Memory enhancing effect of low-dose sevoflurane does not occur in basolateral amygdala-lesioned rats.
BACKGROUND
Certain anesthetics might enhance aversive memory at doses around 0.1 minimum alveolar concentration. This issue was investigated in a rat model of learning and memory. In addition, evidence for basolateral amygdala (BLA) involvement in mediating memory enhancement was sought.


METHODS
First, the memory-enhancing potential of various anesthetics was determined. Rats underwent single-trial inhibitory avoidance training (0.3 mA shock/1 s) during exposure to air, 0.11% sevoflurane, 0.10% halothane, 0.77% desflurane, or 0.12% isoflurane. Memory was assessed at 24 h. Second, the BLA contribution to sevoflurane memory enhancement was determined. Rats received bilateral excitotoxic N-methyl-D-aspartate (12.5 mg in 0.2 microl per BLA) lesions of the BLA 1 week before training. Memory of lesioned and control rats was compared 24 h after training in air or sevoflurane.


RESULTS
Sevoflurane exposure during training significantly enhanced 24-h retention performance for both nonoperated and sham-operated rats (P < 0.005 for both vs. their respective controls). Halothane, but not desflurane or isoflurane, also enhanced retention performance (P < 0.05). However, halothane-induced hyperalgesia during learning clouds interpreting enhanced retention performance solely as a memory consolidation effect. BLA lesions significantly reduced and equalized retention performance for both sevoflurane- and air-exposed animals. Lesions blocked memory enhancement without also causing a generalized inability to learn, because additional training revealed essentially normal task acquisition and 24-h memory.


CONCLUSIONS
Sevoflurane enhances aversive memory formation in the rat. The BLA likely contributes to this effect. The risk of aversive memory formation may be enhanced during exposure to low-dose sevoflurane.
Alkire
Michael T
MT
Department of Anesthesiology, and Center for the Neurobiology of Learning and Memory, University of California-Irvine, 101 The City Drive South, Bldg. 53, Route 81-A, Orange, CA 92868, USA. malkire@uci.edu
Nathan
Sheila V
SV
McReynolds
Jayme R
JR
D000679:Amygdala / Q000502:physiology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D000077335:Desflurane; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D006221:Halothane / Q000494:pharmacology; D006930:Hyperalgesia / Q000139:chemically induced / Q000523:psychology; D007530:Isoflurane / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D008568:Memory / Q000187:drug effects*; D008738:Methyl Ethers / Q000494:pharmacology*; D016202:N-Methylaspartate / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D018690:Excitatory Amino Acid Agonists; D008738:Methyl Ethers; D000077149:Sevoflurane; D016202:N-Methylaspartate; D000077335:Desflurane; D007530:Isoflurane; D006221:Halothane