1.25-Dihydroxyvitamin D3 receptor is partly colocalized with oxytocin immunoreactivity in neurons of the male rat hypothalamus.

With receptor immunocytochemistry, neurons receptive for the steroidhormone 1.25-dihydroxyvitamin D3 have been observed in hypothalamic nuclei. In the present paper we report that a fraction of 1.25-dihydroxyvitamin D3 receptor (VDR) immunoreactive neurons in the hypothalamus of male rats are immunoreactive for oxytocin (OT), suggesting a direct genomic action of this steroid on OT expression. While only 10% of neurons with OT immunofluorescence in the periventricular nucleus contained nuclear VDR immunostaining, up to 50% of the OT neurons in the supraoptic nucleus and 30% in the magnocellular portion of the paraventricular nucleus were VDR positive. VDR immunostaining in the magnocellular nuclei was in many cases confined to the perinuclear cytoplasm. We assume that 1.25-dihydroxyvitamin D3 has effects on hypothalamic peptidergic systems similar to other steroid hormones.