Medial preoptic area and onset of maternal behavior in the rat.

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Abstract
Whether the medial preoptic area (MPOA) is involved in the onset of maternal behavior in the rat was examined. Previously, the MPOA had been shown to be important in the maintenance of maternal behavior in the lactating rat. The effect of estradiol benzoate (EB) acting on the MPOA to facilitate the onset of maternal behavior in the 16 day pregnant, hysterectomized and ovariectomized female rat was studied. Such rats when given EB implants in the MPOA had significantly shorter latencies for the onset of maternal behavior than had females implanted with cholesterol in the MPOA or with EB in the ventromedial hypothalamus, in mammillary bodies, or under the skin. Estrogen-induced prolactin release was not involved in this facilitation. MPOA lesions disrupt the onset of maternal behavior that is induced by pup stimulation in virgin females. The MPOA is involved not only in the maintenance of maternal behavior but in the hormonally mediated onset of maternal behavior and the onset of maternal behavior induced in virgin females by pup stimulation.