Temporal analysis of the rat's behavior in the plus-maze: effect of midazolam.

The aim of the present study was to carry out a temporal analysis of the midazolam (MDZ)-induced anxiolysis in rats submitted to the elevated plus-maze (EPM) test. Male Wistar rats received either MDZ (0.5, 1.0 and 1.5 mg.kg(-1)) or saline (0.9%) and were submitted to the EPM test. Temporal analysis revealed that the group receiving MDZ (1.5 mg.kg(-1)), as well as the group treated with saline, displayed low %Open arm entries, which suggests increased anxiety over the test period. Motor activity, evaluated by the enclosed arm entries, was also decreased in both experimental groups, thus suggesting locomotor habituation. The treatment with MDZ (1.5 mg. kg(-1)) induced a clear anxiolysis during the first 3 min, but not at the end of the test, since only the %Open arm time remained increased. The data are discussed with reference to the lack of the test's sensitivity to alterations in the level of anxiety over time and with respect to a qualitative shift in the experimental anxiety at the end of the session.