BDNF and major depressive disorder: Increases in IL-6 also result in increases in kynurenine, which has been linked to suicide and depression [72], and quinolinic acid, which enhances glutamatergic transmission with associated decreases in brain derived neurotrophic factor (BDNF) in the hippocampus, which may be involved in symptoms of PTSD and depression and mechanisms of action of antidepressants [73,74,75,76].