The Role of Hypothalamic Afferents in the Release of Prolactin Induced by Ovarian Steroids

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Abstract
The importance of frontal and caudal afferents to the hypothalamus in the release of prolactin induced by estrogen and progesterone was studied in gonadectomized female and male rats. The serum prolactin levels 2 or 3 days after the injection of 20 µg estradiol benzoate (EB) into ovariectomized rats were significantly lower in animals with retrochiasmatic section interrupting the anterior inputs to the hypothalamus than in control animals, whereas the prolactin secretion induced by progesterone (2 mg) injection in EB-primed animals was not affected. On the contrary, interruption of caudal afferents to the hypothalamus had no effect on the increase in serum prolactin induced by EB injection. A hypersensitive prolactin response to the injection of estrogen or progesterone occurred in animals with frontal hypothalamic deafferentation. It is concluded that prolactin secretion induced by estrogen injection depends not only on the activation of hypothalamic and pituitary mechanisms, but also on the stimulation of frontal neural afferents to the hypothalamus. The latter mechanism does not operate in male rats.