106 



John W. Everett 



Stimulus parameters were identical in respect to pulse duration (I msec) 

 and frequency (lOO/sec). The differences were as follows: In IV-A, the dual 

 electrode assembly was employed, the stimulus isolation unit was not used, 

 and the over-all stimulation period was 10 min. In IV-B, the single concentric 

 electrode and the isolation unit were employed, and stimulation lasted for 

 only 5 min. In IV-A there were 50 rats, equally divided between diestrus and 

 proestrus. In IV-B there were 21 rats in groups of 10 and 11, respectively. 



Table 1. Results of Preoptic Stimulation Relative to Current and to Stage of the 



EsTROus Cycle 



* Each + and indicates a rat with or without tubal ova. 



Table 1 summarizes the results. The two sets of experiments point to a real 

 difference between diestrus and proestrus. In IV-A alone there is a consider- 

 able overlap and comparisons of the 40-50 /xA categories in the two columns 

 (7/14 vs. 11/12) or of the 50-65 fxA categories (9/15 vs. 10/10) show that in 

 neither case is the difference between the ratios significant at the 5% level.* 

 In IV-B, however, the difference between 6/6 and 0/5 in the 50 /nA categories 

 is significant at 1%*. 



Statistics are perhaps less convincing, however, than the fact that the data 

 from both IV-A and IV-B trend distinctly in the same direction. It seems 

 especially noteworthy that in IV-B currents of 70-75 /uA were less uniformly 

 effective in diestrous rats than were currents of 50 p-A in proestrous rats. 



Effects of Various Parameters 



At this point it is appropriate to discuss the effect of variation of the several 

 parameters of stimulation (Series V): frequency, pulse duration, current and 

 total time. The survey is still far from exhaustive and will be extended from 

 time to time. It has two objectives: (1) to find an effective combination 

 that produces minimum brain damage, for subsequent use with indwelling 



* The estimates of significance were obtained by use of the tables of Mainland and 

 Murray {Science 116, 591, 1952). 



