NEUROSECRETION 



•045 



microscopy (245) permit a distinct differentiation be- 

 tween neurosecretory granules and mitochondria on 

 the basis of density and structure. No final conclusion 

 with respect to functional significance can be drawn 

 from the close spatial relationship between mito- 

 chondria and neurosecretory material. Other electron- 

 microscopic observations (134) indicate that in the 

 region of the median eminence axons contain neuro- 

 secretory particles which are smaller than those found 

 in the posterior lobe and may represent maturation 

 stages. 



In many species, colloid droplets exhibiting aci- 

 dophilic staining properties (32, 37, 38, 289) as well 

 as an affinity for chromhematoxylin (33, 214) are 

 found in the cytoplasm and axons in addition to the 

 characteristic neurosecretory material (fig. 8). It is 

 noteworthy that although the colloid and granular 

 neurosecretory material may be stained with chrom- 

 hematoxylin, they exhibit significantly different 

 histochemical reactions (294). Vacuoles are present 

 also in the cytoplasm of neuro.secretory cells, but their 

 presence is so variable (164) that they may not rep- 

 resent a vital or functionally significant organelle 

 (131, 243). In spite of this great varialjility, however, 

 the presence of vacuoles in neurosecretory cells in both 

 vertebrates and invertebrates is so widespread that it 

 would seem their presence bears some relationship to 

 tlie function of these cells. Further investigation must 

 establish the significance of these vacuoles as well as 

 the large nonstaining vesicles observed in neuro- 

 secretory cells of the dog and wolf (29, 153, 332). The 

 latter may attain such size as to displace almost com- 

 pletely the nucleus (fig. 2) without seriously inter- 

 fering with the secretory performance of the cell (i 72) 

 or producing signs of cell degeneration. Verney (332) 

 interprets these large vesicles as osmoreceptors, but 



their isolated occurrence in only a few species argues 

 against this interpretation. Furthermore, experimental 

 evidence (85, 172, 177) indicates that this is a re- 

 versible phenomenon dependent upon the functional 

 status of the cell. The appearance and structure of the 

 chondriome and Golgi apparatus in neurosecretory 

 cells are similar to those observed in true glandular 

 tissue (223, 309). 



The functional status of neurosecretory cells is 

 clearly reflected by changes in nuclear size (96, loi, 

 173, 237) as well as changes in the nucleoli (167, 188, 

 237), measurements used extensively as indices of 

 cell activity (188, 224). In neurosecretory cells of 

 fishes, villus-like processes as well as deep incisions of 

 the nuclear membrane have been described (fig. 9) 

 similar to those observed in the nuclei of glandular 

 cells (238, 240, 281, 317). The delivery of small 

 segments of the nucleus to the cytoplasm has been 

 observed also in neurosecretory cells (163, 204, 238, 

 2B1, 296, 297), a fact suggesting a regular participa- 

 tion of the nucleus in the secretory activity of the 

 cell. The significance of this is further emphasized by 

 the fact that portions of these nuclear segments con- 

 tain a granular or colloid-like material (fig. 10) which 

 displays several of the staining reactions exhibited by 

 neurosecretory material (30, 164, 199, 238, 310). The 

 occasional presence of degenerating neurosecretory 

 cells has been verified (61, 143, 144, 150, 151, 166, 

 301), but the hypothesis of a physiological degenera- 

 tion of the cells as a necessary preliminary to synthesis 

 of the neurosecretorv material finds acceptance with 

 only a small number of in\'estigators (71, 142, 232, 



303. 314)- 



The a.xons of neurosecretory cells do not all end 



in the posterior lol:>e but terminate also in the pituitary 



stalk as well as in the median eminence. In fish and 



FIG. g. Neurons from the posteroventral portion of the pre- 

 optic nucleus of Cyprinus carpio. Akhough the cells appear to be 

 multinucleate, it can be shown that the several lobules are 

 continuous. Iron-hematoxylin. X 840. [From Ortmann (238).] 



FIG. 10. Neuron from the preoptic nucleus ol Cyprinus carpio, 

 showing a large nuclear inclusion. The cytoplasmic neuro- 

 secretory material and the granular part of the nuclear inclu- 

 sion are stained with paraldehyde-fuchsin while the nucleolus 

 is unstained. Paraldehyde-fuchsin. X 875. 



FIG. 1 1 . Section of the pituitary of the cat, with the posterior 

 lobe darkly stained with paraldehyde-fuchsin while the inter- 

 mediate and anterior lobes are almost colorless. The darkly- 

 staining objects centrally located in the posterior lobe are 

 Herring bodies. Note the accumulation of neurosecretory 

 material around the blood \'essels. 



FIG. 12. Diagrammatic section of the posterior lobe of the 

 opossum. The lobe is subdivided into numerous compartments 

 by connective tissue septa along which the nerve terminations 



and blood vessels are in intimate contact. Nerve fibers of the 

 hypophyseal tract (F), pituicyte cell bodies and three Herring 

 bodies (HB) are shown in the hilum of the lobule {lower right). 

 Surrounding this, the palisade zone iP) is seen to be formed by 

 nerve fiber terminations coated with a rod-like formation of 

 neurosecretory substance. Interspersed are pituicyte fibers 

 (PIT) which extend to the vascular -collagenous septal layer 

 (S). An axon (.4.V) about to form endings coated with neuro- 

 secretory substance is also visible. [From Bodian (55).] 



FIG. 13. Capillaries in the neural lobe of the giraflfe with 

 numerous colloid droplets stained bright red with azan. [From 

 Hanstrom (149).] 



FIG. 14. Rat pituitary, showing a normal content of neuro- 

 secretory material in the posterior lobe (lefl) and its depletion 

 after 14 days of water deprivation (right). Note the changes in 

 size and structure in the depleted organ. Chromhematoxylin. 

 X 50. 



