Versatile Surface Electrodes for Combined Electrophysiology and Two-Photon Imaging of the Mouse Central Nervous System

Abstract

Understanding and modulating CNS function in physiological as well as pathophysiological contexts remains a significant ambition in research and clinical applications. The investigation of the multifaceted CNS cell types including their interactions and contributions to neural function requires a combination of the state-of-the-art in vivo electrophysiology and imaging techniques. We developed a novel type of liquid crystal polymer (LCP) surface micro-electrode manufactured in three customized designs with up to 16 channels for recording and stimulation of brain activity. All designs include spare central spaces for simultaneous 2P-imaging. Nanoporous platinum-plated contact sites ensure a low impedance and high current transfer. The epidural implantation of the LCP micro-electrodes could be combined with standard cranial window surgery. The epidurally positioned electrodes did not only display long-term biocompatibility, but we also observed an additional stabilization of the underlying CNS tissue. We demonstrate the electrode’s versatility in combination with in vivo 2P-imaging by monitoring anesthesia-awake cycles of transgenic mice with GCaMP3 expression in neurons or astrocytes. Cortical stimulation and simultaneous 2P Ca2+ imaging in neurons or astrocytes highlighted the astrocytes’ integrative character in neuronal activity processing. Furthermore, we confirmed that spontaneous astroglial Ca2+ signals are dampened under anesthesia, while evoked signals in neurons and astrocytes showed stronger dependency on stimulation intensity rather than on various levels of anesthesia. Finally, we show that the electrodes provide recordings of the electrocorticogram (ECoG) with a high signal-to noise ratio and spatial signal differences which help to decipher brain activity states during experimental procedures. Summarizing, the novel LCP surface micro-electrode is a versatile, convenient, and reliable tool to investigate brain function in vivo.

Astrocytes and Microglia Exhibit Cell-Specific Ca2+ Signaling Dynamics in the Murine Spinal Cord

“…Also, glial Ca 2+ signaling is differentially affected by anesthesia used during the in vivo recording. In line with our observations, previous work shows a reduced Ca 2+ activity in astroglia both in brain and spinal cord ( Thrane et al, 2012 ; Poskanzer and Yuste, 2016 ; Sekiguchi et al, 2016 ; Schweigmann et al, 2021 ) and an increased Ca 2+ activity in microglia in the brain under anesthesia ( Umpierre et al, 2020 ). Although microglial ROA density is higher in vivo , the ROA area itself is smaller than for astrocytes both ex vivo and in vivo in the early phase ( d1 and d2 ) after the window implantation ( Figures 3F , 5F ), suggesting that activated microglial Ca 2+ dynamics are reduced compared to physiological conditions.…”

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

“…While the initial GFAP response after craniotomy, corresponding to M1, is well described, further testing would certainly strengthen the results of the longest implantation period. Nevertheless, our results correspond well to the described effects of cranial implantation surgery ( Holtmaat et al, 2009 ; Schweigmann et al, 2021 ) and do not suggest an additional, aggravating element introduced by the materials of the ECoG device. Therefore, we recommend Parylene HT as a stable and biocompatible substrate for chronically implanted transparent neural interfaces.…”

“…GFAP expression increases 1–2 weeks after surgery ipsilaterally and remains elevated, to a lesser degree, for up to 6 months ( Brosch et al, 2020 ), although there are reports of regained baseline levels ( Koletar et al, 2019 ; Park et al, 2019 ). The magnitude of these increases covers a wide range, from 17% ( Brosch et al, 2020 ; Fedor et al, 2022 ) and 50% ( Holtmaat et al, 2009 ) to 300% ( Schweigmann et al, 2021 ). In some cases, the reported increase is not quantified ( Xu et al, 2007 ; Guo et al, 2017 ; Brodnick et al, 2019 ; Koletar et al, 2019 ), or the amount of increase is not reported ( Park et al, 2019 ).…”

Transparent Thiol‐ene/Acrylate‐Based MicroECoG Devices Used for Concurrent Recording of Fluorescent Calcium Signals and Electrophysiology in Awake Animals

“…[19] Schweigmann et al used a liquid crystal polymer (LCP)-based array for 28 days to capture GCaMP3 signals of neurons and astrocytes. [38] Even though each of these studies reported on a novel material science approach to create a transparent MEA, none of these studies addressed the longevity of optical signals captured through these devices. Our group was first investigating the optical performance of such a transparent microdevice quantitatively, where a Parylene HT/ITO-based ECoG array was implanted and tested for 51 days.…”