EFFECT OF HYPOTHALAMIC LESIONS ON PROGES-TERONE-INDUCED OVULATION IN THE HEN

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Abstract
Previous work has implicated a ventro-median region in the preoptic hypothalamus of the chicken in the control of normal ovulation. To determine whether or not the hypothalamus is involved also in progesterone-induced ovulation, electrolytic lesions were placed by means of a stereotaxic instrument at various sites within the hypothalamus of birds previously injected with 1 mg. of progesterone. Only those lesions placed within a ventro-median portion of the preoptic hypothalamus (the same region involved in normal ovulation), or along fiber tracts passing caudad from this region regularly prevented ovulations that ordinarily would have been induced by progesterone. Furthermore, only lesions placed in the effective region within about 2 hours after injection of progesterone prevented ovulation. Lesions placed at later times had no influence on progesterone-induced ovulation (but either abolished or delayed subsequent ovulations.) The ventro-median hypothalamic region could be either the actual site of progesterone "excitation" or merely a link in a neural complex mediating the effects of progesterone. Destruction of this region apparently precludes the release of gonadotrophic hormone which usually follows when progesterone is administered at appropriate times.