Further Evidence for the Identity of Hypothalamic Areas Controlling Ovulation and Lactation in the Rabbit

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Abstract
Earlier independent studies in the rabbit indicated that the posterior basal tuberal region of the hypothalamus exerts a stimulatory influence on the release of pituitary gonadotrophin and an inhibitory influence on the release of prolactin. The present experiments test the identity of hypothalamic areas controlling the 2 hormones in the same animal. Forty female New Zealand rabbits were primed with estrogen for 10 days. On day 12, under local anesthesia, an electrode was positioned stereotaxically in the hypothalamus and used first for stimulating and then, under pentobarbital anesthesia, for destroying the stimulation site by electrolysis. Observations were made of the mammary glands at various intervals and the ovaries were studied at autopsy on day 15. Of the 40 rabbits, 22 failed to show activation of the mammary glands and none of these ovulated. With a single exception, the stimulation-lesion sites lay outside the basal tuberal region. Eighteen rabbits with electrode sites in the basal tuberal-posterior median eminence area showed marked gross and histologic evidence of lactogenesis and 6 of them ovulated. The failure of ovulation in the other 12 may have been caused by the prolonged estrogen priming, which stimulates prolactin production but inhibits gonadotrophin secretion. The results are consistent with the hypothesis that the hypothalamic area which activates release of ovulating hormone is the same as that which chronically holds in check the release of prolactin.