| Neurochemical systems are studied by a variety of techniques in order to reveal information about physiological events such as cell firing, chemical changes, and vasoactivity. The aim of this dissertation is to improve upon the characterization ability of several existing methods through instrumental optimization and experimental design. First, microiontophoresis, a qualitative drug delivery technique which uses an electric current to eject drugs from a micropipette, is investigated for its quantitative capabilities. Factors underlying the volume affected by ejections and the concentration distribution of ejected species are determined. Next, the drug delivery rate during ejection from the micropipette is examined under a variety of conditions. From this, it is shown how the delivery rate can be modulated using the iontophoretic current and the concentration of the ejection solution. Further, controlled iontophoresis, which uses a carbon-fiber microelectrode to detect ejected electroactive species, is employed in an attempt to directly measure concentrations from ejections. To determine the accuracy, neurochemical responses following iontophoretic drug delivery are compared to responses from known drug concentrations. These studies reveal how systemic errors in ejection protocols can lead to inaccurate concentration evaluations. Practical experimental solutions to overcome these limitations are presented, and when instituted, lead to more accurate measurements. Lastly, a multi-modal recording method is demonstrated which combines patch clamp electrophysiology and FSCV measurements in a brain slice. This is instituted with iontophoresis to provide a new way to simultaneously monitor cell behavior and chemical changes during drug delivery. In all, this work demonstrates how improvements in analytical methodologies can increase the power and scope of neurochemical investigations. |
