Analytical Techniques to Investigate the Neurochemical Basis of Behavior
My research combines electrochemistry, chromatography, and chemometrics to enable brain neurotransmitter monitoring in vivo. Microdialysis coupled with high performance liquid chromatography with electrochemical detection (HPLC-ECD) and voltammetry capitalize on the electrochemical properties of monoamine neurotransmitters, such as serotonin and dopamine. Electrochemical detection is a sensitive and selective detection method, which is beneficial in neurochemical analyses where brain neurotransmitters are present at nanomolar to micromolar concentrationsFast-scan cyclic voltammetry (FSCV) has spatial and temporal advantages, but has poor analyte selectivity due to overlapping oxidation (and reduction) profiles of structurally similar neurochemicals and cannot be used to determine information on basal (tonic) neurotransmitter levels due to background subtraction. Dopamine is found at higher concentrations than other electroactive neurotransmitters in most brain areas, which makes it difficult to resolve other lower concentration neurotransmitters and to monitor multiple neurotransmitters simultaneously. No voltammetric techniques are currently available to monitor serotonin and dopamine simultaneously across timescales (phasic and tonic), despite the fact that these neurotransmitters play integrated roles in modulating behavior. In my thesis research, I worked on developing a novel method for neurotransmitter co-detection— rapid pulse voltammetry coupled with partial least squares regression (RPV-PLSR). This approach is adapted from multielectrode systems (i.e., electronic tongues). We constructed an initial RPV waveform using key oxidation and reduction potentials. In addition to faradaic currents, RPV utilizes capacitive currents, which are important for analyte identification. Including capacitive current also enables simultaneous tonic and stimulated neurotransmitter measurements. I carried out RPV-PLSR in vivo, to differentiate and quantify tonic and stimulated serotonin and dopamine associated with striatal recording electrode position, optogenetic stimulation frequency, and antidepressant administration. I investigated the contributions of cations and metabolites interferents to RPV and developed strategies to mitigate their effects. My research advanced our understanding of the interplay between the serotonin and dopamine In addition to voltammetry, I used microdialysis for serotonin and dopamine co-detection throughout my thesis work. Microdialysis is used to monitor neurotransmitters in the extracellular fluid when combined with HPLC. Microdialysis experiments have commonly been performed using 20-minute sampling times to collect sufficient analyte for HPLC detection. However, long sampling times cause researchers to miss biologically relevant information happening at shorter timescales. Our group developed fast microdialysis that enables serotonin and dopamine co-detection with 2-5-min real-time sampling in awake-behaving mice. Using microdialysis, we discovered that selective optogenetic stimulation of dopamine neurons produces dopamine and serotonin release in the striatum highlighting the importance of multiplexed measurements and the interconnectedness of these transmitter systems. Recently I discovered that selective optogenetic stimulation of dopamine neurons produces dopamine and serotonin release in the striatum highlighting the importance of being able to make multiplexed measurements and the interconnectedness of these transmitter systems in modulating behavior. I also used microdialysis to probe the effects of maternal stress and/or citalopram administration during pregnancy on adult offspring neurochemistry. Male offspring in the chronic unpredictable stress group had elevated serotonin levels during citalopram infusion and kappa opioid agonist injection compared to other treatment groups. These effects were paralleled with increased depressive- and anxiety like behavior during the forced swim test and novelty suppressed feeding test in male offspring in the chronic unpredictable stress group. Throughout the duration of my graduate studies I was a teaching assistant (TA) for the CHEM 184 Instrumental Analysis course at UCLA. As a TA I developed and implemented a new analytical chemistry lab for the course. Students detected mercury levels in various fish samples using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to learn about standard reference materials, matrix effects, and how to best optimize instrument parameters (kinetic energy discrimination). This work was recently published in the Journal of Chemical Education as a guide to carry out this experiment at other universities.