Development of N-shaped cyclic square-wave voltammetry techniques for serotonin measurement in vivo

Abstract

(1) N-shaped Fast Cyclic Square-Wave Voltammetry (N-FCSWV) is serotonin optimized voltammetry method which provide improved sensitivity and selectivity to measure phasic serotonin changes in vivo, (2) N-shaped Multi Cyclic Square-Wave Voltammetry (N-MCSWV) is serotonin optimized voltammetry method to measure extracellular chemistry measurement in vivo with relatively high temporal resolution. A series of large amplitude square-shaped potential was superimposed onto an N-shaped waveform to provide cycling through multiple redox reactions within the N-shaped waveform to increase sensitivity and selectivity to serotonin when combined with a two dimensional voltammogram. N-FCSWV showed significantly higher sensitivity to serotonin compared to conventional N-shaped FSCV. In addition, N-FCSWV showed better performance than conventional N-shaped FSCV in differentiating serotonin from its major interferents, dopamine and 5-hydroxyindoleascetic acid (5-HIAA). These advanced cyclic square waveforms were expanded to multi waveform ideas to translate our acute animal studies to disease animal models in the future, chronic and tonic neurochemical recording procedures are critically important. Chronic and tonic neurochemical recordings will allow observation and correlation of symptomatic behaviors with in vivo electrochemical measurements of changes in neurochemical release during treatments. N-MCSWV enable to gather more electrochemical information by creating two dimensional voltammograms which provide higher sensitivity and selectivity against dopamine and 5-HIAA. Using N-FCSWV and N-MCSWV, both phasic and tonic serotonin concentration were determined in the substantia nigra pars reticulata (SNr). Pharmacological treatments were designed to evaluate serotonin signal by systemic injection of escitalopram (ESCIT), a serotonin selective reuptake inhibitor, nomifensine, a dopamine selective reuptake inhibitor, desipramine, a selective norepinephrine reuptake inhibitor, and pargyline, a MAO inhibitor.

In following chapters, general method to measure neurochemicals and backgrounds of electroanalytical voltammteric methods are explained in Chapter 1. In Chapter 2, methods and surgical procedures of the whole research are introduced. The results obtained with the both N-FCSWV and N-MCSWV are illustrated and described in Chapter 3, and finally discussion and future works summarized in Chapter 4.; Serotonin is well known neurotransmitter spread out all around cenrtral nervous system, especially thought to be involved in psychiatric process undergo with anxiety, impulsivity and compulsivity, mood, social behavior, and stress. For human patient, serotonin selective reuptake inhibitors (SSRIs) and deep brain stimulation (DBS) method have been used widely to treat major depression and improve psychiatric disorders better. However, the mechanisms that control extracellular serotonin levels are not well-defined. This shortcoming makes it very challenging to diagnose and treat the many psychiatric disorders in which serotonin is implicated. In vivo microdialysis has been useful establishing the role of serotonin in these disorders and others, but its relatively low temporal and spatial mesrurement resolution has been limited its applications. Electrochemical approach, especially fast-scan cyclic voltammetry (FSCV) in combination with N-shaped waveform and carbon fiber microelectrodes (CFM) has been shown to be able to detect serotonin in vivo with greater degree of spatial and temporal measurement resolution. N-shaped FSCV showed relatively high sensitivity and selectivity to serotonin with serotonin detection specialized waveform. Although N-shaped FSCV is well-established as an electroanalytical method to measure extracellular serotonin concentrations in vivo, it is in need of improvement in both sensitivity and selectivity. Also, it is critically important to measure tonic serotonin levels to deeply understand physiological changes and mechanisms of various psychiatric disorders and their cures. FSCV has been used to measure phasic changes which occurred by external stimulations since conventional FSCV method using background subtraction method which measure difference before and after external stimulation.

In this thesis, two novel electroanalytical methods will be introduced