Fig. 4
Metabolomic profiling of hippocampal tissue on basis of GC/TOF–MS technology at 3 d after surgery in aged mice. A OPLS-DA score plots between surgery and control group (R2Xcum = 0.68, R2Ycum = 0.993, Q2cum = 0.685); Classification showed a clear separation between the two groups; B Validation plots for OPLS-DA model with 200 permutation tests, intercepts: R2 = (0.0, 0.979), Q2 = (0.0, −0.215); C Identification of significantly differential endogenous metabolites in hippocampal tissue based on GC/TOF–MS technology; D Heat map reflecting the changing trend of metabolites expressed as fold-change between surgery versus control group. Ranges are indicated in red and blue (up- and downregulation in hippocampal tissue, respectively); E Possible metabolic pathway maps depicts the metabolic changes induced by the surgical trauma. The up arrows represent significantly increased metabolites, while down arrows represent significantly decreased metabolites. VIP indicates variables importance in the projection; OPLS-DA indicates orthogonal partial least squares discriminant analysis; P, significance of the pair t-test between surgery and control group; Fold change, ratio of relative content of metabolite in the surgery group to that of control group; TCA, tricarboxylic acid cycle