101
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Schotten S, Meijer M, Walter AM, Huson V, Mamer L, Kalogreades L, ter Veer M, Ruiter M, Brose N, Rosenmund C, Sørensen JB, Verhage M, Cornelisse LN. Additive effects on the energy barrier for synaptic vesicle fusion cause supralinear effects on the vesicle fusion rate. eLife 2015; 4:e05531. [PMID: 25871846 PMCID: PMC4426983 DOI: 10.7554/elife.05531] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Accepted: 04/13/2015] [Indexed: 01/08/2023] Open
Abstract
The energy required to fuse synaptic vesicles with the plasma membrane
(‘activation energy’) is considered a major determinant in synaptic
efficacy. From reaction rate theory, we predict that a class of modulations exists,
which utilize linear modulation of the energy barrier for fusion to achieve
supralinear effects on the fusion rate. To test this prediction experimentally, we
developed a method to assess the number of releasable vesicles, rate constants for
vesicle priming, unpriming, and fusion, and the activation energy for fusion by
fitting a vesicle state model to synaptic responses induced by hypertonic solutions.
We show that complexinI/II deficiency or phorbol ester stimulation indeed affects
responses to hypertonic solution in a supralinear manner. An additive vs
multiplicative relationship between activation energy and fusion rate provides a
novel explanation for previously observed non-linear effects of
genetic/pharmacological perturbations on synaptic transmission and a novel
interpretation of the cooperative nature of Ca2+-dependent
release. DOI:http://dx.doi.org/10.7554/eLife.05531.001 Information is carried around our nervous system by cells called neurons, which are
connected to each other by junctions known as synapses. Within the neurons, there are
many small compartments known as synaptic vesicles that are essential to the transfer
of information from one neuron to the next. When one neuron is activated, the
synaptic vesicles fuse with the membrane surrounding the cell to release molecules
called neurotransmitters, which cross the synapse and activate the next neuron.
Vesicle fusion is carefully regulated to control the speed and amount of
neurotransmitter release, which determines the level of activation of the next
neuron. Vesicle fusion requires energy, much of which is provided by a set of proteins found
in the synapse. The minimum amount of energy required—called the activation
energy—is influenced by many factors, including the shape of the cell's
membrane at the synapse. It is thought that altering the activation energy required
for fusion may control the activity of synapses, but it is not possible to directly
measure this in living cells. To bypass this problem, Schotten, Meijer, Walter et al. established a new method to
study vesicle fusion. This method combines a mathematical model with experimental
data of the activity of synapses. First, the neurons were placed in a solution
containing the sugar sucrose, which triggered vesicle fusion by lowering the
activation energy. The increase in vesicle fusion was smaller in neurons that lacked
two proteins called complexin I and complexin II—which control vesicle
fusion—than in the normal neurons. A molecule called phorbol ester is also able to activate the release of
neurotransmitters. When cells were treated with both sucrose and phorbol ester, the
speed of vesicle fusion was greater. The experiments show that the effects of
sucrose, phorbol ester, and the complexins multiply together to dramatically alter
vesicle fusion. Schotten, Meijer, Walter et al. suggest a new model for how the activation energy of
vesicle fusion controls the transfer of information across synapses. This might shed
new light on how the efficiency of vesicle fusion is altered when neurons are highly
active, which is thought to have strong implications for how information is processed
in the brain. DOI:http://dx.doi.org/10.7554/eLife.05531.002
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Affiliation(s)
- Sebastiaan Schotten
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Marieke Meijer
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Alexander Matthias Walter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Vincent Huson
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Lauren Mamer
- NeuroCure Cluster of Excellence, Neuroscience Research Center, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Lawrence Kalogreades
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Mirelle ter Veer
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Marvin Ruiter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Christian Rosenmund
- NeuroCure Cluster of Excellence, Neuroscience Research Center, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Jakob Balslev Sørensen
- Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Lennart Niels Cornelisse
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
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Abstract
Astrocytes seem to rely on relatively sluggish and spatially blurred Ca(2+) waves to communicate with fast and point-precise neural circuits. This apparent discrepancy could, however, reflect our current inability to understand the microscopic mechanisms involved. Difficulties in detecting and interpreting astrocyte Ca(2+) signals may have led to some prominent controversies in the field. Here, we argue that a deeper understanding of astrocyte physiology requires a qualitative leap in our experimental and analytical strategies.
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Affiliation(s)
- Dmitri A Rusakov
- UCL Institute of Neurology, University College London, Queen Square, London, WC1N 3BG, UK
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103
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Abstract
Fast synaptic communication in the brain requires synchronous vesicle fusion that is evoked by action potential-induced Ca(2+) influx. However, synaptic terminals also release neurotransmitters by spontaneous vesicle fusion, which is independent of presynaptic action potentials. A functional role for spontaneous neurotransmitter release events in the regulation of synaptic plasticity and homeostasis, as well as the regulation of certain behaviours, has been reported. In addition, there is evidence that the presynaptic mechanisms underlying spontaneous release of neurotransmitters and their postsynaptic targets are segregated from those of evoked neurotransmission. These findings challenge current assumptions about neuronal signalling and neurotransmission, as they indicate that spontaneous neurotransmission has an autonomous role in interneuronal communication that is distinct from that of evoked release.
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104
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Perissinotti PP, Ethington EA, Almazan E, Martínez-Hernández E, Kalil J, Koob MD, Piedras-Rentería ES. Calcium current homeostasis and synaptic deficits in hippocampal neurons from Kelch-like 1 knockout mice. Front Cell Neurosci 2015; 8:444. [PMID: 25610372 PMCID: PMC4285801 DOI: 10.3389/fncel.2014.00444] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Accepted: 12/10/2014] [Indexed: 11/30/2022] Open
Abstract
Kelch-like 1 (KLHL1) is a neuronal actin-binding protein that modulates voltage-gated CaV2.1 (P/Q-type) and CaV3.2 (α1H T-type) calcium channels; KLHL1 knockdown experiments (KD) cause down-regulation of both channel types and altered synaptic properties in cultured rat hippocampal neurons (Perissinotti et al., 2014). Here, we studied the effect of ablation of KLHL1 on calcium channel function and synaptic properties in cultured hippocampal neurons from KLHL1 knockout (KO) mice. Western blot data showed the P/Q-type channel α1A subunit was less abundant in KO hippocampus compared to wildtype (WT); and P/Q-type calcium currents were smaller in KO neurons than WT during early days in vitro, although this decrease was compensated for at late stages by increases in L-type calcium current. In contrast, T-type currents did not change in culture. However, biophysical properties and western blot analysis revealed a differential contribution of T-type channel isoforms in the KO, with CaV3.2 α1H subunit being down-regulated and CaV3.1 α1G up-regulated. Synapsin I levels were also reduced in the KO hippocampus and cultured neurons displayed a concomitant reduction in synapsin I puncta and decreased miniature excitatory postsynaptic current (mEPSC) frequency. In summary, genetic ablation of the calcium channel modulator resulted in compensatory mechanisms to maintain calcium current homeostasis in hippocampal KO neurons; however, synaptic alterations resulted in a reduction of excitatory synapse number, causing an imbalance of the excitatory-inhibitory synaptic input ratio favoring inhibition.
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Affiliation(s)
- Paula P Perissinotti
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA
| | - Elizabeth A Ethington
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA
| | - Erik Almazan
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA
| | - Elizabeth Martínez-Hernández
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA
| | - Jennifer Kalil
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA
| | - Michael D Koob
- Department of Laboratory Medicine and Pathology, Institute for Translational Neuroscience, University of Minnesota Minneapolis, MN, USA
| | - Erika S Piedras-Rentería
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA ; Neuroscience Institute, Loyola University Chicago, Stritch School of Medicine Maywood, IL, USA
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105
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Nakamura Y, Harada H, Kamasawa N, Matsui K, Rothman JS, Shigemoto R, Silver RA, DiGregorio DA, Takahashi T. Nanoscale distribution of presynaptic Ca(2+) channels and its impact on vesicular release during development. Neuron 2014; 85:145-158. [PMID: 25533484 PMCID: PMC4305191 DOI: 10.1016/j.neuron.2014.11.019] [Citation(s) in RCA: 163] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/14/2014] [Indexed: 01/05/2023]
Abstract
Synaptic efficacy and precision are influenced by the coupling of voltage-gated Ca2+ channels (VGCCs) to vesicles. But because the topography of VGCCs and their proximity to vesicles is unknown, a quantitative understanding of the determinants of vesicular release at nanometer scale is lacking. To investigate this, we combined freeze-fracture replica immunogold labeling of Cav2.1 channels, local [Ca2+] imaging, and patch pipette perfusion of EGTA at the calyx of Held. Between postnatal day 7 and 21, VGCCs formed variable sized clusters and vesicular release became less sensitive to EGTA, whereas fixed Ca2+ buffer properties remained constant. Experimentally constrained reaction-diffusion simulations suggest that Ca2+ sensors for vesicular release are located at the perimeter of VGCC clusters (<30 nm) and predict that VGCC number per cluster determines vesicular release probability without altering release time course. This “perimeter release model” provides a unifying framework accounting for developmental changes in both synaptic efficacy and time course. Ca2+ channels form clusters with highly variable numbers of channels EGTA sensitivity suggests that synaptic vesicles are tightly coupled to clusters Ca2+ channel number per cluster alters synaptic efficacy, but not precision A perimeter model accounts for synaptic efficacy and precision during development
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Affiliation(s)
- Yukihiro Nakamura
- Laboratory of Molecular Synaptic Function, Graduate School of Brain Science, Doshisha University, Kyoto 610-0394, Japan; Cellular & Molecular Synaptic Function Unit, Okinawa Institute of Science and Technology (OIST) Graduate University, Okinawa 904-0495, Japan; Laboratory of Dynamic Neuronal Imaging, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France; CNRS UMR 3571, 25 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Harumi Harada
- Division of Cerebral Structure, Department of Cerebral Research, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan; Institute of Science and Technology Austria, A-3400 Klosterneuburg, Austria
| | - Naomi Kamasawa
- Division of Cerebral Structure, Department of Cerebral Research, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan
| | - Ko Matsui
- Division of Cerebral Structure, Department of Cerebral Research, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan
| | - Jason S Rothman
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street London WC1E 6BT, UK
| | - Ryuichi Shigemoto
- Division of Cerebral Structure, Department of Cerebral Research, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan; Institute of Science and Technology Austria, A-3400 Klosterneuburg, Austria
| | - R Angus Silver
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street London WC1E 6BT, UK
| | - David A DiGregorio
- Laboratory of Dynamic Neuronal Imaging, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France; CNRS UMR 3571, 25 rue du Dr Roux, 75724 Paris Cedex 15, France.
| | - Tomoyuki Takahashi
- Laboratory of Molecular Synaptic Function, Graduate School of Brain Science, Doshisha University, Kyoto 610-0394, Japan; Cellular & Molecular Synaptic Function Unit, Okinawa Institute of Science and Technology (OIST) Graduate University, Okinawa 904-0495, Japan.
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106
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Leitz J, Kavalali ET. Fast retrieval and autonomous regulation of single spontaneously recycling synaptic vesicles. eLife 2014; 3:e03658. [PMID: 25415052 PMCID: PMC4270043 DOI: 10.7554/elife.03658] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 11/21/2014] [Indexed: 11/13/2022] Open
Abstract
Presynaptic terminals release neurotransmitters spontaneously in a manner that can be regulated by Ca(2+). However, the mechanisms underlying this regulation are poorly understood because the inherent stochasticity and low probability of spontaneous fusion events has curtailed their visualization at individual release sites. Here, using pH-sensitive optical probes targeted to synaptic vesicles, we visualized single spontaneous fusion events and found that they are retrieved extremely rapidly with faster re-acidification kinetics than their action potential-evoked counterparts. These fusion events were coupled to postsynaptic NMDA receptor-driven Ca(2+) signals, and at elevated Ca(2+) concentrations there was an increase in the number of vesicles that would undergo fusion. Furthermore, spontaneous vesicle fusion propensity in a synapse was Ca(2+)-dependent but regulated autonomously: independent of evoked fusion probability at the same synapse. Taken together, these results expand classical quantal analysis to incorporate endocytic and exocytic phases of single fusion events and uncover autonomous regulation of spontaneous fusion.
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Affiliation(s)
- Jeremy Leitz
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, United States
| | - Ege T Kavalali
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States
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107
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Jepson JEC, Shahidullah M, Liu D, le Marchand SJ, Liu S, Wu MN, Levitan IB, Dalva MB, Koh K. Regulation of synaptic development and function by the Drosophila PDZ protein Dyschronic. Development 2014; 141:4548-57. [PMID: 25359729 DOI: 10.1242/dev.109538] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Synaptic scaffold proteins control the localization of ion channels and receptors, and facilitate molecular associations between signaling components that modulate synaptic transmission and plasticity. Here, we define novel roles for a recently described scaffold protein, Dsychronic (DYSC), at the Drosophila larval neuromuscular junction. DYSC is the Drosophila homolog of whirlin/DFNB31, a PDZ domain protein linked to Usher syndrome, the most common form of human deaf-blindness. We show that DYSC is expressed presynaptically and is often localized adjacent to the active zone, the site of neurotransmitter release. Loss of DYSC results in marked alterations in synaptic morphology and cytoskeletal organization. Moreover, active zones are frequently enlarged and misshapen in dysc mutants. Electrophysiological analyses further demonstrate that dysc mutants exhibit substantial increases in both evoked and spontaneous synaptic transmission. We have previously shown that DYSC binds to and regulates the expression of the Slowpoke (SLO) BK potassium channel. Consistent with this, slo mutant larvae exhibit similar alterations in synapse morphology, active zone size and neurotransmission, and simultaneous loss of dysc and slo does not enhance these phenotypes, suggesting that dysc and slo act in a common genetic pathway to modulate synaptic development and output. Our data expand our understanding of the neuronal functions of DYSC and uncover non-canonical roles for the SLO potassium channel at Drosophila synapses.
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Affiliation(s)
- James E C Jepson
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA UCL Institute of Neurology, London WC1N 3BG, UK
| | - Mohammed Shahidullah
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Die Liu
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Sylvain J le Marchand
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Sha Liu
- Department of Neurology, John Hopkins University, Baltimore, MD 21287, USA
| | - Mark N Wu
- Department of Neurology, John Hopkins University, Baltimore, MD 21287, USA
| | - Irwin B Levitan
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Matthew B Dalva
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Kyunghee Koh
- Department of Neuroscience, The Farber Institute for Neurosciences, Thomas Jefferson University, Philadelphia, PA 19107, USA
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108
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Huo R, Xu WX, Han LM, He JL, Liu Y, Lu XL, Liu SZ, Yuan M, Chen H, Yan JL, Qiao GF, Li BY. Fine tuning of calcium on membrane excitation of baroreceptor neurons in rats. Int J Cardiol 2014; 174:883-7. [DOI: 10.1016/j.ijcard.2014.04.216] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Accepted: 04/19/2014] [Indexed: 11/17/2022]
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109
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Davydova D, Marini C, King C, Klueva J, Bischof F, Romorini S, Montenegro-Venegas C, Heine M, Schneider R, Schröder MS, Altrock WD, Henneberger C, Rusakov DA, Gundelfinger ED, Fejtova A. Bassoon specifically controls presynaptic P/Q-type Ca(2+) channels via RIM-binding protein. Neuron 2014; 82:181-94. [PMID: 24698275 DOI: 10.1016/j.neuron.2014.02.012] [Citation(s) in RCA: 118] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/28/2014] [Indexed: 12/11/2022]
Abstract
Voltage-dependent Ca(2+) channels (CaVs) represent the principal source of Ca(2+) ions that trigger evoked neurotransmitter release from presynaptic boutons. Ca(2+) influx is mediated mainly via CaV2.1 (P/Q-type) and CaV2.2 (N-type) channels, which differ in their properties. Their relative contribution to synaptic transmission changes during development and tunes neurotransmission during synaptic plasticity. The mechanism of differential recruitment of CaV2.1 and CaV2.2 to release sites is largely unknown. Here, we show that the presynaptic scaffolding protein Bassoon localizes specifically CaV2.1 to active zones via molecular interaction with the RIM-binding proteins (RBPs). A genetic deletion of Bassoon or an acute interference with Bassoon-RBP interaction reduces synaptic abundance of CaV2.1, weakens P/Q-type Ca(2+) current-driven synaptic transmission, and results in higher relative contribution of neurotransmission dependent on CaV2.2. These data establish Bassoon as a major regulator of the molecular composition of the presynaptic neurotransmitter release sites.
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Affiliation(s)
- Daria Davydova
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Claudia Marini
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Claire King
- Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Julia Klueva
- Molecular Physiology Group, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Ferdinand Bischof
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Stefano Romorini
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Carolina Montenegro-Venegas
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Martin Heine
- Molecular Physiology Group, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Romy Schneider
- Molecular Physiology Group, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Markus S Schröder
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
| | - Wilko D Altrock
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany; Center for Behavioral Brain Sciences and Medical Faculty, Otto von Guericke University, 39118 Magdeburg, Germany
| | - Christian Henneberger
- Institute of Neurology, University College London, London WC1N 3BG, UK; Institute of Cellular Neuroscience, Medical Faculty, University of Bonn, 53127 Bonn, Germany
| | - Dmitri A Rusakov
- Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Eckart D Gundelfinger
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany; Center for Behavioral Brain Sciences and Medical Faculty, Otto von Guericke University, 39118 Magdeburg, Germany.
| | - Anna Fejtova
- Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany; Presynaptic Plasticity Group, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany.
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110
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Largent-Milnes TM, Hegarty DM, Aicher SA, Andresen MC. Physiological temperatures drive glutamate release onto trigeminal superficial dorsal horn neurons. J Neurophysiol 2014; 111:2222-31. [PMID: 24598529 DOI: 10.1152/jn.00912.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Trigeminal sensory afferent fibers terminating in nucleus caudalis (Vc) relay sensory information from craniofacial regions to the brain and are known to express transient receptor potential (TRP) ion channels. TRP channels are activated by H(+), thermal, and chemical stimuli. The present study investigated the relationships among the spontaneous release of glutamate, temperature, and TRPV1 localization at synapses in the Vc. Spontaneous excitatory postsynaptic currents (sEPSCs) were recorded from Vc neurons (n = 151) in horizontal brain-stem slices obtained from Sprague-Dawley rats. Neurons had basal sEPSC rates that fell into two distinct frequency categories: High (≥10 Hz) or Low (<10 Hz) at 35°C. Of all recorded neurons, those with High basal release rates (67%) at near-physiological temperatures greatly reduced their sEPSC rate when cooled to 30°C without amplitude changes. Such responses persisted during blockade of action potentials indicating that the High rate of glutamate release arises from presynaptic thermal mechanisms. Neurons with Low basal frequencies (33%) showed minor thermal changes in sEPSC rate that were abolished after addition of TTX, suggesting these responses were indirect and required local circuits. Activation of TRPV1 with capsaicin (100 nM) increased miniature EPSC (mEPSC) frequency in 70% of neurons, but half of these neurons had Low basal mEPSC rates and no temperature sensitivity. Our evidence indicates that normal temperatures (35-37°C) drive spontaneous excitatory synaptic activity within superficial Vc by a mechanism independent of presynaptic action potentials. Thus thermally sensitive inputs on superficial Vc neurons may tonically activate these neurons without afferent stimulation.
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Affiliation(s)
- Tally M Largent-Milnes
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon
| | - Deborah M Hegarty
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon
| | - Sue A Aicher
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon
| | - Michael C Andresen
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon
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