IDO1 and Cognitive impairment: The latest study suggested that IDO-kynurenine pathway induced NOD-like receptor protein 3 inflammasome activation-mediated postoperative cognitive impairment in aged mice, whereas, treatment with IDO inhibitor 1-DL-methyl-tryptophan decreased the levels of kynurenine and kynurenic acid, increased tryptophan levels and improved learning and memory abilities 55.