Subanesthetic concentrations of volatile anesthetics may enhance acquired avoidance training in ddN mice

The effects of halothane, enflurane, and isoflurane on avoidance training were assessed in male ddN mice. Animals were trained to escape an aversive unconditioned stimulus (electric foot shock) within 3 s after being exposed to a conditioned stimulus (light and buzzer). Immediately after training (first session), the animals were exposed to halothane, enflurane, or isoflurane for 120 min and were then tested again on the avoidance task (second session) 30 min after cessation of the exposure. The performance ratios [B/A] (i.e., A is the score in the first session, and B the score in the second) were compared between the anesthetic groups and their respective control groups. Performance ratios in the control animals ([B/A]c) did not reach 100% except for those corresponding to the 0.5 and 1.0 MAC (minimal alveolar anesthetic concentration) halothane groups. Four of the nine performance ratios in the anesthetic groups ([B/A]a) exceeded 1.0. [B/A]a exceeded [B/A]c by 18.7% in the 0.25 MAC halothane group (P less than 0.05), by 13.5% in the 0.31 MAC enflurane group (i.e., not significant), and by 17.3% in the 0.29 MAC isoflurane group (P less than 0.01). [B/A]a/[B/A]c decreased dose-dependently for each anesthetic group. These results suggest that low concentrations of halothane, enflurane, and isoflurane may enhance the performance of ddN mice in acquired avoidance training performed 30 min after anesthetic exposure.