Transcytosis of tanycytes in the circumventricular organs of adult mouse brain.

Tanycytes are specialized ependymal cells lining the ventricular spaces of the adult brain and thereby provide an interface between the cerebrospinal fluid (CSF) and brain parenchyma. They act as energy homeostasis, neuroendocrine regulation, and CSF-brain barrier; however, their functional significance in CSF-brain communication currently remains unknown. In the present study, we investigated the presence of tanycytic transcytosis using fluorescent tracers; a GM1 ligand, cholera toxin B (CTB), and a mannose-6-phosphate/insulin-like growth factor-Ⅱ receptor ligand, wheat germ agglutinin (WGA). Both CTB and WGA were incorporated by tanycytes and then released into brain parenchyma in the circumventricular organs such as the organum vasculosum laminae terminalis, subfornical organ, and median eminence, arcuate nucleus, and medullary central canal. Incorporated fluorescent CTB and WGA were released from tanycytes to distribute at neuronal somata. These results indicate that tanycytes of all examined brain regions possess the transport capability of macromolecules from CSF to brain neurons.