A,B Mean sucrose preference (%) and time spent immobile in the forced swim test (s) (± SEM) of mice treated with leucine or vehicle immediately before and 6 h after LPS or PBS (n ≥ 14 per group). C,D Mean kynurenine:tryptophan ratios in plasma and brains (± SEM) of mice treated with 50 mg/kg leucine or vehicle immediately before and 6 h after LPS or phosphate-buffered saline (PBS) (n = 5 per group). **p ≤ 0.01, ***p ≤ 0.0001 for LPS vs PBS main effects. #p ≤ 0.05, ##p ≤ 0.01, ###p ≤ 0.0001 for leucine vs vehicle main effects.