92 



Charles H. Sawyer and M. Kawakami 



lowering of the EEG afterreaction threshold to the point at which a 

 "spontaneous" afterreaction occurred. For some hours thereafter the 

 threshold remained at relatively low levels but ordinarily only one spontaneous 

 afterreaction followed such an injection. In this particular case (Fig. 12) 

 the rabbit had been pretreatcd with estrogen and a temporary condition of 



VOLTS 



a iG 



CO 15 



2 3 4 5 6 7 



TIME IN HOURS AFTER HCG 



[ HIPP. 

 HYPERACT. 



VCESV ECV EVC ECV 



V-VAGINAL STIM.,C-COITUS, E-ELECTRIC STIM., S-SPONTANEGUS 



rr: SPINDLE 

 LiJ BURSTS 



I [latency 



\—i COITUS 

 L-J REFUSED 



Fig. 12. Effect of human chorionic gonadotropin (HCG) on EEG thresholds in the 

 estrogen-primed ovariectomized rabbit. In the unprimed castrate rabbit HCG still depresses 

 the EEG afterreaction threshold but the occurrence of estrus and the slight depression in 

 arousal threshold seen here do not occur in the absence of exogenous estrogen. From 



Kawakami and Sawyer (43). 



estrus followed HCG treatment, although the arousal threshold was only 

 slightly depressed. In the absence of estrogen neither estrus nor any effect on 

 the arousal threshold was usually seen, although the EEG afterreaction 

 threshold was reduced to the level at which a spontaneous response occurred. 

 The results support the concept of a close relationship between the EEG 

 afterreaction threshold and pituitary activation and indicate that the influence 

 of these hormones on the nervous system, as well as that of the steroids, 

 is one of altering thresholds rather than acting as stimulants per se. 



EFFECTS OF THE NEW PROGESTOGENS 



Some of the newer progestational compounds have been reported to have 

 very prolonged actions (46) and to be strongly inhibitory to ovulation (47). 

 Their effects on the two thresholds were naturally of considerable interest. 



