Phasic oxygen dynamics confounds fast choline-sensitive biosensor signals in the brain of behaving rodents

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Abstract

Cholinergic fast time-scale modulation of cortical physiology is critical for cognition, but direct local measurement of neuromodulators in vivo is challenging. Choline oxidase (ChOx)-based electrochemical biosensors have been used to capture fast cholinergic signals in behaving animals. However, these transients might be biased by local field potential and O₂-evoked enzymatic responses. Using a novel Tetrode-based Amperometric ChOx (TACO) sensor we performed highly sensitive and selective simultaneous measurement of ChOx activity (COA) and O₂. In vitro and in vivo experiments, supported by mathematical modeling, revealed that non-steady-state enzyme responses to O₂ give rise to phasic COA dynamics. This mechanism accounts for most of COA transients in the hippocampus, including those following locomotion bouts and sharp-wave/ripples Our results suggest that it is unfeasible to probe phasic cholinergic signals under most behavioral paradigms with current ChOx biosensors. This confound is generalizable to any oxidase-based biosensor, entailing rigorous controls and new biosensor designs.

Data availability

Raw and intermediate data is provided for the in vitro analysis of biosensor's O2 dependence (Figure 7). The code used to model biosensor responses in vitro and obtain the plots in Figure 8 is also provided. Raw data is deposited at http://doi.org/10.5281/zenodo.4020348.

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Ricardo M Santos

Faculty of Medicine, Cognition and Neural Plasticity, Ludwig Maximillian University Munchen, Planegg, Germany

For correspondence
santos@bio.lmu.de

Competing interests
The authors declare that no competing interests exist.
Anton Sirota

Faculty of Medicine, Cognition and Neural Plasticity, Ludwig Maximillian University Munchen, Planegg, Germany

For correspondence
sirota@bio.lmu.de

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-4700-6587

Funding

Bundesministerium für Bildung und Forschung (01GQ0440)

Anton Sirota

Deutsche Forschungsgemeinschaft, Excellence Initiative, Munich Cluster for Systems Neurology (SyNergy EXC 1010)

Anton Sirota

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: All experimental procedures were established, and have been approved in accordance with the stipulations of the German animal welfare law (Tierschutzgesetz )(ROB-55.2-2532.Vet_02-16-170).

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.