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1
Keighron, Jacqueline D., Yuanmo Wang, and Ann-Sofie Cans. "Electrochemistry of Single-Vesicle Events." Annual Review of Analytical Chemistry 13, no. 1 (June 12, 2020): 159–81. http://dx.doi.org/10.1146/annurev-anchem-061417-010032.
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Neuronal transmission relies on electrical signals and the transfer of chemical signals from one neuron to another. Chemical messages are transmitted from presynaptic neurons to neighboring neurons through the triggered fusion of neurotransmitter-filled vesicles with the cell plasma membrane. This process, known as exocytosis, involves the rapid release of neurotransmitter solutions that are detected with high affinity by the postsynaptic neuron. The type and number of neurotransmitters released and the frequency of vesicular events govern brain functions such as cognition, decision making, learning, and memory. Therefore, to understand neurotransmitters and neuronal function, analytical tools capable of quantitative and chemically selective detection of neurotransmitters with high spatiotemporal resolution are needed. Electrochemistry offers powerful techniques that are sufficiently rapid to allow for the detection of exocytosis activity and provides quantitative measurements of vesicle neurotransmitter content and neurotransmitter release from individual vesicle events. In this review, we provide an overview of the most commonly used electrochemical methods for monitoring single-vesicle events, including recent developments and what is needed for future research.
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Omote, Hiroshi, and Yoshinori Moriyama. "Vesicular Neurotransmitter Transporters: An Approach for Studying Transporters With Purified Proteins." Physiology 28, no. 1 (January 2013): 39–50. http://dx.doi.org/10.1152/physiol.00033.2012.
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Vesicular storage and subsequent release of neurotransmitters are the key processes of chemical signal transmission. In this process, vesicular neurotransmitter transporters are responsible for loading the signaling molecules. The use of a “clean biochemical” approach with purified, recombinant transporters has helped in the identification of novel vesicular neurotransmitter transporters and in the analysis of the control of signal transmission.
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Chang, Che-Wei, Chung-Wei Chiang, and Meyer B. Jackson. "Fusion pores and their control of neurotransmitter and hormone release." Journal of General Physiology 149, no. 3 (February 6, 2017): 301–22. http://dx.doi.org/10.1085/jgp.201611724.
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Ca2+-triggered exocytosis functions broadly in the secretion of chemical signals, enabling neurons to release neurotransmitters and endocrine cells to release hormones. The biological demands on this process can vary enormously. Although synapses often release neurotransmitter in a small fraction of a millisecond, hormone release can be orders of magnitude slower. Vesicles usually contain multiple signaling molecules that can be released selectively and conditionally. Cells are able to control the speed, concentration profile, and content selectivity of release by tuning and tailoring exocytosis to meet different biological demands. Much of this regulation depends on the fusion pore—the aqueous pathway by which molecules leave a vesicle and move out into the surrounding extracellular space. Studies of fusion pores have illuminated how cells regulate secretion. Furthermore, the formation and growth of fusion pores serve as a readout for the progress of exocytosis, thus revealing key kinetic stages that provide clues about the underlying mechanisms. Herein, we review the structure, composition, and dynamics of fusion pores and discuss the implications for molecular mechanisms as well as for the cellular regulation of neurotransmitter and hormone release.
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Grabner, Chad P., and Aaron P. Fox. "Stimulus-Dependent Alterations in Quantal Neurotransmitter Release." Journal of Neurophysiology 96, no. 6 (December 2006): 3082–87. http://dx.doi.org/10.1152/jn.00017.2006.
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Neurotransmitter release is a steep function of the intracellular calcium ion concentration ([Ca2+]i) at the release sites. Both the Ca2+ amplitude and the time course appear to be important for specifying neurotransmitter release. Ca2+ influx regulates the number of vesicles exocytosed as well as the amount of neurotransmitter each individual vesicle releases. In our study we stimulated mouse chromaffin cells in two different ways to alter Ca2+ presentation at the release sites. One method, digitonin permeabilization followed by exposure to Ca2+, allows for a large uniform global elevation of [Ca2+]i, whereas the second method, application of nicotine, depolarizes chromaffin cells and activates voltage-dependent Ca2+ channels, thereby producing more phasic and localized changes in [Ca2+]i. Using amperometry to monitor catecholamine release, we show that both kinds of stimuli elicit the exocytosis of similar quantities of neurotransmitter per large dense core vesicles (LDCVs) released. Even so, the release process was quite different for each stimulus; nicotine-elicited events were small and slow, whereas digitonin events were, in comparison, large and fast. In addition, the transient opening of the fusion pore, called the “foot,” was essentially absent in digitonin-stimulated cells, but was quite common in nicotine-stimulated cells. Thus even though both strong stimuli used in this study elicited the release of many vesicles it appears that the differences in the Ca2+ levels at the release sites were key determinants for the fusion and release of individual vesicles.
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Benfenati, Fabio, Franco Onofri, and Silvia Giovedí. "Protein–protein interactions and protein modules in the control of neurotransmitter release." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 354, no. 1381 (February 28, 1999): 243–57. http://dx.doi.org/10.1098/rstb.1999.0376.
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Information transfer among neurons is operated by neurotransmitters stored in synaptic vesicles and released to the extracellular space by an efficient process of regulated exocytosis. Synaptic vesicles are organized into two distinct functional pools, a large reserve pool in which vesicles are restrained by the actin–based cytoskeleton, and a quantitatively smaller releasable pool in which vesicles approach the presynaptic membrane and eventually fuse with it on stimulation. Both synaptic vesicle trafficking and neurotransmitter release depend on a precise sequence of events that include release from the reserve pool, targeting to the active zone, docking, priming, fusion and endocytotic retrieval of synaptic vesicles. These steps are mediated by a series of specific interactions among cytoskeletal, synaptic vesicle, presynaptic membrane and cytosolic proteins that, by acting in concert, promote the spatial and temporal regulation of the exocytotic machinery. The majority of these interactions are mediated by specific protein modules and domains that are found in many proteins and are involved in numerous intracellular processes. In this paper, the possible physiological role of these multiple protein–protein interactions is analysed, with ensuing updating and clarification of the present molecular model of the process of neurotransmitter release.
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Kupchik, Yonatan M., Ofra Barchad-Avitzur, Jürgen Wess, Yair Ben-Chaim, Itzchak Parnas, and Hanna Parnas. "A novel fast mechanism for GPCR-mediated signal transduction—control of neurotransmitter release." Journal of Cell Biology 192, no. 1 (January 3, 2011): 137–51. http://dx.doi.org/10.1083/jcb.201007053.
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Reliable neuronal communication depends on accurate temporal correlation between the action potential and neurotransmitter release. Although a requirement for Ca2+ in neurotransmitter release is amply documented, recent studies have shown that voltage-sensitive G protein–coupled receptors (GPCRs) are also involved in this process. However, how slow-acting GPCRs control fast neurotransmitter release is an unsolved question. Here we examine whether the recently discovered fast depolarization-induced charge movement in the M2-muscarinic receptor (M2R) is responsible for M2R-mediated control of acetylcholine release. We show that inhibition of the M2R charge movement in Xenopus oocytes correlated well with inhibition of acetylcholine release at the mouse neuromuscular junction. Our results suggest that, in addition to Ca2+ influx, charge movement in GPCRs is also necessary for release control.
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Liu, Tianshu, Pankaj Singh, James T. Jenkins, Anand Jagota, Maria Bykhovskaia, and Chung-Yuen Hui. "A continuum model of docking of synaptic vesicle to plasma membrane." Journal of The Royal Society Interface 12, no. 102 (January 2015): 20141119. http://dx.doi.org/10.1098/rsif.2014.1119.
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Neurotransmitter release from neuronal terminals is governed by synaptic vesicle fusion. Vesicles filled with transmitters are docked at the neuronal membrane by means of the SNARE machinery. After a series of events leading up to the fusion pore formation, neurotransmitters are released into the synaptic cleft. In this paper, we study the mechanics of the docking process. A continuum model is used to determine the deformation of a spherical vesicle and a plasma membrane, under the influence of SNARE-machinery forces and electrostatic repulsion. Our analysis provides information on the variation of in-plane stress in the membranes, which is known to affect fusion. Also, a simple model is proposed to study hemifusion.
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Mochida, S., S. Orita, G. Sakaguchi, T. Sasaki, and Y. Takai. "Role of the Doc2 -Munc13-1 interaction in the neurotransmitter release process." Proceedings of the National Academy of Sciences 95, no. 19 (September 15, 1998): 11418–22. http://dx.doi.org/10.1073/pnas.95.19.11418.
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Arroyo, Gloria, Jorge Fuentealba, Natalia Sevane-Fernández, Marcos Aldea, Antonio G. García, and Almudena Albillos. "Amperometric Study of the Kinetics of Exocytosis in Mouse Adrenal Slice Chromaffin Cells: Physiological and Methodological Insights." Journal of Neurophysiology 96, no. 3 (September 2006): 1196–202. http://dx.doi.org/10.1152/jn.00088.2006.
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This study was designed to examine the kinetics of neurotransmitter release using the carbon fiber amperometric technique on cells in slices of mouse adrenal glands superfused with bicarbonate phosphate buffer–based solutions. The exocytotic amperometric response evoked by electrical stimulation was significantly faster than that produced after exogenous application of ACh or K+. Splanchnic nerve–evoked neurotransmitter release was blocked by hexamethonium, indicating the involvement of ACh nicotinic receptors. We discuss the implications of our data for understanding the mechanisms underlying the vesicle fusion process.
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Boll, Inga, Pia Jensen, Veit Schwämmle, and Martin R. Larsen. "Depolarization-dependent Induction of Site-specific Changes in Sialylation on N-linked Glycoproteins in Rat Nerve Terminals." Molecular & Cellular Proteomics 19, no. 9 (June 9, 2020): 1418–35. http://dx.doi.org/10.1074/mcp.ra119.001896.
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Synaptic transmission leading to release of neurotransmitters in the nervous system is a fast and highly dynamic process. Previously, protein interaction and phosphorylation have been thought to be the main regulators of synaptic transmission. Here we show that sialylation of N-linked glycosylation is a novel potential modulator of neurotransmitter release mechanisms by investigating depolarization-dependent changes of formerly sialylated N-linked glycopeptides. We suggest that negatively charged sialic acids can be modulated, similarly to phosphorylation, by the action of sialyltransferases and sialidases thereby changing local structure and function of membrane glycoproteins. We characterized site-specific alteration in sialylation on N-linked glycoproteins in isolated rat nerve terminals after brief depolarization using quantitative sialiomics. We identified 1965 formerly sialylated N-linked glycosites in synaptic proteins and found that the abundances of 430 glycosites changed after 5 s depolarization. We observed changes on essential synaptic proteins such as synaptic vesicle proteins, ion channels and transporters, neurotransmitter receptors and cell adhesion molecules. This study is to our knowledge the first to describe ultra-fast site-specific modulation of the sialiome after brief stimulation of a biological system.
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Lamanna, Jacopo, Antonio Malgaroli, Sergio Cerutti, and Maria G. Signorini. "Detection of Fractal Behavior in Temporal Series of Synaptic Quantal Release Events: A Feasibility Study." Computational Intelligence and Neuroscience 2012 (2012): 1–9. http://dx.doi.org/10.1155/2012/704673.
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Since the pioneering work of Fatt and Katz at the neuromuscular junction (NMJ), spontaneous synaptic release (minis), that is, the quantal discharge of neurotransmitter molecules which occurs in the absence of action potentials, has been unanimously considered a memoryless random Poisson process where each quantum is discharged with a very low release probability independently from other quanta. When this model was thoroughly tested, for both population and single-synapse recordings, some clear evidence in favor of a more complex scenario emerged. This included short- and long-range correlation in mini occurrences and divergence from mono-exponential inter-mini-interval distributions, both unexpected for a homogeneous Poisson process, that is, with a rate parameter that does not change over time. Since we are interested in accurately quantifying the fractal exponentαof the spontaneous neurotransmitter release process at central synaptic sites, this work was aimed at evaluating the sensitivity of the most established methods available, such as the periodogram, the Allan, factor and the detrended fluctuation analysis. For this analysis we matched spontaneous release series recorded at individual hippocampal synapses (single-synapse recordings) to generate large collections of simulated quantal events by means of a custom algorithm combining Monte Carlo sampling methods with spectral methods for the generation of1/fseries. These tests were performed by varying separately: (i) the fractal exponentαof the rate driving the release process; (ii) the distribution of intervals between successive releases, mimicking those encountered in single-synapse experimental series; (iii) the number of samples. The aims were to provide a methodological framework for approaching the fractal analysis of single-unit spontaneous release series recorded at central synapses.
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Puffer, Erik B., Richard B. Lomneth, Hemanta K. Sarkar, and Bal Ram Singh. "Differential Roles of Developmentally Distinct SNAP-25 Isoforms in the Neurotransmitter Release Process†." Biochemistry 40, no. 31 (August 2001): 9374–78. http://dx.doi.org/10.1021/bi010362z.
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Deloye, F., F. Cornille, M. C. Fournié-Zaluski, B. Poulain, and B. P. Roques. "Identification of a v-snare domain playing roles in the neurotransmitter release process." Journal of Physiology-Paris 88, no. 6 (January 1994): 388. http://dx.doi.org/10.1016/0928-4257(94)90054-x.
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Schiavo, Giampietro, Michela Matteoli, and Cesare Montecucco. "Neurotoxins Affecting Neuroexocytosis." Physiological Reviews 80, no. 2 (January 4, 2000): 717–66. http://dx.doi.org/10.1152/physrev.2000.80.2.717.
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Nerve terminals are specific sites of action of a very large number of toxins produced by many different organisms. The mechanism of action of three groups of presynaptic neurotoxins that interfere directly with the process of neurotransmitter release is reviewed, whereas presynaptic neurotoxins acting on ion channels are not dealt with here. These neurotoxins can be grouped in three large families: 1) the clostridial neurotoxins that act inside nerves and block neurotransmitter release via their metalloproteolytic activity directed specifically on SNARE proteins; 2) the snake presynaptic neurotoxins with phospholipase A2activity, whose site of action is still undefined and which induce the release of acethylcholine followed by impairment of synaptic functions; and 3) the excitatory latrotoxin-like neurotoxins that induce a massive release of neurotransmitter at peripheral and central synapses. Their modes of binding, sites of action, and biochemical activities are discussed in relation to the symptoms of the diseases they cause. The use of these toxins in cell biology and neuroscience is considered as well as the therapeutic utilization of the botulinum neurotoxins in human diseases characterized by hyperfunction of cholinergic terminals.
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Gingrich, K. J., and J. H. Byrne. "Simulation of synaptic depression, posttetanic potentiation, and presynaptic facilitation of synaptic potentials from sensory neurons mediating gill-withdrawal reflex in Aplysia." Journal of Neurophysiology 53, no. 3 (March 1, 1985): 652–69. http://dx.doi.org/10.1152/jn.1985.53.3.652.
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The defensive gill-withdrawal reflex in Aplysia has proven to be an attractive system for analyzing the neural mechanisms underlying simple forms of learning such as habituation, sensitization, and classic conditioning. Previous studies have shown that habituation is associated with synaptic depression and sensitization with presynaptic facilitation of transmitter release from sensory neurons mediating the reflex. The synaptic depression, in turn, is associated with a decrease in Ca2+ currents in the sensory neurons, whereas presynaptic facilitation with increased Ca2+ currents produced indirectly by a decrease in a novel serotonergic sensitive K+ current. The present work represents an initial quantitative examination of the extent to which these mechanisms account for each of these types of synaptic plasticity. To address these issues a lumped parameter mathematical model of the sensory neuron release process was constructed. Major components of this model include Ca2+-channel inactivation, Ca2+-mediated neurotransmitter release and mobilization, and readily releasable and upstream feeding pools of neurotransmitter. In the model, release of neurotransmitter has a linear function of Ca2+ concentration and is not affected directly by residual Ca2+. The model not only simulates the data of synaptic depression and recovery from depression, but also qualitatively predicts other features of neurotransmitter release that it was not designed to fit. These include features of synaptic depression with high and low levels of transmitter release, posttetanic potentiation, a steep relationship between action potential duration and transmitter release, enhanced release produced by broadening the sensory neuron action potential (presynaptic facilitation), and dramatic synaptic depression with two closely spaced tetraethylammonium (TEA) spikes. The model cannot account fully for synaptic depression with empirically observed somatic Ca2+-current kinetics. Rather a large component of synaptic depression is due to reduction to the pools of releasable neurotransmitter (depletion). In the model when spike durations are greater than 15-20 ms, spike broadening produces little facilitation. However, when spike durations are more physiological, spike broadening leads to enhanced transmitter release.
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Ravin, R., H. Parnas, M. E. Spira, and I. Parnas. "Partial Uncoupling of Neurotransmitter Release From [Ca2+]i by Membrane Hyperpolarization." Journal of Neurophysiology 81, no. 6 (June 1, 1999): 3044–53. http://dx.doi.org/10.1152/jn.1999.81.6.3044.
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Partial uncoupling of neurotransmitter release from [Ca2+]i by membrane hyperpolarization. The dependence of evoked and asynchronous release on intracellular calcium ([Ca2+]i) and presynaptic membrane potential was examined in single-release boutons of the crayfish opener neuromuscular junction. When a single bouton was depolarized by a train of pulses, [Ca2+]iincreased to different levels according to the frequency of stimulation. Concomitant measurements of evoked release and asynchronous release, from the same bouton, showed that both increased in a sigmoidal manner as a function of [Ca2+]i. When each of the depolarizing pulses was immediately followed by a hyperpolarizing pulse, [Ca2+]i was elevated to a lesser degree than in the control experiments, and the rate of asynchronous release and the quantal content were reduced; most importantly, evoked quantal release terminated sooner. The diminution of neurotransmitter release by the hyperpolarizing postpulse (HPP) could not be entirely accounted for by the reduction in [Ca2+]i. The experimental results are consistent with the hypothesis that the HPP reduces the sensitivity of the release machinery to [Ca2+]i, thereby not only reducing the quantal content but also terminating the quantal release process sooner.
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Schlame, Michael, and Hugh C. Jr Hemmings. "Inhibition by Volatile Anesthetics of Endogenous Glutamate Release from Synaptosomes by a Presynaptic Mechanism." Anesthesiology 82, no. 6 (June 1, 1995): 1406–16. http://dx.doi.org/10.1097/00000542-199506000-00012.
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Background Synaptic transmission is more sensitive than axonal conduction to the effects of general anesthetics. Previous studies of the synaptic effects of general anesthetics have focused on postsynaptic sites of action. We now provide direct biochemical evidence for a presynaptic effect of volatile anesthetics on neurotransmitter release. Methods Rat cerebrocortical synaptosomes (isolated presynaptic nerve terminals) were used to determine the effects of general anesthetics on the release of endogenous L-glutamate, the major fast excitatory neurotransmitter. Basal and evoked (by 4-aminopyridine, veratridine, increased KCl, or ionomycin) glutamate release were measured by continuous enzyme-coupled fluorometry. Results Clinical concentrations of volatile halogenated anesthetics, but not of pentobarbital, inhibited 4-aminopyridine-evoked Ca(2+)-dependent glutamate release. Halothane also inhibited veratridine-evoked glutamate release but not basal, KCl-evoked, or ionomycin-evoked glutamate release. Halothane inhibited both the 4-aminopyridine-evoked and the KCl-evoked increase in free intrasynaptosomal [Ca2+]. Conclusions Inhibition of glutamate release from presynaptic nerve terminals is a potential mechanism of volatile anesthetic action. Comparison of the sensitivity of glutamate release evoked by secretogogues that act at various steps in the neurotransmitter release process suggests that halothane does not affect Ca(2+)-secretion coupling or vesicle exocytosis but inhibits glutamate release at a step proximal to Ca2+ influx, perhaps by blocking presynaptic Na+ channels. Synaptosomal glutamate release evoked by 4-aminopyridine should provide a useful system for further characterization of the presynaptic effects of anesthetics.
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Radhakrishnan, Abhijith, Xia Li, Kirill Grushin, Shyam S. Krishnakumar, Jun Liu, and James E. Rothman. "Symmetrical arrangement of proteins under release-ready vesicles in presynaptic terminals." Proceedings of the National Academy of Sciences 118, no. 5 (January 19, 2021): e2024029118. http://dx.doi.org/10.1073/pnas.2024029118.
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Controlled release of neurotransmitters stored in synaptic vesicles (SVs) is a fundamental process that is central to all information processing in the brain. This relies on tight coupling of the SV fusion to action potential-evoked presynaptic Ca2+ influx. This Ca2+-evoked release occurs from a readily releasable pool (RRP) of SVs docked to the plasma membrane (PM). The protein components involved in initial SV docking/tethering and the subsequent priming reactions which make the SV release ready are known. Yet, the supramolecular architecture and sequence of molecular events underlying SV release are unclear. Here, we use cryoelectron tomography analysis in cultured hippocampal neurons to delineate the arrangement of the exocytosis machinery under docked SVs. Under native conditions, we find that vesicles are initially “tethered” to the PM by a variable number of protein densities (∼10 to 20 nm long) with no discernible organization. In contrast, we observe exactly six protein masses, each likely consisting of a single SNAREpin with its bound Synaptotagmins and Complexin, arranged symmetrically connecting the “primed” vesicles to the PM. Our data indicate that the fusion machinery is likely organized into a highly cooperative framework during the priming process which enables rapid SV fusion and neurotransmitter release following Ca2+ influx.
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Kittel, R. J., S. Hallermann, S. Thomsen, C. Wichmann, S. J. Sigrist, and M. Heckmann. "Active zone assembly and synaptic release." Biochemical Society Transactions 34, no. 5 (October 1, 2006): 939–41. http://dx.doi.org/10.1042/bst0340939.
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Neurotransmitter release at chemical synapses occurs when synaptic vesicles fuse to the presynaptic membrane at a specialized site termed the active zone. The depolarization-induced fusion is highly dependent on calcium ions, and, correspondingly, the transmission characteristics of synapses are thought to be influenced by the spatial arrangement of voltage-gated calcium channels with respect to vesicle release sites. Here, we review the involvement of the Drosophila Bruchpilot (BRP) protein in active zone assembly, a process that is required for the clustering of presynaptic calcium channels to ensure efficient vesicle release.
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Schmich, Robert M., and Michael I. Miller. "Stochastic Threshold Characterization of the Intensity of Active Channel Dynamical Action Potential Generation." Journal of Neurophysiology 78, no. 5 (November 1, 1997): 2616–30. http://dx.doi.org/10.1152/jn.1997.78.5.2616.
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Schmich, Robert M. and Michael I. Miller. Stochastic threshold characterization of the intensity of active channel dynamical action potential generation. J. Neurophysiol. 78: 2616–2630, 1997. This paper develops a stochastic intensity description for action potential generation formulated in terms of stochastic processes, which are direct analogues of the physiological processes of the pre- and postsynaptic complex of the cochlear nerve: 1) neurotransmitter release is modeled as an inhomogeneous Poisson counting process with release intensity μ t , 2) the excitatory postsynaptic conductance (EPSC) process is modeled as a marked, linearly filtered Poisson process resulting from the linear superposition of standard shaped postsynaptic conductances of size G, and 3) action potential generation is modeled as resulting from the EPSC exceeding a random threshold determined by active channel dynamics of the Hodgkin-Huxley type. The random threshold is defined to be the least upper bound in the size of a standard-shaped neurotransmitter release injected at time t given the previous action potential time and the number of releases occurring in a short preconditioning time increment. The action potential process is modeled as a self-exciting point process with stochastic intensity resulting from the probability that the random threshold process crosses the threshold in some small time increment that is a function of time since previous action potential, release intensity, and the probability that a single synaptic event exceeds the stochastic threshold. The stochastic intensity model is consistent with a direct simulation of the nonlinear Hodgkin-Huxley differential equations over a variety of parameters for the vesicle release intensity, vesicle size, vesicle duration, and temperatures. Results are presented showing that the regularity properties seen in the vestibular primary afferent in the lizard, Calotes versicolor, associated with a slow-to-activate potassium channel resulting in a long afterhyperpolarization can be accommodated directly by the stochastic intensity description. The stimulus dependence of the model is attributed to synaptic transmission and the probabilistic nature to the threshold conductance process, which is dependent upon the EPSC process. The stochastic intensity is seen to have a form consistent with the phenomenologically based Siebert-Gaumond model, a stimulus-related function of time multiplied by a refractory-related function of time since previous action potential.
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Reynier-Rebuffel, A. M., J. Callebert, J. M. Launay, J. Seylaz, and P. Aubineau. "NE inhibits cerebrovascular mast cell exocytosis induced by cholinergic and peptidergic agonists." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 273, no. 3 (September 1, 1997): R845—R850. http://dx.doi.org/10.1152/ajpregu.1997.273.3.r845.
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Autonomic and sensory nerves frequently contact mast cells contained in rabbit leptomeningeal arteries. We have previously shown that parasympathetic and peptidergic neurotransmitters can stimulate mast cell granule exocytosis and serotonin (5-HT) release. In the present study, we examined ex vivo the possible action of the main sympathetic neurotransmitter, norepinephrine (NE), on this exocytotic process. NE, which had no effect on mast cell 5-HT content per se, totally inhibited carbachol-induced 5-HT release and partially reduced neuropeptide-induced 5-HT release. Pretreatment with the alpha 1-adrenergic blocker did not affect the inhibitory effect of NE. Pretreatment with specific beta 1- or beta 2-adrenergic blockers antagonized this action, but the beta 2-blocker exerts a more specific dose-dependent antagonism. Together with our previous data, these results indicate that the equilibrium between autonomic and sensory nerves may determine the release of 5-HT from mast cells (parasympathetic and sensory nerves can trigger exocytosis while the sympathetics can inhibit it). Such a mechanism could be implicated in pathophysiological events in which autonomic dysfunction is likely to be involved, such as vascular headache or other phenomena involving inflammation.
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Dhandapani, Krishnan M., and Darrell W. Brann. "The role of glutamate and nitric oxide in the reproductive neuroendocrine system." Biochemistry and Cell Biology 78, no. 3 (April 2, 2000): 165–79. http://dx.doi.org/10.1139/o00-015.
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The preovulatory surge of gonadotropin releasing hormone (GnRH) is essential for mammalian reproduction. Recent work has implicated the neurotransmitters glutamate and nitric oxide as having a key role in this process. Large concentrations of glutamate are found in several hypothalamic nuclei known to be important for GnRH release and glutamate receptors are also located in these key hypothalamic nuclei. Administration of glutamate agonists stimulate GnRH and LH release, while glutamate receptor antagonists attenuate the steroid-induced and preovulatory LH surge. Glutamate has also been implicated in the critical processes of puberty, hormone pulsatility, and sexual behavior. Glutamate is believed to elicit many of these effects by activating the release of the gaseous neurotransmitter, nitric oxide (NO). NO potently stimulates GnRH by activating a heme containing enzyme, guanylate cyclase, which in turn leads to increased production of cGMP and GnRH release. Recent work has focused on identifying anchoring and (or) clustering proteins that target glutamate receptors to the synapse and couple the glutamate-NO neurotransmission system. The present review will discuss these new findings, as well as the role of glutamate and nitric oxide in important mammalian reproductive events, with a focus on the hypothalamic control of preovulatory GnRH release. Key words: glutamate, nitric oxide, GnRH, postsynaptic density, hypothalamus.
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Kiragasi, Beril, Pragya Goel, Sarah Perry, Yifu Han, Xiling Li, and Dion Dickman. "The auxiliary glutamate receptor subunit dSol-1 promotes presynaptic neurotransmitter release and homeostatic potentiation." Proceedings of the National Academy of Sciences 117, no. 41 (September 24, 2020): 25830–39. http://dx.doi.org/10.1073/pnas.1915464117.
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Presynaptic glutamate receptors (GluRs) modulate neurotransmitter release and are physiological targets for regulation during various forms of plasticity. Although much is known about the auxiliary subunits associated with postsynaptic GluRs, far less is understood about presynaptic auxiliary GluR subunits and their functions. At theDrosophilaneuromuscular junction, a presynaptic GluR,DKaiR1D, localizes near active zones and operates as an autoreceptor to tune baseline transmission and enhance presynaptic neurotransmitter release in response to diminished postsynaptic GluR functionality, a process referred to as presynaptic homeostatic potentiation (PHP). Here, we identify an auxiliary subunit that collaborates with DKaiR1D to promote these synaptic functions. This subunit, dSol-1, is the homolog of theCaenorhabditis elegansCUB (Complement C1r/C1s, Uegf, Bmp1) domain protein Sol-1. We find thatdSol-1functions in neurons to facilitate baseline neurotransmission and to enable PHP expression, properties shared withDKaiR1D. Intriguingly, presynaptic overexpression ofdSol-1is sufficient to enhance neurotransmitter release through aDKaiR1D-dependent mechanism. Furthermore,dSol-1is necessary to rapidly increase the abundance of DKaiR1D receptors near active zones during homeostatic signaling. Together with recent work showing the CUB domain protein Neto2 is necessary for the homeostatic modulation of postsynaptic GluRs in mammals, our data demonstrate that dSol-1 is required for the homeostatic regulation of presynaptic GluRs. Thus, we propose that CUB domain proteins are fundamental homeostatic modulators of GluRs on both sides of the synapse.
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Johannes, L., F. Doussau, A. Clabecq, J. P. Henry, F. Darchen, and B. Poulain. "Evidence for a functional link between Rab3 and the SNARE complex." Journal of Cell Science 109, no. 12 (December 1, 1996): 2875–84. http://dx.doi.org/10.1242/jcs.109.12.2875.
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Rab3 is a monomeric GTP-binding protein associated with secretory vesicles which has been implicated in the control of regulated exocytosis. We have exploited Rab3 mutant proteins to investigate the function of Rab3 in the process of neurotransmitter release from Aplysia neurons. A GTPase-deficient Rab3 mutant protein was found to inhibit acetylcholine release suggesting that GTP hydrolysis by Rab3 is rate-limiting in the exocytosis process. This effect was abolished by a mutation in the effector domain, and required the association of Rab3 with membranes. In order to determine the step at which Rab3 interferes with the secretory process, tetanus and botulinum type A neurotoxins were applied to Aplysia neurons pre-injected with the GTPase-deficient Rab3 mutant protein. These neurotoxins are Zn(2+)-dependent proteases that cleave VAMP/synaptobrevin and SNAP-25, two proteins which can form a ternary complex (termed the SNARE complex) with syntaxin and have been implicated in the docking of synaptic vesicles at the plasma membrane. The onset of toxin-induced inhibition of neurotransmitter release was strongly delayed in these cells, indicating that the mutant Rab3 protein led to the accumulation of a toxin-insensitive component of release. Since tetanus and botulinum type A neurotoxins cannot attack their targets, VAMP/synaptobrevin and SNAP-25, when the latter are engaged in the SNARE complex, we propose that Rab3 modulates the activity of the fusion machinery by controlling the formation or the stability of the SNARE complex.
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Trudeau, Louis-Eric, Vladimir Parpura, and Philip G. Haydon. "Activation of Neurotransmitter Release in Hippocampal Nerve Terminals During Recovery From Intracellular Acidification." Journal of Neurophysiology 81, no. 6 (June 1, 1999): 2627–35. http://dx.doi.org/10.1152/jn.1999.81.6.2627.
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Activation of neurotransmitter release in hippocampal nerve terminals during recovery from intracellular acidification. Intracellular pH may be an important variable regulating neurotransmitter release. A number of pathological conditions, such as anoxia and ischemia, are known to influence intracellular pH, causing acidification of brain cells and excitotoxicity. We examined the effect of acidification on quantal glutamate release. Although acidification caused only modest changes in release, recovery from acidification was associated with a very large (60-fold) increase in the frequency of miniature excitatory postsynaptic currents (mEPSCs) in cultured hippocampal neurons. This was accompanied by a block of evoked EPSCs and a rise in intracellular free Ca2+([Ca2+]i). The rise in mEPSC frequency required extracellular Ca2+, but influx did not occur through voltage-operated channels. Because acidic pH is known to activate the Na+/H+ antiporter, we hypothesized that a resulting Na+ load could drive Ca2+influx through the Na+/Ca2+ exchanger during recovery from acidification. This hypothesis is supported by three observations. First, intracellular Na+ rises during acidification. Second, the elevation in [Ca2+]i and mEPSC frequency during recovery from acidification is prevented by the Na+/H+antiporter blocker EIPA applied during the acidification step. Third, the rise in free Ca2+ and mEPSC frequency is blocked by the Na+/Ca2+ exchanger blocker dimethylbenzamil. We thus propose that during recovery from intracellular acidification a massive activation of neurotransmitter release occurs because the successive activation of the Na+/H+ and Na+/Ca2+ exchangers in nerve terminals leads to an elevation of intracellular calcium. Our results suggest that changes in intracellular pH and especially recovery from acidification have extensive consequences for the release process in nerve terminals. Excessive release of glutamate through the proposed mechanism could be implicated in excitotoxic insults after anoxic or ischemic episodes.
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Fujita, Yasuyuki, Hiromichi Shirataki, Toshiaki Sakisaka, Takeshi Asakura, Takeshi Ohya, Hirokazu Kotani, Shigekazu Yokoyama, et al. "Tomosyn: a Syntaxin-1–Binding Protein that Forms a Novel Complex in the Neurotransmitter Release Process." Neuron 20, no. 5 (May 1998): 905–15. http://dx.doi.org/10.1016/s0896-6273(00)80472-9.
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Zakharenko, Stanislav, Sunghoe Chang, Michael O'Donoghue, and Sergey V. Popov. "Neurotransmitter Secretion along Growing Nerve Processes: Comparison with Synaptic Vesicle Exocytosis." Journal of Cell Biology 144, no. 3 (February 8, 1999): 507–18. http://dx.doi.org/10.1083/jcb.144.3.507.
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In mature neurons, synaptic vesicles continuously recycle within the presynaptic nerve terminal. In developing axons which are free of contact with a postsynaptic target, constitutive membrane recycling is not localized to the nerve terminal; instead, plasma membrane components undergo cycles of exoendocytosis throughout the whole axonal surface (Matteoli et al., 1992; Kraszewski et al., 1995). Moreover, in growing Xenopus spinal cord neurons in culture, acetylcholine (ACh) is spontaneously secreted in the quantal fashion along the axonal shaft (Evers et al., 1989; Antonov et al., 1998). Here we demonstrate that in Xenopus neurons ACh secretion is mediated by vesicles which recycle locally within the axon. Similar to neurotransmitter release at the presynaptic nerve terminal, ACh secretion along the axon could be elicited by the action potential or by hypertonic solutions. We found that the parameters of neurotransmitter secretion at the nerve terminal and at the middle axon were strikingly similar. These results lead us to conclude that, as in the case of the presynaptic nerve terminal, synaptic vesicles involved in neurotransmitter release along the axon contain a complement of proteins for vesicle docking and Ca2+-dependent fusion. Taken together, our results support the idea that, in developing axons, the rudimentary machinery for quantal neurotransmitter secretion is distributed throughout the whole axonal surface. Maturation of this machinery in the process of synaptic development would improve the fidelity of synaptic transmission during high-frequency stimulation of the presynaptic cell.
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Peng, Xiao-Rong, Zhengping Jia, Yu Zhang, Jerry Ware, and William S. Trimble. "The Septin CDCrel-1 Is Dispensable for Normal Development and Neurotransmitter Release." Molecular and Cellular Biology 22, no. 1 (January 1, 2002): 378–87. http://dx.doi.org/10.1128/mcb.22.1.378-387.2002.
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ABSTRACT Septins are GTPases required for the completion of cytokinesis in a variety of organisms, yet their role in this process is not known. Septins may have additional functions since the mammalian septin CDCrel-1 is predominantly expressed in the nervous system, a largely postmitotic tissue. While relatively little is known about the function of this protein, we have previously shown that it is involved in regulated secretion. In addition, the gene encoding this protein maps to a locus often deleted in velo-cardiofacial and DiGeorge syndromes, and CDCrel-1 has recently been shown to be a direct target of the E3 ubiquitin ligase activity of Parkin, a causative agent in autosomal recessive forms of Parkinson’s disease. Here we show that CDCrel-1 expression rises at the time of synaptic maturation and that CDCrel-1 is present in a complex that includes the septins Nedd5 and CDC10. To investigate its function in the nervous system, we generated homozygotic CDCrel-1 null mice and showed that these mice appear normal with respect to synaptic properties and hippocampal neuron growth in vitro. Moreover, we found that while the expression of a number of synaptic proteins is not affected in the CDCrel-1 mutant mice, the expression of other septins is altered. Together, these data suggest that CDCrel-1 is not essential for neuronal development or function, and that changes in expression of other septins may account for its functional redundancy.
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Zhang, Min, and Colin A. Nurse. "CO2/pH Chemosensory Signaling in Co-Cultures of Rat Carotid Body Receptors and Petrosal Neurons: Role of ATP and ACh." Journal of Neurophysiology 92, no. 6 (December 2004): 3433–45. http://dx.doi.org/10.1152/jn.01099.2003.
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The neurotransmitter mechanisms that process acid hypercapnia in the mammalian carotid body (CB) are poorly understood. Using a co-culture model containing rat CB chemoreceptor (type 1 cell) clusters and petrosal neurons (PN), we tested the hypothesis that co-released ACh and ATP was an important mechanism. Sensory transmission from type I clusters to PN in co-culture occurred at chemical synapses via co-release of ATP and ACh because isohydric hypercapnia depolarized and/or increased firing in co-cultured PN, but not in PN cultured alone; PN chemoexcitatory responses were inhibited by decreasing the extracellular Ca2+: Mg2+ ratio; partial inhibition of these responses occurred during separate perfusion of cholinergic (hexamethonium or mecamylamine) and P2X (suramin) receptor blockers, although inhibition was often complete with both blockers present; and rapid chemoexcitatory responses to hypercapnia were inhibited by acetazolamide (10 μM), an inhibitor of carbonic anhydrase, localized in type I cells. Acidosis (pH = 7.0, 7.2) enhanced the ATP-induced whole cell current in functional PN relative to that at physiologic pH (7.4), suggesting that increased sensitivity of postsynaptic P2X receptors may contribute to acid chemotransmission. Type I cells in CB tissue sections expressed vesicular acetylcholine transporter (VAChT), a cholinergic marker, as revealed by confocal immunofluorescence. Thus co-release of ACh and ATP is an important neurotransmitter mechanism for processing isohydric and acidic hypercapnia in the rat carotid body.
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Webb, Rodney A. "Release of exogenously supplied [3H]glutamate and endogenous glutamate from tissue slices of the cestode Hymenolepis diminuta." Canadian Journal of Physiology and Pharmacology 66, no. 7 (July 1, 1988): 889–94. http://dx.doi.org/10.1139/y88-145.
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The effect of high potassium depolarization on the release of exogenously supplied [3H]glutamate and endogenous glutamate from tissue slices of the cestode Hymenolepis diminuta was examined. Increasing concentrations of potassium stimulated the release of radiolabel from tissues preloaded with [3H]glutamate. This release was by a partially calcium-dependent, magnesium-antagonized process. In the presence of tetrodotoxin, or absence of sodium, release of radiolabel was depressed, presumably by blockade of sodium-dependent neuronal potentials. The release of glutamate of both exogenous and endogenous origin was specifically and significantly elevated by high potassium; glutamate release was significantly depressed in calcium-free saline. The release of other amino acids of endogenous origin, including aspartate, was not elevated by high potassium. Collectively the data provide strong evidence for glutamate to be viewed as the only acidic amino acid neurotransmitter candidate in the cestodes.
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Trachte, G. J., S. Kanwal, B. J. Elmquist, and R. J. Ziegler. "C-type natriuretic peptide neuromodulates via "clearance" receptors." American Journal of Physiology-Cell Physiology 268, no. 4 (April 1, 1995): C978—C984. http://dx.doi.org/10.1152/ajpcell.1995.268.4.c978.
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A recently discovered endogenous autacoid, C-type natriuretic peptide, was tested in a pheochromocytoma (PC12) cell line for effects on 1) catecholamine release induced by a depolarizing stimulus, 2) guanylyl and adenylyl cyclase activities, and 3) specific 125I-labeled atrial natriuretic peptide (ANP) binding. C-type natriuretic peptide suppressed evoked neurotransmitter release in the absence of guanylyl cyclase activation or adenylyl cyclase inhibition; however, both a "clearance" (ANP-C) receptor binding agent, des-[Gln18Ser19Gly20Leu21Gly22]-ANF-(4-23)-NH2 (cANF), and pertussis toxin prevented this neuromodulatory effect. The C-type natriuretic peptide preferentially bound to receptors that also bound cANF. The results suggest that C-type natriuretic peptide suppressed evoked neurotransmitter efflux by binding to ANP-C receptors coupled to a pertussis toxin-sensitive process; furthermore, the neuromodulatory effect of C-type natriuretic peptide occurred independently of guanylyl cyclase activation or adenylyl cyclase inhibition. The novel aspects of these findings are 1) neuromodulatory effects of C-type natriuretic peptide, 2) guanylyl cyclase-independent actions of C-type natriuretic peptide, and 3) ANP-C receptors mediating C-type natriuretic peptide actions.
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Congar, Patrice, Annie Bergevin, and Louis-Eric Trudeau. "D2 Receptors Inhibit the Secretory Process Downstream From Calcium Influx in Dopaminergic Neurons: Implication of K+ Channels." Journal of Neurophysiology 87, no. 2 (February 1, 2002): 1046–56. http://dx.doi.org/10.1152/jn.00459.2001.
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Dopaminergic (DAergic) neurons possess D2-like somatodendritic and terminal autoreceptors that modulate cellular excitability and dopamine (DA) release. The cellular and molecular processes underlying the rapid presynaptic inhibition of DA release by D2 receptors remain unclear. Using a culture system in which isolated DAergic neurons establish self-innervating synapses (“autapses”) that release both DA and glutamate, we studied the mechanism by which presynaptic D2 receptors inhibit glutamate-mediated excitatory postsynaptic currents (EPSCs). Action-potential evoked EPSCs were reversibly inhibited by quinpirole, a selective D2 receptor agonist. This inhibition was slightly reduced by the inward rectifier K+ channel blocker barium, largely prevented by the voltage-dependent K+channel blocker 4-aminopyridine, and completely blocked by their combined application. The lack of a residual inhibition of EPSCs under these conditions argues against the implication of a direct inhibition of presynaptic Ca2+ channels. To evaluate the possibility of a direct inhibition of the secretory process, spontaneous miniature EPSCs were evoked by the Ca2+ ionophore ionomycin. Ionomycin-evoked release was insensitive to cadmium and dramatically reduced by quinpirole, providing evidence for a direct inhibition of quantal release at a step downstream to Ca2+ influx through voltage-dependent Ca2+ channels. Surprisingly, this effect of quinpirole on ionomycin-evoked release was blocked by 4-aminopyridine. These results suggest that D2 receptor activation decreases neurotransmitter release from DAergic neurons through a presynaptic mechanism in which K+ channels directly inhibit the secretory process.
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Swift, Matthew J., Jesse A. Greene, Zachary R. Welch, and Jennifer Woodell-May. "Concentration of Neurotransmitter and Neurotrophic Factors in Platelet Rich Plasma." Blood 108, no. 11 (November 16, 2006): 3914. http://dx.doi.org/10.1182/blood.v108.11.3914.3914.
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Abstract Use of autologous platelet rich plasma (PRP) is emerging in a variety of clinical settings. Although the desired effects of PRP application vary across indications, the common mechanism of action is the up-regulation of the healing response at the site of application. This effect has largely been attributed to the release of cytokines from alpha-granules during platelet degranulation. Research has demonstrated elevated concentrations of a variety of cytokines in PRP samples when compared to baseline blood. To date, no researchthat quantifies the concentration of neurotransmitter and neurotrophic agents present in activated PRP samples has been reported. A number of these molecules have been reported to be present in the alpha and dense granules of platelets with release occurring upon platelet degranulation. Upon release, these molecules elicit actions related to the hemostatic, inflammatory, and reparative processes during the natural wound healing response. In the current study, a commercially available platelet concentrator (GPS II System, Biomet Biologics, Inc) was used to prepare PRP from whole blood samples obtained from 9 healthy subjects. PRP and whole blood samples from each subject were analyzed using a hematology analyzer (Cell Dyn 3700, Abbot Laboratories) for cellular content and then activated with a bovine thrombin/calcium chloride solution. Following a 10-minute incubation, the activated samples were centrifuged for 5 minutes and the resultant serum was collected and assayed for serotonin, adrenaline, noradrenaline, dopamine, and brain derived neurotrophic factor (BDNF) using commercially available ELISA kits. Platelet concentration averaged 196x103 platelets/ml in the baseline samples and 1230 x103 platelets/ml in the PRP samples, a 6.28 fold increase. Serotonin serum levels increased 4.48 fold (base=201.9 pg/ml, PRP=904.6 pg/ml), noradrenaline serum levels increased 3.02 fold (base=286 pg/ml, PRP=863 pg/ml), and BDNF serum levels increased 3.06 fold (base=3.49ng/ml, PRP=10.6 ng/ml). Adrenaline results were highly inconsistent, a factor attributed to the potential of glandular release in response to the blood draw stick. Dopamine concentrations were not detected in any samples using an ELISA with a sensitivity of 100 pg/ml. This study confirms the presence of elevated neurotransmitter and neurotrophic concentrations in activated PRP samples when compared to corresponding base samples. Further studies are necessary to elucidate the role these elevated concentrations contribute in the up-regulation of the wound repair process reported during the clinical application of PRP.
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Meeusen, Romain, and Phil Watson. "Amino Acids and the Brain: Do They Play a Role in “Central Fatigue”?" International Journal of Sport Nutrition and Exercise Metabolism 17, s1 (February 2007): S37—S46. http://dx.doi.org/10.1123/ijsnem.17.s1.s37.
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It is clear that the cause of fatigue is complex, infuenced by both events occurring in the periphery and the central nervous system (CNS). It has been suggested that exercise-induced changes in serotonin (5-HT), dopamine (DA), and noradrenaline (NA) concentrations contribute to the onset of fatigue during prolonged exercise. Serotonin has been linked to fatigue because of its documented role in sleep, feelings of lethargy and drowsiness, and loss of motivation, whereas increased DA and NA neurotransmission favors feelings of motivation, arousal, and reward. 5-HT has been shown to increase during acute exercise in running rats and to remain high at the point of fatigue. DA release is also elevated during exercise but appears to fall at exhaustion, a response that may be important in the fatigue process. The rates of 5-HT and DA/NA synthesis largely depend on the peripheral availability of the amino acids tryptophan (TRP) and tyrosine (TYR), with increased brain delivery increasing serotonergic and DA/NA activity, respectively. TRP, TYR, and the branched-chained amino acids (BCAAs) use the same transporter to pass through the blood-brain barrier, meaning that the plasma concentration ratio of these amino acids is thought to be a very important marker of neurotransmitter synthesis. Pharmacological manipulation of these neurotransmitter systems has provided support for an important role of the CNS in the development of fatigue. Work conducted over the last 20 y has focused on the possibility that manipulation of neurotransmitter precursors may delay the onset of fatigue. Although there is evidence that BCAA (to limit 5-HT synthesis) and TYR (to elevate brain DA/NA) ingestion can influence perceived exertion and some measures of mental performance, the results of several apparently well-controlled laboratory studies have yet to demonstrate a clear positive effect on exercise capacity or performance. There is good evidence that brain neurotransmitters can play a role in the development of fatigue during prolonged exercise, but nutritional manipulation of these systems through the provision of amino acids has proven largely unsuccessful.
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Kreitzer, Matthew A., Leon P. Collis, Anthony J. A. Molina, Peter J. S. Smith, and Robert Paul Malchow. "Modulation of Extracellular Proton Fluxes from Retinal Horizontal Cells of the Catfish by Depolarization and Glutamate." Journal of General Physiology 130, no. 2 (July 30, 2007): 169–82. http://dx.doi.org/10.1085/jgp.200709737.
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Self-referencing H+-selective microelectrodes were used to measure extracellular proton fluxes from cone-driven horizontal cells isolated from the retina of the catfish (Ictalurus punctatus). The neurotransmitter glutamate induced an alkalinization of the area adjacent to the external face of the cell membrane. The effect of glutamate occurred regardless of whether the external solution was buffered with 1 mM HEPES, 3 mM phosphate, or 24 mM bicarbonate. The AMPA/kainate receptor agonist kainate and the NMDA receptor agonist N-methyl-d-aspartate both mimicked the effect of glutamate. The effect of kainate on proton flux was inhibited by the AMPA/kainate receptor blocker CNQX, and the effect of NMDA was abolished by the NMDA receptor antagonist DAP-5. Metabotropic glutamate receptor agonists produced no alteration in proton fluxes from horizontal cells. Depolarization of cells either by increasing extracellular potassium or directly by voltage clamp also produced an alkalinization adjacent to the cell membrane. The effects of depolarization on proton flux were blocked by 10 μM nifedipine, an inhibitor of L-type calcium channels. The plasmalemma Ca2+/H+ ATPase (PMCA) blocker 5(6)-carboxyeosin also significantly reduced proton flux modulation by glutamate. Our results are consistent with the hypothesis that glutamate-induced extracellular alkalinizations arise from activation of the PMCA pump following increased intracellular calcium entry into cells. This process might help to relieve suppression of photoreceptor neurotransmitter release that results from exocytosed protons from photoreceptor synaptic terminals. Our findings argue strongly against the hypothesis that protons released by horizontal cells act as the inhibitory feedback neurotransmitter that creates the surround portion of the receptive fields of retinal neurons.
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Torri-Tarelli, F., A. Villa, F. Valtorta, P. De Camilli, P. Greengard, and B. Ceccarelli. "Redistribution of synaptophysin and synapsin I during alpha-latrotoxin-induced release of neurotransmitter at the neuromuscular junction." Journal of Cell Biology 110, no. 2 (February 1, 1990): 449–59. http://dx.doi.org/10.1083/jcb.110.2.449.
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The distribution of two synaptic vesicle-specific phosphoproteins, synaptophysin and synapsin I, during intense quantal secretion was studied by applying an immunogold labeling technique to ultrathin frozen sections. In nerve-muscle preparations treated for 1 h with a low dose of alpha-latrotoxin in the absence of extracellular Ca2+ (a condition under which nerve terminals are depleted of both quanta of neurotransmitter and synaptic vesicles), the immunolabeling for both proteins was distributed along the axolemma. These findings indicate that, in the presence of a block of endocytosis, exocytosis leads to the permanent incorporation of the synaptic vesicle membrane into the axolemma and suggest that, under this condition, at least some of the synapsin I molecules remain associated with the vesicle membrane after fusion. When the same dose of alpha-latrotoxin was applied in the presence of extracellular Ca2+, the immunoreactivity patterns resembled those obtained in resting preparations: immunogold particles were selectively associated with the membrane of synaptic vesicles, whereas the axolemma was virtually unlabeled. Under this condition an active recycling of both quanta of neurotransmitter and vesicles operates. These findings indicate that the retrieval of components of the synaptic vesicle membrane is an efficient process that does not involve extensive intermixing between molecular components of the vesicle and plasma membrane, and show that synaptic vesicles that are rapidly recycling still have the bulk of synapsin I associated with their membrane.
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Andor-Ardó, Daniel, A. J. Hudspeth, Marcelo O. Magnasco, and Oreste Piro. "Modeling the resonant release of synaptic transmitter by hair cells as an example of biological oscillators with cooperative steps." Proceedings of the National Academy of Sciences 107, no. 5 (January 13, 2010): 2019–24. http://dx.doi.org/10.1073/pnas.0914372107.
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The initial synapses of the auditory system, which connect hair cells to afferent nerve fibers, display two unusual features. First, synaptic transmission occurs in a multiquantal fashion: the contents of multiple synaptic vesicles are discharged simultaneously. Second, synaptic transmission may be tuned to specific frequencies of stimulation. We developed a minimal theoretical model to explore the possibility that hair-cell synapses achieve both multiquantal release and frequency selectivity through a cooperative mechanism for the exocytotic release of neurotransmitter. We first characterized vesicle release as a four-step cycle at each release site, then generalized the result to an arbitrary number of steps. The cyclic process itself induces some degree of resonance, and may display a stable, underdamped fixed point of the release dynamics associated with a pair of complex eigenvalues. Cooperativity greatly enhances the frequency selectivity by moving the eigenvalues toward the imaginary axis; spontaneously oscillatory release can arise beyond a Hopf bifurcation. These phenomena occur both in the macroscopic limit, when the number of release sites involved is very large, and in the more realistic stochastic regime, when only a limited number of release sites participate at each synapse. It is thus possible to connect multiquantal release with frequency selectivity through the mechanism of cooperativity.
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Prokopiou, Andreas N., and Emm M. Drakakis. "Quantitative Analysis Linking Inner Hair Cell Voltage Changes and Postsynaptic Conductance Change: A Modelling Study." BioMed Research International 2015 (2015): 1–21. http://dx.doi.org/10.1155/2015/626971.
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This paper presents a computational model which estimates the postsynaptic conductance change of mammalian Type I afferent peripheral process when airborne acoustic waves impact on the tympanic membrane. A model of the human auditory periphery is used to estimate the inner hair cell potential change in response to airborne sound. A generic and tunable topology of the mammalian synaptic ribbon is generated and the voltage dependence of its substructures is used to calculate discrete and probabilistic neurotransmitter vesicle release. Results suggest an almost linear relationship between increasing sound level (in dB SPL) and the postsynaptic conductance for frequencies considered too high for neurons to phase lock with (i.e., a few kHz). Furthermore coordinated vesicle release is shown for up to 300–400 Hz and a mechanism of phase shifting the subharmonic content of a stimulating signal is suggested. Model outputs suggest that strong onset response and highly synchronised multivesicular release rely on compound fusion of ribbon tethered vesicles.
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Schafer, William R., Becky M. Sanchez, and Cynthia J. Kenyon. "Genes Affecting Sensitivity to Serotonin in Caenorhabditis elegans." Genetics 143, no. 3 (July 1, 1996): 1219–30. http://dx.doi.org/10.1093/genetics/143.3.1219.
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Abstract Regulating the response of a postsynaptic cell to neurotransmitter is an important mechanism for controlling synaptic strength, a process critical to learning. We have begun to define and characterize genes that may control sensitivity to the neurotransmitter serotonin in the nematode Caenorhabditis ekgans by identifjmg serotonin-hypersensitive mutants. We reported previously that mutations in the gene unc-2, which encodes a putative calcium channel subunit, result in hypersensitivity to serotonin. Here we report that mutants defective in the unc-36 gene, which encodes a homologue of a calcium channel auxiliary subunit, are also serotonin-hypersensitive. Moreover, the unc-36 gene appears to be required in the same cells as unc-2 for control of the same behaviors. Mutations in several other genes, including unc-8, unc-10, unc-20, unc-35, unc-75, unc-77, and snt-1 also result in hypersensitivity to serotonin. Several of these mutations have previously been shown to confer resistance to acetylcholinesterase inhibitors, suggesting that they may affect acetylcholine release. Moreover, we found that mutations that decrease acetylcholine synthesis cause defective egg-laying and serotonin hypersensitivity. Thus, acetylcholine appears to negatively regulate the response to serotonin and may participate in the process of serotonin desensitization.
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Maass, Wolfgang, and Anthony M. Zador. "Dynamic Stochastic Synapses as Computational Units." Neural Computation 11, no. 4 (May 1, 1999): 903–17. http://dx.doi.org/10.1162/089976699300016494.
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In most neural network models, synapses are treated as static weights that change only with the slow time scales of learning. It is well known, however, that synapses are highly dynamic and show use-dependent plasticity over a wide range of time scales. Moreover, synaptic transmission is an inherently stochastic process: a spike arriving at a presynaptic terminal triggers the release of a vesicle of neurotransmitter from a release site with a probability that can be much less than one. We consider a simple model for dynamic stochastic synapses that can easily be integrated into common models for networks of integrate-andfire neurons (spiking neurons). The parameters of this model have direct interpretations in terms of synaptic physiology. We investigate the consequences of the model for computing with individual spikes and demonstrate through rigorous theoretical results that the computational power of the network is increased through the use of dynamic synapses.
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Ziółkowska, N., B. Lewczuk, and B. Przybylska-Gornowicz. "Neuropeptide Y as a presynaptic modulator of norepinephrine release from the sympathetic nerve fibers in the pig pineal gland." Polish Journal of Veterinary Sciences 18, no. 1 (March 1, 2015): 53–61. http://dx.doi.org/10.1515/pjvs-2015-0007.
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Abstract Norepinephrine (NE) released from the sympathetic nerve endings is the main neurotransmitter controlling melatonin synthesis in the mammalian pineal gland. Although neuropeptide Y (NPY) co-exists with NE in the pineal sympathetic nerve fibers it also occurs in a population of non-adrenergic nerve fibers located in this gland. The role of NPY in pineal physiology is still enigmatic. The present study characterizes the effect of NPY on the depolarization-evoked 3H-NE release from the pig pineal explants. The explants of the pig pineal gland were loaded with 3H-NE in the presence of pargyline and superfused with Tyrode medium. They were exposed twice to the modified Tyrode medium containing 60 mM of K+ to evoke the 3H-NE release via depolarization. NPY, specific agonists of Y1- and Y2-receptors and pharmacologically active ligands of α2-adrenoceptors were added to the medium before and during the second depolarization. The radioactivity was measured in medium fractions collected every 2 minutes during the superfusion. NPY (0.1 – 10 μM) significantly decreased the depolarization-induced 3H-NE release. Similar effect was observed after the treatment with Y2-agonist: NPY13-36, but not with Y1-agonist: [Leu31, Pro34]-NPY. The tritium overflow was lower in the explants exposed to the 5 μM NPY and 1 μM rauwolscine than to rauwolscine only. The effects of 5 μM NPY and 0.05 μM UK 14,304 on the depolarization-evoked 3H-NE release were additive. The results show that NPY is involved in the regulation of NE release from the sympathetic terminals in the pig pineal gland, inhibiting this process via Y2-receptors.
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NISHIO, Hideaki, Tadayoshi TAKEUCHI, Fumiaki HATA, and Osamu YAGASAKI. "Ca2+-independent fusion of synaptic vesicles with phospholipase A2-treated presynaptic membranes in vitro." Biochemical Journal 318, no. 3 (September 15, 1996): 981–87. http://dx.doi.org/10.1042/bj3180981.
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To clarify the mechanism of exocytosis in neurotransmitter release, the fusion of synaptic vesicles with presynaptic membranes prepared from rat brain synaptosomes and concomitant acetylcholine (ACh) release induced by fusion of them were studied in vitro. Fusion of the synaptic vesicles with presynaptic membranes was measured by a fluorescence-dequenching assay with octadecyl rhodamine B. Synaptic vesicles fused with presynaptic membranes which had been pretreated with porcine phospholipase A2 (PLA2) in the presence of 20 µM Ca2+ and released ACh, whereas synaptic vesicles did not interact with non-pretreated membranes. The fusion followed by ACh release depended (i) on the activity of PLA2 during the membrane pretreatment, (ii) on the amount of pretreated membrane and (iii) on the duration of the pretreatment. The presence of Ca2+ ions during the pretreatment was essential for inducing a fusogenic activity of the membranes, but Ca2+ ions were not required for the fusion itself because the fusion experiment was carried out in the presence of 5 mM EGTA without added Ca2+. The presence of quinacrine, an antagonist of PLA2, during the membrane pretreatment inhibited their fusogenic activity, suggesting the importance of activation of PLA2. Presence of albumin during the pretreatment, which is an adsorbent of free fatty acids, also inhibited the fusogenic activity. Arachidonic acid, when added during the pretreatment, potentiated the fusogenic activity of the membrane. These findings suggest that the conformational change in the presynaptic membrane phospholipids induced by PLA2 and the presence of arachidonic acid produced by PLA2 are important in the process of fusion of synaptic vesicles with the presynaptic membranes of rat brain, and that the fusion process itself is independent of Ca2+.
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Hyland, Keith. "Clinical Utility of Monoamine Neurotransmitter Metabolite Analysis in Cerebrospinal Fluid." Clinical Chemistry 54, no. 4 (April 1, 2008): 633–41. http://dx.doi.org/10.1373/clinchem.2007.099986.
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Abstract Background: Measurements of monoamine neurotransmitters and their metabolites in plasma and urine are commonly used to aid in the detection and monitoring of neuroblastoma and pheochromocytoma and the evaluation of hypotension or hypertension. Measurements of these neurotransmitters and metabolites can also be helpful in the investigation of disorders that primarily affect the central nervous system, but only when the measurements are made in cerebrospinal fluid (CSF). Content: I describe CSF profiles of monoamine metabolites in the primary and secondary defects affecting serotonin and catecholamine metabolism. I outline the methods required to analyze these metabolites together with details of specific sample handling requirements, sample stability, and interfering compounds, and I emphasize a need for age-related reference intervals. Summary: Measured values of monoamine metabolites in CSF provide only a single-time snapshot of the overall turnover of the monoamine neurotransmitters within the brain. Because these measurements reflect the average concentrations accumulated from all brain regions plus the regional changes that occur within the spinal cord, they may miss subtle abnormalities in particular brain regions or changes that occur on a minute-to-minute or diurnal basis. Clearly defined diagnosed disorders are currently limited to those affecting synthetic and catabolic pathways. In many cases, abnormal monoamine metabolite concentrations are found in CSF and an underlying etiology cannot be found. Molecular screening of candidate genes related to steps in the neurotransmission process, including storage in presynaptic nerve vesicles, release, interaction with receptors, and reuptake, might be a fruitful endeavor in these cases.
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Singh, Pankaj, and Chung-Yuen Hui. "Hydrodynamics govern the pre-fusion docking time of synaptic vesicles." Journal of The Royal Society Interface 15, no. 138 (January 2018): 20170818. http://dx.doi.org/10.1098/rsif.2017.0818.
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Synaptic vesicle fusion is a crucial step in the neurotransmission process. Neurotransmitter-filled vesicles are pre-docked at the synapse by the mediation of ribbon structures and SNARE proteins at the ribbon synapses. An electrical impulse triggers the fusion process of pre-docked vesicles, leading to the formation of a fusion pore and subsequently resulting in the release of neurotransmitter into the synaptic cleft. In this study, a continuum model of lipid membrane along with lubrication theory is used to determine the traverse time of the synaptic vesicle under the influence of hydrodynamic forces. We find that the traverse time is strongly dependent on how fast the driving force decays or grows with closure of the gap between the vesicle and the plasma membrane. If the correct behaviour is chosen, the traverse time obtained is of the order of a few hundred milliseconds and lies within the experimentally obtained value of approximately 250 ms (Zenisek D, Steyer JA, Almers W. 2000 Nature 406 , 849–854 ( doi:10.1038/35022500 )). We hypothesize that there are two different force behaviours, which complies with the experimental findings of pre-fusion docking of synaptic vesicles at the ribbon synapses. The common theme in the proposed force models is that the driving force has to very rapidly increase or decrease with the amount of clamping.
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Pofantis, Ermis, Erwin Neher, and Thomas Dresbach. "Regulation of a subset of release-ready vesicles by the presynaptic protein Mover." Proceedings of the National Academy of Sciences 118, no. 3 (January 11, 2021): e2022551118. http://dx.doi.org/10.1073/pnas.2022551118.
Full textAbstract:
Neurotransmitter release occurs by regulated exocytosis from synaptic vesicles (SVs). Evolutionarily conserved proteins mediate the essential aspects of this process, including the membrane fusion step and priming steps that make SVs release-competent. Unlike the proteins constituting the core fusion machinery, the SV protein Mover does not occur in all species and all synapses. Its restricted expression suggests that Mover may modulate basic aspects of transmitter release and short-term plasticity. To test this hypothesis, we analyzed synaptic transmission electrophysiologically at the mouse calyx of Held synapse in slices obtained from wild-type mice and mice lacking Mover. Spontaneous transmission was unaffected, indicating that the basic release machinery works in the absence of Mover. Evoked release and vesicular release probability were slightly reduced, and the paired pulse ratio was increased in Mover knockout mice. To explore whether Mover’s role is restricted to certain subpools of SVs, we analyzed our data in terms of two models of priming. A model assuming two SV pools in parallel showed a reduced release probability of so-called “superprimed vesicles” while “normally primed” ones were unaffected. For the second model, which holds that vesicles transit sequentially from a loosely docked state to a tightly docked state before exocytosis, we found that knocking out Mover selectively decreased the release probability of tight state vesicles. These results indicate that Mover regulates a subclass of primed SVs in the mouse calyx of Held.
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SOLESSIO, EDUARDO, and ERIC M. LASATER. "Calcium-induced calcium release and calcium buffering in retinal horizontal cells." Visual Neuroscience 19, no. 6 (November 2002): 713–25. http://dx.doi.org/10.1017/s0952523802196039.
Full textAbstract:
Calcium plays an integral role in intracellular signaling and process control in neurons. In the outer retina, it is a key component to the phototransduction cycle and neurotransmitter release in photoreceptor and bipolar cell terminals. It also contributes to the responses of horizontal and bipolar cells. In the dark, horizontal cells are depolarized and calcium enters via calcium permeant AMPA receptors and voltage-activated calcium channels. As a result, horizontal cells must be capable of handling high calcium loads without sustaining damage. The aim of this study was to examine the components determining the intracellular calcium levels in H2 horizontal cells in the retina of white bass. Calcium responses were evoked in isolated cells by depolarizing voltage steps and monitored by conventional imaging techniques. The responses consisted of two components: calcium entry through voltage-gated calcium channels and subsequent release from intracellular stores by calcium-induced calcium release (CICR). Under control conditions, changes in calcium levels reached 541 nM on average from a basal level of 60 nM. When release from CICR stores was blocked with ryanodine or dantrolene, calcium levels barely reached 180 nM. The threshold level needed to trigger CICR was dependent on the duration of the applied depolarization and increased in response to shorter pulses.
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LOOMS, Dagnia K., Katerina TRITSARIS, Birgitte NAUNTOFTE, and Steen DISSING. "Nitric oxide and cGMP activate Ca2+-release processes in rat parotid acinar cells." Biochemical Journal 355, no. 1 (February 26, 2001): 87–95. http://dx.doi.org/10.1042/bj3550087.
Full textAbstract:
We characterized the enzymic properties of ADP-ribosyl cyclase in rat parotid acinar cells by using a fluorescence technique. ADP-ribosyl cyclase is capable of synthesizing the Ca2+-mobilizing nucleotide cADP-ribose (cADPR) from NAD+ and has previously been shown to be regulated by cGMP via a cGMP-dependent protein kinase (G kinase). We therefore investigated whether NO/cGMP-activated pathways are present in rat parotid acinar cells and whether NO/cGMP signalling exerts control over cellular Ca2+ signalling processes. Our results showed that stimulation of acinar cells with adrenaline, isoproterenol, substance P and NO resulted in a rise in the [cGMP]. In addition, NO induced a release of Ca2+ from intracellular ryanodine-sensitive stores via a cGMP/G-kinase-mediated process. Thus our data reveal that a rise in [cGMP], caused by either neurotransmitter or NO activation, activates a G kinase, which in turn controls Ca2+ release from ryanodine-sensitive stores. Since parotid acinar cells possess ADP-ribosyl cyclase activity, we propose a model in which cADPR is the link between NO/cGMP signalling pathways and release of Ca2+ from ryanodine-sensitive stores.
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Burgess, Robert W., David L. Deitcher, and Thomas L. Schwarz. "The Synaptic Protein Syntaxin1 Is Required for Cellularization of Drosophila Embryos." Journal of Cell Biology 138, no. 4 (August 25, 1997): 861–75. http://dx.doi.org/10.1083/jcb.138.4.861.
Full textAbstract:
Syntaxins are membrane proteins involved in vesicle trafficking and are required for the release of neurotransmitter at nerve terminals. The presence of syntaxins on target membranes has been hypothesized to confer specificity to targeting and fusion via interactions with complementary vesicle-associated proteins, the synaptobrevins or VAMPS. We have mutagenized syntaxin1 in Drosophila and have found that it links the mechanism of synaptic transmission to a distinct cell biological process: the cellularization of early embryos. This specialized form of cell division separates the 6,000 nuclei of the syncytial blastoderm into separate cells through the invagination of the surface membrane of the embryo. During this process, syntaxin1 protein is present on the newly forming lateral cell surfaces and invaginating cleavage furrows. This protein is derived both from maternal deposition of mRNA and protein and from early zygotic transcription. To analyze syntaxin1's role in early development, female germ line mosaics mutant for syntaxin1 expression were generated by mitotic recombination to reduce the maternal contribution. Visualizing the actin cytoskeleton and glycosylated surface proteins reveals that embryos with insufficient syntaxin1 have large acellular patches. The patches do not appear until cellularization begins, and the process fails entirely within these regions. These results provide genetic evidence that membrane trafficking is required for the cellularization of the syncytial blastoderm. We propose that the invagination of the surface membrane proceeds by the fusion of intracellular membrane vesicles with the surface. This reaction uses the same syntaxin1 protein as is required for neurotransmitter secretion at synapses. Thus, a single syntaxin can participate in trafficking steps that are functionally as distinct as synaptic transmission and cell division.
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Isokawa, Masako, and Bradley E. Alger. "Ryanodine Receptor Regulates Endogenous Cannabinoid Mobilization in the Hippocampus." Journal of Neurophysiology 95, no. 5 (May 2006): 3001–11. http://dx.doi.org/10.1152/jn.00975.2005.
Full textAbstract:
Endogenous cannabinoids (eCBs) are produced and mobilized in a cytosolic calcium ([Ca2+]i)–dependent manner, and they regulate excitatory and inhibitory neurotransmitter release by acting as retrograde messengers. An indirect but real-time bioassay for this process on GABAergic transmission is DSI (depolarization-induced suppression of inhibition). The magnitude of DSI correlates linearly with depolarization-induced increase of [Ca2+]i that is thought to be initiated by Ca2+ influx through voltage-gated Ca2+ channels. However, the identity of Ca2+ sources involved in eCB mobilization in DSI remains undetermined. Here we show that, in CA1 pyramidal cells, DSI-inducing depolarizing voltage steps caused Ca2+-induced Ca2+ release (CICR) by activating the ryanodine receptor (RyR) Ca2+-release channel. CICR was reduced, and the remaining increase in [Ca2+]i was less effective in generating DSI, when the RyR antagonists, ryanodine or ruthenium red, were applied intracellularly, or the Ca2+ stores were depleted by the Ca2+-ATPase inhibitors, cyclopiazonic acid or thapsigargin. The CICR-dependent effects were most prominent in cultured or immature acute slices, but were also detectable in slices from adult tissue. Thus we suggest that voltage-gated Ca2+ entry raises local [Ca2+]i sufficiently to activate nearby RyRs and that the resulting CICR plays a critical role in initiating eCB mobilization. RyR may be a key molecule for the depolarization-induced production of eCBs that inhibit GABA release in the hippocampus.
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Valtorta, F., R. Jahn, R. Fesce, P. Greengard, and B. Ceccarelli. "Synaptophysin (p38) at the frog neuromuscular junction: its incorporation into the axolemma and recycling after intense quantal secretion." Journal of Cell Biology 107, no. 6 (December 1, 1988): 2717–27. http://dx.doi.org/10.1083/jcb.107.6.2717.
Full textAbstract:
Recycling of synaptophysin (p38), a synaptic vesicle integral membrane protein, was studied by the use of antisera raised against the protein purified from frog brain. When frog cutaneous pectoris muscles were fixed at rest, a bright, specific immunofluorescent signal was observed in nerve-terminal regions only if their plasma membranes had been previously permeabilized. When muscles were fixed after they had been treated for 1 h with a low dose of alpha-latrotoxin in Ca2+-free medium, an equally intense fluorescence could be observed without previous permeabilization. Under this condition, alpha-latrotoxin depletes nerve terminals of their quantal store of acetylcholine and of synaptic vesicles. These results indicate that fusion of synaptic vesicles leads to the exposure of intravesicular antigenic determinants of synaptophysin on the outer surface of the axolemma, and provide direct support for the vesicle hypothesis of neurotransmitter release. After 1 h treatment with the same dose of alpha-latrotoxin in the presence of 1.8 mM extracellular Ca2+, immunofluorescent images were obtained only after permeabilization with detergents. Under this condition, the vesicle population was maintained by an active process of recycling and more than two times the initial store of quanta were secreted. Thus, despite the active turnover of synaptic vesicles and of quanta of neurotransmitter, no extensive intermixing occurs between components of the vesicle and presynaptic plasma membrane.