1
|
Lv C, Stewart WJ, Akanyeti O, Frederick C, Zhu J, Santos-Sacchi J, Sheets L, Liao JC, Zenisek D. Synaptic Ribbons Require Ribeye for Electron Density, Proper Synaptic Localization, and Recruitment of Calcium Channels. Cell Rep 2016; 15:2784-95. [PMID: 27292637 DOI: 10.1016/j.celrep.2016.05.045] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 04/06/2016] [Accepted: 05/10/2016] [Indexed: 10/21/2022] Open
Abstract
Synaptic ribbons are structures made largely of the protein Ribeye that hold synaptic vesicles near release sites in non-spiking cells in some sensory systems. Here, we introduce frameshift mutations in the two zebrafish genes encoding for Ribeye and thus remove Ribeye protein from neuromast hair cells. Despite Ribeye depletion, vesicles collect around ribbon-like structures that lack electron density, which we term "ghost ribbons." Ghost ribbons are smaller in size but possess a similar number of smaller vesicles and are poorly localized to synapses and calcium channels. These hair cells exhibit enhanced exocytosis, as measured by capacitance, and recordings from afferent neurons post-synaptic to hair cells show no significant difference in spike rates. Our results suggest that Ribeye makes up most of the synaptic ribbon density in neuromast hair cells and is necessary for proper localization of calcium channels and synaptic ribbons.
Collapse
Affiliation(s)
- Caixia Lv
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8066, USA
| | - William J Stewart
- The Whitney Laboratory for Marine Bioscience and Department of Biology, University of Florida, St. Augustine, FL 32080, USA
| | - Otar Akanyeti
- The Whitney Laboratory for Marine Bioscience and Department of Biology, University of Florida, St. Augustine, FL 32080, USA
| | - Courtney Frederick
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8066, USA
| | - Jie Zhu
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8066, USA
| | - Joseph Santos-Sacchi
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8066, USA; Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT 06520-8066, USA; Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06520-8066, USA
| | - Lavinia Sheets
- Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA; Department of Otolaryngology, Harvard Medical School, Boston, MA 02114, USA
| | - James C Liao
- The Whitney Laboratory for Marine Bioscience and Department of Biology, University of Florida, St. Augustine, FL 32080, USA
| | - David Zenisek
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8066, USA; Department of Opthalmology and Visual Sciences, Yale University School of Medicine, New Haven, CT 06520-8066, USA.
| |
Collapse
|
2
|
Kantardzhieva A, Liberman MC, Sewell WF. Quantitative analysis of ribbons, vesicles, and cisterns at the cat inner hair cell synapse: correlations with spontaneous rate. J Comp Neurol 2014; 521:3260-71. [PMID: 23787810 DOI: 10.1002/cne.23345] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Revised: 02/26/2013] [Accepted: 04/05/2013] [Indexed: 11/09/2022]
Abstract
Cochlear hair cells form ribbon synapses with terminals of the cochlear nerve. To test the hypothesis that one function of the ribbon is to create synaptic vesicles from the cisternal structures that are abundant at the base of hair cells, we analyzed the distribution of vesicles and cisterns around ribbons from serial sections of inner hair cells in the cat, and compared data from low and high spontaneous rate (SR) synapses. Consistent with the hypothesis, we identified a "sphere of influence" of 350 nm around the ribbon, with fewer cisterns and many more synaptic vesicles. Although high- and low-SR ribbons tended to be longer and thinner than high-SR ribbons, the total volume of the two ribbon types was similar. There were almost as many vesicles docked at the active zone as attached to the ribbon. The major SR-related difference was that low-SR ribbons had more synaptic vesicles intimately associated with them. Our data suggest a trend in which low-SR synapses had more vesicles attached to the ribbon (51.3 vs. 42.8), more docked between the ribbon and the membrane (12 vs. 8.2), more docked at the active zone (56.9 vs. 44.2), and more vesicles within the "sphere of influence" (218 vs. 166). These data suggest that the structural differences between high- and low-SR synapses may be more a consequence, than a determinant, of the physiological differences.
Collapse
Affiliation(s)
- Albena Kantardzhieva
- Eaton-Peabody Laboratory, Department of Otology and Laryngology, Massachusetts Eye and Ear Infirmary and Harvard Medical School, Boston, Massachusetts 02114, USA
| | | | | |
Collapse
|
3
|
Schnee ME, Santos-Sacchi J, Castellano-Muñoz M, Kong JH, Ricci AJ. Calcium-dependent synaptic vesicle trafficking underlies indefatigable release at the hair cell afferent fiber synapse. Neuron 2011; 70:326-38. [PMID: 21521617 DOI: 10.1016/j.neuron.2011.01.031] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2011] [Indexed: 10/18/2022]
Abstract
Sensory hair cell ribbon synapses respond to graded stimulation in a linear, indefatigable manner, requiring that vesicle trafficking to synapses be rapid and nonrate-limiting. Real-time monitoring of vesicle fusion identified two release components. The first was saturable with both release rate and magnitude varying linearly with Ca(2+), however the magnitude was too small to account for sustained afferent firing rates. A second superlinear release component required recruitment, in a Ca(2+)-dependent manner, of vesicles not in the immediate vicinity of the synapse. The superlinear component had a constant rate with its onset varying with Ca(2+) load. High-speed Ca(2+) imaging revealed a nonlinear increase in internal Ca(2+) correlating with the superlinear capacitance change, implicating release of stored Ca(2+) in driving vesicle recruitment. These data, supported by a mass action model, suggest sustained release at hair cell afferent fiber synapse is dictated by Ca(2+)-dependent vesicle recruitment from a reserve pool.
Collapse
Affiliation(s)
- Michael E Schnee
- Department of Otolaryngology, Stanford University School of Medicine, Stanford, CA 94304, USA
| | | | | | | | | |
Collapse
|
4
|
Abstract
PURPOSE To investigate changes in cytokine levels in tears of type 2 diabetics with or without retinopathy. METHODS Tears were collected from 15 type 2 diabetics without retinopathy (DNR), 15 patients with retinopathy (DR), and 15 age and gender matched non-diabetic controls. Tear concentrations of 27 cytokines were measured by multiplex bead immunoassay. Cytokine differences between groups, ratios of type-1 T helper (Th1)/type-2 T helper (Th2) cytokines and anti-angiogenic/pro-angiogenic cytokines were analyzed statistically. RESULTS The most abundant cytokine detected in tears was interferon-induced protein-10 (IP-10). In comparison with controls, IP-10 and monocyte chemoattracant protein-1 (MCP-1) levels were significantly elevated in DR (p=0.016 and 0.036, respectively) and DNR groups (p=0.021 and 0.026, respectively). Interleukin-1 (IL-1) receptor antagonist (IL-1ra) levels were significantly increased in DNR (p=0.016). Th1/Th2 cytokines interferon-gamma (IFN-γ)/IL-5 and IL-2/IL-5 ratios were significantly increased in DR compared to controls (p=0.037 and 0.031, respectively). Anti-angiogenic/angiogenic cytokines IFN-γ/MCP-1 and IL-4/MCP-1 ratios in DR and DNR were significantly decreased compared to controls (p<0.05). IL-4/IL-8 and IL-12p70/IL-8 ratios were also significantly decreased in DR compared to controls (p=0.02 and 0.045, respectively). No significant correlation was demonstrated between tear cytokine concentrations and glycosylated hemoglobin (HbA1c) or fasting plasma glucose (FPG). CONCLUSIONS Diabetic tears exhibited elevated levels of IP-10 and MCP-1. The Th1/Th2 cytokine balance may shift to a predominantly Th1 state in DR patients. Pro-angiogenic cytokines are more highly represented than anti-angiogenic cytokines in the tears of diabetic patients.
Collapse
|
5
|
Hearing requires otoferlin-dependent efficient replenishment of synaptic vesicles in hair cells. Nat Neurosci 2010; 13:869-76. [PMID: 20562868 DOI: 10.1038/nn.2578] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Accepted: 05/14/2010] [Indexed: 12/15/2022]
Abstract
Inner hair cell ribbon synapses indefatigably transmit acoustic information. The proteins mediating their fast vesicle replenishment (hundreds of vesicles per s) are unknown. We found that an aspartate to glycine substitution in the C(2)F domain of the synaptic vesicle protein otoferlin impaired hearing by reducing vesicle replenishment in the pachanga mouse model of human deafness DFNB9. In vitro estimates of vesicle docking, the readily releasable vesicle pool (RRP), Ca(2+) signaling and vesicle fusion were normal. Moreover, we observed postsynaptic excitatory currents of variable size and spike generation. However, mutant active zones replenished vesicles at lower rates than wild-type ones and sound-evoked spiking in auditory neurons was sparse and only partially improved during longer interstimulus intervals. We conclude that replenishment does not match the release of vesicles at mutant active zones in vivo and a sufficient standing RRP therefore cannot be maintained. We propose that otoferlin is involved in replenishing synaptic vesicles.
Collapse
|
6
|
Bartoletti TM, Babai N, Thoreson WB. Vesicle pool size at the salamander cone ribbon synapse. J Neurophysiol 2009; 103:419-23. [PMID: 19923246 DOI: 10.1152/jn.00718.2009] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cone light responses are transmitted to postsynaptic neurons by changes in the rate of synaptic vesicle release. Vesicle pool size at the cone synapse constrains the amount of release and can thus shape contrast detection. We measured the number of vesicles in the rapidly releasable and reserve pools at cone ribbon synapses by performing simultaneous whole cell recording from cones and horizontal or off bipolar cells in the salamander retinal slice preparation. We found that properties of spontaneously occurring miniature excitatory postsynaptic currents (mEPSCs) are representative of mEPSCs evoked by depolarizing presynaptic stimulation. Strong, brief depolarization of the cone stimulated release of the entire rapidly releasable pool (RRP) of vesicles. Comparing charge transfer of the EPSC with mEPSC charge transfer, we determined that the fast component of the EPSC reflects release of approximately 40 vesicles. Comparing EPSCs with simultaneous presynaptic capacitance measurements, we found that horizontal cell EPSCs constitute 14% of the total number of vesicles released from a cone terminal. Using a fluorescent ribeye-binding peptide, we counted approximately 13 ribbons per cone. Together, these results suggest each cone contacts a single horizontal cell at approximately 2 ribbons. The size of discrete components in the EPSC amplitude histogram also suggested approximately 2 ribbon contacts per cell pair. We therefore conclude there are approximately 20 vesicles per ribbon in the RRP, similar to the number of vesicles contacting the plasma membrane at the ribbon base. EPSCs evoked by lengthy depolarization suggest a reserve pool of approximately 90 vesicles per ribbon, similar to the number of additional docking sites further up the ribbon.
Collapse
Affiliation(s)
- Theodore M Bartoletti
- Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, 4050 Durham Research Center, Omaha, NE 68198-5840, USA
| | | | | |
Collapse
|
7
|
Abstract
To better understand synaptic signaling at the mammalian rod bipolar cell terminal and pave the way for applying genetic approaches to the study of visual information processing in the mammalian retina, synaptic vesicle dynamics and intraterminal calcium were monitored in terminals of acutely isolated mouse rod bipolar cells and the number of ribbon-style active zones quantified. We identified a releasable pool, corresponding to a maximum of 7 s. The presence of a smaller, rapidly releasing pool and a small, fast component of refilling was also suggested. Following calcium channel closure, membrane surface area was restored to baseline with a time constant that ranged from 2 to 21 s depending on the magnitude of the preceding Ca2+ transient. In addition, a brief, calcium-dependent delay often preceded the start of onset of membrane recovery. Thus, several aspects of synaptic vesicle dynamics appear to be conserved between rod-dominant bipolar cells of fish and mammalian rod bipolar cells. A major difference is that the number of vesicles available for release is significantly smaller in the mouse rod bipolar cell, both as a function of the total number per neuron and on a per active zone basis.
Collapse
|
8
|
Goutman JD, Glowatzki E. Time course and calcium dependence of transmitter release at a single ribbon synapse. Proc Natl Acad Sci U S A 2007; 104:16341-6. [PMID: 17911259 PMCID: PMC2042208 DOI: 10.1073/pnas.0705756104] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
At the first synapse in the auditory pathway, the receptor potential of mechanosensory hair cells is converted into a firing pattern in auditory nerve fibers. For the accurate coding of timing and intensity of sound signals, transmitter release at this synapse must occur with the highest precision. To measure directly the transfer characteristics of the hair cell afferent synapse, we implemented simultaneous whole-cell recordings from mammalian inner hair cells (IHCs) and auditory nerve fiber terminals that typically receive input from a single ribbon synapse. During a 1-s IHC depolarization, the synaptic response depressed >90%, representing the main source for adaptation in the auditory nerve. Synaptic depression was slightly affected by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor desensitization; however, it was mostly caused by reduced vesicular release. When the transfer function between transmitter release and Ca(2+) influx was tested at constant open probability for Ca(2+) channels (potentials >0 mV), a super linear relation was found. This relation is presumed to result from the cooperative binding of three to four Ca(2+) ions at the Ca(2+) sensor. However, in the physiological range for receptor potentials (-50 to -30 mV), the relation between Ca(2+) influx and afferent activity was linear, assuring minimal distortion in the coding of sound intensity. Changes in Ca(2+) influx caused an increase in release probability, but not in the average size of multivesicular synaptic events. By varying Ca(2+) buffering in the IHC, we further investigate how Ca(2+) channel and Ca(2+) sensor at this synapse might relate.
Collapse
Affiliation(s)
- Juan D. Goutman
- Department of Otolaryngology, Head and Neck Surgery, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 824, Baltimore, MD 21205
| | - Elisabeth Glowatzki
- Department of Otolaryngology, Head and Neck Surgery, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 824, Baltimore, MD 21205
- *To whom correspondence should be addressed. E-mail:
| |
Collapse
|
9
|
Abstract
Hearing relies on fast and sustained neurotransmitter release from inner hair cells (IHCs) onto the afferent auditory nerve fibres. The temperature dependence of Ca(2+) current and transmitter release at the IHCs ribbon synapse has not been investigated thus far. To assess the influence of temperature on calcium-triggered exocytosis, patch-clamp recordings of voltage-gated L-type Ca(2+) influx and exocytic membrane capacitance changes were performed at room (25 degrees C) and physiological (35-37 degrees C) temperatures. An increase in temperature within this range increased the L-type Ca(2+) current amplitude of IHCs (Q(10) = 1.3) and accelerates the activation kinetics. Fast exocytosis, probed by 20 ms depolarization, was enhanced at physiological temperature with a Q(10) of 2.1. The amplitude of fast release was elevated disproportionately to the increase in Ca(2+) influx. In contrast, the rate of sustained exocytosis (exocytic rate between 20 and 100 ms of depolarization) did not show a significant increase at physiological temperature. Altogether, these data indicate that the efficiency of fast exocytosis is higher at physiological temperature than at room temperature and suggest that the number of readily releasable vesicles available at the active zone is higher at physiological temperature.
Collapse
Affiliation(s)
- Régis Nouvian
- InnerEarLab, Department of Otolaryngology, Center for Molecular Physiology of the Brain, Bernstein Center fot Computational Neuroscience, Göttingen University Medical School, Robert-Koch-Strasse 40, 37075 Göttingen, Germany.
| |
Collapse
|
10
|
Crumling MA, Saunders JC. Tonotopic distribution of short-term adaptation properties in the cochlear nerve of normal and acoustically overexposed chicks. J Assoc Res Otolaryngol 2007; 8:54-68. [PMID: 17200911 PMCID: PMC2538420 DOI: 10.1007/s10162-006-0061-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Accepted: 10/18/2006] [Indexed: 10/23/2022] Open
Abstract
Cochlear nerve adaptation is thought to result, at least partially, from the depletion of neurotransmitter stores in hair cells. Recently, neurotransmitter vesicle pools have been identified in chick tall hair cells that might play a role in adaptation. In order to understand better the relationship between adaptation and neurotransmitter release dynamics, short-term adaptation was characterized by using peristimulus time histograms of single-unit activity in the chick cochlear nerve. The adaptation function resulting from 100-ms pure tone stimuli presented at the characteristic frequency, +20 dB relative to threshold, was well described as a single exponential decay process with an average time constant of 18.6+/-0.8 ms (mean+/-SEM). The number of spikes contributed by the adapting part of the response increased tonotopically for characteristic frequencies up to approximately 0.8 kHz. Comparison of the adaptation data with known physiological and anatomical hair cell properties suggests that depletion of the readily releasable pool is the basis of short-term adaptation in the chick. With this idea in mind, short-term adaptation was used as a proxy for assessing tall hair cell synaptic function following intense acoustic stimulation. After 48 h of exposure to an intense pure tone, the time constant of short-term adaptation was unaltered, whereas the number of spikes in the adapting component was increased at characteristic frequencies at and above the exposure frequency. These data suggest that the rate of readily releasable pool emptying is unaltered, but the neurotransmitter content of the pool is increased, by exposure to intense sound. The results imply that an increase in readily releasable pool size might be a compensatory mechanism ensuring the strength of the hair cell afferent synapse in the face of ongoing acoustic stress.
Collapse
Affiliation(s)
- Mark A Crumling
- David Mahoney Institute of Neurological Sciences, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | | |
Collapse
|
11
|
Abstract
Synaptic depression produced by repetitive stimulation is likely to be particularly important in shaping responses of second-order retinal neurons at the tonically active photoreceptor synapse. We analyzed the time course and mechanisms of synaptic depression at rod and cone synapses using paired-pulse protocols involving two complementary measurements of exocytosis: (1) paired whole-cell recordings of the postsynaptic current (PSC) in second-order retinal neurons and (2) capacitance measurements of vesicular membrane fusion in rods and cones. PSCs in ON bipolar, OFF bipolar, and horizontal cells evoked by stimulation of either rods or cones recovered from paired-pulse depression (PPD) at rates similar to the recovery of exocytotic capacitance changes in rods and cones. Correlation between presynaptic and postsynaptic measures of recovery from PPD suggests that 80-90% of the depression at these synapses is presynaptic in origin. Consistent with a predominantly presynaptic mechanism, inhibiting desensitization of postsynaptic glutamate receptors had little effect on PPD. The depression of exocytotic capacitance changes exceeded depression of the presynaptic calcium current, suggesting that it is primarily caused by a depletion of synaptic vesicles. In support of this idea, limiting Ca2+ influx by using weaker depolarizing stimuli promoted faster recovery from PPD. Although cones exhibit much faster exocytotic kinetics than rods, exocytotic capacitance changes recovered from PPD at similar rates in both cell types. Thus, depression of release is not likely to contribute to differences in the kinetics of transmission from rods and cones.
Collapse
|
12
|
Keen EC, Hudspeth AJ. Transfer characteristics of the hair cell's afferent synapse. Proc Natl Acad Sci U S A 2006; 103:5537-42. [PMID: 16567618 PMCID: PMC1414630 DOI: 10.1073/pnas.0601103103] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The sense of hearing depends on fast, finely graded neurotransmission at the ribbon synapses connecting hair cells to afferent nerve fibers. The processing that occurs at this first chemical synapse in the auditory pathway determines the quality and extent of the information conveyed to the central nervous system. Knowledge of the synapse's input-output function is therefore essential for understanding how auditory stimuli are encoded. To investigate the transfer function at the hair cell's synapse, we developed a preparation of the bullfrog's amphibian papilla. In the portion of this receptor organ representing stimuli of 400-800 Hz, each afferent nerve fiber forms several synaptic terminals onto one to three hair cells. By performing simultaneous voltage-clamp recordings from presynaptic hair cells and postsynaptic afferent fibers, we established that the rate of evoked vesicle release, as determined from the average postsynaptic current, depends linearly on the amplitude of the presynaptic Ca(2+) current. This result implies that, for receptor potentials in the physiological range, the hair cell's synapse transmits information with high fidelity.
Collapse
Affiliation(s)
- Erica C. Keen
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6399
| | - A. J. Hudspeth
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6399
- *To whom correspondence should be addressed at:
The Rockefeller University, Box 314, 1230 York Avenue, New York, NY 10021-6399. E-mail:
| |
Collapse
|
13
|
Rutherford MA, Roberts WM. Frequency selectivity of synaptic exocytosis in frog saccular hair cells. Proc Natl Acad Sci U S A 2006; 103:2898-903. [PMID: 16473940 PMCID: PMC1413814 DOI: 10.1073/pnas.0511005103] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ability to respond selectively to particular frequency components of sensory inputs is fundamental to signal processing in the ear. The frog (Rana pipiens) sacculus, which is used for social communication and escape behaviors, is an exquisitely sensitive detector of sounds and ground-borne vibrations in the 5- to 200-Hz range, with most afferent axons having best frequencies between 40 and 60 Hz. We monitored the synaptic output of saccular sensory receptors (hair cells) by measuring the increase in membrane capacitance (deltaC(m)) that occurs when synaptic vesicles fuse with the plasmalemma. Strong stepwise depolarization evoked an exocytic burst that lasted 10 ms and corresponded to the predicted capacitance of all docked vesicles at synapses, followed by a 20-ms delay before additional vesicle fusion. Experiments using weak stimuli, within the normal physiological range for these cells, revealed a sensitivity to the temporal pattern of membrane potential changes. Interrupting a weak depolarization with a properly timed hyperpolarization increased deltaC(m). Small sinusoidal voltage oscillations (+/-5 mV centered at -60 mV) evoked a deltaC(m) that corresponded to 95 vesicles per s at each synapse at 50 Hz but only 26 vesicles per s at 5 Hz and 27 vesicles per s at 200 Hz (perforated patch recordings). This frequency selectivity was absent for larger sinusoidal oscillations (+/-10 mV centered at -55 mV) and was largest for hair cells with the smallest sinusoidal-stimuli-evoked Ca2+ currents. We conclude that frog saccular hair cells possess an intrinsic synaptic frequency selectivity that is saturated by strong stimuli.
Collapse
Affiliation(s)
| | - William M. Roberts
- Institute of Neuroscience, University of Oregon, Eugene, OR 97403
- *To whom correspondence should be addressed at:
Institute of Neuroscience, University of Oregon, 1254 University of Oregon, Eugene, OR 97403. E-mail:
| |
Collapse
|
14
|
Schnee ME, Lawton DM, Furness DN, Benke TA, Ricci AJ. Auditory hair cell-afferent fiber synapses are specialized to operate at their best frequencies. Neuron 2005; 47:243-54. [PMID: 16039566 DOI: 10.1016/j.neuron.2005.06.004] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Revised: 05/05/2005] [Accepted: 06/01/2005] [Indexed: 11/21/2022]
Abstract
Auditory afferent fiber activity is driven by high-fidelity information transfer from the sensory hair cell. Presynaptic specializations, posited to maintain fidelity, are investigated at synapses with characteristic frequencies of 120 Hz and 320 Hz. Morphological data indicate that high-frequency cells have more synapses and higher vesicle density near dense bodies (DBs). Tracking vesicular release via capacitance changes identified three overlapping kinetic components of release corresponding to morphologically identified vesicle pools. High-frequency cells released faster; however, when normalized to release site number, low-frequency cells released faster, likely due to a greater Ca2+ load per synapse. The Ca(2+)-dependence of release was nonsaturating and independent of frequency, suggesting that release, not refilling, was rate limiting. A model of release derived from vesicle equilibration between morphologically defined pools reproduced the capacitance data, supporting a critical role in vesicle trafficking for DBs. The model suggests that presynaptic specializations enable synapses to operate most efficiently at their characteristic frequencies.
Collapse
Affiliation(s)
- M E Schnee
- Neuroscience Center and Kresge Hearing Labs, Louisiana State University, New Orleans, LA 70112, USA
| | | | | | | | | |
Collapse
|
15
|
Abstract
The activity of individual afferent neurones in the mammalian cochlea can be driven by neurotransmitter released from a single synaptic ribbon in a single inner hair cell. Thus, a ribbon synapse must be able to transmit all the information on sound frequency, intensity and timing carried centrally. This task is made still more demanding by the process of binaural sound localization that utilizes separate computations of time and intensity, with temporal resolution as fine as 10 micros in central nuclei. These computations may rely in part on the fact that the response phase (at the characteristic frequency) of individual afferent neurones is invariant with intensity. Somehow, the ribbon synapse can provide stronger synaptic drive to signal varying intensity, without accompanying changes in transmission time that ordinarily occur during chemical neurotransmission. Recent ultrastructural and functional studies suggest features of the ribbon that may underlie these capabilities.
Collapse
Affiliation(s)
- Paul Albert Fuchs
- The Cochlear Neurotransmission Laboratory, Center for Hearing and Balance, Department of Otolaryngology--Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21286, USA.
| |
Collapse
|
16
|
Abstract
Sensory neurons with short conduction distances can use nonregenerative, graded potentials to modulate transmitter release continuously. This mechanism can transmit information at much higher rates than spiking. Graded signaling requires a synapse to sustain high rates of exocytosis for relatively long periods, and this capacity is the special virtue of ribbon synapses. Vesicles tethered to the ribbon provide a pool for sustained release that is typically fivefold greater than the docked pool available for fast release. The current article, which is part of the TINS Synaptic Connectivity series, reviews recent evidence for this fundamental computational strategy and its underlying cell biology.
Collapse
Affiliation(s)
- Peter Sterling
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | | |
Collapse
|
17
|
Griesinger CB, Richards CD, Ashmore JF. Fast vesicle replenishment allows indefatigable signalling at the first auditory synapse. Nature 2005; 435:212-5. [PMID: 15829919 DOI: 10.1038/nature03567] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Accepted: 03/24/2005] [Indexed: 11/09/2022]
Abstract
Ribbon-type synapses in inner hair cells of the mammalian cochlea encode the complexity of auditory signals by fast and tonic release through fusion of neurotransmitter-containing vesicles. At any instant, only about 100 vesicles are tethered to the synaptic ribbon, and about 14 of these are docked to the plasma membrane, constituting the readily releasable pool. Although this pool contains about the same number of vesicles as that of conventional synapses, ribbon release sites operate at rates of about two orders of magnitude higher and with submillisecond precision. How these sites replenish their vesicles so efficiently remains unclear. We show here, using two-photon imaging of single release sites in the intact cochlea, that preformed vesicles derived from cytoplasmic vesicle-generating compartments participate in fast release and replenishment. Vesicles were released at a maximal initial rate of 3 per millisecond during a depolarizing pulse, and were replenished at a rate of 1.9 per millisecond. We propose that such rapid resupply of vesicles enables temporally precise and sustained release rates. This may explain how the first auditory synapse can encode with indefatigable precision without having to rely on the slow, local endocytic vesicle cycle.
Collapse
Affiliation(s)
- Claudius B Griesinger
- Department of Physiology, Universität Freiburg, Hermann Herder Str. 7, 79104 Freiburg, Germany.
| | | | | |
Collapse
|
18
|
Spassova MA, Avissar M, Furman AC, Crumling MA, Saunders JC, Parsons TD. Evidence that rapid vesicle replenishment of the synaptic ribbon mediates recovery from short-term adaptation at the hair cell afferent synapse. J Assoc Res Otolaryngol 2005; 5:376-90. [PMID: 15675002 PMCID: PMC2504567 DOI: 10.1007/s10162-004-5003-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
We have employed both in vitro patch clamp recordings of hair cell synaptic vesicle fusion and in vivo single unit recording of cochlear nerve activity to study, at the same synapse, the time course, control, and physiological significance of readily releasable pool dynamics. Exocytosis of the readily releasable pool was fast, saturating in less than 50 ms, and recovery was also rapid, regaining 95% of its initial amplitude following a 200-ms period of repolarization. Longer depolarizations (greater than 250 ms) yielded a second, slower kinetic component of exocytosis. Both the second component of exocytosis and recovery of the readily releasable pool were blocked by the slow calcium buffer, EGTA. Sound-evoked afferent synaptic activity adapted and recovered with similar time courses as readily releasable pool exhaustion and recovery. Comparison of readily releasable pool amplitude, capture distances of calcium buffers, and number of vesicles tethered to the synaptic ribbon suggested that readily releasable pool dynamics reflect the depletion of release-ready vesicles tethered to the synaptic ribbon and the reloading of the ribbon with vesicles from the cytoplasm. Thus, we submit that rapid recovery of the cochlear hair cell afferent fiber synapse from short-term adaptation depends on the timely replenishment of the synaptic ribbon with vesicles from a cytoplasmic pool. This apparent rapid reloading of the synaptic ribbon with vesicles underscores important functional differences between synaptic ribbons in the auditory and visual systems.
Collapse
Affiliation(s)
- Maria A. Spassova
- />Department of Clinical Studies — New Bolton Center, School of
Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - Michael Avissar
- />Department of Otorhinolaryngology — Head and Neck Surgery, School of
Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - Adam C. Furman
- />Department of Otorhinolaryngology — Head and Neck Surgery, School of
Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - Mark A. Crumling
- />Department of Clinical Studies — New Bolton Center, School of
Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
- />Department of Otorhinolaryngology — Head and Neck Surgery, School of
Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - James C. Saunders
- />Department of Clinical Studies — New Bolton Center, School of
Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - Thomas D. Parsons
- />Department of Clinical Studies — New Bolton Center, School of
Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
- />Department of Otorhinolaryngology — Head and Neck Surgery, School of
Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| |
Collapse
|
19
|
Sikora MA, Gottesman J, Miller RF. A computational model of the ribbon synapse. J Neurosci Methods 2005; 145:47-61. [PMID: 15922025 DOI: 10.1016/j.jneumeth.2004.11.023] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Revised: 11/15/2004] [Accepted: 11/19/2004] [Indexed: 11/19/2022]
Abstract
A model of the ribbon synapse was developed to replicate both pre- and postsynaptic functions of this glutamatergic juncture. The presynaptic portion of the model is rich in anatomical and physiological detail and includes multiple release sites for each ribbon based on anatomical studies of presynaptic terminals, presynaptic voltage at the terminal, the activation of voltage-gated calcium channels and a calcium-dependent release mechanism whose rate varies as a function of the calcium concentration that is monitored at two different sites which control both an ultrafast, docked pool of vesicles and a release ready pool of tethered vesicles. The postsynaptic portion of the program models diffusion of glutamate and the physiological properties of glutamatergic neurotransmission in target cells. We demonstrate the behavior of the model using the retinal bipolar cell to ganglion cell ribbon synapse. The model was constrained by the anatomy of salamander bipolar terminals based on the ultrastructure of these synapses and presynaptic contacts were placed onto realistic ganglion cell morphology activated by a range of ribbon synapses (46-138). These inputs could excite the cell in a manner consistent with physiological observations. This model is a comprehensive, first-generation attempt to assemble our present understanding of the ribbon synapse into a domain that permits testing our understanding of this important structure. We believe that with minor modifications of this model, it can be fine tuned for other ribbon synapses.
Collapse
Affiliation(s)
- Michael A Sikora
- Department of Neuroscience, University of Minnesota, 6-146 Jackson Hall, 321 Church St SE, Minneapolis, MN 55455, USA.
| | | | | |
Collapse
|
20
|
Crumling MA, Saunders JC. Temperature insensitivity of short-term adaptation in single-units of the chick cochlear nerve. Synapse 2005; 58:243-8. [PMID: 16206182 DOI: 10.1002/syn.20204] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Short-term adaptation in acoustically stimulated chick cochlear nerve fibers has recently been shown to have similar kinetics as the readily-releasable vesicle pool in patch-clamped chick hair cells, suggesting that short-term adaptation depends on the dynamics of hair cell exocytosis. Our understanding of the relationship between these two phenomena has been hampered by differences in the temperatures at which the two types of data have been collected. In this report, the effect of temperature on short-term adaptation was studied in single-units of the chick cochlear nerve. Compared to units recorded at 38-41 degrees C, spontaneous and evoked firing rates were markedly decreased when the temperature was lowered to 28-32 degrees C, but the rate of short-term adaptation during 100 ms tone bursts was relatively unchanged, with a temperature Q(10), of approximately 1.2. The continued similarity of the adaptation time-constant of cooled units to vesicle depletion kinetics in chick hair cells measured at room temperature suggests that comparison of in vitro hair cell exocytosis and in vivo cochlear nerve firing properties may not be confounded by temperature differences between the two approaches.
Collapse
Affiliation(s)
- Mark A Crumling
- David Mahoney Institute of Neurological Sciences, University of Pennsylvania, Philadelphia, 19104, USA.
| | | |
Collapse
|
21
|
Edmonds BW, Gregory FD, Schweizer FE. Evidence that fast exocytosis can be predominantly mediated by vesicles not docked at active zones in frog saccular hair cells. J Physiol 2004; 560:439-50. [PMID: 15308677 PMCID: PMC1665261 DOI: 10.1113/jphysiol.2004.066035] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The prevailing model of neurotransmitter release stipulates that Ca2+ influx triggers the rapid fusion of vesicles that are docked at presynaptic active zones. Under this model, slower tonic release is supported by vesicles clustered nearby that have to translocate to the release sites before fusion. We have examined this hypothesis at the afferent synapse of saccular hair cells of the leopard frog, Rana pipiens. Detailed morphological measurements at this ribbon synapse show that on average 32 vesicles are docked at each active zone. We show that at this 'graded' synapse, depolarization produces an exocytotic 'burst' that is largely complete within 20 ms after fusion of 280 vesicles per active zone, almost an order of magnitude more than expected. Recovery from paired pulse depression occurs with a time constant of 29 ms, indicating that replenishment of this fast-fusing pool of vesicles is also fast. Our results suggest that non-docked vesicles are capable of fast fusion and that these vesicles constitute the vast majority of the fast-fusing pool. The view that the population of fast-fusing presynaptic vesicles is limited to docked vesicles therefore requires re-evaluation. We propose that compound fusion, i.e. the fusion of vesicles with each other before and/or after they fuse with the membrane can explain multivesicular release at this synapse.
Collapse
Affiliation(s)
- Brian W Edmonds
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, 650 Charles E. Young Drive South, Los Angeles, CA 90095, USA
| | | | | |
Collapse
|