Tonic Serotonin MeasurementsIn VivoUsing N-Shaped Multiple Cyclic Square Wave Voltammetry

Abstract

Here, we present the development of a novel voltammetric technique, N-shaped multiple cyclic square wave voltammetry (N-MCSWV) and its application in vivo. It allows quantitative measurements of tonic extracellular levels of serotonin in vivo with mitigated fouling effects. N-MCSWV enriches the electrochemical information by generating high dimensional voltammograms, which enables high sensitivity and selectivity against 5-hydroindoleacetic acid (5-HIAA), dopamine, 3,4dihydroxyphenylacetic acid (DOPAC), histamine, ascorbic acid, norepinephrine, adenosine, and pH. Using N-MCSWV, in combination with PEDOT:Nafion-coated carbon fiber microelectrodes, a tonic serotonin concentration of 52 ± 5.8 nM (n = 20 rats, ±SEM) was determined in the substantia nigra pars reticulata of urethane-anesthetized rats. Pharmacological challenges with dopaminergic, noradrenergic, and serotonergic synaptic reuptake inhibitors supported the ability of N-MCSWV to selectively detect tonic serotonin levels in vivo. Overall, N-MCSWV is a novel voltammetric technique for analytical quantification of serotonin. It offers continuous monitoring of changes in tonic serotonin concentrations in the brain to further our understanding of the role of serotonin in normal behaviors and psychiatric disorders.

Software for near-real-time voltammetric tracking of tonic neurotransmitter levels in vivo

“…The current inability to track these concentrations on rapid time scales with high spatial resolution has prevented researchers from understanding the second-to-second effects of stimuli such as drug administration, electrical stimulation, or waking behavior on these tonic 10.3389/fnins.2022.899436 concentrations. This software supports application of cyclic square wave voltammetry, which enables highly sensitive detection of single analytes to the sub-nanomolar range with high temporal resolution (0.1 Hz scan rate) (Oh et al, 2018;Shin et al, 2021). This has enabled, for the first time, a more detailed and robust understanding of how these external stimuli affect tonic extracellular concentrations of analytes such as dopamine and serotonin on a rapid time scale.…”

“…This has enabled, for the first time, a more detailed and robust understanding of how these external stimuli affect tonic extracellular concentrations of analytes such as dopamine and serotonin on a rapid time scale. For example, recent work has employed cyclic square wave voltammetry to measure with high spatiotemporal resolution the effects of cocaine administration on tonic dopamine concentrations in the nucleus accumbens core (Yuen et al, 2021), and has used a modified N-shaped cyclic square waveform to enable highly specific recordings of tonic concentrations of serotonin (Shin et al, 2021). Overall, cyclic square wave voltammetry has the potential to provide an unprecedented level of insight into both physiologic and pathophysiologic neurotransmitter signaling.…”

“…In contrast, voltammetric analysis allows for direct visualization of these alterations in near real time, allowing researchers to confidently compare tonic responses between different drugs or stimulation conditions for the first time. This aspect of the software has a myriad of potential applications for exploring the real-time temporal dynamics of tonic neurotransmitter level alterations in response to various stimuli, such as drugs of abuse (Yuen et al, 2021), social/appetitive behaviors, and seizures, among many others.…”

“…Techniques that fit these criteria are emerging, with many utilizing voltammetry (Oh et al, 2018;Rusheen et al, 2020). Our lab has developed and utilized a novel electrochemical technique utilizing cyclic square wave voltammetry to provide accurate estimations of tonic extracellular concentrations of both dopamine (Oh et al, 2018) and serotonin (Shin et al, 2021) down to the sub-nanomolar range repetitively in 10 s intervals. These voltammetry-based techniques work with carbon-fiber microelectrodes (CFMs), which are composed of chemosensitive tips that are 7-10 µm in diameter and typically 50-100 µm in length.…”

“…Thus, voltammetric techniques lack many of the drawbacks inherent with microdialysis and seem to be more suitable for future clinical applications. Indeed, recent work has demonstrated the utility of cyclic voltammetry for applications such as mechanistic modeling of the mammalian response to drugs of abuse (Yuen et al, 2021).…”