Development of a microelectrode for simultaneous in vivo calcium and electrophysiological recording of hippocampal neuronal activity
- Authors: Erofeev A.I.1, Vinokurov E.K.1, Vlasova O.L.1, Bezprozvannyi I.B.1,2
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Affiliations:
- Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University
- University of Texas Southwestern Medical Center
- Issue: Vol 18, No 4 (2023)
- Pages: 802-805
- Section: Conference proceedings
- URL: https://genescells.ru/2313-1829/article/view/623347
- DOI: https://doi.org/10.17816/gc623347
- ID: 623347
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Abstract
Calcium (Ca2+) imaging is a commonly utilized neuroscience technique for in vivo recording of neuronal activity. It involves the optical measurement of calcium concentration using genetically encoded calcium indicators (GECI) [1]. However, the kinetics of changes in the fluorescence of GECI are relatively slow and limited by the biophysics of the calcium binding [2]. In response to single action potentials (APs) in pyramidal neurons, most of the widely used GECI have a fluorescence half-life of approximately 100 ms [3]. As a result, GECI cannot provide complete information about the dynamics of neural ensembles. To address this issue, new variants of GECI, such as jGCaMP7 [3], and jGCaMP8 [4], have been developed, or genetically encoded voltage indicators (GEVI), such as JEDI-2P [5], have been utilized. However, the speed of GECI or GEVI is still lower than that of electrophysiological registration methods. Thus, we have designed a microelectrode that can be utilized with a gradient lens for in vivo calcium imaging with a miniscope.
The miniscope is a miniature microscope for single photon epifluorescence Ca2+ imaging, which enables recording of neuronal activity in freely moving laboratory animals, unlike the traditionally used two-photon imaging technique. The miniscope utilizes gradient-index (GRIN) lenses that are implanted directly into the brain of a laboratory animal, instead of a conventional lens. The gradient lens is a transparent cylinder with a diameter of 1.8 mm and a length of 3.8 mm. To facilitate electrophysiological recording, we developed a microelectrode that can be aligned with a GRIN lens.
The microelectrode is a three-layer structure consisting of: 1) a polyimide film, 2) conductive copper tracks deposited through thermoforming, and 3) a polyimide film with cutouts for pads. On one side of the microelectrode, there are 12 gold-plated conductive contacts for registering local field potentials, while on the other side, a similar number of conductive tracks are present for connecting to a connector that transmits data to the processing board. The flexible microelectrode is wrapped around a gradient lens and fixed using thermoforming, after which it is implanted in the animal's brain.
Using the developed microelectrode, our aim is to perform a comparative analysis of the calcium and electrophysiological activity of hippocampal neurons in freely moving wild-type mice and in a mouse model of Alzheimer's disease. This study will enable the identification of any abnormalities in Alzheimer's disease at the level of neural ensembles and may suggest new treatment approaches or mechanisms for the development of the progressive memory loss pathology associated with this disease. We would like to express our gratitude to Anastasia Viktorovna Bolshakova for her administrative assistance, and to the staff of the Laboratory of Molecular Neurodegeneration for their invaluable help and advices.
Full Text
Calcium (Ca2+) imaging is frequently used in neuroscience for recording neuronal activity in vivo. This method measures calcium concentration optically using genetically encoded calcium indicators (GECI) [1]. However, the kinetics of GECI fluorescence changes are restrained by the biophysics of calcium binding, resulting in relatively slow responses [2]. In response to single action potentials (APs) in pyramidal neurons, most widely used GECIs exhibit a fluorescence half-life of about 100 ms [3]. As a result, GECI cannot provide exhaustive data about neural ensembles’ dynamics. To tackle this issue, novel GECI variants like jGCaMP7 [3] and jGCaMP8 [4] or GEVI such as JEDI-2P [5] have been implemented. Nonetheless, the velocity of GECI or GEVI remains inferior to electrophysiological recording techniques. Thus, we have developed a microelectrode that is compatible with a gradient lens for in vivo calcium imaging using a miniscope.
The miniscope is a small microscope used for single photon epifluorescence Ca2+ imaging, allowing for recording of neuronal activity in freely moving laboratory animals, in contrast to the traditionally used two-photon imaging technique. Instead of a conventional lens, gradient-index (GRIN) lenses are implanted directly into the brain of laboratory animals. These lenses are transparent cylinders with a 1.8 mm diameter and 3.8 mm length. We developed a microelectrode that can be aligned with a GRIN lens to facilitate electrophysiological recording.
The microelectrode comprises three layers, including a polyimide film, conductive copper tracks deposited through thermoforming, and a polyimide film with cutouts for pads. One side of the microelectrode contains 12 gold-plated conductive contacts for registering local field potentials, and the other side has a similar number of conductive tracks for connection to a connector that transmits data to the processing board. The flexible microelectrode is wrapped around a gradient lens, fixed with thermoforming, and then implanted into the brain of the animal.
Using the microelectrodes developed, we aim to analyze and compare the calcium and electrophysiological activity of hippocampal neurons in freely moving wild-type mice and in a mouse model of Alzheimer’s disease. Through this study, any abnormalities in Alzheimer’s disease at the level of neural ensembles can be identified, possibly suggesting new treatment approaches or mechanisms for the progressive memory loss pathology associated with this disease. We would like to express our appreciation to Anastasia Viktorovna Bolshakova for her administrative support, and to the Laboratory of Molecular Neurodegeneration staff for their valuable assistance and guidance.
ADDITIONAL INFORMATION
Authors’ contribution. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work.
Funding sources. This work was supported by the Russian Science Foundation grant “In Vivo Study of Calcium and Electrophysiological Activity of Hippocampal Neurons in Mouse Model of Alzheimer’s disease” (No. 22-75-00028).
Competing interests. The authors declare that they have no competing interests.
About the authors
A. I. Erofeev
Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University
Author for correspondence.
Email: alexandr.erofeew@gmail.com
Russian Federation, Saint Petersburg
E. K. Vinokurov
Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University
Email: alexandr.erofeew@gmail.com
Russian Federation, Saint Petersburg
O. L. Vlasova
Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University
Email: alexandr.erofeew@gmail.com
Russian Federation, Saint Petersburg
I. B. Bezprozvannyi
Institute of Biomedical Systems and Biotechnologies, Peter the Great St. Petersburg Polytechnic University; University of Texas Southwestern Medical Center
Email: alexandr.erofeew@gmail.com
Russian Federation, Saint Petersburg; Dallas, USA
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