PROGESTERONE-INDUCED LUTEINIZING HORMONE RELEASE IN OESTROGEN-PRIMED OVARIECTOMIZED RATS AFTER DESTRUCTION OF MID-BRAIN INPUTS TO SUPRACHIASMATIC NUCLEI
Department of Biological Sciences, Massachusetts College of Pharmacy, 179 Longwood Avenue, Boston, Massachusetts 02115, U.S.A. (Received 17 January 1975) Suprachiasmatic (SCh) lesions which destroy the SCh nuclei and portions of the medial preoptic and rostral anterior hypothalamic areas block the surge of plasma luteinizing hormone (LH) which occurs 6 h after an injection of progesterone in ovariectomized, oestrogen-primed rats (Bishop, Kalra, Fawcett, Krulich & McCann, 1972). Such lesions interrupt fibres of the preoptico-tuberal path which are probably necessary for induction of the LH surge, as well as fibres which originate in other brain areas but which terminate within the preoptic-anterior hypothalamic area (PO-AHA). Kalra, Kalra, Krulich, Fawcett & McCann (1972) suggested that adrenaline-containing fibres are involved in mediating the progesterone-induced LH surge; however, it is likely that this noradrenergic synapse lies along the preoptico-tuberal path (Kalra & McCann, 1973). It is still not clear whether the site of action