Distribution of stanniocalcin binding sites in the lamina terminalis of the rat

Stanniocalcin (STC-1), a 50 kDa glycoprotein hormone that regulates calcium/phosphate homeostasis in bony fish and mammals, has been shown to be expressed in central neurons and choroid plexus, and to exert a protective effect against hypercalcemic and hypoxic damage to neurons. Circumventricular organs are known to function in the regulation of ion and body fluid balance. Therefore, the possibility exists that STC-1 may be involved in the regulation of calcium/phosphate and fluid homeostasis through its actions on these central sites. In the present study, the distribution of STC-1 binding sites in forebrain circumventricular organs of the rat were investigated by in situ ligand binding using a stanniocalcin-alkaline phosphatase (STC-AP) fusion protein. Cells exhibiting STC-1 binding sites were found throughout the lamina terminalis. Dense cytoplasmic staining was observed predominantly within ependymal cells lining the anterior third ventricle region (AV3V), as well as cells of the choroid plexus. Additionally, neurons of the organum vasculosum of the lamina terminalis, the dorsal and ventral components of the median preoptic nucleus and the rostral aspects of the subfornical organ exhibited dense STC-1 cytoplasmic staining. STC-1 binding sites were also found in cells of the supraoptic nucleus, suprachiasmatic nucleus and anteroventral preoptic nucleus. These data suggest that STC-1 binding sites localized on the ependymal cells of the AV3V region and neurons of circumventricular organs may be associated with neuronal pathways involved in calcium/phosphate and fluid homeostasis.