Quantification of noradrenaline iontophoresis

Abstract

Several problems are encountered when iontophoresis is used to study the effects of putative neurotransmitters. The most significant is that it is not usually practical to estimate the concentration of drug obtained at the tip of the microelectrode by a current of a given strength. The usual methods, rarely used, include measurement of transport numbers, the use of ion-sensitive microelecrodes and quantitative fluorescent microscopy. With the exception of the ion-sensitive microelectrodes developed for acetylcholine, these techniques are elaborate and time consuming and cannot be routinely applied to every electrode used. Conventional multibarrel microelectrodes have high-impedance recording barrels and thus often display low signal-to-noise ratios when recording single-cell activity, the noise being increased during iontophoresis. A technique is described which largely over comes the problem of low spike signal-to-noise ratio in conventional multibarrel electrodes, and which unlike the latter, allows precise determination of the concentration of noradrenaline [norepinephrine, NE] in the environment of the cell, which affects its excitability. The recording and iontophoretic properties of these electrodes were described previously. The use of these electrodes to quantify precisely iontophoresed NE by adapting polarographic techniques is described.