Interactions between the Central Nervous System and Hormones 



91 



benzoate or 5 mg testosterone propionate (Fig. 11) result in lowered EEG 

 arousal thresholds and elevated EEG afterreaction thresholds. At the end of 

 treatment with either steroid, the rabbits are highly estrous but copulation 

 is not followed by ovulation. The latter condition may be described as an 

 elevated pituitary activation threshold; this may be correlated with the 



100% 



12 3 12 3 



EFFECT ON EFFECT ON EEG 



EEG AROUSAL AFTERREACTION 



THRESHOLD THRESHOLD 



0.5 MG ESTRADIOL BENZOATE 

 DAILY FOR 5 DAYS 



4 5 6 4 5 6 



EFFECT ON EFFECT ON EEG 



EEG AROUSAL AFTERREACTION 



THRESHOLD THRESHOLD 



5 MG TESTOSTERONE PROPIONATE 

 DAILY FOR 5 DAYS 



Fig. 1 1 . Relative thresholds (expressed as percentages of pretreatment levels considered 

 to be 100%) of EEG arousal and EEG afterreaction after prolonged treatment with high 

 dosages of estrogen and treatment with androgen. The numbers (1-6) under the bars 



identify individual rabbits. 



elevated afterreaction threshold while continued estrus may be correlated 

 with the lowered EEG arousal threshold. Zondek and Sklow (45) noted the 

 inhibitory effect of high dosages of estrogen and testosterone on electrically 

 stimulated ovulation in the rabbit. 



EFFECTS OF CERTAIN PITUITARY 

 AND PLACENTAL HORMONES 



As was mentioned earlier, treatment with certain pituitary or placental 

 gonadotropins, lactogen and neurohypophysial hormones was often followed 

 by the appearance of a "spontaneous" EEG afterreaction. It was proposed 

 that the response might represent a natural feed-back mechanism to shut off 

 further neural activation of the hypophysis. It was, therefore, of interest to 

 study the effects of these agents on the two thresholds. 



Figure 12 illustrates a representative response to these substances. Exerting 

 little effect on the EEG arousal threshold, the gonadotropin caused a rapid 



