Orexin (hypocretin) gene expression in rat ependymal cells

The expression of prepro-orexin (PPO) mRNA in the rat brain was investigated by in situ hybridization histochemistry. In the lateral and posterior hypothalamic areas, which are considered to produce exclusively PPO mRNA, we found high levels of PPO mRNA expressions. We also localized PPO mRNA hybridization signals at lower levels around the lateral ventricles, the third and fourth ventricle. Cellular analysis by emulsion autoradiography revealed the expression of PPO mRNA in the ependymal cell layer. Our results demonstrate that beside the lateral and posterior hypothalamus PPO mRNA is expressed in ependymal cells.