Combined effects of acute stress and amphetamine on serial memory retrieval pattern in mice.
BACKGROUND
This study investigated the dose-effect of amphetamine on contextual serial (contextual serial discrimination (CSD)) and serial (serial discrimination (SD)) memory in acutely stressed versus nonstressed C57 Bl/6 Jico mice.


METHODS
Memory was first evaluated in nonstress condition. Mice learned two consecutive discriminations (D1 and D2) in a four-hole board involving either distinct (CSD) or identical (SD) internal contextual cues. All mice received i.p. injections of vehicle before acquisition and vehicle or amphetamine 20 min before the memory retrieval phase occurring 24 h after acquisition.


RESULTS
Results showed that: (1) vehicle group expressed in both tasks a similar memory retrieval pattern, D2 being better retrieved than D1; (2) 2 mg/kg amphetamine significantly enhanced D1 but not D2 performance in both tasks, whereas 4 mg/kg amphetamine enhanced D2 but not D1 retrieval. Thus, amphetamine more specifically modulates serial order memory retrieval in a context-independent manner. In a further step, we studied the effect of an acute stress (electric foot shocks 5 min before retrieval) specifically on D1 performance of the CSD task in 2 mg/kg amphetamine-treated mice. Immediately after testing, blood was sampled to measure plasma corticosterone levels. Results showed that acute stress significantly improved D1 performance in vehicles but blocked the memory-enhancing effect of 2 mg/kg amphetamine, as compared to the nonstress condition. However, statistical analysis failed to evidence a significant interaction between treatments and conditions (stress vs nonstress) on corticosterone levels, contrary to another vigilance-enhancing drug, modafinil (Béracochéa, Psychopharmacology 196:1-13, 2008).
Piérard
Christophe
C
Département de Physiologie Intégrée, IMASSA, BP 73, 91223 Brétigny-sur-Orge, France.
Tronche
Christophe
C
Liscia
Pierrette
P
Chauveau
Frédéric
F
Béracochéa
Daniel
D
D000208:Acute Disease; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D000697:Central Nervous System Stimulants / Q000009:adverse effects*; D003345:Corticosterone / Q000097:blood; D003913:Dextroamphetamine / Q000009:adverse effects*; D004193:Discrimination Learning / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D007274:Injections, Intraperitoneal; D008297:Male; D008568:Memory / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D013315:Stress, Psychological / Q000097:blood / Q000503:physiopathology*
D000697:Central Nervous System Stimulants; D003913:Dextroamphetamine; D003345:Corticosterone