DEVELOPMENT OF THE HYPOTHALAMIC VASOPRESSIN SYSTEM AND NEPHRONS IN MERIONES SHAWI DURING ONTOGENY

This study has evaluated the development of the hypothalamic vasopress in system and nephrons of the kidney in desert rodents, Meriones shawl , which effectively retain water by excretion of highly concentrated u rine. The vasopressin system was studied immunocytochemically at the 1 8th fetal day, at the 2nd, 13th, 27th postnatal days and in adulthood. The kidneys were investigated at the 2nd, 13th postnatal days and in adulthood using microdissection technique. Occasional vasopressin-immu noreactive neurons were observed as early as the 18th fetal day, only in the paraventricular nucleus. From the 2nd postnatal day onwards, va sopressin neurons increased progressively in number, being mainly conc entrated in the supraoptic and paraventricular nuclei, as well as in t he ventral retrochiasmatic region. Transient neuronal populations were also observed at the 13th postnatal day in the lateral preoptic area and anterior hypothalamic nucleus. Apart from the neurons, the glandul ar cells of the tuberal lobe showed immunostaining from the 18th fetal day, the first age studied, until the 13th postnatal day. The fibers of differentiating vasopressin neurons grew towards the circumventricu lar/neurohemal organs, terminating in the organum vasculosum of the la mina terminalis and the lateral ventricles as early as the 18th fetal day, as well as the third ventricle, the posterior lobe and the extern al zone of the median eminence between the 2nd and 13th postnatal days . The kidney in 2-day-old Meriones comprised nephrons at different sta ges of development from an S-shaped body to well-differentiated nephro ns. At the 13th postnatal day, as in adulthood, the nephrons were well differentiated and characterized by long, thin loops descending to di fferent levels of papilla. Thus, according to our morphological data t he hypothalamic vasopressin neurons and nephrons in the kidney of Meri ones reach the definitive state by the end of the 2nd postnatal week.