The Preoptic Region of the Brain and its Relation to Ovulation 



107 



electrodes, and (2) to determine the shortest over-all time of stimulation 

 that will be predictably effective. 



Table 2 lists some of the combinations that were tried. The animals 

 represented were all 4-day cyclic rats in proestrus, with a single concentric 

 electrode in the preoptic region. For purposes of later discussion attention 

 is called to the first three lines of the table, which clearly show that a stimulus 

 of no longer than 60 sec can be fully effective. The one positive case among 



Table 2. Results of Certain Modifications of the Parameters of Stimulation 



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



the four in which the stimulus lasted only 15-20 sec was only a partial 

 ovulation (5 tubal ova). The 60-sec examples constitute clear evidence of a 

 triggering action. 



In addition to the sets of parameters given in the remainder of Table 2 

 there are those used in Series I and II, a pulse frequency of 30/sec and pulse 

 duration of 15 msec. Ovulation has thus been evoked, at least in some cases, 

 by pulse frequencies of 30-300/sec, pulse durations of 0.25-15 msec, currents 

 as low as 20 /zA and stimulation periods as short as 15 sec. Any statement 

 about the relative amounts of brain damage associated with the various 

 combinations of parameters would be premature at this time, inasmuch as 

 not all of the brains have been examined histologically. 



Atropine Experiments 



Experiments which pertain to the site of action of atropine as an agent 

 blocking the release of ovulating hormone (Series VI) were carried out by 

 J. R. Harp. The 1 1 subjects were 4-day cyclic rats in proestrus. Pentobarbital 



