hide.chp:Corel VENTURA

acetylcholine (ACh) in prefrontal cortex (mPFC) plays an important role in some domains of cognitive function such as attention (1,2), and sensory gating (3). Therefore, measurement of ACh in a living animal is important for the development of novel drugs, as well as investigation of brain function. Microdialysis has proven to be a useful sampling technique in the brain of awake freelymoving animals. However, it is difficult to determine the basal concentration of ACh via microdialysis due to its rapid hydrolysis by acetylcholinesterase. In order to resolve this problem, acetylcholinesterase (AChE) inhibitors, which increase the extra-cellular concentration of ACh, have been used for the in vivo determination of ACh. However, the AChE inhibitor-induced increase in ACh in the brain has been reported to alter the function of some drugs (4,5,6), which shows the importance of determining ACh without AChE inhibitors for in vivo studies, including microdialysis. Liquid chromatography with electrochemical detection (LC/EC) has been successfully used to determine ACh brain tissue and dialysates. In this method, ACh is separated on the analytical column and converted to hydrogen peroxide on a post-column IMER in which AChE and choline oxidase (ChOx) are immobilized. The H2O2 is oxidized or reduced on the surface of an electrode (platinum or enzymemodified glassy carbon, respectively) and the current is measured using an amperometric detector. Huang et al (7) reported the LC/EC determination of basal ACh in dialysates utilizing microbore ion-exchange chromatography and an enzyme-modified (“wired”) electrode in the absence of AChE inhibitors. This combination of electrode and IMER resulted in a low background current, increasing the signal-to-noise ratio and lowering interferences. High concentrations of Ch can sometimes interfere with the quantitation of ACh. The addition of a pre-IMER (prior to the ionexchange analytical column) containing immobilized ChOx and Feasibility of Ion-Pair Reversed-Phase Liquid Chromatography/Electrochemistry Detection for Determination of Acetylcholine in Microdialysates Collected Without Acetylcholinesterase Inhibitors