Biology subjects

Cullen, D. K.

Publications and source records attributed to Cullen, D. K..

6 recordsLinked to original sources

bioRxiv2018

Multichannel Silicon Probes for Laminar Cortical and Hippocampal Recordings in Large Animals.

Decoding laminar information across deep brain structures and cortical regions is necessary in order to understand the spatiotemporal ensembles that represent cognition and memory. Large animal models are essential for translational research due to their gyrencephalic neuroanatomy and significant white matter composition. One of the major obstacles to applying the approaches currently utilized in lower order animals are technical limitations in silicon probes, specifically a lack of long-length probes with appropriate stiffness to penetrate to deeper structures with minimal damage to the neural interface. We tested various solutions and designs of multichannel silicon probes developed for large animal electrophysiology by recording neurophysiological signals from deep laminar structures in an acute preparation and in chronically implanted awake behaving Yucatan pigs. Electrophysiological parameters of single units and local field potentials were analyzed to evaluate performance over time of given silicon probes in chronic implantations. The cross-sectional area of silicon probes was found to be a crucial determinant of silicon probes single unit performance over time, potentially due to reduction of damage to the neural interface. EDGE-style probes had the highest yields during intra-hippocampal recordings in pigs, making them the most suitable for chronic implantations and awake behavioral experimentation. Novel CAMB 64-channel EDGE-style probes with linear and poly-2 site arrangement tested acutely had optimal single unit separation and a denser sampling of the laminar structure, identifying them as potential candidates for chronic implantations with less cortical damage above the active portion of the probe. This study provides an analysis of multichannel silicon probes designed for large animal laminar electrophysiology of deep brain structures, and suggests that current designs are reaching the physical thresholds necessary for long-term (~ 1 month) recordings from laminar deep structures with single-unit resolution.

neuroscience↗

bioRxiv2018

Cardiac myocyte microtissue aggregates broadcast local field potentials

Muscle tissue has been exploited as a living biopotential amplifier to facilitate transduction of peripheral nerve signals into prosthetic control in patients with limb amputation. Here we sought to address the question of whether microscopically small volumes of muscle tissue could effectively broadcast field potentials to electrodes not immediately in contact with that tissue. Cardiac myocytes were grown as three-dimensional aggregates containing 105 cells comprising a volume of approximately 0.065 mm3 (~500 m in diameter) atop multi-electrode arrays. In addition to the expected spontaneous contraction potentials detected using electrodes in direct contact with the myocytes, potentials could also be detected on distant electrodes not contacting the aggregates. Specifically, while both dissociated and aggregated cardiac myocyte cultures generated spontaneous contractions that could easily be recorded from underlying multi-electrode arrays, only aggregated myocyte cultures generated signals detectable several millimeters away by the electrode grid floating in media. This confirmed the ability of micro-volumes of aggregated muscle tissue to broadcast readily detectible signals. The amplitude of the potentials generated by the aggregates decreased exponentially with distance. The aggregates were sensitive to pharmacologic modification with isoproterenol increasing contraction rate. Simultaneous recordings with electrodes in physical contact to the aggregate and with electrodes several millimeters away revealed that the aggregates function as amplifiers and low-pass filters. This study lays the groundwork for forging myocyte aggregates as \"living amplifiers\" for long-term neural recording in brain-computer interfaces to treat neurological disease and injury.

bioengineering↗

bioRxiv2018

A Computational Model of Bidirectional Axonal Growth in Micro-Tissue Engineered Neuronal Networks (micro-TENNs)

Micro-Tissue Engineered Neural Networks (Micro-TENNs) are living three-dimensional constructs designed to replicate the neuroanatomy of white matter pathways in the brain, and are being developed as implantable microtissue for axon tract reconstruction or as anatomically-relevant in vitro experimental platforms. Micro-TENNs are composed of discrete neuronal aggregates connected by bundles of long-projecting axonal tracts within miniature tubular hydrogels. In order to help design and optimize micro-TENN performance, we have created a new computational model including geometric and functional properties. The model is built upon the three-dimensional diffusion equation and incorporates large-scale uni- and bi-directional growth that simulates realistic neuron morphologies. The model captures unique features of 3D axonal tract development that are not apparent in planar outgrowth, and may be insightful for how white matter pathways form during brain development. The processes of axonal outgrowth, branching, turning and aggregation/bundling from each neuron are described through functions built on concentration equations and growth time distributed across the growth segments. Once developed we conducted multiple parametric studies to explore the applicability of the method and conducted preliminary validation via comparisons to experimentally grown micro-TENNs for a range of growth conditions. Using this framework, this model can be applied to study micro-TENN growth processes and functional characteristics using spiking network or compartmental network modeling. This model may be applied to improve our understanding of axonal tract development and functionality, as well as to optimize the fabrication of implantable tissue engineered brain pathways for nervous system reconstruction and/or modulation.

bioengineering↗

bioRxiv2018

Optically-Controlled \"Living Electrodes\" with Long-Projecting Axon Tracts for a Synaptic Brain-Machine Interface

Achievements in intracortical neural interfaces are compromised by limitations in specificity and long-term performance. A biological intermediary between devices and the brain may offer improved specificity and longevity through natural synaptic integration with deep neural circuitry, while being accessible on the brain surface for optical read-out/control. Accordingly, we have developed the first "living electrodes" comprised of implantable axonal tracts protected within soft hydrogel cylinders for the biologically-mediated monitoring/modulation of brain activity. Here we demonstrate the controlled fabrication, rapid axonal outgrowth, reproducible cytoarchitecture, and simultaneous optical stimulation and recording of neuronal activity within these engineered constructs in vitro. We also present their transplantation, survival, integration, and optical recording in rat cortex in vivo as a proof-of-concept for this neural interface paradigm. The creation and functional validation of these preformed, axon-based "living electrodes" is a critical step towards developing a new class of biohybrid neural interfaces to probe and modulate native circuitry.

bioengineering↗

bioRxiv2018

Three-dimensional human axon tracts derived from cerebral organoids

Reestablishing cerebral connectivity is a critical part of restoring neuronal network integrity and brain function after trauma, stroke, and neurodegenerative diseases. Creating transplantable axon tracts in the laboratory is a novel strategy for overcoming the common barriers limiting axon regeneration in vivo, including growth-inhibiting factors and the limited outgrowth capacity of mature neurons in the brain. We describe the generation and phenotype of three-dimensional human axon tracts derived from cerebral organoid tissue. These centimeter-long constructs are encased in an agarose shell that permits physical manipulation and are composed of discrete cellular regions spanned by axon tracts and dendrites, mirroring the separation of grey and white matter in the brain. Features of cerebral cortex also are emulated, as evidenced by the presence of neurons with different cortical layer phenotypes. This engineered neural tissue has the translational potential to reconstruct brain circuits by physically replacing discrete cortical neuron populations as well as long-range axon tracts in the brain.\n\neTOC BlurbRestoring axonal connectivity after brain damage is crucial for improving neurological and cognitive function. Cullen, et al. have generated anatomically inspired, three-dimensional human axon tracts projecting from cerebral organoids in a transplantable format that may facilitate the reconstruction of large-scale brain circuits.\n\nHighlightsO_LIA neural tissue engineering approach is applied to human cerebral organoids.\nC_LIO_LIThree-dimensional axon tracts are generated in a transplantable format.\nC_LIO_LIThe growth characteristics of the engineered axons are examined.\nC_LIO_LIThe cellular phenotypes of the organoid tissue and axons are characterized.\nC_LI

bioengineering↗

bioRxiv2017

Electrophysiological Signature Reveals Laminar Structure of the Porcine Hippocampus

The hippocampus is integral to working and episodic memory, and is a central region of interest in diseases affecting these processes. Pig models are widely used in translational research, and may provide an excellent bridge between rodents and non-human primates for CNS disease models due to their gyrencephalic neuroanatomy and significant white matter composition. However, the laminar structure of the pig hippocampus has not been well characterized. Therefore, we histologically characterized the dorsal hippocampus of Yucatan miniature pigs and quantified the cytoarchitecture of the hippocampal layers. We then utilized stereotaxis combined with single unit electrophysiological mapping to precisely place multichannel laminar silicon probes into the dorsal hippocampus without the need for image guidance. We used in vivo electrophysiological recordings of simultaneous laminar field potentials and single unit activity in multiple layers of the dorsal hippocampus to physiologically identify and quantify these layers under anesthesia. Consistent with previous reports, we found the porcine hippocampus to have the expected archicortical laminar structure with some anatomical and histological features comparable to the rodent and others to the primate hippocampus. Importantly, we found these distinct features to be reflected in the laminar electrophysiology. This characterization, as well as our electrophysiology-based methodology targeting the porcine hippocampal lamina combined with high channel count silicon probes will allow for analysis of spike-field interactions during normal and disease states in both anesthetized and future awake behaving neurophysiology in this large animal.\n\nSignificance StatementThe hippocampus is central to working and episodic memory and is critically affected by diverse disease processes. In order to investigate hippocampal electrophysiology in translational large animal models, we developed an imaging-free stereotaxis and intraoperative electrophysiology methodology with custom silicon probes to precisely localize probe placement within the hippocampal laminar structure. We report for the first time the profile of single units and local field potentials in the pig dorsal hippocampus and relate them to a histological description. This characterization forms the basis for accessible translational pig models to study diseases of the central nervous system affecting hippocampal circuitry in the large animal gyrencephalic brain, as well as the groundwork for potential awake behaving neurophysiology of the porcine hippocampus.\n\nFunding SourcesThe Department of Veterans Affairs, IK2-RX001479, I01-RX001097. The National Institutes of Health, NINDS R01-NS-101108-01, T32-NS043126. CURE Foundation, Taking Flight Award. DoD ERP CDMRP, W81XWH-16-1-0675.

neuroscience↗