Neuroscience 2005 Abstract
| Presentation Number: | 962.17 |
|---|---|
| Abstract Title: | Optical postsynaptic measurement of vesicle release rates at hippocampal synapses during train stimulation. |
| Authors: |
Awatramani, G. B.*1
; Murphy, T. H.1
1Psy.., UBC, Vancouver, Canada |
| Primary Theme and Topics |
Neural Excitability, Synapses, and Glia: Cellular Mechanisms - Neurotransmitter Release -- Vesicle recycling and biogenesis |
| Secondary Theme and Topics | Neural Excitability, Synapses, and Glia: Cellular Mechanisms<br />- Synaptic Transmission<br />-- Presynaptic organization and structure |
| Session: |
962. Vesicle Recycling and Biogenesis Poster |
| Presentation Time: | Wednesday, November 16, 2005 1:00 PM-2:00 PM |
| Location: | Washington Convention Center - Hall A-C, Board # J2 |
| Keywords: |
Hippocampal networks are capable of maintaining synchronized bursting activity for prolonged periods. Yet, in vitro synaptic terminals undergo a rapid depletion of their readily releasable pool (RRP) of vesicles in response to short trains of stimuli. The rate at which neurons can re-prime vesicles provides an upper limit for the rate of sustained synaptic signaling. Here, we estimate this replenishment rate at individual synapses by measuring postsynaptic Ca2+ transients mediated by NMDA receptors during high frequency stimulation. We reasoned that at the onset of train stimulation, the Ca2+ indicator would saturate in response the release of the RRP. After this initial phase, Ca2+ levels would fall back to baseline and subsequent postsynaptic Ca2+ transients would only arise from release of newly primed vesicles, which would then be used to estimate the rates of recovery.
To monitor activity at single CA1 neuron synapses in acute slices, we measure postsynaptic Ca2+ influx (in response to continuous 20-50 Hz presynaptic stimulation) through NMDA receptors that are activated when a vesicle is released from the presynaptic terminal. Cells were voltage-clamped near 0 mV in order to relieve the Mg2+ block of NMDA receptors thereby promoting Ca2+ influx through these receptors. Responses were completely blocked by the NMDAR antagonist . The stimulation intensity was adjusted such that only one or a few synapses were reliably activated to minimize the spread of Ca2+ from neighboring synapses. We observed a large heterogeneity in steady state release rates at single synapses. At some synapses the steady state release rates were presumably too high to be resolved fluorometrically (>5 quanta/sec).At other synapses, after an apparent depletion synapses reached a steady state between 0.1quanta/sec and 1quanta/sec.
These studies highlight apparently different states of hippocampal synapses on the same dendrite revealed by high frequency train stimulation.
To monitor activity at single CA1 neuron synapses in acute slices, we measure postsynaptic Ca2+ influx (in response to continuous 20-50 Hz presynaptic stimulation) through NMDA receptors that are activated when a vesicle is released from the presynaptic terminal. Cells were voltage-clamped near 0 mV in order to relieve the Mg2+ block of NMDA receptors thereby promoting Ca2+ influx through these receptors. Responses were completely blocked by the NMDAR antagonist . The stimulation intensity was adjusted such that only one or a few synapses were reliably activated to minimize the spread of Ca2+ from neighboring synapses. We observed a large heterogeneity in steady state release rates at single synapses. At some synapses the steady state release rates were presumably too high to be resolved fluorometrically (>5 quanta/sec).At other synapses, after an apparent depletion synapses reached a steady state between 0.1quanta/sec and 1quanta/sec.
These studies highlight apparently different states of hippocampal synapses on the same dendrite revealed by high frequency train stimulation.
Supported by CIHR operating grant to THM.
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2005 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2005. Online.
Copyright © 2005-2025 Society for Neuroscience; all rights reserved. Permission to republish any abstract or part of any abstract in any form must be obtained in writing by SfN office prior to publication.
