Ivan Strinić1,2, Aleksandar Opančar3, Andrea Blažević1,4, Anja Mioković3, Aleksandra Dugandžić1,4,5, Vedran Đerek3, Nikola Habek1,2,5

1Croatian Institute for Brain Research, University of Zagreb School of Medicine, Zagreb, Croatia; 2Centre of Excellence for Basic, Clinical and Translational Neuroscience, School of Medicine, University of Zagreb, Zagreb, Croatia; 3Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia; 4Department of Anatomy and Clinical Anatomy, University of Zagreb School of Medicine, Zagreb, Croatia; 5Department of Physiology, School of Medicine, University of Zagreb, Zagreb, Croatia

Non-optogenetic stimulation of neurons by light has the potential to become a novel, minimally invasive, wireless, and highly specific in terms of time and space method for electrophysiological manipulation. Organic electrolytic photocapacitor (PhotoCap) is a semiconductor device that creates an in-situ electrical field when stimulated by light and is stable in physiological conditions. It was previously shown that PhotoCap can stimulate neurons in culture and in-vivo extracellularly. We performed field excitatory postsynaptic potential (fEPSP) recording that was stimulated by PhotoCap on mouse hippocampal brain slices. The PhotoCap was placed in the CA3 region for Scaffer collateral stimulation and the recording electrode was placed in the pyramidal layer of CA1 region. Stimulation of the device was achieved by delivering pulses of red light through the microscope objective. After light stimulation of the PhotoCap, we recorded responses which are most likely fEPSPs. Duration of the responses was approximately 5 ms and the amplitude 0,3 mV. Our preliminary results indicate that PhotoCaps can be used as stimulation devices in acute brain slices. The nature of the PhotoCap, i.e. its stability in physiological conditions, low invasiveness, high specificity, and its many potential uses allows for advancements in the field of fundamental research and medical applications. The PhotoCap proves to be a new valuable tool in neurophysiological research, especially electrophysiology. New applications, such as, stimulation of specific brain regions and neurons lower in the neuronal pathway in vivo and/or changing the PhotoCap response by changing the light pattern, are yet to be performed.

Acknowledgements: Research was funded by the Scientific Centre of Excellence for Basic, Clinical and Translational Neuroscience (project “Experimental and clinical research of hypoxic-ischemic damage in perinatal and adult brain”; GA KK01. funded by the European Union through the European Regional Development Fund) and by projects of Croatian Science Foundation 3Doptobio (UIP-2019-04-1753) and FURNACE (IP-2018-01-7416).

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