Inflammatory encapsulation of implanted cortical-neuro-probes [the foreign body response (FBR)] severely limits their use in basic brain research and in clinical applications. A better understanding of the inflammatory FBR is needed to effectively mitigate these critical limitations. Combining the use of the brain permeant colony stimulating factor 1 receptor inhibitor PLX5622 and a perforated polyimide-based multielectrode array platform (PPMP) that can be sectioned along with the surrounding tissue, we examined the contribution of microglia to the formation of inflammatory FBR. To that end, we imaged the inflammatory processes induced by PPMP implantations after eliminating 89–94% of the cortical microglia by PLX5622 treatment. The observations showed that: (I) inflammatory encapsulation of implanted PPMPs proceeds by astrocytes in microglia-free cortices. The activated astrocytes adhered to the PPMP’s surfaces. This suggests that the roles of microglia in the FBR might be redundant. (II) PPMP implantation into control or continuously PLX5622-treated rats triggered a localized surge of microglia mitosis. The daughter cells that formed a “cloud” of short-lived (T1/2 ≤ 14 days) microglia around and in contact with the implant surfaces were PLX5622 insensitive. (III) Neuron degeneration by PPMP implantation and the ensuing recovery in time, space, and density progressed in a similar manner in the cortices following 89–94% depletion of microglia. This implies that microglia do not serve a protective role with respect to the neurons. (IV) Although the overall cell composition and dimensions of the encapsulating scar in PLX5622-treated rats differed from the controls, the recorded field potential (FP) qualities and yield were undistinguishable. This is accounted for by assuming that the FP amplitudes in the control and PLX5622-treated rats were related to the seal resistance formed at the interface between the adhering microglia and/or astrocytes and the PPMP platform rather than across the scar tissue. These observations suggest that the prevention of both astrocytes and microglia adhesion to the electrodes is required to improve FP recording quality and yield.
Bibliographical noteFunding Information:
This work was supported by the Israel Science Foundation grant #1808/19. Part of this work was supported by the Charles E. Smith and Prof. Joel Elkes Laboratory for Collaborative Research in Psychobiology. The study is based on an earlier research project supported by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under Award Number U01NS099687.
We thank Plexxikon Inc., for supplying PLX5622 under Materials Transfer Agreement. Drs Shimon Eliav, Galina Chechelnitsky, Maurice Saidian, and Evgenia Blayvas from the Harvey M. Kruger Family Center for Nanoscience for taking part in the fabrication of the perforated polyimide-based MEA platforms. The content is solely the responsibility of the authors and does not necessarily represent any official views of the granting agencies. Funding. This work was supported by the Israel Science Foundation grant #1808/19. Part of this work was supported by the Charles E. Smith and Prof. Joel Elkes Laboratory for Collaborative Research in Psychobiology. The study is based on an earlier research project supported by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under Award Number U01NS099687.
© Copyright © 2021 Sharon, Jankowski, Shmoel, Erez and Spira.
- field potential recordings
- foreign body response
- neural interface