Fig. 4: Effects of HFD and 1-MT administration on brain metabolites in the hippocampus.

A Representative ¹H MRS spectra from the hippocampus of HFD and CD mice. B–D Quantification of B glutamate, C glutamine, and D GABA levels in the hippocampus of CD and HFD mice, with or without 1-MT treatment. E A schematic diagram summarizing the proposed mechanism by which a long-term HFD induces depression-like behaviors through the excessive accumulation of PNN around PV-positive neurons, affecting synaptic transmission in PV-positive neurons, and leading to glutamate-GABA imbalance in the hippocampus. Error bars represent the standard error of the mean. *P < 0.05, **P< 0.01, as determined by the one-way ANOVA in combination with Tukey’s multiple comparisons test. N numbers are indicated in each graph. 1-MT 1-methyltryptophan, CD chow diet, GABA gamma-aminobutyric acid, Gln glutamine, Glu glutamate, HFD high-fat diet, PNN perineuronal net, PV parvalbumin.