The Preoptic Region of the Brain and its Relation to Ovulation 1 1 1 



that stimulations in the preoptic area were "completely ineffective". 

 Christian's observations are now amply confirmed. 



SUMMARY 



The preoptic region, in spite of pentobarbital anesthesia and relative 

 distance from the median eminence, remains highly sensitive to electrical 

 stimulation. 



Stimulation of the preoptic region on diestrus day 3 will advance ovulation 

 approximately 24 hr. 



The preoptic threshold is lower on the day of proestrus than on diestrus 

 day 3. Approximately similar results were obtained with (a) dual concentric 

 electrodes, no isolation, a 10-min stimulation period, and (b) single concentric 

 electrode, with isolation, and a 5-min stimulation period. 



Preoptic stimulation under pentobarbital anesthesia will readily induce 

 ovulation in proestrous rats that have been given atropine in an amount 

 adequate by itself to block ovulation. 



Exploratory study with varied parameters has given positive results in 

 proestrous rats with pulse frequencies of 30 to 300/sec, pulse durations of 

 0.25 to 15 msec, currents as little as 20 [j.A and stimulation periods as short 

 as 60 sec (100/sec, 1 msec, 100 /mA, single electrode). In controls with no 

 current, results were negative. 



The data on the ineffectiveness of atropine show that the atropine-sensitive 

 components of the LH-release mechanism are more remote from the median 

 eminence than are the elements that can be activated by electrical stimulation 

 of the preoptic region. 



COMMENT ADDED IN PROOF 



Since this paper was presented, a direct correlation has been found 

 between positive results and the amount of electricity introduced, without 

 evident relationship to other parameters. In histologic sections of the brains, 

 areas of mild electrolytic damage were observed about the electrode tips in 

 all animals that ovulated. In negative cases, on the other hand, there was 

 often no apparent electrolysis; when it did exist the volume of affected tissue 

 averaged much less than in positive cases. Subsequently, good results have 

 consistently been obtained by use of a direct current of 100 /xA for 30 sec or 

 less, whereas control lesions of comparable dimensions produced by high- 

 frequency electrocautery have been ineffective. Thus, it seems that the positive 

 effect stems from chemical changes caused by the electrolysis. Doubtlessly the 

 irritative effects of the electrolysis persist long after the current is turned off. 

 This eliminates the paradox mentioned with respect to the atropine experi- 

 ments, but complicates interpretation of the difference in "threshold" 

 between diestrous and proestrous rats. 



