In vivo microdialysis--a new approach to the analysis of neurotransmitters in the brain.

Microdialysis is a new technique to monitor levels of chemical compounds in the extracellular space over time. It involves the implantation of a microdialysis probe into the brain tissue. The probe is similar to a push-pull probe but the perfusate is contained inside a semi-permeable membrane located at the tip of the probe. Substances in the extracellular fluid will diffuse into the perfusate while substances included in the perfusate will diffuse into the tissue. This principle opens up a wealth of possibilities to monitor chemical events within the brain and to study the working mechanism of various drugs. The perfusate may be analysed by a number of different techniques. In this paper we give a short summary of various HPLC techniques that have proven particularly useful.