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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



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FIG. 15. Correlation between content of neurosecretory ma- 

 terial and antidiuretic hormone in the posterior lobe following 

 water deprivation. In the upper figure is plotted the content of 

 neurosecretory material expressed as per cent of the mean con- 

 trol value set at 100 percent. [From Ortmann (237).] The lower 

 graph is plotted in the same manner, showing the content of 

 antidiuretic hormone. [From Hickey (162).] 



treatment with homogenates of liver, spleen, lung, 

 kidney and striated muscle, also suggests this conclu- 

 sion (45, 103). Numerous elements in the hypotha- 

 lamic nuclei concerned with neuro.secretory activity ex- 

 hibit pronounced phosphatase activity (26, 102, 292). 



EXPERIMENTAL STUDIES. Oil the basis of changes in the 

 histologically demonstrable neurosecretory activity, 

 several experimental procedures have contributed 

 importantly to an understanding of the functional 

 significance of this system. These have been: a) condi- 

 tions which lead to marked but usually reversible 

 depletion of the neurosecretory material and to 

 characteristic morphological changes in the consti- 

 tuent elements of this system (237); h) stalk section 

 experiments which yield information about the sites 

 of production and delivery of the neurosecretory 

 material (165); and c) the application of assay 

 methods for posterior lobe hormones under experi- 



mental conditions which have demonstrated clearly 

 the relationship between these and the neurosecretory 

 system (168-172, 343, 344). The basic premises 

 derived from these several methods of investigation 

 have been confirmed repeatedly and may be con- 

 sidered as definite and basic facts. Specific details of 

 notable studies will be enlarged upon in the following 

 paragraphs. 



Dehydration, thirst, overloading with .sodium chlo- 

 ride and heat have been proved to be the condition 

 for depletion of neurosecretory material (237). Similar 

 changes are produced by stress (264), adrenalectomy 

 (97), alloxan diabetes (189) and some drugs (55, 285). 

 Many workers have studied the.se conditions in widely 

 different species and by various methods (5, 16, 17, 

 26, 54, 82, 121, 134, 165, 172, 187, 188, 191, 199, 

 202, 234J. 



The effects of depletion of neurosecretory material 

 appear first in the posterior lobe (figs. 14, 15), with the 

 finely granular neurosecretory material disappearing 

 first. In spite of extensive depletion of the neurosecre- 

 tory material, .some Herring bodies in the hypotha- 

 lamic nuclei as well as in the posterior lobe may remain 

 unaffected for a considerable period of time (237). The 

 length of time required to deplete the neurosecretory 

 material varies considerably according to the species 

 investigated and the methods employed. Thirst pro- 

 duces this effect in the rat in 12 to 14 days and in the 

 dog in 7 to 14 days, while stress may deplete the 

 neurosecretory material in the rat within 10 min. 

 (17, 35). Concoinitant with depletion of the neuro- 

 .secretory material there occur the following changes 

 in tlie neuron cell body : nuclear enlargement (96, 

 173, 211), eccentric displacement of the nucleus, 

 enlargement of nucleoli (figs. 16, 17), dissolution of 

 the Nissl material and eventual degeneration of the 

 cell (fig. 16C). Mitotic activity of posterior lobe 

 pituicytes is pronounced in the rat (237) and frog 

 (165), but only minimal in the dog (172). Up to the 

 point of cell degeneration, all of these changes are 

 reversible. It should be pointed out that each of the.se 

 cellular changes is similar to the axon reaction and 

 may represent an increased nervous activity as well as 

 secretory activity of the cell. The fact that these cellu- 

 lar changes are reversible indicates also tliat the 

 occasional presence of degenerating cells is not to be 

 taken as an essential index of the status of secretory 

 activity. The length of tiine required for the complete 

 reaccumulation of the neurosecretory material is 

 generally longer than that required to cause the pre- 

 ceding depletion. Chronic administration of saline 

 drinking water leads to an increased content of neuro- 



