510 



PHYSIOLOGY OF GONADS 



The answer may be long in coming. Mean- 

 while, one would like to know whether cas- 

 tration changes are visible in the hypophysis 

 and whether constant estrus may be invoked 

 by exposure to continuous light or by post- 

 natal treatment of the host with androgen 

 or other steroids (see p. 529 1 . 



D. HYPOTHALAMUS AND GONADOTROPHIN 

 SECRETION. GENERAL CONSIDERATIONS 



Experimental studies, ostensibly ad- 

 dressed to the general problem of neural 

 control of gonadotropin secretion, have in 

 fact often been concerned with the special 

 problems of reflex ovulation <p. 520) or 

 of provoked pseudopregnancy (p. 532). 

 Whereas substantial information is now 

 available w^ith respect to these special phe- 

 nomena, particularly ovulation, information 

 is limited about control of the day-to-day 

 secretion of gonadotrophin that in the fe- 

 male is responsible for follicle stimulation 

 and estrogen secretion (Benoit and Assen- 

 macher, 1955; Harris, 1955). However, evi- 

 dence in regard to induction of precocious 

 puberty and early onset of estrus in seasonal 

 breeders leaves no doubt that the nervous 

 system is in some manner a regulator of 

 follicle-stimulating activitv of the i)ars dis- 

 talis. 



Numerous reports associate precocious 

 l)uberty with lesions in the hypothalamus 

 (Weinberger and Grant, 1941; Bauer, 1954; 

 Harris, 1955). Donovan and van der Werff 

 ten Bosch (1956) reported off-season estrus 

 in ferrets and precocious puberty in rats 

 following retrochiasmatic lesions in the hy- 

 jiotlialamus. Exposure of immature rats to 

 continuous light causes the vagina to open 

 prematurely (Fiske, 1941). When 22-day- 

 old female rats were given electrical stimu- 

 lation of the cervix uteri daily for 10 days 

 (Swingle, Seay, Perlmutt, Collins, Fedor 

 and Barlow, 1951), a large proportion ex- 

 hibited significant increase in uterine weight 

 beyond that found in control animals, with- 

 out change in ovarian weight. In fact, 7 of 

 50 rats ovulated or at least formed "several 

 well-developed corpora lutca." Somewhat 

 similarly, according to Aron and Aron- 

 Brunetierc (1953), mechanical stimulation 

 of the vagina or the adjacent segment of the 

 uterus in innnatur(> guinea pigs regularly 



provoked follicle growth and estrogen secre- 

 tion. In gregarious birds the development of 

 ovulable follicles requires that other indi- 

 viduals of the species be present. In the pi- 

 geon, even the mirror image of the female 

 constitutes a sufficient stimulus (Matthews, 

 1939). 



Studies by Flerko and his associates 

 (1954-1957) present consistent evidence 

 that restricted bilateral lesions in the region 

 of the paraventricular nuclei serve to liber- 

 ate the hypophysis from inhibitory effects 

 of estrogen and androgen. This work is in 

 agreement with that of Donovan and van 

 der Werff ten Bosch in that somewhat simi- 

 larly located lesions brought on precocious 

 puberty. As noted elsewhere, gonadectomy 

 in immature rats quickly results in hyper- 

 secretion of gonadotrophin. 



Transplantation of the hypophysis to 

 sites remote from the hypothalamus has 

 produced divergent results. At the present 

 writing, the chief divergence seems to rest 

 between the sexes. In male guinea pigs and 

 rats several workers have reported main- 

 tenance of male reproductive tracts by in- 

 tra-ocular transplants of hypophyses (May, 

 1937; Schweizer, Charipper and Kleinberg, 

 1940; Cutuly, 1941a; Courrier, 1956; Gold- 

 berg and Knobil, 1957). Quite to the con- 

 trary, however, there has at best been only 

 equivocal evidence of maintenance of fe- 

 male tracts, a matter of sex difference which 

 needs full investigation. JNIay's (1937) re- 

 port of 2 fertile female rats is unacceptable 

 because of inadequate controls. Schweizer, 

 Charipper and Haterius (1937) found in 

 several hypophysectomized guinea pigs that 

 intra-ocular pituitary grafts produced con- 

 stant estrus and significant follicle stimula- 

 tion, accompanied by uterine and mammary 

 gland develoi)inent. Although the search for 

 pituitary remnants in the sella turcica was 

 reported negative, the histologic check was 

 limited to scrapings from the sella floor. 

 Other authors, notably Phelps, Ellison and 

 Burch (1939), Westman and Jacobsohn 

 (1940), Harris and Jacobsohn (1952), and 

 Elverett ( 1956a) obtained in female rats lit- 

 tle or no evidence of gonadotrophin secre- 

 tion from apparently healthy, well vascu- 

 larized grafts. The respective sites were 

 intraniusculai', intra-ocular, in the sub- 



