The Pituitary Stalk and Ovulation 61 



paper plate between the cut ends of the stalk, remained anestrus. Ferrets in 

 which the stalk had been cut, but in which vascular regeneration had occurred 

 across the site of the injury, became estrus on exposure to prolonged 

 illumination. The results of their study indicate that the final connecting link 

 from brain to pituitary gland involves the hypophysial portal vessels 

 [Thomson and Zuckerman (80) have drawn different conclusions]. 



To investigate the possibility that reflex nerve tracts between the chiasmal 

 region of the optic pathway and the upper end of the pituitary stalk (median 

 eminence of the tuber cinereum) were involved in the increased secretion of 

 FSH occurring in the spring, Donovan and van der Werff ten Bosch (22, 24) 

 placed lesions in this part of the hypothalamus of the female ferret during 

 winter. Electrolytic lesions were placed with the aid of a stereotaxic machine, 

 with the animals anesthetized with Nembutal (pentobarbitone sodium). 

 Since the plan of the experiment was to see whether such lesions delayed or 

 prevented the onset of the breeding season in the spring it was surprising to 

 find that about 75% of the animals with anterior hypothalamic lesions 

 became estrous early; that is, at a time of the year when normal animals, 

 blank-operated animals and those with lesions in the posterior hypothalamus 

 and thalamus, or amygdala, were still in the winter anestrum (Fig. 1). Many 

 of the animals that showed early estrus were placed with males, and produced 

 litters which they reared successfully. Serial sections through the brains 

 showed that the effective lesions were situated basally in the anterior part 

 of the hypothalamus, between the optic chiasma and pituitary stalk, extending 

 upward to the level of the paraventricular nuclei (Figs. 2 and 3). The optic 

 chiasma, suprachiasmatic nuclei and fornices were usually involved. In only 

 one animal was the pituitary stalk partly damaged. Ineffective lesions involved 

 the mammillary bodies, medial nuclei of the thalamus and habenular complex, 

 and amygdaloid area. In view of the fact that the hypothalamic lesions might 

 have exerted a stimulating effect by pressure on surrounding structures, 

 Donovan and van der Werff ten Bosch (24) electrically stimulated various 

 regions in the anterior hypothalamus. These experiments were carried out 

 with implanted electrodes and stimulation continued for periods of weeks 

 or months during winter. There was no indication of any release of gonado- 

 tropin by stimulation. 



The specificity of the above results has been questioned by Herbert and 

 Zuckerman (53, 54) who claim that estrus in ferrets is advanced by lesions 

 placed in the thalamus or adjacent areas and by blank operations. The reason 

 for this discrepancy is, at the moment, not clear. 



General Conclusions 



The most hkely explanation of the finding that hypothalamic lesions 

 result in FSH secretion, follicular ripening and estrus, in both the immature, 

 or the mature anestrous, animal, is to be found in terms of a neural mechanism 



