A fast and responsive voltage indicator with enhanced sensitivity for unitary synaptic events.

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• Genetically encoded voltage indicators (GEVIs) are crucial for monitoring neuronal activity.
• Detecting small signals like excitatory postsynaptic potentials (EPSPs) remains a challenge for current GEVIs.

Purpose of the Study:

• To develop a novel GEVI, ASAP5, with enhanced kinetics and responsivity for improved detection of neuronal electrical activity.
• To assess ASAP5's performance in detecting action potentials (APs) and subthreshold events in vivo and in vitro.

Main Methods:

• Development and characterization of the ASAP5 GEVI.
• In vivo imaging of action potentials in response to sensory stimuli.
• In vitro imaging of synaptic events in cultured rat and human neurons.
• Analysis of EPSP propagation and amplitude decay in dendrites.

Main Results:

• ASAP5 demonstrated superior signal-to-noise ratios for in vivo action potential detection compared to previous GEVIs.
• ASAP5 successfully detected subthreshold responses to sensory stimuli in single two-photon trials.
• ASAP5 could detect approximately 1-mV EPSPs in cultured rat and human neurons.
• EPSP amplitude was found to decay exponentially along dendrites, with initiation site amplitude increasing with distance from the soma.

Conclusions:

• ASAP5 significantly advances voltage imaging capabilities, enabling reliable detection of small synaptic events, including in human neurons.
• This technology opens new avenues for high-throughput characterization of neuronal dysfunction in disease models.