Figure 2.
The volcano map of differentially changed metabolites between any two groups. (a) shows the difference in metabolites between the low dose tramadol group and the control group; (b) shows the difference in metabolites between the high dose tramadol group and the control group; (c) shows the difference in metabolites between the high dose tramadol group and the low dose tramadol group. Red represents up-regulation, green represents down-regulation, and gray represents no distinguishable difference between any two groups. VIP represents the importance projection value of this substance obtained in the PLS-DA model.