HYPOPHYSEAL MORPHOLOGY 



pophysis and astrocytic glia in any otlier 

 parts of the central nervous system. Cer- 

 tainly the pituicytes do not show any of 

 the features of secreting cells. Recent de- 

 velopments have made it clear that pitui- 

 cytes are in no way responsible for the 

 production or storage of neurohypophyseal 

 secretion and any role that may be ascribed 

 to them in facilitating the release of the 

 hormones into the circulation is purely 

 speculative. It seems unnecessary to assume 

 that their function is different from that of 

 similar glial cells elsewhere. 



The hormone activity of the neurohy- 

 pophysis is accounted for by two octapep- 

 tides, oxytocin and vasopressin. Both hor- 

 mones contain cystine. There is evidence 

 that in the glands they are combined with 

 a specific protein referred to as the van 

 Dyke protein (van Dyke, Chow, Greep and 

 Rothen, 1942) . This protein has a molecular 

 weight of approximately 30,000 and a strik- 

 ingly high content of cystine (approxi- 

 mately 16.0 per cent; the cystine content 

 of insulin is 12.0 per cent). 



The morphologic studies of the pars ner- 

 vosa which followed Bucy's designation of 

 l)ituicytes as specific cells peculiar to the 

 neurohypophysis did not contribute to the 

 elucidation of neurohypophyseal function. 

 The true explanation of the function of the 

 neurohypophysis resulted from studies on 

 neurosecretion which were proceeding con- 

 temporaneously with the pituicyte investi- 

 gations but were not, before 1949, considered 

 to be related directly to neurohypophyseal 

 secretion. 



"Neurosecretion" is a general term refer- 

 ring to the presence within certain neurons 

 of accumulations of products, usually pro- 

 teins, which are not common to the major- 

 ity of neurones. The first description of 

 8 secretion-containing nerve cells was that 

 by Speidel (1919) who described such cells 

 in the spinal cord of the skate. The further 

 development of the subject is amply re- 

 viewed by Scharrer and Scharrer (1940, 

 1945, 1954). Neurosecretory accumulations 

 in tb.e hypothalamus were first described in 

 the bony fish (Phoxiims laevis L.), and 

 further papers by the Scharrers extended 

 their occurrence to bony fishes generally, 

 amphibians, reptiles, mammals, and man. 



The term "neurosecretion" was first applied 

 by Scharrer in vertebrates, but it is a gen- 

 eral term including a wide variety of secre- 

 tory phenomena in vertebrate and inverte- 

 brate neurones. With the investigations on 

 neurosecretory material in invertebrates we 

 are not here concerned, and further dis- 

 cussion will be limited to the neurosecretory 

 material of certain neurones of the verte- 

 brate hypothalamus. 



Neurosecretion was first investigated by 

 nonspecific methods of staining, and the 

 evidence for the presence of a secretory 

 product in neurones was the accumulation 

 of protein material in large droplets and 

 vesicles often so large as to cause distortion 

 of the cell within which they were enclosed. 

 Investigations by Scharrer and Scharrer 

 (1940), disclosed a wide occurrence of such 

 gross accumulations of an unusual material 

 in neurones of the preoptic or supraoptic 

 and paraventricular nuclei of many verte- 

 brates, but the absence of any known func- 

 tion for this material was a retarding factor 

 in the development of the subject. More- 

 over, man}'- species did not appear to have 

 tliese neurosecretory droplets and in species 

 where they were found they were often 

 not observed in young animals but only in 

 those of older ages. These observations 

 seemed to make it unlikely that any es- 

 sential function was mediated by this ma- 

 terial. Palay (1943) was able to trace a 

 transport of neurosecretory material along 

 the axons of the preopticohypophyseal tract 

 in fishes, but with the staining methods then 

 in use it could not be shown that this was 

 a general phenomenon in all vertebrates. 

 This position has been entirely changed by 

 the development of more specific methods 

 for staining neurosecretion which permit its 

 identification, even in traces, by staining 

 methods which demonstrate the specific 

 quality of the protein instead of the earlier 

 method of recognition which depended on 

 the physical form assumed by gross col- 

 lections of the material. 



Bargmann (1949) found that Gomori's 

 (1941) method for staining the insulin-con- 

 taining granules of the ^-cells of the pan- 

 creatic islets also stained intensely the 

 accumulations of neurosecretory protein in 

 the vertebrate hypothalamus. The intro- 



