Demon Voltammetry and Analysis software: Analysis of cocaine-induced alterations in dopamine signaling using multiple kinetic measures

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Abstract

The fast sampling rates of fast scan cyclic voltammetry make it a favorable method for measuring changes in brain monoamine release and uptake kinetics in slice, anesthetized, and freely moving preparations. The most common analysis technique for evaluating changes in dopamine signaling uses well-established Michaelis–Menten kinetic methods that can accurately model dopamine release and uptake parameters across multiple experimental conditions. Nevertheless, over the years, many researchers have turned to other measures to estimate changes in dopamine release and uptake, yet to our knowledge no systematic comparison amongst these measures has been conducted. To address this lack of uniformity in kinetic analyses, we have created the Demon Voltammetry and Analysis software suite, which is freely available to academic and non-profit institutions. Here we present an explanation of the Demon Voltammetry acquisition and analysis features, and demonstrate its utility for acquiring voltammetric data under in vitro, in vivo anesthetized, and freely moving conditions. Additionally, the software was used to compare the sensitivity of multiple kinetic measures of release and uptake to cocaine-induced changes in electrically evoked dopamine efflux in nucleus accumbens core slices. Specifically, we examined and compared tau, full width at half height, half-life, T20, T80, slope, peak height, calibrated peak dopamine concentration, and area under the curve to the well-characterized Michaelis–Menten parameters, dopamine per pulse, maximal uptake rate, and apparent affinity. Based on observed results we recommend tau for measuring dopamine uptake and calibrated peak dopamine concentration for measuring dopamine release.

Highlights

► We developed Demon Voltammetry and Analysis software for fast scan cyclic voltammetry. ► The software can perform in vitro, and in vivo voltammetry recordings. ► Analysis utility contains many tools for measuring efflux kinetics. ► Exponential decay constant tau is suggested for measuring changes in dopamine uptake. ► Calibrated DA concentration is suggested for measuring changes in dopamine release.

Introduction

Fast scan cyclic voltammetry (FSCV) is an electrochemical detection technique that is acclaimed for its ability to measure presynaptic monoamine activity with high temporal and spatial resolution. It also provides information about transporter kinetics, as well as presynaptic auto-receptor and hetero-receptor activity (Fawaz et al., 2009, Jones et al., 1999, Jones et al., 1996). In this technique, a potentiostat is used to pass a voltage ramp rapidly across a carbon-fiber electrode, while measuring the resultant current. During this voltage ramp, nearby electroactive chemical species, such as monoamines, adenosine, 3,4-dihydroxyphenylacetic acid (DOPAC) or ascorbate, are oxidized/reduced resulting in changes in current amplitude that are proportional to the concentration of the species (Heien et al., 2003, Swamy and Venton, 2007). The current readout during the voltage ramp is referred to as a voltammogram which is collected and compared across time to determine changes in concentrations of electroactive species. Because of its high temporal resolution, voltammetry is an ideal technique for measuring rapid presynaptic signaling events in the brain during in vitro, in vivo anesthetized, and freely moving experiments.

One common application of voltammetry methods is to measure dopamine (DA) release and transporter activity in limbic brain regions. By electrically stimulating DA overflow, one can assess exocytotic release during the rising phase of the overflow, and uptake kinetics of DA transporters during the falling phase. The most commonly used kinetic analysis for evaluating changes in DA release and uptake rates uses methods established in anesthetized rats employing electrically evoked DA release (Wightman et al., 1988, Wightman and Zimmerman, 1990). Under these conditions, it is possible to elicit high enough DA concentrations that uptake can be saturated, thus allowing data to be fitted to a Michaelis–Menten kinetic model. Unfortunately, under some conditions, transient DA release events do not reach concentrations that saturate uptake, and therefore Michaelis–Menten-based curve fitting programs cannot be used reliably (Garris et al., 2003, Robinson and Wightman, 2007, Wightman et al., 1988, Wightman and Zimmerman, 1990). Consequently, researchers have turned to other measures to estimate changes in DA uptake, including tau, full width at half height (FWHH), half-life, T20, T80, slope, peak height, calibrated peak dopamine concentration ([DAc]), and area under the curve (AUC). While these methods may be valid, to our knowledge no systematic comparison amongst these measures has been conducted for voltammetry data, and certainly no standard measure has been established. Further, there is currently no comprehensive, commercially available kinetic analysis software program available for voltammetry data, and thus these types of assessments tend to be cumbersome and difficult to compare across laboratories.

Accordingly, we have embarked on an extensive project to develop freely available voltammetry acquisition and analysis software that provides reliable and efficient data analysis. In the present study, we confirmed that our software is compatible with existing hardware and is capable of detecting and quantifying electrically evoked DA release and uptake. The Demon Voltammetry and Analysis software suite (Demon Voltammetry) is available at no cost to academic and non-profit entities at http://www.wfubmc.edu/OTAM/Technologies/Computer-Software-and-copyright.htm#Demon.

Section snippets

Hardware

Two National Instruments data acquisition cards (NI-DAQ; PCI-6711 and PCI-6052e; National Instruments, Austin, TX) were used for interfacing Demon Voltammetry with a Chem-Clamp potentiostat (Dagan Corporation, Minneapolis, MN) for voltammetric recordings. Other similar NI-DAQ cards may be used as well. The Chem-Clamp was modified to have a gain range of 0.005–5.0 mV/pA, and a headstage with 5 MΩ resistance. The NI-DAQ cards contain multiple on-board high speed clocks, and several 16 bit analog

Results

To validate the utility of Demon Voltammetry we performed FSCV in the NAc core during in vitro slice, in vivo anesthetized, and freely moving experiments. As shown in Fig. 3, Demon Voltammetry was capable of detecting electrically stimulated DA release under these three conditions. Cyclic voltammograms verify that the electroactive species detected was dopamine, with oxidation and reduction peaks at ∼600 mV and ∼−200 mV respectively.

Cocaine induced inhibition of DA uptake was measured using in

Discussion

We have developed Demon Voltammetry and Analysis software to be freely available to academic and non-profit organizations. This software is particularly useful for neurobiological analyses due to its user-friendly analysis tools for measuring parameters relating to release and uptake, as well as for its chemometric analysis capabilities. Additionally, Demon Voltammetry contains useful tools for performing paired pulse stimulations, stimulation trains, automated peak amplitude detection,

Acknowledgments

We would like to thank Erin S. Calipari, Joanne K. Konstantopoulos, James R. Melchior, Paul L. Walsh and Drs. Mark J. Ferris and Kimberly N. Huggins for their patience and willingness to test the software during its development stages. Additionally, we would like to thank Dr. R. Mark Wightman for his expert advice and generous contribution of the Michaelis–Menten analysis algorithms used in the development of the Demon Voltammetry and Analysis software. These studies were supported by K01

References (30)

  • J.J. Clark et al.

    Chronic microsensors for longitudinal, subsecond dopamine detection in behaving animals

    Nature Methods

    (2010)
  • R.A. España et al.

    Hypocretin 1/orexin A in the ventral tegmental area enhances dopamine responses to cocaine and promotes cocaine self-administration

    Psychopharmacology

    (2010)
  • R.A. España et al.

    The hypocretin-orexin system regulates cocaine self-administration via actions on the mesolimbic dopamine system

    The European Journal of Neuroscience

    (2010)
  • C.S. Fawaz et al.

    Presynaptic action of neurotensin on dopamine release through inhibition of D(2) receptor function

    BMC Neuroscience

    (2009)
  • P.A. Garris et al.

    Distinct pharmacological regulation of evoked dopamine efflux in the amygdala and striatum of the rat in vivo

    Synapse (New York, NY)

    (1995)
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