Optimization and application of a high-performance genetically-encoded fluorescent sensor for membrane voltage imaging
Embargo Date
2023-05-23
OA Version
Citation
Abstract
The basal ganglia circuit has long been recognized as an important regulator for movement in the brain, with dysfunction of this circuit resulting in motor disorders such as Parkinson’s and Huntington’s disease. The striatum, the largest nucleus of the basal ganglia, is critical for normal motor control and is implicated in the pathology of various movement disorders. The vast majority (~95%) of striatal neurons are inhibitory spiny projection neurons (SPNs), while the remaining 5% are GABAergic and cholinergic interneurons, thought to modulate striatal function by regulating the output projecting SPNs.
Both striatal SPNs and interneurons are dynamically modulated during movement. In particular, cholinergic interneurons (ChIs) have been shown to promote movement termination by synchronizing SPN activities. ChIs are also thought to contribute to oscillatory dynamics in normal and pathological striatal circuits, with ChI activation resulting in increased beta frequency (~15–30Hz) oscillations in striatal local field potential (LFP) recordings, as well as decreased locomotion akin to deficits observed in Parkinson’s disease.
Current techniques, however, fall short of demonstrating how ChIs can coordinate their activity to influence SPNs and subsequent motor output, due to the inability to record both spiking and subthreshold activity from individual cells during movement. Towards this goal, in this dissertation, we first optimize a high-performance genetically-encoded voltage indicator (GEVI) in multiple electrically active systems, including in cardiac cells and tissue, and in both cortical and subcortical brain regions such as the striatum. We demonstrate that this GEVI, Archon1, can detect action potentials in multiple cells simultaneously, with kinetics and sensitivity comparable to the gold standard in the field, patch clamp electrophysiology. Further, its soma-localized variant, SomArchon, can detect both spiking and subthreshold dynamics in awake, behaving animals with high spatiotemporal precision across multiple brain regions. We then apply SomArchon to the striatum to investigate ChIs and SPNs during movement. We reveal that most ChIs and a subset of SPNs exhibit precisely timed spikes coupled to subthreshold voltage oscillations at delta frequency, as well as to higher frequency LFP beta-gamma oscillations, and that these delta-rhythmic neurons are preferentially modulated by changes in movement speed.
Overall, this dissertation develops the use of a high-performance genetically-encoded voltage sensor to probe the electrical activity of excitable cells with high sensitivity and spatiotemporal precision. When applied to the striatum, SomArchon allowed us to reveal critical insight into how delta oscillations, and in particular, ChIs, coordinate both motor activity and broader oscillation patterns in the striatum. Such an understanding could provide valuable insight into the basis of cholinergic signaling in the brain, as well as strategies for intervention in basal ganglia circuit disorders. Additionally, the novel voltage imaging techniques deployed here could have a broad impact on systems neuroscience, cardiac biology, and the study of other electrically active systems, motivating future voltage imaging analysis of a variety of electrical circuits involved in behavioral and pathological paradigms.
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License
Attribution-NonCommercial 4.0 International