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Release probability modulates short-term plasticity at a rat giant terminal
S Oleskevich1, J Clements, B Walmsley
1Division of Neuroscience, The John Curtin School of Medical Research, and Division of Biochemistry and Molecular Biology, The Australian National University, Canberra, ACT 0200, Australia. sharon.oleskevich@anu.edu.au
The Journal of Physiology
|April 15, 2000
Summary
Release probability (Pr) significantly impacts short-term synaptic plasticity. This study found that while most release sites are active under normal conditions, high release probability can lead to postsynaptic depression, with variability possibly due to vesicle pool differences.
Area of Science:
- Neuroscience
- Synaptic Plasticity
- Auditory System
Background:
- Short-term synaptic plasticity is crucial for information processing in the central nervous system.
- Release probability (Pr) is a key modulator of synaptic strength and plasticity.
- The auditory calyceal synapse (endbulb of Held) offers a model for studying synaptic transmission due to its large size and multiple release sites.
Purpose of the Study:
- To investigate the relationship between release probability (Pr) and paired-pulse modulation at the auditory calyceal synapse.
- To quantify Pr and quantal amplitude under varying physiological conditions.
- To explore the factors contributing to variability in synaptic responses.
Main Methods:
- Whole-cell patch-clamp recordings of excitatory postsynaptic currents (EPSCs) in response to auditory nerve fiber stimulation.
- Quantitative estimation of Pr and quantal amplitude using variance-mean analysis.
- Modulation of Pr via bath application of cadmium, elevated calcium, and phorbol esters (PKC activation).
Main Results:
- Under physiological conditions, mean Pr was 0.6, with mean quantal amplitude (44 pA) consistent with miniature EPSCs (47 pA).
- Elevated calcium or phorbol esters increased Pr to near 1.0, revealing a postsynaptic contribution to paired-pulse depression.
- Significant variability was observed in the paired-pulse ratio-Pr relationship across neurons, potentially linked to morphological differences in vesicle pools.
Conclusions:
- Release probability is a critical determinant of synaptic behavior at the auditory calyceal synapse.
- Postsynaptic mechanisms contribute to paired-pulse depression, particularly under high release probability conditions.
- Variability in synaptic plasticity may arise from differences in the readily releasable and reserve vesicle pools at individual release sites.