Activity-driven synaptic translocation of LGI1 controls excitatory neurotransmission.

The fine control of synaptic function requires robust trans-synaptic molecular interactions. However, it remains poorly understood how trans-synaptic bridges change to reflect the functional states of the synapse. Here, we develop optical tools to visualize in firing synapses the molecular behavior of two trans-synaptic proteins, LGI1 and ADAM23, and find that neuronal activity acutely rearranges their abundance at the synaptic cleft.

A ratiometric ER calcium sensor for quantitative comparisons across cell types and subcellular regions.

The endoplasmic reticulum (ER) is an important regulator of in cells and dysregulation of ER calcium homeostasis can lead to numerous pathologies. Understanding how various pharmacological and genetic perturbations of ER homeostasis impacts cellular physiology would likely be facilitated by more quantitative measurements of ER levels that allow easier comparisons across conditions. Here, we developed a ratiometric version of our original ER-GCaMP probe that allows for more quantitative comparisons of the concentration of in the ER across cell types and sub-cellular compartments.

Frequency of Spontaneous Neurotransmission at Individual Boutons Corresponds to the Size of the Readily Releasable Pool of Vesicles.

Synapses maintain two forms of neurotransmitter release to support communication in the brain. First, evoked neurotransmitter release is triggered by the invasion of an action potential (AP) across en passant boutons that form along axons. The probability of evoked release () varies substantially across boutons, even within a single axon.

Glutamate indicators with improved activation kinetics and localization for imaging synaptic transmission.

The fluorescent glutamate indicator iGluSnFR enables imaging of neurotransmission with genetic and molecular specificity. However, existing iGluSnFR variants exhibit low in vivo signal-to-noise ratios, saturating activation kinetics and exclusion from postsynaptic densities. Using a multiassay screen in bacteria, soluble protein and cultured neurons, we generated variants with improved signal-to-noise ratios and kinetics.

Condensing our understanding of endocytosis.

In this issue of Neuron, Imoto et al. report that a splice variant of dynamin (Dyn1xA) interacts with syndapin to form a molecular condensate at the edge of the presynaptic active zone. This enables rapid recruitment of proteins to endocytic sites essential for powering ultrafast endocytosis.

NMDAR-dependent presynaptic homeostasis in adult hippocampus: Synapse growth and cross-modal inhibitory plasticity.

Homeostatic plasticity (HP) encompasses a suite of compensatory physiological processes that counteract neuronal perturbations, enabling brain resilience. Currently, we lack a complete description of the homeostatic processes that operate within the mammalian brain. Here, we demonstrate that acute, partial AMPAR-specific antagonism induces potentiation of presynaptic neurotransmitter release in adult hippocampus, a form of compensatory plasticity that is consistent with the expression of presynaptic homeostatic plasticity (PHP) documented at peripheral synapses.

Activity-dependent endoplasmic reticulum Ca uptake depends on Kv2.1-mediated endoplasmic reticulum/plasma membrane junctions to promote synaptic transmission.

The endoplasmic reticulum (ER) forms a continuous and dynamic network throughout a neuron, extending from dendrites to axon terminals, and axonal ER dysfunction is implicated in several neurological disorders. In addition, tight junctions between the ER and plasma membrane (PM) are formed by several molecules including Kv2 channels, but the cellular functions of many ER-PM junctions remain unknown. Recently, dynamic Ca uptake into the ER during electrical activity was shown to play an essential role in synaptic transmission.

Dividing communication, at the nanoscale.

Fluorescent glutamate sensors shed light on the microscopic organization underlining spontaneous neurotransmission.

Focused ultrasound stimulation of an ex-vivo Aplysia abdominal ganglion preparation.

Background: A growing body of research demonstrates that focused ultrasound stimulates activity in human and other mammalian nervous systems. However, there is no consensus on which sonication parameters are optimal. Furthermore, the mechanism of action behind ultrasound neurostimulation remains poorly understood.

The potassium channel subunit Kβ1 serves as a major control point for synaptic facilitation.

Analysis of the presynaptic action potential's (AP) role in synaptic facilitation in hippocampal pyramidal neurons has been difficult due to size limitations of axons. We overcame these size barriers by combining high-resolution optical recordings of membrane potential, exocytosis, and Ca in cultured hippocampal neurons. These recordings revealed a critical and selective role for K1 channel inactivation in synaptic facilitation of excitatory hippocampal neurons.

The Photoconvertible Fluorescent Probe, CaMPARI, Labels Active Neurons in Freely-Moving Intact Adult Fruit Flies.

Linking neural circuitry to behavior by mapping active neurons is a challenge. Both genetically encoded calcium indicators (GECIs) and intermediate early genes (IEGs) have been used to pinpoint active neurons during a stimulus or behavior but have drawbacks such as limiting the movement of the organism, requiring knowledge of the active region or having poor temporal resolution. Calcium-modulated photoactivatable ratiometric integrator (CaMPARI) was engineered to overcome these spatial-temporal challenges.

Freeze-frame imaging of synaptic activity using SynTagMA.

Information within the brain travels from neuron to neuron across billions of synapses. At any given moment, only a small subset of neurons and synapses are active, but finding the active synapses in brain tissue has been a technical challenge. Here we introduce SynTagMA to tag active synapses in a user-defined time window.

Genetically Encoded Voltage Indicators Are Illuminating Subcellular Physiology of the Axon.

Everything we see and do is regulated by electrical signals in our nerves and muscle. Ion channels are crucial for sensing and generating electrical signals. Two voltage-dependent conductances, Na and K, form the bedrock of the electrical impulse in the brain known as the action potential.

Subcellular control of membrane excitability in the axon.

Ion channels are microscopic pore proteins in the membrane that open and close in response to chemical and electrical stimuli. This simple concept underlies rapid electrical signaling in the brain as well as several important aspects of neural plasticity. Although the soma accounts for less than 1% of many neurons by membrane area, it has been the major site of measuring ion channel function.

Loss of Neurofascin-186 Disrupts Alignment of AnkyrinG Relative to Its Binding Partners in the Axon Initial Segment.

The axon initial segment (AIS) is a specialized region within the proximal portion of the axon that initiates action potentials thanks in large part to an enrichment of sodium channels. The scaffolding protein ankyrinG (AnkG) is essential for the recruitment of sodium channels as well as several other intracellular and extracellular proteins to the AIS. In the present study, we explore the role of the cell adhesion molecule (CAM) neurofascin-186 (NF-186) in arranging the individual molecular components of the AIS in cultured rat hippocampal neurons.

Sodium Channel β2 Subunits Prevent Action Potential Propagation Failures at Axonal Branch Points.

Neurotransmitter release depends on voltage-gated Na channels (Nas) to propagate an action potential (AP) successfully from the axon hillock to a synaptic terminal. Unmyelinated sections of axon are very diverse structures encompassing branch points and numerous presynaptic terminals with undefined molecular partners of Na channels. Using optical recordings of Ca and membrane voltage, we demonstrate here that Na channel β2 subunits (Naβ2s) are required to prevent AP propagation failures across the axonal arborization of cultured rat hippocampal neurons (mixed male and female).

Adaptor Protein 2 (AP-2) complex is essential for functional axogenesis in hippocampal neurons.

The complexity and diversity of a neural network requires regulated elongation and branching of axons, as well as the formation of synapses between neurons. In the present study we explore the role of AP-2, a key endocytic adaptor protein complex, in the development of rat hippocampal neurons. We found that the loss of AP-2 during the early stage of development resulted in impaired axon extension and failed maturation of the axon initial segment (AIS).

Isoflurane inhibits synaptic vesicle exocytosis through reduced Ca2+ influx, not Ca2+-exocytosis coupling.

Identifying presynaptic mechanisms of general anesthetics is critical to understanding their effects on synaptic transmission. We show that the volatile anesthetic isoflurane inhibits synaptic vesicle (SV) exocytosis at nerve terminals in dissociated rat hippocampal neurons through inhibition of presynaptic Ca(2+) influx without significantly altering the Ca(2+) sensitivity of SV exocytosis. A clinically relevant concentration of isoflurane (0.

Control and plasticity of the presynaptic action potential waveform at small CNS nerve terminals.

The steep dependence of exocytosis on Ca(2+) entry at nerve terminals implies that voltage control of both Ca(2+) channel opening and the driving force for Ca(2+) entry are powerful levers in sculpting synaptic efficacy. Using fast, genetically encoded voltage indicators in dissociated primary neurons, we show that at small nerve terminals K(+) channels constrain the peak voltage of the presynaptic action potential (APSYN) to values much lower than those at cell somas. This key APSYN property additionally shows adaptive plasticity: manipulations that increase presynaptic Ca(2+) channel abundance and release probability result in a commensurate lowering of the APSYN peak and narrowing of the waveform, while manipulations that decrease presynaptic Ca(2+) channel abundance do the opposite.

Intrinsic variability in Pv, RRP size, Ca(2+) channel repertoire, and presynaptic potentiation in individual synaptic boutons.

The strength of individual synaptic contacts is considered a key modulator of information flow across circuits. Presynaptically the strength can be parsed into two key parameters: the size of the readily releasable pool (RRP) and the probability that a vesicle in that pool will undergo exocytosis when an action potential fires (Pv). How these variables are controlled and the degree to which they vary across individual nerve terminals is crucial to understand synaptic plasticity within neural circuits.

α2δ expression sets presynaptic calcium channel abundance and release probability.

Synaptic neurotransmitter release is driven by Ca(2+) influx through active zone voltage-gated calcium channels (VGCCs). Control of active zone VGCC abundance and function remains poorly understood. Here we show that a trafficking step probably sets synaptic VGCC levels in rats, because overexpression of the pore-forming α1(A) VGCC subunit fails to change synaptic VGCC abundance or function.

Multivesicular exocytosis in rat pancreatic beta cells.

Aims/hypothesis: To establish the occurrence, modulation and functional significance of compound exocytosis in insulin-secreting beta cells.

Methods: Exocytosis was monitored in rat beta cells by electrophysiological, biochemical and optical methods. The functional assays were complemented by three-dimensional reconstruction of confocal imaging, transmission and block face scanning electron microscopy to obtain ultrastructural evidence of compound exocytosis.

Progression of diet-induced diabetes in C57BL6J mice involves functional dissociation of Ca2(+) channels from secretory vesicles.

Objective: The aim of the study was to elucidate the cellular mechanism underlying the suppression of glucose-induced insulin secretion in mice fed a high-fat diet (HFD) for 15 weeks.

Research Design And Methods: C57BL6J mice were fed a HFD or a normal diet (ND) for 3 or 15 weeks. Plasma insulin and glucose levels in vivo were assessed by intraperitoneal glucose tolerance test.

De novo lipogenesis and stearoyl-CoA desaturase are coordinately regulated in the human adipocyte and protect against palmitate-induced cell injury.

De novo lipogenesis (DNL) is paradoxically up-regulated by its end product, saturated fatty acids (SAFAs). We tested the hypothesis that SAFA-induced up-regulation of DNL reflects coordinate up-regulation of elongation and desaturation pathways for disposal of SAFAs and production of monounsaturated fatty acids to protect cells from SAFA toxicity. Human preadipocytes were differentiated in vitro for 14 days with [U-(13)C]palmitate (0-200 microM) to distinguish exogenous fatty acids from those synthesized by DNL.