title: Isoflurane impairs odour discrimination learning in rats: differential effects on short- and long-term memory.
abstract: BACKGROUND
  Anaesthetics suppress the formation of lasting memories at concentrations that do not suppress perception, but it is unclear which elements of the complex cascade leading from a conscious experience to a lasting memory trace are disrupted. Experiments in conscious humans suggest that subhypnotic concentrations of anaesthetics impair consolidation or maintenance rather than acquisition of a representation (long-term more than short-term memory). We sought to test whether these agents similarly impair learning in rats.
  
  
  METHODS
  We used operant conditioning in rats to examine the effect of isoflurane on acquisition compared with long-term (24 h) memory of non-aversive olfactory memories using two different odour discrimination tasks. Rats learned the 'valences' of odour pairs presented either separately (task A) or simultaneously (task B), under control conditions and under isoflurane inhalation. In a separate set of experiments, we tested the ability of the animals to recall a learning set that had been acquired 24 h previously.
  
  
  RESULTS
  Under 0.4% isoflurane inhalation, the average number of trials required to reach criterion performance (18 correct responses in 20 successive trials) increased from 21.9 to 43.5 (P<0.05) and 24.2 to 54.4 (P<0.05) for tasks A and B, respectively. Under 0.3% isoflurane inhalation, only task B was impaired (from 24.2 to 31.5 trials, P<0.05). Recall at 24 h was dose-dependently impaired or prevented by isoflurane for both tasks.
  
  
  CONCLUSIONS
  Isoflurane interfered with long-term memory of odour valence without preventing its acquisition. This paradigm may serve as a non-aversive animal model of conscious amnesia.
authors.affiliation: Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA. rapearce@wisc.edu
authors.forename: R A
authors.initials: RA
authors.lastname: Pearce
authors.forename: P
authors.initials: P
authors.lastname: Duscher
authors.forename: K
authors.initials: K
authors.lastname: Van Dyke
authors.forename: M
authors.initials: M
authors.lastname: Lee
authors.forename: A C
authors.initials: AC
authors.lastname: Andrei
authors.forename: M
authors.initials: M
authors.lastname: Perouansky
mesh_terms: D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D003216:Conditioning, Operant; D004193:Discrimination Learning / Q000187:drug effects*; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D057567:Memory, Long-Term / Q000187:drug effects*; D008570:Memory, Short-Term / Q000187:drug effects*; D009812:Odorants; D055696:Olfactory Perception / Q000187:drug effects*; D051381:Rats; D020318:Rats, Long-Evans
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane