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Ramírez A, Monjaraz E, Manjarrez E, Moyaho A, Cebada J, Flores A. Pharmacological characterization and differential expression of NMDA receptor subunits in the chicken vestibular system during development. Synapse 2023; 77:e22252. [PMID: 36099479 DOI: 10.1002/syn.22252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 08/31/2022] [Accepted: 09/04/2022] [Indexed: 01/29/2023]
Abstract
Previous studies demonstrated that in vitro preparations of the isolated vestibular system of diverse animal species still exhibit stable resting electrical activity and mechanically evoked synaptic transmission between hair cells and primary afferent endings. However, there are no reports related to their neurodevelopment. Therefore, this research aimed to examine whether NMDA receptors mediate these electrical signals in an isolated preparation of the chicken vestibular system at three developmental stages, E15, E18, and E21. We found that the spontaneous and mechanically evoked discharges from primary afferents of the posterior semicircular canal were modulated by agonists NMDA and glycine, but not by the agonist d-serine applied near the synapses. Moreover, the individually applied by bath perfusion of three NMDA receptor antagonists (MK-801, ifenprodil, and 2-naphthoic acid) or high Mg2+ decreased the resting discharge rate, the NMDA response, and the discharge rate of mechanically evoked activity from these primary afferents. Furthermore, we found that the vestibular ganglion shows a stage-dependent increase in the expression of NMDA receptor subunits GluN1, GluN2 (A-C), and GluN3 (A-B), being greater at E21, except for GluN2D, which was inversely related to the developmental stage. However, in the crista ampullaris, the expression pattern remained constant throughout development. This could suggest the possible existence of presynaptic NMDA receptors. Our results highlight that although the NMDA receptors are functionally active at the early embryonic stages of the vestibular system, NMDA and glycine reach their mature functionality to increase NMDA responses close to hatching (E21).
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Affiliation(s)
- Ana Ramírez
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México.,Facultad de Medicina, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | - Eduardo Monjaraz
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | - Elías Manjarrez
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | - Alejandro Moyaho
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | - Jorge Cebada
- Facultad de Medicina, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | - Amira Flores
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México
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Yamada R, Kuba H. Dendritic synapse geometry optimizes binaural computation in a sound localization circuit. SCIENCE ADVANCES 2021; 7:eabh0024. [PMID: 34818046 PMCID: PMC8612683 DOI: 10.1126/sciadv.abh0024] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 10/05/2021] [Indexed: 06/13/2023]
Abstract
Clustering of synapses allows neurons to overcome attenuation of electrical signals at dendrites. However, we show in avian binaural coincidence detectors computing interaural time difference for sound localization that clustering of synapses rather promotes the dendritic attenuation but augments the intensity tolerance of the binaural computations. Using glutamate uncaging, we found in the neurons that synapses were clustered at distal dendritic branches. Modeling revealed that this strengthened sublinear integration within a dendritic tree but enabled the integration of signals from different trees when inputs grow stronger, preventing monoaural output and maintaining the dynamic range of binaural computation. The extent of this clustering differed according to dendritic length and frequency tuning of neurons, being most prominent for long dendrites and low-frequency tuning. This ensures binaural spatial hearing for wide intensity and frequency ranges, highlighting the importance of coupling of synapse geometry with dendritic morphology and input frequency in sensory signal processing.
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Role of NMDAR plasticity in a computational model of synaptic memory. Sci Rep 2021; 11:21182. [PMID: 34707139 PMCID: PMC8551337 DOI: 10.1038/s41598-021-00516-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Accepted: 10/12/2021] [Indexed: 11/08/2022] Open
Abstract
A largely unexplored question in neuronal plasticity is whether synapses are capable of encoding and learning the timing of synaptic inputs. We address this question in a computational model of synaptic input time difference learning (SITDL), where N-methyl-d-aspartate receptor (NMDAR) isoform expression in silent synapses is affected by time differences between glutamate and voltage signals. We suggest that differences between NMDARs' glutamate and voltage gate conductances induce modifications of the synapse's NMDAR isoform population, consequently changing the timing of synaptic response. NMDAR expression at individual synapses can encode the precise time difference between signals. Thus, SITDL enables the learning and reconstruction of signals across multiple synapses of a single neuron. In addition to plausibly predicting the roles of NMDARs in synaptic plasticity, SITDL can be usefully applied in artificial neural network models.
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McColgan T, Kuokkanen PT, Carr CE, Kempter R. Dynamics of synaptic extracellular field potentials in the nucleus laminaris of the barn owl. J Neurophysiol 2019; 121:1034-1047. [PMID: 30575430 DOI: 10.1152/jn.00648.2017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Synaptic currents are frequently assumed to make a major contribution to the extracellular field potential (EFP). However, in any neuronal population, the explicit separation of synaptic sources from other contributions such as postsynaptic spikes remains a challenge. Here we take advantage of the simple organization of the barn owl nucleus laminaris (NL) in the auditory brain stem to isolate synaptic currents through the iontophoretic application of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[ f]quinoxaline-7-sulfonamide (NBQX). Responses to auditory stimulation show that the temporal dynamics of the evoked synaptic contributions to the EFP are consistent with synaptic short-term depression (STD). The estimated time constants of an STD model fitted to the data are similar to the fast time constants reported from in vitro experiments in the chick. Overall, the putative synaptic EFPs in the barn owl NL are significant but small (<1% change of the variance by NBQX). This result supports the hypothesis that the EFP in NL is generated mainly by axonal spikes, in contrast to most other neuronal systems. NEW & NOTEWORTHY Synaptic currents are assumed to make a major contribution to the extracellular field potential in the brain, but it is hard to directly isolate these synaptic components. Here we take advantage of the simple organization of the barn owl nucleus laminaris in the auditory brain stem to isolate synaptic currents through the iontophoretic application of a synaptic blocker. We show that the responses are consistent with a simple model of short-term synaptic depression.
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Affiliation(s)
- Thomas McColgan
- Bernstein Center for Computational Neuroscience , Berlin , Germany.,Institute for Theoretical Biology, Department of Biology, Humboldt-Universität zu Berlin, Berlin , Germany
| | - Paula T Kuokkanen
- Bernstein Center for Computational Neuroscience , Berlin , Germany.,Institute for Theoretical Biology, Department of Biology, Humboldt-Universität zu Berlin, Berlin , Germany.,Department of Biology, University of Maryland , College Park, Maryland
| | - Catherine E Carr
- Department of Biology, University of Maryland , College Park, Maryland
| | - Richard Kempter
- Bernstein Center for Computational Neuroscience , Berlin , Germany.,Institute for Theoretical Biology, Department of Biology, Humboldt-Universität zu Berlin, Berlin , Germany.,Einstein Center for Neurosciences , Berlin , Germany
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5
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Adachi R, Yamada R, Kuba H. Tonotopic Differentiation of Coupling between Ca 2+ and Kv1.1 Expression in Brainstem Auditory Circuit. iScience 2019; 13:199-213. [PMID: 30856389 PMCID: PMC6411580 DOI: 10.1016/j.isci.2019.02.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 12/17/2018] [Accepted: 02/22/2019] [Indexed: 12/25/2022] Open
Abstract
Tonotopic differentiations of ion channels ensure sound processing across frequencies. Afferent input plays a critical role in differentiations. We demonstrate here in organotypic culture of chicken cochlear nucleus that expression of Kv1.1 was coupled with Ca2+ to a different degree depending on tonotopic regions, thereby differentiating the level of expression within the nucleus. In the culture, Kv1.1 was down-regulated and not differentiated tonotopically. Chronic depolarization increased Kv1.1 expression in a level-dependent manner. Moreover, the dependence was steeper at higher-frequency regions, which restored the differentiation. The depolarization increased Kv1.1 via activation of Cav1 channels, whereas basal Ca2+ level elevated similarly irrespective of tonotopic regions. Thus, the efficiency of Ca2+-dependent Kv1.1 expression would be fine-tuned in a tonotopic-region-specific manner, emphasizing the importance of neuronal tonotopic identity as well as pattern of afferent input in the tonotopic differentiation of the channel in the auditory circuit. Kv1.1 expression is down-regulated in slice culture of chicken cochlear nucleus Depolarization up-regulates Kv1.1 in a tonotopic-region-specific manner Level of Kv1.1 expression is dependent on basal calcium concentration Efficiency of calcium-dependent Kv1.1 expression is differentiated tonotopically
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Affiliation(s)
- Ryota Adachi
- Department of Cell Physiology, Graduate School of Medicine, Nagoya University, Nagoya 466-8550, Japan
| | - Rei Yamada
- Department of Cell Physiology, Graduate School of Medicine, Nagoya University, Nagoya 466-8550, Japan
| | - Hiroshi Kuba
- Department of Cell Physiology, Graduate School of Medicine, Nagoya University, Nagoya 466-8550, Japan.
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Ahn J, MacLeod KM. Target-specific regulation of presynaptic release properties at auditory nerve terminals in the avian cochlear nucleus. J Neurophysiol 2016; 115:1679-90. [PMID: 26719087 DOI: 10.1152/jn.00752.2015] [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] [Received: 07/30/2015] [Accepted: 12/23/2015] [Indexed: 02/04/2023] Open
Abstract
Short-term synaptic plasticity (STP) acts as a time- and firing rate-dependent filter that mediates the transmission of information across synapses. In the auditory brain stem, the divergent pathways that encode acoustic timing and intensity information express differential STP. To investigate what factors determine the plasticity expressed at different terminals, we tested whether presynaptic release probability differed in the auditory nerve projections to the two divisions of the avian cochlear nucleus, nucleus angularis (NA) and nucleus magnocellularis (NM). Estimates of release probability were made with an open-channel blocker ofN-methyl-d-aspartate (NMDA) receptors. Activity-dependent blockade of NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) with application of 20 μM (+)-MK801 maleate was more rapid in NM than in NA, indicating that release probability was significantly higher at terminals in NM. Paired-pulse ratio (PPR) was tightly correlated with the blockade rate at terminals in NA, suggesting that PPR was a reasonable proxy for relative release probability at these synapses. To test whether release probability was similar across convergent inputs onto NA neurons, PPRs of different nerve inputs onto the same postsynaptic NA target neuron were measured. The PPRs, as well as the plasticity during short trains, were tightly correlated across multiple inputs, further suggesting that release probability is coordinated at auditory nerve terminals in a target-specific manner. This highly specific regulation of STP in the auditory brain stem provides evidence that the synaptic dynamics are tuned to differentially transmit the auditory information in nerve activity into parallel ascending pathways.
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Affiliation(s)
- J Ahn
- Department of Biology, University of Maryland, College Park, Maryland
| | - K M MacLeod
- Department of Biology, University of Maryland, College Park, Maryland; Neuroscience and Cognitive Science Program, University of Maryland, College Park, Maryland; and Center for the Comparative and Evolutionary Biology of Hearing, University of Maryland, College Park, Maryland
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Yang Y, Xu-Friedman MA. Different pools of glutamate receptors mediate sensitivity to ambient glutamate in the cochlear nucleus. J Neurophysiol 2015; 113:3634-45. [PMID: 25855696 DOI: 10.1152/jn.00693.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 04/08/2015] [Indexed: 01/14/2023] Open
Abstract
Ambient glutamate plays an important role in pathological conditions, such as stroke, but its role during normal activity is not clear. In addition, it is not clear how ambient glutamate acts on glutamate receptors with varying affinities or subcellular localizations. To address this, we studied "endbulb of Held" synapses, which are formed by auditory nerve fibers onto bushy cells (BCs) in the anteroventral cochlear nucleus. When ambient glutamate was increased by applying the glutamate reuptake inhibitor TFB-TBOA, BCs depolarized as a result of activation of N-methyl-D-aspartate receptors (NMDARs) and group I metabotropic glutamate receptors (mGluRs). Application of antagonists against NMDARs (in 0 Mg(2+)) or mGluRs caused hyperpolarization, indicating that these receptors were bound by a tonic source of glutamate. AMPA receptors did not show these effects, consistent with their lower glutamate affinity. We also evaluated the subcellular localization of the receptors activated by ambient glutamate. The mGluRs were not activated by synaptic stimulation and thus appear to be exclusively extrasynaptic. By contrast, NMDARs in both synaptic and extrasynaptic compartments were activated by ambient glutamate, as shown using the use-dependent antagonist MK-801. Levels of ambient glutamate appeared to be regulated in a spike-independent manner, and glia likely play a major role. These low levels of ambient glutamate likely have functional consequences, as even low concentrations of TBOA caused significant increases in BC spiking following synaptic stimulation. These results indicate that normal resting potential appears to be poised in the region of maximal sensitivity to small changes in ambient glutamate.
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Affiliation(s)
- Yang Yang
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York
| | - Matthew A Xu-Friedman
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York
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Karim MR, Atoji Y. Distribution of Vesicular Glutamate Transporter 2 and Ionotropic Glutamate Receptors in the Auditory Ganglion and Cochlear Nuclei of Pigeons (Columba livia). Anat Histol Embryol 2015; 45:73-80. [PMID: 25639143 DOI: 10.1111/ahe.12173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Accepted: 01/11/2015] [Indexed: 10/24/2022]
Abstract
Glutamate is a principal excitatory neurotransmitter in the auditory system. Our previous studies revealed localization of glutamate receptor mRNAs in the pigeon cochlear nuclei, suggesting the existence of glutamatergic input from the auditory nerve to the brainstem. This study demonstrated localization of mRNAs for vesicular glutamate transporter 2 (vGluT2) and ionotropic glutamate receptors (AMPA, kainate and NMDA) in the auditory ganglion (AG) and cochlear nuclei (magnocellular, angular and laminar nuclei). VGluT2 mRNA was intensely expressed in AG and intensely or moderately in the cochlear nuclei. The AG and cochlear nuclei showed intense-to-moderate mRNA signals for GluA2, GluA3, GluA4, GluK4 and GluN1. These results suggest that the pigeon AG neurons receives glutamatergic input from hair cells and in turn projects to the magnocellular and angular nuclei. Glutamate may play a pivotal role in the excitatory synapse transmission in the peripheral auditory pathway of birds.
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Affiliation(s)
- M R Karim
- Department of Anatomy and Histology, Bangladesh Agricultural University, Mymensingh, 2202, Bangladesh.,Laboratory of Veterinary Anatomy, Faculty of Applied Biological Sciences, Gifu University, Gifu, 501-1193, Japan
| | - Y Atoji
- Laboratory of Veterinary Anatomy, Faculty of Applied Biological Sciences, Gifu University, Gifu, 501-1193, Japan
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Sanchez J, Ghelani S, Otto-Meyer S. From development to disease: Diverse functions of NMDA-type glutamate receptors in the lower auditory pathway. Neuroscience 2015; 285:248-59. [DOI: 10.1016/j.neuroscience.2014.11.027] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Revised: 11/07/2014] [Accepted: 11/16/2014] [Indexed: 01/19/2023]
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10
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Zhang J, Liu J, Fox HS, Xiong H. N-methyl-D-aspartate receptor-mediated axonal injury in adult rat corpus callosum. J Neurosci Res 2012; 91:240-8. [PMID: 23161705 DOI: 10.1002/jnr.23150] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2012] [Revised: 08/31/2012] [Accepted: 09/07/2012] [Indexed: 02/03/2023]
Abstract
Damage to white matter such as corpus callosum (CC) is a pathological characteristic in many brain disorders. Glutamate (Glut) excitotoxicity through AMPA receptors on oligodendrocyte (OL) was previously considered as a mechanism for white matter damage. Recent studies have shown that N-methyl-D-aspartate receptors (NMDARs) are expressed on myelin sheath of neonatal rat OL processes and that activation of these receptors mediated demyelization. Whether NMDARs are expressed in the adult CC and are involved in excitotoxic axonal injury remains to be determined. In this study, we demonstrate the presence of NMDARs in the adult rat CC and their distributions in myelinated nerve fibers and OL somata by means of immunocytochemical staining and Western blot. Incubation of the CC slices with Glut or NMDA induced axonal injury as revealed by analyzing amplitude of CC fiber compound action potentials (CAPs) and input-output response. Both Glut and NMDA decreased the CAP amplitude and input-output responses, suggesting an involvement of NMDARs in Glut- and NMDA-induced axonal injury. The involvement of NMDAR in Glut-induced axonal injury was further assayed by detection of β-amyloid precursor protein (β-APP) in the CC axonal fibers. Treatment of the CC slices with Glut resulted in β-APP accumulation in the CC fibers as detected by Western blot, reflecting an impairment of axonal transport function. This injurious effect of Glut on CC axonal transport was significantly blocked by MK801. Taken together, these results show that NMDARs are expressed in the adult CC and are involved in excitotoxic activity in adult CC slices in vitro.
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Affiliation(s)
- Jingdong Zhang
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198-5880, USA
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Sanchez JT, Seidl AH, Rubel EW, Barria A. Control of neuronal excitability by NMDA-type glutamate receptors in early developing binaural auditory neurons. J Physiol 2012; 590:4801-18. [PMID: 22826130 DOI: 10.1113/jphysiol.2012.228734] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Precise control of neuronal excitability in the auditory brainstem is fundamental for processing timing cues used for sound localization and signal discrimination in complex acoustic environments. In mature nucleus laminaris (NL), the first nucleus responsible for binaural processing in chickens, neuronal excitability is governed primarily by voltage-activated potassium conductances (K(VA)). High levels of K(VA) expression in NL neurons result in one or two initial action potentials (APs) in response to high-frequency synaptic activity or sustained depolarization. Here we show that during a period of synaptogenesis and circuit refinement, before hearing onset, K(VA) conductances are relatively small, in particular low-voltage-activated K(+) conductances (K(LVA)). In spite of this, neuronal output is filtered and repetitive synaptic activity generates only one or two initial APs during a train of stimuli. During this early developmental time period, synaptic NMDA-type glutamate receptors (NMDA-Rs) contain primarily the GluN2B subunit. We show that the slow decay kinetics of GluN2B-containing NMDA-Rs allows synaptic responses to summate, filtering the output of NL neurons before intrinsic properties are fully developed. Weaker Mg(2+) blockade of NMDA-Rs and ambient glutamate early in development generate a tonic NMDA-R-mediated current that sets the membrane potential at more depolarized values. Small KLVA conductances, localized in dendrites, prevent excessive depolarization caused by tonic activation of NMDA-Rs. Thus, before intrinsic properties are fully developed, NMDA-Rs control the output of NL neurons during evoked synaptic transmission.
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Affiliation(s)
- Jason Tait Sanchez
- VirginiaMerrill Bloedel Hearing Research Center, School of Medicine, University of Washington, Box 357290, Seattle, WA 98195, USA
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12
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Sanchez JT, Wang Y, Rubel EW, Barria A. Development of glutamatergic synaptic transmission in binaural auditory neurons. J Neurophysiol 2010; 104:1774-89. [PMID: 20668278 DOI: 10.1152/jn.00468.2010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/06/2022] Open
Abstract
Glutamatergic synaptic transmission is essential for binaural auditory processing in birds and mammals. Using whole cell voltage clamp recordings, we characterized the development of synaptic ionotropic glutamate receptor (iGluR) function from auditory neurons in the chick nucleus laminaris (NL), the first nucleus responsible for binaural processing. We show that synaptic transmission is mediated by AMPA- and N-methyl-d-aspartate (NMDA)-type glutamate receptors (AMPA-R and NMDA-R, respectively) when hearing is first emerging and dendritic morphology is being established across different sound frequency regions. Puff application of glutamate agonists at embryonic day 9 (E9) revealed that both iGluRs are functionally present prior to synapse formation (E10). Between E11 and E19, the amplitude of isolated AMPA-R currents from high-frequency (HF) neurons increased 14-fold. A significant increase in the frequency of spontaneous events is also observed. Additionally, AMPA-R currents become faster and more rectifying, suggesting developmental changes in subunit composition. These developmental changes were similar in all tonotopic regions examined. However, mid- and low-frequency neurons exhibit fewer spontaneous events and evoked AMPA-R currents are smaller, slower, and less rectifying than currents from age-matched HF neurons. The amplitude of isolated NMDA-R currents from HF neurons also increased, reaching a peak at E17 and declining sharply by E19, a trend consistent across tonotopic regions. With age, NMDA-R kinetics become significantly faster, indicating a developmental switch in receptor subunit composition. Dramatic increases in the amplitude and speed of glutamatergic synaptic transmission occurs in NL during embryonic development. These changes are first seen in HF neurons suggesting regulation by peripheral inputs and may be necessary to enhance coincidence detection of binaural auditory information.
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Affiliation(s)
- Jason Tait Sanchez
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Box 357290, Seattle, WA 98195, USA
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Blackmer T, Kuo SP, Bender KJ, Apostolides PF, Trussell LO. Dendritic calcium channels and their activation by synaptic signals in auditory coincidence detector neurons. J Neurophysiol 2009; 102:1218-26. [PMID: 19553482 DOI: 10.1152/jn.90513.2008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The avian nucleus laminaris (NL) encodes the azimuthal location of low-frequency sound sources by detecting the coincidence of binaural signals. Accurate coincidence detection requires precise developmental regulation of the lengths of the fine, bitufted dendrites that characterize neurons in NL. Such regulation has been suggested to be driven by local, synaptically mediated, dendritic signals such as Ca(2+). We examined Ca(2+) signaling through patch clamp and ion imaging experiments in slices containing nucleus laminaris from embryonic chicks. Voltage-clamp recordings of neurons located in the NL showed the presence of large Ca(2+) currents of two types, a low voltage-activated, fast inactivating Ni(2+) sensitive channel resembling mammalian T-type channels, and a high voltage-activated, slowly inactivating Cd(2+) sensitive channel. Two-photon Ca(2+) imaging showed that both channel types were concentrated on dendrites, even at their distal tips. Single action potentials triggered synaptically or by somatic current injection immediately elevated Ca(2+) throughout the entire cell. Ca(2+) signals triggered by subthreshold synaptic activity were highly localized. Thus when electrical activity is suprathreshold, Ca(2+) channels ensure that Ca(2+) rises in all dendrites, even those that are synaptically inactive.
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Affiliation(s)
- Trillium Blackmer
- Vollum Institute and Oregon Hearing Research Center, Oregon Health and Science University, Portland, Oregon 97239, USA
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Diaz C, Martinez-Galan JR, Juiz JM. Development of glutamate receptors in auditory neurons from long-term organotypic cultures of the embryonic chick hindbrain. Eur J Neurosci 2009; 29:213-30. [PMID: 19200228 DOI: 10.1111/j.1460-9568.2008.06578.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We used long-range organotypic cultures of auditory nuclei in the chick hindbrain to test the development of glutamate receptor activity in auditory neurons growing in a tissue environment that includes early deprivation of peripheral glutamatergic input, subsequent to removal of the otocyst. Cultures started at embryonic day (E)5, and lasted from 6 h to 15 days. Neuronal migration, clustering and axonal extension from the nucleus magnocellularis (NM) to the nucleus laminaris (NL) partially resembled events in vivo. However, the distinctive laminar organization of the NL was not observed. Glutamate receptor (GluR) activity was tested with optical recordings of intracellular Ca2+ in the NM. alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)/kainate receptors had Ca2+ responses with a time course similar to that in control slices. Peak amplitude, however, was significantly lower. N-methyl-D-aspartate (NMDA)-mediated Ca2+ responses were higher in 2-day cultures (E5 + 2d) than in E7 explant controls, returning later to control values. Metabotropic GluRs did not elicit Ca2+ responses at standard agonist doses. Blocking NMDA or AMPA/kainate receptors with specific antagonists for 10 days in culture did not limit neuronal survival. Blocking metabotropic GluRs resulted in complete neuronal loss. Thus, ionotropic GluRs are not required for NM neuronal survival. However, their activity during development is affected when neurons grow in an in vitro environment that includes prevention of arrival of peripheral glutamatergic input.
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Affiliation(s)
- Carmen Diaz
- Departamento de Ciencias Médicas, Facultad de Medicina y Centro Regional de Investigaciones Biomédicas, Universidad de Castilla-La Mancha, Avenida de Almansa 14, 02006 Albacete, Spain
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