The Pituitary Stalk and Ovulation 63 



Szentagothai (33) demonstrated that the hormones released from the 

 graft depressed gonadotropin secretion if in the region of the 

 paraventricular nuclei. 

 (3) Anterior Hypothalamic Lesions. Such lesions result in a discharge of 

 FSH that would not occur in the immature or mature anestrous female 

 (see above). Since pituitary stalk section results in atrophy of the 

 reproductive organs it is necessary to suppose that the inhibitory 

 action of the anterior hypothalamus over FSH release is normally in 

 balance with an excitatory effect exerted by some other hypothalamic 

 area, both acting through the "final common path" of the hypophysial 

 stalk. 



FOLLICULAR RUPTURE — OVULATION 



Non-spontaneous Ovulation 



Ovulation occurs spontaneously in most mammals, but in some forms 

 requires the sensory stimuli normally supplied by the presence of a male and 

 coitus for its occurrence. These latter forms include many birds, the rabbit, 

 ferret, cat, ground squirrel, short tailed shrew and mink, and possibly (see 

 Eckstein and Zuckerman, 25) the hare, weasel, Asiatic vole {Microtus 

 guentheri), certain marsupials (i.e. Didelphus azarae) and a tropical fruitbat 

 (Pteropus giganteus). Marshall (66) and Heape (51) first reported that ovulation 

 follows copulation in the ferret and rabbit, respectively. Early studies showed 

 that ovulation in the rabbit was not due (1) to absorption of semen from the 

 female reproductive tract, (2) to release of a hormone from the vaginal wall, 

 (3) to a direct nervous reflex acting on the ovaries [ovulation occurred in 

 transplanted ovaries — Asdell (1), Friedman (36)], and the idea became 

 current that a neuro-humoral reflex arc was involved: that sensory nerve 

 pathways caused activation of the anterior pituitary gland and the released 

 gonadotropic hormone brought about follicular rupture. This view received 

 support when it was found that hypophysectomy within one hour of coitus 

 prevented ovulation from occurring some nine hours later, though hypo- 

 physectomy later than this was followed by ovulation (28). 



Sensory Stimuli 



The sensory stimuli involved appear to be varied. Since artificial stimulation 

 of the vulva or vagina may result in ovulation, the sensory receptors in these 

 regions would seem of importance. However, local anesthesia of the vulva 

 and vagina (29), or denervation of these structures by removal of the sacral 

 region of the spinal cord (even when supplemented by complete abdominal 

 sympathectomy, hysterectomy and extirpation of the proximal half of the 

 vagina (11)) does not prevent ovulation following coitus. Brooks (11) also 

 studied the effect of bilateral destruction of the labyrinths and auditory 

 apparatus, enucleation of the eyes and the olfactory lobes, and removal of 



