Fig. 6. Hydrogen suppresses the impairment of long-term memory caused by neonatal sevoflurane exposure. (A) , No significant difference between groups was observed in total distance traveled over 10 min in an open-field test (control: n = 18; sevoflurane: n = 20; sevoflurane + hydrogen: n = 19). (B ), No significant difference between groups was observed in the Y-maze test (for the same set of mice as in A ). (C , D ) Hydrogen gas alleviated the impairment of long-term memory caused by neonatal exposure to sevoflurane. Impairments were evaluated by a contextual and cued fear conditioning test (for the same set of mice as in A  and B ). Freezing response was measured in the conditioning chamber (contextual fear response) 24 h after conditioning (C ). Freezing response was measured in an alternate context with distinct visual and tactile cues and an auditory cue 48 h after conditioning (D ). **P < 0.01 or ***P < 0.001 compared with controls. ^##P < 0.01 or ^###P < 0.001.