title: Postoperative pain impairs subsequent performance on a spatial memory task via effects on N-methyl-D-aspartate receptor in aged rats.
abstract: OBJECTIVE
  Pain may be associated with postoperative cognitive dysfunction (POCD); however, this relationship remains under investigated. Therefore, we examined the impact of postoperative pain on cognitive functions in aged animals.
  
  
  METHODS
  Rats were allocated to the following groups: control (C), 1.2 % isoflurane for 2 hours alone (I), I with laparotomy (IL), IL with analgesia using local ropivacaine (IL+R), and IL with analgesia using systemic morphine (IL+M). Pain was assessed by rat grimace scale (RGS). Spatial memory was evaluated using a radial maze from postoperative days (POD) 3 to 14. NMDA receptor (NR) 2 subunits in hippocampus were measured by ELISA. Finally, effects of memantine, a low-affinity uncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, on postoperative cognitive performance were tested.
  
  
  RESULTS
  Postoperative RGS was increased in Group IL, but not in other groups. The number of memory errors in Group I were comparable to that in Group C, whereas errors in Group IL were increased. Importantly, in Group IL+R and IL+M, cognitive impairment was not found. The memory errors were positively correlated with the levels of NMDA receptor 2 subunits in hippocampus. Prophylactic treatment with memantine could prevent the development of memory deficits observed in Group IL without an analgesic effect.
  
  
  CONCLUSIONS
  Postoperative pain contributes to the development of memory deficits after anesthesia and surgery via up-regulation of hippocampal NMDA receptors. Our findings suggest that postoperative pain management may be important for the prevention of POCD in elderly patients.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, Kochi Medical School, Kochi, Japan.
authors.forename: Haidong
authors.initials: H
authors.lastname: Chi
authors.forename: Takashi
authors.initials: T
authors.lastname: Kawano
authors.forename: Takahiko
authors.initials: T
authors.lastname: Tamura
authors.forename: Hideki
authors.initials: H
authors.lastname: Iwata
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Satoru
authors.initials: S
authors.lastname: Eguchi
authors.forename: Fumimoto
authors.initials: F
authors.lastname: Yamazaki
authors.forename: Naoko
authors.initials: N
authors.lastname: Kumagai
authors.forename: Masataka
authors.initials: M
authors.lastname: Yokoyama
mesh_terms: D000367:Age Factors; D000577:Amides / Q000494:pharmacology; D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D006624:Hippocampus / Q000378:metabolism; D007530:Isoflurane / Q000494:pharmacology; D008297:Male; D018782:Maze Learning; D008559:Memantine / Q000494:pharmacology; D008568:Memory / Q000187:drug effects* / Q000502:physiology*; D009020:Morphine / Q000494:pharmacology; D010149:Postoperative Pain / Q000378:metabolism* / Q000503:physiopathology / Q000523:psychology; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D000077212:Ropivacaine
chemical_list: D000577:Amides; D000777:Anesthetics; D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate; D009020:Morphine; D000077212:Ropivacaine; D007530:Isoflurane; D008559:Memantine
keywords: Aging; Cognition; Memantine; NMDA receptor; Postoperative pain