Facilitation of receptivity in estrogen-primed rats during successive mating tests with progestins and methysergide

The role of hormonal and experiential variables in mediating the gradual increase of receptivity occurring during weekly tests was evaluated in adult ovariectomized females. Hormone treatment consisted of estradiol benzoate (EB) injection followed by progesterone (P), 20alpha-hydroxyprogesterone (20alpha-OHP), methysergide maleate (Me), or oil during weekly mating tests. The experiential conditions were vaginal stimulation, mounts only, or no interaction with males. There was a gradual increase in receptivity in all groups even en the one receiving oil. Progressive facilitation occurred even when no interaction with the male was permitted. Interchanging the synergists on the sixth and seventh tests was not detrimental to the display of receptivity attained with synergists given previously. Thus, we concluded that successive injections of EB rather than synergists or experience mediate this increase in receptivity.