et al. Surgery induces activation of indoleamine 2,3-dioxygenase, increases in pro-inflammatory cytokines and cognitive impairment in old rats. J Anesth Perioper Med 2015; 2: 14-21. Background: Postoperative cognitive dysfunction (POCD) is one of the most common complications in senior patients after surgery. However, the cause is largely unknown. Activation of indoleamine 2, 3-dioxygenase (IDO), a rate-limiting enzyme of kynurenine pathway, which converts tryptophan into kynurenine in

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... tic tissues, may contribute to cognitive impairment. We therefore set out to assess whether surgery under anesthesia can induce activation of IDO, neuroinflammation and cognitive impairment in old rats. Methods: Male Sprague-Dawley rats (24-month-old) were randomly assigned into three groups: 40% oxygen inhalation, 1.8% isoflurane anesthesia and left nephrectomy under 1.8% isoflurane anesthesia. Cognitive function was assessed daily in Y maze. Levels of interferon gamma (IFN-γ) and interleukin-6 (IL-6), IDO, tryptophan and kynurenine in serum and hippocampus were determined at 6 hours, 1, 3 and 7 days after anesthesia or surgery by using MILLIPLEX MAP Rat Cytokine Panel, enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC), respectively. Results: Anesthesia with 1.8% isoflurane for three hours increased IL-6 level in serum at six hours which returned to normal level at 24 hours after the anesthesia. The isoflurane anesthesia alone did not induce cognitive impairment. Nephrectomy plus isoflurane elevated IFNγ level in serum, increased levels of IL-6 and IDO, and IDO activity, determined by the ratio of tryptophan and kynurenine, in both serum and hippocampus, and finally induced cognitive impairment. These data showed that surgery under isoflurane anesthesia may induce activation of IDO, neuroinflammation and cognitive impairment in old rats. Conclusions: These results suggested the potential role of IDO pathway in POCD pathogenesis, pending on further studies. ABSTRACT P ostoperative cognitive dysfunction (POCD) is a postoperative complication characterized by impairment of memory or attention, which has become a significant and increasing problem associated with increased mortality, risk of leaving the labor market prematurely, and dependency on social trans-