Opisthotonus during exposure to isoflurane, enflurane, and halothane in mice

Some strains of mice, in whom anesthesia was induced with 1.2% isoflurane in air, developed episodes of intense opisthotonus, lasting 1-2 min. Occasionally, opisthotonus also occurred transiently on emergence from isoflurane anesthesia. The incidence of opisthotonus upon anesthetic induction varied with the strain of mice studied, and was particularly high (nearly 80%) in the ddN and YBR/Ki strains. A significantly lower incidence of opisthotonus was observed in all 14 strains studied when 2.0% enflurane was used. One percent halothane did not produce opisthotonus in any strain of mice except one animal of the YBR/Ki strain, and, in this situation, it occurred only on emergence. These results suggest that, in some strains of mice, induction of anesthesia with isoflurane may apparently excite (disinhibit) the central nervous system more intensely than does anesthesia with enflurane or halothane.