I03O 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



:a^^ 



FIG. 8. To illustrate the main innervation of the neurohy- 

 pophysis, derived from the supraoptic and paraventricular 

 nuclei of the hypothalamus. The neurohypophysis (.\.H.) con- 

 sists of the median eminence {M.E.), the infundibular stem 

 il.S.) and the infundibular process (I. P.). Section of the supra- 

 opticohypophysial tract at B leaves a part of the gland still 

 innervated and may not result in signs of deficiency, whereas 

 section of the tract at A causes atrophy and loss of function of 

 the whole gland. 



(272). A detailed description and a comprehensive 

 list of early references (up to 1938) dealing with this 

 subject may be found in the monograph of Fisher 

 et al. (100). The hypothalamohypophysial tract, which 

 includes all nerve fibers running from the hypothala- 

 mus into the neurohypophysis, may be subdivided 

 into the important supraopticohypophysial tract run- 

 ning in the anterior or ventral wall of the stalk, and a 

 tract about which very little is known, the tubero- 

 hypophysial tract, running in the posterior or dorsal 

 wall of the stalk. The supraopticohypophysial tract 

 can be seen in good microscopic preparations to take 

 origin from the cells of the paraventricular and supra- 

 optic nuclei, and to collect in a definite bundle of 

 fibers [about 10,000 fibers in the rat, 60,000 in the 

 dog and 100,000 in man, according to Rasmussen 

 (275)] in the median eminence, most of wliich pass 

 through the infundibular stem to the neural lobe. The 

 histological termination of these fibers, in all three 

 parts of the neurohypophysis, is obscure although it 

 appears significant that perivascular endings have 

 l)een described as common, especially in certain 

 forms (where they are easy to visualize) such as the 

 opossum (34, 125). 



Section of the supraopticohypophysial tract in the 

 region of the infundibular stem {B in fig. 8) has been 

 shown (100, 215) to result in atrophy and hyper- 



cellularity of the neural lobe and a loss of nerve fibers 

 and of pressor, antidiuretic and oxytocic substances 

 in the denervated gland. The upper end of the stalk 

 and median eminence, howev'er, show an increase in 

 volume (24, 27, 50, 323) and an increase in Gomori 

 stainable material (27, 323). Further an increase in 

 extractable antidiuretic (213, 293) and oxytocic 

 substances (245) in the hypothalamus has been re- 

 ported. The.se data show that any part of the neuro- 

 hypophysis separated from its nerve supply undergoes 

 atrophy and loss of function. If the upper end of the 

 stalk or median eminence is left innervated, some 

 process of reorganization, and return of function, may 

 occur. However, there is little evidence of any residual 

 neurohypophysial activity if the supraopticohypoph- 

 ysial tract is interrupted above the level of the 

 median eminence {A in fig. 8). 



Nervous Refliw Mudificatums of .\etuohypoph\sial Activity 



In the following discussion the phrase 'neurohy- 

 pophysial activity' will be taken to mean the rate of 

 release of hormones from the neurohypophysis into 

 the blood stream. The hypothalamus may be said to 

 be related to neurohypophysial activity in the follow- 

 ing ways. 



.7) The activity of the gland seems entirely de- 

 pendent on its connections with the hypothalamus. 



h) Changes in the 'milieu interieur,' especially 

 changes in the osmotic pressure of the blood, may 

 affect the activity of the gland profoundly through 

 the intermediation of the hypothalamus. 



f) Changes in the external environment, particu- 

 larly those giving rise to stimulation of the repro- 

 ductive organs (nipples and external genitalia) and 

 those calculated to give rise to emotional excitement, 

 also affect the activity of the gland through nervous 

 reflexes acting \ia the hypothalamus. 



REFLEX CONTROL OF .-ANTIDIURETIC HORMONE (."KDh) 



SECRETION. The relationship between hypothalamic 

 lesions and diabetes insipidus was first clarified by 

 the studies of Fisher et al. (100). These workers used 

 the Horsley-Clark sterotaxic apparatus to make small 

 localized electrolytic lesions in the hypothalamus of 

 the cat and found that bilateral lesions in the course 

 of the supraopticohypophysial tract, but in no other 

 hvpothalamic sites, resulted in a condition similar to 

 that of clinical diabetes insipidus. They described the 

 typical phases of onset of the diabetes and gave a de- 

 tailed description of the histological findings in the 

 hypothalamus and pituitary gland of their animals. 



