Faculty Opinions recommendation of Inhibitory synapses are repeatedly assembled and removed at persistent sites in vivo.

Abstract Heparan sulfate proteoglycans contribute to the structural organization of various neurochemical synapses. Depending on the system, their role involves either the core protein or the glycosaminoglycan chains. These linear sugar chains are extensively modified by heparan sulfate modification enzymes, resulting in highly diverse molecules. Specific modifications of glycosaminoglycan chains may thus contribute to a sugar code involved in synapse specificity. Caenorhabditis elegans is particularly useful to address this question because of the low level of genomic redundancy of these enzymes, as opposed to mammals. Here, we systematically mutated the genes encoding heparan sulfate modification enzymes in C. elegans and analyzed their impact on excitatory and inhibitory neuromuscular junctions. Using single chain antibodies that recognize different heparan sulfate modification patterns, we show in vivo that these two heparan sulfate epitopes are carried by the SDN-1 core protein, the unique C. elegans syndecan orthologue, at neuromuscular junctions. Intriguingly, these antibodies differentially bind to excitatory and inhibitory synapses, implying unique heparan sulfate modification patterns at different neuromuscular junctions. Moreover, while most enzymes are individually dispensable for proper organization of neuromuscular junctions, we show that 3-O-sulfation of SDN-1 is required to maintain wild-type levels of the extracellular matrix protein MADD-4/Punctin, a central synaptic organizer that defines the identity of excitatory and inhibitory synaptic domains at the plasma membrane of muscle cells.

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Short-Term Plasticity at Inhibitory Synapses in Rat Striatum and Its Effects on Striatal Output

Journal of Neurophysiology ◽

10.1152/jn.2001.85.5.2088 ◽

2001 ◽

Vol 85 (5) ◽

pp. 2088-2099 ◽

Cited By ~ 25

Author(s):

John S. Fitzpatrick ◽

Garnik Akopian ◽

John P. Walsh

Keyword(s):

Action Potentials ◽

Brain Slices ◽

Current Injection ◽

Inhibitory Synapses ◽

Rat Striatum ◽

Short Term ◽

Short Term Plasticity ◽

Adult Rat ◽

Glutamate Receptor Antagonists

Two forms of short-term plasticity at inhibitory synapses were investigated in adult rat striatal brain slices using intracellular recordings. Intrastriatal stimulation in the presence of the ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (20 μM) andd,l-2-amino-5-phosphonovaleric acid (50 μM) produced an inhibitory postsynaptic potential (IPSP) that reversed polarity at −76 ± 1 (SE) mV and was sensitive to bicuculline (30 μM). The IPSP rectified at hyperpolarized membrane potentials due in part to activation of K+ channels. The IPSP exhibited two forms of short-term plasticity, paired-pulse depression (PPD) and synaptic augmentation. PPD lasted for several seconds and was greatest at interstimulus intervals (ISIs) of several hundred milliseconds, reducing the IPSP to 80 ± 2% of its control amplitude at an ISI of 200 ms. Augmentation of the IPSP, elicited by a conditioning train of 15 stimuli applied at 20 Hz, was 119 ± 1% of control when sampled 2 s after the conditioning train. Augmentation decayed with a time constant of 10 s. We tested if PPD and augmentation modify the ability of the IPSP to prevent the generation of action potentials. A train of action potentials triggered by a depolarizing current injection of constant amplitude could be interrupted by stimulation of an IPSP. If this IPSP was the second in a pair of IPSPs, it was less effective in blocking spikes due to PPD. By contrast, augmented IPSPs were more effective in blocking spikes. The same results were achieved when action potentials were triggered by a depolarizing current injection of varying amplitude, a manipulation that produces nearly identical spike times from trial to trial and approximates the in vivo behavior of these neurons. These results demonstrate that short-term plasticity of inhibition can modify the output of the striatum and thus may be an important component of information processing during behaviors that involve the striatum.

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Cytoplasmic accumulation of FUS triggers early behavioral alterations linked to cortical neuronal hyperactivity and defects in inhibitory synapses

10.1101/2020.06.09.141556 ◽

2020 ◽

Author(s):

Jelena Scekic-Zahirovic ◽

Inmaculada Sanjuan-Ruiz ◽

Vanessa Kan ◽

Salim Megat ◽

Pierre De Rossi ◽

...

Keyword(s):

Neuronal Activity ◽

Rna Binding ◽

Gene Mutations ◽

Neuronal Loss ◽

Inhibitory Neurons ◽

Inhibitory Synapses ◽

Behavioral Alterations ◽

Behavioral Abnormalities ◽

Cytoplasmic Accumulation

AbstractGene mutations causing cytoplasmic mislocalization of the RNA-binding protein FUS, lead to severe forms of amyotrophic lateral sclerosis (ALS). Cytoplasmic accumulation of FUS is also observed in other diseases, with unknown consequences. Here, we show that cytoplasmic mislocalization of FUS drives behavioral abnormalities in knock-in mice, including locomotor hyperactivity and alterations in social interactions, in the absence of widespread neuronal loss. Mechanistically, we identified a profound increase in neuronal activity in the frontal cortex of Fus knock-in mice in vivo. Importantly, RNAseq analysis suggested involvement of defects in inhibitory neurons, that was confirmed by ultrastructural and morphological defects of inhibitory synapses and increased synaptosomal levels of mRNAs involved in inhibitory neurotransmission. Thus, cytoplasmic FUS triggers inhibitory synaptic deficits, leading to increased neuronal activity and behavioral phenotypes. FUS mislocalization may trigger deleterious phenotypes beyond motor neuron impairment in ALS, but also in other neurodegenerative diseases with FUS mislocalization.

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Altered GABAA,slow Inhibition and Network Oscillations in Mice Lacking the GABAA Receptor β3 Subunit

Journal of Neurophysiology ◽

10.1152/jn.00651.2009 ◽

2009 ◽

Vol 102 (6) ◽

pp. 3643-3655 ◽

Cited By ~ 23

Author(s):

Harald Hentschke ◽

Claudia Benkwitz ◽

Matthew I. Banks ◽

Mark G. Perkins ◽

Gregg E. Homanics ◽

...

Keyword(s):

Pyramidal Neurons ◽

Epileptiform Activity ◽

Gamma Oscillations ◽

Theta Oscillations ◽

Network Activity ◽

Inhibitory Synapses ◽

Gabaergic Inhibition ◽

Wild Type ◽

Hippocampal Network

Phasic GABAergic inhibition in hippocampus and neocortex falls into two kinetically distinct categories, GABAA,fast and GABAA,slow. In hippocampal area CA1, GABAA,fast is generally believed to underlie gamma oscillations, whereas the contribution of GABAA,slow to hippocampal rhythms has been speculative. Hypothesizing that GABAA receptors containing the β3 subunit contribute to GABAA,slow inhibition and that slow inhibitory synapses control excitability as well as contribute to network rhythms, we investigated the consequences of this subunit's absence on synaptic inhibition and network function. In pyramidal neurons of GABAA receptor β3 subunit-deficient (β3−/−) mice, spontaneous GABAA,slow inhibitory postsynaptic currents (IPSCs) were much less frequent, and evoked GABAA,slow currents were much smaller than in wild-type mice. Fittingly, long-lasting recurrent inhibition of population spikes was less powerful in the mutant, indicating that receptors containing β3 subunits contribute substantially to GABAA,slow currents in pyramidal neurons. By contrast, slow inhibitory control of GABAA,fast-producing interneurons was unaffected in β3−/− mice. In vivo hippocampal network activity was markedly different in the two genotypes. In β3−/− mice, epileptiform activity was observed, and theta oscillations were weaker, slower, less regular and less well coordinated across laminae compared with wild-type mice, whereas gamma oscillations were weaker and faster. The amplitude modulation of gamma oscillations at theta frequency (“nesting”) was preserved but was less well coordinated with theta oscillations. With the caveat that seizure-induced changes in inhibitory circuits might have contributed to the changes observed in the mutant animals, our results point to a strong contribution of β3 subunits to slow GABAergic inhibition onto pyramidal neurons but not onto GABAA,fast -producing interneurons and support different roles for these slow inhibitory synapses in the generation and coordination of hippocampal network rhythms.

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Spatial distribution of excitatory and inhibitory synapses on a Purkinje cell in a rat cerebellar culture

Journal of Neurophysiology ◽

10.1152/jn.1993.70.4.1316 ◽

1993 ◽

Vol 70 (4) ◽

pp. 1316-1325 ◽

Cited By ~ 55

Author(s):

T. Hirano ◽

K. Kasono

Keyword(s):

Spatial Distribution ◽

Purkinje Cell ◽

Purkinje Cells ◽

Spatial Organization ◽

Lucifer Yellow ◽

Inhibitory Synapses ◽

Presynaptic Neuron ◽

Presynaptic Terminals ◽

Excitatory And Inhibitory Synapses

1. The spatial distribution of excitatory and inhibitory synapses on cultured Purkinje cells was studied with fluorescence, scanning electron microscopy (SEM), and electrophysiological techniques. 2. Presynaptic terminals were identified with immunohistochemical staining of synaptophysin and the results were correlated with SEM micrographs. 3. Excitatory and inhibitory inputs onto the Purkinje cell were identified from the direction and pharmacology of the postsynaptic current. 4. The localization of the presynaptic terminals on the Purkinje cell was observed after electrophysiological identification by filling the presynaptic neuron with Lucifer yellow and the Purkinje cell with Texas red. 5. The axon and presynaptic terminals of excitatory and inhibitory inputs had a different spatial organization. Excitatory inputs from granule cells were exclusively localized on the dendrites of Purkinje cells, whereas inhibitory contacts were found on both the soma and dendrites. This result is similar to that described in vivo.

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Glycinergic inhibition to the medial nucleus of the trapezoid body shows prominent facilitation and can sustain high levels of ongoing activity

Journal of Neurophysiology ◽

10.1152/jn.00864.2013 ◽

2014 ◽

Vol 112 (11) ◽

pp. 2901-2915 ◽

Cited By ~ 9

Author(s):

Florian Mayer ◽

Otto Albrecht ◽

Anna Dondzillo ◽

Achim Klug

Keyword(s):

Meriones Unguiculatus ◽

Inhibitory Synapses ◽

Auditory Information ◽

Activity Levels ◽

Synaptic Currents ◽

Medial Nucleus ◽

Highly Active ◽

Glycinergic Inhibition ◽

Trapezoid Body

Neurons in the medial nucleus of the trapezoid body (MNTB) are well known for their prominent excitatory inputs, mediated by the calyx of Held. Less attention has been paid to the prominent inhibitory inputs that MNTB neurons also receive. Because of their auditory nature, both excitatory and inhibitory synapses are highly active in vivo. These high levels of activity are known to reduce excitatory synaptic currents considerably, such that in vivo synaptic currents produced by the calyx are smaller than typically measured in standard brain slice experiments. The goal of this study was to investigate the properties of the inhibitory inputs in the Mongolian gerbil ( Meriones unguiculatus) under activity levels that correspond to those in the intact brain to facilitate a direct comparison between the two inputs. Our results suggest that inhibitory inputs to MNTB are largely mediated by a fast and phasic glycinergic component, and to a lesser degree by a GABAergic component. The glycinergic component can sustain prolonged high levels of activity. Even when challenged with stimulus patterns consisting of thousands of stimuli over tens of minutes, glycinergic inputs to MNTB maintain large conductances and fast decays and even facilitate substantially when the stimulation frequency is increased. The inhibition is mediated by a relatively small number of independent input fibers. The data presented here suggest that inhibitory inputs to MNTB sustain high levels of activity and need to be considered for a full understanding of mechanisms underlying processing of auditory information in MNTB.

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Synaptic vesicles dynamics in neocortical epilepsy

10.1101/2020.01.05.895029 ◽

2020 ◽

Cited By ~ 1

Author(s):

Eleonora Vannini ◽

Laura Restani ◽

Marialaura Dilillo ◽

Liam McDonnell ◽

Matteo Caleo ◽

...

Keyword(s):

Synaptic Vesicles ◽

Inhibitory Synapses ◽

Excitatory Synapses ◽

Synaptic Release ◽

Spatial Reorganization ◽

Complex Landscape ◽

Specific Proteins ◽

Neocortical Epilepsy ◽

Epileptic Networks

AbstractNeuronal hyperexcitability often results from an unbalance between excitatory and inhibitory neurotransmission, but the synaptic alterations leading to enhanced seizure propensity are only partly understood. Taking advantage of a mouse model of neocortical epilepsy, we used a combination of photoconversion and electron microscopy to assess changes in synaptic vesicles pools in vivo. Our analyses reveal that epileptic networks show an early onset lengthening of active zones at inhibitory synapses, together with a delayed spatial reorganization of recycled vesicles at excitatory synapses. Proteomics of synaptic content indicate that specific proteins were increased in epileptic mice. Altogether, our data reveal a complex landscape of nanoscale changes affecting the epileptic synaptic release machinery. In particular, our findings show that an altered positioning of release-competent vesicles represent a novel signature of epileptic networks.

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Loss of EPAC2 results in altered synaptic composition of dendritic spines and excitatory and inhibitory balance

10.1101/526772 ◽

2019 ◽

Author(s):

Kelly A Jones ◽

Michiko Sumiya ◽

Kevin M Woolfrey ◽

Deepak P Srivastava ◽

Peter Penzes

Keyword(s):

Ampa Receptors ◽

Cortical Neurons ◽

Glutamate Transporter ◽

Autism Spectrum ◽

Small Gtpase ◽

Anterior Cingulate ◽

Synaptic Proteins ◽

Inhibitory Synapses ◽

Nucleotide Exchange

EPAC2 is a guanine nucleotide exchange factor that regulates GTPase activity of the small GTPase Rap and Ras) and is highly enriched at synapses. Activation of EPAC2 has been shown to induce dendritic spine shrinkage and increase spine motility, effects that are necessary for synaptic plasticity. These morphological effects are dysregulated by rare mutations of EPAC2 associated with autism spectrum disorders. In addition, EPAC2 destabilizes synapses through the removal of synaptic GluA2/3-containing AMPA receptors. Previous work has shown that Epac2 knockout mice (Epac2-/-) display abnormal social interactions, as well as gross disorganization of the frontal cortex and abnormal spine motility in vivo. In this study we sought to further understand the cellular consequences of knocking out Epac2 on the development of neuronal and synaptic structure and organization of cortical neurons. Using primary cortical neurons generated from Epac2+/+ or Epac2-/- mice, we confirm that EPAC2 is required for cAMP-dependent spine shrinkage. Neurons from Epac2-/- mice also displayed increased synaptic expression of GluA2/3-containing AMPA receptors, as well as of the adhesion protein N-cadherin. Intriguingly, analysis of excitatory and inhibitory synaptic proteins revealed that loss of EPAC2 resulted in altered of expression of vesicular glutamate transporter 1 (VGluT1) and vesicular GABA transporter (VGAT), indicating a potential imbalance in excitatory/inhibitory inputs onto neurons. Finally, examination of cortical neurons located within the anterior cingulate cortex further revealed subtle deficits in the establishment of dendritic arborization in vivo. These data provide evidence that EPAC2 is required for the correct composition of synapses and that loss of this protein could result in an imbalance of excitatory and inhibitory synapses.

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NG2 glia-derived GABA release tunes inhibitory synapses and contributes to stress-induced anxiety

Nature Communications ◽

10.1038/s41467-021-25956-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Xiao Zhang ◽

Yao Liu ◽

Xiaoqi Hong ◽

Xia Li ◽

Charles K. Meshul ◽

...

Keyword(s):

Gaba Release ◽

Cell Types ◽

Inhibitory Synapses ◽

Physiological Relevance ◽

Chronic Social Defeat Stress ◽

Early Brain Development ◽

Synaptic Complexes ◽

Oligodendrocyte Precursor ◽

Vesicular Exocytosis

AbstractNG2 glia, also known as oligodendrocyte precursor cells (OPCs), play an important role in proliferation and give rise to myelinating oligodendrocytes during early brain development. In contrast to other glial cell types, the most intriguing aspect of NG2 glia is their ability to directly sense synaptic inputs from neurons. However, whether this synaptic interaction is bidirectional or unidirectional, or its physiological relevance has not yet been clarified. Here, we report that NG2 glia form synaptic complexes with hippocampal interneurons and that selective photostimulation of NG2 glia (expressing channelrhodopsin-2) functionally drives GABA release and enhances inhibitory synaptic transmission onto proximal interneurons in a microcircuit. The mechanism involves GAD67 biosynthesis and VAMP-2 containing vesicular exocytosis. Further, behavioral assays demonstrate that NG2 glia photoactivation triggers anxiety-like behavior in vivo and contributes to chronic social defeat stress.

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Synaptic plasticity of inhibitory synapses onto medial olivocochlear efferent neurons

10.1101/2022.01.05.475100 ◽

2022 ◽

Author(s):

Lester Torres Cadenas ◽

Hui Cheng ◽

Catherine J.C. Weisz

Keyword(s):

Brain Slices ◽

Synaptic Depression ◽

Extracellular Calcium ◽

Outer Hair Cells ◽

Inhibitory Synapses ◽

Short Term ◽

Sound Stimulation ◽

Efferent Neurons ◽

Medial Olivocochlear

The descending auditory system modulates the ascending system at every level. The final descending, or efferent stage, is comprised of lateral olivocochlear (LOC) and medial olivocochlear (MOC) neurons. MOC somata in the ventral brainstem project axons to the cochlea to synapse onto outer hair cells (OHC), inhibiting OHC-mediated cochlear amplification. MOC suppression of OHC function is implicated in cochlear gain control with changing sound intensity, detection of salient stimuli, attention, and protection against acoustic trauma. Thus, sound excites MOC neurons to provide negative feedback of the cochlea. Sound also inhibits MOC neurons via medial nucleus of the trapezoid body (MNTB) neurons. However, MNTB-MOC synapses exhibit short-term depression, suggesting reduced MNTB-MOC inhibition during sustained stimuli. Further, due to high rates of both baseline and sound-evoked activity in MNTB neurons in vivo, MNTB-MOC synapses may be tonically depressed. To probe this, we characterized short-term plasticity of MNTB-MOC synapses in mouse brain slices. We mimicked in vivo-like temperature and extracellular calcium conditions, and in vivo-like activity patterns of fast synaptic activation rates, sustained activation, and prior tonic activity. Synaptic depression was sensitive to extracellular calcium concentration and temperature. During rapid MNTB axon stimulation, post-synaptic currents (PSCs) in MOC neurons summated but with concurrent depression, resulting in smaller, sustained currents, suggesting tonic inhibition of MOC neurons during rapid circuit activity. Low levels of baseline MNTB activity did not significantly reduce responses to subsequent rapid activity that mimics sound stimulation, indicating that, in vivo, MNTB inhibition of MOC neurons persists despite tonic synaptic depression.

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