94 



Charles H. Sawyer and M. Kawakami 



the injection of 1 mg of any of these steroids but that such copulation was 

 not followed by ovulation. Their differential elevation of the particular EEG 

 threshold which we have come to associate with the threshold of pituitary 

 activation, while leaving estrous behavior and its associated EEG threshold 

 unaffected, makes these gestagens ideal antifertility agents, at least for the 



5 p 



O D-f-O-U 



■3 z 



< 

 ■2 q: 5 



16 24 32 



HOURS AFTER 



40 



MG 



48 56 



NORETHYNODREL 



Fig. 14. Differential eflFect of norethynodrel on the EEG afterreaction and EEG arousal 

 thresholds. Norlutin and Nilevar exerted similar effects. 



rabbit. It is conceivable that the record of effects of new steroids on the two 

 EEG thresholds in the rabbit might prove a useful index in screening anti- 

 fertility agents. 



DISCUSSION 



The results of the present experiments, as well as those in which injections 

 of hormones directly into the brain influenced behavior (11, 12, 13), leave 

 little doubt that hormones can act directly on elements within the brain. 

 Ralph and Fraps (50), for example, have reported that the intrahypothalamic 

 injection of tiny amounts of progesterone will induce premature ovulation 

 in the hen. 



It may be that the hormone receptors within the brain, the areas most 

 sensitive to the endocrine agents, are identical to the hypothalamic "centers" 

 whose destruction eliminates behavioral or gonadotropic function. It should 

 be possible, under this hypothesis, to activate the "centers" individually by 

 localized hormone injections, and such appears to be the case (12, 13). With 

 systemic treatment with effective dosages of estrogen and progesterone the 

 two systems, behavioral and gonadotropic, are associated with EEG thresholds 

 that change in a remarkably parallel manner. Such parallel changes coordinate 



