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.
Fast-scan cyclic voltammetry along with its background subtraction method has been widely used for detecting neurotransmitters in the brain. The most common application of FSCV is measuring phasic changes of dopamine (DA) in the brain evoked by an external stimulus. The background subtraction method has greatly improved FSCV’s application to the neuroscience field. However, tonic dopamine concentration, which is as vital as phasic change, cannot be measured even though the background is subtracted. In this study, we developed a tailoring FSCV technique which can manipulate the background current by modifying a waveform’s voltage points. By using the technique, the last background current generated by multiple waveform application is tailored to the front background current. As a result, background current is cancelled out by subtracting the tailored (last) voltammagram from the front voltammagram. Therefore, only the DA oxidation/reduction pattern still remained between front and last voltammogram, so that, tailoring FSCV can detect tonic DA concentration without background subtraction method. The tailoring technique is evaluated by comparing it with commercialized enzyme-linked immunosorbent assay (ELISA) kits. By measuring endogenously released DA from DAergic cells, the tailoring method showed a significant correlation with ELISA results.
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