Impact of Synaptic Neurotransmitter Concentration Time Course on the Kinetics and Pharmacological Modulation of Inhibitory Synaptic Currents

The time course of synaptic currents is a crucial determinant of rapid signaling between neurons. Traditionally, the mechanisms underlying the shape of synaptic signals are classified as pre- and post-synaptic. Over the last two decades, an extensive body of evidence indicated that synaptic signals are critically shaped by the neurotransmitter time course which encompasses several phenomena including pre- and post-synaptic ones. The agonist transient depends on neurotransmitter release mechanisms, diffusion within the synaptic cleft, spill-over to the extra-synaptic space, uptake, and binding to post-synaptic receptors. Most estimates indicate that the neurotransmitter transient is very brief, lasting between one hundred up to several hundreds of microseconds, implying that post-synaptic activation is characterized by a high degree of non-equilibrium. Moreover, pharmacological studies provide evidence that the kinetics of agonist transient plays a crucial role in setting the susceptibility of synaptic currents to modulation by a variety of compounds of physiological or clinical relevance. More recently, the role of the neurotransmitter time course has been emphasized by studies carried out on brain slice models that revealed a striking, cell-dependent variability of synaptic agonist waveforms ranging from rapid pulses to slow volume transmission. In the present paper we review the advances on studies addressing the impact of synaptic neurotransmitter transient on kinetics and pharmacological modulation of synaptic currents at inhibitory synapses

Correlating Fluorescence and High-Resolution Scanning Electron Microscopy (HRSEM) for the study of GABAA receptor clustering induced by inhibitory synaptic plasticity

Both excitatory and inhibitory synaptic contacts display activity dependent dynamic changes in their efficacy that are globally termed synaptic plasticity. Although the molecular mechanisms underlying glutamatergic synaptic plasticity have been extensively investigated and described, those responsible for inhibitory synaptic plasticity are only beginning to be unveiled. In this framework, the ultrastructural changes of the inhibitory synapses during plasticity have been poorly investigated. Here we combined confocal fluorescence microscopy (CFM) with high resolution scanning electron microscopy (HRSEM) to characterize the fine structural rearrangements of post- synaptic GABAA Receptors (GABAARs) at the nanometric scale during the induction of inhibitory long-term potentiation (iLTP). Additional electron tomography (ET) experiments on immunolabelled hippocampal neurons allowed the visualization of synaptic contacts and confirmed the reorganization of post- synaptic GABAAR clusters in response to chemical iLTP inducing protocol. Altogether, these approaches revealed that, following the induction of inhibitory synaptic potentiation, GABAAR clusters increase in size and number at the post-synaptic membrane with no other major structural changes of the pre- and post-synaptic elements

Declusterization of GABAA receptors affects the kinetic properties of GABAergic currents in cultured hippocampal neurons.

Speed and reliability of synaptic transmission are essential for information coding in neuronal networks and require the presence of clustered neurotransmitter receptors at the plasma membrane in precise apposition to presynaptic terminals. Receptor clusterization is the result of highly regulated processes involving functional and structural proteins. Among the structural elements, microtubules are known to play a crucial role in anchoring of gamma-aminobutyric acid, type A (GABA(A)) receptors. Here we show that microtubule depolymerization with nocodazole induces the declusterization of GABA(A) receptors and modifies the kinetic properties of GABAergic currents in cultured hippocampal neurons. In particular, this drug, applied either in the bath or via the patch pipette, induced the acceleration of the onset kinetics of miniature inhibitory postsynaptic currents (mIPSCs) without significantly affecting their frequency, thus suggesting a main postsynaptic site of action. After nocodazole treatment, current responses to ultrafast applications of GABA exhibited a faster rise time and an accelerated onset of desensitization. A quantitative analysis of GABA-evoked currents and model simulations suggest that declusterization affects the gating properties of GABA(A) receptors. In particular, a faster entry into the desensitized state of declustered GABA(A) receptors may account for the changes in the kinetic properties of mIPSCs after nocodazole treatment. Hence it appears that the clustered condition of GABA(A) receptors contributes in shaping GABAergic currents

Tuning GABAergic Inhibition: Gephyrin Molecular Organization and Functions

To be highly reliable, synaptic transmission needs postsynaptic receptors (Rs) in precise apposition to the pre - synaptic release sites. At inhibitory synapses, the postsynaptic protein gephyrin self -assembles to form a scaffold that anchors glycine and GABA A Rs to the cytoskeleton, thus ensuring the accurate accumulation of postsynaptic receptors at the right place. This protein undergoes several post -translational modifications which control protein-protein interac- tion and downstream signaling pathways. In addition, through the constant exchange of scaffolding elements and recep- tors in and out of synapses, gephyrin dynamically regulates synaptic strength and plasticity.The aim of the present review is to highlight recent findings on the functional role of gephyrin at GABAergic inhibitory synapses. We will discuss different approaches used to interfere with gephyrin in order to unveil its function. In addition, we will focus on the impact of gephyrin structure and distribution at the nanoscale level on the functional properties of inhibitory synapses as well as the implications of this scaffold protein in synaptic plasticity processes. Finally, we will emphasize how gephyrin genetic mutations or alterations in protein expression levels are implicated in several neuropathological disorders, including aut- ism spectrum disorders, schizophrenia, temporal lobe epilepsy and Alzheimer's disease, all associated with severe def- icits of GABAergic signaling. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries. (c) 2019 The Authors. Published by Elsevier Ltd on behalf of IBRO. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Kainate receptor activation shapes short-term synaptic plasticity by controlling receptor lateral Mobility at glutamatergic synapses

Kainate receptors (KARs) mediate postsynaptic currents with a key impact on neuronal excitability. However, the molecular determinants controlling KAR postsynaptic localization and stabilization are poorly understood. Here, we exploit optogenetic and single-particle tracking approaches to study the role of KAR conformational states induced by glutamate binding on KAR lateral mobility at synapses. We report that following glutamate binding, KARs are readily and reversibly trapped at glutamatergic synapses through increased interaction with the β-catenin/N-cadherin complex. We demonstrate that such activation-dependent synaptic immobilization of KARs is crucial for the modulation of short-term plasticity of glutamatergic synapses. Thus, the present study unveils the crosstalk between conformational states and lateral mobility of KARs, a mechanism regulating glutamatergic signaling, particularly in conditions of sustained synaptic activity

predictive biomarkers of response for pd 1 pd l1 inhibitors a cumbersome gold rush

Programmed cell death protein 1 (PD-1) and its ligand programmed cell death-ligand 1 (PD-L1) are overexpressed in a number of human malignancies. More interestingly, their expression has been associated with patient survival in non-small cell lung cancer (NSCLC), melanoma, renal cell carcinoma, esophageal, pancreatic and colorectal carcinoma, with the data commonly suggesting a negative prognostic role. In this review, we summarize the pros and cons regarding the predictive role of PD-L1 expression in candidate patients for checkpoint inhibitors. Furthermore, we discuss the potential predictive role of other biomarkers, such as tumor mutational burden, microsatellite instability, mismatch repair deficiency and tumor infiltrating lymphocytes. We conclude that PD-L1 testing probably represents simply a "snapshot" of an intricate, fluctuating and dynamic process, that in turn represents the interplay between the immune system and cancer. The PD-L1 assay can be considered more useful for response stratification than in patient selection

HDAC6 and RhoA are novel players in Abeta-driven disruption of neuronal polarity

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