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Understanding percepts, engrams and actions requires methods for selectively modulating synaptic communication between specific subsets of interconnected cells. Here, we develop an approach to control synaptically connected elements using bioluminescent light: Luciferase-generated light, originating from a presynaptic axon terminal, modulates an opsin in its postsynaptic target. Vesicular-localized luciferase is released into the synaptic cleft in response to presynaptic activity, creating a real-time Optical Synapse. Light production is under experimenter-control by introduction of the small molecule luciferin. Signal transmission across this optical synapse is temporally defined by the presence of both the luciferin and presynaptic activity. We validate synaptic Interluminescence by multi-electrode recording in cultured neurons and in mice in vivo. Interluminescence represents a powerful approach to achieve synapse-specific and activity-dependent circuit control in vivo.

 

In vivo fluorescence miniature microscopy has recently proven a major advance, enabling cellular imaging in freely behaving animals. However, fluorescence imaging suffers from autofluorescence, phototoxicity, photobleaching and non- homogeneous illumination artifacts. These factors limit the quality and time course of data collection. Bioluminescence provides an alternative kind of activity-dependent light indicator. Bioluminescent calcium indicators do not require light input, instead generating photons through chemiluminescence. As such, limitations inherent to the requirement for light presentation are eliminated. Further, bioluminescent indicators also do not require excitation light optics: the removal of these components should make a lighter and lower cost microscope with fewer assembly parts. While there has been significant recent progress in making brighter and faster bioluminescence indicators, the advances in imaging hardware have not yet been realized. A hardware challenge is that despite potentially higher signal-to-noise of bioluminescence, the signal strength is lower than that of fluorescence. An open question we address in this report is whether fluorescent miniature microscopes can be rendered sensitive enough to detect bioluminescence. We demonstrate this possibility in vitro and in vivo by implementing optimizations of the UCLA fluorescent miniscope v3.2. These optimizations yielded a miniscope (BLmini) which is 22% lighter in weight, has 45% fewer components, is up to 58% less expensive, offers up to 15 times stronger signal and is sensitive enough to capture spatiotemporal dynamics of bioluminescence in the brain with a signal-to-noise ratio of 34 dB.