MAMMALIAN REPRODUCTIVE CYCLE 



sex function (.see Harris. 1948a, 1955, for 

 references), the majority of these reports 

 do not api^ly to the question at issue — con- 

 trol of ovulation. When ovarian atrophy 

 occurs, as it frequently did in these cases, 

 it reflects a profound depression of gonado- 

 troi)hin secretion and absence of competent 

 follicles. However, Dey, Fisher, Berry and 

 Ranson (1940) and Dey (1941, 1943) 'found 

 in guinea pigs that gross bilateral electro- 

 lytic lesions placed in the rostral hypo- 

 thalamus resulted in persistent follicles with 

 continuous estrogen secretion. Similar re- 

 sults were obtained in rats by Hillarp 

 (1949) when small bilateral electrolytic le- 

 sions were placed in the anterior hypothal- 

 amic area near the paraventricular nuclei 

 or between this region and the median emi- 

 nence. Greer (1953) reported continuous 

 estrus in rats after placing certain small 

 lesions in the ventromedial nucleus, pro- 

 vided they were bilateral. There was no 

 correlation with obesity. There are at least 

 four significant points in common among 

 these several ablation experiments. ( 1 ) The 

 effective lesions were rost rally placed and 

 either were limited to or included the 

 medial group of nuclei. (2) The tuber 

 cinereum, median eminence, and stalk 

 connection to the hypophysis were intact. 

 (3) Although development of competent 

 follicles was not evidently impaired, estro- 

 gen secretion became continuous instead of 

 cyclic. (4) The proper impetus for release 

 of ovulating hormone from the hypophysis 

 was absent. It would be most instructive to 

 learn whether ovulation can be invoked 

 in such animals by reflex stimulation or by 

 direct electrical stimulation of the tuber. 

 AUoiteau and Courvoisier (1953) reported 

 that rats in constant estrus as a result of 

 hypothalamic lesions did not undergo 

 pseudopregnancy after stimulation of the 

 cervix uteri. This observation, confirmed 

 by Greer (1953), could be construed as in- 

 direct evidence of failure of reflex ovulation, 

 for Greer regularly obtained pseudopreg- 

 nancy by cervical stimulation, once corpora 

 lutea had been formed by other means. 



Other findings by Greer are important 

 because of their bearing on the location and 

 character of a presumptive ovulation center. 

 Althougli the onset of persistent estrus after 



making the lesions was sometimes almost 

 immediate (following a brief anestrous in- 

 terval), in other cases it was preceded by 

 several apparently normal cycles. In any 

 event, once the condition had become estab- 

 lished, the daily injection of small amounts 

 of progesterone brought about the recur- 

 rence of cycles and corpus luteum forma- 

 tion. In about half of the cases these cycles 

 continued for awhile after withdrawal of 

 treatment, whereas in the remainder there 

 was a prompt return to persistent estrus. 

 Essentially the same results were reported 

 by AUoiteau (1954), and the observations 

 suggest that the areas involved in such le- 

 sions may be of only secondary importance. 



The use of radioactive phosphorus for 

 estimating energy exchange in tissues af- 

 fords a different approach to the problem 

 of neural control of ovulation (Borell, West- 

 man and Orstrom, 1947, 1948). This method 

 has the virtue that the experimental subject 

 remains undamaged until injection of P'*- 

 compounds 30 minutes before the end of 

 the experiment. In rabbits there is a marked 

 increase in phosphorus turn-over in the 

 tuber cinereum within 2 minutes post 

 coitum, and continuing for about an hour 

 thereafter (Table 8.1). The adenohypoi)h- 

 ysis shows increasing activity during the 

 first 10 minutes which reaches a peak at 

 about 1 hour and then regresses somewhat, 

 although it remains relatively high for 24 

 hours. Response of the ovary to gonado- 

 troi:)hin release is marked by a rapid rise 

 during the second half-hour and another 

 pronounced increase near the time of ovu- 

 lation. In rats, at various stages of the 

 estrous cycle, phosphorus exchange in both 

 tuber cinereum and adenohypophysis is 

 maximal during proestrum. In the ovary 

 high values were reported during diestrum 

 and proestrum, somewhat lower values dur- 

 ing estrus and metestrum. 



Possibly correlated with the above in- 

 formation is the observation (Gitsch, 

 1952b) that in rats the acetylcholine (ACh) 

 content of the tuberal region becomes ele- 

 vated during proestrum and estrus. It is 

 said that ACh synthesis requires high 

 energy phosphate (see Bain, 1952). Further 

 investigation by Gitsch (1952a) and Gitscl: 

 and Reitinger (1953) revealed that ACh 



