb. eLife 2017; 6. [PMID: 29251592 PMCID: PMC5734876 DOI: 10.7554/elife.30809] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 12/05/2017] [Indexed: 01/09/2023] Open
Abstract
Microglia play important roles in perinatal neuro- and synapto-genesis. To test the role of microglia in these processes during adulthood, we examined the effects of microglia depletion, via treatment of mice with the CSF-1 receptor antagonist PLX5622, and abrogated neuronal-microglial communication in CX3C receptor-1 deficient (Cx3cr1−/−) mice. Microglia depletion significantly lowered spine density in young (developing) but not mature adult-born-granule-cells (abGCs) in the olfactory bulb. Two-photon time-lapse imaging indicated that microglia depletion reduced spine formation and elimination. Functionally, odor-evoked responses of mitral cells, which are normally inhibited by abGCs, were increased in microglia-depleted mice. In Cx3cr1−/− mice, abGCs exhibited reduced spine density, dynamics and size, concomitantly with reduced contacts between Cx3cr1-deficient microglia and abGCs' dendritic shafts, along with increased proportion of microglia-contacted spines. Thus, during adult neurogenesis, microglia regulate the elimination (pruning), formation, and maintenance of synapses on newborn neurons, contributing to the functional integrity of the olfactory bulb circuitry.
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Affiliation(s)
- Ronen Reshef
- Department of Psychology, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Elena Kudryavitskaya
- Department of Neurobiology, Institute for Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.,The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Haran Shani-Narkiss
- Department of Neurobiology, Institute for Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.,The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Batya Isaacson
- Department of Immunology and Cancer Research, The Lautenberg Center for General and Tumor Immunology, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Neta Rimmerman
- Department of Psychology, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Adi Mizrahi
- Department of Neurobiology, Institute for Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.,The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Raz Yirmiya
- Department of Psychology, The Hebrew University of Jerusalem, Jerusalem, Israel
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Wallace JL, Wienisch M, Murthy VN. Development and Refinement of Functional Properties of Adult-Born Neurons. Neuron 2017; 96:883-896.e7. [PMID: 29056299 PMCID: PMC5789450 DOI: 10.1016/j.neuron.2017.09.039] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 07/26/2017] [Accepted: 09/22/2017] [Indexed: 01/21/2023]
Abstract
New neurons appear only in a few regions of the adult mammalian brain and become integrated into existing circuits. Little is known about the functional development of individual neurons in vivo. We examined the functional life history of adult-born granule cells (abGCs) in the olfactory bulb using multiphoton imaging in awake and anesthetized mice. We found that abGCs can become responsive to odorants soon after they arrive in the olfactory bulb. Tracking identified abGCs over weeks revealed that the robust and broadly tuned responses of most newly arrived abGCs gradually become more selective over a period of ∼3 weeks, but a small fraction achieves broader tuning with maturation. Enriching the olfactory environment of mice prolonged the period over which abGCs were strongly and broadly responsive to odorants. Our data offer direct support for rapid integration of adult-born neurons into existing circuits, followed by experience-dependent refinement of their functional connectivity.
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Affiliation(s)
- Jenelle L Wallace
- Molecules, Cells, and Organisms training program, Harvard University, Cambridge, MA 02138, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA; Department of Molecular & Cellular Biology, Harvard University, Cambridge, MA 02138, USA
| | - Martin Wienisch
- Center for Brain Science, Harvard University, Cambridge, MA 02138, USA; Department of Molecular & Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
| | - Venkatesh N Murthy
- Center for Brain Science, Harvard University, Cambridge, MA 02138, USA; Department of Molecular & Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
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10
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Smail S, Bahga D, McDole B, Guthrie K. Increased Olfactory Bulb BDNF Expression Does Not Rescue Deficits in Olfactory Neurogenesis in the Huntington's Disease R6/2 Mouse. Chem Senses 2016; 41:221-32. [PMID: 26783111 DOI: 10.1093/chemse/bjv076] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/30/2015] [Indexed: 11/13/2022] Open
Abstract
Huntington's disease (HD) is an inherited neurodegenerative disorder caused by expansion of CAG trinucleotide repeats in the huntingtin gene. Mutant huntingtin protein (mhtt) interferes with the actions of brain-derived neurotrophic factor (BDNF), and BDNF signaling is reduced in the diseased striatum. Loss of this trophic support is thought to contribute to loss of striatal medium spiny neurons in HD. Increasing BDNF in the adult striatum or ventricular ependyma slows disease progression in HD mouse models, and diverts subventricular zone (SVZ)-derived neuroblasts from their normal destination, the olfactory bulb, to the striatum, where some survive and develop features of mature neurons. Most neuroblasts that migrate to the olfactory bulb differentiate as granule cells, with approximately half surviving whereas others undergo apoptosis. In the R6/2 HD mouse model, survival of adult-born granule cells is reduced. Newly maturing cells express the BDNF receptor TrkB, suggesting that mhtt may interfere with normal BDNF trophic activity, increasing their loss. To determine if augmenting BDNF counteracts this, we examined granule cell survival in R6/2 mice that overexpress BDNF in olfactory bulb. Although we detected a decline in apoptosis, increased BDNF was not sufficient to normalize granule cell survival within their normal target in R6/2 mice.
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Affiliation(s)
- Shamayra Smail
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA
| | - Dalbir Bahga
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA
| | - Brittnee McDole
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA
| | - Kathleen Guthrie
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA
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11
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McDole B, Isgor C, Pare C, Guthrie K. BDNF over-expression increases olfactory bulb granule cell dendritic spine density in vivo. Neuroscience 2015. [PMID: 26211445 DOI: 10.1016/j.neuroscience.2015.07.056] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Olfactory bulb granule cells (GCs) are axon-less, inhibitory interneurons that regulate the activity of the excitatory output neurons, the mitral and tufted cells, through reciprocal dendrodendritic synapses located on GC spines. These contacts are established in the distal apical dendritic compartment, while GC basal dendrites and more proximal apical segments bear spines that receive glutamatergic inputs from the olfactory cortices. This synaptic connectivity is vital to olfactory circuit function and is remodeled during development, and in response to changes in sensory activity and lifelong GC neurogenesis. Manipulations that alter levels of the neurotrophin brain-derived neurotrophic factor (BDNF) in vivo have significant effects on dendritic spine morphology, maintenance and activity-dependent plasticity for a variety of CNS neurons, yet little is known regarding BDNF effects on bulb GC spine maturation or maintenance. Here we show that, in vivo, sustained bulbar over-expression of BDNF in transgenic mice produces a marked increase in GC spine density that includes an increase in mature spines on their apical dendrites. Morphometric analysis demonstrated that changes in spine density were most notable in the distal and proximal apical domains, indicating that multiple excitatory inputs are potentially modified by BDNF. Our results indicate that increased levels of endogenous BDNF can promote the maturation and/or maintenance of dendritic spines on GCs, suggesting a role for this factor in modulating GC functional connectivity within adult olfactory circuitry.
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Affiliation(s)
- B McDole
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, United States
| | - C Isgor
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, United States
| | - C Pare
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, United States
| | - K Guthrie
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, United States.
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12
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Konefal S, Elliot M, Crespi B. The adaptive significance of adult neurogenesis: an integrative approach. Front Neuroanat 2013; 7:21. [PMID: 23882188 PMCID: PMC3712125 DOI: 10.3389/fnana.2013.00021] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Accepted: 06/18/2013] [Indexed: 01/15/2023] Open
Abstract
Adult neurogenesis in mammals is predominantly restricted to two brain regions, the dentate gyrus (DG) of the hippocampus and the olfactory bulb (OB), suggesting that these two brain regions uniquely share functions that mediate its adaptive significance. Benefits of adult neurogenesis across these two regions appear to converge on increased neuronal and structural plasticity that subserves coding of novel, complex, and fine-grained information, usually with contextual components that include spatial positioning. By contrast, costs of adult neurogenesis appear to center on potential for dysregulation resulting in higher risk of brain cancer or psychological dysfunctions, but such costs have yet to be quantified directly. The three main hypotheses for the proximate functions and adaptive significance of adult neurogenesis, pattern separation, memory consolidation, and olfactory spatial, are not mutually exclusive and can be reconciled into a simple general model amenable to targeted experimental and comparative tests. Comparative analysis of brain region sizes across two major social-ecological groups of primates, gregarious (mainly diurnal haplorhines, visually-oriented, and in large social groups) and solitary (mainly noctural, territorial, and highly reliant on olfaction, as in most rodents) suggest that solitary species, but not gregarious species, show positive associations of population densities and home range sizes with sizes of both the hippocampus and OB, implicating their functions in social-territorial systems mediated by olfactory cues. Integrated analyses of the adaptive significance of adult neurogenesis will benefit from experimental studies motivated and structured by ecologically and socially relevant selective contexts.
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Affiliation(s)
- Sarah Konefal
- Department of Neurology and Neurosurgery, Centre for Research in Neuroscience, The Research Institute of the McGill University Health Centre, Montreal General HospitalMontreal, QC, Canada
| | - Mick Elliot
- Department of Biological Sciences, Simon Fraser UniversityBurnaby, BC, Canada
| | - Bernard Crespi
- Department of Biological Sciences, Simon Fraser UniversityBurnaby, BC, Canada
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13
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Enhanced synaptic integration of adult-born neurons in the olfactory bulb of lactating mothers. J Neurosci 2012; 32:7519-27. [PMID: 22649230 DOI: 10.1523/jneurosci.6354-11.2012] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
One of the most dramatic events during the life of adult mammals is the transition into motherhood. This transition is accompanied by specific maternal behaviors, displayed by the mother, that ensure the survival and the well-being of her offspring. The execution of these behaviors is most likely accompanied by plastic changes in specific neuronal circuits, but these are still poorly defined. In this work, we studied the mammalian olfactory bulb (OB), which has been shown to be an essential brain region for maternal behaviors in mice. In the OB, we focused on adult-born neurons, which are continuously incorporated into the circuit during adulthood, thus providing a potential substrate for heightened plasticity after parturition. We analyzed the dynamics and morphological characteristics of adult-born granule cells (abGCs), innervating the OB of primiparous lactating mothers, shortly after parturition as well as in naive females. In vivo time-lapse imaging of abGCs revealed that dendritic spines were significantly more stable in lactating mothers compared with naive virgins. In contrast, spine stability of resident GCs remained unchanged after parturition. In addition, while spine size distribution of abGCs was approximately similar between mothers and naive virgins, the spine density of abGCs was lower in lactating mothers and the density of their presynaptic components was higher. These structural features are indicative of enhanced integration of adult-born neurons into the bulbar circuitry of lactating mothers. This enhanced integration may serve as a cellular mechanism, supporting changes in olfactory coding of new mothers during their first days following parturition.
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14
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Studies of olfactory system neural plasticity: the contribution of the unilateral naris occlusion technique. Neural Plast 2012; 2012:351752. [PMID: 22690343 PMCID: PMC3368527 DOI: 10.1155/2012/351752] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Revised: 03/01/2012] [Accepted: 03/19/2012] [Indexed: 01/18/2023] Open
Abstract
Unilateral naris occlusion has long been the method of choice for effecting stimulus deprivation in studies of olfactory plasticity. A significant body of literature speaks to the myriad consequences of this manipulation on the ipsilateral olfactory pathway. Early experiments emphasized naris occlusion's deleterious and age-critical effects. More recent studies have focused on life-long vulnerability, particularly on neurogenesis, and compensatory responses to deprivation. Despite the abundance of empirical data, a theoretical framework in which to understand the many sequelae of naris occlusion on olfaction has been elusive. This paper focuses on recent data, new theories, and underappreciated caveats related to the use of this technique in studies of olfactory plasticity.
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