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Measuring action potential-evoked transmission at individual synaptic contacts.

ABSTRACT: In the neuronal culture experimental system, the total synaptic connection between two neurons can consist of large numbers of synaptic sites, each behaving probabilistically. Studies of synaptic function with paired recordings typically consider the summed response across all of these sites and from this infer the average response. Understanding of synaptic transmission and plasticity could be improved by examination of activity at as few synaptic sites as possible. To this end, we develop a system for recording responses from individual contacts. It relies on a precisely regulated pneumatic/hydrostatic pressure system to create a microenvironment within which individual synapses are active, and an acoustic signature method to monitor the stability of this microenvironment noninvasively. With this method we are able to record action potential-evoked postsynaptic currents consistent with individual quanta. The approach does not distort synaptic current waveforms and permits stable recording for several hours. The method is applied to address mechanisms of short-term plasticity, the variability of latency at individual synaptic sites and, in a preliminary experiment, the independence of nearby synapses on the same axon.

SUBMITTER: Nauen DW

PROVIDER: S-EPMC4049561 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Measuring action potential-evoked transmission at individual synaptic contacts.

Nauen David W DW Bi Guo-Qiang GQ

Journal of neural engineering 20120601 3

In the neuronal culture experimental system, the total synaptic connection between two neurons can consist of large numbers of synaptic sites, each behaving probabilistically. Studies of synaptic function with paired recordings typically consider the summed response across all of these sites and from this infer the average response. Understanding of synaptic transmission and plasticity could be improved by examination of activity at as few synaptic sites as possible. To this end, we develop a sy ...[more]

PMID: 22626987

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Project description:Using postsynaptically tethered calcium sensor GCaMP, we investigated spontaneous synaptic transmission at individual active zones (AZs) at the Drosophila (both sexes) neuromuscular junction. Optical monitoring of GCaMP events coupled with focal electrical recordings of synaptic currents revealed "hot spots" of spontaneous transmission, which corresponded to transient states of elevated activity at selected AZs. The elevated spontaneous activity had two temporal components, one at a timescale of minutes and the other at a subsecond timescale. We developed a three-state model of AZ preparedness for spontaneous transmission and performed Monte Carlo simulations of the release process, which produced an accurate quantitative description of the variability and time course of spontaneous transmission at individual AZs. To investigate the mechanisms of elevated activity, we first focused on the protein complexin, which binds the SNARE protein complex and serves to clamp spontaneous fusion. Overexpression of Drosophila complexin largely abolished the high-activity states of AZs, while complexin deletion drastically promoted it. A mutation in the SNARE protein Syntaxin-1A had an effect similar to complexin deficiency, promoting the high-activity state. We next tested how presynaptic Ca2+ transients affect the states of elevated activity at individual AZs. We either blocked or promoted Ca2+ influx pharmacologically, and also promoted Ca2+ release from internal stores. These experiments coupled with computations revealed that Ca2+ transients can trigger bursts of spontaneous events from individual AZs or AZ clusters at a subsecond timescale. Together, our results demonstrated that spontaneous transmission is highly heterogeneous, with transient hot spots being regulated by the SNARE machinery and Ca2+ SIGNIFICANCE STATEMENT Spontaneous synaptic transmission is a vital component of neuronal communication, since it regulates the neuronal development and plasticity. Our study demonstrated that spontaneous transmission is highly heterogeneous and that nerve terminals create transient "hot spots" of spontaneous release of neuronal transmitters. We show that these hot spots are regulated by the protein machinery mediating the release process and by calcium ions. These results contribute to our understanding of spontaneous synaptic transmission as a dynamic, plastic, and tightly regulated signaling mechanism and unravel fundamental biophysical properties of neuronal communication.

Dataset Information

Measuring action potential-evoked transmission at individual synaptic contacts.

Publications

Measuring action potential-evoked transmission at individual synaptic contacts.

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