Meier TB, et al. - Whether sport-related concussions (SRC) induces a rise of serum kynurenine pathway (KP) metabolites with neurotoxic properties (quinolinic acid [QuinA], 3-hydroxykynurenine) together with a decrease in the neuroprotective metabolite kynurenic acid (KynA), and if post-concussion psychological symptoms would be predicted by these metabolites, was investigated in this study with high school and collegiate football players (N = 1,136). As controls, uninjured contact sport (N = 54) and non-contact sport athletes were included. Researchers also investigated if athletes with acute SRC and a history of previous SRC vs athletes that were concussed for the first time would exhibit raised neurotoxic relative to neuroprotective KP metabolites. Significantly high psychological symptoms, evaluated using the Brief Symptom Inventory-18, were detected among SRC athletes acutely after injury, compared with both control groups. Experts found significantly lower serum KynA/QuinA in SRC athletes with prior concussion, at all visits, vs SRC athletes with no prior concussion, an effect driven by high QuinA among SRC athletes with prior concussion. Based on the findings, it was inferred that the occurrence of depressive symptoms after concussion may be prevented by early-acute activation of the KynA branch of the KP. Serum QuinA was suggested to have potential as a biomarker for repetitive head injury.