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14. Secretion of prolactin releasing factors and prolactin as a motor pattern of the parental, male and female sex motivational systems; facilitated by ACTH and estrogen. Coitus stimulates an increase in prolactin secretion. In male rats, Kamel et al (1977) found an increase in prolactin following mating with a female, but not in response to female odors alone. In female rats, there is also an increase in prolactin following coitus (Moss, 1974). Stimulation of the genital tract apparently serves as a motivating stimulus for the prolactin release in females, since the effect of coitus is reduced if the pelvic nerves have been cut {Spies and Niswander (1971). These data suggest that prolactin secretion is a motor pattern of the male and female sex motivational systems. In females, the function of the coitus-induced prolactin secretion may be the activation of the corpora lutea that is necessary for successful pregnancy and that is responsible for the increased secretion of progestins during pregnancy and pseudopregnancy (Terke1 and Sawyer, 1978; Yoshinaga,1977). In all but one of the muroid rodent species with spontaneous ovulation, it has been found that development of the corpora lutes.depends upon coitus (Dew sb ury. 1977). Suckling or self-licking stimulates prolactin secretion (Roth and Rosenblatt, 1968). It has not been established if this is a motivating or releasing stimulus. Unlike releasing stimuli, it is not necessary for activation of the motor patterning mechanism; prolactin release can occur in response to coitus alone. If' it is a motivating stimulus for the parental motivational mechanism~ however~ one would expect it to prime the animal for various parental behaviors such as retrieval, nest-building, etc.; as far as I know, the relevant studies to determine this have not been done. Exteroceptive stimuli from pups can also stimulate an increase in prolactin secretion, even in the absence of suckling. This has been shown in experienced lactating rats (Grosvenor et al, 1970) and inexperienced postpartum rats whose nipples have been surgically removed (Moltz et a1, 1969). These data suggest that prolactin secretion is a motor pattern of the parental motivational system. The brain mechanisms essential for prolactin release following coitus in the male rat include the medial preoptic hypothalamus (Kamel and Frankel, 1978), which is consistent with the hypothesis that it is a motor pattern of the male sex motivational mechanism. Estrogen facilitates the release of prolactin. Since estrogen activates both the female sex and parental motivational mechanism, one would expect that its action at those points should facilitate prolactin release. However, there may also be effects at the level of the pituitary response to prolactin releasing factors (Grosvenor and Mena, 1974) that would indicate an effect at the level of the motor patterning mechanism as well. ACTH may also facilitate the release of prolactin under experimental conditions (Ogle, 1977 This may be related to the fact that prolactin is secreted in response to stimuli that motivate defense, e.g. stressful restraint (Smith and Gala, 1977). In sum, both the functions of prolactin and its interactions with other hormones are very complex. In addition to its role in the initiation of pregnancy and the maintenance of lactation, it appears to have a role in the responses of the defense motivational system. And the fact that it is secreted by males following coitus suggests that it may have other functions as well.
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