Browsing by Author "Kim, Jongwoon"

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    Granular retrosplenial cortex layer 2/3 generates high-frequency oscillations dynamically coupled with hippocampal rhythms across brain states
    Arndt, Kaiser C.; Gilbert, Earl T.; Klaver, Lianne M.F.; Kim, Jongwoon; Buhler, Chelsea M.; Basso, Julia C.; McKenzie, Sam; English, Daniel Fine (CellPress, 2024-03-26)
    The granular retrosplenial cortex (gRSC) exhibits high-frequency oscillations (HFOs; ~150 Hz), which can be driven by a hippocampus-subiculum pathway. How the cellular-synaptic and laminar organization of gRSC facilitates HFOs is unknown. Here, we probe gRSC HFO generation and coupling with hippocampal rhythms using focal optogenetics and silicon-probe recordings in behaving mice. ChR2-mediated excitation of CaMKII-expressing cells in L2/3 or L5 induces HFOs, but spontaneous HFOs are found only in L2/3, where HFO power is highest. HFOs couple to CA1 sharp wave-ripples (SPW-Rs) during rest and the descending phase of theta. gRSC HFO current sources and sinks are the same for events during both SPW-Rs and theta oscillations. Independent component analysis shows that high gamma (50–100 Hz) in CA1 stratum lacunosum moleculare is comodulated with HFO power. HFOs may thus facilitate interregional communication of a multisynaptic loop between the gRSC, hippocampus, and medial entorhinal cortex during distinct brain and behavioral states.
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    Multifunctional Polymer Fiber Probes for Biomedical Application
    Kim, Jongwoon (Virginia Tech, 2024-06-17)
    Biomedical devices play a crucial role in the healthcare system, enabling more effective treatments, less invasive procedures, and more precise diagnoses. Due to these compelling reasons, development of new biomedical devices and biomaterials have always been in high demand. Exploring and refining fabrication methods are essential to the development of new biomedical devices. Some of the common fabrication methods include microfabrication methods (photolithography and soft lithography), 3D printing (additive manufacturing), laser machining, thermal drawing, and electrospinning. The choice of fabrication methods heavily depends on the materials, geometry, and functionalities of biomedical devices. Currently, the thermal drawing process has proven to be an excellent scalable fabrication platform for neural interface, tissue engineering, tumor/cancer treatment, soft robotics, and smart textiles. This Ph.D. dissertation summarizes my research on the fabrication and validation of thermally drawn multifunctional polymer fiber probes for modern biomedical applications, primarily in the fields of neural interfaces and tumor treatments. Understanding the neural basis of behavior requires monitoring and manipulating combinations of physiological elements and their interactions in behaving animals. Utilizing the thermal drawing process, we developed T-DOpE (Tapered Drug delivery, Optical stimulation, and Electrophysiology) probes and Tetro-DOpE (Tetrode-like Drug delivery, Optical stimulation, and Electrophysiology) probes that can simultaneously record and manipulate neural activity in behaving rodents. Taking advantage of the triple-functionality, we monitored local field potential (LFP) while manipulating cannabinoid receptors (CB1R; microfluidic agonist delivery) and CA1 neuronal activity using optogenetics. Focal infusion of CB1R agonist downregulated theta and sharp wave-ripple oscillations (SPW-Rs). Furthermore, we found that CB1R activation reduces sharp wave-ripples by impairing the innate SPW-R-generating ability of the CA1 circuit. Microscale electroporation devices are mostly restricted to in vitro experiments (i.e., microchannel and microcapillary). We developed a flexible microscale electroporation fiber probe through a thermal drawing process and femtosecond laser micromachining techniques. The novel fiber microprobes enable microscale electroporation and arbitrarily select the cell groups of interest to electroporate. Successful reversible and irreversible microscale electroporation was observed in a 3D collagen scaffold (seeded with U251 human glioma cells) using fluorescent staining. Leveraging the scalable thermal drawing process, we envision a wide distribution of multifunctional polymer fiber probes in research facilities and hospitals. Along with the fiber probes presented in this dissertation, additional insight and future perspective on thermally drawn biomedical devices are discussed.
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    Spatially expandable fiber-based probes as a multifunctional deep brain interface
    Jiang, Shan; Patel, Dipan C.; Kim, Jongwoon; Yang, Shuo; Mills, William A. II; Zhang, Yujing; Wang, Kaiwen; Feng, Ziang; Vijayan, Sujith; Cai, Wenjun; Wang, Anbo; Guo, Yuanyuan; Kimbrough, Ian F.; Sontheimer, Harald; Jia, Xiaoting (Nature Research, 2020)
    Understanding the cytoarchitecture and wiring of the brain requires improved methods to record and stimulate large groups of neurons with cellular specificity. This requires miniaturized neural interfaces that integrate into brain tissue without altering its properties. Existing neural interface technologies have been shown to provide high-resolution electrophysiological recording with high signal-to-noise ratio. However, with single implantation, the physical properties of these devices limit their access to one, small brain region. To overcome this limitation, we developed a platform that provides three-dimensional coverage of brain tissue through multisite multifunctional fiber-based neural probes guided in a helical scaffold. Chronic recordings from the spatially expandable fiber probes demonstrate the ability of these fiber probes capturing brain activities with a single-unit resolution for long observation times. Furthermore, using Thy1-ChR2-YFP mice we demonstrate the application of our probes in simultaneous recording and optical/chemical modulation of brain activities across distant regions. Similarly, varying electrographic brain activities from different brain regions were detected by our customizable probes in a mouse model of epilepsy, suggesting the potential of using these probes for the investigation of brain disorders such as epilepsy. Ultimately, this technique enables three-dimensional manipulation and mapping of brain activities across distant regions in the deep brain with minimal tissue damage, which can bring new insights for deciphering complex brain functions and dynamics in the near future.
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    T-DOpE probes reveal sensitivity of hippocampal oscillations to cannabinoids in behaving mice
    Kim, Jongwoon; Huang, Hengji; Gilbert, Earl T.; Kaiser C., Arndt; English, Daniel Fine; Jia, Xiaoting (Nature Research, 2024-02-24)
    Understanding the neural basis of behavior requires monitoring and manipulating combinations of physiological elements and their interactions in behaving animals. We developed a thermal tapering process enabling fabrication of low-cost, flexible probes combining ultrafine features: dense electrodes, optical waveguides, and microfluidic channels. Furthermore, we developed a semi-automated backend connection allowing scalable assembly. We demonstrate T-DOpE (Tapered Drug delivery, Optical stimulation, and Electrophysiology) probes achieve in single neuron-scale devices (1) highfidelity electrophysiological recording (2) focal drug delivery and (3) optical stimulation. The device tip can beminiaturized (as small as 50 μm) tominimize tissue damage while the ~20 times larger backend allows for industrial-scale connectorization. T-DOpE probes implanted in mouse hippocampus revealed canonical neuronal activity at the level of local field potentials (LFP) and neural spiking. Taking advantage of the triple-functionality of these probes, we monitored LFP while manipulating cannabinoid receptors (CB1R; microfluidic agonist delivery) and CA1 neuronal activity (optogenetics). Focal infusion of CB1R agonist downregulated theta and sharp wave-ripple oscillations (SPWRs). Furthermore, we found that CB1R activation reduces sharp wave-ripples by impairing the innate SPW-R-generating ability of the CA1 circuit.