title: The time profile of morphine effect on different phases of inhibitory avoidance memory in rat.
abstract: BACKGROUND
  The amnesic effect of morphine is well known in the laboratory animals. But, it is unclear that morphine at what times can exactly affect different phases of memory, including acquisition, consolidation, and retrieval. Therefore, we investigated the time profile of morphine's amnesic effect on passive (inhibitory) avoidance learning and memory in male Wistar rats.
  
  
  METHODS
  In order to evaluate the outcomes of pre- and post-training administrations of morphine, the animals were trained in a step-through type of passive avoidance task at various time points, and were tested 24 h after training to measure memory retrieval.
  
  
  RESULTS
  The results showed that acquisition of memory was impaired in the animals that received a dose of 7.5 mg/kg of morphine (Intraperitoneally) at 0, 30 min, and 1 h before training, as evidenced by a decrease in step-through latency on the test day. Post-training administrations of morphine at 30 min and 1h, 4h except for the time immediately after training, did not impair memory consolidation. The results also showed that pre-test administrations of morphine at 0 and 30 min before the test, impaired retrieval of inhibitory avoidance memory.
  
  
  CONCLUSIONS
  Taken together, the results suggest that morphine, when injected at different time points before training, after training, or before testing affects different phases of inhibitory avoidance memory. With regard to the time of injections related to each phase, other experiments can be designed to investigate molecular mechanisms involved in the impairing effect of morphine in each phase.
authors.affiliation: Department of Neuroscience, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Zarrindast
authors.forename: Abolfazl
authors.initials: A
authors.lastname: Ardjmand
authors.forename: Ameneh
authors.initials: A
authors.lastname: Rezayof
authors.forename: Shamseddin
authors.initials: S
authors.lastname: Ahmadi
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004334:Drug Administration Schedule; D007274:Injections, Intraperitoneal; D008297:Male; D008568:Memory / Q000187:drug effects*; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine