Development and Application of Fast-scan Voltammetric Technology for Examining Neurochemical Mechanisms in vivo

Dopamine (DA) is a neurotransmitter that plays a key role in the regulation of various motor functions, motivated behavior, and reward-associated learning by acting in various brain regions. Understanding real-time DA neurotransmission in the brain is necessary to understand how DA neurochemically underlies these behaviors. Electrochemical techniques are well-suited to monitor the chemical dynamics of neurotransmitters in vivo. Particularly, fast-scan cyclic voltammetry (FSCV) coupled with carbon-fiber microelectrodes provides an ideal combination of chemical selectivity, sensitivity, spatial and temporal resolution. These are essential for monitoring rapid fluctuations of DA in live brain tissue and correlating these signals with discrete aspects of real-time behaviors. The research presented here describes the application of FSCV to investigate unknown neurochemical mechanisms underlying motor disorders and drug addiction in vivo. It also describes the improved protocols and sensors for longitudinal DA measurements in freely moving animals.;L-DOPA has been the gold standard treatment for Parkinson's disease since the 1960s. However, remarkably little is known about how L-DOPA therapy alters real-time DA dynamics in the brain. Additionally, reports on the effects of L-DOPA on oxidative stress are contradictory. To address these questions, a reliable procedure for fabricating cylindrical, Nafion-coated, carbon-fiber microelectrodes was developed to prevent electrode fouling by L-DOPA. These sensors were then utilized to simultaneously monitor the effects of L-DOPA on DA and hydrogen peroxide dynamics in the brains of both intact animals and a 6- hydroxydopamine lesioned animal model of PD.;Endogenous opiates play a critical role in reward processing and motivation, as well as the response to pain. Mu opioid receptors (MOR) in the ventral tegmental area (VTA) are of particular interest, as this region contains DA neurons which are highly implicated in various aspects of reward and motivation. However, our understanding of the mechanisms by which these MORs underlie VTA function is limited. This limits our understanding of important medical problems, such as pain and drug addiction. This work monitored the effects of intra-VTA infusion of MOR specific drugs on sub-second DA dynamics in the NAc of awake, freely moving rats using FSCV, and directly correlated these measurements with conditioned place preference experiments, in order to improve the current understanding of the neuronal mechanisms underlying opioid actions in the VTA.;Recent advances in wireless systems are being coupled to FSCV technology, allowing animals more natural motion and behavior by removing the wire tether. However, data transfer and collection requirements are stringent, and present a hurdle that might significantly limit further development and application of these systems. Traditionally, in vivo FSCV protocols collect 10 cyclic voltammograms per second with 1000 data points per cyclic voltammogram. In this work, the in vivo performance of FSCV was evaluated at reduced sampling rates and with reduced data points per cyclic voltammogram. This research characterized the integrity of the chemical information obtained using these reduced parameters in freely moving animals. Adoption of this approach reduces the quantity of data generated per second by two orders of magnitude compared to the traditional protocol.;Overall, the work presented herein will advance our understanding of the brain's DA neuronal circuitry and help advance FSCV technology for additional studies of motor disorders and drug addiction behaviors.