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

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

eLife (2021-02-16)
Ricardo M Santos, Anton Sirota
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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
p-Benzoquinone, reagent grade, ≥98%
Sigma-Aldrich
m-Phenylenediamine, flakes, 99%
Sigma-Aldrich
Chloroplatinic acid hydrate, ≥99.9% trace metals basis
Sigma-Aldrich
Chitosan, low molecular weight
Sigma-Aldrich
Dopamine hydrochloride
Sigma-Aldrich
Choline Oxidase from Alcaligenes sp., lyophilized powder, ≥10 units/mg solid
Sigma-Aldrich
(+)-Sodium L-ascorbate, crystalline, ≥98%
Sigma-Aldrich
Hydrogen peroxide solution, contains inhibitor, 30 wt. % in H2O, ACS reagent
Sigma-Aldrich
Choline chloride, ≥99%
Sigma-Aldrich
Gold Chloride Solution, 200 mg/dL in deionized water