Morphology of the Neurosecretory System in Rats Homozygous and Heterozygous for Hypothalamic Diabetes Insipidus (Brattleboro Strain)

Abstract

Rats homozygous for hypothalamic diabetes insipidus (DI), which appear unable to synthesize arginine vasopressin, show marked hypertrophy in the hypothalamo -neurohypophysial system (HNS). The supraoptic nucleus and the paraventricular nucleus contain enlarged cells with hypertrophic nuclei and nucleoli, and axons with very little or no neurosecretory material (NSM). This dearth of NSM exists also in the nerve fibers of the HNS as they course through the median eminence. The pars nervosa of the pituitary gland is enlarged and shows extreme reduction of NSM, when compared to the normal. But isolated clusters of NSM remain, and these may represent oxytocin which DI rats can produce. Heterozygous rats possess hypothalamic and neurohypophysial features intermediate between the normal and DI conditions. The morphological findings in both DI and heterozygous rats suggest excessive activity of the system responsible for the production, storage and release of neurohypophysial principles.