HYPOTHALAMICO-HYPOPHYSIAL SYSTEM AND ITS RELATION TO WATER BALANCE IN THE DOG

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Abstract
The neurohypophysis is innervated by fibers from the supraoptic and paraven-tricular nuclei. All the cells of the supraoptic nuclei and a high % of the cells of the rostro-ventral portion of the paraventricular nuclei degenerate on removal of all the neurohypophysis. The innervation of the median eminence is apparently uncrossed. Removal of the infundibular process results in the retrograde degeneration of 70-80% of the supraoptic nuclei. The cells of the paraventricular nuclei show little or no degeneration. Removal of the entire infundibular stem and the infundibular process results in retrograde degeneration of 80-85% of the cells of the supraoptic nuclei. Following interruption of the hypothalamico-hypophysial tracts, degeneration, as evidenced by paleness of staining and breaking up of the Nissl substance, begins at 10-14 days. For complete degeneration 45-60 days are required. Maximum and permanent diabetes insipidus follows the removal or the complete denervation of the entire neurohypophysis, resulting in retrograde degeneration of the entire supraoptic nuclei and the rostral ventral portions of the paraventricular nuclei. No nucleus caudal to the paraventricular nuclei contributes fibers to the neurohypophysis. Failure to interrupt the fibers of even 15% of the cells innervating the neurohypophysis will pervent the development of any permanent diabetes insipidus. Failure to interrupt 5% of these fibers will result in a diabetes insipidus of only 4-5 times the normal urine output, while this output is increased 10-20 fold with complete interruption. The normal interphase represents the time during which the denervated neurohypophysis produces pitressin. The adenohypophysis is not necessary for the development and maintenance of a permanent and maximum state of diabetes insipidus in the dog. Evidence is presented that infection in the region of the hypothalamus can prevent the manifestation of diabetes insipidus even in the absence of the entire neurohypophysis. The cells of the supraoptic and paraventricular nuclei do not secrete pitressin.