NEUROSECRETION 



1047 



neurosecretory material in winter months and deple- 

 tion in the summer. Earlier arousal of these species 

 from the hibernating state leads to a more rapid 

 depletion of the neurosecretory material (24). Species 

 which do not remain in constant hibernation exhibit 

 no variations with respect to the supraopticohypophy- 

 seal tract (22). Experimental hypothermia in dogs 

 leads to no apparent changes in the neurosecretory 

 material. In the chicken, much \'ariation in the 

 amount of neurosecretory inaterial was observed at 

 the time of ovulation as well as during nesting, w'ith 

 a particularly interesting differential response of the 

 paraventricular and supraoptic nuclei (195). 



ONTOGENY. The embryological maturation of neurons 

 of the hypothalamoneurohypophy.seal system is com- 

 pleted relatively late and partly only after birth (263). 

 Although there is considerable species variation with 

 respect to the initial appearance of neurosecretory 

 material, it is generally observed first in the posterior 

 lobe or simultaneously in the posterior lobe and in 

 the hypothalamic nuclei and appears along the fiber 

 tracts only at a much later tiine. In the chicken, it 

 appears simultaneously in the supraoptic nucleus 

 and the posterior lobe on the 14th day of incubation, 

 with the paraventricular nucleus exhibiting material 

 several days later (139, 340, 341). Another report 

 (226) suggests a considerably earlier appearance of 

 the neurosecretory material in the chicken. In the 

 European Water Snake, neurosecretory material is 

 demonstrated first in the posterior lobe 3 days before 

 hatching, but not until 14 days after hatching in the 

 supraoptic nucleus (164). A similar situation is ob- 

 served in Tinea (163). Mammals exhibit little neuro- 

 secretory material at birth (29, 42, 79, 84, 134, 263, 

 284). 



HISTOCHEMISTRY. Treatment of unfixed tissues with 

 alcoholic solutions or fat solvents for i 2 hours depletes 

 completely the stainable neurosecretory material with- 

 out removing the biologically acti\e posterior lobe 

 hormones (171). Extraction by these methods removes 

 also those materials which give positive reactions for 

 sulfhydryl groups (35). The solubility properties of 

 the material extractable from the subcommissural 

 organ appear to be fundamentally different (36, 340). 

 After evaporation of the solvents, the granular nature 

 of the extracted neurosecretory material is maintained 

 (293) as well as its usual staining characteristics 

 (164). From these observations, it would appear un- 

 likely that the neurosecretor>- material can identify 

 or represent the hormone content of these tissues. 



Sloper (300), howe\er, has criticized the extraction 

 methods used in those experiments which are claimed 

 to demonstrate the differential solubilitv of neuro- 

 secretory material and the posterior lobe hormones. 

 His observations indicate that lipids do not form an 

 essential component of the neurosecretory material 

 but that they probably play a role in binding the 

 neurosecretory material to other tissue constituents. 

 The relationship between the posterior lobe hormones 

 and neurosecretory material awaits further elucida- 

 tion. It was the subject of discussion by Acher (i) at 

 a recent symposium. 



Using the McManus periodic acid stain, Sudan 

 black. Baker's acid hematin test, as well as the Millon 

 protein reagent, Schiebler (293) came to believe the 

 neurosecretory material to be a glycolipoid-protein 

 complex. Sloper (300) feels that the carbohydrate-fat 

 component is not an essential part of the neurosecre- 

 tory material. The intensity of the McManus reaction 

 is relatively weak in comparison to that exhibited by 

 the colloid of the anterior and intermediate lobes 

 and the basophils of the anterior and posterior lobe 

 (25, 222). Ribonucleic acids do not constitute a 

 significant component of the protein portion of the 

 neurosecretory material in \iew of the fact that no 

 changes are observed after treatment with ribo- 

 nuclease (237, 293J. Trypsin on the other hand 

 destroys the neurosecretory material within 3 hours 

 (300). Periodic acid cannot be substituted for potas- 

 sium permanganate in the oxidation step of the 

 chromhematoxylin staining method (293). It is be- 

 lieved that the presence of reactiv-e aldehyde and 

 sulfhydryl groups makes possible the key steps in the 

 chromhematoxylin and aldehyde-fuchsin staining pro- 

 cedures (i 17). 



In almost all cases the staining methods for sulfhy- 

 dryl groups yield results parallel to those obtained 

 with the usual staining procedures (35). After dehy- 

 dration, for example, reactions for sulfhydryl groups 

 diminish, paralleling the depletion of the neurosecre- 

 tory material, while remaining unaffected in other 

 areas of the nervous system. Another reaction for 

 sulfh\dryl groups, alcean blue following oxidation 

 with performic acid (4, 5), is not destroyed after 24 

 hours of extraction of ti-ssues in hot chloroform- 

 methanol. The staining in this case depends upon the 

 oxidation of sulfhydryl groups to sulfonic acid groups, 

 and in view of the fact that oxytocin contains ig per 

 cent cystein, this reaction may be almost specific for 

 posterior lobe hormones. The sensitivity of neuro- 

 secretory material to tryptic digestion, together with 

 the fact that its staining properties are lost after 



