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

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Abstract
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), 20.alpha.-hydroxyprogesterone (20.alpha.-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 in the one receiving oil. Progressive facilitation occurred even when no interaction with the male was permitted. Interchanging the synergists on the 6th and 7th tests was not detrimental to the display of receptivity attained with synergists given previously. It is concluded that successive injections of EB rather than synergists or experience mediate this increase in receptivity.