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.
Highlights
The perpetuate quest of understanding and modulating brain function continuously confronts the scientific community with a multitude of technical challenges (Rusakov, 2015; Chen et al, 2021)
The electrodes were designed based on triple liquid crystal polymer (LCP) layers (Dyconex AG, Switzerland) allowing flexibility, yet maintaining stability, while the electrical circuit structure was made of a double gold layer (Figure 1B)
The gold electrode sites were coated with galvanized nanoporous platinum (5 g hexachloroplatinic acid dissolved in 375 ml distilled water; pulse electroplating at 0.3 kA/m2, 90 pulses) and electrochemically characterized by determining the electrode impedance and the cathodic charge storage capacity (CSCC; Cogan, 2008) with the multi-chemistry device Gamry Interface 1000 (Gamry Instruments)
Summary
The perpetuate quest of understanding and modulating brain function continuously confronts the scientific community with a multitude of technical challenges (Rusakov, 2015; Chen et al, 2021). Glial cell (dys-) function has been implicated in a variety of CNS disorders including Alzheimer’s (Gómez-Gonzalo et al, 2017; Arranz and De Strooper, 2019), Parkinson’s (Yun et al, 2018; Guo et al, 2020), multiple sclerosis (International Multiple Sclerosis Genetics Consortium, 2019; Yeung et al, 2019; Traiffort et al, 2020) and epilepsy (Heuser et al, 2018; Nikolic et al, 2018; Deshpande et al, 2020). Investigation of those second messenger dynamics in vivo requires the use of fluorescent indicators and sensors, endorsing the refinement and novel development of neuroscientific tools to study neuron-glia interactions by combining electrophysiological and 2P-imaging techniques
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