Ontogeny of vasopressin and oxytocin binding sites in the brain of Wistar and Brattleboro rats as demonstrated by lightmicroscopical autoradiography.

Vasopressin (VP) and oxytocin (OT) binding sites were localized and quantified in the developing brain of the Wistar, heterozygous (Het) and homozygous (Hom) VP-deficient Brattleboro rat using an autoradiographical technique. VP binding sites could be demonstrated from prenatal day 20 onwards in the septum and in the lateral reticular nucleus. Between this and postnatal day 15, VP binding sites appeared in all other brain areas known to contain VP binding sites in adulthood. In the caudate putamen the regional distribution of VP binding changed during development, while in some areas, for instance, the dorsal hippocampus and post cingulate cortex, the concentration of binding sites increased early but decreased with age. Comparison of VP binding between Het and Hom rats showed significant differences in the lateral reticular nucleus during development. Moreover, at postnatal day 15 there was more VP binding in the anterior commissural and suprachiasmatic nucleus and less in the central amygdala, dorsal hippocampus and post cingulate cortex of the Hom rat. This study shows, for the first time, OT binding sites in the developing rat brain. There is a considerable overlap with VP binding in the brain, sometimes with the same developmental pattern, e.g. in the anterior olfactory nucleus and caudate putamen and sometimes with a later appearance, e.g. in the central amygdala and thalamic nuclei. However most areas with VP binding sites did not show OT binding. In some areas only OT binding sites were present, for instance in the islands of Calleja and ventromedial hypothalamus. Similar to some areas with VP binding, OT binding decreased between postnatal day 5 and 15 in the dorsal hippocampus and even completely disappeared in the parietal cortex. The existence of VP binding sites in the Hom rat, together with the only occasional relationship between the previously described ontogeny of VP and OT innervation of the brain and the presently described developmental course of binding sites, indicates that the early expression of binding sites is not initiated by endogenous ligand. However, the setting of the number of VP binding sites has probably been affected by the VP deficiency of the Hom Brattleboro rat.