Probing Presynaptic Regulation of Extracellular Dopamine with Iontophoresis

Abstract

Iontophoresis allows for localized drug ejections directly into brain regions of interest driven by the application of current. Our lab has previously adapted a method to quantitatively monitor iontophoretic ejections. Here those principles have been applied in vivo to modulate electrically evoked release of dopamine in anesthetized rats. A neutral, electroactive marker molecule that is ejected purely by electroosmotic flow (EOF) was used to monitor indirectly the ejection of electroinactive dopaminergic drugs (raclopride, quinpirole, and nomifensine). Electrode placements were marked with an iontophoretically ejected dye, pontamine sky blue. We show that EOF marker molecules, acetaminophen (AP) and 2-(4-nitrophenoxy) ethanol, have no effect on electrically evoked dopamine release in the striatum or the sensitivity of electrode. Additionally, we establish that a short, 30 second ejection of raclopride, quinpirole, or nomifensine with iontophoresis is sufficient to affect autoreceptor regulation and the re-uptake of dopamine. These effects vary in lifetime, indicating that this technique can be used to study receptor kinetics.

Dynamics of rapid dopamine release in the nucleus accumbens during goal-directed behaviors for cocaine versus natural rewards

“…Within distinct NAc microcircuits, rapid dopamine release likely modulates NAc cell activity based on a variety of factors such as dopamine receptor sub-type, phasic activity (excitatory versus inhibitory), reward type (sucrose versus food versus cocaine), and ongoing behavior. Additional studies are being completed that couple iontophoresis with FSCV and electrophysiology (Herr et al, 2010; Belle et al, 2013) to shed further insight into the causal relationship between rapid dopamine signaling and cell firing in the NAc during goal-directed behaviors.…”

Quantitative analysis of iontophoretic drug delivery from micropipettes

“…To accomplish this, the average DOPAC concentration upon ejection was determined by comparison of the oxidation current to a flow analysis calibration. 17 Since glutamate was equimolar with DOPAC in the barrel and has a similar charge and mobility, this value approximates the average ejected glutamate concentration.…”

“…Most notably, ejected solute can be monitored in real time by incorporation of a voltammetric microelectrode adjacent to the iontophoresis barrel. 17 Ejection of electroactive drugs or markers is detected by the microelectrode upon ejection, confirming delivery, and can provide an estimate of the average local concentration. 18, 19 Other techniques involve placing independent electrodes near the ejecting barrel and the incorporation of fluorescent markers in the ejection solution.…”

Nanopipette delivery: influence of surface charge

“…At larger scales, the surface charge of the pipette wall does not impose a significant effect on the concentration of ions in the delivery channel. [20][21][22][23][24] As demonstrated in previous reports, when channel dimensions shrink to small scales, surface-charge controlled concentration polarization becomes a dominant factor in ion transport. 2,6,[25][26][27][28][29][30][31][32] Here, we demonstrate a carbon ring/nanopore electrode geometry and unambiguously demonstrate the importance of surface charge and analyte charge for nanopipettes used for voltage-driven delivery.…”

“…[20][21][22] Addition of a carbon fiber electrode near the delivery barrel allows measurement of the local concentration of electroactive molecules delivered. [20][21][22][23][24] The number of molecules delivered depends on factors such as the applied delivery potential and the size of the pipette tip opening. 3 The surface charge of the nanopipette is also an important factor that has received little attention.…”