I drew this for the Biological Psychology textbook by James W. Kalat [8th & 9th. ed., 2004 & 06, pg. 317/371, (c) Thomson Wadsworth Pub]. In it, I described a microdialysis probe and the technique of microdialysis. During microdialysis, a solution similar to cerebrospinal fluid (minus neurotransmitters) is infused into the probe, it reaches a porous membrane which sits in an area of interest in the brain, there released neurotransmitters will flow down their concentration gradient into the probe and mix with the solution. This solution continues to flow through the probe and out into a collection tube. This solution is later analyzed for concentration of neurotransmitters using HPLC. Changes in levels of released neurotransmitters are compared in response to behavioral stimuli (e.g. mating/ eating) or pharmacological manipulations (e.g. drug administration).