Differential progesterone effects on defensive burying and forced swimming tests depending upon a gradual decrease or an abrupt suppression schedules

A single dose of progesterone reduces the cumulative time in the defensive burying test and the immobility in the forced swim test, whereas the abrupt suppression of repeated doses increases the anxiety indicators. Whether anxiety and despair indicators reduce by a gradually decreased schedule of progesterone is unknown. Therefore, we subjected adult ovariectomized Wistar rats to open field, defensive burying and forced swim tests. One group received a constant schedule of progesterone (0.50 mg, daily), abruptly suppressed (AS) after five days. Another group received a gradual reduction schedule of progesterone (GR: 0.84, 0.67, 0.50, 0.33, 0.17 mg, each day). Control group received vehicle (VEH). The GR group displayed similar crossing in the open field test as the VEH group (F2,19 = 8.78, p < 0.002), but also the shortest cumulative time in defensive burying (F2,28 = 13.3, p < 0.0001) and the shortest time in freezing (F2,24 = 6.39, p < 0.006). In the forced swim test, the GR group displayed the shortest immobility time (F2,19 = 12.1, p < 0.0005), the lowest number of immobility periods (F2,19 = 4.26, p < 0.03) and the longest latency to the first period of immobility (F2,1 = 4.06, p < 0.03). It is concluded that a gradually reduced schedule of progesterone reduces anxiety and despair in the Wistar rat.