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Trends in Neurosciences Jul 2011Rapid communication in the brain relies on the release and diffusion of small transmitter molecules across the synaptic cleft. How these diffuse signals are transformed... (Review)
Review
Rapid communication in the brain relies on the release and diffusion of small transmitter molecules across the synaptic cleft. How these diffuse signals are transformed into cellular responses is determined by the scatter of target postsynaptic receptors, which in turn depends on receptor movement in cell membranes. Thus, by shaping information transfer in neural circuits, mechanisms that regulate molecular mobility affect nearly every aspect of brain function and dysfunction. Here we review two facets of molecular mobility that have traditionally been considered separately, namely extracellular and intra-membrane diffusion. By focusing on the interplay between these processes we illustrate the remarkable versatility of signal formation in synapses and highlight areas of emerging understanding in the molecular physiology and biophysics of synaptic transmission.
Topics: Animals; Brain; Diffusion; Humans; Neurotransmitter Agents; Presynaptic Terminals; Synapses; Synaptic Transmission
PubMed: 21470699
DOI: 10.1016/j.tins.2011.03.002 -
Nature Communications Oct 2015It remains unclear how readiness for Ca(2+)-dependent exocytosis depends on varying degrees of SNARE complex assembly. Here we directly investigate the SNARE assembly...
It remains unclear how readiness for Ca(2+)-dependent exocytosis depends on varying degrees of SNARE complex assembly. Here we directly investigate the SNARE assembly using two-photon fluorescence lifetime imaging (FLIM) of Förster resonance energy transfer (FRET) between three pairs of neuronal SNAREs in presynaptic boutons and pancreatic β cells in the islets of Langerhans. These FRET probes functionally rescue their endogenous counterparts, supporting ultrafast exocytosis. We show that trans-SNARE complexes accumulated in the active zone, and estimate the number of complexes associated with each docked vesicle. In contrast, SNAREs were unassembled in resting state, and assembled only shortly prior to insulin exocytosis, which proceeds slowly. We thus demonstrate that distinct states of fusion readiness are associated with SNARE complex formation. Our FRET/FLIM approaches enable optical imaging of fusion readiness in both live and chemically fixed tissues.
Topics: Animals; Exocytosis; Fluorescence Resonance Energy Transfer; Insulin-Secreting Cells; Mice; Mice, Inbred C57BL; Optical Imaging; Presynaptic Terminals; SNARE Proteins
PubMed: 26439845
DOI: 10.1038/ncomms9531 -
ENeuro Oct 2023The mushroom body (MB) is an important model system for studying the synaptic mechanisms of associative learning. In this system, coincidence of odor-evoked calcium...
The mushroom body (MB) is an important model system for studying the synaptic mechanisms of associative learning. In this system, coincidence of odor-evoked calcium influx and dopaminergic input in the presynaptic terminals of Kenyon cells (KCs), the principal neurons of the MB, triggers long-term depression (LTD), which plays a critical role in olfactory learning. However, it is controversial whether such synaptic plasticity is accompanied by a corresponding decrease in odor-evoked calcium activity in the KC presynaptic terminals. Here, we address this question by inducing LTD by pairing odor presentation with optogenetic activation of dopaminergic neurons (DANs). This allows us to rigorously compare the changes at the presynaptic and postsynaptic sites in the same conditions. By imaging presynaptic acetylcholine release in the condition where LTD is reliably observed in the postsynaptic calcium signals, we show that neurotransmitter release from KCs is depressed selectively in the MB compartments innervated by activated DANs, demonstrating the presynaptic nature of LTD. However, total odor-evoked calcium activity of the KC axon bundles does not show concurrent depression. We further conduct calcium imaging in individual presynaptic boutons and uncover the highly heterogeneous nature of calcium plasticity. Namely, only a subset of boutons, which are strongly activated by associated odors, undergo calcium activity depression, while weakly responding boutons show potentiation. Thus, our results suggest an unexpected nonlinear relationship between presynaptic calcium influx and the results of plasticity, challenging the simple view of cooperative actions of presynaptic calcium and dopaminergic input.
Topics: Animals; Drosophila; Presynaptic Terminals; Mushroom Bodies; Calcium; Dopamine; Dopaminergic Neurons; Neuronal Plasticity
PubMed: 37848287
DOI: 10.1523/ENEURO.0275-23.2023 -
Molecular Brain Sep 2020Variants of the cytoplasmic FMR1-interacting protein (CYFIP) gene family, CYFIP1 and CYFIP2, are associated with numerous neurodevelopmental and neuropsychiatric...
Variants of the cytoplasmic FMR1-interacting protein (CYFIP) gene family, CYFIP1 and CYFIP2, are associated with numerous neurodevelopmental and neuropsychiatric disorders. According to several studies, CYFIP1 regulates the development and function of both pre- and post-synapses in neurons. Furthermore, various studies have evaluated CYFIP2 functions in the postsynaptic compartment, such as regulating dendritic spine morphology; however, no study has evaluated whether and how CYFIP2 affects presynaptic functions. To address this issue, in this study, we have focused on the presynapses of layer 5 neurons of the medial prefrontal cortex (mPFC) in adult Cyfip2 heterozygous (Cyfip2) mice. Electrophysiological analyses revealed an enhancement in the presynaptic short-term plasticity induced by high-frequency stimuli in Cyfip2 neurons compared with wild-type neurons. Since presynaptic mitochondria play an important role in buffering presynaptic Ca, which is directly associated with the short-term plasticity, we analyzed presynaptic mitochondria using electron microscopic images of the mPFC. Compared with wild-type mice, the number, but not the volume or cristae density, of mitochondria in both presynaptic boutons and axonal processes in the mPFC layer 5 of Cyfip2 mice was reduced. Consistent with an identification of mitochondrial proteins in a previously established CYFIP2 interactome, CYFIP2 was detected in a biochemically enriched mitochondrial fraction of the mouse mPFC. Collectively, these results suggest roles for CYFIP2 in regulating presynaptic functions, which may involve presynaptic mitochondrial changes.
Topics: Adaptor Proteins, Signal Transducing; Animals; Heterozygote; Mice; Mitochondria; Prefrontal Cortex; Presynaptic Terminals
PubMed: 32917241
DOI: 10.1186/s13041-020-00668-4 -
The Journal of Neuroscience : the... Apr 2018The timing and probability of synaptic vesicle fusion from presynaptic terminals is governed by the distance between voltage-gated Ca channels (VGCCs) and Ca sensors for...
The timing and probability of synaptic vesicle fusion from presynaptic terminals is governed by the distance between voltage-gated Ca channels (VGCCs) and Ca sensors for exocytosis. This VGCC-sensor coupling distance can be determined from the fractional block of vesicular release by exogenous Ca chelators, which depends on biophysical factors that have not been thoroughly explored. Using numerical simulations of Ca reaction and diffusion, as well as vesicular release, we examined the contributions of conductance, density, and open duration of VGCCs, and the influence of endogenous Ca buffers on the inhibition of exocytosis by EGTA. We found that estimates of coupling distance are critically influenced by the duration and amplitude of Ca influx at active zones, but relatively insensitive to variations of mobile endogenous buffer. High concentrations of EGTA strongly inhibit vesicular release in close proximity (20-30 nm) to VGCCs if the flux duration is brief, but have little influence for longer flux durations that saturate the Ca sensor. Therefore, the diversity in presynaptic action potential duration is sufficient to alter EGTA inhibition, resulting in errors potentially as large as 300% if Ca entry durations are not considered when estimating VGCC-sensor coupling distances. The coupling distance between voltage-gated Ca channels and Ca sensors for exocytosis critically determines the timing and probability of neurotransmitter release. Perfusion of presynaptic terminals with the exogenous Ca chelator EGTA has been widely used for both qualitative and quantitative estimates of this distance. However, other presynaptic terminal parameters such as the amplitude and duration of Ca entry can also influence EGTA inhibition of exocytosis, thus confounding conclusions based on EGTA alone. Here, we performed reaction-diffusion simulations of Ca-driven synaptic vesicle fusion, which delineate the critical parameters influencing an accurate prediction of coupling distance. Our study provides guidelines for characterizing and understanding how variability in coupling distance across chemical synapses could be estimated accurately.
Topics: Animals; Calcium; Calcium Channels; Calcium Chelating Agents; Egtazic Acid; Exocytosis; Models, Theoretical; Presynaptic Terminals; Synaptic Vesicles
PubMed: 29563180
DOI: 10.1523/JNEUROSCI.2061-17.2018 -
Traffic (Copenhagen, Denmark) Dec 2010It has long been known that the maintenance of fast communication between neurons requires that presynaptic terminals recycle the small vesicles from which... (Review)
Review
It has long been known that the maintenance of fast communication between neurons requires that presynaptic terminals recycle the small vesicles from which neurotransmitter is released. But the mechanisms that retrieve vesicles from the cell surface are still not understood. Although we have a wealth of information about the molecular details of endocytosis in non-neuronal cells, it is clear that endocytosis at the synapse is faster and regulated in distinct ways. A satisfying understanding of these processes will require molecular events to be manipulated while observing endocytosis in living synapses. Here, we review recent work that seeks to bridge the gap between physiology and molecules to unravel the endocytic machinery operating at the synaptic terminal.
Topics: Adaptor Proteins, Vesicular Transport; Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Clathrin; Clathrin-Coated Vesicles; Drosophila; Drosophila Proteins; Endocytosis; Mice; Presynaptic Terminals; Rats; Synaptic Vesicles
PubMed: 20633242
DOI: 10.1111/j.1600-0854.2010.01104.x -
International Journal of Molecular... Nov 2020Botulinum neurotoxins (BoNTs) are highly potent, neuroparalytic protein toxins that block the release of acetylcholine from motor neurons and autonomic synapses. The... (Review)
Review
Botulinum neurotoxins (BoNTs) are highly potent, neuroparalytic protein toxins that block the release of acetylcholine from motor neurons and autonomic synapses. The unparalleled toxicity of BoNTs results from the highly specific and localized cleavage of presynaptic proteins required for nerve transmission. Currently, the only pharmacotherapy for botulism is prophylaxis with antitoxin, which becomes progressively less effective as symptoms develop. Treatment for symptomatic botulism is limited to supportive care and artificial ventilation until respiratory function spontaneously recovers, which can take weeks or longer. Mechanistic insights into intracellular toxin behavior have progressed significantly since it was shown that toxins exploit synaptic endocytosis for entry into the nerve terminal, but fundamental questions about host-toxin interactions remain unanswered. Chief among these are mechanisms by which BoNT is internalized into neurons and trafficked to sites of molecular toxicity. Elucidating how receptor-bound toxin is internalized and conditions under which the toxin light chain engages with target SNARE proteins is critical for understanding the dynamics of intoxication and identifying novel therapeutics. Here, we discuss the implications of newly discovered modes of synaptic vesicle recycling on BoNT uptake and intraneuronal trafficking.
Topics: Animals; Antitoxins; Botulinum Toxins; Botulism; Drug Delivery Systems; Humans; Motor Neurons; Presynaptic Terminals; Protein Transport; Synaptic Transmission
PubMed: 33218099
DOI: 10.3390/ijms21228715 -
Journal of Psychopharmacology (Oxford,... Jan 2021The therapeutic effects of antipsychotic drugs (APDs) are mainly attributed to their postsynaptic inhibitory functions on the dopamine D2 receptor, which, however,...
BACKGROUND
The therapeutic effects of antipsychotic drugs (APDs) are mainly attributed to their postsynaptic inhibitory functions on the dopamine D2 receptor, which, however, cannot explain the delayed onset of full therapeutic efficacy. It was previously shown that APDs accumulate in presynaptic vesicles during chronic treatment and are released like neurotransmitters in an activity-dependent manner triggering an auto-inhibitory feedback mechanism. Although closely mirroring therapeutic action onset, the functional consequence of the APD accumulation process remained unclear.
AIMS
Here we tested whether the accumulation of the APD haloperidol (HAL) is required for full therapeutic action in psychotic-like rats.
METHODS
We designed a HAL analog compound (HAL-F), which lacks the accumulation property of HAL, but retains its postsynaptic inhibitory action on dopamine D2 receptors.
RESULTS/OUTCOMES
By perfusing LysoTracker fluorophore-stained cultured hippocampal neurons, we confirmed the accumulation of HAL and the non-accumulation of HAL-F. In an amphetamine hypersensitization psychosis-like model in rats, we found that subchronic intracerebroventricularly delivered HAL (0.1 mg/kg/day), but not HAL-F (0.3-1.5 mg/kg/day), attenuates psychotic-like behavior in rats.
CONCLUSIONS/INTERPRETATION
These findings suggest the presynaptic accumulation of HAL may serve as an essential prerequisite for its full antipsychotic action and may explain the time course of APD action. Targeting accumulation properties of APDs may, thus, become a new strategy to improve APD action.
Topics: Animals; Antipsychotic Agents; Cells, Cultured; Dopamine D2 Receptor Antagonists; Drug Delivery Systems; Haloperidol; Hippocampus; Inhibitory Postsynaptic Potentials; Presynaptic Terminals; Psychotic Disorders; Rats; Receptors, Dopamine D2; Synaptic Vesicles
PubMed: 33274688
DOI: 10.1177/0269881120965908 -
The Neuroscientist : a Review Journal... Aug 2015Synaptic vesicle (SV) retrieval from the presynaptic plasma membrane occurs via a variety of different and complementary modes. The dominant retrieval mode during... (Review)
Review
Synaptic vesicle (SV) retrieval from the presynaptic plasma membrane occurs via a variety of different and complementary modes. The dominant retrieval mode during high-intensity stimulation is activity-dependent bulk endocytosis (ADBE). ADBE involves the generation of endosomes direct from the plasma membrane which then donate membrane and cargo to form SVs that replenish the reserve SV pool. Recent evidence has suggested that ADBE may involve an additional endosomal processing step to produce a mature, functional SV. This suggests that ADBE may utilize key molecules or indeed whole pathways from classical endocytic recycling routes that are ubiquitous across all cell types. This review will assess the current evidence for a contribution of endocytic recycling to the SV life cycle, with a particular focus on ADBE. In doing so it highlights points where both routes may either converge or exploit existing mechanisms to ensure efficient generation of SVs during high-intensity stimulation.
Topics: Animals; Brain; Endocytosis; Endosomes; Humans; Presynaptic Terminals; Protein Transport; Synaptic Vesicles
PubMed: 25027635
DOI: 10.1177/1073858414542251 -
Annals of Neurology Dec 2017The first aim was to demonstrate a previously hypothesized increased sensitivity of corticostriatal glutamatergic terminals in the rodent with brain iron deficiency...
OBJECTIVE
The first aim was to demonstrate a previously hypothesized increased sensitivity of corticostriatal glutamatergic terminals in the rodent with brain iron deficiency (BID), a pathogenetic model of restless legs syndrome (RLS). The second aim was to determine whether these putative hypersensitive terminals could constitute a significant target for drugs effective in RLS, including dopamine agonists (pramipexole and ropinirole) and α δ ligands (gabapentin).
METHODS
A recently introduced in vivo optogenetic-microdialysis approach was used, which allows the measurement of the extracellular concentration of glutamate upon local light-induced stimulation of corticostriatal glutamatergic terminals. The method also allows analysis of the effect of local perfusion of compounds within the same area being sampled for glutamate.
RESULTS
BID rats showed hypersensitivity of corticostriatal glutamatergic terminals (lower frequency of optogenetic stimulation to induce glutamate release). Both hypersensitive and control glutamatergic terminals were significant targets for locally perfused pramipexole, ropinirole, and gabapentin, which significantly counteracted optogenetically induced glutamate release. The use of selective antagonists demonstrated the involvement of dopamine D and D receptor subtypes in the effects of pramipexole.
INTERPRETATION
Hypersensitivity of corticostriatal glutamatergic terminals can constitute a main pathogenetic mechanism of RLS symptoms. Selective D receptor agonists, by specifically targeting these terminals, should provide a new efficient treatment with fewer secondary effects. Ann Neurol 2017;82:951-960.
Topics: Amines; Animals; Cerebral Cortex; Corpus Striatum; Cyclohexanecarboxylic Acids; Dopamine Agonists; Gabapentin; Male; Microdialysis; Optogenetics; Presynaptic Terminals; Rats; Rats, Sprague-Dawley; Restless Legs Syndrome; gamma-Aminobutyric Acid
PubMed: 29171915
DOI: 10.1002/ana.25104