Determination of certain neurochemicals in rat brain microdialysate by analytical methods

An electrospray ionization-liquid chromatography-mass spectrometry (ESI-LCMS) method is applied to the simultaneous determination of certain neurochemicals in rat brain microdialysate. The separation condition was examined for liquid chromatography after evaluation of mass spectra and mass fragments for eight neurochemicals (epinephrine, norepinephrine, dopamine, DOPAC, histamine, g-aminobutiric acid, L-glutamate, acetylcholine) by ion trap mass analyser. The method has been validated using C18 column (2.1x100 mm, 3.5 ?m) and gradient mobile phase containing 0.1 % glacial acetic acid in wateracetonitrile after derivatization of his tamine and g-aminobutiric acid with a fluorescent derivatization reagent of 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBDCl). Characteristic precursor-to-product ion transitions, m/z 267à249 for GABANBD and only m/z 275 for histamin-NBD were monitored for the quantification. Linearity range was 10-500 ng.mL-1 for g-aminobutiric acid and 50-1000 ng.mL-1 for histamine. The limit of quantification was calculated as 10 ng.mL-1 and 50 ng.mL-1 for g-aminobutiric acid and histamine, respectively. Accuracy was shown 98 % method recovery for histamin and GABA. The method precision was shown by day to day repeatability and intermediate precision found as 1.65-2.62 % RSD and % 1.23-4.93 % RSD, respectively. Microdialysate sampling for g- aminobutiric acid and histamine was performed in ventral anterior nucleus, lateral hypothalamus and corpus striatum of rat brain and basal levels of g- aminobutiric acid were determined as 123.25±0.67, 151.41±18.53, 94.96±0.53 ng.mL-1 respectively. Key Words: Neurochemicals, Histamine, g-Aminobutiric Acid, Derivatization, Microdialysis, LC-MS