Monitoring In Vivo Changes in Tonic Extracellular Dopamine Level by Charge-Balancing Multiple Waveform Fast-Scan Cyclic Voltammetry

Abstract

Dopamine (DA) modulates central neuronal activity through both phasic (second to second) and tonic (minutes to hours) terminal release. Conventional fast-scan cyclic voltammetry (FSCV), in combination with carbon fiber microelectrodes, has been used to measure phasic DA release in vivo by adopting a background subtraction procedure to remove background capacitive currents. However, measuring tonic changes in DA concentrations using conventional FSCV has been difficult because background capacitive currents are inherently unstable over long recording periods. To measure tonic changes in DA concentrations over several hours, we applied a novel charge-balancing multiple waveform FSCV (CBM-FSCV), combined with a dual background subtraction technique, to minimize temporal variations in background capacitive currents. Using this method, in vitro, charge variations from a reference time point were nearly zero for 48 h, whereas with conventional background subtraction, charge variations progressively increased. CBM-FSCV also demonstrated a high selectivity against 3,4-dihydroxyphenylacetic acid and ascorbic acid, two major chemical interferents in the brain, yielding a sensitivity of 85.40 ± 14.30 nA/μM and limit of detection of 5.8 ± 0.9 nM for DA while maintaining selectivity. Recorded in vivo by CBM-FSCV, pharmacological inhibition of DA reuptake (nomifensine) resulted in a 235 ± 60 nM increase in tonic extracellular DA concentrations, while inhibition of DA synthesis (α-methyl-dl-tyrosine) resulted in a 72.5 ± 4.8 nM decrease in DA concentrations over a 2 h period. This study showed that CBM-FSCV may serve as a unique voltammetric technique to monitor relatively slow changes in tonic extracellular DA concentrations in vivo over a prolonged time period.

Development of Glass‐sealed Gold Nanoelectrodes for in vivo Detection of Dopamine in Rat Brain

“…When 20 mg kg −1 nomifensine (a dopamine reuptake blocker) was exogenously infused into abdomen, the amperometric response increased immediately, indicating an increase in the extracellular level of DA in response to nomifensine treatment. According to the calibration curve(Figure B), the concentration of DA release evoked by nomifensine was estimated to be 37 nM, which was relatively close to the reported values (Table S1) . This is the first time that concentration of DA in rat brain after nomifensine injection is reported by glass‐sealed Au nanoelectrode.…”

A baseline drift detrending technique for fast scan cyclic voltammetry

“…The amplitude of faradaic current calculated from the background subtraction method can be linked to actual concentration values by pre/post calibration. Although background current subtraction with FSCV has been extensively used to measure phasic (evoked) changes in dopamine in vivo [2, 7], the inherent instability in background currents over prolonged recording time periods (>90 seconds) has been a problem for accurate FSCV analysis [7, 8]. The nonlinear background instability, or drifting, in long-term measurements in vivo can be attributed to various factors such as complex biological neuro-environmental changes, electrode stabilization [9], and electrode surface erosion or fouling [10].…”

Frontiers in electrochemical sensors for neurotransmitter detection: towards measuring neurotransmitters as chemical diagnostics for brain disorders

“…135 In an alternate strategy, Oh et al changed the waveform for FSCV into a "Mexican hat" waveform and introduced a dual-background subtraction protocol to measure tonic DA. 136 They termed this new method charge balancing multiple waveform FSCV. In a follow up study, the group utilized multiple cyclic square wave voltammetry for measuring tonic DA, which, like FSCAV, also utilized a holding potential period to control DA adsorption onto the carbon ber.…”