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ANESTHETIC PHARMACOLOGY

Administration of Epinephrine Does Not Increase Learning of Fear to Tone in Rats Anesthetized with Isoflurane or Desflurane

James M. Sonner, MD^*, Yilei Xing, MD^*, Yi Zhang, MD^*, Anya Maurer, BS^*, Michael S. Fanselow, PhD, MD, Robert C. Dutton, MD^*, and Edmond I. Eger, II, MD^*

*Department of Anesthesia and Perioperative Care, University of California, San Francisco; and Department of Psychology, University of California, Los Angeles

Address correspondence and reprint requests to James M. Sonner, MD, Department of Anesthesia, S-455, University of California, San Francisco, CA 94143-0464. Address e-mail to sonnerj{at}anesthesia.ucsf.edu.

Previous reports suggest that the administration of epinephrine increases learning during deep barbiturate-chloral hydrate anesthesia in rats but not during anesthesia with 0.4% isoflurane in rabbits. We revisited this issue, using fear conditioning to a tone in rats as our experimental model for learning and memory and isoflurane and desflurane as our anesthetics. Expressed as a fraction of the minimum alveolar anesthetic concentration (MAC) preventing movement in 50% of rats, the amnestic 50% effective dose (ED₅₀) for fear to tone in control rats inhaling isoflurane and injected with saline intraperitoneally (i.p.) was 0.32 ± 0.03 MAC (mean ± se) compared with 0.37 ± 0.06 MAC in rats injected with 0.01 mg/kg of epinephrine i.p. and 0.38 ± 0.03 MAC in rats injected with 0.1 mg/kg of epinephrine i.p. For desflurane, the amnestic ED₅₀ were 0.32 ± 0.05 MAC in control rats receiving a saline injection i.p. versus 0.36 ± 0.04 MAC in rats injected with 0.1 mg/kg of epinephrine i.p. We conclude that exogenous epinephrine does not decrease amnesia produced by inhaled isoflurane or desflurane, as assessed by fear conditioning to a tone in rats.

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