Effects of progesterone on open field behavior of food deprived ovariectomized female rats.

The effects of intraperitoneal progesterone administration on the open field behavior of ovariectomized female Wistar rats were studied in two experiments. Subjects were challenged with 5 different doses of progesterone (0, 10, 20, 40, 80 mg/kg body weight) during 5 successive days of open field testing (5 min a day) in the first experiment. Progesterone dose-dependently decreased rearing and object inspection, but did not affect total ambulation. In the second experiment food pellets were presented in the open field and subjects were repeatedly tested at regular intervals after progesterone administration on each of 5 consecutive testing days. Three doses of progesterone (0, 40, 80 mg/kg body weight) were administered during the final 3 days of the second experiment. Eighty mg/kg progesterone decreased rearing activity, but increased ambulation; motivation to retrieve food pellets was not affected. These effects of 80 mg/kg progesterone were observed at least as long as 2 hours after injection. Forty mg/kg progesterone did not produce such effects. These results, in conjunction with those of other experiments show that progesterone affects open field behavior in a way similar to central depressant drugs.