Search bioRxiv⌕ Search

Biology subjects

Gibson, E. A.

Publications and source records attributed to Gibson, E. A..

16 recordsLinked to original sources

Multi-site temporal control of optogenetic stimulation enhances firing frequencies in peripheral nerves

We find that multi-site temporal control of optogenetic photostimulation in peripheral nerves can enhance firing rates by overcoming the intrinsic limitation of opsin photophysics. The benefits of multi-site optogenetic stimulation were demonstrated with three approaches: (1) in silico modeling, (2) ex vivo in the sciatic nerve, and (3) in vivo in the vagus nerve. An in silico model of multi-site optogenetic stimulation was developed in two Hodgkin and Huxley type neuron models, that supported our hypothesis. The ex vivo sciatic nerve showed an increase in firing frequency that is physiologically relevant for functional control. The technique was then applied in vivo for optogenetic vagus nerve stimulation resulting in significant changes in heart rate compared with standard methods of single-site stimulation. Improving the control of optogenetically induced neural firing will have broad impacts for future developments in optical nerve interfaces and brain-machine interfaces.

neuroscience↗

Miniaturized widefield microscope for high speed voltage imaging

Functional imaging in freely moving animals with genetically encoded voltage indicators (GEVIs) will open new capabilities for neuroscientists to study the behavioral relevance of neural activity with high spatial and temporal precision. However, miniaturization of an imaging system with sufficient collection efficiency to resolve the small changes in fluorescence yield from voltage spikes, as well as development of efficient image sensors that are sufficiently fast to capture them, has proven challenging. We present a miniaturized microscope designed for voltage imaging, with a numerical aperture of 0.6, 250 m field of view and 1.3 mm working distance that weighs 16.4 g. We show it is capable of imaging in vivo voltage spikes from Voltron2 with a spike peak-to-noise ratio >3 at a framerate of 530 Hz.

neuroscience↗

Voltage Imaging with Periodic Structured Illumination

We utilize periodic structured illumination with pseudo-HiLo (pHiLo) image reconstruction for in vivo voltage imaging. We demonstrate reduced signal from out-of-focus cells, that contaminates voltage activity for in-focus cells of interest, with pHiLo compared to traditional widefield recordings taken with uniform illumination and pseudo-widefield (pWF) reconstructions. We discuss tradeoffs between signal-to-background ratio, signal-to-noise ratio and temporal resolution for pHiLo in the context of high-speed voltage imaging in awake mice.

neuroscience↗

Opto2P-FCM: A MEMS based miniature two-photon microscope with two-photon patterned optogenetic stimulation

Multiphoton microscopy combined with optogenetic photostimulation is a powerful technique in neuroscience enabling precise control of cellular activity to determine the neural basis of behavior in a live animal. Two-photon patterned photostimulation has taken this further by allowing interrogation at the individual neuron level. However, it remains a challenge to implement imaging of neural activity with spatially patterned two-photon photostimulation in a freely moving animal. We developed a miniature microscope for high resolution two-photon fluorescence imaging with patterned two-photon optogenetic stimulation. The design incorporates a MEMS scanner for two-photon imaging and a second beam path for patterned two-photon excitation in a compact and lightweight design that can be head-attached to a freely moving animal. We demonstrate cell-specific optogenetics and high resolution MEMS based two-photon imaging in a freely moving mouse. The new capabilities of this miniature microscope design can enable cell-specific studies of behavior that can only be done in freely moving animals.

neuroscience↗

Miniscope Recording Calcium Signals at Hippocampus of Mice Navigating an Odor Plume

Mice navigate an odor plume with a complex spatiotemporal structure in the dark to find the source of odorants. This article describes a protocol to monitor behavior and record Ca2+ transients in dorsal CA1 stratum pyramidale neurons in hippocampus (dCA1) in mice navigating an odor plume in a 50 cm x 50 cm x 25 cm odor arena. An epifluorescence miniscope focused through a GRIN lens imaged Ca2+ transients in dCA1 neurons expressing the calcium sensor GCaMP6f in Thy1-GCaMP6f mice. The paper describes the behavioral protocol to train the mice to perform this odor plume navigation task in an automated odor arena. The methods include a step-by-step procedure for the surgery for GRIN lens implantation and baseplate placement for imaging GCaMP6f in CA1. The article provides information on real-time tracking of the mouse position to automate the start of the trials and delivery of a sugar water reward. In addition, the protocol includes information on using of an interface board to synchronize metadata describing the automation of the odor navigation task and frame times for the miniscope and a digital camera tracking mouse position. Moreover, the methods delineate the pipeline used to process GCaMP6f fluorescence movies by motion correction using NorMCorre followed by identification of regions of interest with EXTRACT. Finally, the paper describes an artificial neural network approach to decode spatial paths from CA1 neural ensemble activity to predict mouse navigation of the odor plume. SUMMARYThis protocol describes how to investigate the brain-behavior relationship in hippocampal CA1 in mice navigating an odor plume. This article provides a step-by-step protocol, including the surgery to access imaging of the hippocampus, behavioral training, miniscope GCaMP6f recording and processing of the brain and behavioral data to decode the mouse position from ROI neural activity.

neuroscience↗

Long-term in vivo three-photon imaging reveals region-specific differences in healthy and regenerative oligodendrogenesis

The generation of new myelin-forming oligodendrocytes in the adult CNS is critical for cognitive function and regeneration following injury. Oligodendrogenesis varies between gray and white matter regions suggesting that local cues drive regional differences in myelination and the capacity for regeneration. Yet, the determination of regional variability in oligodendrocyte cell behavior is limited by the inability to monitor the dynamics of oligodendrocytes and their transcriptional subpopulations in white matter of the living brain. Here, we harnessed the superior imaging depth of three-photon microscopy to permit long-term, longitudinal in vivo three-photon imaging of an entire cortical column and underlying subcortical white matter without cellular damage or reactivity. Using this approach, we found that the white matter generated substantially more new oligodendrocytes per volume compared to the gray matter, yet the rate of population growth was proportionally higher in the gray matter. Following demyelination, the white matter had an enhanced population growth that resulted in higher oligodendrocyte replacement compared to the gray matter. Finally, deep cortical layers had pronounced deficits in regenerative oligodendrogenesis and restoration of the MOL5/6-positive oligodendrocyte subpopulation following demyelinating injury. Together, our findings demonstrate that regional microenvironments regulate oligodendrocyte population dynamics and heterogeneity in the healthy and diseased brain.

neuroscience↗

Time Tiling of Learned Stimulus-Based Decision Making in Dorsal CA1 in the Hippocampus

Sequential neural dynamics encoded by "time cells" play a crucial role in hippocampal function. However, the role of hippocampal sequential neural dynamics in associative learning is an open question. In this manuscript, we used two-photon Ca2+ imaging of dorsal CA1 pyramidal neurons in head-fixed mice performing a go-no-go associative learning task. We found that pyramidal cells responded differentially to the rewarded or unrewarded stimuli. The stimuli were decoded accurately from the activity of the neuronal ensemble, and accuracy increased substantially as the animal learned to differentiate the stimuli. Decoding the stimulus from individual pyramidal cells that responded differentially revealed that decision-making took place at discrete times after stimulus presentation. Lick prediction decoded from the ensemble activity of cells in dCA1 correlated linearly with lick behavior indicating that sequential activity of pyramidal cells in dCA1 constitutes a temporal memory map used for decision-making in associative learning.

neuroscience↗

Interplay between ATRX and IDH1 mutations governs innate immune responses in diffuse gliomas

Stimulating the innate immune system has been explored as a therapeutic option for the treatment of gliomas. Inactivating mutations in ATRX, defining molecular alterations in IDH-mutant astrocytomas, have been implicated in dysfunctional immune signaling. However, little is known about the interplay between ATRX loss and IDH mutation on innate immunity. To explore this, we generated ATRX knockout glioma models in the presence and absence of the IDH1R132H mutation. ATRX-deficient glioma cells were sensitive to dsRNA-based innate immune agonism and exhibited impaired lethality and increased T-cell infiltration in vivo. However, the presence of IDH1R132Hdampened baseline expression of key innate immune genes and cytokines in a manner restored by genetic and pharmacological IDH1R132H inhibition. IDH1R132H co-expression did not interfere with the ATRX KO-mediated sensitivity to dsRNA. Thus, ATRX loss primes cells for recognition of dsRNA, while IDH1R132H reversibly masks this priming. This work reveals innate immunity as a therapeutic vulnerability of astrocytoma.

cancer biology↗

Differences in expression of tumor suppressor, innate immune, inflammasome, and potassium/gap junction channel host genes significantly predict viral reservoir size during treated HIV infection

The major barrier to an HIV cure is the persistence of infected cells that evade host immune surveillance despite effective antiretroviral therapy (ART). Most prior host genetic HIV studies have focused on identifying DNA polymorphisms (e.g., CCR5{Delta}32, MHC class I alleles) associated with viral load among untreated "elite controllers" (~1% of HIV+ individuals who are able to control virus without ART). However, there have been few studies evaluating host genetic predictors of viral control for the majority of people living with HIV (PLWH) on ART. We performed host RNA sequencing and HIV reservoir quantification (total DNA, unspliced RNA, intact DNA) from peripheral CD4+ T cells from 191 HIV+ ART-suppressed non-controllers. Multivariate models included covariates for timing of ART initiation, nadir CD4+ count, age, sex, and ancestry. Lower HIV total DNA (an estimate of the total reservoir) was associated with upregulation of tumor suppressor genes NBL1 (q=0.012) and P3H3 (q=0.012). Higher HIV unspliced RNA (an estimate of residual HIV transcription) was associated with downregulation of several host genes involving inflammasome (IL1A, CSF3, TNFAIP5, TNFAIP6, TNFAIP9, CXCL3, CXCL10) and innate immune (TLR7) signaling, as well as novel associations with potassium (KCNJ2) and gap junction (GJB2) channels, all q<0.05. Gene set enrichment analyses identified significant associations with TLR4/microbial translocation (q=0.006), IL-1{beta}/NRLP3 inflammasome (q=0.008), and IL-10 (q=0.037) signaling. HIV intact DNA (an estimate of the "replication-competent" reservoir) demonstrated trends with thrombin degradation (PLGLB1) and glucose metabolism (AGL) genes, but data were (HIV intact DNA detected in only 42% of participants). Our findings demonstrate that among treated PLWH, that inflammation, innate immune responses, bacterial translocation, and tumor suppression/cell proliferation host signaling play a key role in the maintenance of the HIV reservoir during ART. Further data are needed to validate these findings, including functional genomic studies, and expanded epidemiologic studies in female, non-European cohorts. Author SummaryAlthough lifelong HIV antiretroviral therapy (ART) suppresses virus, the major barrier to an HIV cure is the persistence of infected cells that evade host immune surveillance despite effective ART, "the HIV reservoir." HIV eradication strategies have focused on eliminating residual virus to allow for HIV remission, but HIV cure trials to date have thus far failed to show a clinically meaningful reduction in the HIV reservoir. There is an urgent need for a better understanding of the host-viral dynamics during ART suppression to identify potential novel therapeutic targets for HIV cure. This is the first epidemiologic host gene expression study to demonstrate a significant link between HIV reservoir size and several well-known immunologic pathways (e.g., IL-1{beta}, TLR7, TNF- signaling pathways), as well as novel associations with potassium and gap junction channels (Kir2.1, connexin 26). Further data are needed to validate these findings, including functional genomic studies and expanded epidemiologic studies in female, non-European cohorts.

genetics↗

GRINtrode: A neural implant for simultaneous two-photon imaging and extracellular electrophysiology in freely moving animals

SignificanceIn vivo imaging and electrophysiology are powerful tools to explore neuronal function that each offer unique complementary information with advantages and limitations. Capturing both data types from the same neural population in the freely moving animal would allow researchers to take advantage of the capabilities of both modalities and further understand how they relate to each other. AimHere we present a head-mounted neural implant suitable for in vivo two-photon imaging of neuronal activity with simultaneous extracellular electrical recording in head-fixed or freely moving animals. ApproachA GRIN lens-based head-mounted neural implant with extracellular electrical recording provided by tetrodes on the periphery of the GRIN lens was chronically implanted. The design of the neural implant allows for recording from head-fixed animals, as well as freely moving animals by coupling the imaging system to a coherent imaging fiber bundle. ResultsWe demonstrate simultaneous two-photon imaging of GCaMP and extracellular electrophysiology of neural activity in awake head-fixed, and freely moving mice. Using the collected information, we perform correlation analysis to reveal positive correlation between optical and local field potential recordings. ConclusionSimultaneously recording neural activity using both optical and electrical methods provides complementary information from each modality. Designs that can provide such bimodal recording in freely moving animals allow for the investigation of neural activity underlying a broader range of behavioral paradigms.

neuroscience↗

Miniature Structured Illumination Microscope for in vivo 3D Imaging of Brain Structures with Optical Sectioning

We present a high-resolution miniature, light-weight fluorescence microscope with electrowetting lens and onboard CMOS for high resolution volumetric imaging and structured illumination for rejection of out-of-focus and scattered light. The miniature microscope (SIMscope3D) delivers structured light using a coherent fiber bundle to obtain optical sectioning with an axial resolution of 18 m. Volumetric imaging of eGFP labeled cells in fixed mouse brain tissue at depths up to 220 m is demonstrated. The functionality of SIMscope3D to provide background free 3D imaging is shown by recording time series of microglia dynamics in awake mice at depths up to 120 m in the brain.

bioengineering↗

Host Variation in Interferon, MHC Class I, Glycosylation, and Viral Transcription Genes Predict HIV Persistence

ObjectivePrior genomewide association studies have identified variation in MHC Class I alleles and CCR5{Delta}32 as genetic predictors of viral control, especially in "elite" controllers, individuals who remain virally suppressed in the absence of therapy. DesignCross-sectional genomewide association study. MethodsWe analyzed custom whole exome sequencing and direct HLA typing from 202 ART-suppressed HIV+ non-controllers in relation to four measures of the peripheral CD4+ T cell reservoir: HIV intact DNA, total (t)DNA, unspliced (us)RNA, and RNA/DNA. Linear mixed models were adjusted for potential covariates including age, sex, nadir CD4+ T cell count, pre-ART HIV RNA, timing of ART initiation, and duration of ART suppression. ResultsPreviously reported "protective" host genetic mutations related to viral setpoint (e.g., among elite controllers) were found to predict smaller HIV reservoir size. The HLA "protective" B*57:01 was associated with significantly lower HIV usRNA (q=3.3x10-3), and among the largest subgroup, European ancestry individuals, the CCR5{Delta}32 deletion was associated with smaller HIV tDNA (p=4.3x10-3) and usRNA (p=8.7x10-3). In addition, genomewide analysis identified several SNPs in MX1 (an interferon stimulated gene) that were significantly associated with HIV tDNA (q=0.02), and the direction of these associations paralleled MX1 gene eQTL expression. ConclusionsWe observed a significant association between previously reported "protective" MHC class I alleles and CCR5{Delta}32 with the HIV reservoir size in non-controllers. We also found a novel association between MX1 and HIV total DNA (in addition to other interferon signaling relevant genes, PPP1CB, DDX3X). These findings warrant further investigation in future validation studies.

genomics↗

Characterization of red fluorescent reporters for dual-color in vivo three-photon microscopy

SignificanceThree-photon (3P) microscopy significantly increases the depth and resolution of in vivo imaging due to decreased scattering and nonlinear optical sectioning. Simultaneous excitation of multiple fluorescent proteins is essential to study multicellular interactions and dynamics in the intact brain. AimWe characterized the excitation laser pulses at a range of wavelengths for 3P microscopy, and then explored the application of tdTomato or mScarlet and EGFP for dual-color single-excitation structural 3P imaging deep in the living mouse brain. ApproachWe used frequency-resolved optical gating to measure the spectral intensity, phase, and retrieved pulse widths at a range of wavelengths. Then, we performed in vivo single wavelength-excitation 3P imaging in the 1225 - 1360 nm range deep in the mouse cerebral cortex to evaluate the performance of tdTomato or mScarlet in combination with EGFP. ResultsWe find that tdTomato and mScarlet, expressed in oligodendrocytes and neurons respectively, have high signal-to-background in the 1300-1360 nm range, consistent with enhanced 3P cross sections. ConclusionsThese results suggest that a single excitation wavelength source is advantageous for multiple applications of dual-color brain imaging and highlight the importance of empirical characterization of individual fluorophores for 3P microscopy.

neuroscience↗

Selective Modulation of Heart and Respiration by Optical Control of Vagus Nerve Axons Innervating the Heart

Targeting specifics subsets of peripheral pathways of the autonomic nervous system will enable new avenues to study organ control and develop new disease therapies. Vagus nerve stimulation (VNS) has shown many therapeutic benefits but current approaches involve imprecise electrical stimulation that gives rise to adverse effects, and the functionally relevant pathways are poorly understood. One method to overcome these limitations is the use of optogenetic techniques, which facilitate highly specific neural communication with light-sensitive actuators (opsins). Opsins can be targeted to cell populations of interest based on the location of viral delivery and genetic control of expression. Here, we tested whether holographic photostimulation of subsets of axons of the cervical vagus nerve that innervate the heart can be used to modulate cardiac function. Viral injection of retrograde adeno-associated virus (rAAV2-retro) in the heart resulted in robust, primarily afferent, opsin reporter expression in the vagus nerve, nodose ganglion, and brainstem. Selective holographic photostimulation of axons resulted in changes in heart rate, surface cardiac electrogram, and respiratory responses that were different from responses elicited by whole nerve photostimulation.Competing Interest StatementThe authors have declared no competing interest.View Full Text

bioengineering↗

Molecular layer interneurons in the cerebellum encode for valence in associative learning

We used two-photon microscopy to study the role of ensembles of cerebellar molecular layer interneurons (MLIs) in a go-no go task where mice obtain a sugar water reward if they lick a spout in the presence of the rewarded odorant and avoid a time out when they refrain from licking for the unrewarded odorant. In naive animals the MLI responses did not differ between the odorants. With learning, the rewarded odorant elicited a large increase in MLI calcium responses, and the identity of the odorant could be decoded from the differential response. Importantly, MLIs switched odorant responses when the valence of the stimuli was reversed. Finally, mice took a longer time to refrain from licking in the presence of the unrewarded odorant and had difficulty becoming proficient when MLIs were inhibited by chemogenetic intervention. Our findings support a role for MLIs in learning valence in the cerebellum.

neuroscience↗

Three dimensional two-photon imaging of neuronal activity in freely moving mice using a miniature fiber coupled microscope with active axial-scanning

We present a miniature head mounted two-photon fiber-coupled microscope (2P-FCM) for neuronal imaging with active axial focusing enabled using a miniature electrowetting lens. Full three-dimensional two-photon imaging of GCaMP6s showing individual neuron activity in multiple focal planes was achieved in a freely-moving mouse. Two-color simultaneous imaging of GFP and tdTomato fluorescence is also demonstrated. Additionally, dynamic control of the axial scanning of the electrowetting lens allows tilting of the focal plane enabling cells in multiple focal planes to be imaged simultaneously. Two-photon imaging allows increased penetration depth in tissue yielding a working distance of 450 m with an additional 180 m of active axial focusing. The objective NA is 0.45 with a lateral resolution of 1.8 m, an axial resolution of 10 m, and a field-of-view of 240 m diameter. The 2P-FCM has a weight of only [~]2.5 g and is capable of repeatable and stable head-attachment. The 2P-FCM with dynamic axial scanning provides a new capability to record from functionally distinct neuronal layers, opening new opportunities in neuroscience research.

neuroscience↗