Hypoxia-Associated Changes in Striatal Tonic Dopamine Release: Real-Time in vivo Measurements With a Novel Voltammetry Technique

Abstract

Introduction: Striatal tonic dopamine increases rapidly during global cerebral hypoxia. This phenomenon has previously been studied using microdialysis techniques which have relatively poor spatio-temporal resolution. In this study, we measured changes in tonic dopamine during hypoxia (death) in real time with high spatio-temporal resolution using novel multiple cyclic square wave voltammetry (MCSWV) and conventional fast scan cyclic voltammetry (FSCV) techniques. Methods: MCSWV and FSCV were used to measure dopamine release at baseline and during hypoxia induced by euthanasia, with and without prior alpha-methyl-p-tyrosine (AMPT) treatment, in urethane anesthetized male Sprague-Dawley rats. Results: Baseline tonic dopamine levels were found to be 274.1 ± 49.4 nM (n = 5; mean ± SEM). Following intracardiac urethane injection, the tonic levels increased to a peak concentration of 1753.8 ± 95.7 nM within 3.6 ± 0.6 min (n = 5), followed by a decline to 50.7 ± 21.5 nM (n = 4) at 20 min. AMPT pre-treatment significantly reduced this dopamine peak to 677.9 ± 185.7 nM (n = 3). FSCV showed a significantly higher (p = 0.0079) peak dopamine release of 6430.4 ± 1805.7 nM (n = 5) during euthanasiainduced cerebral hypoxia. Conclusion: MCSWV is a novel tool to study rapid changes in tonic dopamine release in vivo during hypoxia. We found a 6-fold increase in peak dopamine levels during hypoxia which was attenuated with AMPT pre-treatment. These changes are much lower compared to those found with microdialysis. This could be due to improved estimation of baseline tonic dopamine with MCSWV. Higher dopamine response measured with FSCV could be due to an increased oxidation current from electroactive interferents.

Cocaine-Induced Changes in Tonic Dopamine Concentrations Measured Using Multiple-Cyclic Square Wave Voltammetry in vivo

“…Our baseline dopamine levels, determined by post- in vivo calibration, were at around 100–200 nM; whereas microdialysis studies commonly report values between 10 to 20 nM ( Bradberry et al, 1993 ; Cadoni et al, 2000 ). Although the order of magnitude differs by a factor of ten, our values are broadly consistent with previous accumbal and striatal dopamine concentrations measured by various electrochemical techniques ( Blaha, 1996 ; Atcherley et al, 2015 ; Johnson et al, 2017 ; Oh et al, 2018 ; Taylor et al, 2019 ; Barath et al, 2020 ). The possibility that other interferents such as norepinephrine, which has similar electrochemical properties as dopamine, may be a contributing factor in the differences is unlikely since other studies have demonstrated that the amount of norepinephrine and serotonin in the NAcc is comparatively low ( Andrews and Lucki, 2001 ; McKittrick and Abercrombie, 2007 ; Zhang et al, 2020 ).…”

Automatic and Reliable Quantification of Tonic Dopamine Concentrations In Vivo Using a Novel Probabilistic Inference Method

“…The predicted tonic DA levels in the striatum of anesthetized rats were estimated to be 252.4 ± 142.8 nM with the peak-based method and 94.7 ± 24.1 nM with the probabilistic inference method. The two methods were not found to be significantly different in the mean value of tonic DA levels (paired t-test, t 5 = 1.12, P = 0.31), and the tonic values are in line with previous work by Oh et al, 15 Atcherley et al, 16 and Barath et al 25 However, the probabilistic inference method demonstrated significantly reduced variance in the tonic DA level prediction across animals (Bartlett's test, χ 2 = 10.14, P = 1.4 × 10 −3 ). This finding indicates that the probabilistic inference method is a more precise and reliable method for determining in vivo tonic DA concentrations.…”

“…An in-house-built electrometer (WINCS Harmoni) was used to determine the optimal placement of the carbon-fiber electrode via MFB electrical stimulation during the application of conventional fast-scan cyclic voltammetry . Upon successful placement of both electrodes, recordings were switched to the MCSWV (Figure ) system using in-house software written in LabVIEW 2016 (National Instruments, Austin, TX) and a commercial electronic interface (NI USB-6363, National Instruments, Austin, TX) with a base-station PC. , MCSWV recordings were then performed to measure tonic DA concentrations in the rat striatum at baseline and following pharmacological manipulation. MATLAB (MathWorks, Inc., Natick, MA) was used to process the data.…”

Applying a Fast-Scan Cyclic Voltammetry to Explore Dopamine Dynamics in Animal Models of Neuropsychiatric Disorders

“…Besides modified FSCV techniques, a number of complex voltammetric waveform methods have been designed and applied [106][107][108]. One particular method utilizes multiple cyclic square waves in combination with dynamic background subtraction and current modeling (multiple-cyclic square wave voltammetry) to retain accuracy and reproducibility in assessing neurotransmitter at its tonic levels [107,109].…”