224 



HYPOPHYSIS AND GOXADOTROPHIC HORMONES 



tricular nuclei have the same function as 

 the supraoptic nuclei, being spatially sepa- 

 rated parts of the same functional unit. 



The organ responsible for neurohypo- 

 physeal secretion is thus more extensive 

 than the neurohypophysis. It includes in 

 addition the supraoptic and paraventricular 

 nuclei and their tracts. Functionally we 

 may distinguish four separate regions in 

 this hypothalamo-neurohypophyseal sys- 

 tem. The first region contains the supra- 

 optic and paraventricular nuclei in which 

 the neurohypophyseal secretion is elabo- 

 rated. The second contains the paraven- 

 triculo- and supraoptico-hypophyseal tracts 

 which serve two functions, the conduction 

 of nerve impulses and the physical trans- 

 port of neurohypophyseal secretion into the 

 neurohypophysis. The third region is the 

 tissue of the neural eminence, neural stalk, 

 and in some species a portion of the neural 

 lobe, which are in this account referred to 

 collectively as the pars eminens. In this 

 tissue some of the axons terminate, usually 

 in relation to blood vessels (Scharrer and 

 Scharrer, 1954; Scharrer, 1954) and medi- 

 ate a secretory activity which could by vir- 

 tue of the vascular link between this region 

 and the pars anterior or pars distalis, mod- 

 ify the function of the adenohypophysis. 

 In some amphibia a very considerable pro- 

 portion of the preopticoneurohypophyseal 

 fibers end in this region (Dawson, 1957). 

 In this region there are also nerve fibers 

 from the general area of the medial fore- 

 brain bundle and fibers from the lateral 

 tuberal area (Green, 1951, 1956; Bargmann, 

 1954). The fourth division of the hypo- 

 thalamo-neurohy])ophyseal system is the 

 pars nervosa which in mammals contains 

 most of the nerve fiber terminations of the 

 neuroiiypophyseal tract and most of the 

 stored secretion. It is also the major site of 

 the release of the characteristic hormones 

 which pass from it by way of systemic veins 

 directly into the systemic circulation with- 

 out contact with the pars anterior or pars 

 distalis. 



The early investigators assumed not un- 

 naturally that the pars nervosa was the site 

 of elal)oration of the hormones which were 

 secreted from it. It is obvious that there 

 must be something unique about the nerve 



fibers or the glial cells, or else some unique 

 structural element must be present to ac- 

 count for the secretory function. Herring 

 (1908) considered that the cells present 

 were ordinary glial cells and did not note 

 any peculiarity of the axons other than 

 that they were of larger caliber than non- 

 medullated fibers elsewhere. He, however, 

 did discover some peculiar masses of protein 

 without any definite structure. These bodies 

 were only found in well fixed material and 

 although they did not look to be likely sites 

 for the formation of hormones attention was 

 focused on them by the fact that they were 

 peculiar to this gland. 



Bucy (1930) found that these Herring 

 bodies were in fact large end bulbs terminat- 

 ing some of the fibers of the neurohy- 

 pophyseal tract. In these end bulbs the 

 fibers were wound about like a ball of twine. 



Bodian (1951) confirmed this explanation 

 of Herring bodies and considered that they 

 are terminal malformations, negligible in 

 number compared with normal endings. 



Bucy (1930) and Weaver and Bucy 

 (1940) claimed that the neurohypophysis 

 contained cells which were peculiar in their 

 morphology and staining reactions and were 

 found nowhere else in the nervous system. 

 For these cells the term "pituicyte" was 

 proposed. For a time the pituicytes con- 

 tended with the Herring bodies and the 

 nerve fibers for the responsibility for the 

 production of the neurohypophyseal hor- 

 mones. As objects to be studied they were 

 certainly more promising in appearance 

 than the nerve fibers, but it cannot be said 

 that the studies of pituicytes have con- 

 tributed to the elucidation of either neuro- 

 hypophyseal or pituicyte function. The sta- 

 tus of the pituicyte as a cell peculiar to 

 the neurohypophysis is at the present time 

 doubtful. Some investigators (Romeis, 1940; 

 Slopcr. 19571 have stressed the great diver- 

 sity of c(^ll types which can be found in the 

 neurohypophysis, but this does not disi)ose 

 of the i)ituicyte of Bucy. Leveque and 

 Scharrer (1953) considered the existence of 

 a cell specific to the neurohypophysis un- 

 |)i'o\-cn. 



ilild ( I95(). in discussion I considcri'd tliat 

 there are no consistent morphologic difTer- 

 cnces between the glia of the neurohy- 



