Estrogen and progesterone interaction in the regulation of scent marking in the female Mongolian gerbil (Meriones unguiculatus)

Ovariectomized female gerbils were treated with either 0, 20, 40, 80 or 160 μg estradiol benzoate (EB) followed in 36 hr by either 0, 250, 500 or 1000 μg progesterone. The animals were tested for ventral scent marking nine hr after progesterone treatment. Treatment with 20, 40 or 80 μg EB resulted in a significant increase in marking in the ovariectomized female for each dose of progesterone used. One hundred and sixty μg EB was not effective while 80 μg was the most effective dose at each dose of progesterone. There were no differences among the 80 μg EB groups in mean marking frequency as long as progesterone was present. Neither estrogen alone nor progesterone alone was effective in stimulating a significant level of marking. An additional sample of ovariectomized females were maintained for four weeks on either 2.5, 5, 10, 20 or 40 μg EB and tested for marking each week 45 hr after EB administration. On the fifth week 250 μg progesterone was given each week 36 hr following EB with behavioral testing nine hr later. Such a regime was followed for four weeks. Marking remained at zero levels on weeks one through four. EB + progesterone on weeks five through eight, however, resulted in a significant increase in marking in animals receiving 10 μg EB (mean = 9.0 ± 3.5), 20 μg EB (mean = 6.6 ± 2.5) and 40 μg EB (mean = 9.2 ± 4.2). It was concluded that both estrogen and progesterone were essential for the support of marking in this sample of low-marking females and that since there were no reliable differences between groups receiving different doses of progesterone, estrogen was the primary stimulus controlling marking behavior, with progesterone perhaps playing a modifying role.