Developmental regulation of the intracellular Ca2+ sensitivity of vesicle fusion and Ca2+-secretion coupling at the rat calyx of Held

Yunyun Han, Olexiy Kochubey, Ralf Schneggenburger
2009
Article

Résumé

Developmental refinement of synaptic transmission can occur via changes in several pre- and postsynaptic factors, but it has been unknown whether the intrinsic Ca2+ sensitivity of vesicle fusion in the nerve terminal can be regulated during development. Using the calyx of Held, a giant synapse in the auditory pathway, we studied the presynaptic mechanisms underlying the developmental regulation of Ca2+-secretion coupling, comparing a time period before, and shortly after the onset of hearing in rats. We found an similar to 2-fold leftward shift in the relationship between EPSC amplitude and presynaptic Ca2+ current charge (Q(Ca)), indicating that brief presynaptic Ca2+ currents become significantly more efficient in driving release. Using a Ca2+ tail current protocol, we also found that the high cooperativity between EPSC amplitude and Q(Ca) was slightly reduced with development. In contrast, in presynaptic Ca2+ uncaging experiments, the intrinsic Ca2+ cooperativity of vesicle fusion was identical, and the intrinsic Ca2+ sensitivity was slightly reduced with development. This indicates that the significantly enhanced release efficiency of brief Ca2+ currents must be caused by a tighter co-localization of Ca2+ channels and readily releasable vesicles, but not by changes in the intrinsic properties of Ca2+-dependent release. Using the parameters of the intrinsic Ca2+ sensitivity measured at each developmental stage, we estimate that during a presynaptic action potential (AP), a given readily releasable vesicle experiences an about 1.3-fold higher 'local' intracellular Ca2+ concentration (Ca2+) signal with development. Thus, the data indicate a tightening in the Ca2+ channel-vesicle co-localization during development, without a major change in the intrinsic Ca2+ sensitivity of vesicle fusion.

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https://infoscience.epfl.ch/record/159742?ln=fr

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Yunyun Han, Olexiy Kochubey, Ralf Schneggenburger
2009
Article

Résumé

Official source

https://infoscience.epfl.ch/record/159742?ln=fr

À propos de ce résultat

Concepts associés (14)

Concepts associés

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Publications associées (23)

Publications associées

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Delayed and Temporally Imprecise Neurotransmission in Reorganizing Cortical Microcircuits

Anne Alison Jorstad, Graham Knott, Yan Liu

Synaptic neurotransmission is modified at cortical connections throughout life. Varying the amplitude of the postsynaptic response is one mechanism that generates flexible signaling in neural circuits. The timing of the synaptic response may also play a role. Here, we investigated whether weakening and loss of an entire connection between excitatory cortical neurons was foreshadowed in the timing of the postsynaptic response. We made electrophysiological recordings in rat primary somatosensory cortex that was undergoing experience-dependent loss of complete local excitatory connections. The synaptic latency of pyramid-pyramid connections, which typically comprise multiple synapses, was longer and more variable. Connection strength and latency were not correlated. Instead, prolonged latency was more closely related to progression of connection loss. The action potential waveform and axonal conduction velocity were unaffected, suggesting that the altered timing of neurotransmission was attributable to a synaptic mechanism. Modeling studies indicated that increasing the latency and jitter at a subset of synapses reduced the number of action potentials fired by a postsynaptic neuron. We propose that prolonged synaptic latency and diminished temporal precision of neurotransmission are hallmarks of impending loss of a cortical connection.

Soc Neuroscience2015

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Imaging of AMPA-type glutamate receptors in hippocampal neurons

Michel Kropf

Synaptic plasticity is the ability of the connections between nerve cells, called synapses, to change in strength. The presence of a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors (AMPAR) at the synapse controls the strength of excitatory transmission and their number can be modulated. Controlled surface insertion of AMPA-type glutamate receptors and their lateral diffusion into synapses are proposed to be major mechanisms for the regulation of synaptic plasticity. Here we applied the recently established Acyl-Carrier-Protein-labeling technique in combination with lentiviral expression in hippocampal neurons to label individually ACP-tagged AMPA receptor subunits at the surface of neurons. This technique uses a carrier protein from the fatty acid synthesis and a mutant therof as a tag, which were fused by genetic engineering to the AMPAR subunits. The labeling procedure is specific for proteins, AMPARs in our case, which are present at the plasma membrane of the cell. We show that this technique allows to differentially label two subunits of the receptor. Moreover, these subunits are integrated into heteromeric receptors together with endogenous subunits, and these labeled receptors are targeted to functional synapses. The diffusion coefficient of labeled GluR2 at the surface of living neurons is significantly higher in GluR2/GluR3-infected neurons compared to GluR1/GluR2-infected neurons suggesting a higher mobility of GluR2/3 receptors compared to GluR1/2 receptors. Finally, in sequential labeling experiments we detected newly inserted receptor subunits colocalized with presynaptic markers. The GluR1 subunit displayed a faster kinetics of insertion compare to the other subunits. Internalized GluR2 receptors have been shown to accumulate in perinuclear late endosomes in HEK 293T cells. Moreover, we expressed and labeled surface tagged-GluR2 receptors in hippocampal slices, using similar labeling technique as ACP. High-resolution images, sub-difraction limited, of hippocampal neurons stained for GluR2 were acquired with an experimental scanning near-field optical microscopy (SNOM). Together our results strongly indicate that receptor insertion is faster for GluR1 and that insertion occurs at or in close vicinity of synapses in mature hippocampal neuron cultures.

EPFL2007

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Avermann M, Tomm C, Mateo C, Gerstner W, Petersen CC. Microcircuits of excitatory and inhibitory neurons in layer 2/3 of mouse barrel cortex. J Neurophysiol 107: 3116-3134, 2012. First published March 7, 2012; doi:10.1152/jn.00917.2011.-Synaptic interactions between nearby excitatory and inhibitory neurons in the neocortex are thought to play fundamental roles in sensory processing. Here, we have combined optogenetic stimulation, whole cell recordings, and computational modeling to define key functional microcircuits within layer 2/3 of mouse primary somatosensory barrel cortex. In vitro optogenetic stimulation of excitatory layer 2/3 neurons expressing channelrhodopsin-2 evoked a rapid sequence of excitation followed by inhibition. Fast-spiking (FS) GABAergic neurons received large-amplitude, fast-rising depolarizing postsynaptic potentials, often driving action potentials. In contrast, the same optogenetic stimulus evoked small-amplitude, subthreshold postsynaptic potentials in excitatory and non-fast-spiking (NFS) GABAergic neurons. To understand the synaptic mechanisms underlying this network activity, we investigated unitary synaptic connectivity through multiple simultaneous whole cell recordings. FS GABAergic neurons received unitary excitatory postsynaptic potentials with higher probability, larger amplitudes, and faster kinetics compared with NFS GABAergic neurons and other excitatory neurons. Both FS and NFS GABAergic neurons evoked robust inhibition on postsynaptic layer 2/3 neurons. A simple computational model based on the experimentally determined electrophysiological properties of the different classes of layer 2/3 neurons and their unitary synaptic connectivity accounted for key aspects of the network activity evoked by optogenetic stimulation, including the strong recruitment of FS GABAergic neurons acting to suppress firing of excitatory neurons. We conclude that FS GABAergic neurons play an important role in neocortical microcircuit function through their strong local synaptic connectivity, which might contribute to driving sparse coding in excitatory layer 2/3 neurons of mouse barrel cortex in vivo.

American Physiological Society2012

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American Physiological Society2012

Imaging of AMPA-type glutamate receptors in hippocampal neurons

Michel Kropf

EPFL2007