Second Harmonic Generation Imaging of Collagen in Chronically Implantable Electrodes in Brain Tissue.

Corinne R Esquibel,Morgan E Urdaneta,Andrew Shoffstall,Heui C Lee,Jenu V Chacko,Kristy D Wendt,Kevin J Otto,Justin C Williams,K W Eliceiri,Jeffrey R Capadona,Janak Gaire,Sarah K Brodnick

doi:10.3389/fnins.2020.00095

Abstract

Advances in neural engineering have brought about a number of implantable devices for improved brain stimulation and recording. Unfortunately, many of these micro-implants have not been adopted due to issues of signal loss, deterioration, and host response to the device. While glial scar characterization is critical to better understand the mechanisms that affect device functionality or tissue viability, analysis is frequently hindered by immunohistochemical tissue processing methods that result in device shattering and tissue tearing artifacts. Devices are commonly removed prior to sectioning, which can itself disturb the quality of the study. In this methods implementation study, we use the label free, optical sectioning method of second harmonic generation (SHG) to examine brain slices of various implanted intracortical electrodes and demonstrate collagen fiber distribution not found in normal brain tissue. SHG can easily be used in conjunction with multiphoton microscopy to allow direct intrinsic visualization of collagen-containing glial scars on the surface of cortically implanted electrode probes without imposing the physical strain of tissue sectioning methods required for other high resolution light microscopy modalities. Identification and future measurements of these collagen fibers may be useful in predicting host immune response and device signal fidelity.

Highlights

Multiphoton microscopy is a widely adopted brain imaging method, and can be used to monitor in vivo neural activity with single spine resolution (Knott et al, 2006; Svoboda and Yasuda, 2006; Kerr and Denk, 2008; Holtmaat et al, 2009; Ozbay et al, 2018)
We report the direct observation of high-resolution collagen fibers encapsulating intact, indwelling silicon NeuroNexus neural devices in thickly sectioned (350–450 μm) rat coronal slices (N = 10 for all varieties of NeuroNexus probes) that contrasts with the absence of non-fibrillar collagen in the unwounded brain (Figures 1, 2)
Collagen fibers that match the geometry of implanted silicon NeuroNexus devices can be observed with second harmonic generation (SHG) imaging independent of probe size and shank number (Figure 3)

Summary

Introduction

Multiphoton microscopy is a widely adopted brain imaging method, and can be used to monitor in vivo neural activity with single spine resolution (Knott et al, 2006; Svoboda and Yasuda, 2006; Kerr and Denk, 2008; Holtmaat et al, 2009; Ozbay et al, 2018). SHG generates its intrinsic contrast from the interaction of light with noncentrosymmetric structures such as collagen I, collagen II, and myosin (Roth and Freund, 1979; Plotnikov et al, 2006; Chen et al, 2012). Though the phenomenon of SHG was first demonstrated in biological tissues over three decades ago, and is observed with the appropriate filter, it remains an underutilized modality by those already using multiphoton microscopy to image brain-implanted devices in vivo and in vitro (Freund and Deutsch, 1986; Chen et al, 2012). One factor might be that the most common application for SHG imaging is examining fibrillar collagen and the role of collagen in the brain is still emerging (Shearer and Fawcett, 2001; Heck et al, 2003)

Methods

Results

Conclusion