1
|
Egger V, Kuner T. Olfactory bulb granule cells: specialized to link coactive glomerular columns for percept generation and discrimination of odors. Cell Tissue Res 2021; 383:495-506. [PMID: 33404844 PMCID: PMC7873091 DOI: 10.1007/s00441-020-03402-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 12/14/2020] [Indexed: 12/16/2022]
Abstract
The role of granule cells in olfactory processing is surrounded by several enigmatic observations, such as the purpose of reciprocal spines and the mechanisms for GABA release, the apparently low firing activity and recurrent inhibitory drive of granule cells, the missing proof for functional reciprocal connectivity, and the apparently negligible contribution to lateral inhibition. Here, we summarize recent results with regard to both the mechanisms of GABA release and the behavioral relevance of granule cell activity during odor discrimination. We outline a novel hypothesis that has the potential to resolve most of these enigmas and allows further predictions on the function of granule cells in odor processing. Briefly, recent findings imply that GABA release from the reciprocal spine requires a local spine action potential and the cooperative action of NMDA receptors and high voltage-activated Ca2+ channels. Thus, lateral inhibition is conditional on activity in the principal neurons connected to a granule cell and tightly intertwined with recurrent inhibition. This notion allows us to infer that lateral inhibition between principal neurons occurs "on demand," i.e., selectively on coactive mitral and tufted cells, and thus can provide directed, dynamically switched lateral inhibition in a sensory system with 1000 input channels organized in glomerular columns. The mechanistic underpinnings of this hypothesis concur with findings from odor discrimination behavior in mice with synaptic proteins deleted in granule cells. In summary, our hypothesis explains the unusual microcircuit of the granule cell reciprocal spine as a means of olfactory combinatorial coding.
Collapse
Affiliation(s)
- Veronica Egger
- Institute of Zoology, Regensburg University, Universitätsstr. 30, 93040, Regensburg, Germany.
| | - Thomas Kuner
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, Heidelberg University, Im Neuenheimer Feld 307, 69120, Heidelberg, Germany
| |
Collapse
|
2
|
Lage-Rupprecht V, Zhou L, Bianchini G, Aghvami SS, Mueller M, Rózsa B, Sassoè-Pognetto M, Egger V. Presynaptic NMDARs cooperate with local spikes toward GABA release from the reciprocal olfactory bulb granule cell spine. eLife 2020; 9:e63737. [PMID: 33252329 PMCID: PMC7704106 DOI: 10.7554/elife.63737] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 11/10/2020] [Indexed: 12/16/2022] Open
Abstract
In the rodent olfactory bulb the smooth dendrites of the principal glutamatergic mitral cells (MCs) form reciprocal dendrodendritic synapses with large spines on GABAergic granule cells (GC), where unitary release of glutamate can trigger postsynaptic local activation of voltage-gated Na+-channels (Navs), that is a spine spike. Can such single MC input evoke reciprocal release? We find that unitary-like activation via two-photon uncaging of glutamate causes GC spines to release GABA both synchronously and asynchronously onto MC dendrites. This release indeed requires activation of Navs and high-voltage-activated Ca2+-channels (HVACCs), but also of NMDA receptors (NMDAR). Simulations show temporally overlapping HVACC- and NMDAR-mediated Ca2+-currents during the spine spike, and ultrastructural data prove NMDAR presence within the GABAergic presynapse. This cooperative action of presynaptic NMDARs allows to implement synapse-specific, activity-dependent lateral inhibition, and thus could provide an efficient solution to combinatorial percept synthesis in a sensory system with many receptor channels.
Collapse
Affiliation(s)
- Vanessa Lage-Rupprecht
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburgGermany
- Department of Bioinformatics, Fraunhofer SCAISankt AugustinGermany
| | - Li Zhou
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburgGermany
| | - Gaia Bianchini
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburgGermany
| | - S Sara Aghvami
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburgGermany
- School of Electrical and Computer Engineering, University of TehranTehranIslamic Republic of Iran
- School of Cognitive Sciences, Institute for Research in Fundamental Sciences (IPM)TehranIslamic Republic of Iran
| | - Max Mueller
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburgGermany
| | - Balázs Rózsa
- Two-Photon Imaging Center, Institute of Experimental Medicine, Hungarian Academy of SciencesBudapestHungary
| | | | - Veronica Egger
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburgGermany
| |
Collapse
|
3
|
Ona Jodar T, Lage-Rupprecht V, Abraham NM, Rose CR, Egger V. Local Postsynaptic Signaling on Slow Time Scales in Reciprocal Olfactory Bulb Granule Cell Spines Matches Asynchronous Release. Front Synaptic Neurosci 2020; 12:551691. [PMID: 33304264 PMCID: PMC7701096 DOI: 10.3389/fnsyn.2020.551691] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Accepted: 10/19/2020] [Indexed: 11/13/2022] Open
Abstract
In the vertebrate olfactory bulb (OB), axonless granule cells (GC) mediate self- and lateral inhibitory interactions between mitral/tufted cells via reciprocal dendrodendritic synapses. Locally triggered release of GABA from the large reciprocal GC spines occurs on both fast and slow time scales, possibly enabling parallel processing during olfactory perception. Here we investigate local mechanisms for asynchronous spine output. To reveal the temporal and spatial characteristics of postsynaptic ion transients, we imaged spine and adjacent dendrite Ca2 +- and Na+-signals with minimal exogenous buffering by the respective fluorescent indicator dyes upon two-photon uncaging of DNI-glutamate in OB slices from juvenile rats. Both postsynaptic fluorescence signals decayed slowly, with average half durations in the spine head of t1 / 2_Δ[Ca2 +]i ∼500 ms and t1 / 2_Δ[Na+]i ∼1,000 ms. We also analyzed the kinetics of already existing data of postsynaptic spine Ca2 +-signals in response to glomerular stimulation in OB slices from adult mice, either WT or animals with partial GC glutamate receptor deletions (NMDAR: GluN1 subunit; AMPAR: GluA2 subunit). In a large subset of spines the fluorescence signal had a protracted rise time (average time to peak ∼400 ms, range 20 to >1,000 ms). This slow rise was independent of Ca2 + entry via NMDARs, since similarly slow signals occurred in ΔGluN1 GCs. Additional Ca2 + entry in ΔGluA2 GCs (with AMPARs rendered Ca2 +-permeable), however, resulted in larger ΔF/Fs that rose yet more slowly. Thus GC spines appear to dispose of several local mechanisms to promote asynchronous GABA release, which are reflected in the time course of mitral/tufted cell recurrent inhibition.
Collapse
Affiliation(s)
- Tiffany Ona Jodar
- Regensburg University, Regensburg, Germany
- Institut D’Investigacions Biomèdiques, Barcelona, Spain
| | - Vanessa Lage-Rupprecht
- Regensburg University, Regensburg, Germany
- Fraunhofer Institute for Algorithms and Scientific Computing, St. Augustin, Germany
| | | | | | | |
Collapse
|
4
|
Mueller M, Egger V. Dendritic integration in olfactory bulb granule cells upon simultaneous multispine activation: Low thresholds for nonlocal spiking activity. PLoS Biol 2020; 18:e3000873. [PMID: 32966273 PMCID: PMC7535128 DOI: 10.1371/journal.pbio.3000873] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 10/05/2020] [Accepted: 08/24/2020] [Indexed: 11/18/2022] Open
Abstract
The inhibitory axonless olfactory bulb granule cells form reciprocal dendrodendritic synapses with mitral and tufted cells via large spines, mediating recurrent and lateral inhibition. As a case in point for dendritic transmitter release, rat granule cell dendrites are highly excitable, featuring local Na+ spine spikes and global Ca2+- and Na+-spikes. To investigate the transition from local to global signaling, we performed holographic, simultaneous 2-photon uncaging of glutamate at up to 12 granule cell spines, along with whole-cell recording and dendritic 2-photon Ca2+ imaging in acute juvenile rat brain slices. Coactivation of less than 10 reciprocal spines was sufficient to generate diverse regenerative signals that included regional dendritic Ca2+-spikes and dendritic Na+-spikes (D-spikes). Global Na+-spikes could be triggered in one third of granule cells. Individual spines and dendritic segments sensed the respective signal transitions as increments in Ca2+ entry. Dendritic integration as monitored by the somatic membrane potential was mostly linear until a threshold number of spines was activated, at which often D-spikes along with supralinear summation set in. As to the mechanisms supporting active integration, NMDA receptors (NMDARs) strongly contributed to all aspects of supralinearity, followed by dendritic voltage-gated Na+- and Ca2+-channels, whereas local Na+ spine spikes, as well as morphological variables, barely mattered. Because of the low numbers of coactive spines required to trigger dendritic Ca2+ signals and thus possibly lateral release of GABA onto mitral and tufted cells, we predict that thresholds for granule cell-mediated bulbar lateral inhibition are low. Moreover, D-spikes could provide a plausible substrate for granule cell-mediated gamma oscillations.
Collapse
Affiliation(s)
- Max Mueller
- Neurophysiology, Institute of Zoology, Universität Regensburg, Regensburg, Germany
| | - Veronica Egger
- Neurophysiology, Institute of Zoology, Universität Regensburg, Regensburg, Germany
| |
Collapse
|
5
|
Wallace J, Lord J, Dissing-Olesen L, Stevens B, Murthy VN. Microglial depletion disrupts normal functional development of adult-born neurons in the olfactory bulb. eLife 2020; 9:e50531. [PMID: 32150529 PMCID: PMC7062469 DOI: 10.7554/elife.50531] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 01/13/2020] [Indexed: 12/11/2022] Open
Abstract
Microglia play key roles in regulating synapse development and refinement in the developing brain, but it is unknown whether they are similarly involved during adult neurogenesis. By transiently depleting microglia from the healthy adult mouse brain, we show that microglia are necessary for the normal functional development of adult-born granule cells (abGCs) in the olfactory bulb. Microglial depletion reduces the odor responses of developing, but not preexisting GCs in vivo in both awake and anesthetized mice. Microglia preferentially target their motile processes to interact with mushroom spines on abGCs, and when microglia are absent, abGCs develop smaller spines and receive weaker excitatory synaptic inputs. These results suggest that microglia promote the development of excitatory synapses onto developing abGCs, which may impact the function of these cells in the olfactory circuit.
Collapse
Affiliation(s)
- Jenelle Wallace
- Molecules, Cells, and Organisms Training Program, Harvard UniversityCambridgeUnited States
- Center for Brain Science, Harvard UniversityCambridgeUnited States
- Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
- FM Kirby Neurobiology Center, Boston Children’s HospitalBostonUnited States
| | - Julia Lord
- Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
| | - Lasse Dissing-Olesen
- FM Kirby Neurobiology Center, Boston Children’s HospitalBostonUnited States
- Harvard Medical SchoolBostonUnited States
| | - Beth Stevens
- FM Kirby Neurobiology Center, Boston Children’s HospitalBostonUnited States
- Harvard Medical SchoolBostonUnited States
- Stanley Center for Psychiatric Research, Broad Institute of MIT and HarvardCambridgeUnited States
- Howard Hughes Medical Institute, Boston Children’s HospitalBostonUnited States
| | - Venkatesh N Murthy
- Molecules, Cells, and Organisms Training Program, Harvard UniversityCambridgeUnited States
- Center for Brain Science, Harvard UniversityCambridgeUnited States
- Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
| |
Collapse
|
6
|
Goaillard JM, Moubarak E, Tapia M, Tell F. Diversity of Axonal and Dendritic Contributions to Neuronal Output. Front Cell Neurosci 2020; 13:570. [PMID: 32038171 PMCID: PMC6987044 DOI: 10.3389/fncel.2019.00570] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 12/09/2019] [Indexed: 11/13/2022] Open
Abstract
Our general understanding of neuronal function is that dendrites receive information that is transmitted to the axon, where action potentials (APs) are initiated and propagated to eventually trigger neurotransmitter release at synaptic terminals. Even though this canonical division of labor is true for a number of neuronal types in the mammalian brain (including neocortical and hippocampal pyramidal neurons or cerebellar Purkinje neurons), many neuronal types do not comply with this classical polarity scheme. In fact, dendrites can be the site of AP initiation and propagation, and even neurotransmitter release. In several interneuron types, all functions are carried out by dendrites as these neurons are devoid of a canonical axon. In this article, we present a few examples of "misbehaving" neurons (with a non-canonical polarity scheme) to highlight the diversity of solutions that are used by mammalian neurons to transmit information. Moreover, we discuss how the contribution of dendrites and axons to neuronal excitability may impose constraints on the morphology of these compartments in specific functional contexts.
Collapse
Affiliation(s)
- Jean-Marc Goaillard
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Estelle Moubarak
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Mónica Tapia
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Fabien Tell
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| |
Collapse
|
7
|
Coincidence Detection within the Excitable Rat Olfactory Bulb Granule Cell Spines. J Neurosci 2019; 39:584-595. [PMID: 30674614 DOI: 10.1523/jneurosci.1798-18.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 09/13/2018] [Accepted: 10/09/2018] [Indexed: 11/21/2022] Open
Abstract
In the mammalian olfactory bulb, the inhibitory axonless granule cells (GCs) feature reciprocal synapses that interconnect them with the principal neurons of the bulb, mitral, and tufted cells. These synapses are located within large excitable spines that can generate local action potentials (APs) upon synaptic input ("spine spike"). Moreover, GCs can fire global APs that propagate throughout the dendrite. Strikingly, local postsynaptic Ca2+ entry summates mostly linearly with Ca2+ entry due to coincident global APs generated by glomerular stimulation, although some underlying conductances should be inactivated. We investigated this phenomenon by constructing a compartmental GC model to simulate the pairing of local and global signals as a function of their temporal separation Δt. These simulations yield strongly sublinear summation of spine Ca2+ entry for the case of perfect coincidence Δt = 0 ms. Summation efficiency (SE) sharply rises for both positive and negative Δt. The SE reduction for coincident signals depends on the presence of voltage-gated Na+ channels in the spine head, while NMDARs are not essential. We experimentally validated the simulated SE in slices of juvenile rat brain (both sexes) by pairing two-photon uncaging of glutamate at spines and APs evoked by somatic current injection at various intervals Δt while imaging spine Ca2+ signals. Finally, the latencies of synaptically evoked global APs and EPSPs were found to correspond to Δt ≈ 10 ms, explaining the observed approximately linear summation of synaptic local and global signals. Our results provide additional evidence for the existence of the GC spine spike.SIGNIFICANCE STATEMENT Here we investigate the interaction of local synaptic inputs and global activation of a neuron by a backpropagating action potential within a dendritic spine with respect to local Ca2+ signaling. Our system of interest, the reciprocal spine of the olfactory bulb granule cell, is known to feature a special processing mode, namely, a synaptically triggered action potential that is restricted to the spine head. Therefore, coincidence detection of local and global signals follows different rules than in more conventional synapses. We unravel these rules using both simulations and experiments and find that signals coincident within ≈±7 ms around 0 ms result in sublinear summation of Ca2+ entry because of synaptic activation of voltage-gated Na+ channels within the spine.
Collapse
|
8
|
Functional Specialization of Interneuron Dendrites: Identification of Action Potential Initiation Zone in Axonless Olfactory Bulb Granule Cells. J Neurosci 2019; 39:9674-9688. [PMID: 31662426 DOI: 10.1523/jneurosci.1763-19.2019] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/25/2019] [Accepted: 09/29/2019] [Indexed: 12/19/2022] Open
Abstract
Principal cells in the olfactory bulb (OB), mitral and tufted cells, play key roles in processing and then relaying sensory information to downstream cortical regions. How OB local circuits facilitate odor-specific responses during odor discrimination is not known but involves GABAergic inhibition mediated by axonless granule cells (GCs), the most abundant interneuron in the OB. Most previous work on GCs has focused on defining properties of distal apical dendrites where these interneurons form reciprocal dendrodendritic connections with principal cells. Less is known about the function of the proximal dendritic compartments. In the present study, we identified the likely action potentials (AP) initiation zone by comparing electrophysiological properties of rat (either sex) GCs with apical dendrites severed at different locations. We find that truncated GCs with long apical dendrites had active properties that were indistinguishable from intact GCs, generating full-height APs and short-latency low-threshold Ca2+ spikes. We then confirmed the presumed site of AP and low-threshold Ca2+ spike initiation in the proximal apical dendrite using two-photon Ca2+ photometry and focal TTX application. These results suggest that GCs incorporate two separate pathways for processing synaptic inputs: an already established dendrodendritic input to the distal apical dendrite and a novel pathway in which the cell body integrates proximal synaptic inputs, leading to spike generation in the proximal apical dendrite. Spikes generated by the proximal pathway likely enables GCs to regulate lateral inhibition by defining time windows when lateral inhibition is functional.SIGNIFICANCE STATEMENT The olfactory bulb plays a central role in processing sensory input transduced by receptor neurons. How local circuits in the bulb function to facilitate sensory processing during odor discrimination is not known but appears to involve inhibition mediated by granule cells, axonless GABAergic interneurons. Little is known about the active conductances in granule cells including where action potentials originate. Using a variety of experimental approaches, we find the Na+-based action potentials originate in the proximal apical dendrite, a region targeted by cortical feedback afferents. We also find evidence for high expression of low-voltage activated Ca2+ channels in the same region, intrinsic currents that enable GCs to spike rapidly in response to sensory input during each sniff cycle.
Collapse
|
9
|
Adams W, Graham JN, Han X, Riecke H. Top-down inputs drive neuronal network rewiring and context-enhanced sensory processing in olfaction. PLoS Comput Biol 2019; 15:e1006611. [PMID: 30668563 PMCID: PMC6358160 DOI: 10.1371/journal.pcbi.1006611] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2018] [Revised: 02/01/2019] [Accepted: 10/29/2018] [Indexed: 11/18/2022] Open
Abstract
Much of the computational power of the mammalian brain arises from its extensive top-down projections. To enable neuron-specific information processing these projections have to be precisely targeted. How such a specific connectivity emerges and what functions it supports is still poorly understood. We addressed these questions in silico in the context of the profound structural plasticity of the olfactory system. At the core of this plasticity are the granule cells of the olfactory bulb, which integrate bottom-up sensory inputs and top-down inputs delivered by vast top-down projections from cortical and other brain areas. We developed a biophysically supported computational model for the rewiring of the top-down projections and the intra-bulbar network via adult neurogenesis. The model captures various previous physiological and behavioral observations and makes specific predictions for the cortico-bulbar network connectivity that is learned by odor exposure and environmental contexts. Specifically, it predicts that-after learning-the granule-cell receptive fields with respect to sensory and with respect to cortical inputs are highly correlated. This enables cortical cells that respond to a learned odor to enact disynaptic inhibitory control specifically of bulbar principal cells that respond to that odor. For this the reciprocal nature of the granule cell synapses with the principal cells is essential. Functionally, the model predicts context-enhanced stimulus discrimination in cluttered environments ('olfactory cocktail parties') and the ability of the system to adapt to its tasks by rapidly switching between different odor-processing modes. These predictions are experimentally testable. At the same time they provide guidance for future experiments aimed at unraveling the cortico-bulbar connectivity.
Collapse
Affiliation(s)
- Wayne Adams
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, IL, USA
| | - James N. Graham
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, IL, USA
| | - Xuchen Han
- Mathematics, Northwestern University, Evanston, IL, USA
| | - Hermann Riecke
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, IL, USA
| |
Collapse
|
10
|
Osinski BL, Kim A, Xiao W, Mehta NM, Kay LM. Pharmacological manipulation of the olfactory bulb modulates beta oscillations: testing model predictions. J Neurophysiol 2018; 120:1090-1106. [PMID: 29847235 DOI: 10.1152/jn.00090.2018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mammalian olfactory bulb (OB) generates gamma (40-100 Hz) and beta (15-30 Hz) local field potential (LFP) oscillations. Gamma oscillations arise at the peak of inhalation supported by dendrodendritic interactions between glutamatergic mitral cells (MCs) and GABAergic granule cells (GCs). Beta oscillations are induced by odorants in learning or odor sensitization paradigms, but their mechanism and function are still poorly understood. When centrifugal OB inputs are blocked, beta oscillations disappear, but gamma oscillations persist. Centrifugal inputs target primarily GABAergic interneurons in the GC layer (GCL) and regulate GC excitability, suggesting a causal link between beta oscillations and GC excitability. Our previous modeling work predicted that convergence of excitatory/inhibitory inputs onto MCs and centrifugal inputs onto GCs increase GC excitability sufficiently to produce beta oscillations primarily through voltage dependent calcium channel-mediated GABA release, independently of NMDA channels. We test some of the predictions of this model by examining the influence of NMDA and muscarinic acetylcholine (ACh) receptors, which affect GC excitability in different ways, on beta oscillations. A few minutes after intrabulbar infusion, scopolamine (muscarinic antagonist) suppressed odor-evoked beta in response to a strong stimulus but increased beta power in response to a weak stimulus, as predicted by our model. Pyriform cortex (PC) beta power was unchanged. Oxotremorine (muscarinic agonist) suppressed all oscillations, likely from overinhibition. APV, an NMDA receptor antagonist, suppressed gamma oscillations selectively (in OB and PC), lending support to the model's prediction that beta oscillations can be supported independently of NMDA receptors. NEW & NOTEWORTHY Olfactory bulb local field potential beta oscillations appear to be gated by GABAergic granule cell excitability. Reducing excitability with scopolamine reduces beta induced by strong odors but increases beta induced by weak odors. Beta oscillations rely on the same synapse as gamma oscillations but, unlike gamma, can persist in the absence of NMDA receptor activation. Pyriform cortex beta oscillations maintain power when olfactory bulb beta power is low, and the system maintains beta band coherence.
Collapse
Affiliation(s)
- Bolesław L Osinski
- Graduate Program in Biophysical Sciences, The University of Chicago , Chicago, Illinois.,Institute for Mind and Biology, The University of Chicago , Chicago, Illinois
| | - Alex Kim
- The College, The University of Chicago , Chicago, Illinois
| | - Wenxi Xiao
- Masters Program in Computational Social Sciences, The University of Chicago , Chicago, Illinois
| | - Nisarg M Mehta
- Institute for Mind and Biology, The University of Chicago , Chicago, Illinois
| | - Leslie M Kay
- Institute for Mind and Biology, The University of Chicago , Chicago, Illinois.,Department of Psychology, The University of Chicago , Chicago, Illinois
| |
Collapse
|
11
|
Burton SD. Inhibitory circuits of the mammalian main olfactory bulb. J Neurophysiol 2017; 118:2034-2051. [PMID: 28724776 DOI: 10.1152/jn.00109.2017] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 07/14/2017] [Accepted: 07/14/2017] [Indexed: 01/15/2023] Open
Abstract
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.
Collapse
Affiliation(s)
- Shawn D Burton
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania; and .,Center for the Neural Basis of Cognition, Pittsburgh, Pennsylvania
| |
Collapse
|
12
|
Dopamine Inhibition Differentially Controls Excitability of Substantia Nigra Dopamine Neuron Subpopulations through T-Type Calcium Channels. J Neurosci 2017; 37:3704-3720. [PMID: 28264982 DOI: 10.1523/jneurosci.0117-17.2017] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Revised: 02/15/2017] [Accepted: 02/21/2017] [Indexed: 11/21/2022] Open
Abstract
While there is growing appreciation for diversity among ventral tegmental area dopamine neurons, much less is known regarding functional heterogeneity among the substantia nigra pars compacta (SNc) neurons. Here, we show that calbindin-positive dorsal tier and calbindin-negative ventral tier SNc dopaminergic neurons in mice comprise functionally distinct subpopulations distinguished by their dendritic calcium signaling, rebound excitation, and physiological responses to dopamine D2-receptor (D2) autoinhibition. While dopamine is known to inhibit action potential backpropagation, our experiments revealed an unexpected enhancement of excitatory responses and dendritic calcium signals in the presence of D2-receptor inhibition. Specifically, dopamine inhibition and direct hyperpolarization enabled the generation of low-threshold depolarizations that occurred in an all-or-none or graded manner, due to recruitment of T-type calcium channels. Interestingly, these effects occurred selectively in calbindin-negative dopaminergic neurons within the SNc. Thus, calbindin-positive and calbindin-negative SNc neurons differ substantially in their calcium channel composition and efficacy of excitatory inputs in the presence of dopamine inhibition.SIGNIFICANCE STATEMENT Substantia nigra dopaminergic neurons can be divided into two populations: the calbindin-negative ventral tier, which is vulnerable to neurodegeneration in Parkinson's disease, and the calbindin-positive dorsal tier, which is relatively resilient. Although tonic firing is similar in these subpopulations, we find that their responses to dopamine-mediated inhibition are strikingly different. During inhibition, calbindin-negative neurons exhibit increased sensitivity to excitatory inputs, which can then trigger large dendritic calcium transients due to strong expression of T-type calcium channels. Therefore, SNc neurons differ substantially in their calcium channel composition, which may contribute to their differential vulnerability. Furthermore, T-currents increase excitation efficacy onto calbindin-negative cells during dopamine inhibition, suggesting that shared inputs are differentially processed in subpopulations resulting in distinct downstream dopamine signals.
Collapse
|
13
|
Ona-Jodar T, Gerkau NJ, Sara Aghvami S, Rose CR, Egger V. Two-Photon Na + Imaging Reports Somatically Evoked Action Potentials in Rat Olfactory Bulb Mitral and Granule Cell Neurites. Front Cell Neurosci 2017; 11:50. [PMID: 28293175 PMCID: PMC5329072 DOI: 10.3389/fncel.2017.00050] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 02/14/2017] [Indexed: 12/05/2022] Open
Abstract
Dendrodendritic synaptic interactions are a hallmark of neuronal processing in the vertebrate olfactory bulb. Many classes of olfactory bulb neurons including the principal mitral cells (MCs) and the axonless granule cells (GCs) dispose of highly efficient propagation of action potentials (AP) within their dendrites, from where they can release transmitter onto each other. So far, backpropagation in GC dendrites has been investigated indirectly via Ca2+ imaging. Here, we used two-photon Na+ imaging to directly report opening of voltage-gated sodium channels due to AP propagation in both cell types. To this end, neurons in acute slices from juvenile rat bulbs were filled with 1 mM SBFI via whole-cell patch-clamp. Calibration of SBFI signals revealed that a change in fluorescence ΔF/F by 10% corresponded to a Δ[Na+]i of ∼22 mM. We then imaged proximal axon segments of MCs during somatically evoked APs (sAP). While single sAPs were detectable in ∼50% of axons, trains of 20 sAPs at 50 Hz always resulted in substantial ΔF/F of ∼15% (∼33 mM Δ[Na+]i). ΔF/F was significantly larger for 80 Hz vs. 50 Hz trains, and decayed with half-durations τ1/2 ∼0.6 s for both frequencies. In MC lateral dendrites, AP trains yielded small ΔF/F of ∼3% (∼7 mM Δ[Na+]i). In GC apical dendrites and adjacent spines, single sAPs were not detectable. Trains resulted in an average dendritic ΔF/F of 7% (16 mM Δ[Na+]i) with τ1/2 ∼1 s, similar for 50 and 80 Hz. Na+ transients were indistinguishable between large GC spines and their adjacent dendrites. Cell-wise analysis revealed two classes of GCs with the first showing a decrease in ΔF/F along the dendrite with distance from the soma and the second an increase. These classes clustered with morphological parameters. Simulations of Δ[Na+]i replicated these behaviors via negative and positive gradients in Na+ current density, assuming faithful AP backpropagation. Such specializations of dendritic excitability might confer specific temporal processing capabilities to bulbar principal cell-GC subnetworks. In conclusion, we show that Na+ imaging provides a valuable tool for characterizing AP invasion of MC axons and GC dendrites and spines.
Collapse
Affiliation(s)
- Tiffany Ona-Jodar
- Neurophysiology, Institute of Zoology, Universität Regensburg Regensburg, Germany
| | - Niklas J Gerkau
- Institute of Neurobiology, Heinrich-Heine-Universität Düsseldorf Düsseldorf, Germany
| | - S Sara Aghvami
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburg, Germany; School of Electrical and Computer Engineering, University of TehranTehran, Iran; School of Cognitive Science, Institute for Research in Fundamental ScienceTehran, Iran
| | - Christine R Rose
- Institute of Neurobiology, Heinrich-Heine-Universität Düsseldorf Düsseldorf, Germany
| | - Veronica Egger
- Neurophysiology, Institute of Zoology, Universität RegensburgRegensburg, Germany; Regensburg Center of Neuroscience, Universität RegensburgRegensburg, Germany
| |
Collapse
|
14
|
Osinski BL, Kay LM. Granule cell excitability regulates gamma and beta oscillations in a model of the olfactory bulb dendrodendritic microcircuit. J Neurophysiol 2016; 116:522-39. [PMID: 27121582 DOI: 10.1152/jn.00988.2015] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 04/25/2016] [Indexed: 01/03/2023] Open
Abstract
Odors evoke gamma (40-100 Hz) and beta (20-30 Hz) oscillations in the local field potential (LFP) of the mammalian olfactory bulb (OB). Gamma (and possibly beta) oscillations arise from interactions in the dendrodendritic microcircuit between excitatory mitral cells (MCs) and inhibitory granule cells (GCs). When cortical descending inputs to the OB are blocked, beta oscillations are extinguished whereas gamma oscillations become larger. Much of this centrifugal input targets inhibitory interneurons in the GC layer and regulates the excitability of GCs, which suggests a causal link between the emergence of beta oscillations and GC excitability. We investigate the effect that GC excitability has on network oscillations in a computational model of the MC-GC dendrodendritic network with Ca(2+)-dependent graded inhibition. Results from our model suggest that when GC excitability is low, the graded inhibitory current mediated by NMDA channels and voltage-dependent Ca(2+) channels (VDCCs) is also low, allowing MC populations to fire in the gamma frequency range. When GC excitability is increased, the activation of NMDA receptors and other VDCCs is also increased, allowing the slow decay time constants of these channels to sustain beta-frequency oscillations. Our model argues that Ca(2+) flow through VDCCs alone could sustain beta oscillations and that the switch between gamma and beta oscillations can be triggered by an increase in the excitability state of a subpopulation of GCs.
Collapse
Affiliation(s)
- Bolesław L Osinski
- Graduate Program in Biophysical Sciences, The University of Chicago, Chicago, Illinois; Institute for Mind and Biology, The University of Chicago, Chicago, Illinois; and
| | - Leslie M Kay
- Institute for Mind and Biology, The University of Chicago, Chicago, Illinois; and Department of Psychology, The University of Chicago, Chicago, Illinois
| |
Collapse
|
15
|
Rapid Feedforward Inhibition and Asynchronous Excitation Regulate Granule Cell Activity in the Mammalian Main Olfactory Bulb. J Neurosci 2016; 35:14103-22. [PMID: 26490853 DOI: 10.1523/jneurosci.0746-15.2015] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Granule cell-mediated inhibition is critical to patterning principal neuron activity in the olfactory bulb, and perturbation of synaptic input to granule cells significantly alters olfactory-guided behavior. Despite the critical role of granule cells in olfaction, little is known about how sensory input recruits granule cells. Here, we combined whole-cell patch-clamp electrophysiology in acute mouse olfactory bulb slices with biophysical multicompartmental modeling to investigate the synaptic basis of granule cell recruitment. Physiological activation of sensory afferents within single glomeruli evoked diverse modes of granule cell activity, including subthreshold depolarization, spikelets, and suprathreshold responses with widely distributed spike latencies. The generation of these diverse activity modes depended, in part, on the asynchronous time course of synaptic excitation onto granule cells, which lasted several hundred milliseconds. In addition to asynchronous excitation, each granule cell also received synchronous feedforward inhibition. This inhibition targeted both proximal somatodendritic and distal apical dendritic domains of granule cells, was reliably recruited across sniff rhythms, and scaled in strength with excitation as more glomeruli were activated. Feedforward inhibition onto granule cells originated from deep short-axon cells, which responded to glomerular activation with highly reliable, short-latency firing consistent with tufted cell-mediated excitation. Simulations showed that feedforward inhibition interacts with asynchronous excitation to broaden granule cell spike latency distributions and significantly attenuates granule cell depolarization within local subcellular compartments. Collectively, our results thus identify feedforward inhibition onto granule cells as a core feature of olfactory bulb circuitry and establish asynchronous excitation and feedforward inhibition as critical regulators of granule cell activity. SIGNIFICANCE STATEMENT Inhibitory granule cells are involved critically in shaping odor-evoked principal neuron activity in the mammalian olfactory bulb, yet little is known about how sensory input activates granule cells. Here, we show that sensory input to the olfactory bulb evokes a barrage of asynchronous synaptic excitation and highly reliable, short-latency synaptic inhibition onto granule cells via a disynaptic feedforward inhibitory circuit involving deep short-axon cells. Feedforward inhibition attenuates local depolarization within granule cell dendritic branches, interacts with asynchronous excitation to suppress granule cell spike-timing precision, and scales in strength with excitation across different levels of sensory input to normalize granule cell firing rates.
Collapse
|
16
|
Pérez de los Cobos Pallarés F, Stanić D, Farmer D, Dutschmann M, Egger V. An arterially perfused nose-olfactory bulb preparation of the rat. J Neurophysiol 2015; 114:2033-42. [PMID: 26108959 DOI: 10.1152/jn.01048.2014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 06/18/2015] [Indexed: 11/22/2022] Open
Abstract
A main feature of the mammalian olfactory bulb network is the presence of various rhythmic activities, in particular, gamma, beta, and theta oscillations, with the latter coupled to the respiratory rhythm. Interactions between those oscillations as well as the spatial distribution of network activation are likely to determine olfactory coding. Here, we describe a novel semi-intact perfused nose-olfactory bulb-brain stem preparation in rats with both a preserved olfactory epithelium and brain stem, which could be particularly suitable for the study of oscillatory activity and spatial odor mapping within the olfactory bulb, in particular, in hitherto inaccessible locations. In the perfused olfactory bulb, we observed robust spontaneous oscillations, mostly in the theta range. Odor application resulted in an increase in oscillatory power in higher frequency ranges, stimulus-locked local field potentials, and excitation or inhibition of individual bulbar neurons, similar to odor responses reported from in vivo recordings. Thus our method constitutes the first viable in situ preparation of a mammalian system that uses airborne odor stimuli and preserves these characteristic features of odor processing. This preparation will allow the use of highly invasive experimental procedures and the application of techniques such as patch-clamp recording, high-resolution imaging, and optogenetics within the entire olfactory bulb.
Collapse
Affiliation(s)
- Fernando Pérez de los Cobos Pallarés
- Systems Neurobiology, Department of Biology II, Ludwigs-Maximilians-Universität München, Martinsried, Germany; Neurophysiology, Zoological Institute, Regensburg University, Regensburg, Germany; and
| | - Davor Stanić
- Florey Institute of Neuroscience and Mental Health, University of Melbourne Victoria, Melbourne, Victoria, Australia
| | - David Farmer
- Florey Institute of Neuroscience and Mental Health, University of Melbourne Victoria, Melbourne, Victoria, Australia
| | - Mathias Dutschmann
- Florey Institute of Neuroscience and Mental Health, University of Melbourne Victoria, Melbourne, Victoria, Australia
| | - Veronica Egger
- Systems Neurobiology, Department of Biology II, Ludwigs-Maximilians-Universität München, Martinsried, Germany; Neurophysiology, Zoological Institute, Regensburg University, Regensburg, Germany; and
| |
Collapse
|
17
|
Simões-de-Souza FM, Antunes G, Roque AC. Electrical responses of three classes of granule cells of the olfactory bulb to synaptic inputs in different dendritic locations. Front Comput Neurosci 2014; 8:128. [PMID: 25360108 PMCID: PMC4197772 DOI: 10.3389/fncom.2014.00128] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 09/25/2014] [Indexed: 11/13/2022] Open
Abstract
This work consists of a computational study of the electrical responses of three classes of granule cells of the olfactory bulb to synaptic activation in different dendritic locations. The constructed models were based on morphologically detailed compartmental reconstructions of three granule cell classes of the olfactory bulb with active dendrites described by Bhalla and Bower (1993, pp. 1948-1965) and dendritic spine distributions described by Woolf et al. (1991, pp. 1837-1854). The computational studies with the model neurons showed that different quantities of spines have to be activated in each dendritic region to induce an action potential, which always was originated in the active terminal dendrites, independently of the location of the stimuli, and the morphology of the dendritic tree. These model predictions might have important computational implications in the context of olfactory bulb circuits.
Collapse
Affiliation(s)
- Fábio M Simões-de-Souza
- Laboratory of Neural Systems (SisNE), Department of Psychology, Faculdade de Filosofia Ciencias e Letras de Ribeirão Preto, Universidade de São Paulo Ribeirão Preto, Brazil ; Center for Mathematics, Computation and Cognition, Federal University of ABC São Bernardo do Campo, Brazil
| | - Gabriela Antunes
- Laboratory of Neural Systems (SisNE), Department of Psychology, Faculdade de Filosofia Ciencias e Letras de Ribeirão Preto, Universidade de São Paulo Ribeirão Preto, Brazil
| | - Antonio C Roque
- Laboratory of Neural Systems (SisNE), Department of Physics, Faculdade de Filosofia Ciencias e Letras de Ribeirão Preto, Universidade de São Paulo Ribeirão Preto, Brazil
| |
Collapse
|
18
|
Pressler RT, Rozman PA, Strowbridge BW. Voltage-dependent intrinsic bursting in olfactory bulb Golgi cells. Learn Mem 2013; 20:459-66. [PMID: 23950193 PMCID: PMC3744043 DOI: 10.1101/lm.031856.113] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In the mammalian olfactory bulb (OB), local synaptic circuits modulate the evolving pattern of activity in mitral and tufted cells following olfactory sensory stimulation. GABAergic granule cells, the most numerous interneuron subtype in this brain region, have been extensively studied. However, classic studies using Golgi staining methods identified many other, nongranule cell types in the OB whose function remains mysterious. Within just the granule cell layer (GCL), Ramón y Cajal described multiple morphologically distinct subtypes of nongranule interneurons including large spiny Blanes cells which exhibit intrinsic persistent activity. Here, we define the intrinsic electrophysiology of a different nongranule interneuronal cell type in the GCL described by Ramón y Cajal, sparsely spiny Golgi cells in the rat OB. Golgi cells exhibit two distinct firing modes depending on the membrane potential: tonic firing and bursting. Golgi cells also generate rebound bursts following the offset of hyperpolarizing steps. We find that both low-threshold burst responses to depolarizing inputs and rebound bursts are blocked by nickel, an antagonist of T-type voltage-gated Ca2+ current. The state-dependent firing behavior we report in OB Golgi cells suggests that the function of these interneurons may dynamically shift from providing rhythmic potent inhibition of postsynaptic target neurons at sniffing frequencies to tonic, subtractive inhibition based on centrifugal modulatory input.
Collapse
Affiliation(s)
- R Todd Pressler
- Department of Neurosciences, Case Western Reserve School of Medicine, Cleveland, Ohio 44106, USA
| | | | | |
Collapse
|
19
|
Crespo C, Liberia T, Blasco-Ibáñez JM, Nácher J, Varea E. The Circuits of the Olfactory Bulb. The Exception as a Rule. Anat Rec (Hoboken) 2013; 296:1401-12. [DOI: 10.1002/ar.22732] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Revised: 02/28/2013] [Accepted: 03/07/2013] [Indexed: 12/22/2022]
Affiliation(s)
- Carlos Crespo
- Department of Cell Biology, Faculty of Biology; University of Valencia; C/ Dr. Moliner, 50, 46100 Burjassot Valencia Spain
| | - Teresa Liberia
- Department of Cell Biology, Faculty of Biology; University of Valencia; C/ Dr. Moliner, 50, 46100 Burjassot Valencia Spain
| | - José Miguel Blasco-Ibáñez
- Department of Cell Biology, Faculty of Biology; University of Valencia; C/ Dr. Moliner, 50, 46100 Burjassot Valencia Spain
| | - Juan Nácher
- Department of Cell Biology, Faculty of Biology; University of Valencia; C/ Dr. Moliner, 50, 46100 Burjassot Valencia Spain
| | - Emilio Varea
- Department of Cell Biology, Faculty of Biology; University of Valencia; C/ Dr. Moliner, 50, 46100 Burjassot Valencia Spain
| |
Collapse
|
20
|
Lepousez G, Valley MT, Lledo PM. The impact of adult neurogenesis on olfactory bulb circuits and computations. Annu Rev Physiol 2012. [PMID: 23190074 DOI: 10.1146/annurev-physiol-030212-183731] [Citation(s) in RCA: 129] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Modern neuroscience has demonstrated how the adult brain has the ability to profoundly remodel its neurons in response to changes in external stimuli or internal states. However, adult brain plasticity, although possible throughout life, remains restricted mostly to subcellular levels rather than affecting the entire cell. New neurons are continuously generated in only a few areas of the adult brain-the olfactory bulb and the dentate gyrus-where they integrate into already functioning circuitry. In these regions, adult neurogenesis adds another dimension of plasticity that either complements or is redundant to the classical molecular and cellular mechanisms of plasticity. This review extracts clues regarding the contribution of adult-born neurons to the different circuits of the olfactory bulb and specifically how new neurons participate in existing computations and enable new computational functions.
Collapse
Affiliation(s)
- Gabriel Lepousez
- Laboratory of Perception and Memory, Institut Pasteur, F-75015 Paris, France.
| | | | | |
Collapse
|
21
|
Giridhar S, Urban NN. Mechanisms and benefits of granule cell latency coding in the mouse olfactory bulb. Front Neural Circuits 2012; 6:40. [PMID: 22754503 PMCID: PMC3385563 DOI: 10.3389/fncir.2012.00040] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 06/10/2012] [Indexed: 11/13/2022] Open
Abstract
Inhibitory circuits are critical for shaping odor representations in the olfactory bulb. There, individual granule cells can respond to brief stimulation with extremely long (up to 1000 ms), input-specific latencies that are highly reliable. However, the mechanism and function of this long timescale activity remain unknown. We sought to elucidate the mechanism responsible for long-latency activity, and to understand the impact of widely distributed interneuron latencies on olfactory coding. We used a combination of electrophysiological, optical, and pharmacological techniques to show that long-latency inhibition is driven by late onset synaptic excitation to granule cells. This late excitation originates from tufted cells, which have intrinsic properties that favor longer latency spiking than mitral cells. Using computational modeling, we show that widely distributed interneuron latency increases the discriminability of similar stimuli. Thus, long-latency inhibition in the olfactory bulb requires a combination of circuit- and cellular-level mechanisms that function to improve stimulus representations.
Collapse
Affiliation(s)
- Sonya Giridhar
- Center for Neuroscience, University of Pittsburgh, Pittsburgh PA, USA
| | | |
Collapse
|
22
|
NMDA receptor-dependent synaptic activation of TRPC channels in olfactory bulb granule cells. J Neurosci 2012; 32:5737-46. [PMID: 22539836 DOI: 10.1523/jneurosci.3753-11.2012] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Canonical transient receptor potential (TRPC) channels are widely expressed throughout the nervous system including the olfactory bulb where their function is largely unknown. Here, we describe their contribution to central synaptic processing at the reciprocal mitral and tufted cell-granule cell microcircuit, the most abundant synapse of the mammalian olfactory bulb. Suprathreshold activation of the synapse causes sodium action potentials in mouse granule cells and a subsequent long-lasting depolarization (LLD) linked to a global dendritic postsynaptic calcium signal recorded with two-photon laser-scanning microscopy. These signals are not observed after action potentials evoked by current injection in the same cells. The LLD persists in the presence of group I metabotropic glutamate receptor antagonists but is entirely absent from granule cells deficient for the NMDA receptor subunit NR1. Moreover, both depolarization and Ca²⁺ rise are sensitive to the blockade of NMDA receptors. The LLD and the accompanying Ca²⁺ rise are also absent in granule cells from mice deficient for both TRPC channel subtypes 1 and 4, whereas the deletion of either TRPC1 or TRPC4 results in only a partial reduction of the LLD. Recordings from mitral cells in the absence of both subunits reveal a reduction of asynchronous neurotransmitter release from the granule cells during recurrent inhibition. We conclude that TRPC1 and TRPC4 can be activated downstream of NMDA receptor activation and contribute to slow synaptic transmission in the olfactory bulb, including the calcium dynamics required for asynchronous release from the granule cell spine.
Collapse
|
23
|
Chow SF, Wick SD, Riecke H. Neurogenesis drives stimulus decorrelation in a model of the olfactory bulb. PLoS Comput Biol 2012; 8:e1002398. [PMID: 22442645 PMCID: PMC3305347 DOI: 10.1371/journal.pcbi.1002398] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Accepted: 01/09/2012] [Indexed: 01/25/2023] Open
Abstract
The reshaping and decorrelation of similar activity patterns by neuronal networks can enhance their discriminability, storage, and retrieval. How can such networks learn to decorrelate new complex patterns, as they arise in the olfactory system? Using a computational network model for the dominant neural populations of the olfactory bulb we show that fundamental aspects of the adult neurogenesis observed in the olfactory bulb--the persistent addition of new inhibitory granule cells to the network, their activity-dependent survival, and the reciprocal character of their synapses with the principal mitral cells--are sufficient to restructure the network and to alter its encoding of odor stimuli adaptively so as to reduce the correlations between the bulbar representations of similar stimuli. The decorrelation is quite robust with respect to various types of perturbations of the reciprocity. The model parsimoniously captures the experimentally observed role of neurogenesis in perceptual learning and the enhanced response of young granule cells to novel stimuli. Moreover, it makes specific predictions for the type of odor enrichment that should be effective in enhancing the ability of animals to discriminate similar odor mixtures.
Collapse
Affiliation(s)
- Siu-Fai Chow
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, Illinois, United States of America
| | - Stuart D. Wick
- Department of Physics, North Central College, Naperville, Illinois, United States of America
| | - Hermann Riecke
- Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, Illinois, United States of America
- Northwestern Institute on Complex Systems, Northwestern University, Evanston, Illinois, United States of America
- * E-mail:
| |
Collapse
|
24
|
Dahlen JE, Jimenez DA, Gerkin RC, Urban NN. Morphological analysis of activity-reduced adult-born neurons in the mouse olfactory bulb. Front Neurosci 2011; 5:66. [PMID: 21602912 PMCID: PMC3092085 DOI: 10.3389/fnins.2011.00066] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Accepted: 04/27/2011] [Indexed: 12/30/2022] Open
Abstract
Adult-born neurons (ABNs) are added to the olfactory bulb (OB) throughout life in rodents. While many factors have been identified as regulating the survival and integration of ABNs into existing circuitry, the understanding of how these factors affect ABN morphology and connectivity is limited. Here we compare how cell intrinsic [small interfering RNA (siRNA) knock-down of voltage gated sodium channels NaV1.1–1.3] and circuit level (naris occlusion) reductions in activity affect ABN morphology during integration into the OB. We found that both manipulations reduce the number of dendritic spines (and thus likely the number of reciprocal synaptic connections) formed with the surrounding circuitry and inhibited dendritic ramification of ABNs. Further, we identified regions of ABN apical dendrites where the largest and most significant decreases occur following siRNA knock-down or naris occlusion. In siRNA knock-down cells, reduction of spines is observed in proximal regions of the apical dendrite. This suggests that distal regions of the dendrite may remain active independent of NaV1.1–1.3 channel expression, perhaps facilitated by activation of T-type calcium channels and NMDA receptors. By contrast, circuit level reduction of activity by naris occlusion resulted in a global depression of spine number. Together, these results indicate that ABNs retain the ability to develop their typical overall morphological features regardless of experienced activity, and activity modulates the number and location of formed connections.
Collapse
Affiliation(s)
- Jeffrey E Dahlen
- Department of Biological Sciences, Carnegie Mellon University Pittsburgh, PA, USA
| | | | | | | |
Collapse
|
25
|
How, when, and where new inhibitory neurons release neurotransmitters in the adult olfactory bulb. J Neurosci 2011; 30:17023-34. [PMID: 21159972 DOI: 10.1523/jneurosci.4543-10.2010] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Adult-born neurons continuously incorporate into the olfactory bulb where they rapidly establish contacts with a variety of synaptic inputs. Little is known, however, about the functional properties of their output. Characterization of synaptic outputs from new neurons is essential to assess the functional impact of adult neurogenesis on mature circuits. Here, we used optogenetics to control neurotransmitter release from new neurons. We found that light-induced synaptic GABA release from adult-born neurons leads to profound modifications of postsynaptic target firing patterns. We revealed that functional output synapses form just after new cells acquire the faculty to spike, but most synapses were made a month later. Despite discrepancies in the timing of new synapse recruitment, the properties of postsynaptic signals remain constant. Remarkably, we found that all major cell types of the olfactory bulb circuit, including output neurons and several distinct subtypes of local interneurons, were contacted by adult-born neurons. Thus, this study provides new insights into how new neurons integrate into the adult neural network and may influence the sense of smell.
Collapse
|
26
|
Mouret A, Murray K, Lledo PM. Centrifugal Drive onto Local Inhibitory Interneurons of the Olfactory Bulb. Ann N Y Acad Sci 2009; 1170:239-54. [DOI: 10.1111/j.1749-6632.2009.03913.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
|
27
|
Egger V, Stroh O. Calcium buffering in rodent olfactory bulb granule cells and mitral cells. J Physiol 2009; 587:4467-79. [PMID: 19635818 DOI: 10.1113/jphysiol.2009.174540] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In the mammalian olfactory bulb, axonless granule cells (GCs) mediate self- and lateral inhibitory interactions between mitral cells (MCs) via reciprocal dendrodendritic synapses. Calcium signals in the GC dendrites and reciprocal spines appear to decay unusually slowly, hence GC calcium handling might contribute to the known asynchronous release at this synapse. By recording fluorescence transients of different Ca(2+)-sensitive dyes at variable concentrations evoked by backpropagating action potentials (APs) and saturating AP trains we extrapolated Ca(2+) dynamics to conditions of zero added buffer for juvenile rat GC apical dendrites and spines and MC lateral dendrites. Resting [Ca(2+)] was at approximately 50 nM in both GC dendrites and spines. The average endogenous GC buffer capacities (kappa(E)) were within a range of 80-90 in the dendrites and 110-140 in the spines. The extrusion rate (gamma) was estimated as 570 s(-1) for dendrites and 870 s(-1) for spines and the decay time constant as approximately 200 ms for both. Single-current-evoked APs resulted in a [Ca(2+)] elevation of approximately 250 nM. Calcium handling in juvenile and adult mouse GCs appeared mostly similar. In MC lateral dendrites, we found AP-mediated [Ca(2+)] elevations of approximately 130 nM with a similar decay to that in GC dendrites, while kappa(E) and gamma were roughly 4-fold higher. In conclusion, the slow GC Ca(2+) dynamics are due mostly to sluggish Ca(2+) extrusion. Under physiological conditions this slow removal may well contribute to delayed release and also feed into other Ca(2+)-dependent mechanisms that foster asynchronous output from the reciprocal spine.
Collapse
Affiliation(s)
- Veronica Egger
- Institut für Physiologie der Ludwig-Maximilians-Universität, 80336 München, Germany.
| | | |
Collapse
|
28
|
Smith RS, Weitz CJ, Araneda RC. Excitatory actions of noradrenaline and metabotropic glutamate receptor activation in granule cells of the accessory olfactory bulb. J Neurophysiol 2009; 102:1103-14. [PMID: 19474170 DOI: 10.1152/jn.91093.2008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Modulation of dendrodendritic synapses by the noradrenergic system in the accessory olfactory bulb (AOB) plays a key role in the formation of memory in olfactory-mediated behaviors. We have recently shown that noradrenaline (NA) inhibits mitral cells by increasing gamma-aminobutyric acid inhibitory input onto mitral cells in the AOB, suggesting an excitatory action of NA on granule cells (GCs). Here, we show that NA (10 microM) elicits a long-lasting depolarization of GCs. This effect is mediated by activation of alpha(1)-adrenergic receptors as the depolarization is mimicked by phenylephrine (PE, 30 microM) and completely blocked by the alpha(1)-adrenergic receptor antagonist prazosin (300 nM). In addition to this depolarization, application of NA induced the appearance of a slow afterdepolarization (sADP) following a stimulus-elicited train of action potentials. Similarly, the group I metabotropic glutamate receptor (mGluR1) agonist DHPG (10-30 microM) also produced a depolarization of GCs and the appearance of a stimulus-induced sADP. The ionic and voltage dependence and sensitivity to blockers of the sADP suggest that it is mediated by the nonselective cationic conductance I(CAN). Thus the excitatory action resulting from the activation of these receptors could be mediated by a common transduction target. Surprisingly, the excitatory effect of PE on GCs was completely blocked by the mGluR1 antagonist LY367385 (100 microM). Conversely, the effect of DHPG was not antagonized by the alpha(1)-adrenergic receptor antagonist prazosin (300 nM). These results suggest that most of the noradrenergic effect on GCs in the AOB is mediated by potentiation of a basal activity of mGluR1s.
Collapse
Affiliation(s)
- Richard S Smith
- Department of Biology, University of Maryland, College Park, Maryland 20742, USA
| | | | | |
Collapse
|
29
|
Sodium channel cluster, betaIV-spectrin and ankyrinG positive "hot spots" on dendritic segments of parvalbumin-containing neurons and some other neurons in the mouse and rat main olfactory bulbs. Neurosci Res 2008; 62:176-86. [PMID: 18786578 DOI: 10.1016/j.neures.2008.08.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 07/31/2008] [Accepted: 08/06/2008] [Indexed: 12/31/2022]
Abstract
Axon initial segments (AISs) and nodes of Ranvier are considered as the sites for spike generation, which are highly enriched in sodium channels and some cytoskeletal molecules such as ankyrinG, betaIV-spectrin. Previously, we showed that most parvalbumin positive cells in the external plexiform layer (EPL) of the mouse main olfactory bulb (MOB) were anaxonic but displayed some patch-like betaIV-spectrin and sodium channel cluster positive segments on their dendrites. In this study we further characterized those particular dendritic segments. AnkyrinG was also located there, whereas phospho-IkappaBalpha was not. Electron-microscopically those dendritic segments displayed the membrane undercoating characteristic to the AISs and nodes of Ranvier, further confirming their resemblance to the spike generation sites, "hot spots". Three-dimensional analysis revealed that each parvalbumin positive EPL neuron had 2-7 hot spots, 3-28 microm in length and located 7-50 microm from the somata. Similar "hot spots" were also encountered on a few calretinin positive granule cells and nitric oxide synthase positive periglomerular cells in the mouse MOB. In addition parvalbumin positive EPL cells in the rat MOB displayed similar multiple dendritic "hot spots". Our study suggested that these morphologically identified dendritic "hot spots" might correspond to dendritic spike generation sites of those neurons.
Collapse
|