L methionine met

L-methionine (MET, Sigma-Aldrich, St. Louis, MO, USA) was dissolved in saline. Haloperidol (HAL, Research Biochemicals International) and clozapine (CLZ, Sigma-Aldrich) were dissolved in saline with 0.3% tartaric acid, after which the pH was adjusted to pH 5–6 with sodium hydroxide. Pregnant mice that mated with the same male mouse were administered with MET (750 mg/kg, 15 ml/kg, s.c.) or saline (SAL) twice a day (0900/1500 hours) for 7 to 8 consecutive days from the 14 day of pregnancy (gestational day 14) until delivery. The daily dose of methionine injected was twofold that of the normal daily dietary methionine intake. In the locomotion and social interaction tests, haloperidol (0.1 mg/kg, 5 ml/kg, i.p.) and clozapine (1.0 mg/kg, 5 ml/kg, i.p.) were administered 40 and 60 min before the test, respectively. In the prepulse inhibition test, haloperidol (0.25 mg/kg, 5 ml/kg, i.p.) and clozapine (2.5 mg/kg, 5 ml/kg, i.p.) were administered 60 min before the test. In the novel object recognition test, haloperidol (0.1 mg/kg, 5 ml/kg, i.p.) and clozapine (1.0 mg/kg, 5 ml/kg, i.p.) were administered 30 min before the training session. Dosages of the drug were selected based on our previous study.²⁵