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HANDBOOK OF PH\-S10L0GV 



NEUROPHYSIOLOGY II 



this part of the hypothalamus and Jewel (89) has 

 described neurons in the supraoptic nuclei which 

 contain large vesicles, the contents of which are not 

 known. However, one questions whether tlie existence 

 of such osmoreceptors is necessary if these neurons 

 resemble functionally those of the respiratory mech- 

 anism in the medulla in being sensitive to changes in 

 the ambient fluids. There is also evidence that the 

 activities of the supraopticohypophysial system may 

 be modified by nervous means. In the stress produced 

 by noxious stimulation there is an increased produc- 

 tion of antidiuretic hormone (120), and it is very likely 

 that its production and release may be modified by 

 psychic influences. 



The paraventricular nucleus has recently been 

 associated with the production of oxytocin by Olive- 

 crona (127). After bilateral destruction of the para- 

 ventricular nuclei in rats by small lesions no oxytocin 

 was produced. These lesions had no effect on the 

 production of vasopressin nor on the thyrotrophic 

 and adrenotrophic activities of the anterior lobe. 

 That the oxytocin also proceeds along the nerve 

 fibers into the posterior lobe is indicated by the 

 findings of Moreno et al. (123) who found that ex- 

 tracts of the tuber cinereum made soon after hypo- 

 physectomy in rats showed oxytocic potency twice as 

 high as that observed in tuber extracts of animals 

 hypophysectomized after being killed. 



b) Anterior Lobe. The neural control of the anterior 

 lobe of the pituitary has provided the subject matter 

 for a fascinating current chapter in neuroendocrine 

 physiology. This subject has been reviewed recently 

 by Harris (70), Fields et al. (50), Benoit & Assen- 

 macher (22), Hume & Wittenstein (81 ) and is 

 discussed in Chapter XXXIX of this work by Harris. 

 However, for the sake of completeness a brief com- 

 ment on this relationship will be included here. 

 It is well known that massive lesions of the hypo- 

 thalamus tend to depress general anterior lobe 

 functions. More discrete lesions in lower animals 

 produce changes in the sex cycle. Thus lesions in the 

 anterior region may be followed by prolonged cycles 

 or even constant estrus, while posterior lesions abolish 

 the cycles. In animals which ovulate only after copu- 

 lation, lesions of the pituitary stalk or of the tuber 

 cinereum prevent ovulation. Apparently the neuro- 

 mechanisms producing ovulation in tliese forms 

 work through the hypothalamus. The route by which 

 the anterior lolje could be affected by these pro- 

 cedures poses a troublesome question because prac- 

 tically no nerve fibers pass from the hypothalamus to 

 the anterior lobe. There is, however, good evidence 



for the existence of a venous portal system through 

 which hormone-like chemicals released into the 

 l>lood by iiypothalamic secretory neurons may be 

 brought into contact with anterior lobe cells (66, 

 175). While tlie primary blood supply of the hypo- 

 thalamus and that of the hypophysis are anatomically 

 distinct, the hypophysial arteries supply a capillary 

 network of the median eminence of the stalk of the 

 pituitary from which a system of veins is in turn 

 formed. These veins communicate eventually with the 

 sinusoids of the anterior lobe. In the neurosecretion 

 theory it is held that neurohumoral substances, pro- 

 duced by hypothalamic neurons and released from 

 the processes of these neurons, enter the blood of the 

 capillaries of the stalk and median eminence. After 

 passing through the portal channels, they exert 

 direct chemical effects tipon the gland cells of the 

 anterior lolje. These humoral substances, which 

 apparently are adrenergic, when released in suffi- 

 cient quantities into the portal blood stream are thus 

 proposed to induce the formation or release of ap- 

 propriate anterior lobe hormones. 



While much evidence exists for the neural regula- 

 tion of both gonadal and adrenocortical functions of 

 the pituitary, it remains to be seen whether other 

 hypophysial activities may also be influenced by the 

 hypothalamus. Thus we may ask if excessive anterior 

 lobe secretion may be so produced by neurohumoral 

 stimuli that diabetes mellitus, acromegaly, gigantism, 

 hyperthyroidism and exophthalamos can result. In 

 this connection, it should be recalled that thyroid 

 activation by cold is brought al:)out through hypo- 

 thalamicohypophysial activity. Thus lesions in the 

 anterior part of the hypothalamus in rats depress the 

 thyrotrophic function of the anterior lobe, and it has 

 already been mentioned that such lesions block the 

 thiouracil effect upon the thyroid (29). A curious 

 aside here is the fact that after such lesions there is a 

 remarkable increase in mitotic activity in the com- 

 pletely mysterious pars tuberalis of the pituitary. 



While considering lupothalamic-pituitary re- 

 lations carljohydrate metabolism should be men- 

 tioned. The important role of the anterior lobe as a 

 regulator of sugar metabolism needs no elaboration 

 here. While the participation of the hypothalamus 

 in such affairs has been somewhat uncertain, changes 

 in carbohydrate utilization ha\e been noted clini- 

 cally in many cases of hypothalamic disease; and 

 there is good evidence that in animals certain hypo- 

 thalamic lesions may alter the course of experimental 

 diabetes mellitus so that insulin requirement is re- 

 duced (43, 84). Lesions in the posterior part of the 



