Novel and simple behavioral paradigm for assessing anxiety in rats: effect of diazepam.

OBJECTIVES: Anxiety is an emotional state experienced by people, and is not readily modeled in animals. In order to extend till now ethologically derived paradigms used in the evaluation of anxiety and fear in rodents, a modified open-field was designed.

METHODS: Spontaneous behavior of male rats was investigated in the elevated arena; the bottom was divided by inter-space of different width (2, 4, 6, 8 and 10 cm) into two identical parts. Anxiolytic effects of diazepam (DZP) at doses 0.5, 1.0, 2.5 and 5.0 mg/kg were investigated in the newly designed device and compared with the effects of similar doses in a large circular open-field arena.

RESULTS: In Experiment 1 the progressive extension of the inter-space prolonged the first passing, decreased the total number of passing, and increased the inter-space sniffing in intact animals. In Experiment 2 DZP at doses 1.0, 2.5 and 5.0 mg/kg significantly enhanced the readiness to cross, the frequency of passing the inter-space and decreased inter-space sniffing as compared to controls. In Experiment 3 we found that DZP at doses 0.1 and 0.3 mg/kg increased behavioral activity both along the perimeter and in the center of the arena, thus indicating lower level of anxiety.

CONCLUSION: The presented modified open-field test is a useful paradigm to investigate risk assessment behavior in rats, and may provide a sensitive novel model of anxiety and fear level.