releasing posterior pituitary liornione, results in 

 increased thyroid activity (especially in adrenalecto- 

 mized animals). 



c) Studies of neurosecretion. A possible relationship 

 of the neurohypophysis to ACTH release has been 

 discussed by workers studying the neurosecretory ma- 

 terial of the hypothalamus and posterior pituitary 

 gland. The fact that stimuli which evoke discharge of 

 ACTH also result in depletion of neurosecretory ma- 

 terial, and that neurosecretory material is closely 

 associated with posterior pituitary hormone, has sug- 

 gested to some workers (244, 254, 287, 303) that this 

 product of the hypothalamohypophysial tract is 

 liberated into the portal vessels and plays the part of a 

 humoral transmitter to the anterior pituitary to ex- 

 cite ACTH release. As mentioned abo\e, Benoit & 

 Assenmacher (22) also associate neurosecretory ma- 

 terial with the stimulus to the release of gonadotrophic 

 hormone. 



The evidence that neurosecretory material or 

 posterior pituitary hormone is concerned as an inter- 

 mediary in hypothalamic regulation of anterior pi- 

 tuitary activity is certainly incomplete and equivocal. 

 For example, the in vitro studies of Guillemin and of 

 Saffran quoted abo\-e show that highly purified prepa- 

 rations of posterior pituitary hormone are not active 

 in causing ACTH discharge. The fact that pitressin 

 is not active in the morphine-treated rat (247) and 

 the results of older studies discussed by Harris (158) 

 would argue against this interesting speculation. More 

 experimental data are clearly required. 



Control of Anterior Pituitary Activity 



GENERAL PICTURE OF RECIPROCAL RELATIONS BETWEEN 

 CENTRAL NERVOUS SYSTEM AND ENDOCRINE SYSTEM. 



The central nervous system and the endocrine system 

 are related in a reciprocal fashion (fig. 4). There are 

 many data which indicate that the nervous system 

 regulates the activity of the adenohypophysis and 

 neurohypophysis, and there can be little doubt that 

 the anterior pituitary gland is in turn the major factor 

 responsible for the activity of the testes, ovaries, 

 thyroid and adrenal cortex. On the other hand there 

 is also much evidence of the reverse reaction, that the 

 hormonal secretion of the anterior pituitary target 

 glands react back on to the central nervous system. 

 Two types of effects appear to be mediated. First, to 

 take for example the ovaries, it is well known that a 

 rise in the blood concentration of o\arian hormones 

 exerts an effect, probably on the nervous system, 

 which results in a decreased secretion of gonado- 



CENTRAL CONTROL OF PITUITARY' SECRETION I0I5 



EXT, ENVIRONMENT 



BEHAVIORAL 



RESPONSES 



FIG. 4. To illustrate the reciprocal relationship between the 

 central nervous system and endocrine system. The central 

 nervous system mediates the effects of environmental changes, 

 and exerts a regulatory influence over the anterior pituitary 

 gland, which in turn controls the ovary, testis, thyroid and 

 adrenal corte.x. The hormones from the latter glands in turn 

 'feed back' to the central nervous system and pituitary gland 

 to influence a) the behavior of the animal and b) the activity 

 of the anterior pituitary. 



trophic hormone. In this way a type of feed-back 

 mechanism exists, maintaining the pituitary-o\arian 

 activity at a constant level. Second, changes in the 

 blood concentration of the target organ hormones 

 affect the nervous system and thereby overt patterns 

 of behavior. The complicated pattern of courtship, 

 coital and after-play responses of the estrous or 

 estrogenized female cat may be cited (see 14). The 

 effect of varying blood concentration of gonadal 

 hormones on reproductive behavior is dealt with in 

 Chapter XLIX by Sawyer on this subject. 



In considering the part played by the central 

 nervous system in maintaining (under constant en- 

 vironmental conditions) and regulating (under condi- 

 tions of changing environment) the activity of the 

 gonads, thyroid and adrenal cortex, it is necessary to 

 know the activity of the endocrine system at different 

 'levels': a) the autonomous activity of the gonads, 

 thyroid and adrenal cortex in the hypophysectomized 

 animal; and h) the activity of the gonads, thyroid and 

 adrenal cortex when anterior pituitary function is 

 autonomous, i.e. the gland is present but i.solated 

 from the central nervous .system (by pituitary stalk 

 section or pituitary transplantation). 



With this background of information it is then 



