Distribution and quantification of immunoreactive orexia A in rat tissues

A sensitive and specific radioimmunoassay for orexin A was developed. Orexi n A immunoreactivity was found to be confined to the central nervous system (CNS) with the highest concentrations in the hypothalamus, inferior and su perior colliculi and brainstem, Within the hypothalamus, the highest levels mere found in the lateral and posterior hypothalamus, These regions had a greater orexin A content in females compared to males. The orexin A content of hypothalamic regions did not change with fasting and no difference was noted in hypothalami of rats fed a high fat diet. The hypothalamic orexin A content was not different in obese Zucker rats compared to lean controls. Thus, orexin A has a wide distribution in the CNS, but appetite regulation may not be its main function. (C) 1999 Federation of European Biochemical S ocieties.