Analysis of Distribution of Neurochemicals in Rat Brain by Desorption Electrospray Ionization Time-of-Flight Mass Spectrometry Imaging

The distribution of small molecular neurochemicals and their metabolites in rat brain was analyzed by desorption electrospray ionization time-of-flight mass spectrometry imaging (DESI-TOF-MSI)technique. The whole brain frozen horizontal sections of rats were prepared and scanned by DESI-TOF-MSI imaging. The influences of composition and proportion of spray solvents on the signal intensity of neurochemicals under positive and negative ion modes were also investigated. By comparison of high resolution mass spectrometry information in positive and negative ion mode and HMDB database searching,25 kinds of neurochemicals and their metabolites were detected in rat brain. Under the condition of 0. 1% formic acid-methanol spray,the molecular ion intensity of neurochemicals was increased mostly. HDImaging v1. 5 was used for fine imaging analysis. Addition of 0. 1% formic acid to the spray solvent could improve the imaging effect similar to the increasing trend of mass signal intensity. The method presented high repeatability. gamma-Aminobutyric acid and aspartic acid were mainly distributed in cerebral cortex. Serine was detected throughout the brain. Glutamine was distributed around the hippocampus. The same spatial distribution of neurochemicals and their precursors and major metabolites in the brain was detected. The DESI-TOF-MSI technique developed here could be used to analyze the distribution of small molecular neurochemicals in rat brain. This work provided a fast and effective visualization method for the study of spatial distribution and metabolism of small molecule neurochemicals in brain.