Intraventricular beta-endorphin accumulates in DARPP-32 immunoreactive tanycytes

Intraventricularly administered beta-endorphin (beta-end) (50-500 pmol) is found to be taken up and accumulated in dopamine and adenosine 3',5'-monophosphate regulated phosphoprotein (DARPP-32) positive tanycytes of the median eminence 15 min after injection as revealed by double immunolabelling procedures in combination with confocal laser microscopy. Exogenous beta-end in the cerebrospinal fluid (CSF) may in this way regulate the hypothalamic hormone release at the nerve terminal level by being released from tanycytes in the external layer or by affecting tanycyte function. The findings open up the possibility that neuronal beta-end via volume transmission in the CSF and internalization into tanycytes may exert in part its actions on hypothalamic hormone secretion by actions in the median eminence.