[Morphometric-ultrastructural studies on the hypothalamo-hypophyseal system before and after milking in the cow]

By use of morphological-electronmicroscopical methods, the Nucleus supraopticus and Nucleus paraventricularis of an unmilked cow as well as the neruohypophysis' main-area of the Zona terminalis and Zona centralis of unmilked and milked cows were investigated. The elementary granules were classified on the basis of idfferent density of its fine-granular content, which covers more or less the also present microvesicles, in various significantly distinguished categories of granules: elementary granules with extremely osmiophilic content, elementary granules with microvesicles without osmiophilic content and elementary granules with osmiophilic centre. This elementary granules were formed in the Golgi complex of the neurons. The observed changes in the ultrastructure of the cows' neurohypophysis after the milk-stimulus - i.e. the decrease of the number of elementary granules, the loss of the electrodense content, its significant increase, and the heaving in sight of the microvesicles in this, and the increase of the number and also the size of the so-called "synaptic vesicles" - were interpreted as a morphological equivalent of the hormone(oxytocin)releasing connected with the stimulus. A hormone releasing by exocytosis has not been seen. The kind of the hormone releasing is discussed, also the origin of the so-called "synaptic vesicles" and the possible participation of the Golgi complex in the preparation of hormone-releasing substances.