title: Divergent short- and long-term effects of acute stress in object recognition memory are mediated by endogenous opioid system activation.
abstract: Acute stress induces short-term object recognition memory impairment and elicits endogenous opioid system activation. The aim of this study was thus to evaluate whether opiate system activation mediates the acute stress-induced object recognition memory changes. Adult male Wistar rats were trained in an object recognition task designed to test both short- and long-term memory. Subjects were randomly assigned to receive an intraperitoneal injection of saline, 1 mg/kg naltrexone or 3 mg/kg naltrexone, four and a half hours before the sample trial. Five minutes after the injection, half the subjects were submitted to movement restraint during four hours while the other half remained in their home cages. Non-stressed subjects receiving saline (control) performed adequately during the short-term memory test, while stressed subjects receiving saline displayed impaired performance. Naltrexone prevented such deleterious effect, in spite of the fact that it had no intrinsic effect on short-term object recognition memory. Stressed subjects receiving saline and non-stressed subjects receiving naltrexone performed adequately during the long-term memory test; however, control subjects as well as stressed subjects receiving a high dose of naltrexone performed poorly. Control subjects' dissociated performance during both memory tests suggests that the short-term memory test induced a retroactive interference effect mediated through light opioid system activation; such effect was prevented either by low dose naltrexone administration or by strongly activating the opioid system through acute stress. Both short-term memory retrieval impairment and long-term memory improvement observed in stressed subjects may have been mediated through strong opioid system activation, since they were prevented by high dose naltrexone administration. Therefore, the activation of the opioid system plays a dual modulating role in object recognition memory.
authors.affiliation: Behavioral Neurophysiology Laboratory, Universidad Nacional de Colombia, Bogotá, Colombia; Basic Sciences Department, School of Medicine, Neuroscience Research Group (NEUROS) Universidad del Rosario, Bogotá, Colombia.
authors.forename: Mauricio O
authors.initials: MO
authors.lastname: Nava-Mesa
authors.forename: Marisol R
authors.initials: MR
authors.lastname: Lamprea
authors.forename: Alejandro
authors.initials: A
authors.lastname: Múnera
mesh_terms: D000818:Animals; D008297:Male; D057567:Memory, Long-Term / Q000187:drug effects / Q000502:physiology; D008570:Memory, Short-Term / Q000187:drug effects / Q000502:physiology; D009271:Naltrexone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D018847:Opioid Peptides / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D021641:Recognition, Psychology / Q000187:drug effects* / Q000502:physiology; D012149:Restraint, Physical; D013312:Stress, Physiological / Q000502:physiology*; D013315:Stress, Psychological / Q000378:metabolism*
chemical_list: D009292:Narcotic Antagonists; D018847:Opioid Peptides; D009271:Naltrexone
keywords: 1mg/kg naltrexone; 1mg/kg naltrexone plus no-stress; 1mg/kg naltrexone plus stress; 3mg/kg naltrexone; 3mg/kg naltrexone plus no-stress; 3mg/kg naltrexone plus stress; ACTH; ANOVA; Acute stress; DI; Endogenous opioid system; FO; N1NS; N1S; N3NS; N3S; NO; Nal 1; Nal 3; Naltrexone; ORM; ORT; Object recognition memory; RI; Retroactive interference; SEM; SNS; SS; TFO; TNO; Veh; adrenocorticotropic hormone; analysis of variance; discrimination index; familiar object; novel object; object recognition memory; object recognition task; retroactive interference; saline plus no-stress; saline plus stress; standard error of the mean; time spent exploring the familiar object; time spent exploring the novel object; vehicle