280 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



seems moreover, that such lesions may also 

 selectively influence the individual gonado- 

 trophins, and recently evidence has been 

 provided that lesions in the ventral hypo- 

 thalamus of sheep may abolish the behav- 

 ioral manifestations of estrus without alter- 

 ing the ovarian cycle (Clegg, Santolucito, 

 Smith and Ganong, 1958). 



The study by Bogdanove and Halmi 

 (1953) also confirms an observation noted 

 by others (Desclin, 1942; May and Stutin- 

 sky, 1947; Stutinsky, Bonvallet and Dell, 

 1950) that lesions in the hypothalamus may 

 lead to a considerable hypertrophy of the 

 pars intermedia. Furthermore, Stutinsky, 

 Bonvallet and Dell (1950) observed great 

 enlargement of the sinusoids in the pars 

 distalis following suitably placed hypotha- 

 lamic lesions, and speculated that one 

 means of hypothalamic mediation of hy- 

 pophyseal function might be by way of 

 vasomotor control of vessels in the pars dis- 

 talis. As a modus operandi this has the 

 drawbacks of nonspecificity and sluggish- 

 ness. The view has not been given credence, 

 but the observation merits study. 



4. Transection of the Hypophyseal Stalk 



An obvious experimental procedure in 

 studying the extent of any control that the 

 hypothalamus may impose on the anterior 

 hypophysis is to interrupt all anatomic con- 

 nections between them. This has been ac- 

 complished by either surgically transecting 

 the stalk or occluding it with a silver clip. 

 In either event the neural and vascular 

 connections between the hypophysis and the 

 brain are disrupted. Such procedures do, in 

 fact, isolate the hypophysis from eveiy pos- 

 sible anatomical connection with the brain, 

 save that of the systemic blood stream. 

 Roundabout as the latter would be, even 

 this avenue is available only in animals 

 having a collateral blood supply to the an- 

 terior lobe. Present evidence indicates that 

 this would include man and, with less cer- 

 tainty, monkey, dog, sheep, and rabbit. A 

 consideration of primary importance in all 

 surgical transections of the stalk concerns 

 the demonstrated capacity of the disrupted 

 vessels to regenerate and reestablish vas- 

 cular connections. Harris (1936-1955) , Har- 

 ris and .lacobsohn (1952) and Harris and 

 Johnson (1950) have taken the in'ccaution 



of placing a plate of impervious material 

 between the severed ends of the stalk as a 

 barrier to the regrowth of vessels. The 

 severed neurons with nuclei in the hypo- 

 thalamic ganglia undergo Wallerian degen- 

 eration. 



Variations exist between species in the 

 length of the pituitary stalk and in the 

 anatomic relationship of the hypophysis to 

 the base of the brain; consequently, it is 

 often possible to divide the stalk at differ- 

 ent levels, i.e., near the base of the brain 

 (high) or near the pituitary (low). In those 

 species, especially the rabbit, monkey, and 

 man, which have a deep sella turcica and a 

 relatively long infundibular stem, there is 

 the likelihood that with high transection, 

 portions of the portal circulation may re- 

 main intact. Man in particular is held to 

 have a collateral blood supply to the pars 

 distalis (Xuereb, Prichard and Daniel, 

 1954a, b) by way of the trabecular and the 

 inferior hypophyseal arteries. 



The level of stalk transection is also 

 known to be important in terms of the di- 

 abetes insipidus which follows this opera- 

 tion. Severance in a plane near the hy- 

 pophysis in rats (as many have already 

 demonstrated) may result in only a mod- 

 erate and transient polyuria, whereas after 

 transection in a more proximal plane the 

 polyuria is more often severe and perma- 

 nent. A plausible explanation of these results 

 is that after low transection, there occurs a 

 compensatory development of neural lobe 

 tissue at the proximal end of the severed 

 stalk. Suprasellar reorganization of neuro- 

 hypojihyseal tissue and restitution of neu- 

 rohyiioi)hyscal functions have been de- 

 scribed by Stutinsky (1951, 1953) and 

 confirmed by Billenstien and Leveque 

 (1955) and Benson and Cowie (1956) after 

 hypophysectomy in the rat. (Jaupp and 

 Spatz (1955) described comi)cnsatory de- 

 velopment of a "suprasellar hyi:)ophysis" 

 on the tuber cinereum following low tran- 

 section of the stalk in rabbits. They found 

 these growths to be composed of fibers rich 

 in Gomori-positive granules. Some of the 

 rabbits bearing such nodules came into late 

 sexual maturity, which led the authors to 

 surmise that these compensatory neural ele- 

 ments were providing gonadotrophic stim- 

 ulation. Tlic nodules thev described are of 



