Optical Quantal Analysis Using Ca²⁺ Indicators: A Robust Method for Assessing Transmitter Release Probability at...

Area of Science:

• Neuroscience
• Cellular Biology
• Biophysics

Background:

• Assessing presynaptic function and transmitter release in intact neural tissue is challenging.
• Traditional electrophysiological methods indirectly measure transmitter release and struggle to resolve single-synapse parameters like release probability (p_r).
• Understanding presynaptic efficacy and plasticity is crucial for circuit function and behavior.

Purpose of the Study:

• To describe and validate optical quantal analysis for measuring presynaptic release probability (p_r) at single glutamatergic synapses.
• To demonstrate the application of this technique in hippocampal slice preparations.
• To highlight its utility in studying activity-dependent presynaptic plasticity.

Main Methods:

• Utilized optical quantal analysis employing Ca²⁺-sensitive dyes to detect Ca²⁺ influx from single quanta of glutamate release.
• Performed measurements at single glutamatergic synapses in ex vivo and in vitro hippocampal slice preparations.
• Assessed the method's robustness to postsynaptic efficacy changes and sensitivity to plasticity induction (LTP/LTD).

Main Results:

• High-affinity Ca²⁺ indicators reliably detected spine Ca²⁺ influx, enabling precise calculation of single-synapse release probability (p_r).
• The optical quantal analysis method proved robust against variations in postsynaptic efficacy.
• The technique successfully detected activity-dependent presynaptic changes following long-term potentiation and long-term depression.

Conclusions:

• Optical quantal analysis provides a direct and precise method for calculating single-synapse release probability (p_r).
• This technique is applicable to various glutamatergic synapses and can be adapted for new optical reporters.
• Optical quantal analysis is a promising strategy for investigating presynaptic function and plasticity, with potential for in vivo applications.