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Michanski S, Henneck T, Mukhopadhyay M, Steyer AM, Gonzalez PA, Grewe K, Ilgen P, Gültas M, Fornasiero EF, Jakobs S, Möbius W, Vogl C, Pangršič T, Rizzoli SO, Wichmann C. Age-dependent structural reorganization of utricular ribbon synapses. Front Cell Dev Biol 2023; 11:1178992. [PMID: 37635868 PMCID: PMC10447907 DOI: 10.3389/fcell.2023.1178992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 07/17/2023] [Indexed: 08/29/2023] Open
Abstract
In mammals, spatial orientation is synaptically-encoded by sensory hair cells of the vestibular labyrinth. Vestibular hair cells (VHCs) harbor synaptic ribbons at their presynaptic active zones (AZs), which play a critical role in molecular scaffolding and facilitate synaptic release and vesicular replenishment. With advancing age, the prevalence of vestibular deficits increases; yet, the underlying mechanisms are not well understood and the possible accompanying morphological changes in the VHC synapses have not yet been systematically examined. We investigated the effects of maturation and aging on the ultrastructure of the ribbon-type AZs in murine utricles using various electron microscopic techniques and combined them with confocal and super-resolution light microscopy as well as metabolic imaging up to 1 year of age. In older animals, we detected predominantly in type I VHCs the formation of floating ribbon clusters, mostly consisting of newly synthesized ribbon material. Our findings suggest that VHC ribbon-type AZs undergo dramatic structural alterations upon aging.
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Affiliation(s)
- Susann Michanski
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
| | - Timo Henneck
- Biology Bachelor Program, University of Göttingen, Göttingen, Germany
| | - Mohona Mukhopadhyay
- Experimental Otology Group, InnerEarLab, Department of Otolaryngology, Institute for Auditory Neuroscience, University Medical Center Göttingen, Göttingen, Germany
| | - Anna M. Steyer
- Electron Microscopy-City Campus, Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Center Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), University of Göttingen, Göttingen, Germany
| | - Paola Agüi Gonzalez
- Department for Neuro-and Sensory Physiology, University Medical Center Göttingen, Center for Biostructural Imaging of Neurodegeneration (BIN), Göttingen, Germany
| | - Katharina Grewe
- Department for Neuro-and Sensory Physiology, University Medical Center Göttingen, Center for Biostructural Imaging of Neurodegeneration (BIN), Göttingen, Germany
| | - Peter Ilgen
- Clinic of Neurology, University Medical Center Göttingen, Göttingen, Germany
- Department of NanoBiophotonics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Fraunhofer Institute for Translational Medicine and Pharmacology ITMP, Translational Neuroinflammation and Automated Microscopy TNM, Göttingen, Germany
| | - Mehmet Gültas
- Faculty of Agriculture, South Westphalia University of Applied Sciences, Soest, Germany
| | - Eugenio F. Fornasiero
- Department for Neuro-and Sensory Physiology, University Medical Center Göttingen, Center for Biostructural Imaging of Neurodegeneration (BIN), Göttingen, Germany
| | - Stefan Jakobs
- Clinic of Neurology, University Medical Center Göttingen, Göttingen, Germany
- Department of NanoBiophotonics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Fraunhofer Institute for Translational Medicine and Pharmacology ITMP, Translational Neuroinflammation and Automated Microscopy TNM, Göttingen, Germany
| | - Wiebke Möbius
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
- Electron Microscopy-City Campus, Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Christian Vogl
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Presynaptogenesis and Intracellular Transport in Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Auditory Neuroscience Group, Institute of Physiology, Medical University Innsbruck, Innsbruck, Austria
| | - Tina Pangršič
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
- Experimental Otology Group, InnerEarLab, Department of Otolaryngology, Institute for Auditory Neuroscience, University Medical Center Göttingen, Göttingen, Germany
| | - Silvio O. Rizzoli
- Department for Neuro-and Sensory Physiology, University Medical Center Göttingen, Center for Biostructural Imaging of Neurodegeneration (BIN), Göttingen, Germany
| | - Carolin Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
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Bronson D, Kalluri R. Muscarinic Acetylcholine Receptors Modulate HCN Channel Properties in Vestibular Ganglion Neurons. J Neurosci 2023; 43:902-917. [PMID: 36604171 PMCID: PMC9908319 DOI: 10.1523/jneurosci.2552-21.2022] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 12/14/2022] [Accepted: 12/22/2022] [Indexed: 01/07/2023] Open
Abstract
Efferent modulation of vestibular afferent excitability is linked to muscarinic signaling cascades that close low-voltage-gated potassium channels (i.e., KCNQ). Here, we show that muscarinic signaling cascades also depolarize the activation range of hyperpolarization-activated cyclic-nucleotide gated (HCN) channels. We compared the voltage activation range and kinetics of HCN channels and induced firing patterns before and after administering the muscarinic acetylcholine receptor (mAChR) agonist oxotremorine-M (Oxo-M) in dissociated vestibular ganglion neurons (VGNs) from rats of either sex using perforated whole-cell patch-clamp methods. Oxo-M depolarized HCN channels' half-activation voltage (V 1/2) and sped up the rate of activation near resting potential twofold. HCN channels in large-diameter and/or transient firing VGN (putative cell bodies of irregular firing neuron from central epithelial zones) had relatively depolarized V 1/2 in control solution and were less sensitive to mAChR activation than those found in small-diameter VGN with sustained firing patterns (putatively belonging to regular firing afferents). The impact of mAChR on HCN channels is not a direct consequence of closing KCNQ channels since pretreating the cells with Linopirdine, a KCNQ channel blocker, did not prevent HCN channel depolarization by Oxo-M. Efferent signaling promoted ion channel configurations that were favorable to highly regular spiking in some VGN, but not others. This is consistent with previous observations that low-voltage gated potassium currents in VGN are conducted by mAChR agonist-sensitive and -insensitive channels. Connecting efferent signaling to HCN channels is significant because of the channel's impact on spike-timing regularity and nonchemical transmission between Type I hair cells and vestibular afferents.SIGNIFICANCE STATEMENT Vestibular afferents express a diverse complement of ion channels. In vitro studies identified low-voltage activated potassium channels and hyperpolarization-activated cyclic-nucleotide gated (HCN) channels as crucial for shaping the timing and sensitivity of afferent responses. Moreover, a network of acetylcholine-releasing efferent neurons controls afferent excitability by closing a subgroup of low-voltage activated potassium channels on the afferent neuron. This work shows that these efferent signaling cascades also enhance the activation of HCN channels by depolarizing their voltage activation range. The size of this effect varies depending on the endogenous properties of the HCN channel and on cell type (as determined by discharge patterns and cell size). Simultaneously controlling two ion-channel groups gives the vestibular efferent system exquisite control over afferent neuron activity.
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Affiliation(s)
- Daniel Bronson
- Hearing and Communications Neuroscience Training Program, University of Southern California, Los Angeles, California 90057
- Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
| | - Radha Kalluri
- Hearing and Communications Neuroscience Training Program, University of Southern California, Los Angeles, California 90057
- Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
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Eatock RA. Specializations for Fast Signaling in the Amniote Vestibular Inner Ear. Integr Comp Biol 2019; 58:341-350. [PMID: 29920589 DOI: 10.1093/icb/icy069] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
During rapid locomotion, the vestibular inner ear provides head-motion signals that stabilize posture, gaze, and heading. Afferent nerve fibers from central and peripheral zones of vestibular sensory epithelia use temporal and rate encoding, respectively, to emphasize different aspects of head motion: central afferents adapt faster to sustained head position and favor higher stimulus frequencies, reflecting specializations at each stage from motion of the accessory structure to spike propagation to the brain. One specialization in amniotes is an unusual nonquantal synaptic mechanism by which type I hair cells transmit to large calyceal terminals of afferent neurons. The reduced synaptic delay of this mechanism may have evolved to serve reliable and fast input to reflex pathways that ensure stable locomotion on land.
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Affiliation(s)
- Ruth Anne Eatock
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA
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Abstract
Afferent nerve fibers in the central zones of vestibular epithelia form calyceal endings around type I hair cells and have phasic response properties that emphasize fast head motions. We investigated how stages from hair-cell transduction to calyceal spiking contribute tuning and timing to central (striolar)-zone afferents of the rat saccular epithelium. In an excised preparation, we deflected individual hair bundles with rigid probes driven with steps and sinusoids (0.5-500 Hz) and recorded whole-cell responses from hair cells and calyces at room temperature and body temperature. In immature hair cells and calyces (postnatal days (P)1-P4), tuning sharpened at each stage. Transducer adaptation and membrane-charging time produced bandpass filtering of the receptor potential with best frequencies of 10-30 Hz and phase leads below 10 Hz. For small stimuli, electrical resonances sharply tuned the hair-cell membrane in the frequency range of 5-40 Hz. The synaptic delay of quantal transmission added a phase lag at frequencies above 10 Hz. The influence of spike thresholds at the calyceal spike initiation stage sharpened tuning and advanced response phase. Two additional mechanisms strongly advanced response phase above 10 Hz when present: (1) maturing (P7-P9) type I hair cells acquired low-voltage-activated channels that shortened the rise time of the receptor potential and (2) some calyces had nonquantal transmission with little synaptic delay. By reducing response time, the identified inner-ear mechanisms (transducer adaptation, low-voltage-activated channels, nonquantal transmission, and spike triggering) may compensate for transmission delays in vestibular reflex pathways and help stabilize posture and gaze during rapid head motions.
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Eatock RA, Songer JE. Vestibular hair cells and afferents: two channels for head motion signals. Annu Rev Neurosci 2011; 34:501-34. [PMID: 21469959 DOI: 10.1146/annurev-neuro-061010-113710] [Citation(s) in RCA: 169] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Vestibular epithelia of the inner ear detect head motions over a wide range of amplitudes and frequencies. In mammals, afferent nerve fibers from central and peripheral zones of vestibular epithelia form distinct populations with different response dynamics and spike timing. Central-zone afferents are large, fast conduits for phasic signals encoded in irregular spike trains. The finer afferents from peripheral zones conduct more slowly and encode more tonic, linear signals in highly regular spike trains. The hair cells are also of two types, I and II, but the two types do not correspond directly to the two afferent populations. Zonal differences in afferent response dynamics may arise at multiple stages, including mechanoelectrical transduction, voltage-gated channels in hair cells and afferents, afferent transmission at calyceal and bouton synapses, and spike generation in regular and irregular afferents. In contrast, zonal differences in spike timing may depend more simply on the selective expression of low-voltage-activated ion channels by irregular afferents.
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Affiliation(s)
- Ruth Anne Eatock
- Department of Otology and Laryngology, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02114, USA.
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Holt JC, Chatlani S, Lysakowski A, Goldberg JM. Quantal and nonquantal transmission in calyx-bearing fibers of the turtle posterior crista. J Neurophysiol 2007; 98:1083-101. [PMID: 17596419 PMCID: PMC3397384 DOI: 10.1152/jn.00332.2007] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Intracellular recordings were made from nerve fibers in the posterior ampullary nerve near the neuroepithelium. Calyx-bearing afferents were identified by their distinctive efferent-mediated responses. Such fibers receive inputs from both type I and type II hair cells. Type II inputs are made by synapses on the outer face of the calyx ending and on the boutons of dimorphic fibers. Quantal activity, consisting of brief mEPSPs, is reduced by lowering the external concentration of Ca2+ and blocked by the AMPA-receptor antagonist CNQX. Poisson statistics govern the timing of mEPSPs, which occur at high rates (250-2,500/s) in the absence of mechanical stimulation. Excitation produced by canal-duct indentation can increase mEPSP rates to nearly 5,000/s. As the rate increases, mEPSPs can change from a monophasic depolarization to a biphasic depolarizing-hyperpolarizing sequence, both of whose components are blocked by CNQX. Blockers of voltage-gated currents affect mEPSP size, which is decreased by TTX and is increased by linopirdine. mEPSP size decreases severalfold after impalement. The size decrease, although it may be triggered by the depolarization occurring during impalement, persists even at hyperpolarized membrane potentials. Nonquantal transmission is indicated by shot-noise calculations and by the presence of voltage modulations after quantal activity is abolished pharmacologically. An ultrastructural study shows that inner-face inputs from type I hair cells outnumber outer-face inputs from type II hair cells by an almost 6:1 ratio.
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Affiliation(s)
- Joseph C Holt
- Department of Otolaryngology, University of Texas Medical Branch, Galveston, Texas, USA
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Bao H, Wong WH, Goldberg JM, Eatock RA. Voltage-gated calcium channel currents in type I and type II hair cells isolated from the rat crista. J Neurophysiol 2003; 90:155-64. [PMID: 12843307 DOI: 10.1152/jn.00244.2003] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
When studied in vitro, type I hair cells in amniote vestibular organs have a large, negatively activating K+ conductance. In type II hair cells, as in nonvestibular hair cells, outwardly rectifying K+ conductances are smaller and more positively activating. As a result, type I cells have more negative resting potentials and smaller input resistances than do type II cells; large inward currents fail to depolarize type I cells above -60 mV. In nonvestibular hair cells, afferent transmission is mediated by voltage-gated Ca2+ channels that activate positive to -60 mV. We investigated whether Ca2+ channels in type I cells activate more negatively so that quantal transmission can occur near the reported resting potentials. We used the perforated patch method to record Ca2+ channel currents from type I and type II hair cells isolated from the rat anterior crista (postnatal days 4-20). The activation range of the Ca2+ currents of type I hair cells differed only slightly from that of type II cells or nonvestibular hair cells. In 5 mM external Ca2+, currents in type I and type II cells were half-maximal at -41.1 +/- 0.5 (SE) mV (n = 10) and -37.2 +/- 0.2 mV (n = 10), respectively. In physiological external Ca2+ (1.3 mM), currents in type I cells were half-maximal at -46 +/- 1 mV (n = 8) and just 1% of maximal at -72 mV. These results lend credence to suggestions that type I cells have more positive resting potentials in vivo, possibly through K+ accumulation in the synaptic cleft or inhibition of the large K+ conductance. Ca2+ channel kinetics were also unremarkable; in both type I and type II cells, the currents activated and deactivated rapidly and inactivated only slowly and modestly even at large depolarizations. The Ca2+ current included an L-type component with relatively low sensitivity to dihydropyridine antagonists, consistent with the alpha subunit being CaV1.3 (alpha1D). Rat vestibular epithelia and ganglia were probed for L-type alpha-subunit expression with the reverse transcription-polymerase chain reaction. The epithelia expressed CaV1.3 and the ganglia expressed CaV1.2 (alpha1C).
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Affiliation(s)
- Hong Bao
- The Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, Texas 77030, USA
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Abstract
The chinchilla crista ampullaris was studied in 10 samples, each containing 32 consecutive ultrathin sections of the entire neuroepithelium. Dissector methods were used to estimate the incidence of various synaptic features, and results were confirmed in completely reconstructed hair cells. There are large regional variations in cellular and synaptic architecture. Type I and type II hair cells are shorter, broader, and less densely packed in the central zone than in the intermediate and peripheral zones. Complex calyx endings are most common centrally. On average, there are 15-20 ribbon synapses and 25-30 calyceal invaginations in each type I hair cell. Synapses and invaginations are most numerous centrally. Central type II hair cells receive considerably fewer afferent boutons than do peripheral type II hair cells, but have similar numbers of ribbon synapses. The numbers are similar because central type II hair cells make more synapses with the outer faces of calyx endings and with individual afferent boutons. Most afferent boutons get one ribbon synapse. Boutons without ribbon synapses were only found peripherally, and boutons getting multiple synapses were most frequent centrally. Throughout the neuroepithelium, there is an average of three to four efferent boutons on each type II hair cell and calyx ending. Reciprocal synapses are rare. Most synaptic ribbons in type I hair cells are spherules; those in type II hair cells can be spherical or elongated and are particularly heterogeneous centrally. Consistent with the proposal that the crista is concentrically organized, the intermediate and peripheral zones are each similar in their cellular and synaptic architecture near the base and near the planum. An especially differentiated subzone may exist in the middle of the central zone.
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Affiliation(s)
- A Lysakowski
- Department of Anatomy and Cell Biology, University of Illinois, Chicago 60612, USA.
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