Does the amygdala mediate anesthetic-induced amnesia? Basolateral amygdala lesions block sevoflurane-induced amnesia.

BACKGROUND: Amnesia for aversive events caused by benzodiazepines or propofol depends on the basolateral amygdala (BLA). Whether the amnesia of volatile anesthesia is also mediated through the BLA is unknown. If so, a general principle of anesthetic-induced amnesia may be emerging. Here, using an inhibitory avoidance paradigm, the authors determine whether BLA lesions prevent sevoflurane-induced amnesia.
METHODS: Male Sprague-Dawley rats were separated into two groups: sham-operated controls (n = 22) and rats given bilateral N-methyl-D-aspartate lesions of the BLA (n = 32). After a 1-week recovery, the rats were randomly assigned to be trained during either air or sevoflurane (0.3% inspired, 0.14 minimum alveolar concentration) exposure. Animals learned to remain in the starting safe compartment of a step-through inhibitory avoidance apparatus for 100 consecutive seconds by administering foot shock (0.3 mA) whenever they entered an adjacent shock compartment. Memory was assessed at 24 h. Longer latencies to enter the shock compartment at 24 h imply better memory.
RESULTS: Sham-air (n = 10) animals had a robust memory, with a median retention latency of 507 s (interquartile range, 270-600 s). Sham-sevoflurane (n = 6) animals were amnesic, with a latency of 52 s (27-120 s) (P < 0.01, vs. sham-air). Both the air-exposed (n = 5) and the sevoflurane-exposed (n = 8) animals with BLA lesions showed robust memory, with latencies of 350 s (300-590 s) and 378 s (363-488 s), respectively. The latencies for both did not differ from the performance of the sham-air group and were significantly greater than the latency of the sham-sevoflurane group (both P < 0.01).
CONCLUSIONS: BLA lesions block sevoflurane-induced amnesia. A role for the BLA in mediating anesthetic-induced amnesia may be a general principle of anesthetic action.