1022 



HANDBOOK OF I'HYSIOLOGY 



NEUROPHYSIOLOGY II 



released from the neurohypophysis may stimulate the 

 secretion of lactogenic hormone from the pars distalis. 

 Any experiment designed to analyze the role of the 

 hypothalamus in lactation must then take cognizance 

 of this possibility as well as the fact that hormones 

 from bcjth lobes of the hypophysis are involved in 

 normal mammary function. Since the above informa- 

 tion is of recent origin, it is clear that the results ol 

 many older studies require re-evaluation. 



The effect of pituitary stalk section on the secretion 

 of the lactogenic hormone is not clear. It has been 

 found that stalk section in lactating rats causes failure 

 of lactation in spite of functioning anterior pituitary 

 tissue and continued suckling {76, 173), results in 

 death of the young and mammary involution, al- 

 though not to the degree as seen after hypophysectomy 

 (igo), and may be followed by normal lactation (75). 

 Dandy (65) described a case of stalk section in a young 

 woman that was followed by normal menstrual 

 cycles, pregnancy, lai:)or and lactation. Since stalk 

 section may leave intact 10 per cent or more of 

 neurohypophysial tissue in the upper part of the 

 stalk and in the tuber cinereum, and since portal 

 vessel regeneration may occur to the pars distalis, the 

 interpretation of these results is open to doubt. A 

 somewhat clearer situation was found in hypophysec- 

 tomized female rats bearing pituitary grafts beneath 

 the median eminence of the tuber cinereum (161). 

 As described above, these animals showed normal 

 estrous cycles, mated and became pregnant, and 

 delivered living young. However, in spite of obvious 

 distension of the mammary glands with milk, the 

 young died from starvation unless the maternal rat 

 received repeated injections of oxytocic hormone after 

 which they survived and grew In these transplanted 

 animals then there existed a posterior pituitary de- 

 ficiency with failure of the milk-cjcction reflex. 

 Oxytocic replacement therapy revealed, however, 

 that anterior pituitary tissue grafted on to the median 

 eminence is capable of maintaining milk secretion. 

 Unfortunately the extent to which pituitary trans- 

 plants remote from the sella turcica support lactation 

 is not known since animals with such transplants do 

 not show estrous cycles or become pregnant. 



TARGET GLAND ACTIVITY AFTER HYPOTHALAMIC 



LESIONS. The fact that hypothalamic lesions may re- 

 sult in endocrine disturbances has been known since 

 Camus & Roussy (51), Bailey & Bremer (12) and 

 Smith (319) noted genital atrophy following damage 

 to this area of the brain. Later studies, using more 

 precise stereotaxic methods, have shown that large 



lesions in the tuberal region of the hypothalamus, 

 which interrupt all hypothalamohypophysial connec- 

 tions, produce the same effects on pituitary function 

 as does complete and permanent stalk section. (The 

 one exception to this statement is the effect of these 

 procedures on stress-stimulated release of ACTH as 

 described below.) Smaller and more localized lesions, 

 placed bilaterally, produce differential effects on the 

 secretion of various pituitary hormones. 



Gunadotropinc Secretion and Hypothalamic Lesions. 

 Gonadal atrophy has been obser\'ed to follow hypo- 

 thalamic lesions by many workers. One of the more 

 detailed studies is that reported by Dey and his co- 

 workers in a series of papers (see 78) in which they 

 studied the effect of such lesions on the estrous cycle 

 of guinea pigs. Loss of cyclical phenomena and genital 

 atrophy were found to follow lesions at the junction of 

 the hypothalamus and pituitary stalk. Sexual atrophy 

 in association with lesions of the tuber cinereum has 

 Ijcen observed in rats (35, 174, 233, 240), dogs (26), 

 rabbits (322) and cats (206). The production of 

 gonadal atrophy however, may not be a highly sig- 

 nificant response in \'iew of the fact that dietary 

 deficiency, metabolic upset and other general dis- 

 turbances could possibly give rise to the same phenom- 

 ena, indirectly. 



A state of persistent estrus after the placement of 

 hypothalamic lesions has been reported in the guinea 

 pig and rat (3, 4, 18, 78, 132, 179). Most authors agree 

 the effectiv-e site for the production of this effect, viz. 

 the abolition of the rhythmic release of LH and the 

 constant secretion of FSH, lies behind the optic 

 chiasma in the region of the paraventricular nuclei. 

 These results cannot be attributed simply to the de- 

 struction of an LH-controlling 'center', for Greer 

 (132) found that the injection of small daily doses of 

 progesterone was followed by a resumption of 4- to 

 6-day vaginal cycles. Similarly, electrical stimulation 

 or caging with a male may also be followed by a dies- 

 trous interval in such persistent estrous animals. 



A recent and striking finding has been the produc- 

 tion of FSH .secretion after placing lesions in the 

 anterior hypothalamus (83). In this study bilateral 

 lesions were placed behind the optic chiasma in female 

 ferrets at a time of year when the normal animal 

 would be anestrous. Within 3 to 7 weeks, 1 1 out of 

 18 animals were in full estrus. Since prolonged elec- 

 trical stimulation of the hypothalamus failed to elicit 

 the same result, the response is probably due to 

 destruction of a hypothalamic region which normally 

 exerts an inhibitory influence over FSH secretion. 

 These results seem in several wavs similar to those 



