.GAMMA.-Aminobutyric acid in the murine brain: Mass fragmentographic assay method and post-mortem changes.

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Abstract
An improved mass fragmentographic assay method for the determination of GABA in the brain is described. Applicability of the method was examined in a study of the effect of semicarbazide on GABA levels and in a separate study to confirm postmortem increase in GABA. The method itself is based on Cattabeni''s procedure in which GABA is assayed as trimethylsilyl derivative. Three improvements were made: application of a more suitable mass spectrometry system for GABA determination; use of 6-aminocaproic acid as the internal standard; and selection of a high intensive ion (m/z 174) for mass fragmentographic analysis. The mass spectrometer used is accurate to as little as 25 pg. GABA levels after semicarbazide treatment decreased 54.4% in rat whole brain and 44.2% in the dorsal hippocampus. Rapid postmortem increases in GABA levels were confirmed by application of the improved assay method; decreases were most clearly observable following microwave irradiation. Postmortem changes in GABA were observed within 3 min after death, as previously reported.