1046 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



amphibia, as well as in mammals, an unbranched 

 neuron may pass directly to the ependyma of the 

 third ventricle in the area of its nucleus of origin or 

 as far as the ventricular surface of the infundibulum 

 and deliver neurosecretory material into the ventricu- 

 lar fluid (29, 39, 73, 163, 164, 214, 231, 243, 282). 

 This phenomenon has been characterized as hy- 

 drencephalocrinie and may take the form of a holo- 

 crine secretion. This release of neurosecretory material 

 into the third ventricle parallels the secretory activity 

 in the rest of the system (164, 198), although no known 

 significance can be attached to this phenomenon at 

 present. Knowledge of the further fate of this material 

 has been obtained by the demonstration of the neuro- 

 secretory material and antidiuretic substances in the 

 plexus of the third ventricle (329). The typical ter- 

 mination in the wall of the infundibulum and in the 

 posterior lobe is the Herring body with its inner and 

 outer zones as described above (figs. 4, 5). The identi- 

 fication of these Herring bodies as degenerating cells 

 or as cytoplasmic fragments with degenerating nuclei 

 (141, 143, 144) is refuted by most investigators (32, 

 61, 134, 149, 151, 172, 243, 265). The question of 

 whether neurosecretory material is deposited and is 

 present in the interstitial space of the posterior lobe 

 (that is outside the nerve fibers and their terminations) 

 cannot be answered with certainty (fig. 1 1) (164). The 

 problem cannot be resolved with light microscopy, 

 while electronmicroscopic observations indicate that 

 the neurosecretory material is restricted to the nerve 

 terminations (34, 89, 244) or that it is present outside 

 of them also (135, 139). The relationship of the pos- 

 terior lobe pituicytes to the neurosecretory material 

 has to date not been clearly defined by either light 

 or electronmicroscopy nor by transplantation experi- 

 ments. Notable amounts of neurosecretory material 

 do not appear to be present in the pituicytes (89, 203). 

 In the case of experimentally altered neurosecretory 

 activity, the pituicytes do exhibit changes such as 

 mitotic activity, changes in cell size, appearance of 

 vacuoles, etc., which may indicate some functional 

 relationship to this activity but which as yet do not 

 define any specific role (165, 189, 237). A model of 

 our conception of the nerve terminations of neuro- 

 secretory fibers is seen in the posterior lobe of the 

 opossum where these structures are arranged in 

 palisades closely associated with the capillaries in 

 the connective tissuesepta (55)( fig. 12). Green & van 

 Breemen (134) hold that other tissue elements par- 

 ticipate in the formation of these palisades. Bargmann 

 (32) has confirmed the observation of Bodian that 

 each nerve termination is surrounded bv an accumu- 



lation of neurosecretory material. This palisade 

 structure and the associated neurosecretory material 

 is seen with some variation in other species also (32). 



The direct transfer of neurosecretory material into 

 the capillaries of the posterior lobe (fig. 13) has been 

 described in several species (21, 148, 149, 285) and 

 is observed readily, under experimental conditions, 

 evoking a strong release of neurosecretory material 

 (197). Electronmicroscopic studies in normal dogs 

 could not establish the fact that neurosecretory ma- 

 terial may penetrate the boundary between the nerve 

 terminations and the perivascular spaces of the cap- 

 illaries of the posterior lobe. The absence of a blood- 

 brain barrier in the 'contact zones' (Spatz) of the 

 posterior lobe, its stalk and the median eminence 

 permits an unimpeded exchange of vital dyes and 

 enzyme-reactive substances between blood and 

 nervous system (239). The ease with which materials 

 may be transferred from the blood vessels into the 

 tissues in these areas makes it easier to accept the 

 possibility of a transfer of substances (neurosecretory 

 material) in the reverse direction (244). Of some im- 

 portance is the consideration that neurosecretory 

 material does not appear to be released from the 

 nerve cell bodies into the capillary beds of the hypo- 

 thalamic nuclei. Besides the fact that neurosecretory 

 material has seldom been observed in the endothelium 

 of the capillary bed (63), most of the experimental 

 evidence speaks against the possibility of a depletion 

 of the neurosecretory material in the region of the 

 hypothalamic nuclei (165, 224, 237). In this connec- 

 tion there still remain unexplained the numerous 

 observations that nerve fibers filled with neurosecre- 

 tory material are present in the intermediate lobe 

 (30, 32. 78, 98, 150. '5'. 164, 233, 339) as well as in 

 the anterior lobe (76, 233). 



Increasing numbers of observations indicate that 

 neurosecretory fibers of the hypothalamus may termi- 

 nate in other areas of the central nervous system (8, 

 40, 81, 125, 164, 283). In the bat, five such areas 

 have been described, including the amygdala, septal 

 region and mesencephalon. In the mouse, termina- 

 tion have been observed in the wall of the lateral 

 ventricles (39, 40), with similar findings being de- 

 scribed in fish, amphibia, reptiles and birds (193, 

 194). No explanation is available for the function of 

 these instances of 'neurocrinie de substances neuro- 

 secretoires" (39). In animals treated with sugar an 

 increased staining of these pathways was shown (194). 

 Seasonal variations in the appearance of the supra- 

 opticohypophyseal system is particularly clear in the 

 true hibcrnators (23, 24, 320), with storage of the 



