Objective        To observe the effect of γ-aminobutyric acid (GABA) on nitric oxide synthase (NOS) activity and NO level in frontal cortex of rats exposed to emotional stress

and to explore its anti-anxiety mechanisms combining with behavioral test.       Methods        The rat model of emotional stress was induced by randomly giving empty water bottles. Forty male Sprague-Dawley rats were divided into 5 groups randomly including (n=8) a control group

a model group

and GABA 0.5 mg/kg

1 mg/kg and 2 mg/kg groups. Rats were pretreated with saline or different doses of GABA orally before suffered from emotional stress. After the treatment for 14 d

animal behaviors were assessed in the open field test

and NOS activity and NO level in frontal cortex of each group were determined.       Results        After the 14-day-emotional stress treatment

the food utilization rate of the control group was significantly higher than that of the other groups (P0.01)

and the time spent at the center of the open field was significantly different among the groups (P0.01). Compared with model group

significantly increased frequency in exploration towards to the center was observed in the control group

GABA 1 mg/kg and 2 mg/kg groups (P0.05). The grooming frequency of the model group was significantly higher than that of the GABA 1 mg/kg and 2 mg/kg groups (P0.05)

but the rearing frequency and the total distance traveled in the open field had no significant differences among the groups (P0.05). The NOS activity and NO level were significantly higher in frontal cortex of the control group and GABA 2 mg/kg group as compared with the model group (P0.05).       Conclusion        GABA has a dose-dependent effect on NOS activity and NO levels in frontal cortex of rats exposed to emotional stress

suggesting GABA may play an anti-anxiety role through modulating NO level in the frontal cortex.