Behavioral and pharmacological validation of the elevated plus maze constructed with transparent walls

In this study we compared the performance of male Wistar rats, weighing 250-300 g, submitted to the standard plus maze (vertical surfaces of the closed arms with opaque walls) to their performance in a modified maze with raised Plexiglas edges in the closed arms (transparent walls). The animals (N = 12 for each group) continued to show a clear preference for the closed arms with transparent walls of the modified elevated plus maze. In addition, exploratory activity was higher in the open arms of the modified plus maze (4.25 +/- 0.42 entries and 53.50 +/- 5.10 s) as compared to that of the standard plus maze (2.10 +/- 0.25 entries and 24.00 +/- 4.91 s). Intraperitoneal injection of midazolam produced an increase in the number of entries (6.40 +/- 1.21 and 8.50 +/- 1.15 for 1.0 and 2.0 mg/kg, respectively) and in the time spend in the open arms (85.32 +/- 14.56 and 125.50 +/- 22.16 s for 1.0 and 2.0 mg/kg, respectively) while pentylenetetrazole caused a decrease in the number of entries (3.68 +/- 0.54 and 2.33 +/- 0.62 for 5.0 and 10 mg/kg, respectively) and in the time spent in the open arms of the modified maze (39.60 +/- 6.67 and 23.60 +/- 6.40 s for 5.0 and 10 mg/kg, respectively). The anxiolytic effect of midazolam and the anxiogenic effect of pentylenetetrazole were similar to those usually reported in the literature by authors using the standard test. These results behaviorally and pharmacologically validate the elevated plus maze with transparent walls and suggest that this test could be a useful tool for the study of anxiolytic drugs and the neurobiology of anxiety.