Rational Engineering of XCaMPs, a Multicolor GECI Suite for In Vivo Imaging of Complex Brain Circuit Dynamics

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• Current genetically encoded calcium indicators (GECIs) have limitations in detecting single action potentials (APs) rapidly, spectral compatibility, and imaging depth.
• Understanding dynamic brain information processing requires advanced tools for monitoring neural activity with high temporal and spatial resolution.

Purpose of the Study:

• To engineer a novel suite of genetically encoded calcium indicators, termed XCaMPs, to overcome the limitations of existing GECIs.
• To enable faster detection of neural activity, improved spectral compatibility, and deeper two-photon imaging for studying complex neuronal circuits.

Main Methods:

• Rational engineering of a quadricolor GECI suite (XCaMPs) with enhanced performance characteristics.
• In vivo electrophysiological recordings and two-photon imaging in mouse models.
• Paired recordings of pre- and postsynaptic neuronal firing in specific brain regions.

Main Results:

• XCaMPs achieved single AP detection within 3-10 ms, enabling measurement of fast-spike trains in parvalbumin (PV)-positive interneurons.
• Successfully recorded distinct inhibitory and excitatory ensembles during pre-motion activity in freely moving mice.
• Revealed spatiotemporal constraints of dendritic inhibition and uncovered somatosensation-evoked activity in hippocampal CA1 neurons using red XCaMP-R.

Conclusions:

• The XCaMP GECI suite represents a significant advancement for studying fast neuronal dynamics and complex circuit computations.
• These indicators provide enhanced capabilities for in vivo neuroscience research, particularly in freely moving animals and subcortical regions.
• XCaMPs expand the possibilities for deciphering brain information processing by offering improved speed, spectral flexibility, and imaging depth.