Basics of microiontophoresis

Microiontophoresis is the technique whereby ions or charged molecules can be ejected in very small amounts from solutions contained in glass micropipettes. Microiontophoresis is most often used for (1) deposition of dyes or neural transport tracers for subsequent histological examination or for (2) administration of neuroactive compounds (e.g. transmitters, modulators, drugs or hormones) by microiontophoresis to examine their effects on firing parameters of single neurons in vivo.

During an experiment the resistance of an iontophoresis pipette may fluctuate for a variety of reasons (mostly biological). This requires a precision constant current source, or iontophoresis pump as it is popularly called, which using Ohm’s Law automatically maintains a constant current flow through the barrel independently of its resistance. An iontophoresis pump, in compensation to fluctuations in tip resistance, automatically changes the voltage applied to the iontophoresis pipette to produce a constant current set by the experimenter.