DOCSLIB.ORG

What Can One Synapse Tell Us About How the Auditory Processing Works?

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
What Can One Synapse Tell Us About How the Auditory Processing Works? What can one synapse tell us about how the auditory processing works? Ian D. Forsythe MRC toxicology Unit University of Leicester. • Introduce you to the calyx of Held • Describe the presynaptic calcium currents. • Pose some questions about the control of synaptic transmission The Calyx of Held -Auditory Brainstem The Synapse • Transmission along nerves/axons is electrical pulses called Action Potentials. Via Voltage-gated ion channels Synaptic cleft EPSP -excitatory postsynaptic potential •Transmission between nerve cells is by a chemical messenger called a Transmitter Via Receptor-gated ion channels Neurotransmitter subtypes Integral transmitter G-protein Coupled- Ion Channel Ionotropic Metabotropic nAchRmusc nAchRbrain acetylcholine M1-5 muscarinic NMDAR AMPAR KainR glutamate mGluR1-8 GABAC GABAA GABA GABAB 5HT3 serotonin/5HT 5HT1/2/4 catecholamines DA1-4 a1/2/b1- Peptides SP Enk VP3 VIP GlyR glycine P2X purines P2Y A1/2 http://www.iuphar-db.org/index_ic.jsp Most synapses in the CNS are small Mitochondria vesicles Release zone Postsynaptic cell 0.5 µm From Sanes & Jessell Mammalian CNS synapse preparations • Mossy fibre terminal – CA3 Hippocampus – Fast glutamatergic (also peptidergic) – Geiger & Jonas. • Cerebellar Pinceau – Basket cell, Cerebellum. – Fast Gaba’ergic synapse – Gary Stephens & Brian Robertson. • Endbulb of Held Auditory brainstem. • Calyx of Held – Fast glutamatergic synapse – Myself, Gerard Borst and many others. Hans Held • Worked in Leipzig, Germany in the 19th Century • Taught Bernard Katz • Published a Golgi study of the brainstem in 1893 describing two large structures at the end of axons….. Became known as the endbulb and calyx of Held. • The irony is…. He did not subscribe to the synaptic hypothesis being developed by Sherrington. Confocal images of the calyx of Held Forsythe, 1994 The medial nucleus of the trapezoid body dorsal lateral midline stimulate 15 µm View down the Rat & mouse experimental 10-14 days old. microscope The calyx of Held synapse is mediated by the transmitter glutamate Experimental patch arrangement pipette MNTB neurone stim. Action potential axon current-clamp Calyx of Held triggered by synaptic response 20 mV ‘All or nothing’ response 40 ms % amplitude b 120 c stimulus 100 80 60 voltage-clamp 40 A slow EPSC - NMDA receptors 20 0.5 nA a 40 ms A fast EPSC - AMPA receptors 0 0 2 4 6 8 10 stimulus intensity (V) Dual component synaptic currents NMDAR-mediated AMPAR-mediated Forsythe & Barnes-Davies, 1993 Fidelity at the Calyx of Held: 4000 stimuli at 200Hz 50 ms VC: EPSC First ‘error’ 6.25 sec 14 nA 50 mV CC: EPSP/AP 5 seconds RMP= -63 mV 50 ms P15 Rat, 38oC Mike Postlethwaite mEPSCs at the calyx of Held/MNTB o Temperature = 25oC Amplitude distribution at 25 & 35 C 0.4 0.35 25 degrees 0.3 35 degrees 0.25 0.2 0.15 0.1 N = 55 0.05 0 10 pA 10 1 ms Tau = 0.64 ms -15 -25 -35 -45 -55 -65 -75 -85 -95 -105 Number of events (normalized) Amplitude (bin width 10 pA) Temperature = 35oC 25oC 35oC N Amplitude (pA) -32.7 -46.0 6 2.3 5.7* Decay Tau (ms) 0.51 0.32 6 N = 220 0.06 0.02* Tau = 0.34 ms Frequency (Hz) 0.10 0.47 6 0.02 0.2* Postlethwaite et al., J. Physiol 2008 NMDAR at the calyx of Held +50 Control 1 nA I (nA) 10 ms 4 + D-AP5 P14 2 -70 -50 -30 0 10 30 50 2 nA V (mV) 50 ms -2 -60 +50 3 I (nA) 1 nA Control 10 ms 2 P18 + D-AP5 1 -70 -50 -30 0 5 nA 10 30 50 50 ms -1 V (mV) -60 -2 +50 4 I (nA) Control 1 nA 3 10 ms 2 P21 + D-AP5 1 -70 -50 -30 0 2 nA 10 30 50 -1 V (mV) 50 ms -60 -2 Steinert et al., submitted Detecting functionally connected synapses •Loading: 7mM Fura2-AM for 5 minutes •Wash for 30 minutes. •Stimulate with short train. •Image at 350/380 nm. •Connected MNTB neurones ‘light up’. Billups et al., 2002 Pflugers Arch - Eur J Physiol 444:663–669 Presynaptic Lucifer yellow fill Simultaneous pre- and post- Post synaptic recording Pre A. AP triggered B. Calcium dependence Post. 0.3nA 20mV 5ms Pre The calyx of Held • Calyx occupies around half of the soma. • Only one forms on each MNTB cell body. • It forms up to 700-1500 release sites. • P-type calcium channels mediate exocytosis. 2+ • Exoytosis requires [Ca ]i rise to 10-20mM. • Endogenous Ca2+ buffering is low (Ca2+ BP). • Mitochondria are a major non-mobile presynaptic sequestration mechanism. • Quantal amplitude is around 50 pA (-60 mV) 70pS. • EPSC 3nA to over 20 nA in amplitude. • Fast kinetics (mEPSC tau 0.31ms 350C). • Dominated by GluRDo AMPAR subunits. Fluo3 loaded into calyx of Held • Exhibits multiple forms of short-term plasticity, calcium transients induced by two including autoreceptor depression. 1 ms step depolarizations 1 ms – other forms include Facilitation, depression, 10 ms depletion and desensitisation. Billups & Forsythe 2002 Schneggenburger & Forsythe 2006 Which calcium channels mediate transmitter release? • Measure the EPSC following application of different calcium channel antagonists: » Dihydropyridines (nimodipine) blocks L- type » Conotoxin GVIA (Ctx GVIA) blocks N-type » Agatoxin IVA (AgaIVA) blocks P/Q type 2+ » Cadmium [Cd ]o blocks ALL calcium channels • Patch the presynaptic terminal and study the calcium current following block of other voltage-gated channels: » Tetrodotoxin (TTX)…….. » Tetraethylammonium (TEA) + » Caesium [Cs ]i • Compare this to channels on different parts of the neurone. Presynaptic calcium current is P-type AgaTx-IVA (200 nM) 10 ConoTx-GVIA (2 µM) Nimodipine (10 µM) i ii iii iv ) 8 A n - ( e 6 d u 2 nA t i 3 ms l p m 4 a C S P 2 0.2 nA E 3 ms v 0 0 5 10 15 20 25 30 time (mins) Forsythe et al., 1998 P-type presynaptic calcium channels Calcium Current (-nA) 5 nM 2 200 nM -Agatoxin-IVA 50 µM Cd2+ 1.5 1 0.5 0 0 10 20 30 40 50 time (min) Forsythe et al., 1998 Voltage-gated Ca2+ currents Takahashi et al., Science 1996 Different Ca2+ currents in Bushy cell somata and terminals…… Soma – in cochlear nucleus Terminal - in the MNTB 60 100 50 80 40 60 30 20 40 10 20 0 0 L N R P L N R P a1C a1B a1E a1A a1C a1B a1E a1A Calcium Channel Subtypes N.B: Developmental shift from N to P/Q type channels in young animals around hearing onset Doughty et al., 1998 Calcium sequestration at the calyx of Held Synaptic current Calcium current 1nA 1nA Presynaptic 20ms 20ms Postsynaptic Fura FF Mitochondrial calcium Presynaptic calcium 10µM 200ms Rhod-2 0.05 AU 200ms mitochondria Calcium, Transmitter Release and Mitochondria • Ca2+ triggers transmitter release. • No evidence for presynaptic calcium stores. • Caffeine • Ryanodine • Thapsigargin • Ca2+ Mopped up: • Buffering proteins • Extrusion by pumps • Into other compartments • MITOCHONDRIA (22%) Cytoplasmic and Mitochondrial Calcium Fura FF Rhod-2 Cytoplasmic Relative [Ca2+] (µM) Ca2+ mito. 40 1.2 30 1.0 Control 0.8 20 Rotenone 0.6 0.4 10 0.2 0 0 0.5 1.0 1.5 2.0 1 2 3 4 Time (sec) Time (sec) 4 x 2 ms @ 100Hz Modulation by mGluRs Glutamate can act presynaptically as an autoreceptor, modulating its own release. This may be observed as reduced EPSC amplitude. • Originally observed in Barnes-Davies & Forsythe 1995 (J. Physiol) • Demonstrated to be of minor significance by von Gersdorff et al 1998. • Re-examined by and shown to be present but masked in older animals. Billups et al., 2005. Gp III mGluR agonists Or glutamate Or synaptic stimulation But remove the agonist and it quickly reverts to control amplitude. In young animals group III mGluRs suppress transmitter release Barnes-Davies & Forsythe J. Physiol, 1995. This is mediated by suppression of the presynaptic P-type calcium currents Takahashi et al., Science, 1996. Summary • The calyx of Held is a glutamatergic synapse which forms on principal neurons in the MNTB. •It is part of an inverting relay in the auditory pathway subserving sound source localization. • Presynaptic recording shows that P-type Ca2+ channels dominate exocytosis at the mature calyx. • Mitochondria are the major presynaptic calcium store. • Short term forms of modulation act at presynaptic P-type Ca2+ channels to regulate release of transmitter. Modulation of synaptic transmission Short-term Presynaptic – changes in transmitter release Facilitation - Ca2+ dependent G-protein-dependent. Depression – Ca2+/calmodulin dependent. Post-tetanic potentiation Auto-receptor activation. Postsynaptic – changes in glutamate receptors Desensitization of the AMPA receptors. Long-term No-one has discovered anything like long-term potentiation (LTP) or long-term depression (LTD)! Why? Your turn……. Ask questions…… form a hypothesis……. What use is giant synapse? Perhaps it is big because it is primitive? Why is it so much bigger than nearly all other synapses? What information does it convey? Why would an ‘ordinary’ synapse not do as good a job What are it’s physiological limitations? It uses the fastest glutamate receptors in the brain. Each target neuron has only one giant synaptic input. It acts as a relay (in contrast to nearly every other synapse). It is 30 times larger than it needs to be to trigger an AP in the target But it still only triggers one AP in the target neuron It can fire APs at over 1000Hz Security at the Calyx of Held: 4000 stimuli at 200Hz 50 ms VC: EPSC First ‘error’ 6.25 sec 14 nA 50 mV CC: EPSP/AP 5 seconds RMP= -63 mV 50 ms P15 Rat, 38oC Mike Postlethwaite The calyx of Held is a secure glutamatergic synapse current-clamp Experimental patch arrangement pipette Action potential triggered by synaptic MNTB neurone response stim.
Load more

Recommended publications
  • Dynamic Development of the Calyx of Held Synapse
    Dynamic development of the calyx of Held synapse Adria´ n Rodríguez-Contreras*, John Silvio Soria van Hoeve, Ron L. P. Habets†, Heiko Locher, and J. Gerard G. Borst Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands Communicated by Erwin Neher, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany, February 12, 2008 (received for review January 11, 2008) The calyx of Held is probably the largest synaptic terminal in the Results brain, forming a unique one-to-one connection in the auditory Relation Between Large Axosomatic Contacts and Synaptic Clusters. ventral brainstem. During early development, calyces have many Brainstem sections containing the MNTB at different postnatal collaterals, whose function is unknown. Using electrophysiological ages were stained immunohistochemically for VGLUT, a pre- recordings and fast-calcium imaging in brain slices, we demon- synaptic marker of excitatory synapses, and analyzed by using strate that these collaterals are involved in synaptic transmission. fluorescence microscopy (Fig. 1). At postnatal day 2 (P2) and We show evidence that the collaterals are pruned and that the younger ages, punctate labeling was observed both in the neu- pruning already begins 1 week before the onset of hearing. Using ropil and around cell bodies in the MNTB. At P3 and beyond, two-photon microscopy to image the calyx of Held in neonate rats, large perisomatic presynaptic clusters (LPCs) of VGLUT stain- we report evidence that both axons and nascent calyces are ing were present (Fig. 1 A and B). The fraction of cells structurally dynamic, showing the formation, elimination, exten- surrounded by LPCs increased with age.
    [Show full text]
  • Deactivation Kinetics of Acid-Sensing Ion Channel 1A Are Strongly Ph
    Deactivation kinetics of acid-sensing ion channel 1a PNAS PLUS are strongly pH-sensitive David M. MacLeana,1 and Vasanthi Jayaramana aCenter for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, TX 77030 Edited by Richard W. Aldrich, The University of Texas at Austin, Austin, TX, and approved February 13, 2017 (received for review December 14, 2016) Acid-sensing ion channels (ASICs) are trimeric cation-selective ion (20). The rapid deactivation combined with ASICs’ slow de- channels activated by protons in the physiological range. Recent sensitization enables these channels to operate at high stimulus reports have revealed that postsynaptically localized ASICs contribute frequencies that desensitize most other NGICs (20). However, to the excitatory postsynaptic current by responding to the transient the synaptic cleft pH waveform is more complicated than the acidification of the synaptic cleft that accompanies neurotransmis- binary alkaline or acidic stimulation previously used. A pH drop sion. In response to such brief acidic transients, both recombinant and of 0.2–0.6 pH units or greater can accompany single-release native ASICs show extremely rapiddeactivationinoutside-out events, but the synaptic cleft pH may not return directly back to patches when jumping from a pH 5 stimulus to a single resting pH physiological pH (21–25). Rather, following brief stimulations, of 8. Given that the resting pH of the synaptic cleft is highly dynamic “ ” and depends on recent synaptic activity, we explored the kinetics of synaptic cleft pH overshoots the physiological range by 0.2 pH ASIC1a and 1a/2a heteromers to such brief pH transients over a wider units or more and remains alkaline for several tens or hundreds of + – [H ] range to approximate neuronal conditions better.
    [Show full text]
  • Structure-Function Relation of the Developing Calyx of Held Synapse in Vivo
    bioRxiv preprint doi: https://doi.org/10.1101/2020.01.07.893685; this version posted January 7, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 Structure-function relation of the developing calyx of Held synapse in vivo 2 3 Abbreviated title: Strength-size relation of the calyx of Held 4 Martijn C. Sierksma1,3, Johan A. Slotman2, Adriaan B. Houtsmuller2 and J. Gerard G. Borst1 5 1Department of Neuroscience or 2Department of Pathology – Optical Imaging Centre, Erasmus MC, 6 University Medical Center Rotterdam, 3000 CA, Rotterdam, The Netherlands. 7 3Sorbonne Université, Inserm, CNRS, Institut de la Vision, 17 Rue Moreau, F-75012 Paris, France. 8 Correspondence to [email protected] 9 10 11 12 13 14 15 16 17 18 19 Conflict of interest: The authors declare no competing financial interests. 20 Contributions 21 JGGB and MCS designed experiments. MCS performed in vivo electrophysiology and imaging 22 experiments, analyzed the electrophysiology and the images. JAS performed imaging experiments 23 and imaging analysis. JAS and ABH designed imaging analysis. MCS drafted the manuscript. JAS, ABH 24 and JGGB commented on manuscript. 25 Acknowledgements 26 This work was financially supported by the Earth and Life Sciences-Netherlands Organisation of 27 Scientific Research (NWO, #823.02.006, ‘Development of a Giant Synapse’). We are very grateful for 28 the help of Elize Haasdijk and Celina Glimmerveen, who performed the immunolabeling. We thank 29 Marcel van der Heijden, Peter Bremen and Aaron Wong for advice on the analyses.
    [Show full text]
  • Sound-Evoked Activity Influences Myelination of Brainstem Axons in the Trapezoid Body
    The Journal of Neuroscience, August 23, 2017 • 37(34):8239–8255 • 8239 Systems/Circuits Sound-Evoked Activity Influences Myelination of Brainstem Axons in the Trapezoid Body James L. Sinclair, Matthew J. Fischl, Olga Alexandrova, Martin He␤, Benedikt Grothe, XChristian Leibold, and Conny Kopp-Scheinpflug Division of Neurobiology, Department Biology II, Ludwig-Maximilians-University Munich, 82152 Planegg-Martinsried, Germany Plasticity of myelination represents a mechanism to tune the flow of information by balancing functional requirements with metabolic and spatial constraints. The auditory system is heavily myelinated and operates at the upper limits of action potential generation frequency and speed observed in the mammalian CNS. This study aimed to characterize the development of myelin within the trapezoid body, a central auditory fiber tract, and determine the influence sensory experience has on this process in mice of both sexes. We find that in vitro conduction speed doubles following hearing onset and the ability to support high-frequency firing increases concurrently. Also in this time, the diameter of trapezoid body axons and the thickness of myelin double, reaching mature-like thickness between 25 and 35 d ofage.Earplugswereusedtoinduceϳ50dBelevationinauditorythresholds.Ifintroducedathearingonset,trapezoidbodyfibersdeveloped thinner axons and myelin than age-matched controls. If plugged during adulthood, the thickest trapezoid body fibers also showed a decrease in myelin. These data demonstrate the need for sensory activity in both development and maintenance of myelin and have important implications in the study of myelin plasticity and how this could relate to sensorineural hearing loss following peripheral impairment. Key words: ABR; auditory brainstem; axonal conduction speed; calyx of Held; MNTB; myelination Significance Statement The auditory system has many mechanisms to maximize the dynamic range of its afferent fibers, which operate at the physiolog- ical limit of action potential generation, precision, and speed.
    [Show full text]
  • The Calyx of Held
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by RERO DOC Digital Library Cell Tissue Res (2006) 326:311–337 DOI 10.1007/s00441-006-0272-7 REVIEW The calyx of Held Ralf Schneggenburger & Ian D. Forsythe Received: 6 April 2006 /Accepted: 7 June 2006 / Published online: 8 August 2006 # Springer-Verlag 2006 Abstract The calyx of Held is a large glutamatergic A short history of the calyx of Held synapse in the mammalian auditory brainstem. By using brain slice preparations, direct patch-clamp recordings can The size of a synapse is a significant technical constraint for be made from the nerve terminal and its postsynaptic target electrophysiological recording. The large dimensions of (principal neurons of the medial nucleus of the trapezoid some invertebrate synapses have been exploited to provide body). Over the last decade, this preparation has been considerable insight into presynaptic function (Llinas et al. increasingly employed to investigate basic presynaptic 1972; Augustine et al. 1985; Young and Keynes 2005). mechanisms of transmission in the central nervous system. However, the progress of similar studies in vertebrates was We review here the background to this preparation and long hampered by the technical difficulty of presynaptic summarise key findings concerning voltage-gated ion recording from small nerve terminals. Over the last 50 years, channels of the nerve terminal and the ionic mechanisms a range of preparations have contributed to our understand- involved in exocytosis and modulation of transmitter ing of presynaptic mechanisms, from the neuromuscular release. The accessibility of this giant terminal has also junction (Katz 1969) to chromaffin cells (Neher and Marty permitted Ca2+-imaging and -uncaging studies combined 1982), chick ciliary ganglion (Martin and Pilar 1963; with electrophysiological recording and capacitance mea- Stanley and Goping 1991), neurohypophysial nerve termi- surements of exocytosis.
    [Show full text]
  • Glial Cell Contributions to Auditory Brainstem Development
    REVIEW published: 21 October 2016 doi: 10.3389/fncir.2016.00083 Glial Cell Contributions to Auditory Brainstem Development Karina S. Cramer 1* and Edwin W Rubel 2 1Department of Neurobiology and Behavior, University of California, Irvine, Irvine, CA, USA, 2 Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, WA, USA Glial cells, previously thought to have generally supporting roles in the central nervous system, are emerging as essential contributors to multiple aspects of neuronal circuit function and development. This review focuses on the contributions of glial cells to the development of auditory pathways in the brainstem. These pathways display specialized synapses and an unusually high degree of precision in circuitry that enables sound source localization. The development of these pathways thus requires highly coordinated molecular and cellular mechanisms. Several classes of glial cells, including astrocytes, oligodendrocytes and microglia, have now been explored in these circuits in both avian and mammalian brainstems. Distinct populations of astrocytes are found over the course of auditory brainstem maturation. Early appearing astrocytes are associated with spatial compartments in the avian auditory brainstem. Factors from late appearing astrocytes promote synaptogenesis and dendritic maturation, and astrocytes remain integral parts of specialized auditory synapses. Oligodendrocytes play a unique role in both birds and mammals in highly regulated myelination essential for proper timing to decipher interaural cues. Microglia arise early in brainstem development and may Edited by: contribute to maturation of auditory pathways. Together these studies demonstrate Joel C. Glover, the importance of non-neuronal cells in the assembly of specialized auditory brainstem University of Oslo, Norway circuits.
    [Show full text]
  • SHORT-TERM SYNAPTIC PLASTICITY Robert S. Zucker Wade G. Regehr
    23 Jan 2002 14:1 AR AR148-13.tex AR148-13.SGM LaTeX2e(2001/05/10) P1: GJC 10.1146/annurev.physiol.64.092501.114547 Annu. Rev. Physiol. 2002. 64:355–405 DOI: 10.1146/annurev.physiol.64.092501.114547 Copyright c 2002 by Annual Reviews. All rights reserved SHORT-TERM SYNAPTIC PLASTICITY Robert S. Zucker Department of Molecular and Cell Biology, University of California, Berkeley, California 94720; e-mail: [email protected] Wade G. Regehr Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115; e-mail: [email protected] Key Words synapse, facilitation, post-tetanic potentiation, depression, augmentation, calcium ■ Abstract Synaptic transmission is a dynamic process. Postsynaptic responses wax and wane as presynaptic activity evolves. This prominent characteristic of chemi- cal synaptic transmission is a crucial determinant of the response properties of synapses and, in turn, of the stimulus properties selected by neural networks and of the patterns of activity generated by those networks. This review focuses on synaptic changes that re- sult from prior activity in the synapse under study, and is restricted to short-term effects that last for at most a few minutes. Forms of synaptic enhancement, such as facilitation, augmentation, and post-tetanic potentiation, are usually attributed to effects of a resid- 2 ual elevation in presynaptic [Ca +]i, acting on one or more molecular targets that appear to be distinct from the secretory trigger responsible for fast exocytosis and phasic release of transmitter to single action potentials. We discuss the evidence for this hypothesis, and the origins of the different kinetic phases of synaptic enhancement, as well as the interpretation of statistical changes in transmitter release and roles played by other 2 2 factors such as alterations in presynaptic Ca + influx or postsynaptic levels of [Ca +]i.
    [Show full text]
  • Reciprocal Developmental Regulation of Presynaptic Ionotropic Receptors
    Reciprocal developmental regulation of presynaptic ionotropic receptors Rostislav Turecek* and Laurence O. Trussell† Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, L-335A, 3181 SW Sam Jackson Park Road, Portland, OR 97239 Edited by Roger A. Nicoll, University of California, San Francisco, CA, and approved August 23, 2002 (received for review July 15, 2002) Activation of ionotropic glycine receptors potentiates glutamate glutamate release. Other studies have described several major release in mature calyceal nerve terminals of the rat medial nucleus changes in inhibitory transmission in nuclei of the superior of the trapezoid body, an auditory brainstem nucleus. In young olivary complex. In the lateral superior olive, inhibitory trans- rats, glycine and its receptors are poorly expressed. We therefore mission shifts from depolarizing to hyperpolarizing in the first asked whether GABA (␥-aminobutyric acid) might play a larger role week after birth (11, 12). Moreover, IPSCs generated by MNTB than glycine in the regulation of glutamate release in the absence neurons in the lateral superior olive and the medial superior of glycine receptors. Indeed, in rats younger than postnatal day 11 olive initially are mediated in part by GABA and, later, become (P11), and before the onset of hearing, calyces expressed high exclusively glycinergic in the 2 weeks after birth (11, 13). Such levels of ionotropic GABAA receptors but few glycine receptors. changes may reflect changes in postsynaptic receptor expression Isoguvacine, a selective agonist at GABAA receptors, strongly or transmitter synthesis by the MNTB neurons themselves. enhanced excitatory postsynaptic currents in young rats but had We have examined presynaptic glycine and GABA receptors little effect in rats older than P11.
    [Show full text]
  • The Molecular Machinery of Neurotransmitter Release Nobel Lecture, 7 December 2013
    The Molecular Machinery of Neurotransmitter Release Nobel Lecture, 7 December 2013 by Thomas C. Südhof Dept. of Molecular and Cellular Physiology, and Howard Hughes Medical Institute, Stanford University, USA. 1. THE NEUROTRANSMITTER RELEASE ENIGMA Synapses have a long history in science. Synapses were frst functionally demon- strated by Emil duBois-Reymond (1818–1896), were morphologically identifed by classical neuroanatomists such as Rudolf von Kölliker (1817–1905) and San- tiago Ramon y Cajal (1852–1934), and named in 1897 by Michael Foster (1836– 1907). Although the chemical nature of synaptic transmission was already sug- gested by duBois-Reymond, it was long disputed because of its incredible speed. Over time, however, overwhelming evidence established that most synapses use chemical messengers called neurotransmitters, most notably with the pioneer- ing contributions by Otto Loewi (1873–1961), Henry Dale (1875–1968), Ulf von Euler (1905–1983), and Julius Axelrod (1912–2004). In parallel, arguably the most important advance to understanding how synapses work was provided by Bernard Katz (1911–2003), who elucidated the principal mechanism of syn- aptic transmission (Katz, 1969). Most initial studies on synapses were carried out on the neuromuscular junction, and central synapses have only come to the fore in recent decades. Here, major contributions by many scientists, including George Palade, Rodolfo Llinas, Chuck Stevens, Bert Sakmann, Eric Kandel, and Victor Whittaker, to name just a few, not only confrmed the principal results obtained in the neuromuscular junction by Katz, but also revealed that synapses 259 6490_Book.indb 259 11/4/14 2:29 PM 260 The Nobel Prizes exhibit an enormous diversity of properties as well as an unexpected capacity for plasticity.
    [Show full text]
  • Formation and Maturation of the Calyx of Held
    Hearing Research 276 (2011) 70e78 Contents lists available at ScienceDirect Hearing Research journal homepage: www.elsevier.com/locate/heares Review Formation and maturation of the calyx of Held Paul A. Nakamura, Karina S. Cramer* Department of Neurobiology and Behavior, University of California, Irvine, 2205 McGaugh Hall, Irvine, CA 92697-4550, USA article info abstract Article history: Sound localization requires precise and specialized neural circuitry. A prominent and well-studied Received 18 September 2010 specialization is found in the mammalian auditory brainstem. Globular bushy cells of the ventral cochlear Received in revised form nucleus (VCN) project contralaterally to neurons of the medial nucleus of the trapezoid body (MNTB), 3 November 2010 where their large axons terminate on cell bodies of MNTB principal neurons, forming the calyces of Held. Accepted 10 November 2010 The VCNeMNTB pathway is necessary for the accurate computation of interaural intensity and time Available online 18 November 2010 differences; MNTB neurons provide inhibitory input to the lateral superior olive, which compares levels of excitation from the ipsilateral ear to levels of tonotopically matched inhibition from the contralateral ear, and to the medial superior olive, where precise inhibition from MNTB neurons tunes the delays of binaural excitation. Here we review the morphological and physiological aspects of the development of the VCNeMNTB pathway and its calyceal termination, along with potential mechanisms that give rise to its precision. During embryonic development, VCN axons grow towards the midline, cross the midline into the region of the presumptive MNTB and then form collateral branches that will terminate in calyces of Held. In rodents, immature calyces of Held appear in MNTB during the first few days of postnatal life.
    [Show full text]
  • G-Protein-Coupled Modulation of Presynaptic Calcium Currents and Transmitter Release by a GABAB Receptor
    The Journal of Neuroscience, May 1, 1998, 18(9):3138–3146 G-Protein-Coupled Modulation of Presynaptic Calcium Currents and Transmitter Release by a GABAB Receptor Tomoyuki Takahashi, Yoshinao Kajikawa, and Tetsuhiro Tsujimoto Department of Neurophysiology, University of Tokyo Faculty of Medicine, Tokyo 113, Japan b Presynaptic GABAB receptors play a regulatory role in central (GDP S) abolished the effect of baclofen on both presynaptic synaptic transmission. To elucidate their underlying mechanism calcium currents and EPSCs. The nonhydrolyzable GTP analog of action, we have made whole-cell recordings of calcium and guanosine 59-O-(3-thiotriphosphate) (GTPgS) suppressed pre- potassium currents from a giant presynaptic terminal, the calyx synaptic calcium currents and occluded the effect of baclofen of Held, and EPSCs from its postsynaptic target in the medial on presynaptic calcium currents and EPSCs. Photoactivation of nucleus of the trapezoid body of rat brainstem slices. The GTPgS induced an inward rectifying potassium current at the GABAB receptor agonist baclofen suppressed EPSCs and pre- calyx of Held, whereas baclofen had no such effect. We con- synaptic calcium currents but had no effect on voltage- clude that presynaptic GABAB receptors suppress transmitter dependent potassium currents. The calcium current–EPSC re- release through G-protein-coupled inhibition of calcium lationship measured during baclofen application was similar to currents. 21 that observed on reducing [Ca ]o , suggesting that the pre- synaptic inhibition generated
    [Show full text]
  • Dynamin 1- and 3-Mediated Endocytosis Is Essential for the Development of a Large Central Synapse in Vivo
    The Journal of Neuroscience, June 1, 2016 • 36(22):6097–6115 • 6097 Development/Plasticity/Repair Dynamin 1- and 3-Mediated Endocytosis Is Essential for the Development of a Large Central Synapse In Vivo Fan Fan, X Laura Funk, and XXuelin Lou Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin–Madison, Madison, Wisconsin 53706 Dynamin is a large GTPase crucial for endocytosis and sustained neurotransmission, but its role in synapse development in the mam- malian brain has received little attention. We addressed this question using the calyx of Held (CH), a large nerve terminal in the auditory brainstem in mice. Tissue-specific ablation of different dynamin isoforms bypasses the early lethality of conventional knock-outs and allows us to examine CH development in a native brain circuit. Individual gene deletion of dynamin 1, a primary dynamin isoform in neurons, as well as dynamin 2 and 3, did not affect CH development. However, combined tissue-specific knock-out of both dynamin 1 and 3 (cDKO) severely impaired CH formation and growth during the first postnatal week, and the phenotypes were exacerbated by further additiveconditionalknock-outofdynamin2.ThedevelopmentaldefectofCHincDKOfirstbecameevidentonpostnatalday3(P3),atime point when CH forms and grows abruptly. This is followed by a progressive loss of postsynaptic neurons and increased glial infiltration late in development. However, early CH synaptogenesis before protocalyx formation was not altered in cDKO. Functional maturation of synaptic transmission in the medial nucleus of the trapezoid body in cDKO was impeded during development and accompanied by an increase in the membrane excitability of medial nucleus of the trapezoid body neurons.
    [Show full text]