Biology subjects

Mount, R.

Publications and source records attributed to Mount, R..

5 recordsLinked to original sources

bioRxiv2023

Large-scale deep tissue voltage imaging with targeted illumination confocal microscopy

Voltage imaging with cellular specificity has been made possible by the tremendous advances in genetically encoded voltage indicators (GEVIs). However, the kilohertz rates required for voltage imaging lead to weak signals. Moreover, out-of-focus fluorescence and tissue scattering produce background that both undermines signal-to-noise ratio (SNR) and induces crosstalk between cells, making reliable in vivo imaging in densely labeled tissue highly challenging. We describe a microscope that combines the distinct advantages of targeted illumination and confocal gating, while also maximizing signal detection efficiency. The resulting benefits in SNR and crosstalk reduction are quantified experimentally and theoretically. Our microscope provides a versatile solution for enabling high-fidelity in vivo voltage imaging at large scales and penetration depths, which we demonstrate across a wide range of imaging conditions and different GEVI classes.

neuroscience↗

bioRxiv2022

Membrane Voltage Dynamics of Parvalbumin Interneurons Orchestrate Hippocampal Theta Rhythmicity

Hippocampal network activity at theta frequencies (5-10Hz) is important for behavior. However, it remains unclear how behaviorally-relevant network theta rhythms arise and interact with cellular dynamics to dictate spike timing. We performed membrane voltage (Vm) imaging of individual CA1 pyramidal cells and parvalbumin interneurons with simultaneous local field potential (LFP) recordings in mice during locomotion. We found that Vm theta rhythms organize spike timing in both cell types regardless of behavioral conditions, but the Vm of parvalbumin interneurons is better synchronized with LFP. The temporal relationships between spikes and LFP theta reliably reflect the Vm-LFP relationships in parvalbumin cells, but not in pyramidal cells. Thus, cellular theta rhythms broadly organize spike timing in CA1 neurons, and parvalbumin interneurons are critical in coordinating network theta rhythms. One-Sentence SummaryCellular membrane voltage of parvalbumin interneurons organizes spiking and network dynamics in the hippocampus.

neuroscience↗

bioRxiv2022

Deep brain stimulation creates information lesion through membrane depolarization

Deep brain stimulation (DBS) is a promising neuromodulation therapy that alters neural activity via intracranial electrical stimulation. However, the neurophysiological mechanisms of DBS remain largely unknown, because of the difficulty of obtaining cellular resolution recordings without electrical interference. Here, we performed high-speed membrane voltage fluorescence imaging of individual hippocampal CA1 neurons during DBS in awake mice. We discovered that DBS, delivered at either 40Hz or 140Hz, reliably depolarizes somatic membrane potentials. Further, DBS enhanced spike rates and paced membrane voltage and spike timing at the stimulation frequency, though more prominent at 40Hz than 140Hz. To determine how DBS induced membrane voltage change impacts neurons ability to process inputs, we optogenetically evoked membrane depolarization. We found that neurons become unreliable in responding to optogenetic inputs during DBS, particularly during 140Hz DBS. These results demonstrate that DBS produces powerful membrane depolarization that interferes with neurons ability to process inputs, creating information lesion.

neuroscience↗

bioRxiv2021

Large-scale voltage imaging in the brain using targeted illumination

Recent improvements in genetically encoded voltage indicators enabled optical imaging of action potentials and subthreshold membrane voltage dynamics from single neurons in the mammalian brain. To perform high speed voltage imaging, widefield microscopy remains an essential tool for recording activity from many neurons simultaneously over a large anatomical area. However, the lack of optical sectioning makes widefield microscopy more prone to background signal contamination, and thus far voltage imaging using fully genetically encoded voltage indicators remains limited to simultaneous sampling of a few cells over a restricted field-of-view. We here demonstrate a strategy for large scale voltage imaging using the fully genetically encoded voltage indicator SomArchon and targeted illumination. We implemented a simple, low-cost digital micromirror device based targeted illumination strategy to restrict illumination to the cells of interest, and systematically quantified the improvement of this microscopy design theoretically and experimentally with SomArchon expressing neurons in single layer cell cultures and in the brains of awake mice. We found that targeted illumination, in comparison to widefield illumination, increased SomArchon signal contrast and reduced background cross-contamination in the brain. Such improvement permitted the reduction of illumination intensity, and thus reduced fluorescence photobleaching and prolonged imaging duration. When coupled with a high-speed, large area sCMOS camera, we routinely imaged tens of spiking neurons simultaneously over minutes in the brain. Thus, the widefield microscopy design with an integrated targeted illumination system described here offers a simple solution for voltage imaging analysis of large neuron populations in behaving animals.

neuroscience↗

bioRxiv2020

Distinct Neuronal Populations Contribute to Trace Conditioning and Extinction Learning in the Hippocampal CA1

Trace conditioning and extinction learning depend on the hippocampus, but it remains unclear how ongoing neural activities in the hippocampus are modulated during different learning processes. To explore this question, we performed calcium imaging in a large number of individual CA1 neurons during both trace eye-blink conditioning and subsequent extinction learning in mice. Using trial-averaged calcium fluorescence analysis, we found direct evidence that in real time, as learning emerges, distinct populations of CA1 cells contribute to trace conditioned learning versus extinction learning. Furthermore, we examined network connectivity by calculating co-activity between CA1 neuron pairs, and found that CA1 network connectivity is different between conditioning and extinction and between correct versus incorrect behavioral responses during trace conditioned learning. However, the overall connectivity density remains constant across these behavioral conditions. Together, our results demonstrate that distinct populations of CA1 neurons, forming different sub-networks with unique connectivity patterns, encode different aspects of learning.

neuroscience↗