In the brain, communication is both electrical and chemical. An electric impulse (action potential) propagates down an axon, and chemicals (neurotransmitters) are released. In neuroscientific research, the application of a neurotransmitter to a specific region may be necessary. One way to do this is via microelectrophoretic techniques like microiontophoresis. With this method, neurotransmitter can be administered to a living cell, and the consequent reactions recorded and studied.
Microiontophoresis takes advantage of the fact that ions flow in an electric field. Basically, during the method, current is passed through a micropipette tip and a solute is delivered to a desired location. A key advantage to this localized delivery and application is that very specific behaviors can be studied within context of location. However, a limitation is that the precise concentration of solute may sometimes be difficult to determine or control.
The main component of this technique is the use of electrical current to stimulate the release of solvent. In other words, it is an “injection without a needle.” The main driver of this electric current is galvanic current. The current is typically applied continuously. The solute needs to be ionic, and must be placed under an electrode of the same charge. That is, positively charged ions must be placed under the positive electrode (anode), and negatively charged ions must be placed under the negative electrode (cathode). This way, the anode will repel the positively charged ion into the skin, and the cathode will repel a negatively charged ion into the skin.