scholarly journals Secreted C-type lectin regulation of neuromuscular junction synaptic vesicle dynamics modulates coordinated movement

2021 ◽  
Author(s):  
Meghana Bhimreddy ◽  
Emma Rushton ◽  
Danielle L. Kopke ◽  
Kendal Broadie
Keyword(s):  
Neuromuscular Junction ◽  
Synaptic Vesicle ◽  
Synaptic Cleft ◽  
Synaptic Function ◽  
Movement Speed ◽  
High Frequency Stimulation ◽  
Glutamatergic Synapses ◽  
Presynaptic Function ◽  
Presynaptic Boutons ◽  
Frequency Stimulation

The synaptic cleft manifests enriched glycosylation, with structured glycans coordinating signaling between presynaptic and postsynaptic cells. Glycosylated signaling ligands orchestrating communication are tightly regulated by secreted glycan-binding lectins. Using the Drosophila neuromuscular junction (NMJ) as a model glutamatergic synapse, we identify a new Ca2+-binding (C-type) lectin, Lectin-galC1 (LGC1), which modulates presynaptic function and neurotransmission strength. We find that LGC1 is enriched in motoneuron presynaptic boutons and secreted into the NMJ extracellular synaptomatrix. We show that LGC1 limits locomotor peristalsis and coordinated movement speed, with a specific requirement for synaptic function, but not NMJ architecture. LGC1 controls neurotransmission strength by limiting presynaptic active zone (AZ) and postsynaptic glutamate receptor (GluR) aligned synapse number, reducing both spontaneous and stimulation-evoked synaptic vesicle (SV) release, and capping SV cycling rate. During high-frequency stimulation (HFS) mutants have faster synaptic depression and impaired recovery while replenishing depleted SV pools. Although LGC1 removal increases the number of glutamatergic synapses, we find LGC1 null mutants exhibit decreased SV density within presynaptic boutons, particularly SV pools at presynaptic active zones. Thus, LGC1 regulates NMJ neurotransmission to modulate coordinated movement.

scholarly journals Light induced synaptic vesicle autophagy

2018 ◽  
Author(s):  
Sheila Hoffmann ◽  
Marta Orlando ◽  
Ewa Andrzejak ◽  
Thorsten Trimbuch ◽  
Christian Rosenmund ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Real Time ◽  
Hippocampal Neurons ◽  
Synaptic Function ◽  
Synaptic Proteins ◽  
Oxygen Species ◽  
Local Damage ◽  
Glutamatergic Synapses ◽  
Presynaptic Boutons ◽  
Presynaptic Proteins

AbstractThe regulated turnover of synaptic vesicle (SV) proteins is thought to involve the ubiquitin dependent tagging and degradation through endo-lysosomal and autophagy pathways. Yet, it remains unclear which of these pathways are used, when they become activated and whether SVs are cleared en-mass together with SV proteins or whether both are degraded selectively. Equally puzzling is how quickly these systems can be activated and whether they function in real time to support synaptic health. To address these questions, we have developed an imaging based system that simultaneously tags presynaptic proteins while monitoring autophagy. Moreover, by tagging SV proteins with a light activated reactive oxygen species (ROS) generator, Supernova, it was possible to temporally control the damage to specific SV proteins and assess their consequence to autophagy mediated clearance mechanisms and synaptic function. Our results show that, in mouse hippocampal neurons, presynaptic autophagy can be induced in as little as 5-10 minutes and eliminates primarily the damaged protein rather than the SV en-mass. Importantly, we also find that autophagy is essential for synaptic function, as light-induced damage to e.g. Synaptophysin only compromises synaptic function when autophagy is simultaneously blocked. These data support the concept that presynaptic boutons have a robust highly regulated clearance system to maintain not only synapse integrity, but also synaptic function.Significance StatementThe real-time surveillance and clearance of synaptic proteins is thought to be vital to the health, functionality and integrity of vertebrate synapses and is compromised in neurodegenerative disorders, yet the fundamental mechanisms regulating these systems remain enigmatic. Our analysis reveals that presynaptic autophagy is a critical part of a real-time clearance system at glutamatergic synapses capable of responding to local damage of synaptic vesicle proteins within minutes and to be critical for the ongoing functionality of these synapses. These data indicate that synapse autophagy is not only locally regulated but also crucial for the health and functionality of vertebrate presynaptic boutons.

scholarly journals The effect of NAMPT deletion in projection neurons on the function and structure of neuromuscular junction (NMJ) in mice

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Samuel Lundt ◽  
Nannan Zhang ◽  
Xiaowan Wang ◽  
Luis Polo-Parada ◽  
Shinghua Ding
Keyword(s):  
Neuromuscular Junction ◽  
Synaptic Vesicle ◽  
Critical Role ◽  
Conditional Knockout ◽  
High Frequency Stimulation ◽  
Mitochondrial Morphology ◽  
Projection Neurons ◽  
Dependent Manner ◽  
Nicotinamide Phosphoribosyltransferase ◽  
The Impact

AbstractNicotinamide adenine dinucleotide (NAD+) plays a critical role in energy metabolism and bioenergetic homeostasis. Most NAD+ in mammalian cells is synthesized via the NAD+ salvage pathway, where nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme, converting nicotinamide into nicotinamide mononucleotide (NMN). Using a Thy1-Nampt−/− projection neuron conditional knockout (cKO) mouse, we studied the impact of NAMPT on synaptic vesicle cycling in the neuromuscular junction (NMJ), end-plate structure of NMJs and muscle contractility of semitendinosus muscles. Loss of NAMPT impaired synaptic vesicle endocytosis/exocytosis in the NMJs. The cKO mice also had motor endplates with significantly reduced area and thickness. When the cKO mice were treated with NMN, vesicle endocytosis/exocytosis was improved and endplate morphology was restored. Electrical stimulation induced muscle contraction was significantly impacted in the cKO mice in a frequency dependent manner. The cKO mice were unresponsive to high frequency stimulation (100 Hz), while the NMN-treated cKO mice responded similarly to the control mice. Transmission electron microscopy (TEM) revealed sarcomere misalignment and changes to mitochondrial morphology in the cKO mice, with NMN treatment restoring sarcomere alignment but not mitochondrial morphology. This study demonstrates that neuronal NAMPT is important for pre-/post-synaptic NMJ function, and maintaining skeletal muscular function and structure.

scholarly journals Tissue-specific dynamin-1 deletion at the calyx of Held decreases short-term depression through a mechanism distinct from vesicle resupply

2016 ◽  
Vol 113 (22) ◽  
pp. E3150-E3158 ◽  
Author(s):  
Satyajit Mahapatra ◽  
Fan Fan ◽  
Xuelin Lou
Keyword(s):  
Steady State ◽  
Synaptic Vesicle ◽  
High Frequency ◽  
Synaptic Depression ◽  
Conditional Knockout ◽  
High Frequency Stimulation ◽  
Latrunculin B ◽  
Short Term ◽  
Tissue Specific ◽  
Frequency Stimulation

Dynamin is a large GTPase with a crucial role in synaptic vesicle regeneration. Acute dynamin inhibition impairs neurotransmitter release, in agreement with the protein’s established role in vesicle resupply. Here, using tissue-specific dynamin-1 knockout [conditional knockout (cKO)] mice at a fast central synapse that releases neurotransmitter at high rates, we report that dynamin-1 deletion unexpectedly leads to enhanced steady-state neurotransmission and consequently less synaptic depression during brief periods of high-frequency stimulation. These changes are also accompanied by increased transmission failures. Interestingly, synaptic vesicle resupply and several other synaptic properties remain intact, including basal neurotransmission, presynaptic Ca2+ influx, initial release probability, and postsynaptic receptor saturation and desensitization. However, acute application of Latrunculin B, a reagent known to induce actin depolymerization and impair bulk and ultrafast endocytosis, has a stronger effect on steady-state depression in cKO than in control and brings the depression down to a control level. The slow phase of presynaptic capacitance decay following strong stimulation is impaired in cKO; the rapid capacitance changes immediately after strong depolarization are also different between control and cKO and sensitive to Latrunculin B. These data raise the possibility that, in addition to its established function in regenerating synaptic vesicles, the endocytosis protein dynamin-1 may have an impact on short-term synaptic depression. This role comes into play primarily during brief high-frequency stimulation.

The Same Synaptic Vesicles Originate Synchronous and Asynchronous Transmitter Release

Acta Naturae ◽  
2015 ◽  
Vol 7 (3) ◽  
pp. 81-88 ◽  
Author(s):  
P. N. Grigoryev ◽  
A. L. Zefirov
Keyword(s):  
Synaptic Vesicle ◽  
High Frequency ◽  
Transmitter Release ◽  
Synaptic Vesicles ◽  
High Frequency Stimulation ◽  
Vesicle Pools ◽  
Bivalent Cations ◽  
Frequency Stimulation ◽  
Nerve Muscle ◽  
Vesicle Pool

Transmitter release and synaptic vesicle exo- and endocytosis during high-frequency stimulation (20 pulses/s) in the extracellular presence of different bivalent cations (Ca2+, Sr2+ or Ba2+) were studied in frog cutaneous pectoris nerve-muscle preparations. It was shown in electrophysiological experiments that almost only synchronous transmitter release was registered in a Ca2+-containing solution; a high intensity of both synchronous and asynchronous transmitter release was registered in a Sr2+-containing solution, and asynchronous transmitter release almost only was observed in a Ba2+-containing solution. It was shown in experiments with a FM 1-43 fluorescent dye that the synaptic vesicles that undergo exocytosis-endocytosis during synchronous transmitter release (Ca-solutions) are able to participate in asynchronous exocytosis in Ba-solutions. The vesicles that had participated in the asynchronous transmitter release (Ba-solutions) could subsequently participate in a synchronous release (Ca-solutions). It was shown in experiments with isolated staining of recycling and reserve synaptic vesicle pools that both types of evoked transmitter release originate from the same synaptic vesicle pool.

scholarly journals Synaptically Released Glutamate Does Not Overwhelm Transporters on Hippocampal Astrocytes During High-Frequency Stimulation

2000 ◽  
Vol 83 (5) ◽  
pp. 2835-2843 ◽  
Author(s):  
Jeffrey S. Diamond ◽  
Craig E. Jahr
Keyword(s):  
Synaptic Transmission ◽  
High Frequency ◽  
Hippocampal Slices ◽  
Synaptic Cleft ◽  
Long Term Potentiation ◽  
High Frequency Stimulation ◽  
Direct Role ◽  
Ca1 Region ◽  
Frequency Stimulation ◽  
Hippocampal Astrocytes

In addition to maintaining the extracellular glutamate concentration at low ambient levels, high-affinity glutamate transporters play a direct role in synaptic transmission by speeding the clearance of glutamate from the synaptic cleft and limiting the extent to which transmitter spills over between synapses. Transporters are expressed in both neurons and glia, but glial transporters are likely to play the major role in removing synaptically released glutamate from the extracellular space. The role of transporters in synaptic transmission has been studied directly by measuring synaptically activated, transporter-mediated currents (STCs) in neurons and astrocytes. Here we record from astrocytes in the CA1 region of hippocampal slices and elicit STCs with high-frequency (100 Hz) stimulus trains of varying length to determine whether transporters are overwhelmed by stimuli that induce long-term potentiation. We show that, at near-physiological temperatures (34°C), high-frequency stimulation (HFS) does not affect the rate at which transporters clear glutamate from the extrasynaptic space. Thus, although spillover between synapses during “normal” stimulation may compromise the absolute synapse specificity of fast excitatory synaptic transmission, spillover is not exacerbated during HFS. Transporter capacity is diminished somewhat at room temperature (24°C), although transmitter released during brief, “theta burst” stimulation is still cleared as quickly as following a single stimulus, even when transport capacity is partially diminished by pharmacological means.

Short- and long-term synaptic depression in rat neostriatum

1993 ◽  
Vol 70 (5) ◽  
pp. 1937-1949 ◽  
Author(s):  
D. M. Lovinger ◽  
E. C. Tyler ◽  
A. Merritt
Keyword(s):  
High Frequency ◽  
Time Course ◽  
Glutamate Release ◽  
Synaptic Depression ◽  
High Frequency Stimulation ◽  
Glutamatergic Synapses ◽  
Glutamatergic Synaptic Transmission ◽  
Frequency Stimulation ◽  
Short And Long Term

1. We have examined plasticity at glutamatergic synapses on neurons in slices of neostriatum, a forebrain area involved in movement and cognitive function. 2. High-frequency stimulation of afferent inputs to neostriatal neurons induced depression of glutamatergic synaptic transmission. Depression could be induced using either prolonged trains or short repetitive bursts of high-frequency stimulation. Depression developed within seconds after such stimulation. Responses recovered to baseline levels within 10 min in most slices but persisted for up to 60 min in others. 3. Postsynaptic passive electrical properties and the ability to elicit action potentials by postsynaptic depolarization were not altered during depression. 4. The magnitude and time course of depression was similar whether postsynaptic responses were mediated by alpha amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or N-methyl-D-aspartate (NMDA) type glutamate receptors. Depression was not altered by antagonism of AMPA or NMDA receptors or potentiation of AMPA receptor function with aniracetam. 5. Depression was blocked by treatments that increase transmitter release including increased extracellular Ca2+, application of 4-aminopyridine, or application of phorbol ester. 6. Our findings indicate that glutamatergic synapses in neostriatum are capable of expressing a form of synaptic depression that may involve decreased glutamate release.

scholarly journals Bidirectional Long-Term Synaptic Zinc Plasticity at Mouse Glutamatergic Synapses

2018 ◽  
Author(s):  
Nathan W. Vogler ◽  
Thanos Tzounopoulos
Keyword(s):  
Low Frequency ◽  
Dorsal Cochlear Nucleus ◽  
High Frequency Stimulation ◽  
Glutamatergic Synapses ◽  
Zinc Signaling ◽  
Frequency Stimulation ◽  
Zinc Levels ◽  
Group 1

AbstractSynaptic zinc is coreleased with glutamate to modulate neurotransmission in many excitatory synapses. In the auditory cortex, synaptic zinc modulates sound frequency tuning and enhances frequency discrimination acuity. In auditory, visual, and somatosensory circuits, sensory experience causes long-term changes in synaptic zinc levels and/or signaling, termed here synaptic zinc plasticity. However, the mechanisms underlying synaptic zinc plasticity and the effects of this plasticity on long-term glutamatergic plasticity remain unknown. To study these mechanisms, we used male and female mice and employed in vitro and in vivo models in zinc-rich, glutamatergic dorsal cochlear nucleus (DCN) parallel fiber (PF) synapses. High-frequency stimulation of DCN PF synapses induced long-term depression of synaptic zinc signaling (Z-LTD), as evidenced by reduced zinc-mediated inhibition of AMPA receptor (AMPAR) excitatory postsynaptic currents (EPSCs). Low-frequency stimulation induced long-term potentiation of synaptic zinc signaling (Z-LTP), as evidenced by enhanced zinc-mediated inhibition of AMPAR EPSCs. Thus, Z-LTD is a new mechanism of LTP and Z-LTD is a new mechanism of LTP. Pharmacological inhibition of Group 1 metabotropic glutamate receptors (G1 mGluRs) eliminated Z-LTD and Z-LTP. Pharmacological activation of G1 mGluRs induced Z-LTD and Z-LTP, associated with bidirectional changes in presynaptic zinc levels. Finally, exposure of mice to loud sound caused G1 mGluR-dependent Z-LTD in DCN PF synapses, consistent with our in vitro results. Together, we show that G1 mGluR activation is necessary and sufficient for inducing bidirectional long-term synaptic zinc plasticity.Key points summarySynaptic zinc is coreleased with glutamate to modulate neurotransmission and auditory processing. Sensory experience causes long-term changes in synaptic zinc signaling, termed synaptic zinc plasticity.At zinc-containing glutamatergic synapses in the dorsal cochlear nucleus (DCN), we show that high-frequency stimulation reduces synaptic zinc signaling (Z-LTD), whereas low-frequency stimulation increases synaptic zinc signaling (Z-LTP).Group 1 metabotropic glutamate receptor (mGluR) activation is necessary and sufficient to induce Z-LTP and Z-LTD. Z-LTP and Z-LTD are associated with bidirectional changes in presynaptic zinc levels.Sound-induced Z-LTD at DCN synapses requires Group 1 mGluR activation.Bidirectional synaptic zinc plasticity is a previously unknown mechanism of LTP and LTD at zinc-containing glutamatergic synapses.

scholarly journals Glycinergic Transmission in the Presence and Absence of Functional GlyT2: Lessons From the Auditory Brainstem

2021 ◽  
Vol 12 ◽  
Author(s):  
Sina E. Brill ◽  
Ayse Maraslioglu ◽  
Catharina Kurz ◽  
Florian Kramer ◽  
Martin F. Fuhr ◽  
...  
Keyword(s):  
Synaptic Cleft ◽  
Auditory Brainstem ◽  
Dominant Factor ◽  
High Frequency Stimulation ◽  
High Fidelity ◽  
Readily Releasable Pool ◽  
Medial Nucleus ◽  
Frequency Stimulation ◽  
Replenishment Kinetics

Synaptic transmission is controlled by re-uptake systems that reduce transmitter concentrations in the synaptic cleft and recycle the transmitter into presynaptic terminals. The re-uptake systems are thought to ensure cytosolic concentrations in the terminals that are sufficient for reloading empty synaptic vesicles (SVs). Genetic deletion of glycine transporter 2 (GlyT2) results in severely disrupted inhibitory neurotransmission and ultimately to death. Here we investigated the role of GlyT2 at inhibitory glycinergic synapses in the mammalian auditory brainstem. These synapses are tuned for resilience, reliability, and precision, even during sustained high-frequency stimulation when endocytosis and refilling of SVs probably contribute substantially to efficient replenishment of the readily releasable pool (RRP). Such robust synapses are formed between MNTB and LSO neurons (medial nucleus of the trapezoid body, lateral superior olive). By means of patch-clamp recordings, we assessed the synaptic performance in controls, in GlyT2 knockout mice (KOs), and upon acute pharmacological GlyT2 blockade. Via computational modeling, we calculated the reoccupation rate of empty release sites and RRP replenishment kinetics during 60-s challenge and 60-s recovery periods. Control MNTB-LSO inputs maintained high fidelity neurotransmission at 50 Hz for 60 s and recovered very efficiently from synaptic depression. During 'marathon-experiments' (30,600 stimuli in 20 min), RRP replenishment accumulated to 1,260-fold. In contrast, KO inputs featured severe impairments. For example, the input number was reduced to ~1 (vs. ~4 in controls), implying massive functional degeneration of the MNTB-LSO microcircuit and a role of GlyT2 during synapse maturation. Surprisingly, neurotransmission did not collapse completely in KOs as inputs still replenished their small RRP 80-fold upon 50 Hz | 60 s challenge. However, they totally failed to do so for extended periods. Upon acute pharmacological GlyT2 inactivation, synaptic performance remained robust, in stark contrast to KOs. RRP replenishment was 865-fold in marathon-experiments, only ~1/3 lower than in controls. Collectively, our empirical and modeling results demonstrate that GlyT2 re-uptake activity is not the dominant factor in the SV recycling pathway that imparts indefatigability to MNTB-LSO synapses. We postulate that additional glycine sources, possibly the antiporter Asc-1, contribute to RRP replenishment at these high-fidelity brainstem synapses.

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