Metabolomic Analysis of Microdialysis Samples from the Frontal Association Cortex (FrA) of C57BL/6J (B6) Mouse during Isoflurane Anesthesia

Abstract

Preliminary data have begun to characterize the metabolome in mouse FrA during sleep (FASEB J 30.1, 2016). Anesthesia and sleep are different states of consciousness that share a number of trait similarities. This ongoing study is quantifying the similarities and differences in the FrA metabolome during sleep and anesthesia. Microdialysis samples have been collected from the FrA of adult, male B6 mice (n=12) anesthetized with isoflurane. All experiments have adhered to FASEB policies on humane use of animals in research. The samples are being analyzed using ultra‐performance liquid chromatography coupled with high‐resolution mass spectrometry on an Exactive Plus Orbitrap instrument. An untargeted metabolomics method is being used to identify brain metabolites (Anal Chem 82:3212, 2010). To date we have analyzed 15 samples from 3 mice during isoflurane (1.1%) anesthesia. The results revealed approximately 90 known molecules in each 25 μL microdialysis sample. In FrA, 44 analytes were common to states of sleep and anesthesia, including myo‐inositol, tryptophan, homovanillic acid, uracil, and pyruvate. State‐specific differences in metabolomic measures included 37 metabolites present during anesthesia that were not observed during sleep, and absence of 6 metabolites during anesthesia that were found during sleep. Known metabolites common to both sleep and anesthesia were analyzed by partial least squares discriminant analysis (PLS‐DA). Variable importance projection scores calculated from PLS‐DA analyses highlighted 20 of the 44 metabolites present during sleep and anesthesia that contributed significantly to the observed separation in the PLS‐DA. Histological comparisons of FrA microdialysis sites during sleep and anesthesia are pending. These emerging results support the interpretation that metabolomic analyses provide a powerful approach for developing a neurochemical cartography of lower level phenotypes putatively regulating states of consciousness.Support or Funding InformationNIH grants HL65252 & Kavli Foundation (RL and HAB); MH099231 & 1P01NS083514 (CC and GT)