If you lesion the midbrain central gray , you decrease lordosis behavior. Estrogen promotes the growth in number and size of sensory receptors during proestrus and information related to male mounting the female is relayed to the medullary retiuclar formation . This area governs muscles that control the reflexive behavior during lordosis. Information is sent from medullary retiruclar formation to the midbrain central gray which receive input from regions of the hypothalamus. If you input estradiol into the ventromedial nucleus or the midbrain central gray, females will engage in lordosis behavior.
Frequency is somewhat less than rats found in the wild.
If you give an injection of estrogen followed 6-8 hours later by an injection of progesterone, lordosis behavior is maximized. This can be greater than lordosis behavior found in proestrus. The highest frequency of sexual behavior occurs with estrogen followed by progesterone. Perhaps estrogen primes the system to facilitate the later progesterone injection. Estrogen tends to cause a change in the electrical activity of the midbrain central gray.