1054 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



237, 261). Complete elucidation of the normal rela- 

 tive content of the individual posterior lobe hormones 

 in the different segments of the system (6, 1 68-1 71, 

 235> 3'5> 333) 2s well as their alteration under experi- 

 mental conditions (3, 172) requires further coopera- 

 tive research between the morphologists, chemists 

 and pharmacologists. A conclusion with respect to any 

 indi\idual posterior lobe hormone based upon content 

 of neurosecretory material must be drawn with 

 considerable caution. Although the hormones appear 

 to be secreted together even if not always in the same 

 relative proportion, it is important to note that con- 

 clusions based upon alteration in the content of 

 neurosecretory material represent only the sum of 

 the components of the posterior lobe hormones. 



In spite of one objection (87) it is evident that 

 parturition and lactation lead to changes in the 

 amount of neurosecretory material (21, 74, 212, 318). 

 No explanation is available for relations between 

 neurosecretory activity and reproductive behavior 



(193. 195. 198, 199. 217. 307> 338)- 



Reflex release of posterior lolje hormones leads to a 

 secretion of both oxytocin and antidiuretic hormone 

 (155, 230). Injections of hypertonic solutions into 

 the internal carotid lead to secretion of antidiuretic 

 hormone but also produce milk flow and increased 

 uterine motility through release of oxytocin. The 

 suckling stimulus produces an antidiuresis as well as 



FIG. 22. Capillary loops from the portal \essels projecting 

 upward into the central (<^^) and peripheral (P^) zones of 

 the wall of the infundibulum. PG, portal vessels draining into 

 the anterior lobe, VL. Injection preparation from Engelhardt. 

 X 90. [From Engelhardt (100).] 



milk ejection. Coitus leads to increased uterine 

 motility as well as simultaneous milk ejection and 

 antidiuresis. Electrical stimulation of the supraoptic 

 and paraventricular nuclei of the goat leads to 

 simultaneous release of antidiuretic hormone and 

 oxytocin (lo). Osmotic stimulation from the carotid 

 artery leads to increased electrical activity in the 

 supraoptic region (228). The observation of Pickford 

 (254) that acetylcholine injected into the carotid 

 artery leads to antidiuretic hormone secretion suggests 

 that stimulation of the cells of the supraoptic nucleus 

 occurs throughout chocinergic synapses. The role ol 

 neurosecretory pathways is further indicated h\ the 

 es'idence of thirst centers in the hypothalamus. By 

 microinjection of sodium chloride, by electrical stim- 

 ulation (in the goat) or by production of suitable 

 hypothalamic lesions in the dog (g-ii), specific 

 thirst centers can be demonstrated. The polydypsia 

 produced by these methods may be associated with 

 chanires in antidiuretic and oxytocic hormone or 

 with other nervous pathways leading to increased 

 diuresis (12). The relationship of the posterior lobe 

 and its hypothalamic connections to the condition 

 of diaf)etcs insipidus has been extensively investigated 

 (104, 105, 184, 263, 332). Chamorro and co-workers 

 (69, 70) succeeded in demonstrating the release of 

 antidiuretic iiormone and oxytocin after brief stimula- 

 tion with application of epinephrine solution to the 

 frontoparietal region of the cortex. Interestinsily, 

 hormone secretion was observed after this stimulus 

 even following hypophysectomy. 



Recent evidence suggests that neurosecretory ac- 

 ti\it\ of the supraoptic and paraventricular nuclei 

 mav be concerned in the control of ACTH release 

 and, therefore, in the control of adrenal cortical 

 function. Administration of adrenal cortical hormones 

 as well as adrenalectomy leads to evidence of in- 

 creased neurosecretory activity (28, 97, 187). Thirst 

 and sodium chloride treatment, while producing 

 heightened neurosecretory activity, lead also to mor- 

 phological changes in the adrenal cortex (77, 97). 



A humoral link between the hypothalamus and the 

 adenohypophysis tra\ersing the pituitary portal ves- 

 sels has iieen sought for some time. In the region of 

 the median eminence (figs. 22, 23), fibers of the 

 supraoptical hypophyseal tract assume an especially 

 close relationship to the primary plexus of the portal 

 vessels (29, 31, 35, 243, 284, 316). Stalk section as well 

 as appropriate lesions in this area has shown quite 

 clearly the significance of these portal vessels (46, 205, 

 206, 220). A transfer of stainable neurosecretory ma- 

 terial into the portal vessels has been observed histo- 



