Background: Although the roles of steroid hormones in the activation and maintenance of reproductive function are proved well, emerging evidence indicated that these steroids influence on performance of learning and memory. These effects are complex and vary with task, gender, and age, as well as the regimens of steroid exposure. This study was carried out in order to assess the role of progesterone administration in newborns rats on Morris water maze learning ability after adolescence.

  Methods and Materials : This experimental study was carried out on 36 newborns Wistar rats. Rats were divided randomly into 6 groups female progesterone, male progesterone, female sesamoide, male sesamoid rats and male and female control rats. Progesterone groups were treated with a single injection of progesterone (100 mg/kg) and sesamoid groups were received the same volume of sesamoid oil as the progesterone vehicle in day 1 or 2 after brith, 60 days later, spatial memory ability was determined in Morris water maze.

  Results : The results of this study show that water maze learning can enhance by administration of sesamoid oil in newborn female pups in compared to progesterone and control groups (p<0.05). In addition, adding progesterone to sesame oil reduce water maze learning to control level.

  Conclusion: The hypothesis that progesterone impaired spatial reference memory in female rats was supported by this experiment.