[Structural characteristics of the hypothalamo-hypophyseal neurosecretory system in the field mouse (Arvicola terrestris)].

The structure of the hypothalamo-hypophysial neurosecretory system (HHNS) has been studied light optically in the Arvicola terrestris that possesses a specific reduction of the concentrating renal function. There are neurosecretory cells (NSC) with cytoplasmic vacuoles in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei that secrete antidiuretic hormone. These cells are situated mainly in the caudal part of the nucleus and, evidently, perform an osmoreceptory function. For the hypothalamic nuclei studied, characteristic are single cells with polyploid nuclei, their appearance is supposed to be connected with a necessity to intensity the processes of the neurohormonal synthesis. In the NSC, PVN and partly in the SON axons, as well as in the hypothalamo-hypophysial tract fibers and their terminals there is, together with the granular neurosecrete, the one having the form of large homogeneous colloid drops, which are, appearantly, some quickly restorted neurohormonal reserve when certain unfavourable conditions appear. These morphological peculiarities of the HHNS appear to be certain signs of an adaptive mechanism of the osmoregulatory system are species-specific, since the ecological specialization of the animals studied is connected with hyperhydratation conditions.