Temporal Differentiation of pH-Dependent Capacitive Current from Dopamine

Abstract

Voltammetric recording of dopamine (DA) with fast-scan cyclic voltammetry (FSCV) on carbon fiber microelectrodes have been widely used, because of its high sensitivity to dopamine. However, since an electric double layer on a carbon fiber surface in a physiological ionic solution behaves as a capacitor, fast voltage manipulation in FSCV induces large capacitive current. The faradic current from oxidation/reduction of target chemicals must be extracted from this large background current. It is known that ionic shifts, including H(+), influence this capacitance, and pH shift can cause confounding influences on the FSCV recordings within a wide range of voltage. Besides FSCV with a triangular waveform, we have been using rectangular pulse voltammetry (RPV) for dopamine detection in the brain. In this method, the onset of a single pulse causes a large capacitive current, but unlike FSCV, the capacitive current is restricted to a narrow temporal window of just after pulse onset (<5 ms). In contrast, the peak of faradic current from dopamine oxidation occurs after a delay of more than a few milliseconds. Taking advantage of the temporal difference, we show that RPV could distinguish dopamine from pH shifts clearly and easily. In addition, the early onset current was useful to evaluate pH shifts. The narrow voltage window of our RPV pulse allowed a clear differentiation of dopamine and serotonin (5-HT), as we have shown previously. Additional recording with RPV, alongside FSCV, would improve identification of chemicals such as dopamine, pH, and 5-HT.

Reward-Induced Phasic Dopamine Release in the Monkey Ventral Striatum and Putamen

“…The carbon fibers supported by tapered glass capillary ( Fig 1A right) seem to have less tissue adhesion, although the deterioration was not perfectly avoided. Compared to our experience in mice [ 19 , 20 , 22 ] , sensitivity loss occurred more often in the monkey brain. We suspect that tissue debris at the tip of the guide cannula is most likely the cause of tissue adhesion and sensitivity loss.…”

“…In the averaged color plot of CS+ responses ( Fig 4A ), positive current response at the peak of triangular applied potential (4.25 ms from the pulse onset) was observed. We have previously observed adenosine response at the peak of 1.3V triangular waveform [ 22 ] . Unique adenosine-like response was detected following CS+ ( S3 Fig ).…”

“…FSCV with a triangular waveform from -0.4 to 1.3V was mainly applied for electrochemical recordings in this study. In a part of sessions, rectangular-pulse voltammetry (RPV) was performed as described previously [ 22 ] . For simultaneous voltammetric recording at multiple locations, a counter electrode grounded type three-channel potentiostat was used (HECS-9139, Huso Electrochemical Systems, Kawasaki, Japan).…”

“…Voltage pulses were applied at 10 Hz. For in vitro evaluation of the current responses of chemicals, carbon fiber microelectrodes were placed in a flow of PBS, and the flow was switched to the test solutions [ 1 , 22 ] .…”

Enhanced dopamine detection sensitivity by PEDOT/graphene oxide coating on in vivo carbon fiber electrodes

“…Observing the real-time kinetics of in vivo neurochemical signaling is paramount to uncovering these functionalities and furthering our understanding of brain function and dysfunction. Electrochemical methods, such as fast scan cyclic voltammetry (FSCV) and chronoamperometry, have been widely employed for the sub second detection of electroactive neurochemicals such as dopamine (Jones et al 1995; Kawagoe et al 1992; Larsen et al 2011; Taylor et al 2013; Taylor et al 2015; Wightman et al 1988), ascorbic acid (Cofan and Radovan 2008; Yoshimi and Weitemier 2014), norepinephrine (Park et al 2011), adenosine (Nguyen et al 2014; Ross et al 2014) and serotonin (Hashemi et al 2012; Hashemi et al 2009; Hashemi et al 2011). The high temporal resolution afforded by these electrochemical detection techniques allows for in vivo concentration monitoring of neurochemicals on a physiologically relevant timescale (Robinson et al 2011).…”