Abstract
In neural prosthetics and stereotactic neurosurgery, intracortical electrodes are often utilized for delivering therapeutic electrical pulses, and recording neural electrophysiological signals. Unfortunately, neuroinflammation impairs the neuron-electrode-interface by developing a compact glial encapsulation around the implants in long term. At present, analyzing this immune reaction is only feasible with post-mortem histology; currently no means for specific in vivo monitoring exist and most applicable imaging modalities can not provide information in deep brain regions. Optical coherence tomography (OCT) is a well established imaging modality for in vivo studies, providing cellular resolution and up to 1.2 mm imaging depth in brain tissue. A fiber based spectral domain OCT was shown to be capable of minimally invasive brain imaging. In the present study, we propose to use a fiber based spectral domain OCT to monitor the progression of the tissue's immune response through scar encapsulation progress in a rat animal model. A fine fiber catheter was implanted in rat brain together with a flexible polyimide microelectrode in sight both of which acts as a foreign body and induces the brain tissue immune reaction. OCT signals were collected from animals up to 12 weeks after implantation and thus gliotic scarring in vivo monitored for that time. Preliminary data showed a significant enhancement of the OCT backscattering signal during the first 3 weeks after implantation, and increased attenuation factor of the sampled tissue due to the glial scar formation.
Highlights
Intracortical electrodes are often employed in neuroprosthetic applications or in clinical stereotactic surgery, to deliver therapeutic electrical pulses and collect neuronal electrophysiological signals (Tronnier and Fogel, 2000; Stieglitz et al, 2009; Raspopovic et al, 2014)
At week 6 and 12, the Optical coherence tomography (OCT) signal attenuated faster featuring a steep declining slope in the axial scans (A-scan) plot while the backscattering intensity from the tissue surrounding the fiber probe stayed steady at 70 dB
spectral domain optical coherence tomography (SDOCT) with an in situ implanted fiber catheter is capable of visualizing the modification in optical properties of the surrounding tissue over time
Summary
Intracortical electrodes are often employed in neuroprosthetic applications or in clinical stereotactic surgery, to deliver therapeutic electrical pulses and collect neuronal electrophysiological signals (Tronnier and Fogel, 2000; Stieglitz et al, 2009; Raspopovic et al, 2014). Any type of the artificial implant is resistant to this bio degradation, which induces a so called frustrated phagocytosis and leads in consequence to a dense glial scar attempting to isolate the implant from the delicate brain tissue (Turner et al, 1999; Biran et al, 2005; Polikov et al, 2005; Winslow et al, 2010; Potter et al, 2012) This isolation performed by glial sheathing changes the electrical coupling to the surrounding parenchyma, but may even cause neuronal loss by neurotoxic factors released from glial cells (Block et al, 2007). This technique is limited to imaging only a shallow part
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