NEUROSECRETION 



!043 



four following methods: a) chromhematoxyliii-phloxin 

 stain according to Gomori (127) introduced first by 

 Bargmann (29) for the demonstration of neurosecre- 

 tory material, the counterstaining with azophloxin 

 here being of no importance (fig. 2); b) the paralde- 

 hyde-fuchsin stain according to Halmi (145), stand- 

 ardized and considerably improved by Gabe (109, 

 fig. 10); c) a series of histochemical methods for the 

 demonstration of sulfhydryl groups (4, 3, 35); and d) 

 the technique of phosphomolybdic acid-congo red 

 staining after formalin fixation (300). 



A definite oxidation step is an essential prerequisite 

 for the success of the staining methods a to c (292), 

 while the congo red method is intensified through a 

 reduction in thioglycolic acid. Furthermore, the 

 staining is dependent upon the interval of time be- 

 tween death and fixation of the tissue (171) as well as 

 the use of definite fixing solutions (Bouin, Helly and 

 Susa fixatives are recommended while alcoholic 

 solutions are contraindicated). With all four methods 

 there is demonstrated a granular intracellular secre- 

 tory material which corresponds in amount and posi- 

 tion to material observed in unfi.xed preparations 

 examined with phase microscopy and darkfield (245, 

 288). Within the cell body the neurosecretory ma- 

 terial is centrally located in the region about the 

 nucleus (164, 242, 245, 317), while in the axon and its 

 terminations it is always situated superficialh'. The 

 perikaryon as well as the axon can exhibit irregular 

 bulbous enlargements on their surfaces, while axons 

 always show a thread-like central portion containing 

 much neuroplasmatic substance free of secretory ma- 

 terial (fig. 3). In any area of a nuclear group, in- 

 dividual cells may exhibit wide variations in content 

 of neurosecretory material (fig. 2). Occasionally, in 

 the perikaryon as well as along the axon there may 

 occur cytoplasmic swellings. Herring bodies, which ex- 

 hibit a granular outer zone and a granule-free inner 

 area (fig. 4). They are demonstrated (151) with 

 special clarity in Callilhrix [Hapale) (fig. 5). Where the 

 fibers are less densely packed with neurosecretory ma- 

 terial, they are often observed as distinct beaded 

 threads (fig. 6). The amount of secretory material 

 observed varies according to species and to the region 

 of the system under investigation as well as its func- 



tional status. The posterior lobe (figs. 7, 11) always 

 exhibits the greatest amount of neurosecretory ma- 

 terial (24, 29, 84, 237). The demonstration and tracing 

 of the neurosecretory pathways may be especially 

 difficult in those forms (rodents) exhibiting little 

 neurosecretory material proximal to the region of the 

 tuber cinereum. 



The similar intracellular localization of the Nissl 

 material and the neurosecretory material, and the 

 general inverse relationship which exists with respect 

 to the relative content of these two substances (29, 

 164, 191), has led to the belief that the origin of the 

 neurosecretory material is closely associated with the 

 Nissl substance (286). Observations with phase con- 

 trast microscopy and embryological work do not 

 support a strict correlation between the Ni.ssl sub- 

 stance and the neurosecretory material (245, 340, 



341)- 



Differential centrifugation of beef pituitary homo- 

 genates has permitted accumulation of the neuro- 

 secretory material in a fraction with granules which 

 range in size from 1 50 to i .5 m (292 ), with the particles 

 having a tendency to aggregate in larger complexes. 

 Electroninicroscopic observ'ations of the neurosecre- 

 tory material in the posterior lobe in reptiles, birds 

 and mammals indicate that it consists of aggregates of 

 granules which exhibit a surprising homogeneity 

 with respect to size (too to 300 n) and density (34, 88, 

 89, 244). The range in size of these particles is ap- 

 proximately the same as that exhibited by mito- 

 chondria. The granules of the neurosecretory material 

 do not stain with Janus green (292). The fraction of 

 neurosecretory material obtained by centrifugation, 

 however, does exhibit distinct reactions for succinic 

 dehydrogenase, an enzyme considered to be associated 

 almost entirely with the mitochondria. This biochem- 

 ical determination correlates well with the histo- 

 chemical demonstration of a rich content of succinic 

 dehydrogenase in the posterior lobe of the white 

 mouse (Ortmann, unpublished observations; fig. 7). 

 To what extent the positive reactions oijtained in both 

 of these experiments are dependent upon the content 

 of sulfhydryl groups in neurosecretory material and 

 their reaction with formazan remains to be examined. 

 Electronmicroscopy (34, 88, 89) as well as phase 



and join its fibers in the tract to the pituitary. The streamlined 

 appearance of the Herring bodies in the left fiber corresponds to 

 the direction of flow of material. Fibers containing all degrees 

 of neurosecretory material are present. Chromhematoxylin- 

 phloxin. X 195. 



FIG. 7. Pituitary gland of the white mouse stained for the 



demonstration of succinic dehydrogenase. The enzyme activity 

 is localized in the posterior lobe. Technique according to 

 Ortmann (239). X 13. 



FIG. 8. Neurons from the supraoptic nucleus of the pigeon 

 with large cytoplasmic colloid inclusions. Chromhematoxy- 

 linphloxin. X 1150. [From Bargmann & Jacob (33).] 



