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. 2023 Aug 31:17:1209913.
doi: 10.3389/fnins.2023.1209913. eCollection 2023.

Immunohistological responses in mice implanted with Parylene HT - ITO ECoG devices

Miklós Madarász  1   2 , Flóra Z Fedor  1   3 , Zoltán Fekete  4   5 , Balázs Rózsa  1   3   6   7
Affiliations

Immunohistological responses in mice implanted with Parylene HT - ITO ECoG devices

Miklós Madarász et al. Front Neurosci. .

Abstract

Transparent epidural devices that facilitate the concurrent use of electrophysiology and neuroimaging are arising tools for neuroscience. Testing the biocompatibility and evoked immune response of novel implantable devices is essential to lay down the fundamentals of their extensive application. Here we present an immunohistochemical evaluation of a Parylene HT/indium-tin oxide (ITO) based electrocorticography (ECoG) device, and provide long-term biocompatibility data at three chronic implantation lengths. We implanted Parylene HT/ITO ECoG devices epidurally in 5 mice and evaluated the evoked astroglial response, neuronal density and cortical thickness. We found increased astroglial response in the superficial cortical layers of all mice compared to contralateral unimplanted controls. This difference was largest at the first time point and decreased over time. Neuronal density was lower on the implanted side only at the last time point, while cortical thickness was smaller in the first and second time points, but not at the last. In this study, we present data that confirms the feasibility and chronic use of Parylene HT/ITO ECoG devices.

Keywords: foreign body response; immunohostochemistry; microECoG; parylene; polymer implants.

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Conflict of interest statement

BR was employed by Femtonics Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Parylene HT device and implantation. (A) Schematics of the surgical arrangement (not to scale). (B) Localization of the electrode array in actual surgical footage. Scale bar shows 5 mm. (C) Cleaned surgical area for the electrode above the dura mater relative to vascular network. Scale bar shows 500 μm.
Figure 2
Figure 2
Images of a Parylene HT/ITO ECoG implanted brain after 75 days of chronic implantation (M2). (A) Composite image of a coronal slice showing the arrangement of ROIs on control (B,E,H) and implanted (C,F,I) cortex. ROIs are divided into superficial (layers I–IV) and deep (layers V–VI). Magnification 3.2X, scale bar 500 μm. (B,C) Cell nuclei stained with DAPI. (E,F) Neurons stained with NeuroTrace, a fluorescent Nissl stain. (H,I) Astrocytes labeled with GFAP. Magnification 20X, scale bar 50 μm. (D,G,J) Comparison of ROI fluorescent intensity of DAPI (D), NeuroTrace (G) and GFAP (J) labeling. Mean ROI intensity was normalized to ROI area and presented here as a percentage of the mean of control, superficial ROIs of their respective stainings. CS – control, superficial. IS – implanted, superficial. CD – control, deep. ID – implanted, deep. Asterisks denote significant differences (p < 0.05).
Figure 3
Figure 3
Characterisation of implanted and control hemispheres in three implantation lengths. (A) Comparison of fluorescence intensities of GFAP stainings between superficial and deep ROIs on control and implanted hemispheres. Mean ROI intensity was normalized to ROI area. CS – control, superficial. IS – implanted, superficial. CD – control, deep. ID – implanted, deep. (B) Neuron density on control and implanted hemispheres. Counted cells in superficial and deep ROIs were summed and normalized to the summed area of both ROIs. (C) Cortical thickness on control and implanted hemispheres. Asterisks denote significant differences (p < 0.05).
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