Distribution of the nuclear receptor for vitamin D in female and male zebra finches, Taeniopygia guttata.

In this study, we describe the distribution of high affinity binding sites for 1,25(OH)₂-vitamin D₃(1,25-D₃) in the zebra finch (Taeniopygia guttata). Four hours following the injection of tritiated 1,25-D₃, binding of the steroid hormone was found primarily in the cell nuclei ofa variety of different organs. Neurons in numerous discrete regions of the forebrain were labeled. These forebrain regions included the nucleus accumbens, nucleus dorsomedialis posterior thalami, lobus parolfactorius,nucleus septalis lateralis and medialis, nucleus septalis,lamina medullaris dorsalis, nucleus striae terminalis,palaeostriatum augmentatum, and stratum griseum. The choroid plexuses, however, remained clear. Labeled cells were seen in several organs of the alimentary canal, in both the exocrine and the endocrine pancreas, in the proximal tubules of the kidney, in the spleen, in the bursa of Fabricius, and in the heart. The basal cells of the uropygial gland were also labeled. No specific retention was evident in the gonads of either sex. Vitamin D is thus bound by cells in systems with widely different functions. Since several of the labeled tissues are not primarily involved in calcium homeostasis, the data support the concept that vitamin D-soltriol is a steroid hormone that acts as a seasonal neuroendocrine regulator regulator and somatotrophic modulator.